1 00:00:00,080 --> 00:00:01,800 The following content is provided 2 00:00:01,800 --> 00:00:04,030 under a Creative Commons license. 3 00:00:04,030 --> 00:00:06,880 Your support will help MIT OpenCourseWare continue 4 00:00:06,880 --> 00:00:10,740 to offer high quality educational resources for free. 5 00:00:10,740 --> 00:00:13,350 To make a donation or view additional materials 6 00:00:13,350 --> 00:00:15,810 from hundreds of MIT courses, visit 7 00:00:15,810 --> 00:00:24,660 MIT OpenCourseWare at ocw.mit.edu 8 00:00:24,660 --> 00:00:28,320 PROFESSOR: I want to talk about the last topic in the Scott 9 00:00:28,320 --> 00:00:28,820 book. 10 00:00:28,820 --> 00:00:34,260 And then, on Friday, we start talking about sociobiology. 11 00:00:34,260 --> 00:00:39,770 So you'll need to be reading the book by Alcock. 12 00:00:44,090 --> 00:00:47,270 Mating and reproduction is very important for sociobiology. 13 00:00:52,260 --> 00:00:57,480 And of course it's important in ethology and other approaches 14 00:00:57,480 --> 00:00:59,530 to study of animal behavior. 15 00:00:59,530 --> 00:01:08,140 And so Scott is using mainly data, experimental ethology, 16 00:01:08,140 --> 00:01:11,240 as well as various observations by ethologists. 17 00:01:11,240 --> 00:01:14,960 But then you'll see it's closely related 18 00:01:14,960 --> 00:01:17,060 to some of the studies of sociobiology 19 00:01:17,060 --> 00:01:18,320 that we'll be talking about. 20 00:01:21,820 --> 00:01:25,400 So when we talk about evolution, we 21 00:01:25,400 --> 00:01:28,790 talk about both natural selection and sexual selection. 22 00:01:28,790 --> 00:01:32,420 They were both discussed by Charles Darwin. 23 00:01:32,420 --> 00:01:34,710 And you should have a clear understanding 24 00:01:34,710 --> 00:01:36,290 of the difference in the meaning. 25 00:01:39,570 --> 00:01:43,780 We've talked about both of them in the class. 26 00:01:43,780 --> 00:01:49,670 You should be able to give examples of each of them. 27 00:01:49,670 --> 00:01:55,310 And for every time you discuss a trait, 28 00:01:55,310 --> 00:02:00,130 besides understanding whether it arose from natural selection 29 00:02:00,130 --> 00:02:03,800 or sexual selection or some combination, 30 00:02:03,800 --> 00:02:07,220 you have to consider the likely costs and benefits. 31 00:02:07,220 --> 00:02:13,940 And what do we mean by costs and benefits? 32 00:02:13,940 --> 00:02:17,730 We always take the sociobiological view 33 00:02:17,730 --> 00:02:21,990 that we're talking about not benefits 34 00:02:21,990 --> 00:02:25,860 for individual survival necessarily, 35 00:02:25,860 --> 00:02:28,930 but for increasing the likelihood of passing 36 00:02:28,930 --> 00:02:30,290 on the genes. 37 00:02:30,290 --> 00:02:32,040 This is the way it's used in sociobiology. 38 00:02:35,710 --> 00:02:40,090 And obviously, traits similar to evolve the benefits 39 00:02:40,090 --> 00:02:41,600 have to exceed the costs. 40 00:02:41,600 --> 00:02:43,070 It doesn't mean there aren't costs. 41 00:02:43,070 --> 00:02:51,140 And sometimes it's a puzzle, because cost is so drastic. 42 00:02:51,140 --> 00:02:54,060 Like if the female eats the male after mating, 43 00:02:54,060 --> 00:02:57,170 it seems to be a rather high cost to the male. 44 00:02:57,170 --> 00:03:01,790 So we bring it up later in class, 45 00:03:01,790 --> 00:03:06,320 because that's a typical Darwinian puzzle when you first 46 00:03:06,320 --> 00:03:10,310 look at the data. 47 00:03:10,310 --> 00:03:12,970 So when we're talking, it's easiest 48 00:03:12,970 --> 00:03:17,260 when trying to contrast natural and sexual selection to first 49 00:03:17,260 --> 00:03:20,140 consider, is it sexual selection? 50 00:03:20,140 --> 00:03:22,460 We've given examples of that already-- 51 00:03:22,460 --> 00:03:29,410 like the tail feathers of the female peacocks, or pheasant. 52 00:03:29,410 --> 00:03:32,450 The bright red color of the male cardinal-- 53 00:03:32,450 --> 00:03:34,920 it makes him stand out particularly 54 00:03:34,920 --> 00:03:36,310 against the snow in winter. 55 00:03:36,310 --> 00:03:40,240 It makes him very conspicuous to predators-- as well as 56 00:03:40,240 --> 00:03:41,760 to the female. 57 00:03:41,760 --> 00:03:46,080 We've talked about the long tail-- the swordtail fish. 58 00:03:46,080 --> 00:03:51,400 The lion's mane of course is a common one. 59 00:03:51,400 --> 00:03:53,660 A stag's antlers. 60 00:03:53,660 --> 00:03:56,320 Why do we say they evolved by sexual selection? 61 00:03:56,320 --> 00:03:59,470 Because they evolved because the female 62 00:03:59,470 --> 00:04:02,000 prefers males with those traits. 63 00:04:06,250 --> 00:04:09,860 So they benefit reproduction of the male 64 00:04:09,860 --> 00:04:11,882 because it makes him more attractive. 65 00:04:11,882 --> 00:04:14,290 If you can't attract females to mate with, 66 00:04:14,290 --> 00:04:19,350 then he won't pass on so many genes-- if any. 67 00:04:19,350 --> 00:04:25,050 Now usually you're talking about the appearance of the male 68 00:04:25,050 --> 00:04:27,000 when you're talking about sexual selection. 69 00:04:27,000 --> 00:04:32,900 But it affects the characteristics of female, too, 70 00:04:32,900 --> 00:04:37,680 especially if males exercise choice. 71 00:04:37,680 --> 00:04:42,310 And so we'll talk about that, too. 72 00:04:42,310 --> 00:04:45,100 Well, if it didn't evolve by sexual selection, 73 00:04:45,100 --> 00:04:51,480 then the traits evolved still by natural selection-- 74 00:04:51,480 --> 00:04:55,390 the factors that enable survival at least 75 00:04:55,390 --> 00:04:56,940 through the age of reproduction. 76 00:04:56,940 --> 00:04:58,940 And in many cases the age of reproduction 77 00:04:58,940 --> 00:05:05,210 includes brood-tending, care of young-- and maybe 78 00:05:05,210 --> 00:05:10,960 in our species care of the young of our young. 79 00:05:13,570 --> 00:05:17,215 So we talked, remember, about the birds of paradise. 80 00:05:21,170 --> 00:05:26,480 This is one of the birds of paradise-- Goldie's 81 00:05:26,480 --> 00:05:29,060 bird of paradise. 82 00:05:29,060 --> 00:05:32,880 In the video clip we saw with the dancing bird of paradise-- 83 00:05:32,880 --> 00:05:37,940 it was paradise riflebird from Australia. 84 00:05:37,940 --> 00:05:43,280 These birds occur within Indonesia 85 00:05:43,280 --> 00:05:45,690 and also in eastern Australia. 86 00:05:45,690 --> 00:05:50,815 I believe the video we saw was all of Australian birds. 87 00:05:53,820 --> 00:05:57,880 Why do you think the elaboration of these feathers 88 00:05:57,880 --> 00:06:00,990 has gone to such extremes? 89 00:06:00,990 --> 00:06:01,990 Doesn't it have costs? 90 00:06:05,030 --> 00:06:09,500 I mean a male that's having to carry around these feathers-- 91 00:06:09,500 --> 00:06:13,120 or look at this the peacock here. 92 00:06:15,980 --> 00:06:17,680 It seems to be somewhat of a burden 93 00:06:17,680 --> 00:06:20,120 to have feathers that long. 94 00:06:20,120 --> 00:06:23,900 And yet the females prefer it. 95 00:06:23,900 --> 00:06:29,190 If you give a female peacock a choice between males 96 00:06:29,190 --> 00:06:32,770 with various-- I took this picture myself 97 00:06:32,770 --> 00:06:36,350 at the Boston Zoological Society park, 98 00:06:36,350 --> 00:06:40,630 and it shows the strutting male. 99 00:06:40,630 --> 00:06:43,220 He's displaying his tail feathers. 100 00:06:43,220 --> 00:06:45,115 There's the peahen in front. 101 00:06:48,360 --> 00:06:50,470 With feathers like that, I mean, how 102 00:06:50,470 --> 00:06:52,880 does he get away from predators? 103 00:06:52,880 --> 00:06:55,470 You see, now in the case of these birds, 104 00:06:55,470 --> 00:07:00,800 it's fairly easy to understand, because in the environments 105 00:07:00,800 --> 00:07:04,960 where these birds are found they don't have many predators. 106 00:07:04,960 --> 00:07:08,250 So are there still costs? 107 00:07:08,250 --> 00:07:12,960 Well, if it went too far, what would the costs be? 108 00:07:12,960 --> 00:07:15,080 It would start interfering with his ability 109 00:07:15,080 --> 00:07:20,890 to forage, just to locomote, get around. 110 00:07:20,890 --> 00:07:24,180 So there's certainly limits to how far 111 00:07:24,180 --> 00:07:26,010 sexual selection can go. 112 00:07:32,832 --> 00:07:36,790 And see, Darwin of course had introduced 113 00:07:36,790 --> 00:07:40,960 this idea of sexual selection. 114 00:07:40,960 --> 00:07:49,100 And he was made fun of among other ways by cartoonists. 115 00:07:49,100 --> 00:07:53,170 And here it shows the Victorian cartoonists 116 00:07:53,170 --> 00:07:57,590 made fun of Darwin's ideas about sexual selection 117 00:07:57,590 --> 00:08:00,310 and the importance of visual displays. 118 00:08:00,310 --> 00:08:08,510 It shows him here inspecting the mimicking of steatopygia. 119 00:08:08,510 --> 00:08:10,740 What is that? 120 00:08:10,740 --> 00:08:14,250 The very large buttocks in females 121 00:08:14,250 --> 00:08:17,750 of certain groups of humans. 122 00:08:17,750 --> 00:08:25,190 And it became a Victorian style to wear bustles. 123 00:08:25,190 --> 00:08:30,620 So Darwin, of course, had a ready interpretation of that. 124 00:08:30,620 --> 00:08:33,776 They wouldn't do it if males didn't like it. 125 00:08:36,970 --> 00:08:41,799 If you want to know more about steatopygia just go to Google. 126 00:08:41,799 --> 00:08:44,390 Don't go to Google Scholar, although you could go there, 127 00:08:44,390 --> 00:08:47,450 too, and you'll find the scholarly papers. 128 00:08:47,450 --> 00:08:49,130 But if you just go to regular Google 129 00:08:49,130 --> 00:08:52,190 you'll find all kinds of information, 130 00:08:52,190 --> 00:08:56,960 photographs, comments-- some of them with tongue in cheek, 131 00:08:56,960 --> 00:09:00,840 some of them claiming it's all racism, 132 00:09:00,840 --> 00:09:05,220 and others-- really most of it's just very interesting. 133 00:09:05,220 --> 00:09:08,275 It illustrates variety in human evolution. 134 00:09:10,780 --> 00:09:13,500 I think when we talk about sociobiology this will come up 135 00:09:13,500 --> 00:09:20,090 again-- this is a particular illustration. 136 00:09:20,090 --> 00:09:21,970 Not in cartoons, but in real people. 137 00:09:24,780 --> 00:09:28,840 Now this is the next concept that Scott brings up-- 138 00:09:28,840 --> 00:09:34,420 the variations in reproductive investment by the male 139 00:09:34,420 --> 00:09:37,390 and the female of the species, because often they 140 00:09:37,390 --> 00:09:41,030 differ considerably. 141 00:09:41,030 --> 00:09:45,090 We saw when we talked about sticklebacks early in the class 142 00:09:45,090 --> 00:09:49,010 that the male does all the nesting and care of the eggs. 143 00:09:49,010 --> 00:09:54,020 So the male is making a big reproductive investment. 144 00:09:54,020 --> 00:10:00,430 The female doesn't make so much reproductive investment. 145 00:10:00,430 --> 00:10:02,100 In other species of fish, the male 146 00:10:02,100 --> 00:10:05,560 just leaves after fertilizing eggs. 147 00:10:05,560 --> 00:10:07,630 And in those species it's the male 148 00:10:07,630 --> 00:10:11,280 that's not making any reproductive investment. 149 00:10:11,280 --> 00:10:14,035 So of course then their strategies are going to differ. 150 00:10:17,310 --> 00:10:20,470 And you can predict very great differences 151 00:10:20,470 --> 00:10:26,180 in behavior choices of those of the male and female. 152 00:10:26,180 --> 00:10:30,610 In lions, the female has to invest more than two years. 153 00:10:30,610 --> 00:10:32,550 That includes gestation and nearly 154 00:10:32,550 --> 00:10:34,710 two years of care of the young. 155 00:10:34,710 --> 00:10:39,610 The males do comparatively little, because even when 156 00:10:39,610 --> 00:10:41,820 the female is rearing young, she often 157 00:10:41,820 --> 00:10:44,810 is still doing much of the hunting, 158 00:10:44,810 --> 00:10:47,850 although the male will hunt as well. 159 00:10:56,370 --> 00:11:00,310 The spotted sandpiper's an example where the males do most 160 00:11:00,310 --> 00:11:03,910 of the brood tending, and the female, 161 00:11:03,910 --> 00:11:06,490 she will help sometimes for a while, 162 00:11:06,490 --> 00:11:08,930 and then she just leaves. 163 00:11:08,930 --> 00:11:13,440 She goes off and lays another clutch of eggs-- 164 00:11:13,440 --> 00:11:17,370 she lays four eggs at a time in each nest. 165 00:11:17,370 --> 00:11:19,740 She goes off to lay another clutch of four eggs 166 00:11:19,740 --> 00:11:20,860 with a different male. 167 00:11:24,070 --> 00:11:28,060 So again, it's the male making that reproductive investment. 168 00:11:28,060 --> 00:11:29,950 And I mean what would happen? 169 00:11:29,950 --> 00:11:31,080 So he leaves. 170 00:11:31,080 --> 00:11:32,750 What about the male? 171 00:11:32,750 --> 00:11:35,300 Well, if he leaves, then his reproductive investment 172 00:11:35,300 --> 00:11:39,100 goes to zero for that span of time. 173 00:11:39,100 --> 00:11:40,950 He's already put time into it. 174 00:11:40,950 --> 00:11:44,790 If he wants his genes to be passed on, 175 00:11:44,790 --> 00:11:49,090 he's got to stay and take care of those chicks. 176 00:11:49,090 --> 00:11:53,960 Whereas the female, she gets it for free. 177 00:11:53,960 --> 00:11:57,670 Or not for free-- she still had to lay the eggs, 178 00:11:57,670 --> 00:12:02,970 and that takes a lot of energy and a lot of foraging. 179 00:12:02,970 --> 00:12:06,950 But she can increase her reproductive output simply 180 00:12:06,950 --> 00:12:13,250 by laying eggs, getting another male to bring the food 181 00:12:13,250 --> 00:12:17,204 and help her rear the eggs. 182 00:12:17,204 --> 00:12:18,620 We'll come back to the sandpipers. 183 00:12:26,770 --> 00:12:33,100 So let's talk a little more about how the male and female 184 00:12:33,100 --> 00:12:35,770 can use very different ways to maximize 185 00:12:35,770 --> 00:12:37,950 their reproductive output. 186 00:12:37,950 --> 00:12:41,720 In many cases-- certainly we just saw examples 187 00:12:41,720 --> 00:12:44,270 where that's not true-- but the male 188 00:12:44,270 --> 00:12:48,820 can increase his number of offspring 189 00:12:48,820 --> 00:12:50,920 just by mating indiscriminately. 190 00:12:50,920 --> 00:12:54,750 Mate with as many females as possible. 191 00:12:54,750 --> 00:12:56,670 If the female is doing the brood-tending, 192 00:12:56,670 --> 00:12:59,650 and he doesn't have to do it, that would be his best strategy 193 00:12:59,650 --> 00:13:02,680 if he wants to maximize reproductive output. 194 00:13:02,680 --> 00:13:03,510 And you see that. 195 00:13:06,970 --> 00:13:11,510 The female has limited egg production, 196 00:13:11,510 --> 00:13:15,120 so she is more interested in the male 197 00:13:15,120 --> 00:13:19,040 than in just maximizing the quality of the offspring-- that 198 00:13:19,040 --> 00:13:25,150 is, given the best chance of surviving 199 00:13:25,150 --> 00:13:28,370 and reproducing themselves. 200 00:13:28,370 --> 00:13:31,310 So she's going to have a great interest in finding 201 00:13:31,310 --> 00:13:39,850 good genes in her mating, or good resources from the male. 202 00:13:42,640 --> 00:13:45,050 So because of these different interests 203 00:13:45,050 --> 00:13:48,560 of the male and female that often are considerably 204 00:13:48,560 --> 00:13:52,420 different, though it various just how in different species. 205 00:13:52,420 --> 00:13:55,600 But you always have this male/female difference 206 00:13:55,600 --> 00:13:59,390 in their production of the gametes. 207 00:13:59,390 --> 00:14:04,130 So the result is various-- you can 208 00:14:04,130 --> 00:14:07,585 call them compromises between the interests of the male 209 00:14:07,585 --> 00:14:10,200 and interests of the female. 210 00:14:10,200 --> 00:14:13,710 And when we say this-- I'm talking about compromises-- 211 00:14:13,710 --> 00:14:17,704 I don't mean these animals are aware of it. 212 00:14:17,704 --> 00:14:21,705 But looked at as an evolutionary biologist 213 00:14:21,705 --> 00:14:28,750 or sociobiologist you interpret it in terms of evolution, 214 00:14:28,750 --> 00:14:30,410 not in terms of what they're aware of. 215 00:14:34,440 --> 00:14:37,070 And of course we know the reproductive investment varies. 216 00:14:37,070 --> 00:14:39,690 We've already talked about that. 217 00:14:39,690 --> 00:14:44,260 And so now we have to talk about mate choice, which 218 00:14:44,260 --> 00:14:48,730 varies a lot, and there's a lot of studies 219 00:14:48,730 --> 00:14:50,380 by sociobiologists and others. 220 00:14:54,830 --> 00:15:01,600 Mate choice by females appears in most cases-- 221 00:15:01,600 --> 00:15:03,670 in almost all cases-- to be based 222 00:15:03,670 --> 00:15:07,780 on one of two properties of the males. 223 00:15:07,780 --> 00:15:09,420 So we want to know what those are. 224 00:15:09,420 --> 00:15:17,355 We want examples of each type of choice. 225 00:15:17,355 --> 00:15:21,040 First of all-- material benefits. 226 00:15:21,040 --> 00:15:26,270 What kind of resources is that male capable of providing? 227 00:15:26,270 --> 00:15:28,780 Why should I choose him? 228 00:15:28,780 --> 00:15:34,610 So for example, in the common tern, if he wants to mate, 229 00:15:34,610 --> 00:15:38,140 he'd better bring her something good to eat. 230 00:15:38,140 --> 00:15:41,430 And he brings freshly caught fish to the female. 231 00:15:41,430 --> 00:15:43,850 The bigger the fish the better. 232 00:15:43,850 --> 00:15:46,837 If he's not such a good forager and doesn't bring her enough, 233 00:15:46,837 --> 00:15:47,920 she may not mate with him. 234 00:15:50,440 --> 00:15:54,020 The black-tipped hanging fly. 235 00:15:54,020 --> 00:15:56,920 We're going to talk about that next. 236 00:15:56,920 --> 00:16:02,300 But he always brings food to the female also. 237 00:16:05,110 --> 00:16:08,090 The difference there is that he mates with her 238 00:16:08,090 --> 00:16:12,150 while she's eating the food. 239 00:16:12,150 --> 00:16:15,870 There's other material benefits that a female can look for. 240 00:16:15,870 --> 00:16:18,880 Let me just jump to the goldfinch. 241 00:16:18,880 --> 00:16:20,320 We can talk about that now. 242 00:16:20,320 --> 00:16:26,440 But when he's got more brightly colored plumage, 243 00:16:26,440 --> 00:16:30,070 it means he's got more carotenoids in his body. 244 00:16:30,070 --> 00:16:31,530 And there have been studies of that 245 00:16:31,530 --> 00:16:38,160 that Scott does review in the reading that 246 00:16:38,160 --> 00:16:40,780 show that carotenoids at high levels 247 00:16:40,780 --> 00:16:44,880 are correlated with strong immune systems. 248 00:16:44,880 --> 00:16:47,370 So it indicates better health. 249 00:16:47,370 --> 00:16:49,225 And that has to be because he's getting 250 00:16:49,225 --> 00:16:51,010 the carotenoids from his diet. 251 00:16:51,010 --> 00:16:52,610 So he's a good forager. 252 00:16:52,610 --> 00:16:58,190 And also studies indicate he's less likely to have parasites. 253 00:16:58,190 --> 00:17:03,910 All important if he's going to be helping the female. 254 00:17:03,910 --> 00:17:06,130 Let's just show that picture here. 255 00:17:10,839 --> 00:17:12,819 There's the goldfinch. 256 00:17:12,819 --> 00:17:15,349 And there's the female on the right, 257 00:17:15,349 --> 00:17:19,220 and a pretty brightly colored goldfinch on the left. 258 00:17:19,220 --> 00:17:23,490 So he's been taking in carotenoids. 259 00:17:23,490 --> 00:17:24,470 He's a good forager. 260 00:17:34,450 --> 00:17:38,280 Well, what things other than material benefits? 261 00:17:38,280 --> 00:17:41,180 Well, how handsome the male is. 262 00:17:41,180 --> 00:17:45,200 How attractive he is just by himself. 263 00:17:45,200 --> 00:17:47,700 Let's just take humans. 264 00:17:47,700 --> 00:17:50,200 The female is wealthy, she's already 265 00:17:50,200 --> 00:17:52,330 got all the material benefits she needs. 266 00:17:52,330 --> 00:17:54,270 Maybe she has servants. 267 00:17:54,270 --> 00:18:00,160 Well then, just choose the best-looking, strongest male. 268 00:18:00,160 --> 00:18:01,620 Get good genes. 269 00:18:01,620 --> 00:18:02,745 Just focus on that. 270 00:18:06,220 --> 00:18:09,500 It might not work so well, because her offspring are 271 00:18:09,500 --> 00:18:13,270 going to inherit her genes and his. 272 00:18:13,270 --> 00:18:16,180 So if he's not good at resource provision, 273 00:18:16,180 --> 00:18:21,230 her offspring might not be as well-off as she is. 274 00:18:21,230 --> 00:18:24,400 But both of these things that are involved. 275 00:18:24,400 --> 00:18:27,210 In some species it seems to be totally amount 276 00:18:27,210 --> 00:18:28,925 of material benefit. 277 00:18:28,925 --> 00:18:33,860 But in many species other factors 278 00:18:33,860 --> 00:18:35,770 of how attractive the male is will 279 00:18:35,770 --> 00:18:39,160 affect the female and her choice. 280 00:18:39,160 --> 00:18:43,610 Let's go back to the hanging flies. 281 00:18:43,610 --> 00:18:46,870 I said he brings food to the female 282 00:18:46,870 --> 00:18:49,315 and he copulates with her while she's eating. 283 00:18:52,080 --> 00:18:54,610 And they found in studies that if he 284 00:18:54,610 --> 00:19:00,500 brings a larger gift of food-- that is, a larger insect-- 285 00:19:00,500 --> 00:19:05,340 that she copulates longer with him. 286 00:19:05,340 --> 00:19:06,070 Why? 287 00:19:06,070 --> 00:19:09,320 Because it takes her longer to eat it. 288 00:19:09,320 --> 00:19:12,350 And the longer he copulates, the more sperm he transfers. 289 00:19:12,350 --> 00:19:14,935 Because it turns out-- and this is what the studies show-- 290 00:19:14,935 --> 00:19:16,560 I'll show you a few graphs here. 291 00:19:16,560 --> 00:19:18,130 This one is done in nature. 292 00:19:18,130 --> 00:19:20,700 This is done in the lab. 293 00:19:20,700 --> 00:19:26,330 And so they plotted there on the ordinate in this case 294 00:19:26,330 --> 00:19:29,210 the duration of copulation, which 295 00:19:29,210 --> 00:19:34,240 is correlated with the amount of sperm being transferred; 296 00:19:34,240 --> 00:19:43,540 and the body size of the prey that he brings for her to eat. 297 00:19:43,540 --> 00:19:44,940 And look at it. 298 00:19:44,940 --> 00:19:50,690 As the prey gets bigger and bigger, up to a certain point 299 00:19:50,690 --> 00:19:52,430 she mates with him longer and longer. 300 00:19:52,430 --> 00:19:54,800 But then it seems to level off. 301 00:19:54,800 --> 00:19:56,820 And it's even clearer in the laboratory studies. 302 00:20:00,060 --> 00:20:04,390 So the payoff to the male if he brings larger insects is 303 00:20:04,390 --> 00:20:08,900 increased quantity of sperm transferred. 304 00:20:08,900 --> 00:20:12,620 I mean, ejaculation takes, it turns out, 305 00:20:12,620 --> 00:20:15,840 about 20 minutes in this animal. 306 00:20:15,840 --> 00:20:19,790 So if she finishes eating before 20 minutes because he didn't 307 00:20:19,790 --> 00:20:23,730 bring a large enough insect, she flies off, finds another male. 308 00:20:26,600 --> 00:20:29,910 So he may not end up being the father-- at least 309 00:20:29,910 --> 00:20:30,830 not of all the eggs. 310 00:20:34,170 --> 00:20:36,250 If there's food left after 20 minutes, 311 00:20:36,250 --> 00:20:39,327 well, the male gets a doggy bag. 312 00:20:45,686 --> 00:20:46,810 So there's the goldfinches. 313 00:20:49,590 --> 00:20:52,280 Now I brought this up in the introduction. 314 00:20:52,280 --> 00:20:56,620 We talk about evolution as survival of the fittest. 315 00:20:56,620 --> 00:20:59,470 The question is, what do we mean by that? 316 00:20:59,470 --> 00:21:01,310 If it's survival of the fittest, then why 317 00:21:01,310 --> 00:21:05,410 is it that certain species of spiders-- and also 318 00:21:05,410 --> 00:21:08,710 occurs in certain insects-- the male is eaten 319 00:21:08,710 --> 00:21:11,170 by the female in the act of copulation? 320 00:21:11,170 --> 00:21:13,670 It happens in the Australian redback spider. 321 00:21:16,240 --> 00:21:18,260 And there are some reasons we can discern 322 00:21:18,260 --> 00:21:20,600 for how it's still benefiting him. 323 00:21:20,600 --> 00:21:22,610 But there are other species, too, that do that. 324 00:21:22,610 --> 00:21:24,950 The praying mantis is the best-known. 325 00:21:28,000 --> 00:21:30,100 The female tarantula-- it commonly 326 00:21:30,100 --> 00:21:34,000 eats-- that's the burrowing spider in the American 327 00:21:34,000 --> 00:21:36,080 Southwest, for example. 328 00:21:36,080 --> 00:21:37,990 They often eat males. 329 00:21:37,990 --> 00:21:40,680 But it's not always their mate, but it might be. 330 00:21:43,420 --> 00:21:46,065 So here's the Australian redback spider, 331 00:21:46,065 --> 00:21:47,730 just to see what they look like. 332 00:21:51,740 --> 00:21:54,450 These are the reasons why it can still 333 00:21:54,450 --> 00:21:57,820 benefit the male in terms of his passing on his genes. 334 00:21:57,820 --> 00:22:03,050 First of all, he's not likely to survive long enough 335 00:22:03,050 --> 00:22:04,760 to find a second mate. 336 00:22:04,760 --> 00:22:08,230 They're short-lived animals. 337 00:22:08,230 --> 00:22:13,350 And again, if she eats him she's less 338 00:22:13,350 --> 00:22:18,380 likely to mate again if she's well fed. 339 00:22:18,380 --> 00:22:21,690 And more nutrition, it can benefit her. 340 00:22:21,690 --> 00:22:24,635 She's more likely then to have his offspring. 341 00:22:28,420 --> 00:22:30,660 So what the hell? 342 00:22:30,660 --> 00:22:31,240 Go ahead. 343 00:22:33,830 --> 00:22:35,810 Here's the praying mantis. 344 00:22:35,810 --> 00:22:39,170 There you see in the center I put the center picture 345 00:22:39,170 --> 00:22:41,280 of the male and a female. 346 00:22:41,280 --> 00:22:42,860 The female's the bigger one. 347 00:22:46,800 --> 00:22:50,750 And in the lower right, there she's eating the male. 348 00:22:53,730 --> 00:22:58,350 This is a study I found in the literature-- 349 00:22:58,350 --> 00:23:01,460 "Sexual Cannibalism in the Praying Mantis"-- 350 00:23:01,460 --> 00:23:03,160 this particular praying mantis. 351 00:23:06,290 --> 00:23:10,960 They found that if the females are well fed, 352 00:23:10,960 --> 00:23:12,510 they usually don't eat the male. 353 00:23:15,510 --> 00:23:18,760 Females that are fed more are heavier, 354 00:23:18,760 --> 00:23:22,065 and they produce heavier eggs, and so more likely to survive. 355 00:23:25,470 --> 00:23:27,633 If you feed the females less-- these 356 00:23:27,633 --> 00:23:31,300 are in experiments where they control that-- then the females 357 00:23:31,300 --> 00:23:35,490 are much more likely to eat the male. 358 00:23:35,490 --> 00:23:37,620 So they did an experiment where some females 359 00:23:37,620 --> 00:23:39,310 were prevented from eating the male. 360 00:23:39,310 --> 00:23:41,860 Others were not prevented. 361 00:23:41,860 --> 00:23:46,030 Those that ate the male produced heavier eggs, 362 00:23:46,030 --> 00:23:51,580 indicating that the cannibalism was adaptive for the female. 363 00:23:51,580 --> 00:23:55,180 But the males-- unlike those spiders 364 00:23:55,180 --> 00:23:57,330 we talked about-- the males do try 365 00:23:57,330 --> 00:24:00,380 to avoid being eaten, indicating from that behavior 366 00:24:00,380 --> 00:24:02,880 that it's probably less adaptive to the males. 367 00:24:02,880 --> 00:24:05,635 That may mean that if he was not eaten, maybe 368 00:24:05,635 --> 00:24:09,530 he would have a chance to mate with another female. 369 00:24:09,530 --> 00:24:15,850 That's not certain, but that's what the study indicates. 370 00:24:15,850 --> 00:24:21,820 So how adaptive the behavior is can be different for the female 371 00:24:21,820 --> 00:24:22,910 and for the male. 372 00:24:22,910 --> 00:24:26,420 It's clearly adaptive for the female. 373 00:24:26,420 --> 00:24:31,160 The males of some species, as we said for the spider, probably 374 00:24:31,160 --> 00:24:32,907 benefits him more than it hurts him, 375 00:24:32,907 --> 00:24:35,240 because he's not going to live long enough to mate again 376 00:24:35,240 --> 00:24:36,410 anyway. 377 00:24:36,410 --> 00:24:39,980 But maybe for some, like the praying mantis, 378 00:24:39,980 --> 00:24:43,350 it may not be the most adaptive for him. 379 00:24:47,920 --> 00:24:50,780 So what are the conditions that make the female more 380 00:24:50,780 --> 00:24:57,900 likely to be the one that is making the choice of mates? 381 00:24:57,900 --> 00:25:01,770 The studies have tended to focus on species 382 00:25:01,770 --> 00:25:03,220 with sex-role reversal. 383 00:25:03,220 --> 00:25:06,860 That is, the male's doing all the brood-tending and so forth. 384 00:25:06,860 --> 00:25:09,750 But there are exceptions. 385 00:25:09,750 --> 00:25:13,170 So they look into the conditions that 386 00:25:13,170 --> 00:25:17,360 seem to facilitate the evolution of selective mate choice 387 00:25:17,360 --> 00:25:25,280 by the male instead of the female. 388 00:25:25,280 --> 00:25:27,810 First of all, if the male defends 389 00:25:27,810 --> 00:25:32,800 the nest-- like in the sticklebacks-- 390 00:25:32,800 --> 00:25:37,930 there's a limited number of eggs he can defend. 391 00:25:37,930 --> 00:25:40,500 He certainly would have a lot of difficulty 392 00:25:40,500 --> 00:25:41,730 defending more than one nest. 393 00:25:45,090 --> 00:25:47,700 So he can't maximize reproduction just 394 00:25:47,700 --> 00:25:49,040 by indiscriminate mating. 395 00:25:51,660 --> 00:25:57,290 So it's in his best interest to choose the best female-- either 396 00:25:57,290 --> 00:26:01,000 with the most eggs for that one nest-- and that seems 397 00:26:01,000 --> 00:26:08,310 to be true for the sticklebacks-- or other signs 398 00:26:08,310 --> 00:26:13,130 that it's a female that's producing perhaps heavier eggs 399 00:26:13,130 --> 00:26:17,140 and so forth that have a better chance of survival. 400 00:26:17,140 --> 00:26:20,540 And if there's many more females than males-- and that's 401 00:26:20,540 --> 00:26:25,830 true of some species-- then mate choice-- males 402 00:26:25,830 --> 00:26:29,160 making the choice-- is more likely, especially 403 00:26:29,160 --> 00:26:31,690 if the male's also in charge of the nest. 404 00:26:37,220 --> 00:26:41,810 Now you also have variations in mating strategies 405 00:26:41,810 --> 00:26:44,230 even within a species. 406 00:26:44,230 --> 00:26:47,540 So that's what I want to talk about here-- the different male 407 00:26:47,540 --> 00:26:48,290 mating strategies. 408 00:26:51,310 --> 00:26:54,010 I asked, for example, of how in some species 409 00:26:54,010 --> 00:26:57,360 different individual males adopt very different mating 410 00:26:57,360 --> 00:27:02,990 strategies, even though these males may all 411 00:27:02,990 --> 00:27:03,900 have the same genes. 412 00:27:06,550 --> 00:27:08,630 And these are the examples we'll talk 413 00:27:08,630 --> 00:27:12,220 about-- the scarab beetles, some of which are very big 414 00:27:12,220 --> 00:27:13,430 and they have horns. 415 00:27:13,430 --> 00:27:17,450 Some of them are smaller and don't have horns. 416 00:27:17,450 --> 00:27:22,040 So it looks like those big ones are a lot more fit. 417 00:27:22,040 --> 00:27:26,050 So we want to know, what are the smaller ones doing? 418 00:27:26,050 --> 00:27:29,650 We find the same problem in toads, because some of them 419 00:27:29,650 --> 00:27:33,780 are very big and can croak loudly and attract females. 420 00:27:33,780 --> 00:27:35,075 Some are not. 421 00:27:35,075 --> 00:27:36,910 They're much smaller. 422 00:27:36,910 --> 00:27:38,380 Same is true of iguanas. 423 00:27:38,380 --> 00:27:39,960 As we saw in the picture earlier, 424 00:27:39,960 --> 00:27:43,300 we were talking about foraging strategies. 425 00:27:43,300 --> 00:27:46,045 We found out the foraging strategies were quite different 426 00:27:46,045 --> 00:27:50,280 in the large iguanas and the smaller ones. 427 00:27:50,280 --> 00:27:53,390 They have a more unusual mating strategy. 428 00:27:53,390 --> 00:27:56,280 So first of all, the scarab beetles. 429 00:27:56,280 --> 00:28:01,010 They evolved two distinct morphologies. 430 00:28:01,010 --> 00:28:03,470 As I mentioned, the smaller ones have horns, 431 00:28:03,470 --> 00:28:05,534 but they're more agile. 432 00:28:05,534 --> 00:28:06,200 They're quicker. 433 00:28:13,120 --> 00:28:17,660 They have underground nests, and the male will defend the nest. 434 00:28:17,660 --> 00:28:24,030 He will try to keep other males from getting at his eggs, 435 00:28:24,030 --> 00:28:29,070 or from getting at the female who's there in the tunnel. 436 00:28:29,070 --> 00:28:35,500 But those small males are often able to get past the big male, 437 00:28:35,500 --> 00:28:40,080 avoid his horns, and get to the female. 438 00:28:40,080 --> 00:28:43,390 Now he's got to be quick, because why 439 00:28:43,390 --> 00:28:45,870 doesn't the male just turn around and get him? 440 00:28:45,870 --> 00:28:49,650 Well, he's so big with these big wide horns, 441 00:28:49,650 --> 00:28:54,260 he usually has to come clear out of the tunnel and turn around. 442 00:28:54,260 --> 00:29:00,100 Well, that gives that small male just time 443 00:29:00,100 --> 00:29:07,280 to sneak a quick one with the female before he can attack. 444 00:29:07,280 --> 00:29:10,580 And then he just has the problem of getting past him, 445 00:29:10,580 --> 00:29:11,810 because he will come in. 446 00:29:14,460 --> 00:29:18,375 Now with a small marine iguana, it's even more interesting. 447 00:29:20,930 --> 00:29:24,500 The copulation normally requires several minutes 448 00:29:24,500 --> 00:29:27,760 for the male to ejaculate. 449 00:29:27,760 --> 00:29:34,100 But these small iguanas have the ability to ejaculate in advance 450 00:29:34,100 --> 00:29:38,290 and store the sperm in a groove in their penis. 451 00:29:38,290 --> 00:29:42,610 So he only needs a very brief copulation, deposits the sperm, 452 00:29:42,610 --> 00:29:45,900 and gets out of there. 453 00:29:45,900 --> 00:29:48,090 And of course the bigger males will 454 00:29:48,090 --> 00:29:50,920 be trying to prevent him from mating. 455 00:29:50,920 --> 00:29:52,730 So they've evolved a strategy. 456 00:29:52,730 --> 00:29:55,210 They don't need so much time. 457 00:29:55,210 --> 00:29:59,150 So both the large and the small males are able to mate. 458 00:30:06,220 --> 00:30:09,870 Let's talk about the various mating systems 459 00:30:09,870 --> 00:30:11,975 and why there is so many different ones. 460 00:30:15,130 --> 00:30:19,730 And here we mean polygyny, polyandry, polygynandry. 461 00:30:22,830 --> 00:30:27,980 This was studied extensively in birds by Nick Davies. 462 00:30:27,980 --> 00:30:31,430 Most of the studies were done on the reproductive behavior 463 00:30:31,430 --> 00:30:32,170 of the dunnock. 464 00:30:32,170 --> 00:30:33,900 It's a small European songbird. 465 00:30:33,900 --> 00:30:36,250 The hedge sparrow is its common name. 466 00:30:38,930 --> 00:30:44,450 And they found all the different varieties of mating strategy 467 00:30:44,450 --> 00:30:49,460 in this one species of bird. 468 00:30:49,460 --> 00:30:54,470 And this is the way he summarized that issue. 469 00:30:54,470 --> 00:30:56,470 He said, "We should view the mating game 470 00:30:56,470 --> 00:30:59,350 not as a cooperation between the sexes, 471 00:30:59,350 --> 00:31:02,320 but as a conflict resulting in a compromise 472 00:31:02,320 --> 00:31:09,820 in the interests of one or both of them." 473 00:31:09,820 --> 00:31:16,550 It doesn't sound like lyric love poetry, does it? 474 00:31:16,550 --> 00:31:20,520 No, we're talking about evolution. 475 00:31:20,520 --> 00:31:25,460 And yes, it has affected humans very strongly. 476 00:31:25,460 --> 00:31:29,440 Here's the basic mating systems. 477 00:31:29,440 --> 00:31:31,860 Monogamy. 478 00:31:31,860 --> 00:31:34,860 We all know what monogamy is, but we 479 00:31:34,860 --> 00:31:38,570 have to distinguish between social monogamy 480 00:31:38,570 --> 00:31:40,800 and genetic monogamy. 481 00:31:40,800 --> 00:31:43,200 What's the difference? 482 00:31:43,200 --> 00:31:49,150 Social monogamy means the female lives 483 00:31:49,150 --> 00:31:53,520 with the same male-- all the time, the same male. 484 00:31:53,520 --> 00:31:55,520 She's monogamous. 485 00:31:55,520 --> 00:32:00,870 Genetic monogamy is who fathers her children. 486 00:32:00,870 --> 00:32:07,000 And here in many cases they thought social monogamy always 487 00:32:07,000 --> 00:32:08,490 meant genetic monogamy. 488 00:32:08,490 --> 00:32:11,980 But now we have the ability to look at the DNA, 489 00:32:11,980 --> 00:32:16,260 and we find out that that's often not true. 490 00:32:16,260 --> 00:32:19,030 Not for humans, not for birds. 491 00:32:19,030 --> 00:32:21,570 Well, these are where most of the studies have been done. 492 00:32:21,570 --> 00:32:22,440 Especially birds. 493 00:32:26,250 --> 00:32:27,130 Polygyny. 494 00:32:27,130 --> 00:32:31,070 That's when you have one male mating 495 00:32:31,070 --> 00:32:32,205 with more than one female. 496 00:32:36,100 --> 00:32:40,850 And you have the resource-base polygyny, 497 00:32:40,850 --> 00:32:47,680 where females choose by the value of the territory. 498 00:32:47,680 --> 00:32:52,510 That's done in the iguana, the pied flycatcher. 499 00:32:58,960 --> 00:33:01,140 And there you find interesting choices. 500 00:33:01,140 --> 00:33:04,020 The female faced with a choice between a single male 501 00:33:04,020 --> 00:33:06,680 and a male that already has one female 502 00:33:06,680 --> 00:33:10,640 will often choose the male that already has another female. 503 00:33:10,640 --> 00:33:12,740 Why? 504 00:33:12,740 --> 00:33:15,030 Better territory. 505 00:33:15,030 --> 00:33:18,076 She's looking at the whole picture. 506 00:33:18,076 --> 00:33:24,690 If that male is capable, because of the value of his territory, 507 00:33:24,690 --> 00:33:30,270 of mating with more than female, she's happy to join the family. 508 00:33:34,860 --> 00:33:38,270 Female defense polygyny. 509 00:33:38,270 --> 00:33:41,050 Well you know what that is-- the harem. 510 00:33:41,050 --> 00:33:46,810 If a male can defend more females, 511 00:33:46,810 --> 00:33:51,910 as some sea mammals-- marine mammals-- do that. 512 00:33:51,910 --> 00:34:01,810 The sea lions, seals-- the large males will have a harem. 513 00:34:01,810 --> 00:34:05,410 But they have to be strong enough and quick enough 514 00:34:05,410 --> 00:34:08,300 to defend those females. 515 00:34:08,300 --> 00:34:17,030 And that will limit the size of their group. 516 00:34:17,030 --> 00:34:19,730 But that's female defense polygyny. 517 00:34:19,730 --> 00:34:21,480 And then lek-based polygyny. 518 00:34:21,480 --> 00:34:23,400 We'll bring that up again at the end. 519 00:34:23,400 --> 00:34:26,300 There's about 200 species that have leks. 520 00:34:26,300 --> 00:34:29,980 That occurs in the snipe, it occurs 521 00:34:29,980 --> 00:34:33,790 in certain fruit flies and various birds. 522 00:34:33,790 --> 00:34:39,739 This is when the female chooses among males 523 00:34:39,739 --> 00:34:41,440 that are lined up in front of her. 524 00:34:41,440 --> 00:34:43,360 That's the lek. 525 00:34:43,360 --> 00:34:50,840 It's like nature's singles bar, where the female comes in, 526 00:34:50,840 --> 00:34:53,850 she can get everything done. 527 00:34:53,850 --> 00:34:59,360 The whole group of females can deal with it at once, 528 00:34:59,360 --> 00:35:01,380 because the males are all there. 529 00:35:01,380 --> 00:35:03,865 And there's various reasons why leks form, 530 00:35:03,865 --> 00:35:06,070 and we'll bring that up in the end. 531 00:35:06,070 --> 00:35:12,340 But that's another kind of polygyny, 532 00:35:12,340 --> 00:35:16,280 because often only one male's doing almost all the mating. 533 00:35:19,180 --> 00:35:21,520 The hotshot male. 534 00:35:24,550 --> 00:35:27,800 And then polyandry, where we mentioned the sandpiper, where 535 00:35:27,800 --> 00:35:30,075 the female will leave the first male 536 00:35:30,075 --> 00:35:32,070 and then have a second brood of eggs. 537 00:35:32,070 --> 00:35:34,300 So she's mating with at least two males. 538 00:35:38,180 --> 00:35:42,530 But this occurs in various other birds as well. 539 00:35:42,530 --> 00:35:48,930 And it occurs in some human groups. 540 00:35:48,930 --> 00:35:50,970 And then polygynandry, where you have 541 00:35:50,970 --> 00:35:53,020 more than one male and more than one female. 542 00:35:55,620 --> 00:36:00,200 And you have all of these mating systems in the dunnock. 543 00:36:00,200 --> 00:36:04,860 And I've underlined here Figure 8.3, 544 00:36:04,860 --> 00:36:08,870 because I want you to study that. 545 00:36:08,870 --> 00:36:10,900 I didn't get a copy of it. 546 00:36:10,900 --> 00:36:11,750 I'm sorry. 547 00:36:11,750 --> 00:36:15,250 I actually have a disk, I think, that has these. 548 00:36:15,250 --> 00:36:17,760 But it's an interesting figure. 549 00:36:22,620 --> 00:36:26,600 And in it, he shows the four kinds of mating. 550 00:36:26,600 --> 00:36:40,010 And then he shows what happens if the female leaves 551 00:36:40,010 --> 00:36:45,220 the monogamous situation, how can she benefit? 552 00:36:45,220 --> 00:36:47,406 And what happens if the male leaves? 553 00:36:47,406 --> 00:36:48,280 How can they benefit? 554 00:36:48,280 --> 00:36:50,780 And they've collected data on this. 555 00:36:50,780 --> 00:36:56,300 And then those groups, what are the selective factors that 556 00:36:56,300 --> 00:37:05,240 make them become polygynandrous in the last one? 557 00:37:05,240 --> 00:37:08,550 And the data-- as I read it, I think 558 00:37:08,550 --> 00:37:12,140 there's a mistake in the figure, because it doesn't fully 559 00:37:12,140 --> 00:37:12,790 make sense. 560 00:37:12,790 --> 00:37:14,510 But most of it makes very good sense. 561 00:37:14,510 --> 00:37:26,790 And these studies by this guy Davies, 562 00:37:26,790 --> 00:37:30,090 I believe that was his group that collected that data. 563 00:37:30,090 --> 00:37:31,840 But I want you to look at that, because it 564 00:37:31,840 --> 00:37:40,120 shows how the counts of genetic success 565 00:37:40,120 --> 00:37:42,590 can vary just depending on the mating system. 566 00:37:42,590 --> 00:37:45,590 And sometimes moving to another mating system 567 00:37:45,590 --> 00:37:51,390 affects one sex a bit more than another. 568 00:37:51,390 --> 00:37:53,390 And that's what's led-- because all of these 569 00:37:53,390 --> 00:37:59,070 occur in the dunnock, it was a good species to study for that. 570 00:37:59,070 --> 00:38:01,940 And he certainly did find different benefits 571 00:38:01,940 --> 00:38:07,220 to male and to female if they moved to another mating system. 572 00:38:07,220 --> 00:38:11,040 So what makes monogamy happen? 573 00:38:11,040 --> 00:38:14,740 There must be some situations that favor monogamy. 574 00:38:14,740 --> 00:38:21,450 And these are specific examples of monogamous animals-- 575 00:38:21,450 --> 00:38:24,840 the Siberian hamster, the Djungarian hamster Phodopus. 576 00:38:27,850 --> 00:38:32,190 It lives in nature under very harsh conditions. 577 00:38:32,190 --> 00:38:38,770 It's very cold, food is limited, foraging is difficult. 578 00:38:38,770 --> 00:38:41,090 It makes it unlikely that pups could 579 00:38:41,090 --> 00:38:45,710 survive unless they have at least two caregivers. 580 00:38:45,710 --> 00:38:49,290 So that's a very good reason. 581 00:38:49,290 --> 00:38:59,350 If neither of them can mate-- if there's only one of them, 582 00:38:59,350 --> 00:39:02,750 the female can't do it by herself. 583 00:39:02,750 --> 00:39:04,310 So it's not good for the male either, 584 00:39:04,310 --> 00:39:07,310 because he can mate with her, but if he 585 00:39:07,310 --> 00:39:10,890 doesn't stay to take care of the young, they won't survive. 586 00:39:10,890 --> 00:39:12,510 And they've collected data on this, 587 00:39:12,510 --> 00:39:16,210 and this appears to be the case with Siberian hamsters. 588 00:39:16,210 --> 00:39:18,870 The deep sea anglerfish has a different problem. 589 00:39:18,870 --> 00:39:20,890 He's one of these sit-and-wait predators. 590 00:39:20,890 --> 00:39:27,770 He sits in one place until something he can eat 591 00:39:27,770 --> 00:39:28,820 comes along. 592 00:39:28,820 --> 00:39:32,330 And he hardly ever sees another anglerfish. 593 00:39:32,330 --> 00:39:35,720 So when he does, the male attaches himself 594 00:39:35,720 --> 00:39:39,650 to the female as a kind of parasite. 595 00:39:39,650 --> 00:39:44,310 Otherwise he's not likely to see another female. 596 00:39:44,310 --> 00:39:45,670 Too much time may go by. 597 00:39:45,670 --> 00:39:47,300 He may never have another chance. 598 00:39:47,300 --> 00:39:52,015 So it's good reason for a peculiar kind of monogamy. 599 00:39:55,560 --> 00:40:00,500 But monogamy isn't as common as other mating strategies. 600 00:40:00,500 --> 00:40:03,440 In many species they have a kind of monogamy, 601 00:40:03,440 --> 00:40:05,940 but it's not that the female wouldn't 602 00:40:05,940 --> 00:40:07,510 go off and mate with another male. 603 00:40:07,510 --> 00:40:11,120 So the male simply practices mate-guarding. 604 00:40:14,620 --> 00:40:18,282 He watches her and drives away other males 605 00:40:18,282 --> 00:40:19,490 if they try to mate with her. 606 00:40:19,490 --> 00:40:20,170 He watches her. 607 00:40:20,170 --> 00:40:22,640 He guards her until she lays the eggs. 608 00:40:25,700 --> 00:40:31,650 He wants to make sure that it's his sperm-- the only sperm-- 609 00:40:31,650 --> 00:40:33,000 that inseminates those eggs. 610 00:40:37,340 --> 00:40:40,680 So that reduces the chances of extra pair copulations. 611 00:40:40,680 --> 00:40:42,840 And it occurs in many species, as we 612 00:40:42,840 --> 00:40:44,450 will see when we study sociobiology. 613 00:40:47,840 --> 00:40:50,770 So what strategies do you have other than mate-guarding 614 00:40:50,770 --> 00:40:55,670 to enforce a kind of monogamy? 615 00:40:55,670 --> 00:40:57,480 So in other words, it may not always 616 00:40:57,480 --> 00:41:01,900 be the natural preference, especially if the female, 617 00:41:01,900 --> 00:41:03,840 she might readily mate with another male. 618 00:41:03,840 --> 00:41:05,920 So the males have evolved strategies 619 00:41:05,920 --> 00:41:07,320 other than mate-guarding. 620 00:41:07,320 --> 00:41:09,990 For example, there are crabs in which 621 00:41:09,990 --> 00:41:14,400 the males' ejaculate forms a plug that 622 00:41:14,400 --> 00:41:17,240 makes it almost impossible for another male 623 00:41:17,240 --> 00:41:18,790 to get any sperm in there. 624 00:41:22,600 --> 00:41:25,180 It works. 625 00:41:25,180 --> 00:41:27,400 And of course, what would you expect in evolution? 626 00:41:27,400 --> 00:41:31,760 If that goes on too long, you'd expect other males perhaps 627 00:41:31,760 --> 00:41:34,900 will evolve a strategy to overcome that. 628 00:41:34,900 --> 00:41:36,775 Or the female will evolve a strategy, 629 00:41:36,775 --> 00:41:37,995 if it's to her benefit. 630 00:41:41,090 --> 00:41:43,530 In dunnocks, you have the phenomena 631 00:41:43,530 --> 00:41:46,760 of last sperm precedence. 632 00:41:46,760 --> 00:41:51,892 That means the last male that mates with her, 633 00:41:51,892 --> 00:41:54,210 it is his sperm that are the most 634 00:41:54,210 --> 00:41:59,840 likely to be successful in fertilizing her eggs. 635 00:41:59,840 --> 00:42:03,705 So the males, before they mate with a female, 636 00:42:03,705 --> 00:42:07,370 will peck at her cloaca region. 637 00:42:07,370 --> 00:42:11,250 And they first weren't sure about why he does that. 638 00:42:11,250 --> 00:42:13,780 It seemed to be part of the mating ritual. 639 00:42:13,780 --> 00:42:17,160 But then they observed that if he does that for a while 640 00:42:17,160 --> 00:42:21,400 she excretes a fluid. 641 00:42:21,400 --> 00:42:23,850 And if they look at that fluid under the microscope, 642 00:42:23,850 --> 00:42:27,130 they find out she's actually getting rid 643 00:42:27,130 --> 00:42:31,790 of sperm put there by an earlier male. 644 00:42:31,790 --> 00:42:35,080 In other words, that male wants to be not only the last one 645 00:42:35,080 --> 00:42:38,410 to mate, but he wants to reduce the chances 646 00:42:38,410 --> 00:42:41,730 that previous males' sperm will be 647 00:42:41,730 --> 00:42:46,040 able to fertilize any of her eggs. 648 00:42:46,040 --> 00:42:48,440 The male invertebrates are even more interesting, 649 00:42:48,440 --> 00:42:52,520 because they've evolved special methods 650 00:42:52,520 --> 00:42:54,600 to get rid of the sperm of the female. 651 00:42:54,600 --> 00:42:58,680 Some of them have penises that looks like a bottle brush. 652 00:42:58,680 --> 00:43:01,370 They can put it in and scrub her out. 653 00:43:01,370 --> 00:43:02,577 Get rid of the sperm. 654 00:43:06,240 --> 00:43:08,885 And you can read about that on page 186 there. 655 00:43:13,590 --> 00:43:17,770 Now there's still more to the story. 656 00:43:17,770 --> 00:43:22,160 In polyandry situations, in some species 657 00:43:22,160 --> 00:43:25,650 last sperm precedence doesn't predict paternity 658 00:43:25,650 --> 00:43:33,310 the way it does in the dunnock. 659 00:43:33,310 --> 00:43:35,470 And if it doesn't predict paternity, 660 00:43:35,470 --> 00:43:42,350 then it raises the possibility that somehow the female 661 00:43:42,350 --> 00:43:45,790 is able to control the situation. 662 00:43:45,790 --> 00:43:48,960 Maybe she can decide which male-- 663 00:43:48,960 --> 00:43:52,961 which sperm-- is going to fertilize her offspring. 664 00:43:52,961 --> 00:43:54,810 So that will certainly come up again. 665 00:43:57,550 --> 00:44:00,970 And then you have really more straightforward things. 666 00:44:00,970 --> 00:44:03,830 Because the more sperm there is, the more likely 667 00:44:03,830 --> 00:44:09,300 it's going to contain the ones that fertilize the eggs. 668 00:44:09,300 --> 00:44:15,180 So in the dragon lizard, if they see their female 669 00:44:15,180 --> 00:44:20,280 with another male, they will mate longer with her 670 00:44:20,280 --> 00:44:23,210 to increase the quantity of the ejaculate. 671 00:44:23,210 --> 00:44:25,250 That increases the probability. 672 00:44:25,250 --> 00:44:27,790 It's similar to last sperm precedence. 673 00:44:27,790 --> 00:44:31,210 It may be a major reason why last sperm precedence works. 674 00:44:34,070 --> 00:44:36,940 And there are many species that do that. 675 00:44:36,940 --> 00:44:39,810 The female is encountering other males a lot. 676 00:44:39,810 --> 00:44:41,700 They'll just mate for longer periods. 677 00:44:41,700 --> 00:44:43,480 They produce more sperm. 678 00:44:43,480 --> 00:44:46,950 And also, when they do that they occupy the female for a longer 679 00:44:46,950 --> 00:44:48,400 period of time-- and the more they 680 00:44:48,400 --> 00:44:50,230 can occupy her the less chance she's 681 00:44:50,230 --> 00:44:53,950 going to get to copulate with another male. 682 00:44:53,950 --> 00:44:56,750 And of course they can also evolve 683 00:44:56,750 --> 00:45:00,400 production of more energetic sperm. 684 00:45:00,400 --> 00:45:02,590 They can beat the competition. 685 00:45:02,590 --> 00:45:05,550 It takes a while in the reproductive tract 686 00:45:05,550 --> 00:45:08,100 for the sperm to even find the egg. 687 00:45:08,100 --> 00:45:10,470 So that's another strategy. 688 00:45:10,470 --> 00:45:15,360 And sociobiologists have found evidence 689 00:45:15,360 --> 00:45:19,010 for these various things, as we will be discussing later. 690 00:45:23,400 --> 00:45:25,660 I mentioned DNA analysis. 691 00:45:25,660 --> 00:45:28,330 It's been done on the sandpipers. 692 00:45:28,330 --> 00:45:32,222 Remember, they lay one clutch of eggs-- four eggs. 693 00:45:32,222 --> 00:45:33,430 They stay for a little while. 694 00:45:33,430 --> 00:45:36,590 Then they fly off and they lay another clutch of eggs. 695 00:45:36,590 --> 00:45:38,780 The first male has to stay with the first four, 696 00:45:38,780 --> 00:45:41,825 so she gets another male to take care of her second group. 697 00:45:41,825 --> 00:45:44,340 So what have they found? 698 00:45:44,340 --> 00:45:45,800 The second clutch of eggs may have 699 00:45:45,800 --> 00:45:48,355 been fathered by the first mate and not the second. 700 00:45:51,020 --> 00:45:53,800 So in that case there's only one way this could happen. 701 00:45:53,800 --> 00:45:56,630 She stored sperm from the first mate 702 00:45:56,630 --> 00:45:59,760 and simply delayed its use. 703 00:45:59,760 --> 00:46:03,630 We call it a covert choice, because it's not 704 00:46:03,630 --> 00:46:06,690 overt behavior. 705 00:46:06,690 --> 00:46:14,036 So she's simply enslaving the second male, 706 00:46:14,036 --> 00:46:17,050 getting him to raise her eggs. 707 00:46:17,050 --> 00:46:21,970 You see, she's made a choice in the quality of the genes 708 00:46:21,970 --> 00:46:24,860 by assessing the two males. 709 00:46:24,860 --> 00:46:28,290 And so when she meets the second male, 710 00:46:28,290 --> 00:46:33,550 he might be perfectly capable of nesting and brood-tending, 711 00:46:33,550 --> 00:46:36,830 but maybe not as attractive to her 712 00:46:36,830 --> 00:46:38,820 in other ways as that first male. 713 00:46:38,820 --> 00:46:41,900 So she stored up sperm from the first male. 714 00:46:41,900 --> 00:46:45,640 So she can make that choice. 715 00:46:45,640 --> 00:46:50,370 It's comparable to what I know about kangaroos. 716 00:46:50,370 --> 00:46:55,210 Kangaroos will generally carry two fetuses, 717 00:46:55,210 --> 00:46:57,540 but only one of them will mature. 718 00:46:57,540 --> 00:47:02,860 The other one will be held in a kind of suspended animation. 719 00:47:02,860 --> 00:47:08,430 And then, if something happens to her first little joey-- 720 00:47:08,430 --> 00:47:13,902 he dies-- the second one will start growing in her. 721 00:47:13,902 --> 00:47:15,790 So she's got a spare. 722 00:47:15,790 --> 00:47:19,110 Similar to this in that it's the same father, 723 00:47:19,110 --> 00:47:23,870 but at a later time. 724 00:47:23,870 --> 00:47:27,270 She's got a backup fetus. 725 00:47:27,270 --> 00:47:28,830 Last topic here-- the lek. 726 00:47:31,880 --> 00:47:34,510 How can a male in a lek who never 727 00:47:34,510 --> 00:47:38,125 seems to succeed in meeting with a female nevertheless 728 00:47:38,125 --> 00:47:42,150 benefit by participating in that lek? 729 00:47:42,150 --> 00:47:45,690 Why does he participate if he's obviously not the hotshot? 730 00:47:48,410 --> 00:47:50,800 Well there's various models to deal 731 00:47:50,800 --> 00:47:55,950 with that whole issue of the lek-- the hotspot model. 732 00:47:55,950 --> 00:47:58,210 This is the advantage. 733 00:47:58,210 --> 00:48:02,180 Let's say the females are not going to mate for very long. 734 00:48:02,180 --> 00:48:04,820 Then you've gotta position yourself 735 00:48:04,820 --> 00:48:06,940 where all the females are coming. 736 00:48:06,940 --> 00:48:09,260 So they go to a place where all the females come. 737 00:48:09,260 --> 00:48:10,960 That's called the hotspot model. 738 00:48:10,960 --> 00:48:15,270 Hotshot model, well, you can benefit by being near a hotshot 739 00:48:15,270 --> 00:48:17,010 because he will attract the females, 740 00:48:17,010 --> 00:48:20,540 and maybe you'll get a chance. 741 00:48:20,540 --> 00:48:23,780 There's some evidence for that. 742 00:48:23,780 --> 00:48:25,490 Another of the female preference model 743 00:48:25,490 --> 00:48:28,640 is simply that females, because they're 744 00:48:28,640 --> 00:48:33,820 facing predators-- and leks, groups of animals making mate 745 00:48:33,820 --> 00:48:36,230 choices-- are going to attract predators, too. 746 00:48:36,230 --> 00:48:39,840 So she wants this to be over with very quickly. 747 00:48:39,840 --> 00:48:42,970 So maybe leks have evolved in those species just 748 00:48:42,970 --> 00:48:45,330 to speed it up, get the whole thing done 749 00:48:45,330 --> 00:48:48,470 in a very brief period of time. 750 00:48:48,470 --> 00:48:51,020 The model that is preferred by Scott-- 751 00:48:51,020 --> 00:48:53,900 and it doesn't mean these other things 752 00:48:53,900 --> 00:48:56,210 aren't factors in the evolution of the lek. 753 00:48:56,210 --> 00:48:58,630 And since it occurs in over 200 species, 754 00:48:58,630 --> 00:49:00,865 it's likely that more than one factor 755 00:49:00,865 --> 00:49:02,865 has influenced its evolution. 756 00:49:02,865 --> 00:49:06,130 But kin selection simply means that in many leks, 757 00:49:06,130 --> 00:49:08,970 most of those males are related to each other. 758 00:49:08,970 --> 00:49:13,190 So even if many of those males don't get a chance 759 00:49:13,190 --> 00:49:15,690 to mate at all, maybe they're still 760 00:49:15,690 --> 00:49:18,014 benefiting because they share genes with that hotshot. 761 00:49:21,210 --> 00:49:25,280 Big brother can mate, but he carries 762 00:49:25,280 --> 00:49:28,580 a lot of the same genes I do. 763 00:49:28,580 --> 00:49:34,220 So you see, because when you look at genetic fitness, 764 00:49:34,220 --> 00:49:38,560 you have to consider how many copies of your genes 765 00:49:38,560 --> 00:49:41,610 are getting passed on. 766 00:49:41,610 --> 00:49:46,550 And you increase your fitness by helping your brother. 767 00:49:46,550 --> 00:49:49,970 So the females are more attracted to the lek. 768 00:49:49,970 --> 00:49:51,950 OK, only your brother gets to mate, 769 00:49:51,950 --> 00:49:55,980 but you're still passing on genes. 770 00:49:55,980 --> 00:49:58,880 That's the kin-selection model. 771 00:49:58,880 --> 00:50:01,390 And I'm just pointing out they're not mutually exclusive, 772 00:50:01,390 --> 00:50:03,530 these models. 773 00:50:03,530 --> 00:50:06,810 And yet we know it seems like it's 774 00:50:06,810 --> 00:50:09,300 a set-up for reducing genetic variation. 775 00:50:09,300 --> 00:50:11,620 And yet the genetic studies indicate 776 00:50:11,620 --> 00:50:15,440 that somehow the females do manage 777 00:50:15,440 --> 00:50:17,560 to preserve a lot of variability, 778 00:50:17,560 --> 00:50:20,550 indicating that even though the behavioral studies 779 00:50:20,550 --> 00:50:25,280 by scientists haven't seen many of those other males mating, 780 00:50:25,280 --> 00:50:27,840 it's clear that a lot of them do. 781 00:50:27,840 --> 00:50:32,570 So my guess is that the females are, in fact, in addition 782 00:50:32,570 --> 00:50:35,200 to mating with the hotshot male, they're 783 00:50:35,200 --> 00:50:38,500 probably mating additional times with other males 784 00:50:38,500 --> 00:50:41,270 before they leave. 785 00:50:41,270 --> 00:50:45,655 But this is unclear from the studies. 786 00:50:45,655 --> 00:50:48,340 All right. 787 00:50:48,340 --> 00:50:51,240 Sorry I went over a little bit.