Good afternoon everyone [it's] [a] real pleasure to [be] back at the Royal institution and the [last] time I was here was almost a year ago And I was contacted after the talk by a london artist named Clara [Lacey] [and] she had decided that she wanted to do a project Around the theme [of] the talk which was the evolution of males and females It's quite similar to what I'm going to talk about today and her project involves a series of illustrations of Males and females in different animals that I wanted to show some of them to you today because I think they make two points really quite beautifully, so one is that Sex differences differences between males and females are incredibly common in animals So we say in science that it's one of the the most common forms of diversity that we see out there And the other thing that I think these illustrations really show is How profound sex differences can really be so whether or not you're born male [or] female can influence not just how you look? But how you act your life [your] like history? Disease trajectories are often quite different the physiological differences can be very profound In this case in particular, I think brings this point home quite well, so this is what's called an [anglerfish] These are deep sea dwelling fish and the female you can see is the large one and she sits on the bottom of the ocean Very very deep in a sea And it's quite hard to one both see down there and two because they're quite rare to [find] a mate and so the male is the small one [and] [he] goes around when he finds a female He doesn't want to let go so he actually burrows into her flesh And he acts as a parasite and all of him sort of melts away except as for his reproductive organs And so people have pulled these fish up through massive trawling expeditions and females can have dozens of parasitic males sort of embedded in them And you can only imagine really how different these things are we thought that they were different species for a long time and it took us quite a lot of Work to figure out that. They're really simply two forms of the same species males and females So I want to talk about two different things today one How we make different males and females so the genetic triggers that initiate that? Differentiation between the sexes and once you have the evolution or the origin of males and females you have the opportunity for some Within either males or females to be more beautiful [and] we've been looking at sort of the genetics of beauty as well in species that you might not consider beautiful, but are sort of quite useful in this regard, [so] [I] was part of a working group a couple years ago [called] the tree of sex and our job was really just to map out How sex is Determined? so the initial genetic triggers between males and [females] And we came up we ultimately decided that that goal was impossible It was too much variation too much diversity But we thought we could get sort of a handle on some of the basic systems and today I just want to walk you [through] some [of] the more common forms of sex Determination And to start things out quite easily. [I] thought we'd start with what we are. So we have xy sex Determination not only mammals have this type of sex determination, but lots of other things, so most beetles lots of flies including house flies have xy sex determination lots of fish like salmon all sorts of other insects and invertebrates as well and so this is called a karyotype, and it's basically a stain of all your chromosomes and Males and females are quite similar so most of the chromosomes are exactly the same so at chromosomes are large chunks of DNa that carry lots and lots of genes and the only difference between males and females are the presence or the dose of the x in the y chromosome So females have sorry males have one of what we call the x chromosome which is quite large It has lots of genes, and they have one y chromosome which is quite small and has relatively few genes in contrast to females Where they have [2x] hums? so There we go so The [x-Chromosome] as I said is quite gene rich it has about 800 different genes And they seem to be many of the genes on the axe seem to be particularly important in Brain formation We don't really know why the gene seems to be the chromosome seems to be the brain chromosome But otherwise the x is just like any other chromosome you've got in your genome it's the y that's sort of unusual, so it only has about 70 genes and only about 27 unique genes so many of the genes on the wire and multiple copies about 27 of them are unique and the important one in sex determination is one called sry If you have sry on your y chromosome you develop as a male if you don't have sry Or you don't have a white chromosome you develop as a female and the other genes on the y their job is mostly involved in sperm formation and that's why a lot of genetic cases of Male Infertility are due to Deletions or loss of genes on the y chromosome so they seem to sort of have a very important role in male reproductive function? So even though they look [very] different today the x and the y they were once actually exactly the same So even you have pairs all your chromosomes come in pairs and every time your cells divide those those pairs come together So it comes in one pairs with the other Chromosome one and they exchange genetic material through what's called recombination and that recombination Sort of you swap bits back and Forth between the chromosomes And it keeps the chromosome pairs looking identical to one another and for reasons that we don't entirely Understand at some point the x and the y stopped recombining They stop sharing genetic information and [at] that point they began to diverge and we can sort of map this progress and people have done this in mammals sort of through this evolutionary history of The group so the x and the y chromosome that we know today that we have Originated at some point between the divergence of the monotremes so the platypus and all the other mammals [and] over time Sort of throughout the [elution] history of the mammals recombination was suppressed on a larger and larger and larger fraction of the x in the y chromosome until we sort of end up with the chromosomes that we see today in Humans a very small x And the very large y and There's this theory that you may have heard of if you read the newspaper a few years ago that [the] x chromosome Might be born to die Anyone heard about this? Right yeah, so it's sort of I think it struck a chord in the sort of post-feminist Society as well There were a couple scientists sort of pushing this theory and it got picked up by the Media and it's almost inescapable now And you can sort of see evidence of it. It's in the [newspapers]. There's there's whole books about it I'm sure all the men in the audience are terrified of this possibility Because as the y goes so goes men and so goes the species and several years ago I started to be get invitations to conservation genetics meetings And I work on things like chickens and turkeys and guppies, and they're not really a conservation concern So I was asking the organizers what they wanted me to talk about and they were actually very Concerned because they figured if the human y chromosome was endangered the y chromosome of all the animals that they were working on could be possibly? Endangered and did they need to worry about this in their conservation strategies And it made me realize that this really had sort of pervaded into pop culture and have been sort of then also Sort of secondarily moving into various fields of genetics as well Because most population geneticists never really bought into this theory I have to be honest so we know sort of the evolutionary trajectory of the y chromosome throughout time and There are chunks of the y that stopped recombining with the x at different periods right and there's sort of three or four big chunks in the mammalian lineage and Once they stopped recombining genes on the y I start to disappear. They sort of become silent right and The scientists who are pushing this theory drew a line across that this here is sort of the time since separation with the x chromosome so at what point the x and the y stopped recombining and this is the number of active genes remaining on that chunk and these it's true sort of a very straight line right and they predicted that in about five million years all the genes on the human y will disappear and so with the y will go men and so with men will go the species and Humans will be wiped from the face of the Earth, right? so It was actually quite a strong counter-argument to that in that you do who's quite a lot of genes But then there are sort of some genes that are quite essential to male fertility The sperm genes that are left on the y chromosome that will be maintained through selection, so evolution will act to maintain them right? And so instead of sort of this decrepit decaying y you have a y chromosome that's that small, but quite mighty in its functions [and] I wanted to tell you a little bit of Story about some of that we've been doing in guppies to sort of illustrate that you guys don't need to worry about your y chromosomes disappearing So guppies are very beautiful It's the males that are very beautiful in guppies and females actually prefer males that are really novel that have Interesting combinations of color and a lot of these color genes are actually on the guppy y chromosome and so my lab We've actually been sequencing white chromosomes from guppies to try and understand this relationship for female preference for novelty male Coloration and y chromosome decay and If you look at the karyotype of the guppy the y is actually very very large, right? And that's it's been sort of protected in many ways by this female preference for color so if the y was decaying or if the y did decay Males wouldn't be as vivid they wouldn't be as beautiful and they wouldn't actually get to reproduce Females wouldn't prefer them and so this female preference for coloration actually maintains and preserves the y against any sort of degrading forces So that's it about xy sex chromosomes with there lots of other ways of determining sex So the second most common way is the zw sex chromosome system, and we see this throughout all birds Things like the lepidopteras, so butterflies and moths lots of fish like eels Some flatfish some reptiles there are several snakes that have the w sex chromosomes, and this is just a converse of the xy system So this is a karyotype of Most birds the z and the Wware analogous to the x and the y Except the male has two copies of the z Just like the female and mammals have two copies of the x and the female has one zed and one w and the w is Transmitted from mother to daughter Analogous to the y in mammals being transmitted from father to son So there about 600 genes on the zed, and it's essentially the same as any other chromosome The w, it has about 50 genes that are our best estimate and they seem to be really important in female fertility and in birds they seem to be quite key to ovary formation and oo genesis so all those eggs that they lay and Sex is determined in a different way so in mammals sex is determined with the y chromosome right sry, and birds at our best understanding at this point Is that sex is actually determined By your dosage of the z so if you have two copies of the zed you make more of [a] gene product Called DMR T1 and you develop as a male If you have one copy of a z you make less of that product and you develop as a female so it's kind of a very different sort of genetic mechanism causing sex determination in these different groups, so That sort of a chromosomal based mechanism, but there are also other different ways of determining sex and lots of different animals [so] lots of reptiles and a few fish do it through environmental triggers, so in reptiles it tends to be temperature based sex Determination so high incubation temperatures introduce, in most turtles, Introduce Estradiol production. Estradiol hormone is a sex hormone And they develop into a female with the formation of an ovary. Lower temperatures result in in more males in the brood and this has actually become a legitimate concern with conservation particularly with global warming you can imagine so as the incubation temperature is just because of Global warming increase there is concern that [the] sex ratios will be an issue and to illustrate several conservation efforts in the 70s were focused on sea turtles which had become critically endangered for various reasons and [there] were lots of well-meaning Biologists who would go out every night so turtles sea turtles most of them. They hold himself up on a beach In the evening and the females [dig] a huge nest in the sand and then they deposit the eggs. They They bury the eggs again And then they go off and then some weeks or months later the baby Turtles emerge and then they sort of run as quickly as they can down to [the] sea and they do this through this sort of Gauntlet of death right so all these seagulls line up and just wait for these baby turtles to emerge because they're a great snack They're all sorts of predators that line up And so these these conservation Biologists would actually go out and they would get schools involved and I remember because as a child I grew up in Florida And we would go out and we would mark where the females had laid nests it was very exciting to be able to stay up that late when you're very young and [the] conservation biologists will come out take up the nest take the eggs into the lab Incubate them under controlled [conditions] get the young up until they were big enough to sort of survive Better on their own and then release them into the sea The problem is we didn't really know until quite recently how this temperature based mechanism worked and So they had the incubator set a little bit too low And from a conservation standpoint males aren't super useful, they're not, right? So you need a few around for the next generation, but you don't want lots and lots of them And you certainly don't want a majority of them because it's the females that make more right? So the more females you have in population the higher or the more quickly that population grows and so these conservation Biologists were very well-meaning you can't actually identify the sexes when a turtle in today They're about 20 years old So 20 years later as these things haul them back, themselves back onto the beach to lay the next generation It was so strongly male biased They finally put it together that it was the well-meaning conservation biologists that were actually sort of accurate acting counter to their goals suggest sort of small tweaks in temperature can [be] quite important And that's the story. I told you so really sea turtle was was one of the the turtles of most concern And now they're quite a few groups that have very carefully Calibrated their incubators to figure out exactly the ratio that they need [and] this has led to all sorts of theoretical modeling about What rising sea temperature rising global temperatures will do to the sex ratio and the concern is that? You know the turtles themselves. There's a lot of genetic variation among different populations So different populations have different [temperatures] set points Depending on where they live because temperatures in different locations vary right and so in theory they may be able to adapt to different Differences in temperature the concern is that if global temperatures change too fast [and] the turtles can't adapt? That we will lose [sort] [of] one sex and that could lead to all [sorts] of conservation issues [some] fish are what are called sex changers and these are Really common so quite a large share of fish start their life as one sex [and] at some point switch To the other and they do it in both directions. So did anyone see the movie finding nemo Right so remember the premise of the movie. It was a widower right whose wife or partner Had died along with all the other offspring he was left with one right so in reality all clownfish start out as male And then when the female on the anemone dies they switch they they switch sexes? and become female now the biological reality was I don't think well reflected in that movie But it would have been a very different movie than the one you all saw had they encompass the full biological reality of the clownfish [and] you also have things like gobies, so this is a bluebanded goby It's a small fish, but nests in these holes that snails drill out of the coral reef They'll actually start life as a female And they have this sort of size hierarchy and where the the largest individual is a male And then the females are also ranked in a hierarchy if that male dies the largest female becomes a male in three days so Remember how confusing Puberty was for you? And it lasted for years right just think about it, so We don't really understand why these species have different mechanisms of sex determination like this, but we think that in There's an advantage to being large only [if] you're female in the clownfish because females lay many many more eggs And so you only reach that sort of benefit once you reach a certain size right if you're large in a male It doesn't help you at all But it only does as a female so there may be sort of an evolutionary advantage to being able to switch sexes The Blue [Bended] [Goby] is a little bit different So those nest sites those those holes in the coral reef are very limited and males compete fiercely Against each other and the aggression is based the competition is based almost entirely on size So you have to reach a certain size? Before you're actually able to defend a nest and so it only makes sense to reproduce as a male Once you have a nesting and to defend it until you reach that certain size So I think there are a couple other things that I wanted to go through on this yeah so haplodiploidy so this is actually a difference in chromosome dose in Genome dose between males and females and it's Particularly common in the hymenoptera so bees, wasps, ants things like that So the queen and the workers all the females they develop from fertilized eggs So they have two copies of every chromosome just like we do right leave two copies of every chromosome Males develop from unfertilized eggs, so the female lays an unfertilized egg [it] only has one copy of every chromosome from its mother and that's what gives you a male and this through some sort of Weird math and genetics means that sisters are more related to each other than [they] would be to their own sons and so their evolutionary Interest is not in their offspring and and helping them get along But actually in helping their sisters through the colony or the hive and that leads to all sorts of weird things like this This is rafting so in the Amazon or in places where there are seasonal floods Lots of ant colonies will form these rafts And it it's essentially all the workers sort of blinking legs together to sort of float along the river so that they can find a new site for the Colony or the nest right the problem is that the ants on the bottom will drown? [and] so it leads to these sort of interesting altruistic situations where females will give up their own life Sacrifice their own life for the benefit of the colony and their sisters aphids do it with sex chromosomes, but only some of the time so they have a very interesting sex determining mechanism so Males are what's called x naught so they have two copies of every chromosome? except the x they don't have a y so it's just a single x females have two copies of every chromosome including the x But yet Sexual reproduction is quite rare so in the beginning of the the growing season females disperse And they reproduce what's called parthenogenesis. Oh, they essentially clone themselves [and] only at the end of the growing season Do they actually generate males there's one round of sex and then all the eggs sort of store go Dormant and survive through the winter And that's what's sort of showing here, so in the beginning of the season you have a female dispersing to a plant Making lots and lots of daughters and only at the end making a few sons There's a round of mating and that everyone goes quiet through the winter and this sort of mechanism is how in your garden [I] need a point here you get a single aphid and the next day all your roses are completely covered because they're making nothing but daughters And those daughters are making nothing But daughters and the population grows incredibly rapidly. It's a very successful strategy, that kind of life cycle And the last one I want to talk about is the Amazon molly, so it only pretends to have sex really interesting so The Amazon molly is another what's called parthenogenetic species, so they give birth to daughters, clones, females give birth to clone daughters But they need to have some sort of they sort of need to pretend to have sex Because they actually need a sperm cell to sort of Pierce the their Zona Pellucida the area around the egg to Initiate Development right so they sort of pretend that there are the same species as the sailfin mulling and they mate with a male so the sperm [Pierces] the egg And then it's completely ejected so none of the genetic matter makes it through into the egg and you get more Amazon mollies looking just like the mom and it's a really interesting system because the Amazon molly can only reproduce in the presence of the sailfin molly and yet because it's nothing but females its population grows much much more quickly than the sailfin molly right and The Sailfin Molly male, all their effort at sperm production is completely wasted in this model they're not getting any of their genes into the next generation and So if the density of the Amazon molly gets too high it can cause local extinction of that Sailfin Molly which leads to local extinction of the Amazon molly, so it's this sort of Very complicated population dynamics where you get the sailfin molly colonizing a new lake the Amazon Molly moving in Parasitizing the sperm driving the local extinction of the sailfin molly leading to its own extinction leading to another round of colonization It's very complicated So I hope I've convinced you that sex determination is very weird and very cool and very diverse But there's this other thing that happens once you've got males and females There's the opportunity for some of those Individuals within each sex to be more attractive than others [we] think of this humans as beauty, right? animals have beauty as well only Humans are a bit odd right. We think of women as being more beautiful than men in most animals It's the males that are actually competing quite fiercely for female attention and in many cases leads to these sort of what we might think of a beautiful traits color behavior size all Sorts of different [things] Now when I talk about beauty in two different animals that you might not think are particularly beautiful But the females in those species think that they're just dead sexy, and that's the wild turkey And it's hard to believe that this is actually a very very sexy male and the ocellated wrasse and I think we might be more inclined with human aesthetics to sort of think that this is an attractive male But I'll explain why he's particularly attractive in a moment But first I'm going to talk about sort of what makes males and females different, so we have these initial mechanisms of sex Determination But then they in turn affect a huge proportion of our genomes So our bodies the processes within our bodies are all regulated by proteins they're encoded by genes and we've got thousands of genes that make even more proteins so a Single Gene can make several different kinds of proteins and most vertebrate genomes Hold somewhere between 12 to 20 thousand different genes so it's very very complex and the amount of protein that you make from these genes is one way of creating sort of differences between individuals right and when you look there's been some technology changes recently you've probably heard about all the sequencing that people are doing [now], so The NHS is sequencing I think 10,000 people doing full genome sequences We look at what's called Gene expression So it's a measure of how much protein a given individual is making in a different tissue And we can do this for all the genes expressed in a given tissue at any time And you get pictures kind of like this [so] just to unpack it This is what's called a transcriptome each column is what's called a transcriptome? And it's a way of visualizing the expression patterns for all the proteins that are expressed in a given tissue or what type of cell or part of the body and proteins at High level so high Abundance are in yellow low Abundance are in Black and I sort of clustered all the female samples together and all the male samples together and and what you can see is that all the Female Samples are more similar to each other than they are to the male samples or vice versa So sex has a profound effect on how your genome works, right, and we think that genes expressed more in females are important for females right so they're important for female function female form It's what makes a female different from a male is the expression of these genes And the genes that are expressed more in males. There's more of the protein in these males. We think these genes are important for Males for the function and the form And it's quite difficult to test this assumption right because you're talking about thousands of genes, and we can't do functional genetics on all genome like this and so we've been sort of Cheating in various ways and using the diversity that we see in the animal kingdom to test these different assumptions So as I said most genes are differentially expressed between males and females Different protein amounts even though they share the same gene they use it in different ways [and] We call this sex bias gene expression, and it's greatest in reproductive tissue. Which we might expect, intermediate in some somatic organs, so for some reason the liver shows a lot of sex differences in Gene expression make what you will of that at the pub at least in the brain. so brain expression seems to be the least different between the sexes [and] [as] I said it's difficult to sort of test this relationship between The expression level of specific proteins and sex across the entire genome because there's just so many genes [so] we [actually] started working with a breeder up in New York sure who keeps a large population of essentially wild American turkeys and Turkeys are really interesting because they've got two types of males They have a dominant male and a subordinate male and so the winter before they reach sexual maturity all the males in a clutch so all the brothers and half-brothers come together and they have a series of really [epic] and quite vicious battles and The ultimate winner becomes the dominant male and all the losers become subordinate males and once this hierarchy is Established the subordinate males don't challenge their dominant brother, but they actually work with them To defend the best spot that they can find on the breeding ground from other groups of males so there's an element of male-male competition and they actually advertise with him to attract females to their dominant male brother and So we know that these males the subordinate males are capable of reproduction They actually do produce sperm But we know that they also never seem to say spring either because the females don't find them very attractive Or because they never take the opportunity if there is any and so their entire evolutionary Fitness Is tied up in getting females to their dominant male brothers, so this is an example of what's called Hamilton's rule of Kin Selection [and] it's a what. We call it plastic phenotype so if you remove that Dominant male all the remaining brothers come together and they have another series of battles and the winner becomes the new dominant male So subordinate and dominant males are both clearly male, and they share several main male traits, so they both have a large body size They both have iridescent plumage, and I don't know if you can see it But there's this sort of oily sheen on the feathers of the male so birds can see well into the UV spectrum they have a whole other opsin gene that helps them see into this and this is actually [to] a female a really vivid beacon of male quality that they key in on They both have a beard which is this collection of long thin feathers here, and they both display And there's some evidence suggesting that having more and more Vigorously displaying subordinate male brothers helps attract more females to the dominant male And yet, they're slightly less male in certain traits. So they have less pivothead coloration [you] [can] see the dominant male here is really Vivid blue with with some vivid red as well, subordinate Male Is more muted it's primarily red and pink they have less developed caruncles and wattles which are these sort of Woody things on the head on the neck and don't ask me why but females really keen on it They [think] it's very [attractive] and they [have] a shorter snood And if you don't know what a snood is it's this long thin thing that hangs down the beak of the male so males actually can expand and contract them in real time, the snood, and There's there's a lot of evidence that having a longer snood helps in male-male competition Battles and you can almost predict this females prefer males with Longer snoods And I was at a poultry show a few years ago where they had domestic Turkeys in cages, and there was a male In one cage and to one side was a female that he was really Trying to Impress And on the other side of them was another male that he really didn't want to antagonize and so every time this trick he would Turn his head to the female He would expand his snood and then he would turn his head to the male He didn't want to antagonize him, so he would shrink his snood And he would go back and forth, and I spent like an hour watching this thing it was amazing So if you really want to see it, I used to have a video this in my talk but it's really it verges on the pornographic, so Once you're done Hanging out on the Royal institute Youtube channel type in turkey snood into Youtube and you will be amazed But you might want to make sure that your kids and grandkids aren't your room? So we've worked with this breeder To try and understand what was going on between these two types of males And these are the transcriptomes So I'm showing you the gene expression for the dominant male and Dark blue the Subordinate male and light blue and the female in red, and you can see here, so this is sort of a Measure of similarity at the top between the different morphs, right, and this is the confidence so that the higher that number The more confident we are that these two? Transcriptomes are more similar to each other than that one so you can see that the with very very high statistical confidence The two male morphs cluster most closely together so they're both clearly male We're not making a case that this is a third sex, or intersex in any way but yeah There's some subtle differences when you look you can see sort of color differences here between the morphs and to some extent here as well And we were curious to sort of the finer scale patterns as well And so when we looked at male bias genes genes expressed more in males that we think are really important for male function and phenotype Subordinate males which are a little bit less male in many ways Express many of those genes a little bit less So they're sort of demasculinized across thousands of male bias genes and when we look at female bias genes that we think are important for females the subordinate males express them a little bit more So they're sort of a little bit feminized for these genes And this was true, not only in the gonad where you might expect it, but in the soma as well, I Mean we looked at Several different somatic issues But there's one thing about this system It's a little bit weird, and that's that the subordinate males even though they technically can mate they make sperm They don't make a lot of it right because they don't need it. They're never mating and so usually when we think of Male Beauty In animals we think about sort of a trade-off between investment in the bright colors and the long tails and the costly behaviors and reproductive function Which is also quite costly so how much can a male Sort of invest in one versus the other and that sort of a trade-off that they have to to make And so we started [worki ng] with a collaborator [Suzanne] alonso Who's at University of California Santa Cruz and she works on the ocellated wrasse and They have different types of males and in this case all the males are reproductive And they're competing against each other fiercely to fertilize eggs, so in addition to the female. There's what's called a territorial male And he's bigger, and he's brighter. He has lots of bright colors. You can't see it super well here, but They're almost fluorescent They're so bright right and there's a lot of effort [that] they put into maintaining that Bright coloration They also attract females to the nest they build the nest they defend it. They attract females to it. They're expressing all these bright traits and then there are these other little Annoying cheater males, so there's they're smaller [they] don't invest in the traits. They don't build a nest they have satellite males who are tolerated by that territorial male But they actually sort of help clean and defend the nest with him in exchange for that They're allowed to fertilize some eggs from some females So that they sort of make a bit of effort not as much, and then there are what are called sneaker males Right, so a friend of mine who works on similar things described these is basically Swimming Gonads so They sort of sneak into the nest is the females about to spawn They blast the place with sperm and then they head out as fast as they can so they make absolutely [no] investment in the nest or in these Vivid coloration patterns that the Territorial male has and so Suzanne has done a lot of work and shown that almost every nest out On the reef is it has multiple Paternity so multiple males Sneakers satellites and territorial male are all contributing to the paternity of those eggs. So there's really fierce competition amongst these different males To sort of fertilize these eggs, and so we wanted to know in this system It's a bit different than the turkeys because all the males are reproductive We're all making is much sperm as fast as they can and yet that territorial male has to do something else as well He has [to] invest in all these bright colors, right? [but] he has the benefit of proximity so he's in the nest and so in theory [he] might have sort of an advantage just by proximity to the eggs alone in that fertilization event And so this is sort of the the cost of being beautiful this question and The Data sort of suggests that these beautiful territorial males might be genetically a little bit less of a man So for genes that are expressed more in females. They actually express them a little bit more This is completely the opposite of what we see in [this] turkey story, right? So they express them a little bit more which is not what we might expect and From male biased genes they express them a little bit less suggesting that there is a trade-off with being beautiful they can invest less This was from gonad tissue in sort of sperm production Because they're investing so much in these bright colors [and] So overall this might sort of reduce their total sperm production But because they're right there in the nest when the females spawn and the females actually prefer to spawn With these territorial males it might compensate for that sort of trade-off and that cost. Very briefly we've found a whole different, a whole bunch of different animals in the lab various questions about sex and beauty and Conflict between males and [females] and for more about sort of what we do Everyone's different project you're welcome to sort of check out. What's going on there links to popular Sites are there as well as well as all the papers. We've published and thanks again for your attention It's in the female's best interest to keep the mail around and interested [and] one way to do that is through sex I know when we think of humans it gets quite dark very quickly
Original description:
There is also a Q & A session (wherein someone asks about the evolution of females eating males after sex in some species, among other interesting things) here: https://youtu.be/v-DROlBbZ8s
It's a great lecture. Was kinda sad to see it get so few upvotes here. It's a must watch.
I’m sure this won’t be controversial, right everybody?