How Is Genetic Variance Maintained Through Sexual Selection?
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00:00
Meeting/Interview
05:41
Meeting/Interview
Transcript: English(auto-generated)
00:04
Our main question is how sexual selection contributes to biodiversity on Earth. And there are a gazillion species on Earth and, for example, there are 160,000 moth and butterfly species that have evolved over the past 80 million years, and we would
00:23
like to understand how this evolution occurred. Evolution consists of reproduction and survival, and we are thus interested in reproduction. So who mates with whom, and who gets to reproduce most of the offspring.
00:41
In many species, like in birds, mate choice is happening for those mates that are the most beautiful or have the most elaborate tails or the longest tails. So the most extreme variants, but there are many species, including moths, where attraction happens
01:02
to the most common individuals. So those individuals that exhibit the most common signal of the species are selected for and the ones that deviate away from the mean are selected against. Now in these selection processes, you would expect that there is less and less variation
01:21
because either you have more, only the most elaborate, the most beautiful ones left over or you have the most common ones left over and all the other variants are selected away from the population. But this is generally not what we are seeing. We are seeing a lot of variants within the species and we would like to understand
01:40
how is this genetic variance maintained, how does the selection forces contribute to the divergence of new species. And that is especially an interesting question when you have stabilizing selection, thus when the species are choosing those mates that are the most common ones.
02:01
Because how can you then have a change into a new type of mate signal or mate response? How do we approach this question? So first of all, we try to understand the mechanisms of the variation in the signal
02:20
and the variation in the response. And we do that by identifying the genes underlying the signal variation and the genes underlying the signal responses. Not only are we trying to identify the mechanism underlying signal variation and response variation, but we also have started to question the general assumption
02:41
that the average is always chosen over the extremes. Is this always the case? And we address this question by detailed behavioral analysis in the lab and in the field. So our model organism of choice are moths. Because in moths the sexual communication is very well defined,
03:02
females produce a sex pheromone in a well-defined sex pheromone gland to which males are attracted and females produce a number of offspring, about between 200 and 1,000 offspring over a generation time of just a month.
03:24
So our main findings are that on one side the signaling itself changes. So the genes underlying the signals and the responses change through time. And we have identified already the gene that underlies the signal variation. And we have now identified new genes that underlie the responses to those signal variants.
03:47
In addition, we also found that not always the most common individuals are being chosen. There are variations on this theme. So, for example, we found that in one species there is a lot of variation
04:04
in every population that we sampled over the years. And there were attractive and very unattractive females. And we did not understand how these unattractive females could persist in the population. So we brought these populations back into the lab and we selected for the most attractive and the unattractive blend
04:22
and we fixed that into two selection lines. That allowed us to then test these attractive and unattractive females in the field. And what we found there is that these two unattractive females, when they are sitting next to each other, they indeed never attract any males, as we had expected.
04:42
But when these unattractive females were sitting next to an attractive female, she was sometimes mated by those males that were attracted to the attractive females. And when they encountered this unattractive female, then they sometimes would mate with her instead.
05:00
And interestingly, these attractive females sitting next to the unattractive female was even mated faster than when she was by herself or when she was sitting next to another attractive female. So there is a selective advantage also for attractive females to have these unattractive females in the population.
05:21
And this example shows that it's not always the common ones that are being chosen. There are variation on this theme and this variation may cause diversity in signaling and responses to these signals. So to wrap up, both of our assumptions are correct.
05:41
So on the one hand, signals do change through times as well as responses and we know now more of the genes that underlie these variations and these changes. And on the other hand, the common ones are not always chosen, so there are variants to the theme and there can be selection for different variants
06:03
so that these variants can be maintained in populations. So the relevance of our findings are that we get a better understanding of how sexual selection and the evolution of sexual attraction in itself
06:22
can maybe be the drivers of diversity on Earth. So in general, the basic assumption has been that the environment causes adaptation in species and that leads to species diversification.
06:41
And of course sexual selection is then part of it and maybe also later is involved in the changes that happen in the environment. But our research poses the possibility that maybe sexual selection may be a driver of species diversity and speciation.
07:05
So if there is a mutation happening in the signal or in the response and that leads to a signal variant and that signal variant is then chosen under certain circumstances, then that immediately can lead to population divergence
07:21
because those different populations, if they have different mating signals, they will mate with each other and not cross mate anymore and thus you have immediate genetic divergence and that could lead to new species.
07:43
So where do we go from here? Well first of all we need to identify more genes underlying the signals and especially the genes underlying the pheromone response because we're not there yet. We only have a clue of what type of genes are involved but we don't know the exact genetic variants that have led to these differences in responses.
08:05
But also we need to go much deeper into the sexual selection process overall. So I have focused now mostly on the female pheromone signal and the male response but we know that the sexual communication system
08:23
is much more complex than that and there are actually both sexes that are signaling and both sexes that are responding. And we know also with our genetic studies that the female signal and the male signal are genetically related to each other.
08:41
So it's really important to understand the selection forces that not only are expressed to the female signal at long range but also at the male signal at close range.