Posts Tagged ‘sex’
Sex and Sexual Selection in Economic Terms
In 2019 I published a paper in Biological Theory that sex is trade in somewhat different naturally-selected strategies which reduces risk and that sexual selection is conflict over the profits of that trade. Recently, while exchanging some views and papers with Ugo Pagano, I was drawn to the conclusion that that theory, put in economic terms, is that sex is profit-seeking and sexual selection is rent-seeking.
One of Pagano’s papers that was published in the Journal of Bioeconomics led me to browse further in that unfamiliar journal. Low and behold, I came across there a paper published in 2016 by a great evolutionary biologist, Michael Ghiselin, (whom I had met a couple of times at ISHPSSB meetings and who is well known for his work on sequential hermaphroditism among other things), titled “What is sexual selection? A rent-seeking approach”! Great company obviously – I just wished I had seen the paper in time to cite it!
Feminist Views on a Theory of Sexes, Sex and Sexual Selection
In an article in Biological Theory in 2019 on mating markets and in two posts here, one in September 2019 on the two-fold cost of sex and in May 2020 on mating markets, together I hope made clear that a single premise, if justified, could solve the three major evolutionary puzzles about sex. The premise is that in a dioecious population for example, i.e. one composed of males and females, the two are ecologically, i.e. naturally selected, to be somewhat different. That would solve:
a) the puzzle of what compensates for the two-fold cost of sex because of the advantages of specialization
b) the puzzle of why they engage in sex at all because such trade is a form of bet hedging which produces diversity reducing the risk of extinction, and
c) the puzzle of why they engage in sexual competition and selection and why it takes the form that it does because sexual competition and selection are conflict over the profits of the sexual trade and the form it takes depends on what the naturally-selected differences are.
However, there is one thing not discussed in any of the three (possible feminist views of such a theory) and one briefly discussed in the article (the potential role of centrioles) but not in the posts. The former is discussed here and the latter will be in a subsequent post.
As noted in the article and in the most recent post, if the naturally-selected sex allocation is with males/male gametes at high frequency but low quality, i.e. low per capita cost, and females/female gametes at low frequency but high quality, i.e. high per capita cost, then sexually males/male gametes would compete intrasexually for female mates/female gametes and females/female gametes would compete intersexually choosing high quality male mates/male gametes. Feminists might find both something to both dislike and to like about this explanation of “conventional” sex roles. On the one hand, one can imagine some people reacting, “I see, on this view the sexes are naturally different, well then that justifies etc.” On the other hand, in this scenario, females/female gametes choose not just as a side effect of high male/male gamete frequency, nor even necessarily because they invest more in each offspring, both of which theories are popular. They can choose because they are of higher quality, i.e. have more invested in them than do males/male gametes, and hence they can afford to choose. Of course, where the naturally-selected strategies are different – sex role reversed, or both sexes high quantity but low quality, or both high quality but low quantity, then sex roles would be different than the conventional ones. And as previously noted, if the naturally-selected population were for some reason completely out of sex allocation equilibrium, then sexual selection could restore it as, or perhaps even more easily than by Fisher’s principle.
What is the difference between LGT in prokaryotes and sex in eukaryotes?
Biologists are typically adamant that lateral or horizontal (used interchangeably) gene transfer in prokaryotes is not “sex” and should not be called that. Yet I keep running into people in print and in person, who, with little if any explanation, want to call it that. Are they just naive or could there be something more to it? So I decided to give the question some thought and here is what I came up with. Actually, it is quite difficult to pin down a principled difference between LGT in prokaryotes and sex in eukaryotes.
Consider a stereotypical case of LGT – conjugation in E-coli. Superficially it seems easy to characterize the difference. LGT is lateral (genes move between peers rather than being transmitted from parents to offspring), partial (only some of them do), and unidirectional (they move in one direction only).
Further consideration however suggests that things are not so simple. Eukaryotic recombination is, at least in part, just as “lateral” as is the prokaryote. Imagine an A1B1 haploid eukaryote engaging in sex and recombination with an A2B2. Whether the two loci are on different or on the same chromosome, together, they give rise to four offspring – two parental types an A1B1 and an A2B2 and two recombinant types an A1B2 and an A2B1. One way of looking at the recombinants is that a B2 has been transferred into an A1B1 displacing B1 while a B1 has been transferred into an A2B2 displacing B2 (or alternatively, an A2 has been transferred into a A1B1 displacing A2 and A1 has been transferred into a A2B2 displacing A2). Eukaryotic recombination then, is no less “lateral” than is the prokaryotic. This suggests we should stop talking about prokaryotic sexual processes as “lateral gene transfer” as if “lateral” were unique to them and talk about them simply as “gene transfer” (as some indeed already do).
Moreover, both prokaryotic and eukaryotic transfers are only partial. In eukaryotes, the non-recombinants A1B1 and A2B2 are, in effect, transmitted vertically rather than laterally, and with the recombinants, in the first version above A1 and A2 are as well, while only B1 and B2 are being transmitted through peers. This is not in principle unlike prokaryotes in which part only of the donor genome is transferred.
Is the bi-directional transfer in eukaryotes rather than uni-directional transfer in prokaryotes then the defining difference? With isogamy in eukaryotes, that seems to be the case. However, once anisogamy/oogamy has evolved from isogamy (as is thought to have been the case), genes are transferred there unidirectionally as well i.e. from the microgamete/sperm or its producer to the macrogamete/egg or its producer. Eukaryotic sex is associated with cellular reproduction (and involves syngamy, gene duplication and a pair of meiotic divisions) while prokaryote sexual processes are not and do not. In the eukaryotic case, cells “go”, at least initially, while in the prokaryotic case only genes do. So to some degree bidirectionality seems to be a fundamental difference with isogamy, but ultimately with anisogamy and oogamy in eukaryotes, that distinction too loses its force.
Another possibility is that prokaryotes are not organized into “good biological species” with sexual processes possible within species boundaries but not outside them as eukaryotes tend to be (occasional hybridizations notwithstanding). At first blush, it seems obvious that prokaryotes could not be. If F+ were driving through a closed population, sooner or later F- would go extinct and that would be that. However, negative frequency dependence could obtain between transmission of F+ through peers and F- through offspring with each being favoured when the other is rare as has been suggested. But that is not unlike the eukaryotic case in which Fisher’s ‘one mother, one father principle’ means that one mating type/gender is favoured when the other is common, and vice-versa.
Perhaps, related to uni and bi-directionality, the difference is based on the different natures of the social relationships among the parties involved. It has often been suggested that gene donors in prokaryotes are parasites, F+ and their like commonly being a plasmid, transposon or other mobile genetic element with a few host genes being dragged along with it (parasites of the parasite?). In some cases however, gene transfer seems to be in the interest of the recipient – antibiotic resistant factors can be transferred for example. However, gene transfer in prokaryotes may be in the interests of only one, or the other, but not both partners in various cases, while sex understood as genetic recombination in eukaryotes has historically universally been thought of as in the two parties mutual interest. Ultimately of course like bi-directionality, the cooperative theory of eukaryotic sex fails with the coming of anisogamy and oogamy if (and it is becoming a bigger if) the traditional explanation of gender differences and relations is accepted. There proto-males in anisogamy and males in oogamy are viewed as reproductive parasites of proto-females and females respectively.
If principled distinctions based on laterally, partiality, unidirectionality, good species and antagonistic versus cooperative social relationships all fail, at least ultimately, where does that leave us? In a muddle actually.
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