Discussion of the transition from hermaphroditism to dioecy as an example of non-classical development of a scientific hypothesis. Column for Kompyuterrа #137

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Dmytro Shabanov
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← Dmytro Shabanov → We live long. About Ukrainian protest, "Molotov cocktails" and oxytocin wave Discussion of the transition from hermaphroditism to gonochorism as an example of non-classical development of a natural-scientific hypothesis On the nature of the male and female, or from conjugation to oogamy

Computerra Column #136 Computerra Column #137 Computerra Column #138 I am glad how the column before last was received (not the last one, the political one, but precisely the one before last, devoted to the transition from hermaphroditism to gonochorism). It seems I managed to convince many readers of its main idea. However, persuasiveness in popular exposition is not the most important thing for a scientific idea.

For a hypothesis to go through a normal cycle of maturation and development, the following is necessary: — to place it in the history of the issue, analyze the argumentation expressed regarding this and similar ideas; — to test the hypothesis for compatibility with accumulated knowledge and existing facts; — to formulate predictions based on the hypothesis that can be confirmed or refuted. This is a large task, and I myself will almost certainly not be able to handle it alone. The passage of these stages can be ensured by interaction between different specialists. Thinking about how to organize this, I realized that the maturation of this idea proceeded in an obviously "non-classical" manner. A key role in it was played by interaction through the Network of people for whom studying this problem is not the main task. Therefore, in this column I want to describe in detail the trajectory that this idea has followed to the present. By my narrow specialization, I am a population ecologist of tailless amphibians. My dissertation was devoted to population diversity of toads (I became interested in it while working through the variability of toad venom composition). In 1999, I met colleagues from the St. Petersburg Zoological Institute of the Russian Academy of Sciences at a scientific conference and, at their invitation, joined the study of hybridization in frogs. Together we discovered what was later called the Siversky Donets Center of diversity of the hybridogenetic complex of green frogs. The specific situation of myself and my Kharkiv colleagues is that we work with perhaps the most interesting frog population systems in the world, but are seriously inferior to both Western and even Russian specialists in access to modern technology and necessary funding. In the West, one can collect a batch of material, run it through super-modern technologies, and get an interesting and publishable result. To stay afloat, we must think very well, comprehending the problem we are working on. Alas, scientific pursuits are not my main occupation. I am a teacher, and also a popularizer (that's why you are reading my text now). Many things have to be retold to students over and over again. Besides the standard truths written in textbooks, over time one develops one's own ways of explanation. For lecturing, I started assembling clips from popular films downloaded through torrent trackers. A fragment from a National Geographic film devoted to battles of hermaphrodites (the same one I referenced in the previous column) also ended up in my arsenal. Thanks to Alexander Markov's synopses on Elements, and also as a result of working as a science news reviewer for Computerra, I learned what disputes are connected with the problem of the origin of gonochorism. From my point of view, the answer evidently followed from the fact of hermaphrodites' battles. For several years I repeated it to students, postponing for the future the search for a source where this explanation is presented. Teachers and other professional retellers often forget the sources of their ideas, and sometimes one has to double-check oneself. I proceeded from the fact that if this idea came to my mind, it should have come to someone's mind before me. In 2009, thanks to another Markov news item, I realized that the explanation sitting in my head is at least not widely known. Approximately at the same time, I came to understand that the evolution of hemiclonal inheritance in hybrid frogs is part of the general process of evolution of recombination (from horizontal transfer to cultural inheritance). Since that is the case, I decided that figuring out this topic would be useful for the "frog" work. I consulted with Markov. Alexander wrote that in explicit form this idea is not familiar to him, and advised in what direction it would be worth searching for its analogues. I gave a conference presentation and published an article in its proceedings (expressing gratitude to Alexander for criticizing its draft version). I decided: the main thing I can do for developing understanding of the transition from hermaphroditism to gonochorism is to model this transition using approximately the same toolkit that we used for studying transformations of frog population systems. I tried. Made one, second, third model... I was met with disappointment. Males did not displace hermaphrodites, but established a dynamic equilibrium with them, reaching a certain stable "concentration." Under these conditions, females also did not receive the expected advantage. I found myself at an impasse. It became clear to me that it was necessary to find out under what conditions it is advantageous for hermaphrodites to compete for the male role. I could not solve this problem myself: there was no one to discuss it with. I tried to lure first a sensible student, and then a sensible student, to study this problem using models. Alas, they also did not get anywhere with it. Markov again led me out of this impasse. In his LiveJournal blog, he posted the following entry: "After all, sperm are much cheaper than eggs, and therefore each hermaphrodites can potentially leave many more offspring acting as a father than as a mother. Hence the competition for the male role. Hence the evolutionary instability of hermaphroditism in active animals. If a mutation appears that redistributes the organism's resources in favor of increasing 'male competitiveness' and to the detriment of the female function, this mutation will most likely be supported by selection. The population of hermaphrodites will be overrun by 'social parasites' — specialized mutant males. The remaining hermaphrodites will then no longer have reason to maintain the male function. They still cannot defeat the newly emerged 'specialists' in competition for the male role. Accordingly, it will become advantageous for the remaining hermaphrodites to specialize in the female function. Perhaps that is why among animals (especially mobile, fast ones, such as chordates, most arthropods, cephalopods...) gonochorism nevertheless predominates, not hermaphroditism with cross-fermutation. Despite all its advantages in terms of both efficiency and gender equality." This idea was enthusiastically received by Markov's blog readers. I reminded him that it was, as it were, mine. He immediately agreed, citing that he does not always remember where this or that thought sitting in his head came from. I do not doubt that this is the case: I suffer from the same thing myself. Significant for me was the reaction of one of our mutual acquaintances with Markov. In his LiveJournal, he raved about the quoted fragment from Markov. I sent him a link to my article. He remembered that he had even read it. I responded in the spirit of "Such is the role of authority: when I expressed this thought, you didn't believe it, but from Markov's words you immediately agreed." My correspondent assured me that the matter was not distrust of me, but that my article required effort to understand the references to game theory, whereas Markov's was presented much more simply. Simpler! But, in my opinion, due to this simplicity, his explanation lacks essential arguments in favor of the discussed idea. Among other things, I would emphasize not the "cheapness" of sperm (I still plan to discuss this in detail), but the possibility of a male participating in many matings (which, of course, is closely connected with this very "cheapness"). On the other hand, perhaps Markov is right in allowing not an instantaneous shutdown of the female function in hermaphrodites, but a gradual shift of priorities in favor of the male... The reaction to Markov's post made me return to this idea. I decided to take advantage of my position. In two lecture courses that I taught in the autumn semester of last year (courses in batrachology and history of biological systems), I allocated three sessions each to explaining the ideas that I wanted to refine. From articulating this problem, I myself, as it seems, advanced in understanding it. Since December of last year, I have been writing a series of columns devoted to this question (here is the first one, and this one is already the seventh). A substantial part of the New Year holidays had to be spent on modeling, in which I tried to reflect my new understanding. Something worked out; I will tell you about it now. Even before I described the idea discussed here, two readers presented it in comments. I see my merit here: I qualitatively prepared the ground for it. Moreover, even before I described my model, one of Computerra's readers, Kasum Ahmedli from Azerbaijan, sent me his modeling results! Kasum's model is constructed in a way unexpected to me. Using clever techniques, it was created based on a program for modeling chemical equilibrium. I disagree with some aspects of this model (and the conclusions of Kasum connected with them). Currently we are slowly advancing in discussing and understanding our disagreements. A mathematician from Kyiv has also expressed desire to participate in modeling the transition from gonochorism to hermaphroditism. We will see what comes of it. I am very interested. So, in this column I want to share with readers two surprises. The first — how it turns out with the evolution of reproduction in hermaphrodites. The second — to what extent the interaction of competent people, united by suitable nodes in the Network, promotes the development of ideas that interest them. If I am right, this is some new way of "doing science." Of course, the result of such work should be a scientific article in a decent journal, but the path to writing it turns out to be non-classical. I am glad: such interaction helps me not to stew in my own juice, but in the course of interaction with other people to advance in understanding the problem interesting to me. To whom the idea I am discussing truly belongs is difficult to say. Surely it came to various minds before me. I have not found clear predecessors so far. My reasoning resembles the idea of G.A. Parker and co-authors, published in 1972 — the very one concerning the "cheapness" of sperm. If everything works out as I want, we will discuss it in detail. And now the time has come to tell about what came of my modeling. I described my model in detail in the online outline of the course on modeling in ecology using Microsoft Excel. There is also a link where you can download the model itself. The idea is this. An initial distribution of fertilized egg types is set. Taking it into account, a breeding herd of 100 individuals is randomly formed, which can belong to one of three sexes: be hermaphrodites, males, or females. From this herd, 100 pairs of individuals are randomly extracted, which mate (or try to mate) with each other. Hermaphrodites and females, upon becoming pregnant, exit the game; males can attempt mating an unlimited number of times. Based on the results of the matings that took place, the distribution of fertilized egg types is determined, and the cycle repeats. Based on the results of two hundred cycles, a graph of the dynamics of the three sexes is constructed. The model allows easily changing the offspring composition for different types of crosses, as well as accounting for different survival of the sexes and their different attractiveness to each other. I discussed the history of the idea in such detail that there is almost no space left for retelling the model results. I will say about the main conclusions. After experiments with the model, they seem quite trivial. Strangely, before modeling I could not come to such conclusions; in this effect for me is one of the meanings of the hassle with models. Here, look. [IMG_1] Pay attention to two things — the table where the results of crosses are set, and the graph reflecting the dynamics of the three sexes. For all types of crosses, the sex distribution of offspring corresponds to the sex distribution of parents, with the exception that hermaphrodites gradually produce both males and females. We see that under these conditions an equilibrium sex ratio is established, around which random fluctuations occur. Being a male is advantageous in this situation: males can leave more offspring than hermaphrodites. But since in offspring from crosses of males and hermaphrodites half are hermaphrodites, males cannot displace them. Since males do not receive a significant advantage, the situation also does not arise where females receive an advantage. Let's try otherwise. In crosses of males and hermaphrodites, males should have at least a slight advantage (in the number of offspring or in their survival). In crosses of females and males, hermaphrodites should not appear again; only in this case can the population get rid of them. What does this depend on? On the mechanism of sex inheritance. [IMG_2] One way or another, under certain conditions (which may concern not only the offspring composition but also differences in survival and (or) mutual attractiveness of different forms), the transition from hermaphroditism to gonochorism, which we expected, nevertheless occurs. What follows from this? Another time...

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Dmytro Shabanov
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← Dmytro Shabanov → We live long. About Ukrainian protest, "Molotov cocktails" and oxytocin wave Discussion of the transition from hermaphroditism to gonochorism as an example of non-classical development of a natural-scientific hypothesis On the nature of the male and female, or from conjugation to oogamy

Computerra Column #136 Computerra Column #137 Computerra Column #138