The Evolution of Sexual Systems in Animals

Leonard, Janet L.

doi:10.1007/978-3-319-94139-4_1

Cited by 31 publications

(44 citation statements)

References 199 publications

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“…It is an important life‐history trait affecting the fitness of an individual and hence is subject to selection pressure under given environmental conditions (Charnov, ). Since the first formalization by Charnov, theoretical predictions and empirical tests of the optimal sex allocation under these conditions have been a touchstone in modern evolutionary biology (Janicke et al, ; Leonard, ; Schärer, ; West, ).…”

Section: Introductionmentioning

confidence: 99%

Different effects of mating group size as male and as female on sex allocation in a simultaneous hermaphrodite

Tamechika

Matsuno

Wada

et al. 2020

Ecology and Evolution

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Sex allocation theory predicts that the optimal sexual resource allocation of simultaneous hermaphrodites is affected by mating group size (MGS). Although the original concept assumes that the MGS does not differ between male and female functions, the MGS in the male function (MGSm; i.e., the number of sperm recipients the focal individual can deliver its sperm to plus one) and that in the female function (MGSf; the number of sperm donors plus one) do not always coincide and may differently affect the optimal sex allocation. Moreover, reproductive costs can be split into “variable” (e.g., sperm and eggs) and “fixed” (e.g., genitalia) costs, but these have been seldom distinguished in empirical studies. We examined the effects of MGSm and MGSf on the fixed and variable reproductive investments in the sessilian barnacle Balanus rostratus. The results showed that MGSm had a positive effect on sex allocation, whereas MGSf had a nearly significant negative effect. Moreover, the “fixed” cost varied with body size and both aspects of MGS. We argue that the two aspects of MGS should be distinguished for organisms with unilateral mating.

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Section: Introductionmentioning

confidence: 99%

Different effects of mating group size as male and as female on sex allocation in a simultaneous hermaphrodite

Tamechika

Matsuno

Wada

et al. 2020

Ecology and Evolution

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“…Among vertebrates, fishes exhibit the broadest diversity in sexual systems [1][2][3] , ranging from gonochorism (separate sexes) to hermaphroditism (sequential and simultaneous), unisexuality (all individuals are females) and mixed sexual systems (i.e., co-occurrence of hermaphrodites and males, as in Kryptolebias killifish 4,5 ). Sex allocation theory aims to answer questions such as what allocation of resources to males and females is favoured in gonochoristic species, when and in which direction to change sex in sequential hermaphrodites (from male to female in protandry and from female to male in protogyny), how much energy should be devoted to male vs. female function in simultaneous hermaphrodites, and under what ecological conditions these different sexual systems are evolutionary stable strategies 6 .…”

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confidence: 99%

A phylogenetic comparative analysis on the evolution of sequential hermaphroditism in seabreams (Teleostei: Sparidae)

Pla

Benvenuto

Capellini

et al. 2020

Sci Rep

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systems, particularly for both types of sequential hermaphroditism, given that it contains many gonochoristic, protogynous and protandrous species, with differences in sexual systems even between species belonging to the same genus. The main theoretical framework to explain the evolutionary advantage of sequential hermaphroditism based on sex allocation theory is the size-advantage model (SAM) 9,19-21. The SAM proposes that individuals should switch sex when the second sex achieves a greater fitness at a larger body size than the first sex, thus increasing lifetime fitness 22. When larger males have higher reproductive success than smaller males and similar sized females, fish should reproduce initially as female and change later to male (protogyny) 19,23,24. Conversely, protandry is expected when large females have greater fitness than smaller females and similar sized males 19,20. Empirical studies support this model in several fish families, explaining quantitatively the size or age at which an individual should change sex, as well as the overall population sex ratio 25,26. Typically, male-biased sex ratios are observed in populations of protandrous species, while female-biased sex ratios are observed in populations of protogynous species, especially in haremic groups 19,26,27. Mating systems (the number and social dominance of mates involved) and spawning mode (i.e., group spawning, where several males spawn with one or several females, or pair-mating, where a single male spawns with a single female), determine the fitness that a fish of a given size can achieve as a female or as a male 23,28. Fish mating systems range from monogamy or pair-mating, to harem polygyny (one dominant male controls access to multiple females 29), lek-type polygyny (temporary harems 25), and large polygamous or promiscuous aggregations (where group spawning occurs 30). Sperm competition is particularly intense in large aggregations with multiple males 31,32 while it is absent in monogamy and pair-mating, and low in polygynous mating systems. Sperm competition and spawning modes have been used to infer mating systems 33-35 , which are relevant when testing the predictions of SAM since they can generate sex-specific differences in reproductive expectations 23,24,36,37. Thus, the first study that tested the predictions of SAM incorporating the mating system in a phylogenetic context focused on the evolution of protogynous groupers according to pair spawning mode 35. Indeed, protandry should be favored when sperm competition is low (mating occurs between members of monogamous or random pairs 19,22-24), and mate monopolization by large males should occur in protogynous species 23. Even though sperm competition was not included in the original formulation of the model 9,19 , it was subsequently mentioned as absent in protogyny 21,23,24,38 , limited in protandry (considered typical of random pairing and small groups) 22,23 and high in gonochorism (when mating occurs in large groups) 21,23,35,39. The influence of sperm competition on sex c...

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“…However, the coexistence of the three sexes within a single species, termed trioecy or subdioecy, is uncommon. The fact that numerous evolutionary transitions between dioecy (separate sex individuals) and cosexuality have occurred, each presumably through an intermediate trioecious stage, suggests that the evolution of trioecy is not rare (Barrett 2002; Leonard 2018). Instead, it is thought that trioecy is usually unstable: under most conditions either cosexuals will outcompete unisexuals (e.g., if selfing insures against failure to find a mate) or vice versa (e.g., if selfers suffer severe inbreeding depression) (e.g., Wolf and Takabayashi 2004).…”

Section: Figurementioning

confidence: 99%

Digest: Three sexes from two loci in one genome: A haploid alga expands the diversity of trioecious species*

Roy

2021

Evolution

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Multicellular eukaryotes exhibit a remarkable diversity of sexual systems; however, trioecy, the coexistence of male, female, and cosexual or hermaphrodite individuals in a single species, is remarkably rare. Takahashi et al. ( 2021) report the first known instance of trioecy in a haploid organism. In contrast to other known cases of trioecy, the authors report evidence for genetic control of all three sexes by two loci. These results complicate models for sexual system turnover and expand the known diversity of trioecy species in several ways.

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The Evolution of Sexual Systems in Animals

Cited by 31 publications

References 199 publications

Different effects of mating group size as male and as female on sex allocation in a simultaneous hermaphrodite

Different effects of mating group size as male and as female on sex allocation in a simultaneous hermaphrodite

A phylogenetic comparative analysis on the evolution of sequential hermaphroditism in seabreams (Teleostei: Sparidae)

Digest: Three sexes from two loci in one genome: A haploid alga expands the diversity of trioecious species*

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