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Fu X, Meyer-Rochow VB, Ballantyne L, Zhu X, Zhang Q. Sperm Competition and Paternity in the Endangered Firefly Pyrocoelia pectoralis (Coleoptera: Lampyridae: Lampyrinae). INSECTS 2024; 15:66. [PMID: 38249072 PMCID: PMC10817000 DOI: 10.3390/insects15010066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Revised: 01/13/2024] [Accepted: 01/15/2024] [Indexed: 01/23/2024]
Abstract
The endangered terrestrial firefly Pyrocoelia pectoralis (Olivier) is endemic to China. Populations of P. pectoralis have decreased dramatically due to urbanization and pollution. Breeding and re-introduction to a suitable habitat may save the species from becoming extinct. Because of its polyandrous character, an investigation into the possibility of sperm competition and paternity outcomes from multiple matings was initiated to better understand its reproductive physiology. To achieve these goals, 13 SSR markers were developed. The results of paternity experiments indicate there is a significant difference between P3 and P1 or P2. The female reproductive system has three spermathecae which accept sperm from different matings, and no bursa or spermatophore-digesting organ is developed. Our research established that multiple inseminations with sperm from different males occur, leading to competition between ejaculates. The benefits of such competition include an increasing number of sperm in the ejaculates of competing males and the consequential increase in fertilized eggs (thus, fecundity), and thereby a higher chance of genetic diversity and fitness in the offspring of the firefly P. pectoralis.
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Affiliation(s)
- Xinhua Fu
- College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China;
- Firefly Conservation Research Centre, Wuhan 430070, China;
| | - Victor Benno Meyer-Rochow
- Department of Ecology and Genetics, Oulu University, SF-90140 Oulu, Finland;
- Agricultural Science and Technology Research Institute, Andong National University, Andong 36729, Republic of Korea
| | - Lesley Ballantyne
- School of Agricultural, Environmental and Veterinary Sciences, Charles Sturt University, P.O. Box 588, Wagga Wagga 2678, Australia;
| | - Xinlei Zhu
- Firefly Conservation Research Centre, Wuhan 430070, China;
| | - Qiyulu Zhang
- College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, China;
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2
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Lehtonen J, Otsuka J. Evolutionary game theory of continuous traits from a causal perspective. Philos Trans R Soc Lond B Biol Sci 2023; 378:20210507. [PMID: 36934761 PMCID: PMC10024988 DOI: 10.1098/rstb.2021.0507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/21/2023] Open
Abstract
Modern evolutionary game theory typically deals with the evolution of continuous, quantitative traits under weak selection, allowing the incorporation of rich biological detail and complicated nonlinear interactions. While these models are commonly used to find candidates for evolutionary endpoints and to approximate evolutionary trajectories, a less appreciated property is their potential to expose and clarify the causal structure of evolutionary processes. The mathematical step of differentiation breaks a nonlinear model into additive components which are more intuitive to interpret, and when combined with a proper causal hypothesis, partial derivatives in such models have a causal meaning. Such an approach has been used in the causal analysis of game-theoretical models in an informal manner. Here we formalize this approach by linking evolutionary game theory to concepts developed in causal modelling over the past century, from path coefficients to the recently proposed causal derivative. There is a direct correspondence between the causal derivative and the derivative used in evolutionary game theory. Some game theoretical models (e.g. kin selection) consist of multiple causal derivatives. Components of these derivatives correspond to components of the causal derivative, to path coefficients, and to edges on a causal graph, formally linking evolutionary game theory to causal modelling. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.
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Affiliation(s)
- Jussi Lehtonen
- Department of Biological and Environmental Science, University of Jyväskylä, 40014 Jyväskylä, Finland
| | - Jun Otsuka
- Department of Philosophy, Kyoto University, Yoshida-Hommachi, 606-8501 Kyoto, Japan
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3
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Shadmany J, Lee SF, Nguyen TNM, Taylor PW. Patterns of sperm use by twice-mated female Queensland fruit flies. INSECT SCIENCE 2022; 29:1159-1169. [PMID: 34957684 DOI: 10.1111/1744-7917.12985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 11/04/2021] [Accepted: 11/24/2021] [Indexed: 06/14/2023]
Abstract
Multiple mating by females, polyandry, is common in insects, including in tephritid fruit flies. Female insects that remate commonly store sperm of multiple males. How the sperm of different males contribute to paternity is an important element of sexual selection. Sexual behavior and reproduction of the Queensland fruit fly (Qfly), Bactrocera tryoni, has been extensively investigated both in relation to understanding this economically important species' reproductive biology and in relation to implications for Sterile Insect Technique (SIT), whereby sterile flies are released to constrain reproduction of pest populations. Despite numerous studies of pre- and postcopulatory sexual selection in Qfly, there have been no direct studies of paternity patterns in polyandrous female Qflies. We used two morphologically distinguishable lines to investigate patterns of sperm use in Qfly. The two lines showed comparable mating performance evidenced by similar mating and remating frequency, copula duration, and proportion of second mate paternity (P2) between reciprocal crosses. The mechanism of sperm usage, with P2 close to 0.5 immediately after the second mating followed by gradual decrease of P2 as females aged, is most consistent with stratification or repositioning of sperm. Patterns observed in the present study are compared with the available information from other tephritid fruit flies, and are discussed in relation to this species' reproductive biology, known patterns of sperm storage, and SIT.
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Affiliation(s)
- Jason Shadmany
- Applied BioSciences, Macquarie University, North Ryde, NSW, Australia
| | - Siu F Lee
- Applied BioSciences, Macquarie University, North Ryde, NSW, Australia
- CSIRO Land and Water, Black Mountain, ACT, Australia
| | - Thu N M Nguyen
- School of BioSciences, University of Melbourne, Parkville, Victoria, Australia
| | - Phillip W Taylor
- Applied BioSciences, Macquarie University, North Ryde, NSW, Australia
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Loo SL, Rose D, Hawkes K, Kim PS. Mate guarding in primates arises due to partner scarcity, even if the father provides no paternal care at all. Theor Popul Biol 2021; 142:100-113. [PMID: 34648764 DOI: 10.1016/j.tpb.2021.09.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 09/24/2021] [Accepted: 09/25/2021] [Indexed: 10/20/2022]
Abstract
Paternal care is unusual among primates; in most species males compete with one another for the acquisition of mates and leave the raising of offspring to the mothers. Callitrichids defy this trend with both fathers and older siblings contributing to the care of offspring. We extend a two-strategy population model (paternal care versus male-male competition) to account for various mechanisms that could possibly explain why male callitrichids invest in paternal care over male-male competition, and compare results from callitrichid, chimpanzee and hunter-gatherer life history parameters. The survival benefit to offspring due to care is an insufficient explanation of callitrichid paternal care, and the additional inclusion of differences in lactation-related biology similarly do not change that picture. Instead, paternal care may arise in parallel with, or even as a result of, mate guarding, which in turn is only beneficial when partners are scarce as modelled by the birth sex ratio in callitrichids and menopause in hunter-gatherers. In that situation, care need not even provide any benefit to the young (in the form of a survival bonus) for guarding to out-compete multiple mating competition.
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Affiliation(s)
- Sara L Loo
- University of New South Wales, Sydney, NSW, Australia.
| | - Danya Rose
- University of Sydney, Sydney, NSW, Australia.
| | | | - Peter S Kim
- University of Sydney, Sydney, NSW, Australia.
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5
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Lehtonen J, Horinouchi Y, Togashi T, Parker GA. Evolution of Anisogamy in Organisms with Parthenogenetic Gametes. Am Nat 2021; 198:360-378. [PMID: 34403316 DOI: 10.1086/715185] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractThe two sexes are defined by the sizes of the gametes they produce, anisogamy being the state with two differing gamete sizes (hence, females and males). The origin of this divergence has received much research interest, both theoretically and empirically. The gamete dynamics (GD) theory is a widely accepted theoretical explanation for anisogamy, and green algae have been an important empirical testing ground for the theory. However, some green and brown algae produce parthenogenetic gametes (gametes that can develop without fusing with another gamete), in contrast to an assumption in GD theory that unfused gametes do not develop. Here, we construct a GD model accounting for parthenogenetic gametes. We find that under conditions of panmixia and highly efficient fertilization (i.e., conditions of classical GD models from 1972 onward), the results remain largely unaltered by parthenogametes. However, under gamete-limited conditions anisogamy evolves less easily in the new model, and a novel result emerges: whereas previous models typically predict the evolution of either anisogamy or small isogamy, the current model shows that large isogamy can evolve when parthenogenetic gametes evolve under conditions of inefficient fertilization. Our analyses uncover unexplored complications relating to sex ratios under this relatively uncharted gametic system. We discuss limitations these complications impose on our models and suggest avenues for future research. We compare model results to algae with parthenogenetic gametes in nature.
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Lehtonen J. The Legacy of Parker, Baker and Smith 1972: Gamete Competition, the Evolution of Anisogamy, and Model Robustness. Cells 2021; 10:573. [PMID: 33807911 PMCID: PMC7998237 DOI: 10.3390/cells10030573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/02/2021] [Accepted: 03/03/2021] [Indexed: 11/17/2022] Open
Abstract
The evolution of anisogamy or gamete size dimorphism is a fundamental transition in evolutionary history, and it is the origin of the female and male sexes. Although mathematical models attempting to explain this transition have been published as early as 1932, the 1972 model of Parker, Baker, and Smith is considered to be the first explanation for the evolution of anisogamy that is consistent with modern evolutionary theory. The central idea of the model is ingenious in its simplicity: selection simultaneously favours large gametes for zygote provisioning, and small gametes for numerical competition, and under certain conditions the outcome is anisogamy. In this article, I derive novel analytical solutions to a 2002 game theoretical update of the 1972 anisogamy model, and use these solutions to examine its robustness to variation in its central assumptions. Combining new results with those from earlier papers, I find that the model is quite robust to variation in its central components. This kind of robustness is crucially important in a model for an early evolutionary transition where we may only have an approximate understanding of constraints that the different parts of the model must obey.
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Affiliation(s)
- Jussi Lehtonen
- Faculty of Science, School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW 2006, Australia
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7
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Cameron H, Johnson DW, Monro K, Marshall DJ. Multilevel Selection on Offspring Size and the Maintenance of Variation. Am Nat 2021; 197:448-460. [PMID: 33755536 DOI: 10.1086/712890] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractMultilevel selection on offspring size occurs when offspring fitness depends on both absolute size (hard selection) and size relative to neighbors (soft selection). We examined multilevel selection on egg size at two biological scales-within clutches and among clutches from different females-using an external fertilizing tube worm. We exposed clutches of eggs to two sperm environments (limiting and saturating) and measured their fertilization success. We then modeled environmental (sperm-dependent) differences in hard and soft selection on individual eggs as well as selection on clutch-level traits (means and variances). Hard and soft selection differed in strength and form depending on sperm availability-hard selection was consistently stabilizing; soft selection was directional and favored eggs relatively larger (sperm limitation) or smaller (sperm saturation) than the clutch mean. At the clutch level, selection on mean egg size was largely concave, while selection on within-clutch variance was weak but generally negative-although some correlational selection occurred between these two traits. Importantly, we found that the optimal clutch mean egg size differed for mothers and offspring, suggesting some antagonism between the levels of selection. We thus identify several pathways that may maintain offspring size variation: environmentally (sperm-) dependent soft selection, antagonistic multilevel selection, and correlational selection on clutch means and variances. Multilevel approaches are powerful but seldom-used tools for studies of offspring size, and we encourage their future use.
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8
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Parker GA. How Soon Hath Time… A History of Two "Seminal" Publications. Cells 2021; 10:287. [PMID: 33535413 PMCID: PMC7912719 DOI: 10.3390/cells10020287] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/26/2021] [Accepted: 01/28/2021] [Indexed: 12/19/2022] Open
Abstract
This review documents the history of the two papers written half a century ago that relate to this special issue of Cells. The first, "Sperm competition and its evolutionary consequences in the insects" (Biological Reviews, 1970), stressed that sexual selection continues after ejaculation, resulting in many adaptations (e.g., postcopulatory guarding phases, copulatory plugs, seminal fluid components that modify female reproduction, and optimal ejaculation strategies), an aspect not considered by Darwin in his classic treatise of 1871. Sperm competition has subsequently been studied in many taxa, and post-copulatory sexual selection is now considered an important sequel to Darwinian pre-copulatory sexual selection. The second, "The origin and evolution of gamete dimorphism and the male-female phenomenon" (Journal of Theoretical Biology, 1972) showed how selection, based on gamete competition between individuals, can give rise to anisogamy in an isogamous broadcast spawning ancestor. This theory, which has subsequently been developed in various ways, is argued to form the most powerful explanation of why there are two sexes in most multicellular organisms. Together, the two papers have influenced our general understanding of the evolutionary differentiation of the two forms of gametic cells, and the divergence of sexual strategies between males and females under sexual selection.
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Affiliation(s)
- Geoff A Parker
- Department of Evolution, Ecology and Behaviour, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK
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9
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Evans JP, Lymbery RA. Sexual selection after gamete release in broadcast spawning invertebrates. Philos Trans R Soc Lond B Biol Sci 2020; 375:20200069. [PMID: 33070722 DOI: 10.1098/rstb.2020.0069] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Broadcast spawning invertebrates offer highly tractable models for evaluating sperm competition, gamete-level mate choice and sexual conflict. By displaying the ancestral mating strategy of external fertilization, where sexual selection is constrained to act after gamete release, broadcast spawners also offer potential evolutionary insights into the cascade of events that led to sexual reproduction in more 'derived' groups (including humans). Moreover, the dynamic reproductive conditions faced by these animals mean that the strength and direction of sexual selection on both males and females can vary considerably. These attributes make broadcast spawning invertebrate systems uniquely suited to testing, extending, and sometimes challenging classic and contemporary ideas in sperm competition, many of which were first captured in Parker's seminal papers on the topic. Here, we provide a synthesis outlining progress in these fields, and highlight the burgeoning potential for broadcast spawners to provide both evolutionary and mechanistic understanding into gamete-level sexual selection more broadly across the animal kingdom. This article is part of the theme issue 'Fifty years of sperm competition'.
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Affiliation(s)
- Jonathan P Evans
- Centre for Evolutionary Biology, School of Biological Sciences, University of Western Australia
| | - Rowan A Lymbery
- Centre for Evolutionary Biology, School of Biological Sciences, University of Western Australia
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10
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Lehtonen J, Dardare L. Mathematical Models of Fertilization—An Eco-Evolutionary Perspective. THE QUARTERLY REVIEW OF BIOLOGY 2019. [DOI: 10.1086/703633] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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11
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Lehtonen J, Parker GA. Evolution of the Two Sexes under Internal Fertilization and Alternative Evolutionary Pathways. Am Nat 2019; 193:702-716. [PMID: 31002575 DOI: 10.1086/702588] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Transition from isogamy to anisogamy, hence males and females, leads to sexual selection, sexual conflict, sexual dimorphism, and sex roles. Gamete dynamics theory links biophysics of gamete limitation, gamete competition, and resource requirements for zygote survival and assumes broadcast spawning. It makes testable predictions, but most comparative tests use volvocine algae, which feature internal fertilization. We broaden this theory by comparing broadcast-spawning predictions with two plausible internal-fertilization scenarios: gamete casting/brooding (one mating type retains gametes internally, the other broadcasts them) and packet casting/brooding (one type retains gametes internally, the other broadcasts packets containing gametes, which are released for fertilization). Models show that predictions are remarkably robust to these radical changes, yielding (1) isogamy under low gamete limitation, low gamete competition, and similar required resources for gametes and zygotes, (2) anisogamy when gamete competition and/or limitation are higher and when zygotes require more resources than gametes, as is likely as multicellularity develops, (3) a positive correlation between multicellular complexity and anisogamy ratio, and (4) under gamete competition, only brooders becoming female. Thus, gamete dynamics theory represents a potent rationale for isogamy/anisogamy and makes similar testable predictions for broadcast spawners and internal fertilizers, regardless of whether anisogamy or internal fertilization evolved first.
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12
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da Silva J, Drysdale VL. Isogamy in large and complex volvocine algae is consistent with the gamete competition theory of the evolution of anisogamy. Proc Biol Sci 2018; 285:rspb.2018.1954. [PMID: 30404882 DOI: 10.1098/rspb.2018.1954] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 10/16/2018] [Indexed: 11/12/2022] Open
Abstract
Although the gamete competition theory remains the dominant explanation for the evolution of anisogamy, well-known exceptions to its predictions have raised doubts about the completeness of the theory. One of these exceptions is isogamy in large or complex species of green algae. Here, we show that this exception may be explained in a manner consistent with a game-theoretic extension of the original theory: a constraint on the minimum size of a gamete may prevent the evolution of continuously stable anisogamy. We show that in the volvocine algae, both gametes of isogamous species retain an intact chloroplast, whereas the chloroplast of the microgamete in anisogamous species is invariably degenerate. The chloroplast, which functions in photosynthesis and starch storage, may be necessary to provision a gamete for an extended period when gamete encounter rates are low. The single chloroplast accounts for most of the volume of a typical gamete, and thus may constrain the minimum size of a gamete, preventing the evolution of anisogamy. A prediction from this hypothesis, that isogametes should be larger than the microgametes of similar-size species, is confirmed for the volvocine algae. Our results support the gamete competition theory.
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Affiliation(s)
- Jack da Silva
- School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia
| | - Victoria L Drysdale
- School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia
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Seed CE, Tomkins JL. Positive size-speed relationships in gametes and vegetative cells of Chlamydomonas reinhardtii; implications for the evolution of sperm. Evolution 2018; 72:440-452. [PMID: 29345308 DOI: 10.1111/evo.13427] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Revised: 12/19/2017] [Accepted: 12/27/2017] [Indexed: 11/26/2022]
Abstract
It is commonly held that differences in gametes of the two sexes (anisogamy) evolved from ancestors whose gametes were similar in size and behavior (isogamy). Underlying many hypotheses explaining anisogamy are assumed relationships between cell size and speed in the ancestral isogamous population. Using the isogamous alga Chlamydomonas reinhardtii, we explored size-speed distributions in vegetative and gamete cells of 10 cell lines, and clonal data from within two cell lines. We applied an independent speed selection approach to gamete populations of C. reinhardtii, monitoring correlated responses in size following selection for high speed. We demonstrate positive size-speed relationships in clones, cell lines, and artificially selected speed selection lines. We found different size-speed relationships in the two cell types of C. reinhardtii even though they overlap in size, suggesting that cell composition and/or programs of gene expression are capable of altering this relationship, and that the relationship is evolvable. The positive genetic size-speed correlation means that the division of parent vegetative cells into numerous gametes trades off against not only size, but also speed, a trade-off that has not received previous attention. Our results support reevaluating the role of speed selection in the evolution of anisogamy.
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Affiliation(s)
- Catherine E Seed
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, Australia
| | - Joseph L Tomkins
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, Australia
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da Silva J. The evolution of sexes: A specific test of the disruptive selection theory. Ecol Evol 2018; 8:207-219. [PMID: 29321864 PMCID: PMC5756833 DOI: 10.1002/ece3.3656] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2017] [Revised: 11/02/2017] [Accepted: 11/02/2017] [Indexed: 01/24/2023] Open
Abstract
The disruptive selection theory of the evolution of anisogamy posits that the evolution of a larger body or greater organismal complexity selects for a larger zygote, which in turn selects for larger gametes. This may provide the opportunity for one mating type to produce more numerous, small gametes, forcing the other mating type to produce fewer, large gametes. Predictions common to this and related theories have been partially upheld. Here, a prediction specific to the disruptive selection theory is derived from a previously published game-theoretic model that represents the most complete description of the theory. The prediction, that the ratio of macrogamete to microgamete size should be above three for anisogamous species, is supported for the volvocine algae. A fully population genetic implementation of the model, involving mutation, genetic drift, and selection, is used to verify the game-theoretic approach and accurately simulates the evolution of gamete sizes in anisogamous species. This model was extended to include a locus for gamete motility and shows that oogamy should evolve whenever there is costly motility. The classic twofold cost of sex may be derived from the fitness functions of these models, showing that this cost is ultimately due to genetic conflict.
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Affiliation(s)
- Jack da Silva
- School of Biological SciencesUniversity of AdelaideAdelaideSAAustralia
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15
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Monro K, Marshall DJ. Unravelling anisogamy: egg size and ejaculate size mediate selection on morphology in free-swimming sperm. Proc Biol Sci 2017; 283:rspb.2016.0671. [PMID: 27412273 DOI: 10.1098/rspb.2016.0671] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 06/20/2016] [Indexed: 01/28/2023] Open
Abstract
Gamete dimorphism (anisogamy) defines the sexes in most multicellular organisms. Theoretical explanations for its maintenance usually emphasize the size-related selection pressures of sperm competition and zygote survival, assuming that fertilization of all eggs precludes selection for phenotypes that enhance fertility. In external fertilizers, however, fertilization is often incomplete due to sperm limitation, and the risk of polyspermy weakens the advantage of high sperm numbers that is predicted to limit sperm size, allowing alternative selection pressures to target free-swimming sperm. We asked whether egg size and ejaculate size mediate selection on the free-swimming sperm of Galeolaria caespitosa, a marine tubeworm with external fertilization, by comparing relationships between sperm morphology and male fertility across manipulations of egg size and sperm density. Our results suggest that selection pressures exerted by these factors may aid the maintenance of anisogamy in external fertilizers by limiting the adaptive value of larger sperm in the absence of competition. In doing so, our study offers a more complete explanation for the stability of anisogamy across the range of sperm environments typical of this mating system and identifies new potential for the sexes to coevolve via mutual selection pressures exerted by gametes at fertilization.
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Affiliation(s)
- Keyne Monro
- Centre for Geometric Biology, School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
| | - Dustin J Marshall
- Centre for Geometric Biology, School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
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16
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Parker GA, Ramm SA, Lehtonen J, Henshaw JM. The evolution of gonad expenditure and gonadosomatic index (GSI) in male and female broadcast-spawning invertebrates. Biol Rev Camb Philos Soc 2017; 93:693-753. [PMID: 28921784 DOI: 10.1111/brv.12363] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 07/22/2017] [Accepted: 08/09/2017] [Indexed: 01/05/2023]
Abstract
Sedentary broadcast-spawning marine invertebrates, which release both eggs and sperm into the water for fertilization, are of special interest for sexual selection studies. They provide unique insight into the early stages of the evolutionary succession leading to the often-intense operation of both pre- and post-mating sexual selection in mobile gonochorists. Since they are sessile or only weakly mobile, adults can interact only to a limited extent with other adults and with their own fertilized offspring. They are consequently subject mainly to selection on gamete production and gamete success, and so high gonad expenditure is expected in both sexes. We review literature on gonadosomatic index (GSI; the proportion of body tissue devoted to gamete production) of gonochoristic broadcast spawners, which we use as a proxy for gonad expenditure. We show that such taxa most often have a high GSI that is approximately equal in both sexes. When GSI is asymmetric, female GSI usually exceeds male GSI, at least in echinoderms (the majority of species recorded). Intriguingly, though, higher male GSI also occurs in some species and appears more common than female-biased GSI in certain orders of gastropod molluscs. Our limited data also suggest that higher male GSI may be the prevalent pattern in sperm casters (where only males release gametes). We explore how selection might have shaped these patterns using game theoretic models for gonad expenditure that consider possible trade-offs with (i) somatic maintenance or (ii) growth, while also considering sperm competition, sperm limitation, and polyspermy. Our models of the trade-off between somatic tissue (which increases survival) and gonad (which increases reproductive success) predict that GSI should be equal for the two sexes when sperm competition is intense, as is probably common in broadcast spawners due to synchronous spawning in aggregations. Higher female GSI occurs under low sperm competition. Sperm limitation appears unlikely to alter these conclusions qualitatively, but can also act as a force to keep male GSI high, and close to that of females. Polyspermy can act to reduce male GSI. Higher male than female GSI is predicted to be less common (as observed in the data), but can occur when ova/ovaries are sufficiently more resource-intensive to produce than sperm/testes, for which some evidence exists. We also show that sex-specific trade-offs between gonads and growth can generate different life-history strategies for males and females, with males beginning reproduction earlier. This could lead to apparently higher male GSI in empirical studies if immature females are included in calculations of mean GSI. The existence of higher male GSI nonetheless remains somewhat problematic and requires further investigation. When sperm limitation is low, we suggest that the natural logarithm of the male/female GSI ratio may be a suitable index for sperm competition level in broadcast spawners, and that this may also be considered as an index for internally fertilizing taxa.
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Affiliation(s)
- Geoff A Parker
- Department of Evolution, Ecology and Behaviour, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, U.K
| | - Steven A Ramm
- Evolutionary Biology, Bielefeld University, 33615, Bielefeld, Germany
| | - Jussi Lehtonen
- Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, 2052, Australia
| | - Jonathan M Henshaw
- Division of Ecology and Evolution, Research School of Biology, The Australian National University, 2601, Canberra, Australia.,Institute of Zoology, University of Graz, Graz, 8010, Austria
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Multilevel Selection in Kin Selection Language. Trends Ecol Evol 2016; 31:752-762. [PMID: 27590987 DOI: 10.1016/j.tree.2016.07.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 07/16/2016] [Accepted: 07/20/2016] [Indexed: 11/22/2022]
Abstract
Few issues have raised more debate among evolutionary biologists than kin selection (KS) versus multilevel selection (MLS). They are formally equivalent, but use different-looking mathematical approaches, and are not causally equivalent: for a given problem KS can be a more suitable causal explanation than MLS, and vice versa. Methods for analyzing a given model from both viewpoints would therefore be valuable. I argue that there is often an easy way to achieve this: MLS can be written using the components of KS. This applies to the very general regression approach as well as to the practical evolutionarily stable strategy (ESS) maximization approach, and can hence be used to analyze many common ESS models from a multilevel perspective. I demonstrate this with example models of gamete competition and limitation.
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Okamoto DK. Competition among Eggs Shifts to Cooperation along a Sperm Supply Gradient in an External Fertilizer. Am Nat 2016; 187:E129-42. [DOI: 10.1086/685813] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Affiliation(s)
- G. A. Parker
- Institute of Integrative Biology; University of Liverpool; Liverpool UK
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Lehtonen J. Models of fertilization kinetics. ROYAL SOCIETY OPEN SCIENCE 2015; 2:150175. [PMID: 26473043 PMCID: PMC4593677 DOI: 10.1098/rsos.150175] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 08/19/2015] [Indexed: 06/05/2023]
Abstract
Fertilization functions describe how the number of realized fertilizations depends on gamete numbers or density. They provide insight into the fertilization process, and are important components in models on the evolution of reproductive and sex-specific traits. Existing fertilization functions generally examine the proportion of fertilized eggs as a function of sperm numbers or density in a given fertilization environment. Because these functions have been developed for species with highly diverged gametes, there is an inbuilt (and well justified) asymmetry in them: they treat eggs and sperm, and therefore the two sexes, differently. Although very useful, such functions cannot therefore be used to consistently model early stages in the evolution of the two sexes, or extant species where sex-specific gamete sizes and numbers are similar. Here, I derive fertilization functions that describe the fertilization process without making prior assumptions about the two sexes, and are therefore consistent under any level of gamete dimorphism. These functions are compatible with simpler fertilization functions under appropriate conditions. Such functions can be particularly useful in understanding the early stages in the differentiation of the two sexes, as well as its consequences, where the gametes from the two sexes should be treated on an equal basis.
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Ramm SA. Sperm competition and the evolution of reproductive systems. ACTA ACUST UNITED AC 2014; 20:1159-60. [DOI: 10.1093/molehr/gau076] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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Lehtonen J, Parker GA. Gamete competition, gamete limitation, and the evolution of the two sexes. ACTA ACUST UNITED AC 2014; 20:1161-8. [DOI: 10.1093/molehr/gau068] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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