prospective model and a house sparrow investigation
Studies of the yellow dungfly in the 1960s provided one of the first quantitative demonstrations of the costs and benefits associated with male and female reproductive behaviour. These studies advanced appreciation of sexual selection as... more
Studies of the yellow dungfly in the 1960s provided one of the first quantitative demonstrations of the costs and benefits associated with male and female reproductive behaviour. These studies advanced appreciation of sexual selection as a significant evolutionary mechanism and contributed to the 1970s paradigm shift toward individual selectionist thinking. Three behaviours in particular led to the realization that sexual selection can continue during and after mating: (i) female receptivity to remating, (ii) sperm displacement and (iii) post-copulatory mate guarding. These behaviours either generate, or are adaptations to sperm competition, cryptic female choice and sexual conflict. Here we review this body of work, and its contribution to the development of post-copulatory sexual selection theory. This article is part of the theme issue ‘Fifty years of sperm competition’.
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Page 1. 47 3. SPERM COMPETITION, MALE PRUDENCE AND SPERM-LIMITED FEMALESNina Wedell1, Matthew JG Gage2 and Geoffrey A. Parker3 ABSTRACT ... Sci. 350, 391399. h. Fu, P. et al. (2001). Tactic-specific success in sperm competition. Proc. R.... more
Page 1. 47 3. SPERM COMPETITION, MALE PRUDENCE AND SPERM-LIMITED FEMALESNina Wedell1, Matthew JG Gage2 and Geoffrey A. Parker3 ABSTRACT ... Sci. 350, 391399. h. Fu, P. et al. (2001). Tactic-specific success in sperm competition. Proc. R. Soc. Lond. Ser. ...
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Gamete dynamics theory proposes that anisogamy arises by disruptive selection for gamete numbers versus gamete size and predicts that female/male gamete size (anisogamy ratio) increases with adult size and complexity. Evidence has been... more
Gamete dynamics theory proposes that anisogamy arises by disruptive selection for gamete numbers versus gamete size and predicts that female/male gamete size (anisogamy ratio) increases with adult size and complexity. Evidence has been that in volvocine green algae, the anisogamy ratio correlates positively with haploid colony size. However, green algae show notable exceptions. We focus on Bryopsidales green algae. While some taxa have a diplontic life cycle in which a diploid adult (=fully grown) stage arises directly from the zygote, many taxa have a haplodiplontic life cycle in which haploid adults develop indirectly: the zygote first develops into a diploid adult (sporophyte) which later undergoes meiosis and releases zoospores, each growing into a haploid adult gametophyte. Our comparative analyses suggest that, as theory predicts, (i) male gametes are minimized, (ii) female gamete sizes vary, likely optimized by number versus survival as zygotes, and (iii) the anisogamy ratio correlates positively with diploid (but not haploid) stage complexity. However, there was no correlation between the anisogamy ratio and diploid adult stage size. Increased environmental severity (water depth) appears to drive increased diploid adult stage complexity and anisogamy ratio: gamete dynamics theory correctly predicts that anisogamy evolves with the (diploid) stage directly provisioned by the zygote.
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The chapter focuses on how a male allocates sperm among different ejaculates and summarizes a model framework for the analysis of this problem. It consolidates a prospective theory base for empirical advances. Since the sperm competition... more
The chapter focuses on how a male allocates sperm among different ejaculates and summarizes a model framework for the analysis of this problem. It consolidates a prospective theory base for empirical advances. Since the sperm competition involves sexual conflict, the interests of male and female differ. However, it is clear that the mating or ejaculatory strategy, which is best for a male need not be best for the female. Moreover, the resolution of mating conflict depends on the circumstances, and that either sex can exert a strong or even overriding influence. It also illustrates, whether the female has a strong influence on the evolution of ejaculate characteristics, depending on how much control she can exercise on an ejaculate within her reproductive tract. In many cases, there are no conflicts between the male strategy and female interests, and thus, the present models serve a fair approximation of the selective forces shaping ejaculate characteristics. There is now ample evidence, particularly from heterospermic inseminations (females inseminated with ejaculates from different males) in domestic mammals that genetic variation among males is correlated with differences in paternity prospects.
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Research Interests: Evolutionary Biology, Psychology, Game Theory, Altruism, Medicine, and 15 moreMultidisciplinary, Nature, Humans, Aggression, Female, Animals, Evolutionary Stable Strategy, Male, Punishment, Biological evolution, Agonistic Behavior, Offspring, Predatory Behavior, Cooperative Behavior, and punishment psychology
We currently classify sexual selection into pre- and post-copulatory components. In fact, pre-copulatory sexual selection (as envisaged by Darwin) represents the final stages of a cascade of events in the evolution of sexual strategy (the... more
We currently classify sexual selection into pre- and post-copulatory components. In fact, pre-copulatory sexual selection (as envisaged by Darwin) represents the final stages of a cascade of events in the evolution of sexual strategy (the ‘sexual cascade’), each stage arising as a consequence of the stage before. The cascade begins with the evolution of recombination and syngamy in ancestral eukaryotic unicells. As zygote provisioning becomes an important component of zygote fitness (e.g. during the evolution of multicellularity), anisogamy arises by gamete competition (ancestral sperm competition) and/or gamete limitation in a broadcast spawning ancestor —these two selective forces act in concert. Recent models show more clearly the conditions under which the evolutionarily stable strategy (ESS) is for one sex (isogamy) or two sexes (anisogamy): gamete competition is always the greater selective force favouring anisogamy if an average of just one (or more) spawning competitor is present. The primordial sexual conflict probably involved a form of gamete conflict. With the evolution of two sexes, selection would operate to generate a unity sex ratio. The earliest multicellular animals would have been immobile or weakly mobile organisms with high gonad masses in both sexes, their only outlet for their reproductive effort being expenditure on gametes, with high sperm expenditure maintained by sperm competition and/or sperm limitation. Gradually, once weak mobility developed (for whatever initial reason), the selective pressures of gamete competition/limitation favours female targeting (males moving towards females to release sperm), leading to increased expenditure on female targeting and reduced expenditure on sperm. This process ultimately drives the evolution of copulation and internal fertilisation and greatly reduces sperm expenditure as pre-copulatory sexual selection then leads to the evolution of Darwinian sex roles and sexual conflict. There is, therefore, an evolutionary shift from sexual selection by sperm competition and sperm selection to sexual selection by an increasingly pre-copulatory component (the form of sexual selection that Darwin envisaged). Sperm competition nevertheless remains an important component of sexual selection, and a rich diversity in sperm allocation patterns is shaped by evolutionary sperm competition games. Different forms of pre-copulatory competition may also affect sperm allocation, sperm form and function.
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Parasitic worms (i.e., helminths) commonly infect multiple hosts in succession. With every transmission step, they risk not infecting the next host and thus dying before reproducing. Given this risk, what are the benefits of complex life... more
Parasitic worms (i.e., helminths) commonly infect multiple hosts in succession. With every transmission step, they risk not infecting the next host and thus dying before reproducing. Given this risk, what are the benefits of complex life cycles? Using a dataset for 973 species of trophically transmitted acanthocephalans, cestodes, and nematodes, we tested whether hosts at the start of a life cycle increase transmission and whether hosts at the end of a life cycle enable growth to larger, more fecund sizes. Helminths with longer life cycles, that is, more successive hosts, infected conspicuously smaller first hosts, slightly larger final hosts, and exploited trophic links with lower predator–prey mass ratios. Smaller first hosts likely facilitate transmission because of their higher abundance and because parasite propagules were the size of their normal food. Bigger definitive hosts likely increase fecundity because parasites grew larger in big hosts, particularly endotherms. Helminths with long life cycles attained larger adult sizes through later maturation, not faster growth. Our results indicate that complex helminth life cycles are ubiquitous because growth and reproduction are highest in large, endothermic hosts that are typically only accessible via small intermediate hosts, that is, the best hosts for growth and transmission are not the same.
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Research Interests: Genetics, Economics, Coevolution, Sexual Conflict, Biology, and 15 moreResource Allocation, Ecology, Population ecology, Conflict Resolution, Conflict of Interest, Gene expression, Parental investment, Mating System, Empirical Research, Regression Model, Parent-Offspring Conflict, Genetic variation, Music Information Dynamics, Offspring, and Supply and Demand
Abstract Correction of an error in earlier simulations which show how anisogamy could evolve by selection on individuals (Parker et al. , 1971) now indicates that anisogamy can evolve when the range of gamete size is very much smaller... more
Abstract Correction of an error in earlier simulations which show how anisogamy could evolve by selection on individuals (Parker et al. , 1971) now indicates that anisogamy can evolve when the range of gamete size is very much smaller than previously thought. These models assumed random fusion of gametes, external fertilization, and that zygote viability is dependent on the volume of provisioning it receives from one or both gametes. The present analysis concerns the success of strategies for selective fusion of gametes arising in a randomly-fusing parental population. On a priori grounds selection is expected to favour assortative fusion in ova but disassortative fusion in sperm; anisogamy can persist only if genes for assortative fusion of ova will not spread, and “perfect” anisogamy where genes for disassortative fusion fixate. Mutant strategies for assortatively-fusing ova may not be successful if such ova must compete with sperm for fusions with the randomly-fusing ova. Particularly at high levels of anisogamy, very few of the mutant ova will be fused by the time all other ova have become zygotes; hence their spread may be checked by the enhanced chances of death before fusion, or by problems associated with selfing if they do manage to fuse. In contrast, disassortatively-fusing sperm generally have an advantage when anisogamy would be favoured under random fusion. Genetic simulations (involving two loci, one with alleles for fusion behaviour and the other with alleles for gamete size) were used to confirm these conclusions. Where there is some degree of asynchrony of spawning, disassortative fusion alleles do even better than with perfect synchrony. Simulations with various sex-limited fusion strategies show that non-limited disassortative fusion, i.e. for both ova and sperm, is likely to be an ESS at high anisogamy against all strategies but the one which plays random fusion in ova, disassortative fusion in sperm. This is the ultimate ESS and it does not disrupt anisogamy, but at high anisogamy it has an extremely small advantage over non-limited disassortative fusion. The reasons for the establishment of non-limited disassortative fusion are probably related to avoiding selfing, and to the cost of maintaining random-fusion in ova (in terms of motility, etc.) outweighing the benefits of becoming obligatorily disassortative (non-motile).
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The relationship between continuous input and interference models of ideal free distributions with unequal competitors. WJ SUTHERLAND, GA PARKER Animal behaviour 44, 345-355, Elsevier, 1992. Fretwell's ...
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Though the first attempts to introduce game theory into evolutionary biology failed, new formalism by Maynard Smith and Price in 1973 had almost instant success. We use information supplied by early workers to analyse how and why... more
Though the first attempts to introduce game theory into evolutionary biology failed, new formalism by Maynard Smith and Price in 1973 had almost instant success. We use information supplied by early workers to analyse how and why evolutionary game theory (EGT) spread so rapidly in its earliest years. EGT was a major tool for the rapidly expanding discipline of behavioural ecology in the 1970s; each catalysed the other. The first models were applied to animal contests, and early workers sought to improve their biological reality to compare predictions with observations. Furthermore, it was quickly realized that EGT provided a general evolutionary modelling method; not only was it swiftly applied to diverse phenotypic adaptations in evolutionary biology, it also attracted researchers from other disciplines such as mathematics and economics, for which game theory was first devised. Lastly, we pay attention to exchanges with population geneticists, considering tensions between the two modelling methods, as well as efforts to bring them closer. 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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Hamilton's rule and conditionality. GA Parker Ethology Ecology & Evolution 1:22, 195-211, 1989. Hamilton's rule is that an altruistic act should be performed when r times the benefit to a... more
Hamilton's rule and conditionality. GA Parker Ethology Ecology & Evolution 1:22, 195-211, 1989. Hamilton's rule is that an altruistic act should be performed when r times the benefit to a recipient is greater than the cost to the ...
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Evolutionary theory for expenditure on gonads attracted little attention until studies in the past 3–4 decades of allocation to male and female function in hermaphrodites, and of relative testes size (RTS) in animals with separate sexes.... more
Evolutionary theory for expenditure on gonads attracted little attention until studies in the past 3–4 decades of allocation to male and female function in hermaphrodites, and of relative testes size (RTS) in animals with separate sexes. RTS appears to have varied enormously over evolutionary time, from extremely high (over 40%) in some broadcast spawners to less than 1% in some taxa with copulation and internal fertilization. Reasons for this wide evolutionary diversity in testes expenditure deserve attention. Sperm demand (the product of expenditure per ejaculate and mating rate) increases expenditure on testes, and is moulded by a number of selective forces: sperm competition, mating rate and sperm limitation are identified as the three typically most powerful. Trade-offs between somatic and testes expenditures can be complex, particularly those between pre- and post-copulatory expenditure. Theoretical models predict that RTS should correlate positively with sperm demand, and there is much evidence from many taxa that RTS increases with sperm competition level. The relation between RTS and expenditure on each ejaculate is predicted to be positive over low sperm competition (risk) levels, and negative over high (intensity) sperm competition levels. Sexual cascade logic suggests that gonad expenditure should be high and equal for the two sexes soon after the early evolution of anisogamy, but should diverge widely through evolutionary time, with RTS reducing notably in those taxa that have evolved advanced mobility and internal fertilization.
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ABSTRACT Sperm competition is the competition between the ejaculates of different males for the fertilization of a given set of ova. Charles Darwin (1871) proposed sexual selection as a process that operates on variation in male ability... more
ABSTRACT Sperm competition is the competition between the ejaculates of different males for the fertilization of a given set of ova. Charles Darwin (1871) proposed sexual selection as a process that operates on variation in male ability to compete with other males for access to reproductive opportunities, and which promotes traits that confer an advantage in reproductive competition. In most taxa individual females may copulate (or spawn) with multiple males (i.e., are polyandrous). As a consequence, the ejaculates of different males may co-occur around a set of ova at the time of fertilization, resulting in sperm competition. Sperm competition introduces variation in male reproductive success determined by the relative competitive fertilizing efficiency of the ejaculates of different males, and generates postcopulatory, intrasexual selection, which promotes traits that increase the fertilization success of an ejaculate under competitive conditions. A second consequence of polyandry is the potential for intersexual selection to continue after copulation through mechanisms that enable females (or ova) to bias the outcome of sperm competition in favor of the sperm of certain males, a process known as sperm selection or cryptic female choice. The past three decades have seen an explosion of interest in postcopulatory sexual selection that has highlighted the importance of sperm competition and cryptic female choice as engines of evolutionary change. This chapter reviews recent empirical and theoretical advances to discuss various ways in which sperm competition may shape the evolution of sperm and ejaculate traits.
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An organism's maximum gonad investment (MGI) typically indicates its reproductive season and is often measured by the peak of the gonadosomatic index. Since external sexual dimorphism is often not evident, intrinsic sex differences... more
An organism's maximum gonad investment (MGI) typically indicates its reproductive season and is often measured by the peak of the gonadosomatic index. Since external sexual dimorphism is often not evident, intrinsic sex differences remain unstudied. We analysed the reproductive seasonality of each sex of the broadcast-spawning sea cucumber Holothuria (Halodeima) inornata in two populations (Caleta de Campos, Michoacán ‘CC’ and Puerto Madero, Chiapas ‘PM’) in the southern coast of the Mexican Pacific by examining: intensity and duration of MGI, frequency of each gonadal developmental stage (GDS) through time, sexual asymmetry in GSI, sexual asymmetry in GDS, and adult sex ratio. We observed a trade-off between the intensity (%) and duration (months) of each sex's MGI: as intensity decreases, duration increases and conversely. The frequency of ripe and spawning stages was consistently higher in females than males. Sexual asymmetry in GSI was slightly female-biased in the PM population, but male-biased in the CC population. Sexual asymmetry in GDS showed a more recurrent sexual equality at PM than at CC. The adult sex ratio of each population did not differ significantly from unity, but showed a near-significant trend for male bias in the CC. Although H. inornata exhibited different MGI responses between males and females and more markedly in CC than in PM, it also showed a synchronized relation between its mass investment (GSI) and physiological investment (GDS), possibly reflecting an optimum reproductive strategy. Lastly, changes in GSI were not underpinned by changes in local temperature, but rather by regional temperature.