Evolutionary Modeling Predicts a Decrease in Postcopulatory Sperm Viability as a Response to Increasing Levels of Sperm Competition

Engqvist, Leif

doi:10.1086/665000

Cited by 9 publications

(15 citation statements)

References 58 publications

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“…For example, if males respond to sperm competition by investing preferentially in sperm numbers at the expense of sperm longevity [57,58], the net effect on female mating interval will depend on the relative change in these two traits, as increased sperm number favours longer remating intervals while decreased longevity favours shorter intervals (figure 4). In contrast, if higher levels of sperm competition select instead for greater total investment in ejaculates, then high remating rates may favour increased sperm quantity and quality [59], which then further selects for longer remating intervals (and may subsequently lead to selection on males for decreased allocation to ejaculates).…”

Section: Discussionmentioning

confidence: 99%

Selection on female remating interval is influenced by male sperm competition strategies and ejaculate characteristics

Alonzo

Pizzari

2013

Phil. Trans. R. Soc. B

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Female remating rate dictates the level of sperm competition in a population, and extensive research has focused on how sperm competition generates selection on male ejaculate allocation. Yet the way ejaculate allocation strategies in turn generate selection on female remating rates, which ultimately influence levels of sperm competition, has received much less consideration despite increasing evidence that both mating itself and ejaculate traits affect multiple components of female fitness. Here, we develop theory to examine how the effects of mating on female fertility, fecundity and mortality interact to generate selection on female remating rate. When males produce more fertile ejaculates, females are selected to mate less frequently, thus decreasing levels of sperm competition. This could in turn favour decreased male ejaculate allocation, which could subsequently lead to higher female remating. When remating simultaneously increases female fecundity and mortality, females are selected to mate more frequently, thus exacerbating sperm competition and favouring male traits that convey a competitive advantage even when harmful to female survival. While intuitive when considered separately, these predictions demonstrate the potential for complex coevolutionary dynamics between male ejaculate expenditure and female remating rate, and the correlated evolution of multiple male and female reproductive traits affecting mating, fertility and fecundity.

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Section: Discussionmentioning

confidence: 99%

Selection on female remating interval is influenced by male sperm competition strategies and ejaculate characteristics

Alonzo

Pizzari

2013

Phil. Trans. R. Soc. B

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“…At each mating, male i transfers s i sperm to the female. The number of sperm ζ i still viable at the time of fertilization t depends on s i , on the male's sperm mortality rate (μ i ), and the time at which he mated with the female ( t i ; as determined by the female's remating interval) (Parker ; Engqvist ):

ζ_{i, t} = s_{i} e^{- μ_{i} (t - t_{i})} .

…”

Section: The Modelmentioning

confidence: 99%

“…We assume the males’ two evolving sperm traits, s and μ, trade‐off such that the amount of resources a male i allocates to sperm is:

ρ_{i} = s_{i} β \frac{1}{μ_{i}},

where β determines the cost of a single sperm cell (Engqvist ; Bocedi and Reid ). There is ample empirical evidence that sperm is costly (Wedell et al.…”

Section: The Modelmentioning

confidence: 99%

“…) as well as survival (Van Voorhies ). We applied a trade‐off between s and μ to examine the potential interactions between sperm competition, allocation to different sperm traits and inbreeding depression in driving polyandry evolution, and to facilitate comparison with previous models that did not consider inbreeding, or resulting inbreeding depression in sperm traits (Engqvist ; Bocedi and Reid ). Although results will depend quantitatively on the specific form of the trade‐off, they are likely to be qualitatively robust to alternative formulations (Supporting Information S3).…”

Section: The Modelmentioning

confidence: 99%

“…1F) and of polyandry itself (Fig. 1C-D;Engqvist 2012;Alonzo and Pizzari 2013;Abe and Kamimura 2015;Bocedi and Reid 2016).…”

mentioning

confidence: 95%

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Feed-backs among inbreeding, inbreeding depression in sperm traits, and sperm competition can drive evolution of costly polyandry

Bocedi

Reid

2017

Evolution

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Ongoing ambitions are to understand the evolution of costly polyandry and its consequences for species ecology and evolution. Emerging patterns could stem from feed‐back dynamics between the evolving mating system and its genetic environment, defined by interactions among kin including inbreeding. However, such feed‐backs are rarely considered in nonselfing systems. We use a genetically explicit model to demonstrate a mechanism by which inbreeding depression can select for polyandry to mitigate the negative consequences of mating with inbred males, rather than to avoid inbreeding, and to elucidate underlying feed‐backs. Specifically, given inbreeding depression in sperm traits, costly polyandry evolved to ensure female fertility, without requiring explicit inbreeding avoidance. Resulting sperm competition caused evolution of sperm traits and further mitigated the negative effect of inbreeding depression on female fertility. The evolving mating system fed back to decrease population‐wide homozygosity, and hence inbreeding. However, the net overall decrease was small due to compound effects on the variances in sex‐specific reproductive success and paternity skew. Purging of deleterious mutations did not eliminate inbreeding depression in sperm traits or hence selection for polyandry. Overall, our model illustrates that polyandry evolution, both directly and through sperm competition, might facilitate evolutionary rescue for populations experiencing sudden increases in inbreeding.

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Sperm form and function in the absence of sperm competition

Horst

Maree

2013

Molecular Reproduction Devel

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SUMMARYSperm competition is a post-copulatory, sexual selection force that, together with phylogeny and fertilization mode, has been regarded as one of the main factors explaining the diversity in sperm size across species. This universal sperm selection mechanism favors traits that enhance a male's fertilizing ability and paternity success. Surprisingly, however, sperm characteristics and semen quality in monogamous species, with low risk of sperm competition, have barely received any attention. In this review, we consider sperm competition and monogamy as two ends of the selective spectrum, and discuss its effect on sperm structure and function. We address the issue of a lack of sperm competition by comparing sperm traits of essentially monogamous speciesÀ Àtheir largely degenerative sperm features and high degree of polymorphisms could be norms for monogamous species. Further, the level of sperm competition in humans is discussed by comparing its mating strategy, relative testis size, and sperm traits to other primate species. In terms of sperm concentration, sperm swimming speed, and sperm morphology, humans seem to be closer aligned to the low-risk sperm competition situation in gorillas than to promiscuous chimpanzees.

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Evolutionary Modeling Predicts a Decrease in Postcopulatory Sperm Viability as a Response to Increasing Levels of Sperm Competition

Cited by 9 publications

References 58 publications

Selection on female remating interval is influenced by male sperm competition strategies and ejaculate characteristics

Selection on female remating interval is influenced by male sperm competition strategies and ejaculate characteristics

Feed-backs among inbreeding, inbreeding depression in sperm traits, and sperm competition can drive evolution of costly polyandry

Sperm form and function in the absence of sperm competition

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