Pitfalls in experiments testing predictions from sperm competition theory

Engqvist, Leif; Reinhold, Klaus

doi:10.1111/j.1420-9101.2004.00792.x

Cited by 90 publications

(117 citation statements)

References 48 publications

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“…strategic sperm allocation), available theoretical and empirical evidence fails to support this possibility. Sperm competition theory predicts that sperm allocation should increase at high SCR levels until sperm competition is certain, but then drops consistently when a male has to face more than one competing ejaculate at high SCI levels (Parker et al 1996;Parker 1998;Wedell et al 2002;Engqvist & Reinhold 2005). Therefore, if extended copula duration was caused by an increase in the amount of sperm transferred to the female during mating, we would expect longer copula durations in the 'one male' treatment (Gage & Baker 1991), not in the '10 males' treatment.…”

Section: Discussionmentioning

confidence: 99%

“…All males and females used were at least 10 days post-eclosion at the beginning of the experiments. Before each trial, experimental males were given a 24 h mating period with a non-experimental female to ensure adequate motivation (Carazo et al 2004) and to control male perception of mean SCR and intensity prior to testing (Engqvist & Reinhold 2005). Trials were conducted at a temperature of 22-258C, at ambient humidity and under dim red light.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, the risk of spermatophore inhibition is highest when male density is high (i.e. high SCI), precisely when theoretical models predict that sperm expenditure should be low (Parker et al 1996;Parker 1998;Wedell et al 2002;Engqvist & Reinhold 2005). Under these circumstances, male assessment of rival density at mating is crucial as it will not only reflect SCR and intensity levels, but also prevailing sperm competition sources that may require specific behavioural responses on the part of the male.…”

Section: Introductionmentioning

confidence: 99%

“…Recent empirical and theoretical work has focused on the study of strategic reproductive behaviours that have evolved as a response to varying levels in sperm competition risk (SCR; the probability that a male's sperm will compete against the sperm of other males) and sperm competition intensity (SCI; average number of competing ejaculates; e.g. Parker et al 1996Parker et al , 1997Parker 1998;Wedell et al 2002;Engqvist & Reinhold 2005).…”

Section: Introductionmentioning

confidence: 99%

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Chemosensory assessment of sperm competition levels and the evolution of internal spermatophore guarding

2006

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Males of many species adjust their reproductive behaviour according to the perceived risk of sperm competition. Although this phenomenon is widespread in insects and other animals, the mechanisms that allow mates to assess sperm competition levels remain largely unexplored. In this study, we analysed the mating behaviour of pairs of Tenebrio molitor beetles under three odour treatments representing increasing levels of sperm competition risk (SCR) and sperm competition intensity (SCI). Copula duration and male and female post-copulatory behaviour varied significantly with odour treatment. Both copula duration and post-copulatory associations (PCAs) increased significantly in odour treatments reflecting high male density. To our knowledge, this is the first study to report that insects may assess the actual density of potential competitors at the time of mating, a cue to SCR and SCI, on the basis of chemical cues. In T. molitor, males inhibit sperm release from the spermatophore of a rival male when remating takes place at short intervals. We show that, when sperm competition levels are high, PCAs increase female remating interval just above that necessary to prevent spermatophore inhibition by rival males. This finding strongly suggests that strategic male behaviour plays a 'spermatophore guarding' role in this species. Although common in insects with external spermatophore transfer, spermatophore guarding is not expected in species with rapid ejaculate transfer and internal spermatophore delivery. Our results reveal that spermatophore guarding may evolve, even under these circumstances, as an evolutionary response to short-term spermatophore inhibition or displacement mechanisms.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chemosensory assessment of sperm competition levels and the evolution of internal spermatophore guarding

2006

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“…The relations between sperm allocation (s) and average risk (q) shown in Figs 2, 3 and 5 imply comparisons across species (or subpopulations, Engqvist & Reinhold, 2005) differing in q but with otherwise similar ecologies. These figures suggest that relative allocations to females in different perceived risk states (e.g.…”

Section: Discussionmentioning

confidence: 99%

Sperm competition games: the risk model can generate higher sperm allocation to virgin females

Ball

Parker

2006

J of Evolutionary Biology

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We examine the risk model in sperm competition games for cases where female fertility increases significantly with sperm numbers (sperm limitation). Without sperm competition, sperm allocation increases with sperm limitation. We define ‘average risk’ as the probability q that females in the population mate twice, and ‘perceived risk’ as the information males gain about the sperm competition probability with individual females. If males obtain no information from individual females, sperm numbers increase with q unless sperm limitation is high and one of the two competing ejaculates is strongly disfavoured. If males can distinguish between virgin and mated females, greater sperm allocation to virgins is favoured by high sperm limitation, high q, and by the second male's ejaculate being disfavoured. With high sperm limitation, sperm allocation to virgins increases and to mated females decreases with q at high q levels. With perfect information about female mating pattern, sperm allocation (i) to virgins that will mate again exceeds that to mated females and to virgins that will mate only once, (ii) to virgins that mate only once exceeds that for mated females if q is high and there is high second male disadvantage and (iii) to each type of female can decrease with q if sperm limitation is high, although the average allocation increases at least across low q levels. In general, higher sperm allocation to virgins is favoured by: strong disadvantage to the second ejaculate, high sperm limitation, high average risk and increased information (perceived risk). These conditions may apply in a few species, especially spiders.

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Seasonal effects on egg production and level of paternity in a natural population of a simultaneous hermaphrodite snail

Janssen

Baur

2015

Ecology and Evolution

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In a seasonal environment, the suitable time window for females to reproduce is restricted by both environmental conditions and the availability of males. In simultaneous hermaphrodites, which are female and male at the same time, selection on a trait that is solely beneficial for one sexual function cannot occur independently. Therefore, it is assumed that the optimal time window for reproduction is a compromise between the two sexual functions in simultaneous hermaphrodites, mediated by environmental conditions. We examined seasonal patterns of reproduction and the resulting paternity in a natural population of the simultaneously hermaphroditic land snail Arianta arbustorum. Adult and premature individuals (snails in a short protandric phase) were collected on four occasions over the entire active season. The snails were allowed to deposit eggs after which we assessed the level of paternity in their hatched offspring. Individuals mated throughout the reproductive season, whereas egg production – the major task of the female function – was restricted to the first half of the season. Snails collected in autumn were allowed to hibernate under laboratory conditions. As a result, we found that premature individuals began to mate late in the reproductive season, but did not start to produce eggs before emerging from hibernation. Our results demonstrate a temporal shift of reproductive activities; the egg production and oviposition occur mainly in the first half of the season, while sperm production and mating occur over the entire season. In subadult and adult snails, sperm obtained from several partners in the second part of the reproductive season are stored during hibernation for the fertilization of eggs in the successive years. These results extend our understanding of the influence of both natural and sexual selection on reproductive strategies in hermaphrodites.

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Pitfalls in experiments testing predictions from sperm competition theory

Cited by 90 publications

References 48 publications

Chemosensory assessment of sperm competition levels and the evolution of internal spermatophore guarding

Chemosensory assessment of sperm competition levels and the evolution of internal spermatophore guarding

Sperm competition games: the risk model can generate higher sperm allocation to virgin females

Seasonal effects on egg production and level of paternity in a natural population of a simultaneous hermaphrodite snail

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