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

Abstract

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.

Nocturnal mating behaviour and dynamic male investment of copulation time in the southern blue-ringed octopus, Hapalochlaena maculosa (Cephalopoda: Octopodidae)

“…It is not known how many spermatophores were passed during these observations. However, if it is assumed that longer copulation times enable males to transfer more spermatophores to females, as has been reported for some insects (Sakaluk & Eggert, 1996), then this behaviour was consistent with the risk model outlined by Ball and Parker (2007). These researchers suggested that when sperm supply is limited and female mating status is known, it is advantageous for males to allocate more sperm to virgin females in order to ensure paternity amongst future competing sperm given to that female.…”

“…Relevant models of sperm competition, where sperm supply is limited, imply that male cephalopods could potentially achieve optimal fertilisation success by investing less time copulating with females that they have already mated with (Parker, 1970), with females that are holding less sperm from competing males and therefore pose less risk of sperm competition (Ball & Parker, 2007), and/or when additional factors such as male mating order might give males an inherent advantage towards successful fertilisation (Parker, 1990). Likewise, male cephalopods should be expected to invest more time and/or spermatophores with novel females and females posing a high-risk of sperm competition (Parker, 1970;1990;Parker et al, 1997;Ball & Parker, 2007).…”

Sperm competition games: Sperm size (mass) and number under raffle and displacement, and the evolution of P2

“…where N f , N m are the number of breeding females and males, respectively Ball 2005, Ball andParker 2007). Thus at the ESS, remembering that…”

Experience of mating rivals causes males to modulate sperm transfer in the fly Drosophila pseudoobscura

“…In contrast, as intensity increases above one competitor, resource allocation should decrease as returns diminish with more competition (Parker et al, 1996Ball and Parker, 1997). In general, the outcome of sperm competition models is dependent on the mating status of females, the probability of female remating and number of competitors, but crucially also on the quality of information that the male has about these parameters (Ball and Parker, 2007;Parker and Pizzari, 2010). A further consideration is whether the competition is a fair or loaded raffle, and if the latter, which is the favoured role (i.e.…”