Can voluntary nutritional gifts in seminal flow evolve?

Abstract

In many species that have internal fertilization, seminal flow includes various elements and materials in addition to the fertilizing sperm. The roles of these components are unknown. One hypothesis is that they are nutritional gifts to the female as a paternal investment. We made game theoretical models from the point of view of sperm competition among males and examined this hypothesis. The evolutionary stable strategy (ESS) of the models showed that (1) when multiple mating in the female is relatively low, gifts in seminal flow or other types of gift may evolve, at least, a male does not resist a female digesting his sperm; and (2) the ratio of nutritional gift rapidly decreases to zero with the probability or frequency of multiple mating in the female. Hence, we concluded that nutritional gifts in seminal flow can exist only in species in which sperm competition among males is rare. Furthermore, we concluded that if an element or material eminently decreases when sperm competition becomes intense, it may be a gift as a paternal investment; if not, other hypotheses concerned with more agonistic roles are more feasible.

The seminal symphony: how to compose an ejaculate

“…Three recent models investigate how selection should act on ejaculate composition, given distinct functions for different ejaculate components and production trade-offs among them [20, 70, 71]. These models assume that greater investment in sperm yields greater paternity (i.e., by ‘purchasing tickets’ in a sperm competition raffle), whereas increased investment in non-sperm ejaculate stimulates female fecundity.…”

“…When ejaculates greatly stimulate female fecundity, females experience selection to increase remating, which feeds back on optimal ejaculate composition: sperm competition is intensified and generates selection for investment in sperm rather than fecundity-stimulants [20] (see also [71]). This prediction results from a model in which male investment per ejaculate is fixed and relative allocation to sperm and non-sperm evolve, and ejaculate investment does not entail costs for males.…”

All that Glisters is not Gold: Sensory Bias, Sexual Conflict and Nuptial Feeding in Insects and Spiders

“…If a gift functions as paternal investment, then providing the right nutrients for egg production would be in the interests of the male. Vahed (1998), however, proposed that there is little empirical support for the hypothesis that nuptial gifts in general function as paternal investment in insects, due partly to the prevalence of polyandry and, therefore, the low probability that the nutrient-donating male will fertilize the eggs that benefit from his nutrient donations in most nuptial feeding species (see also Kura & Yoda 2001).…”

Sperm Competition and the Evolution of Ejaculate Composition

“…This phenomenon has formed the focus of a number of theoretical analyses aimed at understanding the evolution of male ejaculate expenditure strategies over the past decade. However, although models of sperm competition have explored ejaculate allocation patterns under a variety of conditions, they have typically been concerned only with the sperm-containing portion of the ejaculate (e.g., Parker 1984Parker , 1990aParker , 1990bParker , 2000Parker et al 1996;Ball and Parker 1998, 2000, 2003Mesterton-Gibbons 1999a, 1999bGreef and Parker 2000;Williams et al 2005; but see Kura and Yoda 2001).…”