On Nuptial Gifts and Paternity5

Evolution of nuptial gifts and its coevolutionary dynamics with male-like persistence traits of females for multiple mating

BACKGROUND

Many male animals donate nutritive materials during courtship or mating to their female mates. Donation of large-sized gifts, though costly to prepare, can result in increased sperm transfer during mating and delayed remating of the females, resulting in higher paternity. Nuptial gifting sometimes causes severe female-female competition for obtaining gifts (i.e., sex-role reversal in mate competition) and selection on females to increase their mating rate, changing the intensity of sperm competition and the resultant paternity gains. We built a theoretical model to simulate such coevolutionary feedbacks between nuptial gift size (male trait) and propensity for multiple mating (female trait). Donation of nuptial gifts sometimes causes development of female persistence trait for gift acquisition. We also analyzed the causes and consequences of this type of traits, taking double receptacles for nutritious seminal gifts, which are known to occur in an insect group with a "female penis" (Neotrogla spp.), as an illustrative example.

RESULTS

Our individual-based simulations demonstrated that female-female competition for male-derived nutrients always occur when the environment is oligotrophic and mating costs are low for females. However, a positive correlation between donated gift size and the resultant paternity gain was a requisite for the co-occurrence of large gifts and females' competitive multiple mating for the gifts. When gift donation satisfied female demands and thus resulted in monandry, exaggeration of nuptial gift size also occurred under the assumption that the last male monopolizes paternity. The evolution of double slots for gift acquisition and digestion (female persistence trait) always occurred when males could not satisfy the demands of females for gifts. However, through coevolutionary reduction in male gift size, fixation of this trait in a population drastically reduced the average female fitness.

CONCLUSION

Sperm usage patterns, which have rarely been examined for animals with nuptial gifts, can be a critical factor for determining the extent of exaggeration in nuptial gifting. Sex-role reversals in mate competition, as a result of donation of nuptial gifts from males to females, can involve the evolution of male-like, persistent traits in females that reduce population productivity, as is the case with persistence traits in males.

Female bushcrickets fuel their metabolism with male nuptial gifts

In many arthropods, such as bushcrickets, males donate protein-rich nuptial gifts-so-called spermatophores-to females, which females ingest while the sperm enter the female's reproductive tract. Previously, it was shown that females route spermatophore nutrients over the course of hours and days to egg production or body synthesis. We investigated whether female bushcrickets fuel their metabolism with spermatophores immediately after consumption. We fed two male groups diets that were either enriched or depleted in 13C, and then tracked the isotopic changes in exhaled breath in female bushcrickets after spermatophore consumption. Within 3 hours, the stable carbon isotope ratio (delta13C) of female breath converged on the ratio of the male donor of the nuptial gift. This supports the idea that females quickly routed nutrients to metabolism, receiving immediate benefits from spermatophore feeding.

Courtship feeding in tree crickets increases insemination and female reproductive life span

Courtship feeding in the majority of insects may influence female reproductive patterns either directly, through effects of the gift material, or indirectly, through correlated effects of prolonged copulation and larger ejaculates. This distinction is important because the cause of changes in fecundity may influence patterns of the allocation of resources between the sexes, with implications for the intensity of sexual selection and magnitude of sexual conflict. I show that post-copulatory feeding on the secretions of a gland on the metanotum of male Oecanthus nigricornis. Walker correlates with oviposition and affects the number of sperm remaining within the spermatophore. Manipulations of gland feeding and insemination duration showed that changes in fecundity are due to the gift rather than the ejaculate. Metanotal gland feeding increased female fecundity by increasing reproductive life span without significantly increasing oviposition rate. These changes in reproduction were directly due to the gift itself. Although gland feeding was positively correlated with the duration of insemination and thus the number of sperm transferred from the spermatophore to the female, experimentally prolonging or reducing insemination had no significant effect on reproductive life span. Male phenotype was also associated with female fecundity but in this case the effect was caused by an increase in the oviposition rate of females that mated with relatively large males. Male size had no significant effect on female reproductive life span, suggesting that its effect is not simply due to a quantitative increase in gift size. Three other measures of male phenotype, fluctuating asymmetry, condition (i.e. size-standardized wet body mass) and age, had no significant effects on female reproduction.Copyright 1997 The Association for the Study of Animal BehaviourCopyright 1997The Association for the Study of Animal Behaviour.

Formation, transfer, and assimilation of the spermatophore of the hermaphroditic flatworm Dugesia gonocephala (Tricladida, Paludicola)

The spermatophore of the simultaneously hermaphroditic planarian Dugesia gonocephala consists of a large stalked bladder that gradually forms inside the ejaculatory duct of the penis between successive copulations. In solitary individuals, spermatophore formation begins with the development in the penis of a tube that is sealed at the distal end and may protrude slightly from the penis tip. In courting individuals, this protruding part is widened into a bladder that further increases in size when penises are mutually inserted. Spermatozoa are pumped into the bladder after the first few minutes of copulation and the resultant spermatophores are exchanged 3–4½ h after the start of copulation. Reciprocal transfer is slightly asynchronous. After the spermatophore is transferred into the bursa copulatrix, the stalk of the spermatophore is usually in or near the entrance to the bursal canal. Sperm start to leave the spermatophore immediately after the partners separate and continue to do so for 3–4 days. During this period, the bladder of the spermatophore shrinks but remains intact. Following spermatophore donation, the penis may hold a new spermatophore after 1–2 days. Individuals that engage in a new copulation rarely do so because they are allosperm depleted. In fact, the bursa may still hold a spermatophore from a previous copulation. We discuss the adaptive significance of spermatophore formation, transfer, and assimilation.