Female crickets trade offspring viability for fecundity.

A growing number of studies are suggesting that females can improve the viability of their embryos by mating with multiple males. However, the reason why females should have low rates of embryo viability is puzzling. Here we conduct a quantitative genetic study of maternal effects on embryo viability in the field cricket Teleogryllus oceanicus. After controlling for female body size, we find significant additive genetic variance for ovary weight, a measure of fecundity, and egg hatching success, a measure of embryo viability. Moreover, we show a genetic trade-off between these traits that is predicted from life-history theory. High rates of embryo mortality in this highly fecund species might therefore be explained by selection favouring an optimum balance between fecundity and embryo viability that maximizes maternal fitness. Paternal effects on female fecundity and embryo viability are often seen as benefits driving the evolution of polyandrous behaviour. However, we raise the alternative possibility that paternal effects might shift females from their naturally selected optimum, and present some support for the notion that sexual conflict over a female's optimal fecundity and embryo viability might generate antagonistic coevolution between the sexes.

Simmons LW ，García-González F 《JOURNAL OF EVOLUTIONARY BIOLOGY》

The evolution of polyandry: intrinsic sire effects contribute to embryo viability.

Females typically mate with more than one male despite the costs incurred, thus questioning Bateman's principle. A series of genetic benefits have been proposed to account for the evolution of polyandry, including the acquisition of viability genes for offspring. The 'intrinsic male quality' hypothesis suggests that polyandry increases the probability that females produce offspring sired by males that bestow high viability on their offspring. Heritable variation in viability is the basic requirement for the occurrence of this genetic benefit. By using a half-sib breeding design with a species of cricket in which polyandry is known to increase hatching success, we present clear experimental evidence that intrinsic male quality contributes to embryo viability. Despite recent support for the evolution of polyandry based on compatibility of genotypes between males and females, we show that hatching success is not determined by an interaction between paternal and maternal genotypes but rather that sons inherit paternal genes that influence the viability of eggs laid by their mates. Moreover, our data implicate a potential role for indirect genetic effects of male accessory gland products on embryo viability. Additive genetic contributions to embryo viability may be an important factor underlying the frequently observed benefits of polyandrous behaviour.

García-González F ，Simmons LW 《JOURNAL OF EVOLUTIONARY BIOLOGY》

Do female black field crickets Teleogryllus commodus benefit from polyandry?

Female insects that mate multiply tend to have increased lifetime fitness, apparently because of greater access to male-derived resources (e.g. sperm, nuptial gifts) that elevate fertility/fecundity. Experiments that standardize the number of matings per female also show that polyandry can improve aspects of offspring performance, most notably early embryo survival (egg hatching success). This improvement is widely attributed to genetic benefits which would arise if polyandrous females skew paternity to produce fitter offspring. In two separate experiments with field crickets (Teleogryllus commodus) polyandrous females (two, three or four mates) did not have higher egg hatching success than monandrous females (effect sizes: r = 0.03 and 0.08 for the respective experiments), which is consistent with our finding of no sire effect on hatching success. Polyandry also had no effect on post-hatching offspring survival. Polyandrous females' offspring took significantly longer to mature but their sons were not heavier and their daughters were actually significantly smaller than those of monandrous females. Finally, after controlling for relative male size, monandrous females' sons were more successful when directly competing for a mate.

Jennions MD ，Drayton JM ，Brooks R ，Hunt J ... -  《JOURNAL OF EVOLUTIONARY BIOLOGY》

Polyandry promotes enhanced offspring survival in decorated crickets.

Although female multiple mating is ubiquitous in insects, its adaptive significance remains poorly understood. Benefits to multiple mating can accrue via direct material benefits, indirect genetic benefits, or both. We investigated the effects of multiple mating in the decorated cricket, Gryllodes sigillatus, by simultaneously varying the number of times that females mated and the number of different males with which they mated, measuring aspects of female fecundity and elements of offspring performance and viability. Multiple matings resulted in enhanced female fitness relative to single matings when females mated with different partners, but not when females mated repeatedly with the same male. Specifically, polyandrous females produced significantly more offspring surviving to reproductive maturity than did monogamous females mating once or mating repeatedly with the same male. These results suggest that the benefit females gain from multiple mating is influenced primarily by genetic and not material benefits.

Ivy TM ，Sakaluk SK 《EVOLUTION》

Paternal indirect genetic effects on offspring viability and the benefits of polyandry.

Although females are expected to maximize their reproductive success with only one or a few matings, the females of many species mate with multiple partners. Experimental studies have found evidence for an increase in egg or embryo viability when females mate polyandrously. These studies have been interpreted in the context of genetic-benefit models that propose that multiple mating increases offspring viability because it allows females to select male genotypes that influence viability directly or because it allows females to avoid genetic incompatibility. However, no studies have examined directly the precise mechanisms by which parents influence embryo viability. Using a morphological marker that enabled us to determine paternity and survival of embryos sired by individual male crickets in both sperm-competitive and -noncompetitive situations, we show that males inducing high embryo viability enhance the viability of embryos sired by inferior males. These results indicate that paternal effects and interacting phenotypes determine embryo viability. They show that a male's reproductive success is modified by the interaction between indirect genetic effects of sperm competitors. Importantly, our findings show that the benefits accruing to offspring of multiply mated females need not be transmitted genetically.

García-González F ，Simmons LW 《CURRENT BIOLOGY》