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In many animal systems, females exhibit a localized immune response to insemination that helps defend against sexually transmitted disease. However, this response may also kill sperm, reducing a male's reproductive potential. If males could suppress this response, they may be able to increase their sperm's representation in the female's reproductive tract, thereby increasing their fitness. Here we address the hypothesis that, under conditions of sperm competition, males interfere with female immunity. To test our hypothesis, we manipulated levels of female mating frequency (single vs. multiply mated) and seminal diversity (monandrous vs. polyandrous) in the cricket, Allonemobius socius and measured female immune response. As mating frequency increased, female hemocyte load decreased, indicating a general reproductive cost. As seminal diversity increased, phenoloxidase (PO) activity ( in vitro measure of ‘potential’ macroparasitic defense) increased and encapsulation ability ( in vivo measure of ‘realized’ macroparasitic defense) decreased in polyandrous females. These results suggest that males may manipulate female immunity by interrupting the pro-PO cascade, which begins with the activation of PO and ends in the encapsulation of invading foreign bodies. In other words, female immune function may serve as a battleground over which a sexual conflict is fought. [ABSTRACT FROM AUTHOR]

Indirect-benefit models of sexual selection assert that females gain heritable offspring advantages through a mating bias for males of superior genetic quality. This has generally been tested by associating a simple morphological quality indicator (for example, bird tail length) with offspring viability. However, selection acts simultaneously on many characters, limiting the ability to detect significant associations, especially if the simple indicator is weakly correlated to male fitness. Furthermore, recent conceptual developments suggest that the benefits gained from such mating biases may be sex-specific because of sexually antagonistic genes that differentially influence male and female reproductive ability. A more suitable test of the indirect-benefit model would examine associations between an aggregate quality indicator (such as male mating success) and gender-specific adult fitness components, under the expectation that these components may trade off. Here, we show that a father's mating success in the cricket, Allonemobius socius, is positively genetically correlated with his son's mating success but negatively with his daughter's reproductive success. This provides empirical evidence that a female mating bias can result in sexually antagonistic offspring fitness. [ABSTRACT FROM AUTHOR]