Paternity sharing in insects with female competition for nuptial gifts

Abstract

When males contribute costly investments to offspring (i.e., paternal care or nuptial gifts), they are expected to have high confidence of paternity. While studies of species with exclusive male parental care have provided support for this hypothesis, paternity may be more uncertain in systems where males feed each mate. While mating co-occurs with each oviposition in many male-care systems, allowing control over insemination, mating is separated from egg-laying in nuptial-gift systems so that males typically compete more with rivals for fertilizations. Given the costly gift investment, and long refractory periods that limit male ability to gain fitness from frequent copulations, there should be strong selection to avoid cuckoldry, especially complete paternity failure. Further, because females are expected to mate frequently to obtain male-supplied nutrition prior to oviposition, males may be unable to avoid sperm competition because virgins will be rare (and lower quality), and females are expected to undermine male traits that limit remating or manipulate sperm stores. Thus, paternity sharing, in which males are not excluded from siring offspring completely, is an expected outcome of sperm competition in these systems. Using wild-caught females in two species (an orthopteran and a dipteran), in which sexually selected females compete for important male nuptial gifts, we examined paternity patterns and compared them to findings in other insects. Using microsatellite analysis of offspring and sperm stores, we found evidence of shared paternity in both study species, where very few males failed to sire offspring. Although paternity was not equal among sires, our estimates of paternity bias were similar to other insects with valuable nuptial gifts and contrasted with patterns in gryllid crickets where males supply little more than sperm and are frequently excluded from siring offspring. Further support for paternity-sharing is the lack of last-male sperm precedence in either of our study species.