Crickets detect the genetic similarity of mating partners via cuticular hydrocarbons

Animals should decipher information about the genetic make‐up of conspecifics in order to enhance the fitness benefits associated with mate choice. Although there is increasing evidence to suggest that animals make genetically informed decisions about their mating partners, we understand relatively little about the sensory mechanisms informing these decisions. Here, we investigate whether cuticular hydrocarbons, chemical compounds found on the cuticle of most terrestrial arthropods, provide a means of discerning genetic similarity during mate choice in the cricket, Teleogryllus oceanicus. We found that individuals preferentially mated with partners who share more dissimilar cuticular hydrocarbon profiles and that similarity in cuticular hydrocarbon profiles between mating pairs correlated with their genetic similarity. Our results provide good evidence that cuticular hydrocarbon profiles offer a means of assessing genetic compatibility in T. oceanicus, enabling individuals to choose their most genetically suitable mate.     

Consequence of emergence pattern on inbreeding risk in the aphid parasitoid Aphidius matricariae (Hymenoptera: Braconidae)

In insect parasitoids, mating strategy depends on mate availability and is influenced by the spatial and temporal emergence patterns of adults. For quasi-gregarious species, simultaneous emergence favors local mating and reduces search costs for partners while increasing the risk of inbreeding, particularly when only one female parasitizes the initial host patch. Consequently, in inbreeding sensitive species, mating on the place of adult emergence (patch mating) between siblings should be counter selected. In practice, the timing of male and female emergence and of their dispersal influences mate availability and can limit on patch mating. To test the role of these two factors, we analyzed the daily distribution of emergence and patch residence time of a cohort in the aphid parasitoid Aphidius matricariae (Hymenoptera: Braconidae). We observed that adult emergence is concentrated on the morning with males emerging on average before females with some overlaps. A more precise evaluation of emergence pattern within a brood suggests that brothers and sisters rarely emerge at the same time and rapid dispersal of males and females favors off-patch mating. The relationships between timing of emergence including differences between sex and consequences on inbreeding probability in these species are thus discussed.     

DOES GENETIC RELATEDNESS OF MATES INFLUENCE COMPETITIVE FERTILIZATION SUCCESS IN GUPPIES?

A growing number of studies highlight the nontransitive properties of ejaculates when they are in competition to fertilize a female's eggs. Increasingly, these studies suggest that postcopulatory processes act as a filter against sperm from closely related males or those with similar genotypes, limiting the deleterious effects of inbreeding on offspring fitness. We investigated the potential for such postcopulatory mechanisms of inbreeding avoidance in the guppy (Poecilia reticulata), a promiscuous livebearing fish. We used artificial insemination as a method of delivering to a female the combined ejaculates from a first cousin (relatedness coefficient r = 0.125) and an unrelated male. This method of sperm delivery controls behavioral processes of pre- and postcopulatory female choice, which can bias paternity toward unrelated males. Our genetic analysis revealed no effect of parental relatedness on paternity outcomes. The observed mean paternity share for related males (0.47) and associated variance did not differ significantly from an expected binomial distribution that assumes no biased use of sperm with respect to relatedness (0.5). Although our data provide no evidence for postcopulatory mechanisms of inbreeding avoidance, the ability of female guppies to influence ejaculate transfer and retention offers an alternative and easily testable mechanism of inbreeding avoidance in this species.     

Sequence-based evidence for major histocompatibility complex-disassortative mating in a colonial seabird

The major histocompatibility complex (MHC) is a polymorphic gene family associated with immune defence, and it can play a role in mate choice. Under the genetic compatibility hypothesis, females choose mates that differ genetically from their own MHC genotypes, avoiding inbreeding and/or enhancing the immunocompetence of their offspring. We tested this hypothesis of disassortative mating based on MHC genotypes in a population of great frigatebirds (Fregata minor) by sequencing the second exon of MHC class II B. Extensive haploid cloning yielded two to four alleles per individual, suggesting the amplification of two genes. MHC similarity between mates was not significantly different between pairs that did (n = 4) or did not (n = 42) exhibit extra-pair paternity. Comparing all 46 mated pairs to a distribution based on randomized re-pairings, we observed the following (i): no evidence for mate choice based on maximal or intermediate levels of MHC allele sharing (ii), significantly disassortative mating based on similarity of MHC amino acid sequences, and (iii) no evidence for mate choice based on microsatellite alleles, as measured by either allele sharing or similarity in allele size. This suggests that females choose mates that differ genetically from themselves at MHC loci, but not as an inbreeding-avoidance mechanism.     

Dispersal, philopatry, and genetic relatedness in a social carnivore: comparing males and females

A balance must be maintained between the proportion of individuals dispersing and the proportion remaining philopatric such that inbreeding and resource competition are minimized. Yet the relative importance of dispersal and philopatric behaviour is uncertain, especially for species with complex social systems. We examine the influence of dispersal on genetic relationships of a white-nosed coati ( Nasua narica : Procyonidae) population from Panama. Field studies of the coati indicate a social system in which all females are highly philopatric and live in bands while all adult males become solitary at maturity, but do not disperse from the home range of their natal band. Based on analyses of multilocus DNA fingerprints, we confirm that female philopatry is the rule, long-distance dispersal is rare, and that relatedness between most bands is low. However, some new bands result from fission events and these bands retain relatively high relatedness to one another for several years. Adult males inhabiting the home range of a band are closely related to band members. In contrast, males and band members whose ranges do not overlap are unrelated or only slightly related. Adult males are also more closely related to other males whose home ranges they overlap extensively than to males whose home ranges they overlap only slightly. These results indicate that males initially disperse from their natal bands to reduce resource competition and not to avoid inbreeding. Inbreeding avoidance, if it occurs, results from more extensive range movements by males during the mating season.     

Causes of hatching failure in endangered birds

About 10 per cent of birds'' eggs fail to hatch, but the incidence of failure can be much higher in endangered species. Most studies fail to distinguish between infertility (due to a lack of sperm) and embryo mortality as the cause of hatching failure, yet doing so is crucial in order to understand the underlying problem. Using newly validated techniques to visualize sperm and embryonic tissue, we assessed the fertility status of unhatched eggs of five endangered species, including both wild and captive birds. All eggs were classified as ‘infertile’ when collected, but most were actually fertile with numerous sperm on the ovum. Eggs of captive birds had fewer sperm and were more likely to be infertile than those of wild birds. Our findings raise important questions regarding the management of captive breeding programmes.