Mate availability contributes to maintain the mixed-mating system in a scolytid beetle.

We investigated the mating system and population genetic structure of the beetle, Coccotrypes dactyliperda, with life history characteristics that suggest the presence of a stable mixed-mating system. We examined the genetic structure of seven populations in Israel and found significant departures from the Hardy-Weinberg equilibrium and an excess of homozygosity. Inbreeding coefficients were highly variable across populations, suggesting that low levels of outbreeding occur in nature. Experiments were conducted to determine whether the observed high inbreeding in these populations is the result of a reproductive assurance strategy. Females reared in the laboratory took longer to mate with males from the same population (inbreeding) than with males from a different population (outbreeding). These results suggest that females delayed inbreeding, and were more inclined to outbreed when possible. Thus inbreeding, which predominates in most populations, may be due to a shortage of mates for outbreeding rather than a preference for inbreeding. We conclude that C. dactyliperda has a mixed-mating system that may be maintained by a reproductive assurance strategy.

Inbreeding variability and population structure in the invasive haplodiploid palm-seed borer (Coccotrypes dactyliperda).

We investigated the mating system and population genetic structure of the invasive haplodiploid palm-seed borer Coccotrypes dactyliperda in California. We focused on whether these primarily inbreeding beetles have a 'mixed-breeding' system that includes occasional outbreeding, and whether local inbreeding coefficients (F(IS)) varied with dominant environmental factors. We also analysed the genetic structure of C. dactyliperda populations across local and regional scales. Based on the analysis of genetic variation at seven microsatellite loci in 1034 individual beetles from 59 populations, we found both high rates of inbreeding and plentiful evidence of mixed-breeding. F(IS) ranged from -0.56 to 0.90, the highest variability reported within any animal species. There was a negative correlation between F(IS) and latitude, suggesting that some latitude-associated factor affecting mating decisions influenced inbreeding rates. Multiple regressions suggested that precipitation, but not temperature, may be an important correlate. Finally, we found highly significant genetic differentiation among sites, even over short geographic distances (< 1000 m).