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.     

Population studies of two colonial orb-weaving spiders

Colonial spiders have individual capture webs (territories) within a communally shared web structure. I describe here the life histories and colony population dynamics of two communal species, Ctrtophora moluccensis (Doleschall) (Araneidae) in Papua New Guinea and Philoponella republicana (Simon) (Uloboridae) in the Panama Canal Zone. In both species, dispersal and foundation of new colonies are primarily by groups of immatures. Population growth of new-colonies was rapid during the first generation, but then colony population size decreased markedly. Colonies of P. republicana rarely lasted more than one generation, whereas those of C. moluccensis attained an equilibrium population size and often persisted for many generations at the same site. Reproduction occurred during the wet season in P. republicana colonies and year-round in colonies of C. moluccensis. Reproduction was synchronized in widely separated colonies of P. republicana. Factors controlling population growth and survival of colonies are discussed. Cyrtophora moluccensis colonies were probably regulated by density dependant factors, especially predation and parasitism, and perhaps a shortage of flying insects due to colony visibility. Philoponella republicana colonies were most likely limited by climatic conditions and instability of the habitat (i.e. density independent factors). Colonial social organization influences both dispersal and colony population growth. Coloniality is, however, compatible with various life history strategies.