Bark beetles and reproduction

Competition between inbreeding and outbreeding bark beetle species which breed in palm seeds

Outbreeding sex has been enormously successful, despite clear short-term advantages to reproducing asexually (by parthenogenesis) or by repeated inbreeding. Occasional inbreeding generally leads to severe inbreeding depression; nonetheless, a variety of animals and plants inbreed regularly, and in many cases have done so for tens of millions of years. Inbreeding reduces the time and energy a female uses to find and select mates; inbreeding regularly leads to the faithful reproduction of successful genotypes. Nonetheless, the natural world is dominated by outbreeding—why?

Fallen palm seeds are a natural arena for competition between inbreeders and outbreeders. Dactylotrypes longicollis is an outbreeding bark beetle (Curculionidae, Scolytinae) endemic to the Canary Islands but which has recently spread to many parts of the Mediterranean and North Africa including Madeira. In most of its current range, it competes with one or both of two non-native inbreeding bark beetles (Coccotrypes carpophagus and C. dactyliperda); various combinations of the three species can even be found in the same palm seed.

In direct competition, outbreeders should in some circumstances have the advantage of greater genetic variability and thus be able to compete well under a wider variety of environmental conditions. Inbreeders should have advantages in colonization: dispersing females are already mated, and regular inbreeders presumably suffer little or no inbreeding depression when forced to breed in small populations. In competition with outbreeders, they could also have an advantage in reproductive rate: extreme inbreeders such as these invest very little in males (usually one or two per brood), while outbreeders ‘waste’ 50% of their resources on making males. Given these various advantages and disadvantages, under what circumstances does outbreeding ‘win’ or ‘lose’? This master’s project will design and carry out experiments to help us answer this question.

Konkuranse mellom innavl og utavl hos barkbiller i palmefrø