Beetle Kinship Project

During the Fall semester of 2015, Professor Elena Berg and undergraduate Shannon Monahan examined reproductive cooperation in male seed beetles (Callosobruchus maculatus). Not unlike fruit flies, male seed beetles physically harm females when they mate with them (Hotzy & Arnqvist 2009) but the ways in which kinship might moderate that conflict remain unknown. To that end, Professor Berg and Shannon measured the lifespan and reproductive success of females and males, the latter divided into “related” and “unrelated” groups. Once the data has been analyzed, their results will be written up as a scientific research paper and submitted for publication in a peer-reviewed journal.

Animals often compete aggressively for access to mates, and this competition between members of one sex often harms members of the opposite sex. In fruit flies (Drosophila melanogaster) and other insects, males frequently physically injure females when they mate with them (Arnqvist & Rowe 2005). This strategy can actually benefit males, since injured or dying females may be more likely to pour greater amounts of energy into the current batch of eggs (sired by that male), or the injuries may prevent them from mating with other males in the future. But what happens when those competing males are close relatives? Related individuals share genes, so by helping relatives produce more offspring, individuals indirectly pass on their own genetic material (Hamilton 1964).

Indeed, studies of many animal species have confirmed that relatives frequently help each other in various ways, including by sharing mates or resources, or alerting each other to danger (West et al. 2007). An intriguing recent study of fruit flies (Carazo et al. 2014) indicated that males were significantly less likely to harm their mates when in the presence of brothers, rather than in the presence of unrelated males. This suggests that brothers may indeed cooperate with each other, protecting the female from harm so that each male can sire young with her. However, two follow-up studies showed conflicting evidence (Chippindale et al. 2015; Hollis et al. 2015), highlighting the need for further experiments, in fruit flies and other organisms.