Paternal care enhances male reproductive success in pine engraver beetles

Male pine engravers, Ips pini, assist their mates during reproduction by clearing debris from breeding galleries constructed beneath the bark of host trees. I measured duration of parental care provided by individual male pine engravers in the field, as well as the reproductive success of these males as indicated by the total number of eggs laid in their galleries and the mean distance between the eggs. Males remained in their galleries for 13-54 days (N=78, X̄±SE=33.0 ± 0.9 days). Male residence time was positively correlated with the mean distance between eggs in a gallery, as well as the total number of eggs laid in a gallery when the effect of male length was controlled statistically. Male-removal experiments corroborated these effects of male care on reproductive success, and showed that female mortality was higher in galleries from which the male had been removed than in controls. Duration of male care was inversely related to breeding density and male length. Despite remaining for less time in their galleries, larger males acquired the biggest harems. There was a positive correlation between the length of a male and the number of eggs laid per female, but this was not due to size-assortative mating. Because large male size is associated with a number of traits that are advantageous for securing mating opportunities, earlier departure from the gallery by larger males may be a consequence of those males having greater opportunities for future reproduction.