Sperm influences female hibernation success, survival and fitness in the bumble-bee Bombus terrestris.

We present evidence that in the absence of the transfer of male gland compounds in the ejaculate as well as of behavioural male traits, such as mate guarding or harming of females, sperm itself affects female life-history traits such as hibernation success, female longevity and female fitness. Using the bumble-bee Bombus terrestris, we artificially inseminated queens (females) with sperm from one or several males and show that sire groups (groups of brother males) vary in their effects on queen hibernation survival, longevity and fitness. In addition, multiply inseminated queens always had a lower performance as compared to singly inseminated queens. Apart from these main effects, sire groups (in situations of multiple insemination) affected queen longevity and fitness not independently of each other, i.e. certain sire group combinations were more harmful to queens than others. So far, the cause(s) of these effects remain(s) elusive. Harmful male traits as detected here are not necessarily expected to evolve in social insects because males depend on females for a successful completion of a colony cycle and thus have strong convergent interests with their mates.