The effect of sibship on fitness parameters (survival and reproductive output) of primary reproductives following immunization and challenge with the fungus Metarhizium anisopliae was studied in the primitive dampwood termite Zootermopsis angusticollis. Alates (n=19 stock colonies) were haphazardly assigned to sibling (n=180) and non-sibling pairs (n=183). Termites were immunized and challenged with various concentrations of fungal spores. Survival of primary reproductives was followed for 80 days after pairing. We also recorded the number of eggs and larvae as well as time to oviposition and hatching. Genetic relatedness between alates was a significant and independent predictor of survival. After controlling for the effects of sex, colony of origin, and immunization/challenge dosage, sibling pairs had significantly higher survival than non-sibling pairs [Wald Statistic=7.056, df=1, p=.05, Cox Proportional Regression (CPR)]. The hazard ratio of death of non-sibling pairs was 1.5x higher than that of sibling pairs (overall comparison, p=.008, CPRM). Sibling pairs had significantly higher survival distributions than non-sibling pairs (Breslow Statistic=11.74, p<.001). Reproductive parameters did not differ significantly between sibling and non-sibling pairs. These results suggest that non-sibling primary reproductives infected with M. anisopliae during the incipient stages of colony foundation are more susceptible than sibling pairs despite the fact that those that survive do not differ in reproductive parameters. Possible mechanisms of increased sibling survival include nepotistic behaviors such as increased allogrooming and transfer of nutrients between siblings.
Species 1: Isoptera Termopsidae Zootermopsis angusticollis (dampwood termite)
Species 2: Deuteromycotina Hypomycetes Metarhizium anisopliae (green muscardine fungus)
Keywords: genetic relatedness, incipient colony
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