The genetic architecture of lifespan and mortality rates: Gender and species differences in inbreeding load of two seed-feeding beetles

We examine the inbreeding load for adult lifespan and mortality rates of two seed beetle species, Callosobruchus maculatus and Stator limbatus. Inbreeding load differs substantially between males and females in both study populations of C. maculatus - lifespan of inbred females was 9-13% shorter than the lifespan of outbred females, whereas the lifespan of inbred males did not differ from the lifespan of outbred males. The effect of inbreeding on female lifespan was largely due to an increase in the slope of the mortality curve. In contrast, inbreeding had only a small effect on the lifespan of S. limbatus - lifespans of inbred beetles were ~5% shorter than those of outbred beetles, and there was no difference in inbreeding load between the sexes. The inbreeding load for mean lifespan was ~0.4 and 0.6 lethal equivalents per haploid gamete for female lifespan in C. maculatus, and ~0.2 to 0.3 for both males and females of S. limbatus, all within the range of estimates commonly obtained for Drosophila. However, contrary to the predictions of mutation accumulation models, inbreeding load for loci affecting mortality rates did not increase with age in either species, despite an effect of inbreeding on the initial rate of increase in mortality. This was because mortality rates decelerated with age and converged to a mortality plateau for both outbred and inbred beetles.

Key Words: genetic load, inbreeding depression, life span, longevity, mutation accumulation

Online ISS 1091-6490
Copyright 2008 by the Genetics Society of America
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