Variation in inbreeding depression among populations of the seed beetle, Stator limbatus

Inbreeding depression has been documented in many insect species, but the degree to which it varies among traits within populations and among populations within species is poorly understood. We used a single-generation factorial breeding design to examine variation in inbreeding depression among three populations of the seed-feeding beetle, Stator limbatus Horn (Coleoptera: Chrysomelidae: Bruchinae), from the southwestern USA. Eggs from sib matings were less likely to develop and hatch, and larval hatch-to-adult mortality was higher for offspring of sib matings. Overall, inbreeding resulted in a reduction in the proportion of eggs that produced an adult from >80% for outbred matings in all three populations to an average of only 54% for inbred matings. Of those larvae that survived to adult, inbred beetles took ∼ 1.5 days (>5%) longer to reach adult. The only measured trait not affected by inbreeding was adult body mass. The degree to which inbreeding increased mortality varied among the populations – inbreeding depression was lowest in the population that is most isolated. Although populations of S. limbatus are generally large in nature our results suggest that increased inbreeding associated with population fragmentation can have substantial effects on fitness of S. limbatus .