Genetic diversity and sperm characteristics are not associated in two bluethroat (Luscinia svecica) populations

Individual heterozygosity may influence the expression of fitness-related
traits, via genome-wide or local genetic effects. Earlier studies have
shown negative relationships between heterozygosity and sperm variation,
predominantly in captive, highly inbred populations. Little is known about
the possible influence of variation in heterozygosity on sperm traits in
wild, outbred populations. We studied two populations of the bluethroat,
one from the widely distributed northern subspecies (Luscinia. s. svecica)
and the other from the smaller, more patchily distributed subspecies
breeding along the French coast of Brittany (L. s. namnetum). The two
subspecies differed significantly in body size, plumage colour, sperm
traits and the degree of genetic diversity. However, there was no evidence
that sperm traits (total length and motility) were influenced by the
degree of heterozygosity at the individual level. In contrast, we found
that male body size was positively related to heterozygosity across both
populations, indicating a possible relationship between overall genetic
diversity and general vigour or ability to obtain food. We conclude that
sperm traits are unrelated to levels of heterozygosity in the studied
outbred and weakly genetically depauperate bluethroat populations.