Sexual selection in natural populations of seaweed flies: variation in the offspring fitness of females carrying different inversion karyotypes

Abstract

The effect of indirect sexual selection on offspring fitness with respect to a large chromosomal inversion system was estimated in nine widely separated populations of the seaweed fly, Coelopafrigida. The pattern of female rejection was determined for each population and estimates were made of the relative fitnesses of the inversion karyotypes. Two sets of progeny frequencies were calculated: the first on the basis of the observed pattern of mating, and the second on the hypothetical basis that all females had accepted the male available: in other words, random mating. The relative fitnesses of the offspring produced by these two mating regimes were compared. In seven of the populations the exercise of choice resulted in a modest change in progeny fitness. The change depended on the karyotype of the female: (3(3 females produced fitter offspring in all populations, eta's usually produced less fit offspring, and there was little effec progeny of oe(3's. An association was also found between a physical factor, tidal range, and the offspring fitness of ctct females, but no association exists for a(3 or (3$ females. It is suggested that the relevant genes have been subject to different evolutionary forces on the two forms of the inversion.

Paternal genetic contribution to offspring condition predicted by size of male secondary sexual character

“…Consistent with these findings, there was a positive relationship between the size of a male's forehead patch and the proportion of nestlings within a brood that he sired, suggesting that females may use the size of their mate's forehead patch as a cue for pursuing extra-pair copulations. Population genetic theory, in combination with empirical studies attempting to measure additive genetic variation in fitness in natural populations (Charlesworth 1987 ;Burt 1995), suggests that the benefits females can obtain, in terms of offspring fitness, by choosing fathers on the basis of genes should be small relative to other sources of variation in offspring fitness (see Gilburn et al 1996). Our results are generally consistent with that expectation, because much of fledging condition is explained by rearing environment (table 1 ; Merila$ 1996).…”

A supergene in seaweed flies modulates male traits and female perception

“…In the wild, genotype frequencies deviate from Hardy–Weinberg and heterozygotes are found in excess (1.1–1.6× their expected frequency; [ 25 , 27 , 28 ]. In experimental populations, the egg-to-adult survival of homozygotes is reduced by 10–20% at low density and by 50–70% at high density when compared to heterozygote survival [ 29 – 31 ], suggesting that each supergene haplotype has accumulated a significant deleterious load. Non-random mating with respect to Cf-Inv(1) has been shown in several experimental and natural populations [ 25 , 29 , 32 ].…”

The effect of an inversion system and the time interval between matings on postcopulatory sexual selection in the seaweed fly, Coelopa frigida

“…The inversion karyotypes of the female offspring were determined using starch gel electrophoresis and staining for Adh alleles . This has been successfully used as a marker for inversion karyotype in many previous studies (Gilburn et al, 1992(Gilburn et al, , 1993(Gilburn et al, , 1996. Only female offspring were scored to minimise the effects of heterosis (which has a much greater effect on egg-toadult survival of males).…”