Research on life sciences published by scientists at University of California.

"For many species in nature, a sire's progeny may be distributed among a few or many dams. This poses logistical challenges - typically much greater across males than across females - for assessing means and variances in mating success (number of mates) and reproductive success (number of progeny)," scientists writing in the journal Molecular Ecology report (see also Life Sciences).

"Here we overcome these difficulties by exhaustively analyzing a population of green swordtail fish (Xiphophorus helleri) for genetic paternity (and maternity) using a suite of highly polymorphic microsatellite loci. Genetic analyses of 1476 progeny from 69 pregnant females and 158 candidate sires revealed pronounced skews in male reproductive success both within and among broods. These skews were statistically significant, greater than in females, and correlated in males but not in females with mating success. We also compare the standardized variances in swordtail reproductive success to the few such available estimates for other taxa, notably several mammal species with varied mating systems and degrees of sexual dimorphism. The comparison showed that the opportunity for selection on male X. helleri is among the highest yet reported in fishes, and it is ...