The imbalanced reproductive success of polygynous mammals results in sexual selection on male traits like body size. Males and females might have more balanced reproductive success under polygynandry, where both sexes mate multiply. Using 4 years of microsatellite DNA analyses
of paternity and known maternity, we investigated variation in reproductive success of Columbian ground squirrels, Urocitellus columbianus (Ord, 1815); a species with multiple mating by both sexes
and multiple paternity of litters. We asked whether male reproductive success was more variable than that of females under this mating system. The overall percentage of confirmed paternity was 61.4% of 339 offspring. The mean rate of multiple paternity in litters with known fathers was 72.4%
(n = 29 litters). Estimated mean reproductive success of males (10.27 offspring) was about thrice that of females (3.11 offspring). Even after this difference was taken into account statistically, males were about three times as variable in reproductive success as females (coefficients
of variation = 77.84% and 26.74%, respectively). The Bateman gradient (regression slope of offspring production on number of successful mates) was significantly greater for males (β
M = 1.44) than females (β
F = 0.28). Thus, under
a polygynandrous mating system, males exhibited greater variation in reproductive success than females.
No Supplementary Data
gradient de Bateman;
operational sex ratio;
rapport des sexes opérationnel;
succès de reproduction
Document Type: Research Article
Department of Microbiology, College of Medicine, University of Iowa, Iowa City, IA 52246, USA.
Department of Biological Sciences, Auburn University, 331 Funchess Hall, Auburn, AL 36849, USA.
Publication date: 2012-06-10
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