Oral presentation- Open Session 12th International Mammalogical Congress

What makes a stud?  Understanding high reproductive skew in male African ground squirrels with no dominance or territoriality (#364)

Jane M. Waterman 1 , Kelsey O'Brien 1
  1. University of Manitoba, Winnipeg, Manitoba, Canada

Reproductive skew among male mammals is common, often reflecting differences in morphology, physiology, and/or behaviour, with some males gaining a high number of matings compared to others. Differences in competitive abilities (e.g., territories or dominance) are often the most important factors influencing copulatory success, although post-copulatory mechanisms (e.g. sperm competition) can confound these pre-copulatory mechanisms. Less is known about the factors influencing reproductive distribution in what appear to be egalitarian societies that do not use aggressive pre-copulatory means of competing for mates.  Male Cape ground squirrels (Xerus inauris) typically associate in all-male bands where aggressive interactions are rare. In our study population in central South Africa, males do not form dominance hierarchies, and all males are equally likely to copulate; however less than 30% of all adult males sire offspring. Males competitively search for females but there is no relationship between fertilization success and mate order. We examined the factors that may influence male reproductive success, including reproductive tactic (dispersed vs non-dispersed), years on site, scrotal size, parasites, hormones, and body condition. We found that factors such as tactic, body condition, scrotal size, and age appeared to influence male reproductive success, but the importance of these factors appeared to vary from year to year and may reflect annual fluctuations in resources.  Why male reproduction is so highly skewed in this highly social species is still unclear.