“Failure to launch”: is there a reproductive cost to males living at home?

Abstract

Differential reproductive success commonly reflects variations in reproductive physiology, behavior, and morphology. In some species, competition among males results in the evolution of alternative reproductive tactics that confer a fitness advantage relating to social status, density, or myriad other factors. In the Cape ground squirrel (Xerus inauris), a species that is highly competitive but lacks typical mammalian aspects of intrasexual competition (e.g., territoriality and aggression), 2 alternative reproductive tactics occur relating to dispersal. While physiological and behavioral differences have been demonstrated between dispersed males and males that delay dispersal, we used microsatellite markers to quantify variations in reproductive success between tactics. We found that dispersed males are in better body condition with larger home ranges likely allowing greater encounter frequencies with estrous females. However, we found no difference in copulation frequency between tactics, and the decision to delay dispersal does not preclude reproduction. Over 70% of males did not sire any offspring, yet the average number of offspring sired was equal between tactics. Thus, all males are equally likely of copulating, but paternity is strongly skewed toward a few males regardless of tactic. Natal philopatry may be a conditiondependent tactic that does not reduce reproductive success.

Not playing by the rules: mixed support of ecogeographic rules in an arid‐adapted African ground squirrel

“…The degree of sexual dimorphism may not increase with increasing resource availability if reproductive competition among males does not increase from one location to the next. Since operational sex ratios (which reflect reproductive competition) do not differ between South Africa and the Kalahari, reproductive competition is also most likely similar (Manjerovic, 2010; Manjerovic & Waterman, 2015). Larger males may also be subject to higher mortality due to selective predation, where predators may be more likely to see larger individuals and may prefer them to smaller prey (Isaac, 2005), though in Namibia male Cape ground squirrels had better survival than females (Waterman, 1995).…”

Intraspecific variation in male mating strategies in an African ground squirrel (Xerus inauris)

“…Sexually mature males either disperse at reproductive maturity and join a male band (Waterman, 1995 ), or delay dispersal and remain with their natal group (O'Brien et al, 2021 ; Waterman, 1995 ; Waterman, 1997 ). Dispersal tactics result in similar reproductive success (Manjerovic & Waterman, 2015 ), but physiological and behavioral differences are affected by resources (O'Brien et al, 2021 ; Scantlebury et al, 2008 ). Band males are more mobile, with higher resting metabolic rates and larger home ranges and consequently spend less time feeding (Manjerovic & Waterman, 2015 ; Scantlebury et al, 2008 ).…”

“…We recorded standard measurements including body mass (measured with a spring scale to ±5.0 g), sex, reproductive condition, and age; individuals were uniquely marked for short‐and long‐term identification using hair dye and pit tags (Hillegass et al, 2008 ; Waterman, 1995 ). We collected a 1‐ to 3‐mm sample of tail tissue for genetic analysis and stored samples in 95% EtOH at room temperature (Manjerovic & Waterman, 2015 ). After handling, we released all animals at the site of capture.…”

“…Adult males either disperse at reproductive maturity or delay dispersal and remain with their natal group (O'Brien et al, 2021 ; Waterman, 1995 , 1997 ). Both dispersal tactics result in reproductive success (Manjerovic & Waterman, 2015 ); thus all adult males present were included, regardless of dispersal tactic, in our calculations for the number of males per hectare. Site comparisons were analyzed using a t‐test.…”

“…This program assigns paternity based on confidence levels calculated using simulated data that includes population allele frequencies, proportion of population sampled and genotyped, and error rates. We ran a total of 100,000 iterations using a 1% genotyping error rate (Manjerovic & Waterman, 2015 ). We calculated a mean of four adult female candidates per social group and 11 candidate males based on the operational sex ratio at the time of breeding (Waterman, 1998 ).…”