High Reproductive Success Despite Queuing – Socio-Sexual Development of Males in a Complex Social Environment

Abstract

The start of actual breeding in male social mammals can occur long after individuals attain sexual maturity. Mainly prevented from reproduction by older and dominant males, young males often queue until strong enough to compete for favorable social positions and, in this way, to obtain access to females. However, to what extent maturing males also apply tactics to reproduce before this time is largely unknown. Therefore, the aim of the present study was to elucidate male socio-sexual development from onset of sexual maturity through first mating success until the achievement of a stable social position in a complex social environment. For this purpose, guinea pigs were used as a model system and reproductive success of males living in large mixed-sex colonies was assessed during their first year of life. As a reference, males in a mixed-sex pair situation were examined. Pair-housed males reproduced for the first time around the onset of sexual maturity whereas colony-housed males did so much later in life and with a considerably higher variance. In colonies, reproductive success was significantly affected by dominance status. Dominance itself was age-dependent, with older males having significantly higher dominance ranks than younger males. Surprisingly, both younger and older colony-housed males attained substantial reproductive success of comparable amounts. Thus, younger males reproduced irrespective of queuing and already before reaching a high social status. This mating success of maturing males was most likely achieved via several reproductive tactics which were flexibly applied with the onset of sexual maturity. The period of socio-sexual development before a stable social position is established may, therefore, be a time during which male mammals use flexible behavioral tactics to achieve reproductive success more frequently than commonly is presumed. In addition, the findings strongly indicate that high behavioral plasticity exists well beyond sexual maturity.

Adaptive reshaping of the hormonal phenotype after social niche transition in adulthood

“…Regardless of initial differences in behaviour, all males reproduced with their partner females. This was, however, to be expected as no competitors were present and as there are no indications for differences in reproductive function between pair-housed and colony-housed males [54].…”

Shaped by you: The effect of social partner on cortisol and behavior during adolescence in a female rodent

“…While the age class of the housing partner affected several behavioral parameters, this was limited to female housing partners. Since male guinea pigs become reproductively active at approximately 70 days of age, focal females housed with an adult male partner would become pregnant (Mutwill et al., 2019), affecting behavior and cortisol concentrations (Boyd, 1988; Michel et al., 2011). Therefore, a comparative effect of age class with male partners could not be investigated.…”

“…In addition, the total amount of displaces by the focal female and her housing partner were combined into total displaces , and rank index was calculated as displace (instances where the female housing partner was displaced by the focal female) ÷ total displaces . Therefore, focal females with a female housing partner had a rank index between 0 and 1, with 0 being completely subdominant and 1 being completely dominant (Mutwill et al., 2019, 2021; Sachser, 1986).…”

“…÷ total displaces. Therefore, focal females with a female housing partner had a rank index between 0 and 1, with 0 being completely subdominant and 1 being completely dominant (Mutwill et al, 2019(Mutwill et al, , 2021Sachser, 1986).…”

“…Play generally decreases with age (Caro, 1995;Gomendio, 1988;Pellegrini, 2010;Smaldino et al, 2019), and low social status and the presence of adult females have been shown to inhibit pubertal maturation of female rodents (Freeman, 2021) and primates (Beehner & Lu, 2013). Therefore, increased play behav- would become pregnant (Mutwill et al, 2019), affecting behavior and cortisol concentrations (Boyd, 1988;Michel et al, 2011).…”