Hormone levels of male African striped mice change as they switch between alternative reproductive tactics

Abstract

Alternative reproductive tactics occur when individuals of the same species follow alternative ways to maximize reproductive success. Often younger and smaller males follow tactics which result in lower fitness than that of dominant larger males. The relative plasticity hypothesis predicts that hormone levels change as males change tactics, but direct tests of this hypothesis are missing. It has been demonstrated in a number of studies that males following different tactics also differ in hormone levels (unpaired data), but not that individual males change their hormone levels as they change tactic (paired data). We compared hormone levels in the same individuals before and after they changed their tactic, using field samples collected over a period of 6 years. We studied male striped mice (Rhabdomys pumilio) following three alternative reproductive tactics: 1. alloparental philopatric males; 2. solitary roaming males, and 3. group-living dominant breeders. Testosterone level increased and corticosterone levels decreased when philopatric males became roamers or breeders. The increase in testosterone levels tended to be higher in philopatric males that became roamers than in philopatric males that became breeders. Testosterone levels decreased when roamers became breeders. Prolactin levels increased when males of any other tactic became breeders. Thus, males significantly changed their hormone profile as they changed tactic. These results are in agreement with the hypothesis that changes in hormone levels are associated with the switch from one alternative reproductive tactic to another.

Extinction or Survival? Behavioral Flexibility in Response to Environmental Change in the African Striped Mouse Rhabdomys

“…In R. pumilio, the three alternative male reproductive tactics are associated with changes in sex steroid hormones, in particular, testosterone, prolactin and corticosterone [105,109]. Philopatric males that leave their group increase their testosterone levels while at the same time decreasing their corticosterone levels, and philopatrics and roamers males that become paternal territorial breeders additionally increase their prolactin levels [110]. However, patterns of hormonal secretion can also be influenced during the early neonatal environment by the mother (i.e., maternal effects [108]), which influence behavior.…”

Alternative reproductive tactics in female striped mice: Solitary breeders have lower corticosterone levels than communal breeders

“…We focussed on these two hormones because they have been studied in detail in male striped mice (e.g. Schradin et al, 2009b;Schradin and Yuen, 2011). Where additional aliquots of serum were available, we tested for (iii) differences between ARTs in progesterone and oestrogen.…”

Androgen responses to reproductive competition of males pursuing either fixed or plastic alternative reproductive tactics

“…spermatogenesis, Schreibman et al, 1986;Miura et al, 1992). Moreover, androgens are important regulators and modulators of alternative reproductive tactics (ARTs) governing the transitions between different lifehistory stages (Oliveira et al, 2001a;Schradin and Yuen, 2011). ARTs are generally characterized by differences in behavioural, physiological and sometimes morphological traits among same-sex conspecifics, which result from disruptive sexual selection Taborsky and Brockmann, 2010).…”