Testosterone Levels in Dominant Sociable Males Are Lower than in Solitary Roamers: Physiological Differences between Three Male Reproductive Tactics in a Sociably Flexible Mammal

Schradin, Carsten; Scantlebury, Michael; Pillay, Neville; König, Barbara

doi:10.1086/596535

Cited by 84 publications

(147 citation statements)

References 55 publications

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“…Female tactics determine male tactics, with males adopting one of three tactics: territorial dominant breeding; solitary roaming; or socially philopatric [105]. Territorial breeding males are the largest, heaviest males [105], are better at winning territorial encounters [98] and can defend a territory and a group of communally breeding females.…”

Section: Social Flexibility In R Pumiliomentioning

confidence: 99%

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

2013

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Abstract:The rapid rate of anthropogenic-related climate change is expected to severely impact ecosystems and their constituent organisms, leading to mass extinction. A rapid adaptive response of animals to such change could be due to reversible phenotypic flexibility, including behavioral flexibility. Our model, the African striped mouse Rhabdomys, is a small rodent widely distributed in southern Africa. The desert-living species R. pumilio displays social flexibility, whereby individuals switch their social organization in response to prevailing conditions, potentially allowing for persistence in rapidly changing environments. Individuals of the species from the moist grasslands (R. dilectus) show some flexible traits, but opportunities to utilize this potential are apparently not realized. The climate in southern Africa is predicted to become drier, making both desert and grassland species vulnerable to environmental change. Based on realized or potential social flexibility in striped mice, we provide three (not mutually exclusive) scenarios that consider: (i) extinction of the desert species as its habitat changes; (ii) range expansion and utilization of pre-existing adaptations of the desert species to displace the current grassland species; and (iii) grassland species exploiting their potential flexibility (behavioral adaptation) and surviving in their current OPEN ACCESSSustainability 2013, 5 164 habitat. Behavioral flexibility is costly but could allow species to persist in rapidly changing environments.

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Section: Social Flexibility In R Pumiliomentioning

confidence: 99%

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

2013

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“…Two factors have been identified to be likely candidates for the switch to another 85 reproductive tactic (Schradin et al, 2009a): a change in body condition and/or in hormone 86 levels. Both might be triggered by social and environmental conditions (Schradin et al, 2012).…”

Section: Introduction 51mentioning

confidence: 99%

Differential investment into testes and sperm production in alternative male reproductive tactics of the African striped mouse (Rhabdomys pumilio)

Schradin¹,

Eder²,

Müller³

2012

Hormones and Behavior

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Males that follow alternative reproductive tactics might differ in their investment into testis development and sperm production. The resource-allocation hypothesis predicts that males following a sneaker tactic should invest more into sperm production than dominant territorial males which should invest more into mate guarding. This hypothesis is supported by studies in species where individual males cannot switch between tactics (fixed tactics). Here we present the first data for a species where males can switch between tactics (plastic tactics). We studied African striped mice (Rhabdomys pumilio) in captivity, mimicking three tactics observed in the field: philopatric group-living males, singly-housed males representing roaming males, and group-living breeding males. We measured quantitative and qualitative reproductive traits, as well as serum and testis hormone concentrations. We found no support for the resource-allocation hypothesis, since breeding and singly-housed males invested similarly in testes and sperm. However, philopatric males had significantly smaller testes and epididymides, lower sperm counts, lower testosterone and higher corticosterone levels than males of the two other tactics. Philopatric males did not reach a larger body mass than singly-housed males with well developed reproductive traits, indicating that they did not trade investment in sperm production against growth. Interestingly, testis testosterone concentrations of philopatric males did not differ from those of other males. Our data suggest that philopatric males are reproductively suppressed by the breeding male, but might be ready to increase their serum testosterone levels when social and environmental conditions allow for this physiological switch accompanying the behavioral switch between tactics.

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“…The most competitive individuals follow the tactic that yields the 63 greatest fitness payoff, called the bourgeois tactic. Less competitive males, which are 64 often smaller and younger than the bourgeois male, make the best of a bad job 65 (Dawkins, 1980) by following an alternative tactic with low reproductive success 66 (often called the sneaker or satellite tactic) but are able to change to the bourgeois 67 tactic when they grow larger (Gross, 1996;Schradin et al, 2009a). 68…”

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“…We tested whether hormone levels if individual males changed after they 139 changed their tactics, in the ways as suggested by a previous study using unpaired 140 data (Schradin et al 2009a). For philopatric males, corticosterone levels were 141 expected to decrease and testosterone levels to increase when becoming roamers.…”

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“…This is because of the high variation in 300 endogenous testosterone levels between individuals of the same social category within 301 a single population (Kempenaers et al, 2008). For example, striped mouse males 302 show high intra-specific variation in testosterone levels even within the same tactics 303 and the (traditional) conclusion was that males of different tactics differ in hormone 304 levels because hormone secretion changes when males change tactics (see figure 5 in 305 Schradin et al 2009a). However, alternative explanations are possible: If philopatric 306 males with higher testosterone levels disperse and change their tactic at an earlier age 307 than philopatric males with lower testosterone levels, this alone could explain why on 308 philopatric males have lower mean value of testosterone levels than roamers.…”

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

Schradin

Yuen

2011

Hormones and Behavior

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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.

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Testosterone Levels in Dominant Sociable Males Are Lower than in Solitary Roamers: Physiological Differences between Three Male Reproductive Tactics in a Sociably Flexible Mammal

Cited by 84 publications

References 55 publications

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

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

Differential investment into testes and sperm production in alternative male reproductive tactics of the African striped mouse (Rhabdomys pumilio)

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

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