Experimental increase of testosterone increases boldness and decreases anxiety in male African striped mouse helpers

Abstract

Males of many species can adjust their behaviors to environmental conditions by changing reproductive tactics. Testosterone surges in adult breeding males typically inhibit the expression of paternal care while facilitating the expression of aggression during environmental changes. Similarly, in non-breeding philopatric males of cooperatively breeding species, up-regulation of testosterone may inhibit alloparental care while facilitating dispersal, i.e. males might become bolder and more explorative. We tested this hypothesis in philopatric male African striped mice, Rhabdomys pumilio. Striped mouse males can either remain in their natal group providing alloparental care or they can disperse seeking mating opportunities. Compared to philopatric males, dispersed males typically show higher testosterone levels and lower corticosterone levels, and more aggression towards pups and same sex conspecifics. We experimentally increased the testosterone levels of philopatric males kept in their family group when pups were present. Testosterone-treated males did not differ significantly from control males in alloparental care and in aggression toward same-sex conspecifics. Compared to control males, testosterone treated males were bolder, more active, less anxious; they also showed lower corticosterone levels. Philopatric males were sensitive to our testosterone treatment for dispersal-and anxiety-like behavior but insensitive for social behaviors. Our results suggest a role of testosterone in dispersal. We tested this hypothesis in philopatric male African striped mice, Rhabdomys pumilio. 28Striped mouse males can either remain in their natal group providing alloparental care or 29 they can disperse seeking mating opportunities. Compared to philopatric males, dispersed 30 males typically show higher testosterone levels and lower corticosterone levels, and more 31 aggression towards pups and same sex conspecifics. We experimentally increased the 32 testosterone levels of philopatric males kept in their family group when pups were present. 33Testosterone-treated males did not differ significantly from control males in alloparental 34 care and in aggression toward same-sex conspecifics. Compared to control males, 35 testosterone treated males were bolder, more active, less anxious; they also showed lower 36 corticosterone levels. Philopatric males were sensitive to our testosterone treatment for 37 dispersal-and anxiety-like behavior but insensitive for social behaviors. Our results 38 suggest a role of testosterone in dispersal. 39

Corticosterone Levels Correlate With Alloparental Care in a Sex‐Dependent Manner in African Striped Mice, Rhabdomys pumilio

“…Natural variation of testosterone levels in helpers of different sex and age did not correlate with alloparental care. Our present results are in agreement with an experimental study, where an increase of testosterone levels via implants in male philopatric helpers did not decrease the amount of alloparental care (Raynaud & Schradin ). In sum, our testosterone data revealed expected sex and age differences, but without any evidence of a role of testosterone in the regulation of alloparental care.…”

Testosterone and reproductive effort in male primates

“…Animals treated with testosterone have shown reductions in fear-related behaviors in response to diverse stimuli, including isolation from conspecifics, human approach, unfamiliar environments, novel objects, and surprising events (rodents: Aikey et al 2002, Fernandez-Guasti & Martinez-Mota 2005, Frye & Seliga 2001, Hodosy et al 2012, Raynaud & Schradin 2014; cattle: Boissy & Bouissou 1994; sheep: Bouissou & Vandenheede 1996). Experimentally lowering testosterone levels has the opposite effect, increasing fear-related behaviors (King et al 2005).…”

Into the wild: developing field tests to examine the link between elasmobranch personality and laterality

“…An alternative, though somewhat related, explanation is the link between boldness and aggression (Sih et al, 2004), which can be driven by sex-specific reproductive hormones. The relationship between androgen production in males and aggressive mating behaviours and higher boldness has been well documented in many species (Borg, 1994;Oliveira et al, 2002;Raynaud & Schradin, 2014). Whilst limited studies exist on elasmobranchs, it has been suggested that an increase in production of certain androgens in males at specific times in the breeding cycle promotes aggressive mating behaviour.…”