What can animal research tell us about the link between androgens and social competition in humans?

Abstract

A contribution to a special issue on Hormones and Human Competition. The relationship between androgenic hormones, like testosterone (T), and aggression is extensively studied in human populations. Yet, while this work has illuminated a variety of principals regarding the behavioral and phenotypic effects of T, it is also hindered by inherent limitations of performing research on people. In these instances, animal research can be used to gain further insight into the complex mechanisms by which T influences aggression. Here, we explore recent studies on T and aggression in numerous vertebrate species, although we focus primarily on males and on a New World rodent called the California mouse (Peromyscus californicus). This species is highly territorial and monogamous, resembling the modern human social disposition. We review (i) how baseline and dynamic T levels predict and/or impact aggressive behavior and disposition; (ii) how factors related to social and physical context influence T and aggression; (iii) the reinforcing or "rewarding" aspects of aggressive behavior; and (iv) the function of T on aggression before and during a combative encounter. Included are areas that may need further research. We argue that animal studies investigating these topics fill in gaps to help paint a more complete picture of how androgenic steroids drive the output of aggressive behavior in all animals, including humans.

The challenge hypothesis revisited: Focus on reproductive experience and neural mechanisms

“…This creative perspective was pioneered by Wingfield et al (1990) and developed primarily on data from birds. These ideas were rapidly applied to other taxa (reviews by Fuxjager et al (2017), Hau et al (2008), Hirschenhauser andOliveira, 2006, andTibbetts andCrocker (2014). An important feature of this hypothesis was the idea that social interactions can induce rapid but transient increases in testosterone (T), which we refer to as a T pulse.…”

“…A virtually identical delayed T pulse can also occur after male-female encounters (Amstislavskaya and Popova, 2004) (Zhao and Marler, unpublished data). Research with California mice has focused on the functions of these rapid and transient T pulses before, during, or after an encounter (see Fuxjager et al, 2017). The goal of the current review is to expand on the relationship with timing of the behavioral changes and the T pulses with a focus on mammals, and also put it in the framework of both initiating and maintaining territoriality.…”

“…The most well developed mammalian models for the challenge effect are the California mouse (Peromyscus californicus) and humans. Here we focus on the rodent literature as the challenge effect in humans has been reviewed elsewhere (Fuxjager et al, 2017;Gray et al, 2019: this issue).…”

“…Courtship, as assessed from laboratory studies, includes at least following behavior and the production of ultrasonic vocalizations (Gleason and Marler, 2010;Pultorak et al, 2015;Pultorak et al, 2018). Pair bond formation involves a series of behavioral and hormonal changes (Becker et al, 2012;Pultorak et al, 2015Pultorak et al, , 2018Zhao and Marler, 2014;Zhao and Marler, 2016) and coincides with the pair defending an exclusive territory against both male and female intruders with high levels of aggression (field: Ribble, 1992a, b;lab: Davis and Marler, 2003;Oyegbile and Marler, 2005;Fuxjager et al, 2017;Rieger et al, 2019). Among mammals, including Peromyscus species, infanticide occurs and may be a driving force for territorial behavior by both males and females (Agrell et al, 1998;Alexander et al, 1994).…”

Testosterone pulses at the nest site modify ultrasonic vocalization types in a monogamous and territorial mouse

“…Both baseline and socially induced transient T release are composed of smaller pulses of T release that result in larger secretory episodes of T (review by Velduis, Keenan, & Pincus, ; Nelson & Kriegsfeld, ). Testosterone that is released after a fight or competition between males may influence the ongoing encounter or future encounters (referred to as the “Challenge Effect”; Wingfield, Hegner, Dufty, & Ball, ; reviewed in Fuxjager, Trainor, & Marler, ; Hirschenhauser & Oliveira, ).…”