ARTICLE Inter-male aggression with regard to polygynous mating system in Pampean grassland mouse, Akodon azarae (Cricetidae: Sigmodontinae) Florencia Bonatto • Jose ´ Coda • Daniela Gomez • Jose ´ Priotto • Andrea Steinmann Received: 9 January 2013 / Accepted: 12 March 2013 / Published online: 2 April 2013 Ó Japan Ethological Society and Springer Japan 2013 Abstract Based on the hypothesis that, in Akodon aza- rae, polygyny operates through female defence, we studied inter-male aggression in order to test the following pre- dictions: during the breeding period (1) resident males are more aggressive than intruder males in the presence of females (FP), and (2) aggressive behaviour is independent of male condition (resident or intruder) in the absence of females (FA). To test our predictions, we used the resident male behavioural response towards an intruder male in relation to FP or FA. We conducted 30 encounters in FP and 27 in FA in 0.79-m 2 round enclosures placed in the Espinal Reservation. Our results support the prediction that, in FP, the intensity of aggressive behaviour exhibited by males varied in relation to resident or intruder condition. Resident males showed high levels of aggression towards intruders, and intruders exhibited the greatest values of submissive behaviours with residents. In FA, the intensity of aggressive behaviour did not vary in relation to resident or intruder condition. Both resident and intruder males exhibited low aggressive behaviour and inter-male encounters resulted mainly in non interactive behaviours. Our results support the hypothesis that, in A. azarae, the polygynous mating system operates through female defence. Keywords Aggressive behaviour Á Cricetidae Á Mating system Á Polygyny Á Resident motivation Á Territoriality Introduction In mammals, promiscuity and polygyny have been con- sidered the predominating mating systems (Emlen and Oring 1977; Clutton-Brock 1989; Heske and Ostfeld 1990; Wolff and Macdonald 2004; Waterman 2007). Polygyny is a mating system in which a minority of males control or gain access to multiple females leaving other males without access to them, and females typically mate with only one male (Emlen and Oring 1977; Shuster and Wade 2003; McEachern et al. 2009). Larger male’s home ranges that overlap with several females, male territoriality, and sexual dimorphism are considered typical features of voles and mice with a polygynous mating system (Emlen and Oring 1977; Gaulin and FitzGerald 1988; Clutton-Brock 1989; Heske and Ostfeld 1990; Wolff et al. 1994; Waterman 1998, 2007). Polygyny can be classified into defence polygyny (resource defence and female defence polygyny) and male dominance polygyny (lek polygyny and explo- sive breeding assemblages) (Emlen and Oring 1977; Clutton-Brock 1989). Defense polygyny is the result of an intense reproductive competition between males in order to gain exclusive access to multiple receptive females (Emlen and Oring 1977; Clutton-Brock 1989). According to the strategies that polygynous males use to control receptive F. Bonatto (&) Á J. Coda Á D. Gomez Á J. Priotto Á A. Steinmann Departamento de Ciencias Naturales, Consejo Nacional de Investigaciones Cientı ´ficas y Te ´cnicas (CONICET), Universidad Nacional de Rı ´o Cuarto, Agencia Postal N°3, 5800 Rı ´o Cuarto, Co ´rdoba, Argentina e-mail: mfbonatto@yahoo.com.ar J. Coda e-mail: joseacoda@yahoo.com.ar D. Gomez e-mail: dgomez@exa.unrc.edu.ar J. Priotto e-mail: jpriotto@gmail.com A. Steinmann e-mail: asteinmann@exa.unrc.edu.ar 123 J Ethol (2013) 31:223–231 DOI 10.1007/s10164-013-0370-4