Intrasexual selection: Kin competition increases male‐male territorial aggression in a monogamous cichlid fish

Abstract

During intrasexual competition, individuals of the same sex compete for access to breeding sites and mating partners, often accompanied by aggressive behavior. Kin selection theory predicts different kin‐directed social interactions ranging from cooperation to aggression depending on the context and the resource in question. Kin competition reducing indirect fitness might be avoided by actively expelling relatives from territories and by showing higher aggression against kin. The West‐African cichlid Pelvicachromis taeniatus is a monogamous cave breeder with males occupying and defending breeding sites against rivals. This species is capable of kin recognition and shows kin‐preference during juvenile shoaling and mate choice. However, subadults of P. taeniatus seem to avoid the proximity of same‐sex kin. In the present study, we examined territorial aggression of territory holders against intruding related and unrelated males as well as intruder's behavior. We observed higher aggression among related competitors suggesting that related males are less tolerated as neighbors. Avoidance of intrasexual competition with relatives might increase indirect fitness of males in monogamous species.

Sex-specific effects of inbreeding on body colouration and physiological colour change in the cichlid fish Pelvicachromis taeniatus

“…during competition for food resources, territories or mating partners. In P. taeniatus , adult males and females face strong intrasexual competition [ 45 , 57 , 58 ]. Here, a rapid-onset unpredictable stress event caused an acute stress response in form of intensified colouration which may be advantageous during a sudden attack by a conspecific as it may visually signal alertness and defensiveness.…”

“…In addition, the defence of territories is mediated by aggressive behaviour of males against rivals which makes males the more competitive sex in this species. Related competitors elicited higher aggression in territorial males than unrelated competitors [ 57 ]. Explorative behaviour [ 63 ] and increased risk of kin competition also increases juvenile shoaling behaviour [ 64 ].…”