Male Xiphophorus multilineatus behavioral, brain weight, and testes weight data

Behavioural plasticity may require energetically expensive sensory and neural adaptations to detect, process, and respond to social cues. These costs could lead to selection against behavioural plasticity and its eventual loss. We show that males from the behavioural plastic alternative reproductive tactic (ART) in the swordtail fish Xiphophorus multilineatus have relatively larger brains, in addition to a trade off with testes size, that is not detected in the males from the behaviourally fixed ART. Given these costs, we consider the hypothesis that plasticity in mating behaviours is maintained due to intralocus tactical conflict, where a shared genome can constrain one or both ARTs from evolving to their optima. When we reduced any potential for intralocus tactical conflict by removing the behaviourally fixed ART from long-term breeding mesocosms, the males from the behaviourally plastic ART were less plastic and had smaller brains as compared to their counterpart from control mesocos..., ARTs in the swordtail fish Xiphophorus multilineatus
Males of the high-backed pygmy swordtail fish Xiphophorus multilineatus (Rauchenberger et al. 1990) are classified into two genetically influenced ARTs (Lampert et al. 2010): behaviorally fixed males, who are larger than their counterparts due to a later maturation and increased growth time-period; contrastingly, behaviorally plastic males mature earlier and thus remain small for their adult life (Zimmerer & Kallman 1989). Therefore, in addition to differences between the ARTs in behavioral plasticity, there is a bimodal distribution in body size, and various degrees of tactical dimorphism (significant differences in the mean expression of a trait between the ARTs) for additional traits with known associations with reproductive success (e.g., body shape). This relationship between morphological differences (body size and shape) between the ARTs and differences in use of mating behavior (Zimmerer & Kallman 1988; Liotta et al. 2...,