Intra-sexual variation in male reproduction in teleost fish: a comparative approach

Abstract

The occurrence of intra-sexual variation in reproduction is a widespread phenomenon in teleosts. One such form of variation consists in the occurrence of alternative male types: males that invest resources in mate attraction and males that exploit the investment of the former males, by trying to sneak fertilizations during spawning. These alternative reproductive tactics can be classified according to their plasticity during the life span of the individuals (i.e., fixed vs. sequential vs. reversible). Furthermore, the differences between morphs within a given species may involve a set of different traits, including reproductive behavior, the differentiation of male morphological traits, and the patterns of gonad tissue allocation and the differentiation of gonadal accessory glands. In this paper, we review the available data on four species exhibiting different types of intra-sexual plasticity in reproduction that have been studied in our lab. The data on the proximate mechanisms, androgens and forebrain arginine-vasotocin (AVT), underlying these alternative tactics suggest that between-morph differences in androgen levels, especially in 11-ketotestosterone, are especially present in species where the alternative male types have evolved morphological traits that are tactic-specific (i.e., sexual polymorphisms) and that differences in AVT appear to be related to between-morph differences in the expression of courtship behavior. Therefore, this comparative approach leads us to propose that the different endocrine systems are involved in the differentiation of different sets of traits that make up alternative phenotypes, and that the differentiation of alternative tactics is not controlled by a single endocrine system (e.g., androgens).

Testosterone Levels in Dominant Sociable Males Are Lower than in Solitary Roamers: Physiological Differences between Three Male Reproductive Tactics in a Sociably Flexible Mammal

“…5), which is in accordance with the relative plasticity hy- pothesis proposed by Moore (1991). However, in contrast to previous studies on fish and reptiles (e.g., Wikelski et al 2004;Oliveira et al 2005), it is not the large dominant males but solitary roaming males that have the highest testosterone levels, suggesting that testosterone levels depend not entirely on status but also on the social tactic employed.…”

“…5), which states that changes in behavioral phenotypes during adulthood are regulated by hormones (Moore et al 1998). It is known that in species with alternative male reproductive tactics, the dominant males are most aggressive and have the highest androgen levels (Moore et al 1998;Wikelski et al 2004;Oliveira et al 2005Knapp and Neff 2007). However, in sociable species, high testosterone levels might not be compatible with high levels of amicable behavior (Wingfield et al 1990).…”

“…Androgens may increase male aggression, mate attraction, and the frequency of mate searching and copulation but negatively affect parental care (Wingfield et al 1990). Dominant breeders typically have higher testosterone levels than sneakers or satellites (Moore 1991;Moore et al 1998;Sinervo et al 2000;Wikelski et al 2004;Oliveira et al 2005;Knapp and Neff 2007). Most studies show a synchronous increase of energy expenditure and testosterone level (e.g., Buchanan et al 2001), suggesting that increased reproductive activity is energetically costly (Gittleman and Thompson 1988).…”

“…In contrast, activational (reversible) effects may occur in adults when different tactics yield different fitness payoffs, indicating a conditional strategy (Moore et al 1998). In all fish and reptile species studied to date, dominant males show the highest level of aggression and the highest androgen levels (Moore 1991;Moore et al 1998;Sinervo et al 2000;Wikelski et al 2004;Oliveira et al 2005;Knapp and Neff 2007). In some group-living mammals, however, dominant males engage in amicable behaviors in which they court females by grooming them, sitting in body contact, or providing them with food (Stopka and Graciasova 2001;Schradin and Anzenberger 2003;Kutsakake and CluttonBrock 2006).…”

Intrasexual competition underlies sexual selection on male breeding coloration in the orangethroat darter, Etheostoma spectabile

“…2005), but rather a plastic behavioral response to relative competitive inferiority. Given that sneaking is an opportunistic act, our finding that male coloration correlates weakly, if at all, with sneaking behavior is not surprising.…”