Environmental modulation of androgen levels and secondary sex characters in two populations of the peacock blenny Salaria pavo

Abstract

Morphology and endocrinology were studied in two populations of the peacock blenny Salaria pavo, with different regimes of sexual selection imposed by differences in nest site availability. The peacock blenny is a small, sexually dimorphic benthic fish that presents exclusive paternal care of the clutch and inhabits rocky shores of the Mediterranean and adjacent Atlantic areas. In a population from the Gulf of Trieste (Northern Adriatic sea) inhabiting rocky shores where nest sites are abundant, male-male competition for nests is low, males court females and a low frequency of alternative reproductive tactics (small, parasitic femalemimicking sneaker males that change tactic into nest holders in subsequent breeding seasons) occurs. Conversely at Ria Formosa, a coastal lagoon in Southern Portugal, where nest sites are scarce and highly aggregated, male-male competition for nests is very high, there is sex-role reversal with female courtship and a high frequency of alternative reproductive tactics is observed. Concomitantly, at Ria Formosa nest holder males are larger and present more developed secondary sex characters and higher levels of 11KT than at the Gulf of Trieste. However, the gonads of nest holders and parasitic males were larger in the Gulf of Trieste population. Competition for nests at Ria Formosa seems to promote more developed secondary sex characters in nest site scarcity conditions, while competition for females at the Gulf of Trieste seems to be spurring sperm competition among males in populations where nest sites are more abundant. 11KT was thus associated with the development and expression of secondary sex characters in contrasting environments. These results exemplify how the modulation of behavioral plasticity and secondary sex characters by the social environment can be mediated by androgens.

Interpopulational variation of the mating system in the peacock blenny Salaria pavo

“…There seems to be a preference for holes with one of the openings obstructed and the other narrowed by concrete, sand or other debris (Almada et al 1994;personal observation). Facing this scarcity of adequate cavities, nests become an extremely valuable resource, and only the largest and more competitive males can occupy a nest (Almada et al 1994;Saraiva et al 2010), even if it is very close to a neighbour. This excludes many mature males from reproduction, which keep on searching for nests, so nest holders probably restrain from leaving the nest as a mechanism to prevent nest takeovers (Almada et al 1995).…”

“…This excludes many mature males from reproduction, which keep on searching for nests, so nest holders probably restrain from leaving the nest as a mechanism to prevent nest takeovers (Almada et al 1995). Interestingly, this does not seem to compromise their ability to attract females since nest holders from Ria Formosa display their large crest (larger than those from Gulf of Trieste; Saraiva et al 2010) whilst they lay at the entrance of the nest with their head protruding (Almada et al 1995). As there are many more females searching for spawning opportunities in Ria Formosa than in the Gulf of Trieste and they rely on visual cues to assess male quality (Gonçalves et al 2002), nest holders from Ria Formosa do not need to exit the nest to attract females.…”

“…Whilst this enhances the nest holders' resource holding potential, it should also limit females' potential reproductive rate and drive females into actively courting males . Conversely, in the Gulf of Trieste, there are cavities in excess and even very small males can acquire nests and develop SSC (Saraiva et al 2010). But as males leave the nest to court, they face a high risk of other males stealing fertilizations of their clutch.…”

“…But as males leave the nest to court, they face a high risk of other males stealing fertilizations of their clutch. This higher sperm competition regime is reflected on the higher gonadosomatic index (gonad weight/body weight) found among males in the Gulf of Trieste relatively to the Ria Formosa (Saraiva et al 2010). Even females, which are reported to practise egg cannibalism (Gonçalves and Almada 1997), may present a risk to the clutch whilst the male is away.…”

“…Besides having an effect on sex roles, the scarcity of nest sites in Ria Formosa also seems to promote male ARTs. As only the largest males can acquire and secure nests, the only reproductive option for lower size class males is to reproduce parasitically (Taborsky 1998;Saraiva et al 2010). In fact, there is a clear separation of sizes among Ria Formosa males, with parasitic males being much smaller than nest holders (Gonçalves et al 1996(Gonçalves et al , 2008.…”