Effects of Androgens on Social Behavior and Morphology of Alternative Reproductive Males of the Azorean Rock-Pool Blenny

Abstract

In the Azorean rock-pool blenny Parablennius sanguinolentus parvicornis two sequential reproductive tactics occur. Larger and older males establish breeding territories, while some of the smaller males become attached to nest-holder territories, acting as satellites on these territories, which they help to defend while trying parasitic fertilizations when females go in the nests to spawn. In the present paper we tested the effects of the androgens 17␣-methyltestosterone (MT) and 11-ketotestosterone (KT) in the expression of male secondary sex characters and bourgeois behavior in satellite males. One week after satellites were implanted with Silastic tubes containing MT, KT, or castor oil (control), androgen-treated satellites had developed male secondary sex traits such as longer and wider male-type genital papilla and anal glands that secrete a sex pheromone, both traits being less expressed or absent, respectively, in satellite males. Androgen treatment had no effect on the gonadosomatic index or on the development of the testicular gland. KT treatment had a positive effect on relative liver weight. In terms of behavior, androgen-implanted individuals were less aggressive both in a mirror test and toward females when these were introduced into their tanks. MT-treated individuals spend more time inside the provided nests. Only androgen-implanted satellites managed to have the females entering their nests. When given a chance in a group tank either to try to attract females to their own nest or to act as satellites of an already established nest-holder's nest, MT-implanted males spent significantly more time in their own nest than near the nest-holder nest. These data suggest that androgens, particularly testosterone, may be involved in mating tactic switching in this species.

Regulation of immunocompetence by different androgen metabolites in a blenny with alternative reproductive tactics

“…As expected, treatment with KT induced the development of the anal gland, a secondary sexual character in P. parvicornis (Oliveira et al, 2001d). The anal gland grows as a modification of the first and second anal fin rays and has been found to produce pheromones in a related species (Laumen et al,'74;Zeeck and Ide,'96).…”

“…Androgen treatment was given in the form of silastic implants that are known to elevate androgen levels for at least 1 week and that have behavioral effects for at least 2 weeks (Oliveira et al, 2001d;Modesto and Canário, 2003;Ros et al, 2004). In this study, measured about 2 weeks after treatment, we found increased levels of KT in the KT group, and relatively high T levels in comparison to KT levels in the T group.…”

“…Similar hormonal implants as we used in this experiment have been shown to moderately elevate androgen levels for at least 1 week (for validation of KT implants see Ros et al, 2004; for validation of T implants see Modesto and Canário, 2003), and have been used previously to test hormonal effects on behavior and morphology in P. parvicornis (Oliveira et al, 2001d;Ros et al, 2004). In this experiment, we checked whether implants still affect levels of androgens 2 weeks after the start of the treatment.…”

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

“…This suggests that either a longer time frame or other neuroendocrine or social triggers may be needed for a complete tactic switching in this species. In the rock-pool blenny, androgen-treated satellite males did not show a clear change towards the nest-holder type of behavior, and an unexpected decrease in aggressive behavior was found in KT-treated fish (Oliveira et al, 2001e). Contrastingly, nestholder males treated with KT increased the expression of aggressive behavior and concomitantly also increased the size of their breeding territories (Ros et al, 2004).…”

The role of androgens in the trade-off between territorial and parental behavior in the Azorean rock-pool blenny, Parablennius parvicornis

“…Eight males lost their nest during the first days after treatment and were left out of the analyses, resulting in an n of 11 males in the C-group and of 12 males in the 11-KT group (mean F SEM: C: body weight: 24.3 F 1.9 g; standard length: 11.5 F 0.3 cm; 11-KT: body weight: 27.7 F 2.9 g; standard length: 12.0 F 0.4 cm; MannWhitney U tests: U > 49, n.s.). The same procedure was used as described in Oliveira et al (2001c). Fish were anesthetized with a light dose of MS222 (tricaine methanesulfonate, Sigma -Aldrich; dilution 1:10,000), and a small incision was made in the belly through which the silastic tube was inserted.…”