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Publication
Male sexual polymorphism, alternative reproductive tactics, and androgens in combtooth blennies (Pisces: Blenniidae)
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Advisor(s)
Abstract(s)
In species in which intense intermale competition for the
access to females is present males of lower competitive
ability may adopt alternative reproductive tactics (ART)
to get access to mates. These ART translate in many
cases into male sexual polymorphism, with individuals
following distinctly different tactics. Usually two alternative
male morphs can be recognized in species with
ART: (1) bourgeois males that compete for access to
mates invest in typically male behaviors, such as building
elaborated nests or displaying ornaments; and (2)
parasitic males that take advantage of the success of
the bourgeois males in attracting females and attempt
“sneaker” fertilizations (e.g., sneaker and satellite
males). In combtooth blennies (Blenniidae) the co-occurrence
of ART and male sexual polymorphism has
been described for two temperate species: the peacock
blenny, Salaria pavo, and the Azorean rock-pool blenny,
Parablennius sanguinolentus parvicornis. Interestingly,
while in the peacock blenny the alternative male morph
adopts a sneaker tactic, in the rock-pool blenny parasitic
males act as satellites to nest-holder males. Thus,
this variation in the ART expressed in these two closely
related species allows for a comparative study of the
proximate and ultimate factors affecting the expression
of the two ART. In this article we summarize the available
information on androgen levels in bourgeois and
parasitic males of natural populations of the two species
and of recent studies on the effect of exogenous administration
of androgens on tactic switching in parasitic
males of the two species. The information is discussed
within the frame of the relative plasticity hypothesis,
which predicts that plastic alternative morphs should
show differences in hormone levels and that the administration
of sex steroids should be effective in promoting
the switch from the parasitic to bourgeois tactic. The
evidence is only partly consistent with this hypothesis.
Alternatively, a social transduction hypothesis that better
fits the available data on androgens and ART in
teleost is proposed. It states that the observed differences
in androgen levels between alternative morphs
should not be interpreted as an organization vs activation
effect of steroids, but rather as the limited vs lifelong
responsiveness of the neuroendocrine axis to social regulation.
Description
Keywords
Sexual polymorphism Alternative reproductive tactics Androgens 11-ketotestosterone Teleosts Blenniids Social transduction hypothesis Relative plasticity hypothesis
Citation
Hormones and Behavior, 40, 266-275