Divergent expression of 11beta-hydroxysteroid dehydrogenase and 11beta-hydroxylase genes between male morphs in the central nervous system, sonic muscle and testis of a vocal fish

Abstract

The vocalizing midshipman fish, Porichthys notatus, has two male morphs that exhibit alternative mating tactics. Only territorial males acoustically court females with long duration (minutes to >1h) calls, whereas sneaker males attempt to steal fertilizations. During the breeding season, morph-specific tactics are paralleled by a divergence in relative testis and vocal muscle size, plasma levels of the androgen 11-ketotestosterone (11KT) and the glucocorticoid cortisol, and mRNA expression levels in the central nervous system (CNS) of the steroid-synthesizing enzyme aromatase (estrogen synthase). Here, we tested the hypothesis that the midshipman's two male morphs would further differ in the CNS, as well as in the testis and vocal muscle, in mRNA abundance for the enzymes 11beta-hydroxylase (11betaH) and 11beta-hydroxysteroid dehydrogenase (11betaHSD) that directly regulate both 11KT and cortisol synthesis. Quantitative real-time PCR demonstrated male morph-specific profiles for both enzymes. Territorial males had higher 11betaH and 11betaHSD mRNA levels in testis and vocal muscle. By contrast, sneaker males had the higher CNS expression, especially for 11betaHSD, in the region containing an expansive vocal pacemaker circuit that directly determines the temporal attributes of natural calls. We propose for territorial males that higher enzyme expression in testis underlies its greater plasma 11KT levels, which in vocal muscle provides both gluconeogenic and androgenic support for its long duration calling. We further propose for sneaker males that higher enzyme expression in the vocal CNS contributes to known cortisol-specific effects on its vocal physiology.

Figure 1

Overview of synthetic pathways for glucocorticoids and androgens in fish. See text and Bury and Sturm (2007) for details.

Figure 2

Normalized mRNA values are plotted against tissue type for 11βHSD and 11βH genes for each midshipman reproductive morph (see legend, top left). Note break in y-axis of the 11βH bar graph to accomodate high values for type I male gonad (testis). Standard errors are shown. Single and double asterisks indicate significance over, respectively, one and two other morph(s). See text and Supplemental Tables 3 and 4 for numerical data. The CNS was divided into three regions: forebrain, including olfactory bulb (OB), telencephalon (Tel) and preoptic area (POA); a middle region including the midbrain tectum and tegmentum (Mid), diencephalon (Di) and cerebellum (Cbl); the remaining hindbrain (Hind) and rostral spinal cord (SC) that is predominated by an expansive vocal pattern generator circuit (Bass et al., 1994).