Title

Experimental increases in foraging costs affect pectoralis muscle mass and myostatin expression in female, but not male, zebra finches (Taeniopygia guttata)

Abstract

Skeletal muscle remodeling is an important component of phenotypic flexibility in birds and impacts organismal metabolism and performance, which could potentially influence fitness. One regulator of skeletal muscle remodeling is myostatin, an autocrine/ paracrine muscle growth inhibitor that may be down-regulated under conditions promoting heavier muscle masses. In this study, we employed protocols requiring hovering while foraging to increase foraging costs and modify phenotypes of zebra finches (Taeniopygia guttata). We examined the effects of high-cost foraging (HF) on skeletal muscle masses and used real-time reverse-transcription polymerase chain reaction and Western blots to measure gene and protein expression of myostatin and its met-alloproteinase activators tolloid-like proteases TLL-1 and TLL-2 in pectoralis muscle. Female finches average shorter wings and higher wing loading than males, so increased flight costs might be expected to disproportionately affect females. Indeed, HF female finches exhibited reduced total fat masses, increased pectoralis muscle masses, and lower myostatin protein levels than controls. Male finches showed no significant differences in pectoralis muscle masses or myostatin protein levels between HF and control birds. Myostatin, TLL-1, and TLL-2 messenger RNA (mRNA) expression remained stable between treatments for both female and male finches. Myostatin mRNA and protein levels showed variable directions of correlations with pectoralis mass residuals among treatments. Thus, these data offer only mixed support for a regulatory role for myostatin in mediating the flexibility of pectoralis muscle phenotypes of small birds.

Publication Title

Physiological and Biochemical Zoology

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