Most animals show seasonal cycles of reproduction (including cycling of sex steroids). Environmental cues (e.g., temperature) likely play important roles in these seasonal variations but their exact contributions remain unclear. We conducted a two-factor experiment to elucidate the effects of thermal environments and food availability on growth in body mass, testosterone (T) levels and testes morphology in male Chinese skinks [Plestiodon (Eumeces) chinensis]. Skinks in the thermal environment mimicking spring (April) conditions grew slowly but had higher plasma T levels and larger testes with more viable sperms than those in the thermal environment mimicking summer (July) conditions. Skinks exposed to high food treatment grew faster and had higher plasma T levels and more viable sperms than those exposed to low food treatment. Male growth was negatively correlated with reproductive activity as indicated by T levels and testes size. Therefore, both temperature and food availability are important environmental factors that can affect the reproductive cycle of male lizards, and the mechanisms underlying the trade-off between growth and reproduction could involve the regulation of T levels.
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