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Seasonal endocrine cycles in the European hedgehog, Erinaceus europaeus

Summary. Adult hedgehogs, maintained in captivity under natural environmental conditions of photoperiod and ambient temperature, were bled monthly. Plasma was assayed for melatonin, testosterone, prolactin, thyroxin, β-endorphin and both plasma and urine for cortisol. Melatonin concentrations followed a circannual pattern, maximal between November and February at photoperiods less than 10L:14D, which is suggested as a key photoperiod. β-Endorphin concentrations were maximal between March and September, coinciding with the reproductively active season of the hedgehog. Prolactin values were elevated during hibernation, indicating continued hypothalamo–pituitary axis activity. Testosterone and thyroxin levels were high between February and July and February and August respectively. During spring thyroxin concentrations rose 1 month later in females than males, reflecting the earlier arousal of the males from hibernation. There were no marked seasonal cycles of plasma or urinary cortisol. The results indicate photoperiod as the main factor in regulating hedgehog seasonality, with melatonin, β-endorphin and prolactin important in the timing of reactivation of reproduction. Sexual differences in hedgehogs suggests environmental fine tuning of endogenous cycles, males being ready to inseminate females early in spring, while females only begin full breeding activity when conditions are suitable.

Keywords: European hedgehog; seasonal endocrine cycles