IS THERE A DIFFERENCE BETWEEN TESTOSTERONE CONTENTS IN TWO POPULATIONS OF THE BLACK EARED MOUSE, LIVING UNDER SIMILAR CONDITIONS BUT WITH DIFFERENCES IN POPULATION PATTERNS?

摘要

In order to answer this question, we compare intragonadal contents of testosterone (T) in males of two neighboring populations of Peromyscus melanotis J. A. Allen and Chapman, 1897, that differ in their population density and in its seasonal fluctuations, even though they inhabit in quite similar habitat conditions. Although an affirmative answer to this question would corroborate the idea that this androgen has a density-dependent effect, since it has been proposed that T increases at low densitiesand vice versa, our results did not confirm this thesis: T showed no differences between the two populations, since both had the same seasonal pattern for the androgen, throughout four years of study, with a maximum in the summer, as would be expected in this temperate species whose reproductive optimum occurs at that time of the year. Therefore, density differences between both populations must be rather due to subtle microhabitat differences.