THE REPRODUCTIVE-CYCLE AND DETERMINATION OF SEXUAL MATURITY IN MALE BROWN LONG-EARED BATS, PLECOTUS-AURITUS (CHIROPTERA, VESPERTILIONIDAE)

Observations of the external morphology of wild-caught and captive mal e brown long-eared bats (Plecotus auritus) revealed a marked seasonal pattern of spermatogenesis, similar to that established by histologica l examination of other temperate-zone vespertilionids, with a peak in testes size in August and a lag between testicular growth and epididym al distension. This was followed by complete cessation of spermatogene sis and shrinkage of the testes to prepubertal size. The period of pea k spermatogenesis coincided with a reduction in the incidence of torpo r and also a decline in body mass. This suggests that torpor and sperm atogenesis may be incompatible in this species. Outside the season of testicular growth and epididymal distension, sexual maturity could not be confidently determined in P. auritus by the pigmentation of the tu nica vaginalis surrounding the epididymis, a characteristic which has become established in other species. Instead, the size and shape of th e caudae epididymides appeared to be a better criterion for defining s exual maturity in this species. Most males underwent testicular growth and epididymal distension, and were assumed to have reached sexual ma turity, at an age of 15 months. However, some individuals (29%), parti cularly those in good condition (relatively heavy individuals), showed a degree of testicular and epididymal development in their first autu mn, i.e. at 3 months of age, indicating that the onset of puberty may be dependent on body condition. Poor body condition was associated wit h delayed spermatogenesis in adult males.