Reproductive strategies of a warm temperate vespertilionid, the large-footed myotis, Myotis moluccarum (Microchiroptera:Vespertilionidae)

Abstract

A population of M. moluccarum, which is known to be polyoestrous and monotocous, giving birth to two consecutive offspring annually, was investigated to determine the female reproductive cycle. The population was visited, and observations recorded, at approximately 5-week intervals from July 1994 to February 1995. At each visit, 2–4 females were collected and their reproductive tracts were removed, fixed and processed for light microscopy. During visits conducted after parturition periods, the age of the offspring was estimated in order to determine the duration of parturition.

The two gestation periods of the breeding season were of approximately equal duration (11.5–12 weeks) despite the initial pregnancy occurring over much cooler months. While some copulations take place prior to ovulation, sperm storage is not a necessity, and copulation can occur until the time of ovulation. First ovulations of the season take place in early August and although several follicles may mature only one is ovulated. Analysis of climatic variables indicates that females undergo the first ovulation and pregnancy of the season during the cooler part of the year whereas lactation occurs during the warmer, wetter months. A post-partum oestrus occurs soon after parturition and adult males leave the population before the birth of the second offspring. Individual variation in the time before the post-partum oestrus may account for the reduced synchrony noted in the second parturition period. Monthly changes in the corpus luteum and ovaries are documented.

The reproductive cycle of M. moluccarum resembles most closely that of tropical and sub-tropical vespertilionids; however, pre-ovulatory copulation, a short period of sperm storage and the development of typical over-wintering follicles (aspects of reproduction seen in species from cooler climates) remain inherent in the large-footed myotis.