Patterns of Leydig cell and LH gonadotroph activity, and plasma testosterone concentrations in the seasonally reproducing Schreibers' long-fingered bat (Miniopterus schreibersii)

Abstract

Spermatogenesis in Schreibers' long-fingered bat from approximately 33 degrees S in South Africa was seasonal, and occurred in the 3 months (February-April) preceding ovulation. The ultrastructure of the Leydig cells indicated a period of increased steroidogenesis at this time, and plasma testosterone concentrations were elevated from March to May (10.3 ng/ml). The reproductive accessory glands were secretorily active between March and May, and copulation occurred at the end of this period of activity. Changes in LH-beta immunoreactivity suggest that the LH gonadotrophs were secretorily active 1 month before the onset of spermatogenesis and that peak activity coincided with peak plasma testosterone concentrations, spermiogenesis and spermiation. During winter (May-August) there was no reproductive activity and the bats remained active, only entering prolonged periods of torpor during particularly cold spells. A secondary elevation in plasma testosterone concentration, during reproductive inactivity (October; 9.3 ng/ml), was not accompanied by any change in Leydig cell ultrastructure, and the biological significance of this peak is unknown. Such synchronous activity of the pituitary, Leydig cells, seminiferous epithelium and accessory glands is associated with the typical reproductive cycle of long-fingered bats in which copulation and fertilization are restricted to a brief period at the end of summer, and in which neither sperm storage nor a prolonged period of copulation occur.

Endocrine Control of the Reproductive Activity in Hibernating Bats

“…Such a reciprocal relation between the immunoreactivity and cell size of gonadotrophs in both sexes may reflect seasonal differences in the dynamics of secretion, storage and synthesis of these hormones during the annual reproductive cycle. These findings are consistent with previous results in other species of bats (Anthony and Gustafson 1984a;Bernard et al ., 1991a;Mikami et al ., 1988a;Singh and Krishna, 1996a). Such analyses are useful for evaluating the functional status of gonadotrophs in the pars distalis, but do not yield information on the variation in the rate of hormonal secretion and in the responsiveness to secretagogues.…”

“…After copulation with a female, these activities decrease, resulting in a regression of testicular mass and accessory organs, and a decline in circulating androgen levels. This pattern has been reported in vespertilinonid bats, M. schreibersii (Gustafson, 1979;Bernard et al, 1991a) and pteropodid bats, Pteropus poliocephalus and P. scapulatus (McGuckin and Blackshaw, 1991a, b).…”

Comparative morphology of the pituitary gland in Australian flying foxes (megachiroptera: GenusPteropus)

“…In male Ceruus elaphus (red deer), pituitary weights in summer are twice that during the autumn breeding season (Lincoln, 1971), and changes of similar scale occur in male Nyctalus noctula (Racey, 1974) in which testicular recrudescence and regression occur while the pituitary weight is low. In contrast, male Minopterus schreibersii have no seasonality of pituitary weights (Bernard et al, 1991), nor do male P. poliocephalus or P. scapulatus (Table 2). BW changes seen in males confirm reports of a seasonal pattern of BW in P. poliocephalus (McGuckin and Blackshaw, 1991).…”