Reproductive phenology in Megalonaias nervosa (Bivalvia: Unionidae) in Wheeler Reservoir, Tennessee River, Alabama, USA

Abstract

Two hundred and sixty-nine specimens of Megalonaias nervosa (Rafinesque, 1820) were collected approximately monthly from the Wheeler Reservoir (Tennessee River mile 298), Alabama, USA, between July 1995 and June 1997. Microscopic and gross examinations of gonadal tissue and marsupia were used to determine the phenology of gamete production, spawning, brooding, and glochidia discharge. In addition, 11 females were collected in October 2001 to obtain estimates of brood size. Little reproductive activity was observed through most of the year, culminating in a bout of activity in late summer and early autumn. In males, spermatozoa were seen only in individuals collected in August and September. In females, oocytes developed and grew quickly during the same period and all oocytes were released to the marsupia over a relatively short period, showing a high degree of spawning synchronicity with males. Glochidia quickly matured and were present in both inner and outer demibranchs until December. The average number of glochidia per female was 740,379 ± 72,854 (95% CI). The reproductive cycle observed differed from those reported for other members of the Ambleminae and was more similar to members of Lampsilinae. This suggests that the lengths of the gametogenic and spawning periods may be related to the timing of fertilization, rather than to the length of the brooding period or to the species phylogeny.