Insemination and fertilization are temporally separate events in most insects and, therefore, create potential opportunities for female mediated processes to influence paternity outcomes. One way in which females may influence paternity outcomes is by the differential storage of sperm from multiple matings, and the distribution and quantity of sperm stored in first matings may predetermine paternity outcomes from subsequent matings. Sperm storage patterns in singly-mated females were examined in a tephritid fly, Anastrepha suspensa, which has 3 spermathecae and mates multiply. The fine structure of a 4th storage organ, the ventral receptacle (VR), is described by TEM, u.v. fluorescent microscopy, and thick-sectioning. The VR is a cuticular extension of the ventral wall of the bursa copulatrix and overlaid by a mitochondria-rich osmoregulatory layer of cells surrounded by muscle fibers. The mitochondria are loosely arranged in columns flanked by longitudinal infoldings (canaliculi) of the cell membrane, which form a complex series of extracellular channels. The outer surface of the alveoli have cuticular extensions that interdigitate with the canaliculi and mitochondria of the overlying cells. The VR includes a lumen approximately 27.5 mm in diameter surrounded by 176 spherical "alveoli". Sperm are stored within the lumen and up to 4 sperm are coiled within each alveolus. The quantity of sperm stored in females and the time spent in copulation was highly variable. There were no copulations in which the VR was found empty, but 26% of females had one or more of their spermathecae empty and 24% of all females had fewer than 100 sperm in their 3 spermathecae collectively. Thus, variation in the quantity of sperm stored is primarily attributable to sperm number stored amongst the 3 spermathecae.
Species 1: Diptera Tephritidae Anastrepha suspensa
Keywords: insemination, morphology
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