Abstract
BackgroundInternal reproductive organ size is an important determinant of male reproductive success. While the response of testis length to variation in the intensity of sperm competition is well documented across many taxa, few studies address the importance of testis size in determining other components of male reproductive success (such as mating frequency) or the significance of size variation in accessory reproductive organs. Accessory gland length, but not testis length, is both phenotypically and genetically correlated with male mating frequency in the stalk-eyed fly Cyrtodiopsis dalmanni. Here we directly manipulate male mating status to investigate the effect of copulation on the size of both the testes and the accessory glands of C. dalmanni.ResultsAccessory gland length was positively correlated with male mating frequency. Copulation induced a significant decrease in accessory gland size. The size of the accessory glands then recovered slowly over the next 8–48 hours. Neither testis length nor testis area was altered by copulation.ConclusionThese results reveal that the time course of accessory gland recovery corresponds to field observations of mating behaviour and suggest that accessory gland size may limit male mating frequency in C. dalmanni.
Highlights
Internal reproductive organ size is an important determinant of male reproductive success
Few studies have addressed the importance of internal reproductive organ size to other components of male reproductive success, or the significance of size variation in accessory reproductive organs which are often vital for sperm transfer, fertility, and essential for success in sperm competition [8,9]
Mating resulted in a significant decrease in accessory gland length, but glands returned to their original size over the course of the 8 to 48 hours
Summary
Internal reproductive organ size is an important determinant of male reproductive success. While the response of testis length to variation in the intensity of sperm competition is well documented across many taxa, few studies address the importance of testis size in determining other components of male reproductive success (such as mating frequency) or the significance of size variation in accessory reproductive organs. There is a considerable body of evidence that reproductive organ size contributes to male reproductive success This mainly derives from interspecific comparisons that have found positive relationships between testis size and the risk of sperm competition [1,2,3,4,5]. Accessory gland size, but not testis size, is phenotypically correlated with male mating frequency in Drosophila melanogaster [16] and accessory glands become completely depleted and reduced in volume after 4–5 matings, leading to decreased fertility even though motile sperm remain in the seminal vesicles [17,18]. This resynthesis reaches a maximum after 2–4 hours and decreases to basal levels after 48 hours in Drosophila funebris [20]
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