Reproductive morphology in relation to alternative male reproductive tactics in Scartella cristata

The relationship between reproductive morphology and reproductive tactics was examined in Scartella cristata, a combtooth blenny, which exhibits three behaviourally distinct mature male types: nesters, big males that care for eggs; hole-dwellers, medium-sized, non-reproducing males that are site-attached to a hole; sneakers, small, vagrant males that release sperm in the nests of the big males. The anal fin gland was a densely folded, mucous-secreting structure probably involved in pheromone synthesis. It was relatively larger in nesters than hole-dwellers, and altogether rudimentary in sneakers. Sneakers invested more in sperm production than nesters or hole-dwellers, suggesting adaptation to sperm competition. Approximately half of the testes of nesters and hole-dwellers was comprised of a highly developed efferent duct system or ‘testicular gland’, but this was extremely reduced in sneakers. In nesters the gland was characterized by many large vacuoles. A pair of secretory blind pouches was present in nesters and hole-dwellers, but barely visible in sneakers. In nesters, the sperm duct walls were thickened and highly secretory containing sperm dispersed in a granular matrix. In sneakers they were thinwalled and packed with concentrated sperm. Such differences probably represent different priorities for sperm production in relation to sperm competition and sperm economy. Thus it appears the accessory structures are traits developed specifically for a nesting tactic, whereas the gonad of sneakers is simply organized to produce as much sperm as possible.