Spawning in Ancistrus (Siluriformes: Loricariidae) with comments on the evolution of snout tentacles as a novel reproductive strategy: larval mimicry

Most species of Ancistrus exhibit a striking sexual dimorphism, mature males having an elaborate complex of enlarged fleshy tentacles on the snouts. Snout tentacles appear to be modifications of the fleshy cutaneous sheath that surrounds the base of an odontode (integumentary tooth) and are best developed in breeding males. The tentacles are thought to serve as accessory sensory structures because they are covered with taste buds. We propose an additional function related to reproductive biology. Male Ancistrus guard eggs and larvae for up to 10 days after hatching in a cavity nest. In several cavity-nesting fishes with paternal care, females preferentially spawn with males guarding eggs over males in empty nests, and this preference has led to the evolution of deceptive mating strategies whereby males with empty nests can compete successfully with males guarding eggs. We hypothesize that female Ancistrus preferentially spawn with males guarding larvae, and that the male's snout tentacles stimulate this bias by mimicking the presence of larvae in an otherwise empty nest. We also provide information on our field observations of Ancistrus spawning in the rio Aguaro, a tributary of the rio Orinoco in central Venezuela.