Respiratory CO2 Mediates Sperm Chemotaxis in Squids

Abstract

The squid Loligo ( Heterololigo ) bleekeri uses two distinct insemination sites, inside or outside the female's body, which links to the mating behavior of two distinct types of males, consort or sneaker, respectively. We found that sperm release a self-attracting molecule, which causes only sneaker sperm to swarm. We identifi ed respiratory CO 2 as the sperm chemoattractant and its sensor, membrane-bound fl agellar carbonic anhydrase. Downstream signaling results from generation of an extracellular proton gradient, intracellular acidosis, and concomitant recovery from acidosis. This cycle in turn elicits Ca 2+ -dependent fl agellar turning/tumbling, resulting in chemotactic swarming.