Digest: Evolution of sperm size and number in external fertilizers *

Ejaculate evolution in externally fertilizing species is influenced by competition among sperm as well as the rate at which sperm and eggs encounter one another. Liao et al. (2017) found that ejaculate evolution in external fertilizers depended on spawning conditions. In anurans, gametes are released very close to eggs and are relatively protected from dispersal by water currents, thus sperm competition is more important. However, in fish, sperm-egg encounter rate plays a much more important role in ejaculate evolution because gametes may be easily dispersed when released into the aquatic environment. This article is protected by copyright. All rights reserved.