Sperm heteromorphism
From Biocrawler, the free encyclopedia.
Sperm heteromorphism is the simultaneous production of two or more distinguishable types of sperm by a single male. The sperm types might differ in size, shape and/or chromosome complement. Sperm heteromorphism is also called sperm polymorphism or sperm dimorphism (for species with two sperm types). Typically, only one sperm type is capable of fertilising eggs. Fertile types have been called "eusperm" and infertile types "parasperm".
Distribution
Sperm heteromorphism is known from several different groups of animals.
Insects:
Lepidoptera (i.e. butterflies and moths): Almost all known species produce two sperm types. The fertilising type has a longer tail and contains a nucleus. The other type is shorter and lacks a nucleus, meaning it contains no genetic information at all.
Drosophila: one species group in the genus Drosophila is sperm heteromorphic. Similarly to the Lepidoptera, there is a long, fertile type and a short, infertile type. However, the infertile type has a nucleus with a normal, haploid chromosome complement. It is infertile for reasons unknown, though it has been suggested that the slightly wider head of the infertile type might prevent it from entering the micropyle of the egg.
Diosidae (stalk-eyed flies): several species have a long, fertile type and a shorter infertile type.
Carabidae (ground beetles): some species produce large, infertile sperm which may contain up to 100 sets of chromosomes.
Molluscs:
Some prosobranch gastropods (snails) produce two or three sperm types. The infertile types may be large "carrier" types to which the ferile sperm attach for transport, or "lancet" types. The lancet sperm sometimes contain many lysosomes.
Fish:
Some Sculpin may be sperm heteromorphic. Their ejaculates appear to contain fertile sperm as well as disc-shaped, infertile sperm.
References
Till-Bottraud, I., D. Joly, D. Lachaise and R.R. Snook. 2005. Pollen and sperm heteromorphism: convergence across kingdoms? Journal of Evolutionary Biology 18(1): 1-18.
Swallow, J.G., and G.S. Wilkinson. 2002. The long and the short of sperm polymorphisms in insects. Biological Reviews 77: 153-182.
