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May 23, 2012
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1 Introduction
[F] Gynecology / Sexual anatomy /
Sperm heteromorphism

Wikipedia

  

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 ovum|eggs. Fertile types have been called "eusperm" or "eupyrene sperm" and infertile types "parasperm" or "apyrene sperm".


Image:Affinis sperm.jpg|frame|The two sperm types of the fly Drosophila affinis. Photograph by Rhonda Snook.

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 (fruit-flies): the D. obscura group of species 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 fertile 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.

Possible functions of sperm heteromorphism



Non-adaptive

The non-fertilising morph(s) have no function, and are simply developmental errors. This is thought to be unlikely in many sperm heteromorphic species because the production of infertile sperm may be tighly regulated, and infertile sperm can make up >90% of the total sperm in some Lepidoptera and Drosophila.

Provisioning

The non-fertilising morph(s) are a means in which males can provide nutrition to the female, her eggs or the fertilising sperm.

Facilitation

The non-fertilising sperm help the fertilising sperm by assisting their transport or capacitation (i.e. the acquisition of fertilisation competence).

Sperm competition

Non-fertile sperm increase the fertilisation success of the male producing them when sperm competition occurs. This might be through sperm offence (e.g. displacing or even killing rival fertilising sperm) or sperm defence (e.g. by blocking areas of the female tract or creating a hostile pre-fertilisation environment). Alternatively, infertile sperm might depress female remating behaviour, so that the fertile sperm can avoid sperm competition.

Female disinterest

In Lepidoptera, butterflies and moths, it has been shown that the abundance of sperm in the female spermathecum (sac which holds sperm until she is ready to fertilize an egg) signals to not reproduce with another male until the sperm has been used (Cook 1999). However, apyrene sperm, the infertile sperm, breaks down over a matter of hours and may result in a second mating session. If the female lays eggs during this time, she will fertilize any of those offspring with the first males sperm (eupyrene sperm). Currently, this theory is the most supported by empirical evidence.

References



  • Cook, P.A., and Wedell, N. 1999. Non-fertile sperm delay female remating. Nature 397: 486.

  • Swallow, J.G., and G.S. Wilkinson. 2002. The long and the short of sperm polymorphisms in insects. Biological Reviews 77: 153-182.

  • 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.



category:Reproductive system

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sperm heteromorphism".


Last Modified:   2005-12-19


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