Premium
THE EVOLUTION OF EUTHERIAN SPERMATOZOA AND UNDERLYING SELECTIVE FORCES: FEMALE SELECTION AND SPERM COMPETITION
Author(s) -
ROLDAN E. R. S.,
GOMENDIO M.,
VITULLO A. D.
Publication year - 1992
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1992.tb01193.x
Subject(s) - biology , sperm competition , sperm , evolutionary biology , sexual selection , female sperm storage , phylogenetic tree , range (aeronautics) , zoology , genetics , gene , materials science , composite material
Sumary We have examined sperm morphology and dimensions in Eutherian mammals. In most Eutherians, sperm heads are round or oval and spermatozoa have short tails (average sperm length about 65 μm; range = 33–121 μm). Rodents, however, clearly depart from the typical Eutherian pattern in that they show a broad array of head morphs and an extreme range of sperm dimensions (35–250 μm). In order to trace the evolutionary changes that rodent sperm have undergone, we have used phylogenetic relationships based on biogeographical, morphological, chromosomal and genic data, and we have superimposed onto them the information available on sperm traits. Analyses were carried out for five rodent groups on which enough information was available. The evolutionary trends which emerged from these studies have two main points in common throughout evolution spermatozoa have become enlarged and morphologically more complex, and this process seems to have taken place independently in different lineages. A general model was developed which outlines the different evolutionary pathways that rodent sperm have undergone. The adaptive significance of the increase in head complexity and the elongation of the sperm tail remains obscure. We have integrated information from evolutionary, physiological and behavioural studies to address this issue. We argue that two main selective forces may have favoured these changes: female selection within the reproductive tract and sperm competition. The female tract represents a formidable barrier for spermatozoa and it provides an environment where numerous interactions take place. The extent of these barriers and the complexity of these poorly understood interactions suggest that females may be exercising a strong selection, which may enable them to favour particular types of spermatozoa or ejaculates from particular males. Throughout their evolution males must have evolved adaptations to overcome these barriers, and the conflicting interests of choosy females. Sperm competition is a potent evolutionary force among mammals, which has influenced not only the evolution of sperm numbers but also changes in sperm dimensions. Thus, sperm competition has favoured the elongation of the sperm tail, which has led to the attainment of faster swimming speed, an important factor when sperm from rival males compete to reach the ova first.