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Sperm Form (sperm + form)
Selected AbstractsThe spermatozoon of the Old Endemic Australo-Papuan and Philippine rodents , its morphological diversity and evolutionACTA ZOOLOGICA, Issue 3 2010William G. Breed Abstract Breed, W.G. and Leigh, C.M. 2010. The spermatozoon of the Old Endemic Australo-Papuan and Philippine rodents , its morphological diversity and evolution.,Acta Zoologica (Stockholm) 91: 279,294 The spermatozoon of most murine rodents contains a head in which there is a characteristic apical hook, whereas most old endemic Australian murines, which are part of a broader group of species that also occur in New Guinea and the Philippines, have a far more complex sperm form with two additional ventral processes. Here we ask the question: what is the sperm morphology of the New Guinea and Philippines species and what are the trends in evolutionary changes of sperm form within this group? The results show that, within New Guinea, most species have a highly complex sperm morphology like the Australian rodents, but within the Pogonomys Division some species have a simpler sperm morphology with no ventral processes. Amongst the Philippines species, many have a sperm head with a single apical hook, but in three Apomys species the sperm head contains two additional small ventral processes, with two others having cockle-shaped sperm heads. When these findings are plotted on a molecular phylogeny, the results suggest that independent and convergent evolution of highly complex sperm heads containing two ventral processes has evolved in several separate lineages. These accessory structures may support the sperm head apical hook during egg coat penetration. [source] Spermicide, cryptic female choice and the evolution of sperm form and functionJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2006L. HOLMAN Abstract Sperm competition and cryptic female choice profoundly affect sperm morphology, producing diversity within both species and individuals. One type of within-individual sperm variation is sperm heteromorphism, in which each male produces two or more distinct types of sperm simultaneously, only one of which is typically fertile (the ,eusperm'). The adaptive significance of nonfertile ,parasperm' types is poorly understood, although numerous sperm-heteromorphic species are known from many disparate taxa. This paper examines in detail two female-centred hypotheses for the evolution and maintenance of this unconventional sperm production strategy. First, we use game theoretical models to establish that parasperm may function to protect eusperm from female-generated spermicide, and to elucidate the predictions of this idea. Second, we expand on the relatively undeveloped idea that parasperm are used by females as a criterion for cryptic female choice, and discuss the predictions generated by this idea compared to other hypotheses proposed to explain sperm heteromorphism. We critically evaluate both hypotheses, suggest ways in which they could be tested, and propose taxa in which they could be important. [source] Evolution of the spermatozoon in muroid rodentsJOURNAL OF MORPHOLOGY, Issue 3 2005William G. Breed Abstract In the rodent superfamily Muroidea, a model for the evolution of sperm form has been proposed in which it is suggested that a hook-shaped sperm head and long tail evolved from a more simple, nonhooked head and short tail in several different subfamilies. To test this model the shape of the sperm head, with particular emphasis on its apical region, and length of sperm tail were matched to a recent phylogeny based on the nucleotide sequence of several protein-coding nuclear genes from 3 families and 10 subfamilies of muroid rodents. Data from the two other myomorph superfamilies, the Dipodoidea and kangaroo rats in the Geomyoidea, were used for an outgroup comparison. In most species in all 10 muroid subfamilies, apart from in the Murinae, the sperm head has a long rostral hook largely composed of acrosomal material, although its length and cross-sectional shape vary across the various subfamilies. Nevertheless, in a few species of various lineages a very different sperm morphology occurs in which an apical hook is lacking. In the outgroups the three species of dipodid rodents have a sperm head that lacks a hook, whereas in the heteromyids an acrosome-containing apical hook is present. It is concluded that, as the hook-shaped sperm head and long sperm tail occur across the muroid subfamilies, as well as in the heteromyid rodents, it is likely to be the ancestral condition within each of the subfamilies with the various forms of nonhooked sperm heads, that are sometimes associated with short tails, being highly derived states. These findings thus argue against a repeated evolution in various muroid lineages of a complex, hook-shaped sperm head and long sperm tail from a more simple, nonhooked sperm head and short tail. An alternative proposal for the evolution of sperm form within the Muroidea is presented in the light of these data. J. Morphol. © 2005 Wiley- Liss, Inc. [source] | ||||||||||