Gasterosteiformes

Abstract: Members of the currently recognized acanthopterygian order Pegasiformes have an unusual feeding mechanism in which enlarged maxillovomerine cartilages are closely associated with the maxillae, premaxillae and dentaries forming a highly protrusible mouth. This is a unique mechanism among living teleosts, but apparently present in the Lower Eocene Ramphosidae, currently placed among the aulostomoid gasterosteiforms. This and other evidence support a gasterosteiform ancestry for the Pegasidae. The Pegasiformes are synonymized with the Gasterosteiformes. The fossil Ramphosidae are resurrected from the synonymy of the Macrorhamphosidae and placed with the Pegasidae in a new superfamily, the Pegasoidea. The Pegasoidea are proposed as the primitive sister-group of the Solenostomidae and Syngnathidae. The Solenostomidae and Syngnathidae are included in a new superfamily, the Syngnathoidea, which together with the Pegasoidea form the primitive sister-group of the Macrorhamphosidae, Centriscidae, Aulostomidae and Fistulariidae.

Abstract: The threespine stickleback Gasterosteus aculeatus is an important model in evolutionary and ethologic studies. Its utility would greatly be increased by the availability of molecular markers distinguishing individuals and populations. Such markers can be provided by the major histocompatibility complex (Mhc) genes, which are well known for their extensive polymorphism. In the present study, both class I and class II B Mhc genes have been identified and sequenced. Fifteen distinct class I exon 2 and exon 3 sequences were obtained and assigned to 12 loci on the basis of intron 2 length differences. Some of the loci appear to be related to class I loci identified previously in cichlid fish. The intron 2 sequences and insertions/deletions in exon 2 group the loci into three families (with one family divided further into two subfamilies) derived from different ancestral genes. The ancestors presumably diverged from one another before the divergence of Gasterosteiformes from Perciformes. The 12 distinct class II B sequences may be derived from six loci, which are, however, closely related to one another in both exonic and intronic parts and may have diverged from a single common ancestor after the divergence of Gasterosteiformes from Perciformes. The intron 2 of some of the class I genes contains two microsatellites that can be used as markers, in addition to the polymorphism of the Mhc genes in their exonic regions.

Abstract: In the past decade, there has been a new effort to understand the ecology that drives population divergence and speciation. It is well established in theory that speciation is most likely to occur when a trait that is under divergent natural selection in different populations is also used in mate choice. Such traits have been dubbed ‘magic traits’ (Gavrilets, 2004) and, although there appears to be good evidence that they exist, the ecological mechanisms that underlie their divergence are not well understood. Size at maturity in three-spined sticklebacks is an archetypal example of a magic trait. The present study documents for the first time that differences in body size at maturity in sympatric species pairs of lacustrine three-spined sticklebacks in British Columbia, Canada, are caused by differences in age at maturity. It is also shown that there are differences between the sympatric species in the patterns of infection with a virulent cestode, Schistocephalus solidus. Although the evidence is circumstantial, these differences in infection are consistent with the hypothesis that they have contributed to the observed divergence in age and size at maturity in these populations. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 425–433.