Abstract
Catostomid fishes (suckers) have duplicate copies of the growth hormone gene and other nuclear genes, due to a genome duplication event early in the group’s history. Yet, paralogs of GH in suckers are more than 90% conserved in nucleotide (nt) and amino acid (aa) sequence. Within paralogs across species, variation in nt and aa sequence averages 3.33% and 4.46% for GHI, and 3.22% and 2.43% for GHII, respectively. Selection tests suggest that the two GH paralogs are under strong purifying selection. Consensus trees from phylogenetic analysis of GH coding region data for 23 species of suckers, other cypriniform fishes and outgroups resolved cypriniform relationships and relationships among GHI sequences of suckers more or less consistently with analyses based on other molecular data. However, the analysis failed to resolve all sucker GHI and GHII sequences as monophyletic sister groups. This unexpected topology did not differ significantly from topologies constrained to make all GH sequences monophyletic. We attribute this result either to limitations in our GHII data set or convergent adaptive changes in GHII of tribe Catostomini.
Highlights
Genome duplication has long been thought to play an important role in evolution, giving rise to duplicate copies of genes which subsequently diverge and assume other functions [1,2].Recent work has highlighted three episodes of genome duplication in vertebrates, which have been linked to the diversification of vertebrates, gnathostomes and teleosts, respectively [3,4,5,6]
Partial to complete sequences of two distinct copies of Growth hormone (GH) were determined for 14 catostomid species; complete sequences for one of the GH copies were obtained from nine additional species (Table 1)
GHII based on their sequence homology with GH copies in I. bubalus [16]
Summary
Genome duplication has long been thought to play an important role in evolution, giving rise to duplicate copies of genes (paralogs) which subsequently diverge and assume other functions [1,2]. Amino acid (aa) sequences from the protein-coding region of GH were first used for inferring the phylogeny of ‘‘bony” fishes by Bernardi et al [17]. GH intron sequences have been used to infer sub-familial phylogenetic relationships of salmonids [20] and labeonines of family Cyprinidae [21], and to characterize intraspecific, population genetic structures of various groups of fishes [8,18,22,23]. GH coding region sequences are being used as part of a multi-gene study of phylogenetic relationships of fishes of Order Cypriniformes [24]. We use GH coding DNA to infer variation in amino acid composition and structure of the GH protein
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