Cytogenetic analysis of the Asian Plethodontid salamander, Karsenia koreana: Evidence for karyotypic conservation, chromosome repatterning, and genome size evolution

Abstract

A cytogenetic analysis, including the karyotype, C-bands, silver-stained nucleolus organizer regions and genome size, was performed on the recently discovered species, Karsenia koreana, the first plethodontid salamander from Asia.

Evolutionary cytogenetics in salamanders

“…Sessions (1984) interpreted this pattern as the result of persistent independent evolutionary increases in genome size with distance from a presumed centre of origin for the family in the Appalachian Mountains of eastern N. America. Recent phylogenetic analyses, however, suggest that plethodontids may have originated elsewhere (Vieites et al submitted), in which case it seems likely that the small genomes of species in eastern N. America were derived from larger genomes that characterize the family (Sessions et al 2008). Most of the groups with the smallest genomes in the family have aquatic larvae with metamorphosis, which fits the relationship between genome size and life history already noted in the order as a whole.…”

“…Observed variation in interstitial C-bands and AgNOR loci in various groups of salamanders suggests that conservation of chromosome number and shape is accompanied by rearrangements of genes and other sequences on the chromosomes, as expected for highly diverged species (Sessions et al 2008). Variation in NOR positions for species of salamandrids, for example, was interpreted as Fchromosome repatterning_ via translocations (Mancino et al 1977).…”

“…Genome size variation also shows strong correlations with biogeography, at least in some groups ( Figure 10) (Sessions 1984, Litvinchuk et al 2007, Sessions et al 2008. Within the Plethodontidae, species found in eastern North America, regardless of clade, have smaller genomes than those found elsewhere, including western N. America, Middle America, South America, Asia, and southern Europe.…”

“…Three exclusively North American families, the western N. American Dicamptodontidae (with the single genus Dicamptodon), the widespread Ambystomatidae (two genera, Ambystoma and Rhyacosiredon) and the south-east N. American Amphiumidiae (with the single genus Amphiuma), have 2n=28 chromosomes and a fourth family, the Plethodontidae (primarily North American but with a few species in southern Europe and one newlydiscovered species in Asia; Sessions et al 2008), includes species with either 2n=26 or 2n=28 chromosomes (Morescalchi 1973, Sessions & Kezer 1991, Green & Sessions 2007. The western North American family Rhyacotritonidae, with the single genus Rhyacotriton, is characterized by 2n=26 chromosomes (Humphrey 1958, Morescalchi 1973, Sessions 1984.…”

Mechanisms of action and co-optive evolution for hypervariable courtship pheromones in plethodontid salamanders.

“…Unfortunately, efforts to fully sequence all of the PMF genes has been impeded by a number of factors: (1) the P. shermani genome is exceptionally large (30 Gb or ~10x the size of the human genome) [162], (2) salamander introns are typically >10x larger than those in vertebrate orthologs [163], (3) there exist several processed PMF pseudogenes that compete for primer binding during PCR, and (4) the number of duplications within a cluster make it difficult to target a single locus. Current data, however, supports at least one PMF gene for each of the 13 [143,[164][165][166].…”