Genetic divergence between island and continental populations of the parasitic nematode Labiosimplex australis in Australia

Abstract

Sequences of the first and second internal transcribed spacers (ITS-1 and ITS-2) of nuclear ribosomal (r) DNA were characterised for Labiosimplex australis, a parasitic nematode of macropodid marsupials from continental Australia and from island populations which have been isolated from mainland Australia for relatively short periods of time (<40,000 years). The results showed that the geographically isolated populations of L. australis on Kangaroo Island and Tasmania were genetically different from each other and from populations on the mainland. There were two unequivocal nucleotide differences sites within the ITS-1 rDNA sequence between the two island populations; however, the ITS-1 sequences of individuals from mainland populations contained one or both of these nucleotides. In contrast, L. australis from each island population had unique nucleotides in ITS-2 sequence that were not detected in any individual from the mainland. Although these results are consistent with the hypothesis that L. australis represents a single species, the genetic divergence in the ITS-2 sequences amongst individuals from different isolated populations suggests that the island populations of L. australis may be in the initial stages of allopatric speciation.

Genetic diversity and variation of Chinese fir from Fujian province and Taiwan, China, based on ISSR markers

“…‘Sea level’ is supposed to produce different pressures on natural selection that forces colonization toward higher altitude. Populations located at different elevations were motivated by different levels of potential adaptation to the local environment [41,42], leading to the occurrence of loci diverging. Limited by the number of the populations and the size of the populations plus due to some types of bottleneck events [43], expansion of the populations upon one species was not always observed.…”

Improved Molecular Detection ofAngiostrongylus cantonensisin Mollusks and Other Environmental Samples with a Species-Specific Internal Transcribed Spacer 1-Based TaqMan Assay

“…The first and second internal transcribed spacers (ITS1 and ITS2) are comparatively more variable than the rRNA coding regions and have thus been used for differentiation of closely related species (1,4,6,10,22,23). We PCR amplified and sequenced ITS1 from A. costaricensis (two laboratory strains from Costa Rica and Brazil), A. vasorum (from naturally infected hosts in United Kingdom), and A. cantonensis from three geographical regions (one laboratory strain from Japan plus nine environmental isolates from Hawaii and New Orleans, LA) to assess the variability of this potential PCR target.…”

Analysis of genetic variation in Globocephaloides populations from macropodid marsupials using a mutation scanning‐based approach

“…ITS-1 and ITS-2) known to allow the specific identification of strongylid nematodes of macropodids and other vertebrates [16][17][18][19][20][21]. The low degree of nucleotide variation (r0.2%) detected in the ITS-1 region within G. trifidospicularis from five host species and 13 geographical locations was less than the levels of intraspecific variation (usually r1%) detected for a wide range of strongylid nematodes [18,19,[22][23][24][25][26][27], including those of the superfamily Trichostrongyloidea, to which the genus Globocephaloides belongs [28]. The sequence homogeneity in ITS rDNA within G. trifidospicularis contrasts with previous MEE results, showing a fixed allelic difference of 17% between (pooled) samples of G. trifidospicularis from sympatric hosts in Tasmania [7], and does not support a previous proposal that G. trifidospicularis represents a complex of at least two species.…”

“…There is a clear precedent for cryptic species in strongylid nematodes of macropodid marsupials. A number of previous studies have discovered cryptic species and/or proposed adaptive speciation [13,23,24,[30][31][32][33]. For example, Huby-Chilton et al [31] used a mutation scanning-sequencing approach to detect 5.2% sequence variation in ITS-2 between two forms of Zoniolaimus mawsonae (Nematoda: Strongyloidea) from M. rufus and concluded that they represented sibling species.…”