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The freshwater mussel Contradens contradens (Lea, 1838) occurs in most types of freshwater habitats throughout Thailand. The species shows extensive variation in shell morphology, which has led to the recognition of six different subspecies. In this study, the validity of these six subspecies plus one unknown species was assessed using an integrative taxonomic approach. Geometric morphometric analyses revealed significant differences in shell shapes among these six nominal morphological subspecies, although a considerable degree of overlap was detected in some groups. In contrast, the phylogenetic tree obtained from the concatenated data of mitochondrial COI and nuclear H3 gene sequences and molecular species delimitation analyses revealed only three supported clades. These clades are proposed herein as three distinct species, and strongly corresponded to the biogeographically disjunct drainage systems in Thailand. They consisted of the (i) C. contradens clade found in the Chao Phraya Basin and other rivers that drain into the Gulf of Thailand, (ii) C. crossei clade that is restricted to the Middle Mekong Basin, and (iii) a clade containing only the newly discovered species from Huai Luang River in the north-east of Thailand, which is described herein as Contradens rolfbrandti Jeratthitikul & Panha, sp. nov. Speciation among these congeners was probably caused by the restriction of gene flow due to the past geomorphology of the river systems. The intraspecific variation in the shell shape detected here does not reflect the evolution of the mussel, but rather is evidence of phenotypic plasticity.http://zoobank.org/urn:lsid:zoobank.org:pub:649B6093-E1DD-4FD8-8185-A4696C43AD36; http://zoobank.org/urn:lsid:zoobank.org:act:777DDE86-8397-4FF3-AA78-0BE0F34611F4

The phylogeography of Simulium siamense complex was inferred from mitochondrial DNA sequences. A 586-bp fragment of the cytochrome oxidase I was sequenced for 92 individuals from 13 populations throughout Thailand, representing five cytoforms (A, B, C, F and G). The cytoforms are not genetically different at the molecular level except for cytoform B, which is genetically distinct from the others. This might indicate that cytoform B is a distinct species. Further morphological and molecular work using other genes is needed to clarify this. Our results also argue for the need of integrated approach, both cytological and molecular studies to understanding biodiversity of black flies. The star-like shape of the mtDNA genealogy is consistent with the sudden population expansion of the mismatch distribution analysis and large negative values of Fu's Fs and Tajima's D-tests, indicating a population demographic expansion. The expansion time is estimated to be in the late Pleistocene (about 120 000 years ago). Therefore, the overall low level of genetic structure could be due to sharing a recent history. The ancestral haplotype was found in the mountainous area in northeastern Thailand, suggesting that this area could have been the refugium of the species complex during the Pleistocene glaciations. Our results are consistent with previous findings about population expansion in response to the Pleistocene climatic change, thus revealing the importance of this historical event in shaping the genetic structure and diversity of Southeast Asian mainland species.

Summary Although earliest known records of the Cyclophoridae are from the European Mesozoic, Cyclophorus is a genus of dioecious terrestrial prosobranchs that currently ranges from South Asia to the Western Pacific region. Karyotypes of ten species of Cyclophorus have been examined from Thailand. Haploid and diploid chromosome numbers were invariant (n = 14, 2n = 28, FN = 56), but the karyotypes varied along a continuum with 14 metacentric chromosomes in C. volvulus while the remaining species contain unique representatives of every summed combination of metacentric and submetacentric types from 13m + 1sm to 6m + 8sm. The two larger species, C. aurantiacus and C. malayanus, exhibit the same karyotypes of 7m + 7sm. Karyotypes among populations of C. fulguratus showed variation between the central (12m + 2sm) and northeastern regions (13m + 1sm) of Thailand. Among the species with unique karyotypes, northern species possess a higher metacentric number relative to southern species. The ZZ-ZW sex-determining ...