Somsak Panha

Evolution of whole-body enantiomorphy in the tree snail genus Amphidromus

Diverse animals exhibit left–right asymmetry in development. However, no example of dimorphism for the left–right polarity of development (whole‐body enantiomorphy) is known to persist within natural populations. In snails, whole‐body enantiomorphs have repeatedly evolved as separate species. Within populations, however, snails are not expected to exhibit enantiomorphy, because of selection against the less common morph resulting from mating disadvantage. Here we present a unique example of evolutionarily stable whole‐body enantiomorphy in snails. Our molecular phylogeny of South‐east Asian tree snails in the genus Amphidromus indicates that enantiomorphy has likely persisted as the ancestral state over a million generations. Enantiomorphs have continuously coexisted in every population surveyed spanning a period of 10 years. Our results indicate that whole‐body enantiomorphy is maintained within populations opposing the rule of directional asymmetry in animals. This study implicates the need for explicit approaches to disclosure of a maintenance mechanism and conservation of the genus.

Systematic relationships of Oriental tiny frogs of the family Microhylidae (Amphibia, Anura) as revealed by mtDNA genealogy

We estimated the genealogical relationships and assessed systematic relationships among 45 out of 89 named species and four unnamed taxa from 11 of 14 genera of the Oriental microhylids from 1767 bp sequences of the mitochondrial DNA genes 12S rRNA and 16S rRNA using maximum parsimony, maximum likelihood, and Bayesian inference methods. Monophyly was rejected for the subfamily Microhylinae, and our data reveal four well-supported clades whose relationships to each other are unresolved: (A) Microhyla, Calluella, and Glyphoglossus, (B) Chaperina, (C) Kaloula, Phrynella, and Metaphrynella, and (D) Micryletta. They were genetically as divergent from each other as from another Oriental subfamily Kalophryninae, and could be recognized as distinct subfamilies. Within Clade A, our data reveal three well-supported subclades whose relationships to each other are unresolved: (AI) Microhyla-I, (AII) Calluella and Glyphoglossus, and (AIII) Microhyla-II. Of the two enigmatic Malaysian genera, whose subfamilial placement has been undetermined, Phrynella was found to be the sister species of Metaphrynella in Clade C, whereas Gastrophrynoides was grouped in the Papua-Australian subfamily Asterophryinae. Currently recognized subgenera and species groups within Microhyla based on morphology were not supported phylogenetically, and require thorough reassessments.

Phylogenetic and taxonomic relationships of the Polypedates leucomystax complex (Amphibia)

Kuraishi, N., Matsui, M., Hamidy, A., Belabut, D. M., Ahmad, N., Panha, S., Sudin, A., Yong, H. S., Jiang, J.‐P., Ota, H., Thong, H. T. & Nishikawa, K. (2012). Phylogenetic and taxonomic relationships of the Polypedates leucomystax complex (Amphibia). —Zoologica Scripta, 42, 54–70.

Speciation and Radiation in a River: Assessing the Morphological and Genetic Differentiation in a Species Flock of Viviparous Gastropods (Cerithioidea: Pachychilidae)

The Kaek River in central Thailand is unique in harbouring a diverse species assemblage of viviparous gastropods of the genus Brotia. A stretch of this river less than 100 km long is inhabited by seven, mostly endemic species that are essentially differentiated by their shell morphology. Earlier, it has been suggested that this species flock fulfils some basic requirements of a radiation (monophyly and phenotype–habitat correlation). However, the present study has shown that there is no strict correlation between radula and shell morphology and the utilisation of substrates, such as rock or sand, thereby refuting the hypothesis that ecological speciation may have played a significant role. Phylogenetic analyses based on mtDNA show that haplotypes cluster together in drainage-specific clades rather than according to the taxonomy. There are also strong indications that introgressive hybridisation has occurred, which may have resulted from secondary contact of previously isolated species due to dispersal or river captures during the Cenozoic. It is assumed that the high species diversity in the Kaek River results from two phenomena that interdigitate. Firstly, the Kaek River fauna may have originated from multiple species invasions from different source areas, while traces of these events may have been obscured by introgression of Kaek River-specific haplotypes. Secondly, waterfalls in the Kaek River seem to affect the directionality and amount of gene flow between local populations within the river and several smaller tributaries. Together with temporally changing water regimes, this highly structured environment may have conserved local genetic differentiation and triggered diversification and speciation in peripheral isolates within relatively short periods of time.

Karyotypes of operculate land snails of the genus Cyclophorus (Prosobranchia: Cyclophoridae) in Thailand

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 chromosomes were observed in C. fulguratus from Phuwiang, C. malayanus from Sramorakot and C. volvulus from Wang Kanlueang. Taxonomic and evolutionary implications of the present findings are discussed.

A New Species of Rhacophorus from Eastern Thailand (Anura: Rhacophoridae)

Abstract A new tree frog of the genus Rhacophorus is described on the basis of specimens collected from Kalasin and Roi Et Provinces, eastern Thailand. It can be distinguished from all other congeners by the combination of: moderate body size (about 38 mm in males and 44 mm in females); brownish dorsum with irregular, dark marking; third finger webbed broadly to base of disk or less on outer side, and fourth finger to distal subarticular tubercle or base of disk; and no dermal appendage on snout, vent, or heel. It is currently known only around the type locality, where habitats suitable for anurans are limited.

The Centipede Genus Scolopendra in Mainland Southeast Asia: Molecular Phylogenetics, Geometric Morphometrics and External Morphology as Tools for Species Delimitation

Seven Scolopendra species from the Southeast Asian mainland delimited based on standard external morphological characters represent monophyletic groups in phylogenetic trees inferred from concatenated sequences of three gene fragments (cytochrome c oxidase subunit 1, 16S rRNA and 28S rRNA) using Maximum likelihood and Bayesian inference. Geometric morphometric description of shape variation in the cephalic plate, forcipular coxosternite, and tergite of the ultimate leg-bearing segment provides additional criteria for distinguishing species. Colouration patterns in some Scolopendra species show a high degree of fit to phylogenetic trees at the population level. The most densely sampled species, Scolopendra dehaani Brandt, 1840, has three subclades with allopatric distributions in mainland SE Asia. The molecular phylogeny of S. pinguis Pocock, 1891, indicated ontogenetic colour variation among its populations. The taxonomic validation of S. dawydoffi Kronmüller, 2012, S. japonica Koch, 1878, and S. dehaani Brandt, 1840, each a former subspecies of S. subspinipes Leach, 1814 sensu Lewis, 2010, as full species was supported by molecular information and additional morphological data. Species delimitation in these taxonomically challenging animals is facilitated by an integrative approach that draws on both morphology and molecular phylogeny.

Enantiomorphs differ in shape in opposite directions between populations

Abstract Development is left–right reversed between dextral and sinistral morphs of snails. In sympatry, they share the same gene pool, including polygenes for shell shape. Nevertheless, their shell shapes are not the mirror images of each other. This triggered a debate between hypotheses that argue either for a developmental constraint or for zygotic pleiotropic effects of the polarity gene. We found that dextrals can be wider or narrower than sinistrals depending on the population, contrary to the prediction of invariable deviation under a developmental constraint. If the pleiotropy is solely responsible instead, the mean shape of each morph should change, depending on the frequency of polarity genotype. Our simulations of this mean shape change under zygotic pleiotropy, however, show that the direction of interchiral difference remains the same regardless of genotype frequency. Our results suggest the presence of genetic variation among populations that changes the maternal or zygotic pleiotropic effect of the polarity gene.

Glochidiosis and juvenile production in a freshwater pearl mussel, Chamberlainia hainesiana

Summary Experiments on glochidiosis of the freshwater pearl mussel, Chamberlainia hainesiana, were carried out using the fry of four species of fish, namely Temmincks kissing gourami (Helostoma temmincki), striped tiger nandid (Pristolepis fasciatus), walking catfish (Clarius macrocephalus) and sand goby (Oxyeleotris marmoratus). The fry were exposed to four concentrations of glochidia, and the LE50 values (the concentrations that killed 50% of the fry) were determined. The most resistant species was O. marmoratus, which also gave the highest production of juvenile mussels. Juveniles appeared 18–27 days after infection.

The Middle Pleistocene vertebrate fauna from Khok Sung (Nakhon Ratchasima, Thailand): biochronological and paleobiogeographical implications

Abstract The fluviatile terrace deposits of Khok Sung, Nakhon Ratchasima province, have yielded more than one thousand fossils, making this the richest Pleistocene vertebrate fauna of Thailand. The excellent preservation of the specimens allows precise characterization of the faunal composition. The mammalian fauna consists of fifteen species in thirteen genera, including a primate, a canid, a hyaenid, proboscideans, rhinoceroses, a suid, cervids, and bovids. Most species correspond to living taxa but globally (Stegodon cf. orientalis) and locally (Crocuta crocuta ultima, Rhinoceros unicornis, Sus barbatus, and Axis axis) extinct taxa were also present. The identification of Axis axis in Khok Sung, a chital currently restricted to the Indian Subcontinent, represents the first record of the species in Southeast Asia. Three reptilian taxa: Crocodylus cf. siamensis, Python sp., and Varanus sp., are also identified. Faunal correlations with other Southeast Asian sites suggest a late Middle to early Late Pleistocene age for the Khok Sung assemblage. However, the Khok Sung mammalian fauna is most similar to that of Thum Wiman Nakin, dated to older than 169 ka. The Khok Sung large mammal assemblage mostly comprises mainland Southeast Asian taxa that migrated to Java during the latest Middle Pleistocene, supporting the hypothesis that Thailand was a biogeographic pathway for the Sino-Malayan migration event from South China to Java.