One northward, one southward: Contrasting biogeographical history in two benthic freshwater fish genera across Southeast Asia (Teleostei: Cobitoidea: Nemacheilus, Pangio)

Influence of limestone and anthropogenic activities on land snail communities in Satun Province, Thailand

Southeast Asia is renowned for its rich biodiversity and serves as a global hotspot for organisms. Satun Province, located in southern Thailand, represents a significant biogeographic and biodiversity region situated in the transition zone between the Indochinese and Sundaland hotspots. Thus, Satun Province has high diversity and abundance of organisms, especially land snails. However, Satun Province has been largely understudied for both diversity and biogeography. Our study aimed to investigate land snail communities, emphasizing comparisons between the mainland and island sites, and the influence of limestone and other rock types in Satun Province. Our exploration efforts identified a diverse land snail community comprising 17 families, which updated the total reported species in the province from 22 to 58 species. The results showed that islands had significantly greater land snail species richness and abundance, and larger Shannon index values in comparison to the mainland. Anthropogenic activities on the mainland led to habitat transformation and had detrimental impacts on native land snail diversity while promoting the spread of invasive species. In contrast, the presence of little-disturbed limestone habitats on some of the islands contributed to higher richness of land snails, as limestone areas are known for their high diversity and endemism. Snail communities varied along site characteristics; especially, limestone versus non-limestone areas and human activity levels (which were associated with national park protection), with limestone and protected areas having the highest diversity. Our study illustrates the value of protected areas as potential hotspots of biodiversity, especially for islands that are little disturbed by human activities and that have habitats that support high diversity, such as limestone outcrops. This study provides valuable insights into the biogeography of land snails in Satun Province and Southeast Asia and contributes to our understanding of the factors influencing land snail diversity.

Cryptic diversity impacts model selection and macroevolutionary inferences in diversification analyses

Species persist in landscapes through ecological dynamics but proliferate at wider spatial scales through evolutionary mechanisms. Disentangling the contribution of each dynamic is challenging, but the increasing use of dated molecular phylogenies opened new perspectives. First, the increasing use of DNA sequences in biodiversity inventory shed light on a substantial amount of cryptic diversity in species-rich ecosystems. Second, explicit diversification models accounting for various eco-evolutionary models are now available. Integrating both advances, we explored diversification trajectories among 10 lineages of freshwater fishes in Sundaland, for which time-calibrated and taxonomically rich phylogenies are available. By fitting diversification models to dated phylogenies and incorporating DNA-based species delimitation methods, the impact of cryptic diversity on diversification model selection and related inferences is explored. Eight clades display constant speciation rate model as the most likely if cryptic diversity is accounted, but nine display a signature of diversification slowdowns when cryptic diversity is ignored. Cryptic diversification occurs during the last 5 Myr for most groups, and palaeoecological models received little support. Most cryptic lineages display restricted range distribution, supporting geographical isolation across homogeneous landscapes as the main driver of diversification. These patterns question the persistence of cryptic diversity and its role during species proliferation.

Phylogeny and biogeography of Indochinese freshwater mussels in the genus Pilsbryoconcha Simpson, 1900 (Bivalvia: Unionidae) with descriptions of four new species

The body of knowledge regarding the classification and evolution of freshwater mussels in the family Unionidae (Bivalvia) in Indochina has recently increased. However, the taxonomic revision of all extant taxa in the region is still ongoing. In this study, the genus Pilsbryoconcha was revised based on an integrative analysis of shell morphology, biogeography, and molecular data. Multi-locus phylogeny indicated the availability of eight species within the genus. Four previously recognized species are P. exilis (Lea, 1838), P. schomburgki (Martens, 1860) stat. rev., P. linguaeformis (Morelet, 1875), and P. carinifera (Conrad, 1837), while four other species are described herein as P. acuta sp. nov., P. mekongiana sp. nov., P. kittitati sp. nov., and P. hoikaab sp. nov. In addition, the neotype of P. carinifera is also designated to clarify its long taxonomic ambiguity. Divergent time estimation and historical biogeography analysis revealed that Pilsbryoconcha originated in the area now called the Khorat Plateau around the middle of the Eocene (mean age = 43.12 Mya), before its range was expanded across Indochina through a series of complex geomorphological changes of river systems, which also led to diversification of the genus.

Using Species Groups to Approach the Large and Taxonomically Unresolved Freshwater Fish Family Nemacheilidae (Teleostei: Cypriniformes)

Large animal families with unresolved taxonomy are notoriously difficult to handle with respect to their biodiversity, systematics, and evolutionary history. We approach a large and taxonomically unresolved family of freshwater fishes (Nemacheilidae, >600 species) by proposing, on the basis of morphologic data, a species group within the family and study its phylogeny with conclusions regarding its diversity, taxonomy, and biogeographic history. Phylogenetic analyses of two mitochondrial and three nuclear genes of 139 specimens, representing about 46 species (17 candidate species from the proposed species-group, plus 29 comparative species), revealed that the proposed species group does not form a distinct monophyletic lineage, but that the candidate and comparative species mixed in three different lineages. However, the results revealed more than 20% of undescribed species within the ingroup and showed that species do not cluster according to the presently recognised genera. At least one of the genetic clades shows signs of an eastward range expansion during the second half of Miocene from north India via Myanmar into Laos, western China, and western Thailand. We conclude that the approach of picking monophyletic lineages to study biodiversity, systematics, and evolutionary history helps to open the door to large animal families.