Morphological and molecular diversity patterns of the genus Tropodiaptomus Kiefer, 1932 (Copepoda, Calanoida, Diaptomidae) in Thailand

Abstract

Tropodiaptomus is one of the most specious genera in the family Diaptomidae, but it is often rare in terms of distribution and abundance. Moreover, Tropodiaptomus species show a noteworthy variability in some of the morphological characters considered of prime importance in diaptomid taxonomy, and the presence of cryptic or pseudocryptic species is likely. Thus, through a geographically-wide sampling in Thailand, we aimed to investigate the local diversity of the genus and to compare the morphological and molecular diversity pattern based on mitochondrial and nuclear genes sequences. DNA taxonomy was also implemented in order to check whether the Tropodiaptomus lineages were independent species according to the “evolutionary genetic species concept”. Six Tropodiaptomus morphospecies were found, three of which are putative species new to Science pending a formal description. The finding of such a high incidence of undescribed species stresses the existence of a significant “Linnean shortfall” affecting Thai diaptomids. The molecular results showed that most of the studied species could be identified consistently with their morphology-based taxonomy. However, Tropodiaptomus vicinus and T. cf. lanaonus showed a high level of genetic diversity, suggesting that traditional morphological techniques might be inadequate for correctly assessing their taxonomical status.

Genome-Based Taxa Delimitation (GBTD): A New Approach

“…This threshold raised the suspicion that it might be taxon-specific, so newer approaches capable of leveraging divergence times [3], branching patterns [4], and genetic distance frequencies [5] were developed. These methods were successfully applied to different groups, e.g., leeches [6], gastropods [7] and copepods [8]. However, all these approaches are confined to a single taxonomic level, i.e., species, neglecting the rest of the hierarchic levels of taxonomy.…”

Distribution and Diversity of Diaptomid Copepods in Freshwater Habitats of Cambodia (Crustacea: Copepoda: Calanoida: Diaptomidae)

“…More than 440 diaptomid species are reported worldwide, and 92 and 94 species have been recorded from the Oriental and Western Palearctic regions, respectively [1,2]. The biodiversity of diaptomid copepods in the lower Mekong River Basin is rather well studied, particularly in Thailand [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], where at least 42 species have been recorded. A total of 33 species have been reported in Vietnam [21][22][23][24][25].…”