Due to the lack of visible barriers to gene flow, it was a long-standing assumption that marine coastal species are widely distributed, until molecular studies revealed geographically structured ...intraspecific genetic differentiation in many taxa. Historical events of sea level changes during glacial periods are known to have triggered sequential disjunctions and genetic divergences among populations, especially of coastal organisms. The Parasesarma bidens species complex so far includes three named plus potentially cryptic species of estuarine brachyuran crabs, distributed along East to Southeast Asia. The aim of the present study is to address phylogeography and uncover real and hidden biological diversity within this complex, by revealing the underlying genetic structure of populations and species throughout their distribution ranges from Japan to West Papua, with a comparison of mitochondrial COX1 and 16S rRNA gene sequences. Our results reveal that the P. bidens species complex consists of at least five distinct clades, resulting from four main cladogenesis events during the mid to late Pleistocene. Among those clades, P. cricotum and P. sanguimanus are recovered as monophyletic taxa. Geographically restricted endemic clades are encountered in southeastern Indonesia, Japan and China respectively, whereas the Philippines and Taiwan share two clades. As individuals of the Japanese clade can also be found in Taiwan, we provide evidence of a third lineage and the occurrence of a potential cryptic species on this island. Ocean level retreats during Pleistocene ice ages and present oceanic currents appear to be the main triggers for the divergences of the five clades that are here addressed as the P. bidens complex. Secondary range expansions converted Taiwan into the point of maximal overlap, sharing populations with Japan and the Philippines, but not with mainland China.
Abstract
Parasesarma is a species-rich genus whose representatives are common in wetlands and mangroves of the Indo-Pacific. Morphologically, the genus is heterogeneous and has been postulated to ...constitute a polyphyletic taxon. In the present study, most species of Parasesarma are re-evaluated phylogenetically, using mitochondrial and nuclear molecular markers. The results show that the majority of the examined species cluster consistently with the type species Parasesarma plicatum. However, some species, among them the tree-climbing Parasesarma leptosoma, are clearly separated from this main clade of Parasesarma, forming a second stable monophyletic group, distinct from other known genera. Based on these results, and with additional support by morphological diagnoses highlighting consistent differences between the two species groups, we propose a new genus for the species clustering around P. leptosoma, proposing the new name Leptarma gen. nov.
A new species of Parasesarma, P. rahayuae n. sp., is described from Sulawesi, Indonesia. Genetically, the new species is distinct from all other known species of Parasesarma and has a close ...phylogenetic relationship with P. anambas Yeo, Rahayu & Ng, 2004 and P. gemmatum Li, Shih & Ng, 2019. Morphologically, the new species most closely resembles P. anambas and P. gemmatum, but can be distinguished from these two species by the shape of the dactylar tubercles of the male chela and of the male first gonopod. This is the fourth species of Parasesarma recorded from Sulawesi, and with its description, the number of species assigned to the genus Parasesarma is 58.
Fiddler crabs (Brachyura, Ocypodidae), like many other marine organisms, disperse via planktonic larvae. A lengthy pelagic larval duration is generally assumed to result in genetic connectivity even ...among distant populations. However, major river outflows, such as of the Amazon or Orinoco, or strong currents may act as phylogeographic barriers to ongoing gene flow. For example, the Mona Passage, located between Puerto Rico and Hispaniola, has been postulated to impair larval exchange of several species. In this study, Cox1 mtDNA data was used to analyze population genetic structure of two fiddler crab species from the western Atlantic, comparing the continental coastline and Caribbean islands. The results indicate genetic homogeneity in Minuca rapax among Atlantic (continental) populations (Suriname, Brazil), whereas Caribbean populations show significantly restricted gene flow among the constituent islands and towards continental populations. Our data support the hypothesis of the Mona Passage hindering larval exchange. Contrastingly, Caribbean Leptuca leptodactyla populations appear to be devoid of detectable variation, while Atlantic-continental (i.e. Brazilian) populations show much higher haplotype and nucleotide diversities and display slight genetic differentiation among populations within the Atlantic region, though not statistically significant. Both species show a pronounced divergence between regions, supporting the presence of a phylogeographic barrier.
Crabs of the infra-order Brachyura are one of the most diverse groups of crustaceans with approximately 7,000 described species in 98 families, occurring in marine, freshwater, and terrestrial ...habitats. The relationships among the brachyuran families are poorly understood due to the high morphological complexity of the group. Here, we reconstruct the most comprehensive phylogeny of Brachyura to date using sequence data of six nuclear protein-coding genes and two mitochondrial rRNA genes from more than 140 species belonging to 58 families. The gene tree confirms that the “Podotremata,” are paraphyletic. Within the monophyletic Eubrachyura, the reciprocal monophyly of the two subsections, Heterotremata and Thoracotremata, is supported. Monophyly of many superfamilies, however, is not recovered, indicating the prevalence of morphological convergence and the need for further taxonomic studies. Freshwater crabs were derived early in the evolution of Eubrachyura and are shown to have at least two independent origins. Bayesian relaxed molecular methods estimate that freshwater crabs separated from their closest marine sister taxa ∼135 Ma, that is, after the break up of Pangaea (∼200 Ma) and that a Gondwanan origin of these freshwater representatives is untenable. Most extant families and superfamilies arose during the late Cretaceous and early Tertiary.
The Pleistocene cyclic sea-level fluctuations are thought to have markedly affected the distribution and genetic architecture of Atlanto-Mediterranean biota. Despite the acknowledged key role played ...by these historical events in shaping population genetic structure of marine species, little is still known about the processes involved in shaping the spatial distribution of genetic variation within intertidal species. We intended in this study to reconstruct the phylogeography of a common and widely distributed coastal species across the East Atlantic and Mediterranean Sea (the warty crab Eriphia verrucosa), aiming to unravel potential microevolutionary processes likely involved in shaping its genetic polymorphism. For this purpose, a total of 155 specimens of E. verrucosa from 35 locations across the entire distribution range were analyzed by comparing a 453 basepairs region of the mitochondrial gene cytochrome oxidase subunit 1 (Cox1).
Our results unveiled the prevalence of high genetic connectivity among East Atlantic and Mediterranean populations, with noticeable genetic distinctiveness of the peripheral population from the Azores. Spatio-temporal patterns of genetic diversification and demographic history allowed retrieving genetic imprints of late Pleistocene vicariant event across the Gibraltar Strait followed by subsequent postglacial expansion events for both the East Atlantic and Mediterranean regions. Integrative evidences from the outcomes of comparison of regional genetic diversification, as well as evolutionary and biogeographic histories reconstructions, support the existence of potential glacial refugia for E. verrucosa in the East Atlantic and western Mediterranean. Our results also revealed low levels of genetic variability along with recent demographic and spatial expansion events for eastern Mediterranean warty crabs, suggesting that the eastern areas within the distribution range of the species might have been recently colonized from putative glacial refugia.
These findings provide new insights into the phylogeography and evolutionary history of a common but poorly studied Atlanto-Mediterranean decapod species. Specifically, they contribute to the understanding of the impact of historical processes on shaping contemporary population genetic structure and diversity in intertidal marine species.
Abstract
The crab genus Perisesarma De Man, 1895 has been shown to be a polyphyletic taxon comprising morphologically heterogeneous species. Some members of the genus have a close phylogenetic ...relationship with the sister genus Parasesarma De Man, 1895, with which it shares many morphological similarities, except for the existence of an epibranchial tooth in Perisesarma. This study uses morphological and molecular approaches to reconstruct phylogenetic relationships of Perisesarma and related genera and to evaluate the phylogenetic importance and taxonomic usefulness of the epibranchial tooth. As genetic markers we use two mitochondrial and one nuclear gene. A comparative morphological analysis reveals that a clean separation between species of Parasesarma and Perisesarma is not possible, because of intermediate conformations of the epibranchial tooth. In our molecular analysis, most species of Perisesarma cluster solidly together with species of Parasesarma, but without being reciprocally monophyletic. Morphology and genetics also indicate that the West African species of Perisesarma and the Indo-Pacific P. fasciatum are markedly different from all other species of the genus. Therefore, we here suggest with robust double support a new classification, transferring most species of Perisesarma to Parasesarma and the three West African representatives and P. fasciatum into new genera, thereby restricting the genus Perisesarma to the type species P. dusumieri.
A new freshwater crab of the potamid genus Candidiopotamon Bott, 1967, is described from eastern Taiwan. Candidiopotamon penglai sp. nov. is morphologically similar to C. rathbuni (De Man, 1914) from ...western Taiwan, but can be distinguished by the morphology of the male first gonopod (G1), as well as by their mitochondrial DNA (16S rRNA and COI genes). In the G1 of C. rathbuni, the subterminal segment shows a cline from robust in northern populations to slender in southern populations. In the G1 of C. penglai sp. nov., a distinctly larger and more distally directed keel-like projection is found on the distal inner edge of the terminal segment, with northern populations having an inward-curving subterminal segment and southern populations a straight subterminal segment. The genetic differentiation of the two species of Candidiopotamon within Taiwan is discussed, and morphological differences are compared. A key to the species of Candidiopotamon is also provided.
The faunal and floral relationship of northward-drifting India with its neighboring continents is of general biogeographic interest as an important driver of regional biodiversity. However, direct ...biogeographic connectivity of India and Southeast Asia during the Cenozoic remains largely unexplored. We investigate timing, direction and mechanisms of faunal exchange between India and Southeast Asia, based on a molecular phylogeny, molecular clock-derived time estimates and biogeographic reconstructions of the Asian freshwater crab family Gecarcinucidae.
Although the Gecarcinucidae are not an element of an ancient Gondwana fauna, their subfamily Gecarcinucinae, and probably also the Liotelphusinae, evolved on the Indian Subcontinent and subsequently dispersed to Southeast Asia. Estimated by a model testing approach, this dispersal event took place during the Middle Eocene, and thus before the final collision of India and the Tibet-part of Eurasia.
We postulate that the India and Southeast Asia were close enough for exchange of freshwater organisms during the Middle Eocene, before the final Indian-Eurasian collision. Our data support geological models that assume the Indian plate having tracked along Southeast Asia during its move northwards.
The swimming crab
Charybdis hellerii
is an invader with global distribution in warm waters. Native to the Indo-Pacific, this species invaded the eastern Mediterranean Sea after the Suez Canal ...opening. In 1987, it was first reported in the Western Atlantic, probably transported via ballast water of ships. Since then, it has been registered from many localities along the American coast from the USA to southern Brazil where it has rapidly established reproducing populations. Our main aim was to investigate the introduction history of this species along the American coast, using a phylogeographic approach. Additionally, we attempted to clarify the identity of this invasive species by molecular analyses and morphological assessment in order to provide a basis for our main investigation.
C. hellerii
was confirmed as a single species, but both cytochrome c oxidase subunit I and 16S rDNA revealed a genetic structure, splitting the potential source populations of American introductions into two groups: “western Indian Ocean and Mediterranean Sea” (WIO + MS) versus “eastern Indian + western Pacific oceans” (EIO + WPO). Most specimens from America clustered with the former group, supporting the hypothesis that the Mediterranean Sea represented the main source of Western Atlantic populations. However, the clustering of animals from southern Brazil with the latter group indicates that introductions from the eastern Indian or Pacific oceans must also have occurred. The existence of a third group, found exclusively within the American range and genetically related to EIO + WPO, also indicates an independent introduction from an unsampled locality from the native range. The haplotype and nucleotide diversities of American localities were comparable to those of source populations, contradicting a founder effect prediction. This finding might be related to the high propagule pressure associated with introductions via ballast water and the occurrence of multiple introductions from genetic distinct sources. The direct comparison of the haplotype numbers suggested no genetic bottleneck during introduction from the Mediterranean Sea, but a bottleneck might have occurred during introductions from the eastern Indian or Pacific oceans.
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