Let's get high: Cladogenesis in freshwater crabs (Decapoda: Potamonautidae: Potamonautes) supports the mountain gradient speciation hypothesis in the Cape Fold and Drakensberg Mountains, South Africa

During the present study, the evolutionary relationship within a clade of mountain clade of freshwater crabs (Potamonautes) was examined using mtDNA sequence data for species from the Cape Fold Mountain (CFM) and Great Escarpment (Drakensberg Mountain range). We undertook phylogenetic analyses, divergence time estimation, and an ancestral area reconstruction to explore the period of cladogenesis and understand the biogeographic history in this high-altitude clade. Furthermore, we applied four species delimitation methods using ASAP, bPTP, bGMYC, and STACEY on the latter clade. Bayesian phylogenetic analyses retrieved a monophyletic freshwater crab clade comprised of two major sister clades, one comprised of the Cape Fold (clade A) and two comprised of Drakensberg Mountains (clade B) species. Divergence time estimation indicated that the two clades underwent Mio/Pliocene cladogenesis. Within the CFM clade (A), P. amathole (Amathola Mountains) was sister to P. parvispina (Cederberg and Kouebokkeveld Mountains) and the latter species were sister to P. parvicorpus (Cape Peninsula, Jonkershoek, and Helderberg Mountains) sister to P. tuerkayi (Overberg Mountains) and P. brincki (Hottentots Holland Mountains). Within the Drakensberg Mountain clade (B), we observed in situ diversification. Specimens from the southcentral Drakensberg Mountains (Dargle Forest, Injasuti, Karkloof, and Impendle) represent a new undescribed lineage Potamonautes sp. nov. 1. The second clade from the northern Drakensberg, representing P. clarus, was sister to a central Drakensberg Mountain clade that comprised P. depressus that was in turn sister to P. baziya from the Eastern Cape Province. The application of species delimitation methods generally overestimated the number of species. The biogeographic analyses indicated that the Eastern Cape Province is the most likely ancestral range area. Ecological niche modelling of representative species in clades A (Cape Fold Mountains) and B (Drakensberg Mountains) demonstrated that temperature and rainfall were the major abiotic drivers that differentiated the two clades. Our data favours the mountain gradient speciation hypothesis.

Description of a new montane freshwater crab (Arthropoda, Malacostraca, Decapoda, Potamonautidae) from the Eastern Cape, South Africa

A new species of freshwater crab, Potamonautesamatholesp. nov., is described from the Winterberg-Amathole mountain range in the Eastern Cape Province, South Africa. Morphologically, P.amathole Peer & Gouws, sp. nov. most closely resembles P.tuerkayi but can be distinguished by key morphological characters including the variation in the shape of the subterminal segment of gonopod 2 between both species. Genetically, P.amathole Peer & Gouws, sp. nov. is placed within the clade of small-bodied, mountain-dwelling crabs including P.parvispina, P.parvicorpus, P.brincki, P.tuerkayi, P.baziya, and P.depressus. The new species is found in slow-moving mountain streams and pools at high altitudes. The continued discovery and description of new freshwater crab species reinforces the need for ongoing research, especially in under-sampled regions.

Cryptic and widespread: a recipe for taxonomic misidentification in a freshwater crab species (Decapoda: Potamonautidae:Potamonautes sidneyi) as evident from species delimitation methods

We examined the systematics of a ubiquitously distributed southern African freshwater crab, Potamonautes sidneyi s.l. species complex. Specimens were subjected to DNA sequence analyses of two mitochondrial loci (16S rRNA + COI). We applied three species delimitations methods (ASAP, bGMYC and bPTP) to test their utility in delineating species boundaries in Potamonautes and three additional Afrotropical genera (Liberonautes, Nesonautes and Seychellum). The combined mtDNA dataset retrieved five clades. Clade 1 comprised of P. barbarai, clade 2 comprised of specimens from the interior of the Great Karoo Basin, sister to P. sidneyi s.s. in clade 3. Clade 4 was confined to Eswatini and the Mpumalanga Province of South Africa, and sister to clade 5 that comprised P. danielsi. The three species delimitation methods either over- or underestimated the number of species. Phylogenetically, specimens from the Great Karoo Basin (clade 2) were equidistant to P. sidneyi s.s. and P. perlatus, while the Eswatini and Mpumalanga specimens (clade 4) were sister to P. danielsi. Clades 2 and 4 are herein described as P. karooensis sp. nov. and P. valles sp. nov., respectively.

A new multilocus phylogeny reveals overlooked diversity in African freshwater crabs (Brachyura: Potamoidea): a major revision with new higher taxa and genera

The taxonomy of 185 species of Afrotropical freshwater crabs is revised to conform to the updated phylogenetic relationships within this large assemblage, based on the largest taxonomic sampling to date (that includes almost all genera and 57% of the species). Four DNA loci were sequenced including three mitochondrial loci (COI, 12S rRNA, 16S rRNA) and one nuclear locus (histone 3), and evolutionary relationships were estimated using maximum likelihood and Bayesian approaches. The divergence times of the major clades were estimated with a Yule tree prior and an uncorrelated lognormal relaxed molecular clock. The taxonomic acts proposed here include the recognition of two Afrotropical families of freshwater crabs (Potamonautidae and Deckeniidae) each with two subfamilies. In the revised Potamonautidae, three new tribes and three new genera (Maritimonautes gen. nov., Nesonautes gen. nov., Occidensonautes gen. nov.), are established, three previously published genera are revised and four subgenera are raised to genus (Arcopotamonautes, Lirrangopotamonautes, Longipotamonautes, Rotundopotamonautes). An updated species list and identification keys for the new taxa, revised distribution maps, digital images and illustrations of diagnostic characters are provided.

Divergent evolutionary origins and biogeographic histories of two freshwater crabs (Brachyura: Potamonautes) on the West African conveyer belt islands of São Tomé and Príncipe

We examined the colonization history and phylogeographic structure of the two endemic freshwater crab species (Potamonautes margaritarius and P. principe) inhabiting the volcanic islands of São Tomé and Príncipe, respectively, using mitochondrial and nuclear DNA sequence data. All samples were sequenced for the mtDNA COI locus and used in the phylogeographic analyses, while a single specimen per lineage was sequenced for the two remaining loci (16S rRNA and histone 3) and used in the phylogenetic reconstruction. Phylogenetic results reveal that P. principe diverged early within a clade of East/Southern African Potamonautes during the Miocene, while P. margaritarius diverged between the Late Eocene to Early Miocene. Furthermore, the two species are not sister taxa and are distantly related. These results corroborate previously hypothesised independent transoceanic dispersal events that resulted in the establishment of the endemic freshwater crab fauna of the two islands. Within P. margaritarius, we observed two reciprocally monophyletic clades on São Tomé Island. Clade one occurred in the southeast and southwest of the island, while clade two occurred in the northeast and the northwest; the divergence between the latter two clades was estimated to be of Pleistocene age. The two clades within P. margartarius are genetically highly structured and characterised by the absence of shared maternal haplotypes, suggesting possible speciation within P. margartarius. In contrast P. principe exhibits a shallow population genetic structure. Possible mechanisms of colonization and cladogenesis in the two freshwater crabs are discussed.