What is Sesarmops impressus (H. Milne Edwards, 1837) (Crustacea: Brachyura: Sesarmidae)?

Minuca panema (Coelho, 1972): Resurrection of a Fiddler Crab Species from Brazil Closely Related to Minuca burgersi (Holthuis, 1967) (Crustacea, Decapoda, Brachyura, Ocypodidae)

We redescribe a species of fiddler crab, Minuca panema (Coelho, 1972), from the Atlantic coast of South America. It is closely related to M. mordax (Smith, 1870), and until now, the taxon has been considered to be synonymous with another closely related species Minuca burgersi (Holthuis, 1967). However, we found that two clades of M. burgersi sensu lato were restricted to the Caribbean Basin. This distribution differs from than that of M. panema, which occurs primarily along the eastern coast of South America, ranging from the island of Trinidad to Praia da Armação, Santa Catarina, Brazil. Based on our field studies, the geographical boundary between M. burgersi sensu stricto and M. panema is the Tobago Basin, north of Trinidad. Since the two species diverged only 3 to 4 million years ago, as dated from the phylogeny of the genus Minuca Bott 1954, there are few reliable morphological features that can be used to distinguish them clearly. In live crabs, there is a striking difference in coloration between the cherryred South American M. panema and the rusty-red Caribbean M. burgersi sensu lato. In males, the pattern of tubercles on the inner surface of the major cheliped varies between the two species. In females, the vulva is slightly larger in M. burgersi sensu stricto. Ocean tides and currents together with siltation owing to freshwater outflow from the Amazon and Orinoco rivers most likely have driven the divergence of these species. In the Caribbean, small tidal amplitudes have minimized long-distance gene flow in M. burgersi sensu stricto from isolated insular lagoons. In contrast, large tidal amplitudes and exposed habitats on riverbanks along the eastern Atlantic coast of South America have enabled long-distance dispersal in M. panema. DNA analysis reveals that haplotypes of cytochrome c oxidase subunit 1 are not shared between the species. Since natural selection and/or genetic drift have yet to produce extensive morphological divergences between M. panema and M. burgersi sensu stricto, we speculate that changes in the genes regulating mitochondrial DNA functions have led to speciation at the molecular level. According to the mitonuclear compatibility concept, we propose that mitochondrial DNA may be at the forefront of speciation events and that co-evolved mitonuclear interactions are responsible for some of the earliest genetic incompatibilities arising among isolated populations.

Diversity in the Taiwanese Swimming Crabs (Crustacea: Brachyura: Portunidae) Estimated through DNA Barcodes, with Descriptions of 14 New Records

The swimming crabs (family Portunidae) are distributed worldwide and commonly inhabit estuaries, mangroves, reefs, shallow and the deep sea. Previously, 75 species and 19 genera in this family were known to Taiwan. Our study examined specimens in Taiwanese waters, including the islands, collected between 2016 and 2020 or deposited in museums. Through the cytochrome oxidase subunit I DNA barcode marker and morphological examination, 71 species were identified. The minimum interspecific distances were greater than 4.09%, except in two unresolved groups: Charybdis miles (De Haan, 1835) and Ch. sagamiensis Parisi, 1916, as well as Thranita pelsarti (Montgomery, 1931) and Thr. prymna (Herbst, 1803). In addition, 14 species belonging to nine genera were confirmed as new records to Taiwan, viz. Carupa ohashii Takeda, 1993, Lupocyclus inaequalis (Walker, 1887), Luu. tugelae Barnard, 1950, Lupocycloporus minutus (Shen, 1937), Monomia gladiator (Fabricius, 1798), M. lucida Koch & Ďuriš, 2018, Podophthalmus minabensis Sakai, 1961, Thalamita gatavakensis Nobili, 1906, Tha. spinifera Borradaile, 1902, Thalamitoides quadridens A. Milne-Edwards, 1869, Tho. tridens A. Milne-Edwards, 1869, Thr. cerasma (Wee & Ng, 1995), Thr. coeruleipes (Hombron & Jacquinot, 1846) and Xiphonectes tuberculosus (A. Milne-Edwards, 1861). This study thus raises the total number of Portunidae species in Taiwan to 89.

The role of anthropogenic disturbance and invasion of yellow crazy ant in a recent decline of land crab population

The yellow crazy ant, Anoplolepis gracilipes was first reported in Kenting National Park, Taiwan, in the 2000s, raising the concern of this invasive ant's potential effects on the native land crab populations. We investigated the distribution and abundance of A. gracilipes and its adverse effect on the land crab populations at four land crab hotspots within the park. Our survey results indicated that A. gracilipes was widespread and abundant at three of the study sites (Hsiangchiaowan, Shadao, and Natural Spring), while the distribution was much more confined at the fourth site (Houwan). Land crab populations experienced a notable decline at all the study sites except Houwan, indicating an inverse relationship between the population of land crabs and distribution/abundance of A. gracilipes. Combining the results of visual observations, the decline of land crab populations can be attributed, at least partially, to direct attacks by A. gracilipes on land crabs in their natural habitat and during the breeding migration season. Generalized additive model showed that worker abundance of this ant is associated with human disturbance levels, suggesting that anthropogenic disturbance may have contributed to the decline in land crab populations via promoting the abundance of A. gracilipes.

Diversity of Taiwanese Brackish Crabs Genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) based on DNA Barcodes, with Descriptions of Two New Species

Species in the brackish crab genus Ptychognathus are common in the seashore and estuary habitats with freshwater input. Due to their similar morphologies and dull colorations, it is always difficult to distinguish the species in this genus. In this study, the DNA barcode gene COI (cytochrome c oxidase subunit I) was used to help identify Ptychognathus from Taiwan. The results showed that the 10 species can be identified successfully based on COI, with intraspecific distances below 1.54% and interspecific distances of 12.2%-19.57%. In addition, two new species of Ptychognathus are described from Taiwan. Ptychognathus makii sp. nov. from southern Taiwan is similar to P. altimanus (Rathbun, 1914), and P. stimpsoni sp. nov. from southern Taiwan and the southern Philippines resembles P. aff. barbatus (A. Milne-Edwards, 1873) and P. pusillus Heller, 1865. Both species can be distinguished from other congeners by a suite of characters, including the carapace, orbital region, frontal region, telson of male pleon, male first gonopod, and setae on ambulatory legs.