No abstract

The crabs of the family Pinnotheridae are well known as commensals or parasites, mainly of molluscs and tubeworms. The phylogeny of the group, however, is poorly understood, with preliminary morphological and molecular studies questioning its monophyly. Here we used molecular genetic markers (16S, 12S mitochondrial; histone 3 nuclear) to infer a phylogeny for the family Pinnotheridae De Haan, 1833 to reevaluate the phylogeny and systematics at the level of its subfamilies and genera. Our molecular phylogeny indicated that Parapinnixa cortesi Thoma, Heard, & Vargas, 2005, Parapinnixa hendersoni Rathbun, 1918, Pinnotherelia laevigata H. Milne Edwards & Lucas, 1844, Sakaina yokoyai (Glassell, 1933), Tetrias fischerii (A. Milne-Edwards, 1867) and Tetrias scabripes Rathbun, 1898 should be removed from the family Pinnotheridae, while composition of the present subfamilies, Pinnotherinae De Haan, 1833 and Pinnothereliinae Alcock, 1900, must be revised. At generic level, Clypeasterophilus Campos, 1990, Dissodactylus Smith, 1870, Fabia Dana, 1851, Nepinnotheres Manning, 1993 and Pinnixa White, 1846 were not monophyletic in our analyses. With the exclusion of Pinnotherelia from Pinnotheridae, remaining species of Pinnothereliinae are assigned to Pinnixinae Števčić, 2005, a new subfamily based upon revision and elevation of rank for the tribe Pinnixini Števčić, 2005. In addition, we restructure membership of the subfamily Pinnotherinae and propose Pinnixulalinae, subfam. nov. to accommodate species that were excluded by molecular analyses from the other two subfamilies. These have a firm, wider-than-long carapace with clearly defined regions, strong legs that are usually tuberculate and very setose, and a third maxilliped with an elongate ischiomerus in which the ischium and merus may or may not be indistinguishably fused. Our analyses included 169 pinnotherid exemplars, representing almost half of the genera and about a quarter of the species presently recognised for the family. The relationships within and among some taxa are resolved to greater or lesser extent and the phylogenetic biodiversity of pinnotherid crabs is revealed. However, future publications will most likely result in a further increase in the number of taxa.

For much of terrestrial biodiversity, the evolutionary pathways of adaptation from marine ancestors are poorly understood, and have usually been viewed as a binary trait. True crabs, the decapod crustacean infraorder Brachyura, comprise over 7,600 species representing a striking diversity of morphology and ecology, including repeated adaptation to non-marine habitats. Here, we reconstruct the evolutionary history of Brachyura using new and published sequences of 10 genes for 344 species spanning 88 of 104 families. Using 36 newly vetted fossil calibrations, we infer that brachyurans most likely diverged in the Triassic, with family-level splits in the late Cretaceous and early Paleogene. By contrast, the root age is underestimated with automated sampling of 328 fossil occurrences explicitly incorporated into the tree prior, suggesting such models are a poor fit under heterogeneous fossil preservation. We apply recently defined trait-by-environment associations to classify a gradient of transitions from marine to terrestrial lifestyles. We estimate that crabs left the marine environment at least five and up to 15 times convergently, and returned to the sea from non-marine environments three or four times. Although the most highly terrestrial- and many freshwater-adapted crabs are concentrated in Thoracotremata, Bayesian threshold models of ancestral state reconstruction fail to identify shifts to higher terrestrial grades due to the degree of underlying change required. Lineages throughout our tree inhabit intertidal and marginal marine environments, corroborating the inference that the early stages of terrestrial adaptation have a lower threshold to evolve. Our framework and newly compiled fossil and natural history datasets will enable future comparisons of non-marine adaptation at the morphological and molecular level. Crabs provide an important window into the early processes of adaptation to novel environments, and different degrees of evolutionary constraint that might help predict these pathways.

No abstract

We used the mitochondrial 16S–NADH1 complex, mitochondrial 12S, and nuclear histone 3 genes to examine evolutionary relationships among members of the genus Austinixa Heard & Manning, 1997, and their relationships to other pinnotherids. The monophyly of Austinixa was confirmed by maximum likelihood, Bayesian, and maximum parsimony analyses. Clades recovered on the basis of molecular data agreed with current morphology-based taxonomy at species rank. Morphological characters presently used to distinguish species of Austinixa are not synapomorphic at higher levels and therefore cannot be used to infer cladistic relationships among them. High genetic and morphological intraspecific variation was observed, consistent with patterns of restricted gene flow likely attributable to climatic and geographic history, physical characteristics of contemporary habitats, and host-related constraints on the symbiotic life styles of Austinixa spp. Molecular and morphological characters warrant description of three new species, herein named and illustrated: Austinixa cuestai sp. nov., from Pacific waters of Panama and Nicaragua; Austinixa artankeri sp. nov., from the Caribbean waters of Panama, Colombia, and Venezuela; and Austinixa roblesi sp. nov., from Belize and Panama. All three species inhabit intertidal zones, as do their congeners. To facilitate comparisons and augment the very limited original description, a redescription of the Pacific species Austinixa felipensis (Glassell, 1935) is provided on the basis of paratypes labelled by Glassell and more recently collected topoptypic specimens.