Convergent adaptation of true crabs (Decapoda: Brachyura) to a gradient of terrestrial environments.

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 tips spanning 88 of 109 brachyuran 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 seven and up to 17 times convergently, and returned to the sea from non-marine environments at least twice. 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 extensive new 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.

The Homolidae of the Hawaiian Islands, with notes on the taxonomy of Moloha major (Kubo, 1936) (Crustacea: Decapoda: Brachyura).

Based partly on a collection of homolid crabs captured from baited traps in deep waters off French Frigate Shoals, Northwest Hawaiian Islands, in October 2006, the Hawaiian species of the family Homolidae are reviewed. Known genera and species in the Hawaiian Islands now include two species of Homola (H. orientalis and H. dickinsoni), two species of Lamoha (L. williamsi and L. personata), and five genera that are each represented by a single species (Paramola japonica, Moloha major, Yaldwynopsis hawaiiana, Latreillopsis okala, and Homologenus namakae). Seven of the 14 currently recognized genera of the Homolidae and nine of the 74 known species are now known from Hawaiian waters. Colour notes are included for the first time for two species (H. dickinsoni and Y. hawaiiana). A key to the family Homolidae in Hawaiian waters is included.

A new species of Alvinocaris (Crustacea: Decapoda: Caridea: Alvinocarididae) from Costa Rican methane seeps.

A new caridean shrimp, Alvinocaris costaricensis, is described from methane seeps in the eastern Pacific off Costa Rica. The new species is the 16th described species of the genus, and by molecular analysis appears closest to Alvinocaris komaii from the Lau Basin, southwestern Pacific, but shares certain morphological characters with A. lusca from the Galapagos Rift and A. muricola from the West Florida Escarpment, as well as with A. kexueae from the Manus Basin in the Southwest Pacific.

A 150-million-year-old crab larva and its implications for the early rise of brachyuran crabs.

True crabs (Brachyura) are the most successful group of decapod crustaceans. This success is most likely coupled to their life history, including two specialised larval forms, zoea and megalopa. The group is comparably young, starting to diversify only about 100 million years ago (mya), with a dramatic increase in species richness beginning approximately 50 mya. Early evolution of crabs is still very incompletely known. Here, we report a fossil crab larva, 150 mya, documented with up-to-date imaging techniques. It is only the second find of any fossil crab larva, but the first complete one, the first megalopa, and the oldest one (other fossil ca. 110 mya). Despite its age, the new fossil possesses a very modern morphology, being indistinguishable from many extant crab larvae. Hence, modern morphologies must have been present significantly earlier than formerly anticipated. We briefly discuss the impact of this find on our understanding of early crab evolution.

The emergence of lobsters: phylogenetic relationships, morphological evolution and divergence time comparisons of an ancient group (decapoda: achelata, astacidea, glypheidea, polychelida).

Lobsters are a ubiquitous and economically important group of decapod crustaceans that include the infraorders Polychelida, Glypheidea, Astacidea and Achelata. They include familiar forms such as the spiny, slipper, clawed lobsters and crayfish and unfamiliar forms such as the deep-sea and "living fossil" species. The high degree of morphological diversity among these infraorders has led to a dynamic classification and conflicting hypotheses of evolutionary relationships. In this study, we estimated phylogenetic relationships among the major groups of all lobster families and 94% of the genera using six genes (mitochondrial and nuclear) and 195 morphological characters across 173 species of lobsters for the most comprehensive sampling to date. Lobsters were recovered as a non-monophyletic assemblage in the combined (molecular + morphology) analysis. All families were monophyletic, with the exception of Cambaridae, and 7 of 79 genera were recovered as poly- or paraphyletic. A rich fossil history coupled with dense taxon coverage allowed us to estimate and compare divergence times and origins of major lineages using two drastically different approaches. Age priors were constructed and/or included based on fossil age information or fossil discovery, age, and extant species count data. Results from the two approaches were largely congruent across deep to shallow taxonomic divergences across major lineages. The origin of the first lobster-like decapod (Polychelida) was estimated in the Devonian (∼409-372 Ma) with all infraorders present in the Carboniferous (∼353-318 Ma). Fossil calibration subsampling studies examined the influence of sampling density (number of fossils) and placement (deep, middle, and shallow) on divergence time estimates. Results from our study suggest including at least 1 fossil per 10 operational taxonomic units (OTUs) in divergence dating analyses. [Dating; decapods; divergence; lobsters; molecular; morphology; phylogenetics.].

Redescription of Microprosthema semilaeve (von Martens, 1872) (Decapoda: Stenopodidea: Spongicolidae) and description of a new species of Microprosthema from Dry Tortugas, Florida.

Microprosthema semilaeve, a fairly common spongicolid shrimp of reefal habitats in the Western Atlantic and Caribbean is redescribed and figured based on type material and an additional 78 specimens from the majority of its known zoogeographical range. It is distinguished from the Indo-Pacific species of M. validum and an undescribed species of Microprosthema with which it has been confused in the literature by a number of morphological characters. A new species of Microprosthema from deeper waters off the Dry Tortugas and closely related to M. inornatum Manning & Chace, 1990, is described and illustrated. Microprosthema jareckii Martin, 2002 is synonymized with M. manningi Goy & Felder, 1988. A key to the Western Atlantic species of Microprosthema is presented.

Phylogenetics links monster larva to deep-sea shrimp.

Mid-water plankton collections commonly include bizarre and mysterious developmental stages that differ conspicuously from their adult counterparts in morphology and habitat. Unaware of the existence of planktonic larval stages, early zoologists often misidentified these unique morphologies as independent adult lineages. Many such mistakes have since been corrected by collecting larvae, raising them in the lab, and identifying the adult forms. However, challenges arise when the larva is remarkably rare in nature and relatively inaccessible due to its changing habitats over the course of ontogeny. The mid-water marine species Cerataspis monstrosa (Gray 1828) is an armored crustacean larva whose adult identity has remained a mystery for over 180 years. Our phylogenetic analyses, based in part on recent collections from the Gulf of Mexico, provide definitive evidence that the rare, yet broadly distributed larva, C. monstrosa, is an early developmental stage of the globally distributed deepwater aristeid shrimp, Plesiopenaeus armatus. Divergence estimates and phylogenetic relationships across five genes confirm the larva and adult are the same species. Our work demonstrates the diagnostic power of molecular systematics in instances where larval rearing seldom succeeds and morphology and habitat are not indicative of identity. Larval-adult linkages not only aid in our understanding of biodiversity, they provide insights into the life history, distribution, and ecology of an organism.

Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences.

The remarkable antiquity, diversity and ecological significance of arthropods have inspired numerous attempts to resolve their deep phylogenetic history, but the results of two decades of intensive molecular phylogenetics have been mixed. The discovery that terrestrial insects (Hexapoda) are more closely related to aquatic Crustacea than to the terrestrial centipedes and millipedes (Myriapoda) was an early, if exceptional, success. More typically, analyses based on limited samples of taxa and genes have generated results that are inconsistent, weakly supported and highly sensitive to analytical conditions. Here we present strongly supported results from likelihood, Bayesian and parsimony analyses of over 41 kilobases of aligned DNA sequence from 62 single-copy nuclear protein-coding genes from 75 arthropod species. These species represent every major arthropod lineage, plus five species of tardigrades and onychophorans as outgroups. Our results strongly support Pancrustacea (Hexapoda plus Crustacea) but also strongly favour the traditional morphology-based Mandibulata (Myriapoda plus Pancrustacea) over the molecule-based Paradoxopoda (Myriapoda plus Chelicerata). In addition to Hexapoda, Pancrustacea includes three major extant lineages of 'crustaceans', each spanning a significant range of morphological disparity. These are Oligostraca (ostracods, mystacocarids, branchiurans and pentastomids), Vericrustacea (malacostracans, thecostracans, copepods and branchiopods) and Xenocarida (cephalocarids and remipedes). Finally, within Pancrustacea we identify Xenocarida as the long-sought sister group to the Hexapoda, a result confirming that 'crustaceans' are not monophyletic. These results provide a statistically well-supported phylogenetic framework for the largest animal phylum and represent a step towards ending the often-heated, century-long debate on arthropod relationships.

Resolving arthropod phylogeny: exploring phylogenetic signal within 41 kb of protein-coding nuclear gene sequence.

This study attempts to resolve relationships among and within the four basal arthropod lineages (Pancrustacea, Myriapoda, Euchelicerata, Pycnogonida) and to assess the widespread expectation that remaining phylogenetic problems will yield to increasing amounts of sequence data. Sixty-eight regions of 62 protein-coding nuclear genes (approximately 41 kilobases (kb)/taxon) were sequenced for 12 taxonomically diverse arthropod taxa and a tardigrade outgroup. Parsimony, likelihood, and Bayesian analyses of total nucleotide data generally strongly supported the monophyly of each of the basal lineages represented by more than one species. Other relationships within the Arthropoda were also supported, with support levels depending on method of analysis and inclusion/exclusion of synonymous changes. Removing third codon positions, where the assumption of base compositional homogeneity was rejected, altered the results. Removing the final class of synonymous mutations--first codon positions encoding leucine and arginine, which were also compositionally heterogeneous--yielded a data set that was consistent with a hypothesis of base compositional homogeneity. Furthermore, under such a data-exclusion regime, all 68 gene regions individually were consistent with base compositional homogeneity. Restricting likelihood analyses to nonsynonymous change recovered trees with strong support for the basal lineages but not for other groups that were variably supported with more inclusive data sets. In a further effort to increase phylogenetic signal, three types of data exploration were undertaken. (1) Individual genes were ranked by their average rate of nonsynonymous change, and three rate categories were assigned--fast, intermediate, and slow. Then, bootstrap analysis of each gene was performed separately to see which taxonomic groups received strong support. Five taxonomic groups were strongly supported independently by two or more genes, and these genes mostly belonged to the slow or intermediate categories, whereas groups supported only by a single gene region tended to be from genes of the fast category, arguing that fast genes provide a less consistent signal. (2) A sensitivity analysis was performed in which increasing numbers of genes were excluded, beginning with the fastest. The number of strongly supported nodes increased up to a point and then decreased slightly. Recovery of Hexapoda required removal of fast genes. Support for Mandibulata (Pancrustacea + Myriapoda) also increased, at times to "strong" levels, with removal of the fastest genes. (3) Concordance selection was evaluated by clustering genes according to their ability to recover Pancrustacea, Euchelicerata, or Myriapoda and analyzing the three clusters separately. All clusters of genes recovered the three concordance clades but were at times inconsistent in the relationships recovered among and within these clades, a result that indicates that the a priori concordance criteria may bias phylogenetic signal in unexpected ways. In a further attempt to increase support of taxonomic relationships, sequence data from 49 additional taxa for three slow genes (i.e., EF-1 alpha, EF-2, and Pol II) were combined with the various 13-taxon data sets. The 62-taxon analyses supported the results of the 13-taxon analyses and provided increased support for additional pancrustacean clades found in an earlier analysis including only EF-1 alpha, EF-2, and Pol II.

Phylogenetic relationships within the coral crab genus Carpilius (Brachyura, Xanthoidea, Carpiliidae) and of the Carpiliidae to other xanthoid crab families based on molecular sequence data.

The coral crab genus Carpilius currently includes three widely distributed species that inhabit tropical coral reefs and adjacent waters. The relationship of Carpilius to other xanthoid crabs is unknown. Previously, carcinologists considered Carpilius to be allied with crabs of the family Xanthidae (e.g., Euryozius, Liagore, and Liomera), however, recent workers have considered it to be a monotypic genus within its own family, Carpiliidae. Mitochondrial 12S- and 16S-rDNA gene fragments confirm the monophyly and distinct status of the family Carpiliidae. Within the genus Carpilius, the Caribbean species C. corallinus is basal to the two Pacific species C. maculatus and C. convexus. The Pacific species are sister taxa, despite the greater morphological resemblance of C. corallinus to the Pacific C. convexus. The relationship of the Carpiliidae (Carpilius) to other xanthoid crabs is investigated, and results of a preliminary analysis of higher xanthoid relationships did not resolve the relationships of Carpiliidae, "Xanthidae," Menippidae, Trapeziidae, and Ocypodidae to one another. A Menippidae and Carpilius relationship could not be rejected, although a Liomera, Liagore, and Carpilius relationship was.

Comparison of the carpal cleaning brush in two genera of hydrothermal vent shrimp (Crustacea, Decapoda, Bresiliidae).

Clusters of specialized serrate setae in patches called "carpal cleaning brushes," or carpal-propodal brushes, are found on the distal margins of the chelipedal carpus in many species of caridean shrimps and other decapod crustaceans. These brushes, used to clean the antennal flagellum, occur in some bresiliid shrimp species associated with hydrothermal vents in the Pacific and Atlantic oceans, and recently their presence has been proposed as a distinguishing taxonomic character at the genus level. Occurrence of such brushes in shrimp that live near hydrothermal vents is of interest because of the high number of bacteria associated with these vents. These shrimp have the potential to be heavily fouled with bacteria, whereas at the same time preliminary studies suggest that they may depend upon these bacteria at least in part (or possibly exclusively) for food. We employ scanning electron microscopy to examine and describe the general morphology and location of carpal brushes on the chelipeds of all known species in two vent shrimp genera, Rimicaris Williams and Rona and Chorocaris Martin and Hessler. The brush is well developed and clearly delimited in all known species of Chorocaris, where it consists of a triangular field of serrate setae and a posterior blunt spine that possibly functions as a "stop" to keep the antennal flagellum in place during grooming. Rimicaris exoculata has no recognizable carpal cleaning brush or any serrate setae on the chelipedal carpus and thus appears derived relative to species of Chorocaris with regard to this feature. A newly described species, R. aurantiaca, is somewhat intermediate, having no carpal brush but with two serrate setae and a blunt spine in the region occupied by the brush in species of Chorocaris. Possible implications and comparisons to the genera Alvinocaris and Opapaele are discussed briefly. J. Morphol. 235:31-39, 1998. © 1998 Wiley-Liss, Inc.

Ultrastructure of the frontal sensory fields in the Lynceidae (Crustacea, Branchiopoda, Laevicaudata).

The clam shrimp family Lynceidae is unusual in possessing paired fields of short setae on either side of the rostral carina. We describe the position of these fields relative to the direction of water movement in live animals as well as the external and internal structure of these setae. The majority of morphological features support a presumed chemosensory role for these sensilla. These features include the lack of a setal socket and the relatively short length of each seta. The low number of enveloping cells (three or four) is uncharacteristic of chemosensory setae and is more typical of mechanoreceptors, as is the absence of any pores on the setae; these characteristics indicate that these fields may have both functions. © 1994 Wiley-Liss, Inc.