Phylogeny of the genus Austinixa Heard & Manning, 1997, inferred from mitochondrial and nuclear molecular markers, with descriptions of three new species and redescription of Austinixa felipensis (Glassell, 1935) (Decapoda: Brachyura: Pinnotheridae)

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.

A Review of the Ecomorphology of Pinnotherine Pea Crabs (Brachyura: Pinnotheridae), with an Updated List of Symbiont-Host Associations

“…In contrast to the morphological variation within the Pinnotherinae, members within the Pinnixinae, Pinixulalinae, and Pinnothereliinae all share a similar body shape. All representatives of these taxonomic groups have a flattened, wide carapace shape, and usually a third ambulatory leg that is larger in size than the other ones ( Figure 1D-F) [18]. This body shape is thought to be the result of the symbiotic lifestyle of these crabs within the tubes and burrows of worms and decapods such as mud shrimps [50].…”

“…Although the crabs from these three subfamilies appear to be morphologically similar, Manning and Felder [51] discuss very slight intraspecific ecophenotypic variation, resulting from the crabs living in burrows from related but separate species of Callianassa mud shrimps. In addition, Palacios Theil and Felder [18] mentioned that the diversity of body shapes is the result of convergent evolution, resulting from host choices, rather than shared synapomorphies. Furthermore, a few non-pinnotherine pea crabs are known from atypical hosts: living inside and on hosts usually inhabited by pinnotherines.…”

“…A few examples are the last pair of ambulatory legs of sponge crabs (Dromiidae) and carrier crabs (Dorippidae), the subchelate ambulatory legs of zebra crabs (Pilumnidae: Eumedoninae), and flexible dactylo-propodal articulation of coral-clinging crabs (Tetraliidae) [2]. The Pinnotheridae form no exception, since the most apparent feature of the tube-dwelling pinnixine, pinnixulaline, and pinnothereliine crabs are the wide third pair of ambulatory legs for gripping the walls of shared burrows and tubes [18]. The Pinnotherinae have more subtle morphological adaptations of the ambulatory legs, which are discussed below.…”

“…The phylogenetic significance of the morphological adaptations can be examined by linking the adaptations with recent molecular phylogenetic reconstructions [5,18]. Most adaptive features seem to be the result of convergent evolution, rather than shared synapomorphies [5], and these are: the size, ornamentations, colour patterns, and setation of the carapace, in addition to the differences between male and female carapaces; the morphology of the eyes, rostrum, third maxillipeds [85], and the specialised feeding structures on the chelipeds.…”

“…Due to their small size and cryptic way of living, the adaptations pinnotherines have evolved in order to live in and on their host are barely understood [18]. This study aims to review the anatomy and hypothesized functional roles of the anatomical structures in pinnotherines, and to illustrate a number of these anatomical features.…”