Phylogeny and phylogeography of the land hermit crab Coenobita purpureus (Decapoda: Anomura: Coenobitidae) in the Northwestern Pacific Region

Hermit crabs of the family Coenobitidae comprise the land hermit crabs, with 16 Coenobita species, and the coconut crab Birgus latro. They are terrestrial but spend their marine life as planktonic larvae. Some coenobitid crabs are widely distributed in the Indo‐West Pacific region, and some species occupy narrower ranges. To improve our knowledge of coenobitid crab speciation and geographical distribution patterns, we examined the phylogenetic relationship between Coenobita purpureus, which has a narrow distribution in the Northwestern Pacific, and its more widely distributed coenobitids including B. latro, Coenobita brevimanus, Coenobita cavipes, Coenobita perlatus, Coenobita rugosus and Coenobita violascens based on the mtDNA cytochrome c oxidase subunit I (COI) and 16S rDNA genes. We also assessed the phylogeography of Co. purpureus populations based on the COI gene. Our phylogenetic and phylogeographical analyses revealed that (i) Co. purpureus clustered with Co. rugosus and (ii) the Co. purpureus population in the Ogasawara Islands was genetically distinct from those in other regions, which showed genetic panmixia. It has been hypothesized that Co. purpureus evolved in the isolated landmasses of the Ryukyu region during the Pliocene, and that its population expanded and colonized the Ogasawara Islands in the late Pleistocene. Further phylogeographical studies on Coenobita species with relatively narrow distributions coupled with characterization of their phylogenetic relationships with widely distributed congeners will advance our knowledge of the speciation and geographical distribution history of coenobitid crabs.     

Fine‐scale phylogeography reveals cryptic biodiversity in Pederson's cleaner shrimp,Ancylomenes pedersoni (Crustacea: Caridea: Palaemonidae), along the Florida Reef Tract

Populations of continuously distributed marine organisms that disperse via pelagic larvae are often assumed to exist in a state of genetic panmixia because of their potential ability for long‐distance dispersal. However, obligate symbionts may have more restricted gene flow due to recruitment limitations, making host specificity an important potential driver of biodiversity. To explore the tension between broad dispersal ability and limited recruitment potential, we used sequences of mtDNA cytochrome c oxidase subunit I (COI) to assess the fine‐scale phylogeography of the cleaner shrimp, Ancylomenes pedersoni, an obligate symbiont of sea anemones, along 300 km of the Florida Reef Tract (FRT). The results indicate high genetic diversity within A. pedersoni populations along the FRT. Pair‐wise ?_ST values indicate significant genetic structuring between northern (Fort Lauderdale and Upper Keys) and southwestern (Lower Keys) populations, with significant isolation by distance. Two divergent COI haplotype lineages were detected through statistical parsimony analysis: one evenly distributed across the entire FRT (Clade 1) and one found primarily in two sample localities in the Lower Keys (Clade 2). Phylogenetic analyses using 16S‐rDNA indicates that this genetic diversity is of paraphyletic origin, and possibly the result of multiple colonization events. These results reveal a complex demographic and evolutionary history for A. pedersoni populations and provide the first evidence of highly divergent intra‐specific lineages independently colonizing the FRT. Because the FRT is a highly impacted coral reef system, understanding phylogeographic patterns along it has value beyond documentation of the factors that generate genetic diversity in tropical reef systems: these data are critical for creating scientifically based management strategies.     

Phylogeography of the mud crab (Scylla serrata) in the Indo‐West Pacific reappraised from mitochondrial molecular and oceanographic clues: transoceanic dispersal and coastal sequential colonization

The widespread mud crab, Scylla serrata, of the Indo‐West Pacific is an excellent model species to demonstrate how the colonization history of a species can be influenced by complex oceanographic conditions. Through the combination of ecological data (fossil records and paleo‐oceanographic conditions) and molecular data (coalescent simulations, network analysis, and nucleotide diversity tests), the phylogeographic history of S. serrata was re‐analyzed. Based on the analysis of mtDNA cytochrome oxidase I sequences, two major clades were identified for S. serrata, including a widespread clade (Clade I) with three disjunct geographic clusters (IA, IB and IC) and an endemic Northwest Australian clade (Clade II). Moreover, a significant phylogeographic structure corresponding to four subpopulations was revealed: Northwest Australia, West Indian Ocean, Red Sea‐South China Sea and West Pacific. A colonization history of a Northwest Australia origin for S. serrata followed by westward transmarine dispersal across the Indian Ocean for Clade I and sequential colonization from the West Indian Ocean to Red Sea‐South China Sea and West Pacific was corroborated. The Pleistocene fluctuations of paleo‐oceanographic conditions including surface circulations and physical topography in the Indo‐West Pacific might be responsible for the wide distribution, colonization history and genetic divergence of this species.     

Spatio‐temporal variation in biomass of the deep‐sea red crab Chaceon affinis in Gran Canaria Island (Canary Islands,Eastern‐Central Atlantic)

The spatial and temporal biomass distribution of Chaceon affinis and its vulnerability to fishing activity in Gran Canaria (Canary Islands) were investigated. The first goal was to assess the influence of the slope steepness and substrate on the size of crab patches, size of the crabs, and crab biomass. The second goal was to evaluate spatial and temporal variation in the biomass over a 15‐month period. The last goal was to assess the influence of fishing activity upon the reduction in the biomass over the same 15‐month period. Only two or three locations in the sampling area generated high‐biomass contour patches. When these patches were superimposed on the isobath lines, they were coincident with the main depth range described for the species in the area. The map of the biomass values clearly showed three structures with cores of the highest biomass in both muddy and rocky‐muddy areas. The biomass was higher on muddy than on rocky‐muddy bottoms. Biomass was twice as high when steepness was reduced to one third between isobaths of 500 and 900 m. The size of crab patches increases linearly with the decrease in slope steepness. The spatial structure of crabs remained fairly stable over time, showing that biomass changes with depth over time. Maps of the estimated biomass values over the 15‐month period showed the same two main patches over time with the cores of highest biomass separated by a distance of between 4.2 and 4.5 km. Although the bathymetric distribution by sexes showed temporal changes, with a displacement to deeper areas made by both sexes over the studied period, only a partial temporal segregation between males and females was observed. During the study period, crabs underwent a significant decline in biomass and this was consistent with the combined catches of both commercial and experimental fishing in the area. Due to its low mobility, C. affinis is highly vulnerable to local depletion by intensive fishing efforts.     

Multiple paternity in the common long‐armed octopus Octopus minor (Sasaki, 1920) (Cephalopoda: Octopoda) as revealed by microsatellite DNA analysis

Multiple paternity was assessed in Octopus minor using microsatellite DNA markers. Octopus minor adults were captured in traps and kept in indoor cement ponds. The females spawned after several days. Ten broods (B1–B10), each containing 15 embryos and the maternal octopus, were maintained until the embryos reached the stage at which DNA could be extracted and used for genotyping. Multiple paternity was tested using five microsatellite DNA markers and the results proved the hypothesis that multiple paternity occurs in O. minor (observed in six out of the 10 broods). Analysis with GERUD software gave the minimum number of fathers and showed that four broods were sired by a single male, three were sired by two different males and three were sired by three different males. In brood B10, the number of fathers identified by the single‐locus method was one fewer than that by the GERUD method. Of the six multiple paternity broods, four (66.7%) showed significant skew from equal paternal contributions, which indicated that sperm competition and/or cryptic female choice may be important for post‐copulatory paternity bias in this species.