No description available.

Thesis (M.A.)--Central Connecticut State University, 2004. / Thesis advisor: Jeremiah Jarrett. " ... in partial fulfillment of the requirements for the degree of Master of Arts in Biological Sciences." Includes bibliographical references (leaves 17-20). Also available via the World Wide Web.

No description available.

Most models of the impacts of climate change on the distributions of animals have focused on limits to thermal tolerances of individual species. Such "bioclimatic envelope" models do not consider the importance of interactions among species, each of which may respond to climate change in its own way. Hermit crabs (Paguridae) cannot exist without shells produced by gastropods. Thus, their ranges are expected to depend not only on their own physiological tolerances, but also on tolerances of gastropod species that produce shells of suitable sizes for growing crabs that use successively larger shells. To assess their potential importance to range shifts of hermit crabs, I characterized these commensal relationships over a large area of the northern Bering Sea in May to early June. Of 1539 hermit crabs collected, Pagurus rathbuni comprised 55%, P. trigonocheirus 44%, and Labidochirus splendescens 1%, with only four individuals of three other Pagurus species. Species richness for all living gastropods in my study area was 26 species, of which 18 were used by hermit crabs. P. rathbuni used shells of mostly moon snails (Naticidae); only 7 to 19% used whelk shells (Buccinidae) in the first four size classes, and 34% in the largest size class. P. trigonocheirus also used shells of mainly moon snails, but its use of whelk shells ranged from 18 to 44% in the first four size classes, and 70% in the largest size class. Densities of P. rathbuni and P. trigonocheirus varied independently of each other (r2 = 0.08, p = 0.09, N = 36 stations). Other studies suggest that hermit crabs obtain most of their shells from gastropods that have recently died, and that such empty shells are available for a relatively short period before being buried in sediments; thus, available shells should resemble the local pool among living gastropods. Correlation of P. rathbuni densities with densities of living gastropods with suitable shells was weak (r2 = 0.18, p < 0.01, N = 36 stations), while there was no correlation for P. trigonocheirus (r2 < 0.01, p = 0.59). Density patterns of hermit crabs within the five size classes did not correspond to those of living gastropods with suitable shells (randomization tests of independence, all p < 0.002). These results suggest that in the northern Bering Sea, initial effects of climate change on hermit crab distributions will depend more strongly on factors other than concurrent effects on dispersion of gastropods.

Clibanarius virescens (Krauss) is a common and abundant hermit crab along the East coast of South Africa. Despite this, its biology is poorly known, both in South Africa and throughout the rest of its range in the West Indo-Pacific region. This study focuses on the descriptive analysis of the shell resource used by C. virescens and of the effects of this resource on crab populations. The underlying hypothesis of the study is that biogeographically imposed gradients in the morphology of intertidal gastropod shells used by hermit crabs affect hermit crab population parameters. The gradient of potential change in the shell resource was captured by sampling at 12 localities, encompassing the range of C. virescens in South Africa. Seasonal changes in shell use, population structure and reproduction at a single locality (Cape Recife) were recorded over a period of 13 months. The breeding season of C. virescens at the southern extreme of its range extended from December to June. The population structure shows some seasonal change, but no clear trends emerge. The shell resource changed substantially in nature over the region studied. Based on shell use, localities clustered into separate southern and northern groups with a break occurring between Dwesa and Coffee Bay. Southern localities were characterised by use of Burnupena cincta, B. lagenaria and B. pubescens. Northern localities were characterised by the use of Morula granulata, M. nodosa and Peristernia forskalii. Intertidal shells used by C. virescens show fewer adaptations to predation in southern localities than shells from northern localities. Southern shells ii are relatively large, light and have wider apertures than those from northern localities which are generally smaller, heavier and have decreased aperture widths. Shell parameters affect population size-distributions as southern crabs were larger and heavier than northern crabs. C. virescens show sexual size dimorphism in which male crabs uniformly dominate the larger size classes at all localities. Differences in the sex ratio between males and females show more variable patterns. Most southern localities show no difference in the number of male and female crabs, but most northern localities show a skewed sex ratio in favour of females. Shell use and population size distributions of females affect reproductive output. Southern females produced significantly larger clutches than northern females. Reproductive output was related to crab mass and shell volume. Shell use patterns conform to the biogeographical regions in the range of the study and have a clear effect on both the population size distributions and reproductive output of Clibanarius virescens.

No description available.

I examine some of the ecological and evolutionary implications of body size in hermit crabs, with special emphasis on the upper intertidal species Clibanarius digueti. In Chapter 1 I show that body size had a far greater effect than species identity on desiccation tolerance for shell-less individuals of C. digueti, Paguristes anahuacus, Pagurus lepidus, and Phimochirus roseus. In contrast with other intertidal taxa, there was no correlation between the upper tidal limit of a species and the expected desiccation tolerance of an average-sized, shell-less individual of that species. This suggests that the gastropod shell that normally houses the hermit crab is sufficient to eliminate desiccation as a community-structuring force in this guild. Clibanarius digueti exhibits strong sexual dimorphism in body size, with almost no overlap in size between adult males and females. In Chapter 2 I show that sexual differences in the intensity of selection on size favor this dimorphism. Specifically, male mating success depended more strongly on body size than did female fecundity. In fact, the rate of increase in fecundity with body size equalled the lowest previously recorded for decapod crustaceans, suggesting that sexual size dimorphism in this species may depend more on weak fecundity selection on females than on strong sexual selection on males. Documenting contemporary selection on a character, however, is not the same as documenting that selection caused the character to evolve. Chapter 3 presents the first empirical test in a single species (C. digueti) of the hypothesis that sexual size dimorphism represents an evolutionary response to sexual differences in selection on size. The test is based on a general model that predicts crab body size as a function of shell limitations, shell fit and body size. Both males and females occupied optimally sized shells of non-preferred species, but the greater the desirability of a shell species, the greater the tendency for males to occupy tighter-fitting shells than females. Males also apparently suffere higher mortality than similarly-sized females. According to the general model, these results agree with the hypothesis that differential selection is causally involved in the evolution of sexual size dimorphism, and contradict the alternative hypothesis that energetic constraints on females produce the dimorphism.

Hermit crabs form an important component of the marine benthos and globally more than 1,200 species have been described. In the unique bioregion of South Africa, hermit crabs are poorly known, and the last taxonomic revision of the group was that of K. H. Barnard in 1950, who recorded only 32 species. This study combines morphological taxonomy, threedimensional (3D) micro-computed tomography (µCT) visualisations, and molecular barcoding to add to, revise, and provide an updated listing of, the regional fauna. The first section of the thesis comprises four chapters, each giving a detailed account of a species either new to science, or to the region. The pagurid hermit crab Goreopagurus poorei, a new species and genus record to the country, is reported and described from deep sea habitats along the Agulhas Shelf, extending the distribution by >10,000 km across the Indian Ocean. Furthermore, three species are described as new to science, one each from the three most common families. The first of these, a deep-water species from a genus of the family Parapaguridae that was previously unknown to South Africa, Paragiopagurus atkinsonae n. sp., is fully described and illustrated, and compared with two other parapagurids that each play a dominant role in the regional benthic offshore invertebrate community. The other two species new to science, Diogenes n. sp. from the family Diogenidae, and Pagurus n. sp. from the family Paguridae, inhabit coastal reefs in subtidal waters off southern KwaZulu-Natal. For the first time in crustacean taxonomy, species descriptions, particularly the one of Pagurus n. sp., are informed by, or based on, µCT imagery of calcified body parts. Following on this technique, Chapter 6 is a short presentation of the 3D raw dataset of seven µCT scans of types and rare museum specimens used in this thesis, which is made publicly available for download. The taxonomic use of the scanning method, with disseminating volumetric data of hermit crabs, is discussed briefly. The final section investigates the fauna as a whole. In Chapter 7, 194 cytochrome c oxidase subunit I gene segments (COI ‘barcodes’) of 43 nominal species plus 12 additional putative species (n = 55 species-like units) were used to validate morphological identifications. Testing this dataset revealed high barcoding efficacy, with nearly 99% identification success rates, and with the best Kimura 2-parameter distance to safely delimit species of hermit crabs of about 3.5%. Chapter 8 updates the regional fauna and provides taxonomic accounts for 62 nominal species which have either been added subsequent to the previous monographic review, or which have undergone taxonomic revision since that time. Of these, 12 are added for the first time here, increasing the number of known South African hermit crab species to 72, an expansion of 56% since Barnard, and about 20% since a recent species list published by W. Emmerson in 2016. Because colour images are provided for 51 out of 72 species, Chapter 8 can also be used as a preliminary guide. However, this study has shown that the hermit crabs of South Africa are by far more diverse than originally thought, and the summary, which includes only the 72 nominal taxa and none of the additional 10 putative species included in the barcoding dataset, is speculated to be only 60–70% complete. Future taxonomic work, especially in the genera Diogenes and Paguristes, will most likely result in many more species descriptions. Therefore, this current study is to be seen as important step towards a fully illustrated taxonomic catalogue on the South African hermit crabs to be produced in the near future.

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 54-56). Description: 56 leaves : photos. ; 29 cm.

In the present study, aspects of the behavior and ecology of two sympathetic intertidal hermit crabs, Pagurus hirsutiusculus and Pagurus samuelis were studied with the intention of expanding the use of fitness set analysis to other species, particularly extending studies over the entire breeding season.