Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean

Schejter, L. and Mantelatto, F.L. 2011. Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean. —Acta Zoologica (Stockholm) 92 : 141–149. The available literature on zoanthid–hermit crab associations deals only with records of this phenomenon, providing no detailed information. We describe, for the first time, the shell‐like colonies of Epizoanthus paguricola associated with the hermit crab Sympagurus dimorphus from benthic samples taken in the Argentine Sea, between 85 and 131 m depth, and provide information about morphometric relationships between the hermits and the zoanthids. In total, 260 specimens (137 males and 123 females) of S. dimorphus were collected, 240 (92.3%) of which were living in symbiosis with E. paguricola. The remaining 20 (7.7%) were living inside gastropod shells. As the initial structure of the pseudoshell, 12 different gastropod species were found (all were almost totally covered with colonies of E. paguricola). The hermit crab lives in the spiral cavity inside the soft colony, which seemed to be slightly different depending on the initial gastropod. Aperture pseudoshell morphology did not seem to be related to the sex of the hermit crab host, although males showed larger apertures for a given colony size. This fact is probably related to a larger size of male’s cheliped (sexual dimorphic character) used like a gastropod operculum and that may serve as a template for the growing of the aperture pseudoshell edge. The number of epizoanthid polyps per colony increased in relation to the weight of the colony and to the size of the hermit crab. A process of selection of the initial shell was evident, because species of Naticidae were not the most common gastropods in this benthic community, but were those most used by hermit crabs (>60%). The puzzling association between hermit crab, shell and zoanthid presumably occurs during the hermit juvenile phase, when the crab occupies a small shell, and a zoanthid larva settles on it. Given the close relationship between S. dimorphus and E. paguricola found in this region, we support the idea that due to the low availability of adequate gastropod shells for hermit life cycle, this association allows the establishment and the continuity of the hermit crab population in the studied area.     

Evolutionary morphology of the hemolymph vascular system in hermit and king crabs (Crustacea: Decapoda: Anomala)

The morphological transformation of hermit crabs into crab‐like king crabs in the evolution of decapod crustaceans represents a remarkable case of carcinization or evolutionary shaping into a crab‐like form. In this study, we focus on internal organs such as the hemolymph vascular system and adjacent anatomical structures of several Recent hermit crab (Paguridae) and king crab (Lithodidae) species. There are various correspondences in the morphology of the arterial systems in the dorsal cephalothorax of the two taxa, especially with regard to the anterior aorta, anterior lateral arteries, and hepatic arteries. In the pleon, the posterior aorta in both taxa displays a proximal bifurcation and follows an asymmetrical course. The ventral vessel system, on the other hand, which mainly supplies the limbs, differs significantly between the taxa, with pagurids displaying the plesiomorphic condition. The pattern of the ventral vessel system in Lithodidae is influenced by morphological transformations of integumental structures during carcinization. One of these transformations was the broadening of the sternites, which resulted in a widening of the space between the endosternites. In addition, changes in the morphology of the endophragmal skeleton in Lithodidae led to an increase in the potential for intraspecific variability and interspecific variation in the arterial branching pattern. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.     

The use of pleopods for shell water circulation and respiration by hermit crabs

The use of the pleopods was investigated in two species of Diogenid hermit crabs, Dardanus arrosor and D. calidus. A transparent glass shell was used to observe the movements of the pleopods in hermit crabs. The movements consisted of periodic, irregular beating, which generated an irregular flow of the water within the shell.

A strong, regular beating movement was elicited when there was detritus or faeces in the shell, as was occupation of a new shell. Injection of water with a low oxygen concentration into the shell failed to induce any variation in the pleopod beating frequency (PBF), while the injection of water with a high CO₂ concentration induced a sudden PBF increase. When pH was varied and CO₂ concentration held at normal atmospheric level, there was a change in PBF. However, CO₂ variation alone, at constant pH, did not trigger any visible reaction. This suggests that there is a receptor for pH, which acts independently of the CO₂ concentration.

The function of males hermit crabs pleopods has always been obscure. However, at least in Dardanus, they are actively involved in water circulation within the shell for shell-cleaning and probably for ventilation.     

Evolutionary palaeoecology of symbioses between bryozoans and hermit crabs

Modern hermit crabs form associations with many organisms which encrust, bore into, or cohabit the living chambers of gastropod shells occupied by the crabs. Among these hermit crab symbionts are bryozoan species which develop massive, commonly multilayered, colonies encrusting hermit crab shells. These colonies extend the living chamber of the crab through a characteristic process of helicospiral tubular growth originating from the shell aperture. The scant information available on the ecology of Recent bryozoan‐hermit crab symbioses is reviewed. Symbioses have been recorded from intertidal to upper slope environments, and from tropical to cold temperate zones. None of the hermit crab species are obligatory symbionts of bryozoans, and the majority of the modern bryozoan species involved are also not obligatory symbionts. Fossil examples always lack the hermit crabs, which have a poor fossilization potential; however, the distinctive tubular growth pattern and other features of the bryozoans enable recognition of ancient examples of the symbiosis. The earliest inferred associations between bryozoans and hermit crabs date from the Mid Jurassic, but associations remained uncommon until the Neogene. A remarkably wide taxonomic diversity of Recent and fossil bryozoans are known or inferred symbionts of hermit crabs. The broad evolutionary pattern of the association demonstrates multiple originations of the symbiosis by bryozoans belonging to at least 5 cyclostome and 12 cheilostome families. Only the Miocene‐Recent cheilostome family Hippoporidridae has an evolutionary history closely tied to symbiosis with hermit crabs. There is no evidence for coevolution.     

Use of pleopod morphology to determine sexual dimorphism and maturity in hermit crabs: <Emphasis Type="Italic">Isocheles sawayai</Emphasis> as a model

In the Anomura, studies on growth patterns are infrequent, possibly because the heterogeneity of the group, especially in terms of morphology, makes it difficult to construct generalized growth models. Particularly hermit crabs are an interesting group to evaluate aspects of growth, because of their unique body. Isocheles sawayai, a hermit crab found only in the western Atlantic Ocean, poorly known with respect to its sexual dimorphism and maturity, was investigated here based on morphometry. Monthly collections (July 2001 through June 2003) were made from a shrimp fishing boat in the Caraguatatuba region on the northern coast of the state of São Paulo, Brazil. The specimens were measured and weighed, and had their sex checked. Throughout the sampling period, 374 specimens of I. sawayai were collected (11.23% nonovigerous females, 6.69% ovigerous females, 79.41% males and 2.67% intersexes). The size at which morphological sexual maturity was reached by both sexes ranged from 4.0 to 4.3 mm shield length, according to the relative growth and the size of the smallest ovigerous female. Sexual dimorphism was shown by males, which were significantly larger than females, and by differences in growth pattern between the sexes, especially for relationships that involved the pleopods, which is related to their different functions in males and females. The present study is one of the first to use pleopod morphometry to determine sexual maturity and dimorphism in hermit crabs, especially for species with intersexuality such as I. sawayai.     

Volatile constituents and antimicrobial activities of nine South African liverwort species

The volatile constituents of nine liverworts species (Asterella marginata, Dumortiera hirsuta, Fossombronia swaziensis, Marchantia pappeana, Marchantia polymorpha subsp. ruderalis, Pallavicinia lyellii, Plagiochasma rupestre, Riccia albolimbata and Symphyogyna podophylla) from South Africa were determined by gas chromatography. Where possible the volatile constituents identified were compared to those reported for the same species from other countries. Among the analysed liverworts, the chemical compositions of A. marginata, F. swaziensis, M. pappeana, and R. albolimbata are reported for the first time. Each of the analysed liverwort species produced its own characteristic components. Thujopsanes, chamigranes and cuparanes were found to be the most characteristic components of M. polymorpha subsp. ruderalis. The presence of dumortane-type sesquiterpenoids in D. hirsuta indicated that this species is similar in chemistry to an Argentinean sample. This is one of only a handful of reports on the presence of this sesquiterpene-type in liverworts. Simple thallose liverworts, S. podophylla and P. lyellii, were characterized by the presence of labdane-type diterpenoids. In addition, the antimicrobial activities of chloroform:methanol (1:1) extracts of the liverworts were evaluated against several important human pathogens using the serial dilution assay. Four of the liverwort species were active against Pseudomonas aeruginosa with MIC values ranging from 0.50 to 1.0 mg/mL. Some activity (MIC value of 1.0 mg/mL) was also recorded for the crude extracts of P. lyellii and M. pappeana against Escherichia coli. The extract of S. podophylla displayed the best activity towards the yeast Cryptococcus neoformans (MIC = 1.0 mg/mL). Although approximately 300 liverwort species occur in southern Africa, a Scopus search confirmed that this is the first report of the volatile profiles and biological properties of species from the region.     

South African populations of Littorina rudis

Littorina rudis was collected from stands of Spartina capensis in saltmarsh habitats within Langebaan and knysna lagoon, Cape Province. It was absent from rocky sores and from saltmarshes east of Knysna. The shell, radular and penial morphology are described. L. rudis from both localities bore tessellated colour patterns similar to those of British saltmarsh ecotypes. The Knysna population contained individuals with a unique amber background colour. The shells from Knysna and Langebaan were very thin in accordance with the sheltered habitats. The number of embryos carried in the brood puch was similar in both countries. Sexual maturity was attained at about 4 mm shell length; the male and female modal sizes were 4.9 mm and 5.1 mm respectively at Langebaan. No. published records were found for L. rudis in South West Africa. Some possible origins of the South African L. rudis populations are discussed.     

South African Museums and the Creation of a New National Identity

Museums are important sites of national cultural production, collective memory making, and the construction of national narratives. Contemporary South Africa is a particularly interesting place to study these processes. With the demise of apartheid, South Africa faces the difficult challenge of creating a new national identity that incorporates an examination of past oppression yet leaves the way open for building a national identity that incorporates all its diverse groups. The museums reviewed below, the Robben Island Prison Museum, the District Six Museum in Capetown, and the Kwa Muhle local history museum in Durban all make important contributions to this process.     

The biology of Dendropoma corallinaceum and Serpulorbis natalensis, two South African vermetid gastropods

D. corallinacewn forms sheet-like colonies at Mean Low Water (MLW) on exposed rocky shores: S. natalensis forms loose aggregations under stones below MLW in more sheltered situations. Both species released young from July— December. D. corallinaceun has single embryos in capsules brooded free in the mantle cavity; S. natalensis has 20–40 embryos per capsule, the latter being attached to the roof of the shell and hanging through a dorsal slit in the mantle. The morphology of the crawling young is similar in both species, resembling adult errant prosobranchs. D. corallinaceum has a stouter, more streamlined protoconch than S. natalensis correlated with the more turbulent water of its habitat. The crawling young secrete a sticky mucous trail for adhesion to the substratum. They are strongly photopositive until settlement. D. corallinaceum can settle within 24 hours but may delay settlement to 4–5 days if suitable substrata are absent. Metamorphosis is complete 2 days after settlement. D. corallinaceum prefer to settle on Lithothamnion which is easily eroded by the radula to provide a groove for rapid, firm attachments to the substratum. Both species feed from mucous nets, S. natalensis having a slower feeding rhythm commensurate with its larger size. Contiguous pairs of S. natalensis have synchronised feeding rhythms, probably to reduce mutual net robbing. Particles are also filtered out of suspension; many particles are rejected in the pseudofaeces but some are ingested. D. corallinaceum and S. natalensis have many similar ecologically equivalent species throughout the warm temperate and tropical seas of the world.     

On the genetic interrelationships of South African Negroes

This study addresses the comparative genetic interrelationships between South African Negro groups. For this the genetic distances between seven ethnically defined Negro subsamples (total of 998 individuals) based on 24 genetic loci/polymorphisms are calculated by applying standard distance formulae. These computations offer an opportunity to evaluate the different polymorphisms in terms of their effects on the genetic distances. The genetic interrelationships thus computed are illustrated by way of dendrograms and are discussed in terms of their comparative significance. It follows from the findings that the Ndebele, Northern Sotho (Pedi), and Tswana form a closely related subcluster and that the Zulu and Swazi as well as the Venda and Shangana-Tsonga form two additional, more distant, subclusters. These results are discussed and tentatively interpreted against the background of the reported Khoisan admixture of the populations concerned as well as their ethnological history. The data are also compared to those derived from metric and dermatoglyphic studies. It is concluded that whereas there is some agreement between these categories of variation (genetic, metric, and dermatoglyphic) as far as the comparative evaluation of South African Negro groups is concerned, there also are discrepancies. These conclusions need to be explained in terms of evolutionary mechanisms (such as historic origins, hybridization, natural selection, and genetic drift) in order to obtain a more consistent and comprehensive comparative picture of the physical anthropology of southern African populations.     

Chronotype of South African adults is affected by solar entrainment

Our daily lives are influenced by three different daily timers: the solar clock, our endogenous circadian clock and the societal clock. The way an individual’s endogenous clock synchronises to the solar clock, through either advances or delays relative to sunrise and sunset, results in a phenomenon known as diurnal preference or chronotype. South Africa uses just one time zone, but in the most easterly regions of the country, the sun rises and sets up to an hour earlier than in the most westerly regions throughout the year. It was hypothesised first that South Africans living in the east of the country may have a greater preference for mornings (more morning chronotypes) than those living in the west; and second, that this difference would not be due to genetic differences in the populations, particularly a genetic polymorphism previously shown to influence chronotype. Here, we describe and compare the distribution of chorotype and PERIOD3 variable number tandem repeat (VNTR) polymorphism frequency in eastern (n = 129) and western (n = 175) sample populations. Using the Horne–Östberg Morningness, Eveningness Questionnaire we found that there was a significantly higher proportion of morning-types in the eastern population (56.6%) than in the western population (39.4%), and there were higher proportions of neither-types and evening-types in the western population (51.4% and 9.1%, respectively) than in the eastern population (37.2% and 6.2%, respectively) (p = 0.009). There were no significant differences in distribution of the PER3 genotype (p = 0.895) and allele (p = 0.636) frequencies. Although previous studies have shown associations between chronotype and PER3 VNTR genotypes, no significant associations were observed in either the eastern (p = 0.695) or the western (p = 0.630) populations. These findings indicate that, in South African populations, longitude influences chronotype independently of PER3 genotype. The impacts of the differences in chronotype whilst maintaining the same societal temporal organisation in the eastern and western regions were not assessed.     

Morphological variation in the Cape Dwarf Chameleon (Bradypodion pumilum) as a consequence of spatially explicit habitat structure differences

An organism's phenotype is to some extent influenced by costs and benefits in terms of natural and sexual selection. The intensity of natural selection can in part be driven by habitat structure, which may result in varying levels of crypsis and/or selection on traits related to maximizing performance in that habitat. This may be countered by sexual selection, which can lead to sexual dimorphism in body size and/or the expression of conspicuous ornamentation relating to maximizing reproductive success. The intensity of these forces can also be different between the sexes, resulting in complex patterns of phenotypic variation. With this in mind, we examined morphological variation within the Cape Dwarf Chameleon, Bradypodion pumilum. The species inhabits two geographically disjunct habitat types and, in the present study, we demonstrate that chameleons from the two habitats show morphological differences. Large, conspicuous individuals inhabit closed vegetation, whereas small, drab individuals inhabit open vegetation. However, when morphological traits are size‐adjusted, the open vegetation morph displays many traits that are larger for its body size than the closed vegetation morph, especially for characters related to locomotion (limbs) and bite force (head width). Sexual dimorphism is also present, although the degree and number of dimorphic characters was very different between the two morphs, with size‐adjusted male‐biased dimorphism much more pronounced in the closed morph. Overall, our findings suggest that natural selection in open habitats limits both body size and conspicuous characters, although sexual selection in closed habitats favours the development of ornamentation related to display. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 878–888.     

Larval life history strategies of sub-tropical southern African estuarine brachyuran crabs and implications for tidal inlet management

Soon after hatching the larvae of many estuarine crabs migrate from estuaries to adjacent coastal waters soon, where larval development is completed before the post larval stages recruit to estuaries to settle. This study investigated the larval flux of several brachyuran crabs resident within a subtropical estuary on the east coast of South Africa. Plankton sampleswere collected over two intensive sampling periods during the spring of1997 (19 days) and the summer of 1998 (26 days). Larvae were releasedmaximally when high tide within the estuary was crepuscular, whilerecruitment occurred during nocturnal flood tides, with peak abundanceson the maximum amplitude nocturnal flood tides. The data are discussedin relation to freshwater inflow problems facing South African estuaries andthe active management of the tidal inlets of affected systems.     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

The oral susceptibility of South African field populations of Culicoides to African horse sickness virus

Twenty‐two isolates of African horse sickness virus (AHSV), representing its distinct serotypes, geographical and historical origins, were fed to three populations of South African livestock‐associated Culicoides spp. (Diptera, Ceratopogonidae). Infective blood meals included 12 recent isolates, nine historical reference strains and one live attenuated vaccine strain serotype 7 (AHSV‐7) of the virus. Field‐collected midges were fed through a chicken‐skin membrane on sheep blood spiked with one of the viruses, which concentrations ranged from 5.4 to 8.8 log₁₀TCID₅₀/mL of blood. After 10 days incubation at 23.5°C, AHSV was isolated from 11 Culicoides species. Standard in vitro passaging of AHSV‐7, used for the preparation of live attenuated vaccine, did not reduce its ability to infect Culicoides species. Virus recovery rates in orally infected Culicoides midges differed significantly between species and populations, serotypes, isolates and seasons. Significant variations in oral susceptibility recorded in this study emphasize a complex inter‐relationship between virus and vector, which is further influenced by multiple intrinsic and extrinsic factors. As it is not possible to standardize all these factors under laboratory conditions, conclusive assessment of the role of field‐collected Culicoides midges in the transmission of orbiviruses remains problematic. Nevertheless, results of this study suggest the potential for multi‐vector transmission of AHSV virus in South Africa.     

Reproduction and larval development of Polydora robi (Polychaeta: Spionidae), an obligate commensal of hermit crabs from the Philippines

Abstract. The reproduction of a recently described spionid polychaete, Polydora robi , is examined from the Philippines. Adults inhabit a burrow in the apex of gastropod shells occupied by hermit crabs. Females were found to deposit broods of 18–94 egg capsules in the summer (June–August) and winter months (January–March) sampled. Paired or single egg capsules are attached by stalks to the inside wall of the burrow and contain 40–106 eggs which average 97 μm in diameter. The total number of eggs per brood ranges from 941–8761 eggs and is positively correlated with the total number of segments and length of female worms. Adults of P. robi are polytelic, producing ≤9 successive broods over a 3-month period; a mean of 6.7 d was exhibited between broods in the laboratory. Females utilize sperm stored in the seminal receptacles during successive spawnings. Development occurs within egg capsules until the 3-segment stage, at which time the planktotrophic larvae are released. Juveniles of ∼20 segments are competent to settle on gastropod shells inhabited by hermit crabs. Members of P. robi are relatively fecund, semicontinuous breeders; the life-cycle in this species is similar to the only other known obligate polydorid commensal of hermit crabs.     

Taxonomic patterns of bleaching within a South African coral assemblage

In 1998, the Indian Ocean coral reefs suffered a severe and extensive mass bleaching event. The thermal tolerances of corals were exceeded and their photosynthetic symbionts (zooxanthellae) lost. Mortalities of up to 90% were recorded on the reefs of Seychelles, Maldives, Kenya and Tanzania. South African coral reefs were among the few that largely escaped the 1998 mass bleaching event, but may be threatened in the future if global warming increases. This study assessed the extent of coral bleaching and partial recovery at Sodwana Bay, South Africa during 2000 and 2001. Bleaching levels in this study varied over the course of a year, which suggested that seasonally varying parameters such as sea temperature were the most likely cause of bleaching. Bleaching levels were highest at the shallowest site. However, these bleaching levels were very low in comparison with those of reefs elsewhere in the Indian Ocean. The greater volume of water over the relatively deeper reefs of Sodwana Bay may have protected the reefs from severe bleaching. Field measurements on the three reefs indicated that, although the reefs at Sodwana Bay are still healthy, bleaching increased from <1% in 1998 to 5–10% in 2002. Bleaching occurred in 26 coral genera. The Alcyonacea were highly susceptible to bleaching, especially Sarcophyton sp. Among the hard corals, Montipora spp. were the species most susceptible to bleaching. The sensitivity of these genera to early and slight increases in temperature suggests that they can forewarn of a possible greater bleaching event. In contrast, the coral genera Turbinaria and Stylophora were most resistant to bleaching.     

Fire and the chemistry of a South African mountain stream

The effects of a late-summer prescribed burn on the chemistry of a second-order mountain stream in the south-western Cape, South Africa, were investigated. Nitrate concentrations in stream water were significantly higher during the winter of the post-burn year. Increased concentrations of chloride, bicarbonate, polyphenols and potassium and decreased sodium concentrations were also recorded. Concentrations of ammonium, phosphate, calcium, magnesium, total dissolved solids and hydrogen ions were not significantly affected by the burn. Ionic export from the catchment was generally greater in the post-burn year. Apart from nitrate, however, values probably lie within the natural range of year-to-year variation. It is predicted that enhanced losses of nitrate will decrease progressively with the recovery of the vegetation and the re-establishment of soil/plant nutrient cycles. Atmospheric losses of nutrients in smoke were unquantified, but may be of more significance to site productivity than losses through surface runoff, which, in the case of nitrogen, appear to be compensated by precipitation inputs.