Reproductive biology of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in sub-Antarctic waters

Halicarcinus planatus is the only member of the family Hymenosomatidae that occurs in the southern tip of South America. The aim of this study is to determine both the reproductive cycle and reproductive traits of the population of H. planatus nearest to southern limit of its geographical distribution. Results of this work allow us to determine two consecutive reproductive periods in this species. Maximum values of gonadosomatic index, oocyte diameter and ovarian development in March and August indicate that spawning takes place in May and September. The simultaneous ovarian maturity and the embryonic development show that female H. planatus can re-mature its ovary. The capability of H. planatus to develop their ovaries while females are ovigerous is a unique feature among the sub-Antarctic decapods and probably an adaptative advantage to extreme environments. Based on the different biological features and recent environmental changes along the Western Antarctic Peninsula, our hypothesis is that H. planatus possesses the potential to invade shallow waters and intertidal zones in this region.     

Toxic strains of the Alexandrium ostenfeldii complex in southern South America (Beagle Channel,Argentina)

During phytoplankton monitoring in the Beagle Channel (≈54°52′ S, 67°32′ W) a previously undetected Alexandrium species was observed in coincidence with mouse bioassay toxicity. Detailed thecal plates analysis using epifluorescence and scanning electron microscopy revealed the presence of the Alexandrium ostenfeldii species complex, showing a mixture of the diagnostic features usually used to discriminate between the morphospecies A. ostenfeldii and A. peruvianum. Cells of the A. ostenfeldii complex were commonly observed during spring after the main annual diatom bloom, when temperatures and salinities were respectively around 7.5–10 °C and 30–30.5 psu, and nutrients showed a seasonal decrease. Toxin analysis by liquid chromatography–mass spectrometry revealed the production of 13-desmethyl spirolide C and 20-methyl spirolide G in cell cultures. The cellular contain of spirolides during exponential phase growth was 0.5906 ± 0.0032 and 0.1577 ± 0.0023 pg cell⁻¹ for 13-desMe-C and 20-Me-G, respectively. A third unknown compound, with a structure resembling that of spirolides was also detected in culture. Moreover, an additional compound with a similar m/z (692) than that of 13-desMe-C but presenting a higher retention time (Rt = 40.5 min) was found in high proportions in mussel samples. PSP toxins were present at low concentration in mussels but were not detected in cultures. These results extend the world-wide distribution of toxic strains of the A. ostenfeldii complex to the Beagle Channel (southern South America), where toxic events have been traditionally linked to the presence of Alexandrium catenella. This is the first confirmed occurrence of spirolides in mussels and plankton from Argentina, which highlights the importance of monitoring these toxins and their producing organisms to protect public health and improve the management of shellfish resources.     

Breeding experiments to distinguish two sibling species of Halicarcinus (Crustacea, Brachyura)

Hybridization experiments and various salinities were used in investigating the status of two Halicarcinus lacustris-like , forms, one of which has no free larval stages (direct-development) and the other of which has normal larval stages (indirect-development).
Hybrids were produced, at least from indirect-development female x direct-development male crosses, but introgression of genetic material was limited to F₂ hybrids from the female parental form. There were no intergrades between the two modes of development in F₁ and F₂ hybrids or as a response to salinity.
These forms are established as sibling species. The name lacustris applies to the direct-development form and the other is a new species, H. paralacustris , which is described. Hybridization in the field is unlikely due to geographical and reproductive isolating mechanisms. Contrary to a previous view, it seems that H. lacustris had a recent origin in Australia and transport by water birds is suggested as the mode of dispersal through south-east Australasia.     

Growth and reproduction in the freshwater crab, Potamon fluviatile (Decapoda, Brachyura)

SUMMARY. 1. The patterns of relative and absolute growth and the reproductive biology of the freshwater crab Potamon fluviatile were studied in a natural population inhabiting a hill stream close to Florence, Italy, over an annual cycle. Periodical inspections of a stretch of the stream were made and morphological and anatomical analysis carried out.
2. As in other decapods, the females are smaller than the males (they can however occasionally reach larger dimensions). This may be determined by a lengthening of the moulting interval in the females, by their higher energetic cost of reproduction (since reproduction occurs simultaneously with moulting, at least in this habitat) and/or by a higher mortality rate resulting from the risks associated with carrying eggs and vagility.
3. The analysis of relative growth in secondary sexual characters (abdomen width and major chela length) with respect to carapace length, shows that the pre-puberty and puberty ecdysis occur at 15 and 35 mm carapace length respectively, which was also confirmed by the gonad weight, vas deferens in males, and the onset of vitellogencsis in females.
4. A delay between anatomical and functional (i.e. the ability to copulate successfully) maturity was observed in the males. Being larger may be an advantage in intra-sexual competition for mating, but larger males, being more vagile, are also more likely to meet receptive females. The females may mate before their puberty moult and store sperms in their seminal receptacles for when they attain full maturity; this could be adaptive since opportunities of encountering males are few and far between in their adult phase, characterized by their vagile and amphibious habits.     

New genus and species of brachyuran crab from the southern East Pacific Rise (Crustacea Decapoda Brachyura Bythograeidae)

A new genus and species of a brachyuran crab, Allograea tomentosa n. gen. and n. sp., of the family Bythograeidae, collected at a hydrothermal vent locality south of the Easter Microplate (31 degrees 09'S) on the southern East Pacific Rise, is described. The genus Allograea is distinguished by lacking modifications of the fronto-orbital region, and by the absence of coloured fields and setal patches on the carapace and chelipeds. The body and legs are smooth but densely covered by a brown tomentum, the eyestalks are not reduced, but the cornea is unfaceted and unpigmented. Comparison of mitochondrial DNA sequences among all known bythograeid genera confirms the novelty of this taxon.     

Phylogeography of the Chinese endemic freshwater crab Sinopotamon acutum (Brachyura,Potamidae)

Phylogeographical inferences based on multiple molecular markers from different modes of inheritance (i.e. mtDNA and nucDNA) can help to explore drivers of current species divergence over different timescales and allow a deeper understanding of evolutionary processes. River systems and mountains, owing to their drainage networks and complex topography, are often a high priority when inferring external causes of phylogeographical patterns. Here, we selected the Chinese endemic freshwater crab Sinopotamon acutum inhabiting drainage networks across the Qinling–Daba Mountains, a watershed that divides northern from southern fauna in China, as a model species (1) to investigate whether river networks and mountain systems act as barriers in shaping the phylogeography of freshwater crabs and (2) to test the impact of historic environments and ecological habitats on crab distribution. Phylogenetic tree and network analyses based on mtDNA revealed divergence between eastern and western populations, but microsatellite DNA did not recover this. Frequent and male‐biased gene flow is evident. The adjacent tributaries, such as Weihe River 1 and Hanjiang River 1, although isolated by Qinling Mts, have low genetic variation in mtDNA. In addition, microsatellite DNA showed low variation between all rivers. Frequent gene flow, genetic variation and mitochondrial genetic structure in S. acutum indicated that the Qinling–Daba Mountains have had no effect on divergence in this species; instead, hydrological networks across these mountains serve as a continuous migration corridor for these crabs. Glacial refugia are probably responsible for the initial isolation of the eastern and western clades, and local adaptations after dispersal have further driven divergence. Cytonuclear discordance in phylogeographical patterns may be attributable to ongoing male‐biased gene flow.     

Leverage and muscle type in crab chelae (Crustacea: Brachyura)

The chelae of Cancer pagurus and Macropipus depurator were examined with respect to mechanical advantage. The closer muscles were investigated with respect to sarcomere length in the constituent fibres and to the force developed by the whole muscle during isometric contraction. Cancer chelae have a relatively high mechanical advantage, 0.329 ± 001. Cancer closer muscles contain a high proportion of fibres with long sarcomeres, mean lengths mostly falling between 12 and 15 μm, and develop a maximum stress of about 496 kN.m⁻² during contraction. These figures are typical for "slow" crustacean muscle. The chelae of M. depurator are dimorphic. In one, the strong chela, the mechanical advantage is 0.248 ± 0.066 while in the other, the fast chela, the mechanical advantage is 0.177 ± 0.006. M. depurator closer muscles contain fibres with mean sarcomere lengths mostly falling between 6 and 10 μm. The muscle develops a maximum stress of about 145 kN.m⁻² during contraction. These figures are typical of "intermediate" crustacean muscles. "Fast" muscle fibres with short sarcomeres (about 30 um) were found in the chelae of both Cancer and M. depurator but were much commoner in the latter. Thus in Cancer a high mechanical advantage is correlated with slow muscle while in M. depurator lower mechanical advantages are broadly correlated with faster muscle. Consistent correlation between mechanical advantage and muscle type in the dimorphic chelae of M. depurator , however, is lacking. No consistent regionation of fibres with similar properties was found in the muscles.     

New species of Ruellia (Acanthaceae) from southern South America

Two new species ofRuellia,R. epallocaulos from northeastern Argentina, southern Brazil, and eastern Paraguay, andR. kleinii from southern Brazil, are described, illustrated and compared to related species.     

Foregut morphology and ontogeny of the spider crab Maja brachydactyla (Brachyura,Majoidea, Majidae)

We describe the morphology of the foregut of the spider crab Maja brachydactyla Balss, 1922, from first larval stage to adult, with detailed stage‐specific documentation using light and scanning electron microscopy. A total of 40 ossicles have been identified in the foregut of adults of M. brachydactyla using Alizarin‐Red staining. The morphological pattern of the ossicles and gastric mill is very similar to other Majoidea species with only a few variations. The foregut of the zoeae stages appeared as a small and simple cavity, with a cardio‐pyloric valve that separates the stomach into cardiac and pyloric regions. The pyloric filter is present from the first zoea, in contrast to the brachyuran species which have an extended larval development. Calcified structures have been identified in the cardio‐pyloric valve and pyloric region of the zoeal stages. The most significant changes in foregut morphology take place after the metamorphosis from ZII to megalopa, including the occurrence of the gastric mill. In the megalopa stage, the foregut ossicles are recognizable by their organization and general morphology, but are different from the adult phase in shape and number. Moreover, the gastric teeth show important differences: the cusps of the lateral teeth are sharp (no molariform); the dorsal tooth have a small, dentate cusp (not a well‐developed quadrangular cusp); and the accessory teeth are composed of one sharp peak (instead of four sharp peaks). The gastric mill ontogeny from megalopa to adult reveals intermediate morphologies during the earlier juvenile stages. The relationship between gastric mill structures with food preferences and their contribution to the brachyuran phylogeny are briefly discussed. J. Morphol. 276:1109–1122, 2015. © 2015 Wiley Periodicals, Inc.     

Spermatogenesis of the spider crab Maja brachydactyla (Decapoda: Brachyura)

This study describes spermatogenesis in a majid crab (Maja brachydactyla) using electron microscopy and reports the origin of the different organelles present in the spermatozoa. Spermatogenesis in M. brachydactyla follows the general pattern observed in other brachyuran species but with several peculiarities. Annulate lamellae have been reported in brachyuran spermatogenesis during the diplotene stage of first spermatocytes, the early and mid‐spermatids. Unlike previous observations, a Golgi complex has been found in mid‐spermatids and is involved in the development of the acrosome. The Golgi complex produces two types of vesicles: light vesicles and electron‐dense vesicles. The light vesicles merge into the cytoplasm, giving rise to the proacrosomal vesicle. The electron‐dense vesicles are implicated in the formation of an electron‐dense granule, which later merges with the proacrosomal vesicle. In the late spermatid, the endoplasmic reticulum and the Golgi complex degenerate and form the structures–organelles complex found in the spermatozoa. At the end of spermatogenesis, the materials in the proacrosomal vesicle aggregate in a two‐step process, forming the characteristic concentric three‐layered structure of the spermatozoon acrosome. The newly formed spermatozoa from testis show the typical brachyuran morphology. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Cytochemistry of the neurosecretory cells in the crab Menippe rumphii (Fabricius, Crustacea: Brachyura)

In Menippe rumphii five types of neurosecretory cells are found in the cerebral, commissural and thoracic ganglia. Detailed cytochemical observations on the neurosecretory cells revealed that they have responded strongly to saliva resistant PAS staining. Among proteins those rich in disulfides and sulhydryl groups are observed. Greater amounts of cytoplasmic RNA are observed in the reproductive season. Considerable amounts of lipids and phospholipids are also observed in the AS cells. The cytochemical differences between the NS cells and the nonsecretory neurons are also discussed.     

The ecology and biology of Southeast Asian false spider crabs (Crustacea: Decapoda: Brachyura: Hymenosomatidae)

The false spider crabs of the family Hymenosomatidae are one of the most poorly known group of brachyuran crabs in Southeast Asia. This is largely attributed to their small size and cryptic behaviour. Despite the many studies of decapods in Southeast Asia, only eleven species of hymenosomatids are known. Of these, two genera and six species were only described in the last two years. From Singapore the largest number of species (five) has been reported probably because it has been the best explored, while from Thailand three species and Peninsular Malaysia two species are known. There are no published records of hymenosomatids from Borneo or Java. The hymenosomatid fauna is perhaps best known in Australia and New Zealand. It is anticipated that when proper collections are made and studies implemented, the Southeast Asian hymenosomatid fauna will prove to be more diverse than what has been reported. The ecology of the Southeast Asian species is reviewed, especially in the view that two species are completely freshwater, one of which is a troglobite. Most species are littoral or sublittoral in habit and very sensitive to human activities (e.g. pollution).     

Differential growth of the barnacle Notobalanus flosculus (Archaeobalanidae) onto artificial and live substrates in the Beagle Channel, Argentina

In the Beagle Channel, southern South America (ca. 55°S 67°W), about 20% of false king crabs (Paralomis granulosa) >80 mm carapace length are fouled with the barnacle Notobalanus flosculus. To evaluate differences in growth rates of barnacles attached to artificial and live substrates, clay tiles were anchored as collectors to the bottom at two different sites in the Beagle Channel in September 1996: in Ushuaia harbour (low currents and high levels of suspended matter) and around the Bridges Islands (strong currents and low level of suspended matter). Another set of collectors was deployed at the same sites in October 1998 to collect barnacles for histological studies. Tiles were removed from each place, approximately, on a monthly basis. Carapaces of P. granulosa with the epizoic N. flosculus were sampled between November 1996 and 1997, and between March 1998 and September 1999, to study sexual maturation of barnacles. Growth of barnacles was compared between the collectors and P. granulosa carapaces following a qualitative approach. A sexual maturity scale was defined, based on the stage of development of the female reproductive apparatus of N. flosculus. Growth rate of barnacles was highest in the harbour, intermediate on P. granulosa, and lowest around the Bridges Islands. Presence of oocytes was registered only in epizoic barnacles, suggesting that at least a proportion of these individuals is able to spawn on the carapaces. The potential advantages of settling on a living substrate, namely increased availability of food particles and decreased predation risks are discussed.     

Phylogenetic relationships of the ubiquitous coral reef crab subfamily Chlorodiellinae (Decapoda,Brachyura, Xanthidae)

The xanthid subfamily Chlorodiellinae is one of the most ubiquitous coral reef crab taxa in the Indo‐West Pacific region. Many species are common in coral rubble and rocky shores from Hawaii to eastern Africa, often dominating reef cryptofauna in terms of biomass. Phylogenetic analyses of mitochondrial (COX1, 12S rRNA and 16S rRNA) and nuclear (histone H3) gene sequences of 202 specimens indicate that the Chlorodiellinae is polyphyletic as presently defined. Three genera, Pilodius, Cyclodius and Chlorodiella, and two previously undescribed lineages were recovered as a well‐supported clade. In combination with morphological data, the subfamily is redefined and restricted to this clade. Two new genera, Soliella gen. n., and Luniella gen. n., are described based on features of the carapace, male thoracic sternum and male gonopods. The remaining chlorodielline genera and members of the Etisinae, a subfamily with supposedly close morphological affinities to the Chlorodiellinae, were recovered at various positions throughout the xanthid phylogeny, although with relatively low support values. These results reiterate the unresolved status of xanthid subfamilial relationships, but nevertheless provide progress for xanthid systematics.     

Foregut morphology and ontogeny of the mud crab Dyspanopeus sayi (Smith, 1869) (Decapoda,Brachyura, Panopeidae)

The morphology of the foregut of the Say's mud crab Dyspanopeus sayi was described in adults and larvae. The ossicle system was illustrated based on a staining method with Alizarin-Red. The gastric teeth and cardio-pyloric valve were dissected and examined using optical and scanning electron microscopy. In the adults, the morphology of ossicles and gastric teeth of D. sayi is very similar to the related species Rhithropanopeus harrisii. The foregut of first zoea (ZI) presented a functional cardio-pyloric valve while the filter press was lacking. The filter press was observed in the pyloric chamber from ZII. The most significant changes in morphology take place after metamorphosis from ZIV to megalopa, including the occurrence of the gastric mill. The organization and morphology of many megalopal foregut ossicles are recognizable in the adult phase, although the morphology of the gastric teeth differs from the morphology of adults. A correlation of gastric mill structures with food preferences and their contribution to the phylogeny are briefly discussed.     

Spore morphology and ultrastructure of Cyathea (Cyatheaceae,Pteridophyta) species from southern South America

Spore sculpture and wall structure of eight Cyathea (Cyatheaceae) species from southern South America were studied using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Two layers, i.e. an inner and an outer layer, were observed in the perispore. The inner layer has two strata: the inner stratum is attached to the exospore and composed of rodlets tangentially oriented to the spore surface and randomly intermixed; the outer stratum consists of a three-dimensional network of rodlets with either free or fused distal edges forming spinules. The outer layer is thin, darkly contrasted and covers the rodlets. In most cases, the exospore has two layers and a pitted surface. In Cyathea atrovirens, the exospore surface is smooth, while in C. delgadii and C. myriotricha it is verrucate. The homogeneity of perispore features within the genus Cyathea is evident, while exospore features are heterogeneous. The exospore has different kinds of surface-structures that are of potential interest for assessing evolutionary trends within the group.     

Size-related mating success in the shore crab Carcinus maenas (Crustacea: Brachyura)

The relationship between the size of a given mating male Carcinus maenas (L.) (Brachyura, Portunidae) and the size of the female with which it was paired was studied for 1248 pairs of crabs collected from the shore In 764 of these pairs the female was in pre-moult and so the pair were in pre-copula. In the remaining 484 pairs the female had already moulted and the pairs were in copula. There were significant correlations between the sizes of the males and females in both pre-copula and copula pairs. It was found that male Carcinus collected in mating pairs and tested in the laboratory were unable to distinguish between females in terms of their size or stage of pre-moult. The positive correlation between the sizes of males and females in mating pairs on the shore is proposed to be, in part, a function of a mechanical constraint of the size of female that a given male can hold, defend and copulate with. In addition, encounters between solitary males and males carrying females, resulting in the formation of new pairs, appear to enhance the size-related mating pattern observed.