Moult cycle and growth of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in the Beagle Channel, southern tip of South America

The crab Halicarcinus planatus is the only hymenosomatid crab that inhabits the southern tip of South America and is the only decapod species that reproduces twice a year in the Beagle Channel. In this article, we study the moult cycle in the field (moult frequency, analysis of size frequency distribution) and linked it with growth studied in the laboratory (absolute and per cent growth increment, Hiatt function). Hiatt functions were similar for males and females. Moult frequency was seasonal: in early austral spring and in austral summer. In females, the pubertal moult is the terminal moult, whereas males continue moulting after attaining the size of morphometric maturity. Moult increment was highly variable. The relationship between absolute moult increment and crab size was described by a quadratic function. Per cent growth increment decreased with size, and relationships were different for each sex: linear for females and quadratic for males. Seven and eight modal groups explained the size frequency distributions for females and males from the field, respectively, and revealed the existence of two cohorts of recruits per year. Further modal analysis was mainly hampered by the high variability of size increment that could make any moulting individual fall in its own or one of two following modal groups. The antagonism between growth and reproduction was evident in small males. We hypothesize that the terminal pubertal moult is an advantageous feature that allows females to maximize their investment in reproduction after their terminal moult, which allows this species to have two spawnings per year.     

Competing for last place: Mating behaviour in a pill-box crab, Halicarcinus cookii (Brachyura: Hymenosomatidae)

The mating strategy of Halicarcinus cookii was investigated to ascertain how males maximised their fitness through mate choice. An intertidal population at Kaikoura, New Zealand, was dominated by mature crabs of both sexes in summer and by immature crabs in the colder months. More than 95% of mature females were ovigerous with early stage and late stage broods found in almost every month, indicating that egg production and larval release is continuous. The operational sex ratio was less than 1 male/female in summer, but often more than 1.0 in the colder months. The gonosomatic index increased along with brood development so that as soon as zoeae were released, the next clutch of eggs was ready to be fertilised. Males searched for receptive females and began pre-copulatory mate guarding without any courtship display. They mated preferentially with late stage or non-ovigerous females: copulation duration was longest for stage 5 females as was post-copulatory guarding (mean 18.3 h). Late stage females were up to 14% of the female population. Mate attraction seems to be the result of an ovarian signal rather than from the developing brood. Manipulation of the sex ratio had effects upon copulation duration and post-copulatory guarding: presence of a rival male increased duration of guarding. Females showed precocious mating in the penultimate instar and were able to lay fertilised eggs after their pubertal moult in the absence of males. H. cookii females have many mates, but males attempt to ensure paternity by preferentially pursuing mature females close to egg laying and by guarding these females after copulation. These behaviours are all elements of a competitive strategy to ensure that a male loses (not wins) the race to copulate because females have a ventral seminal receptacle, giving sperm precedence to the last male to mate. Male mating behaviour is a consequence and evolutionary response to female morphology.     

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.     

Aspects of the biology of the deep-sea spider crab, Dorhynchus thomsoni (Crustacea: Brachyura)

Pelagic first crab stages of the deep-sea spider crab, Dorhynchus thomsoni , are reported from mid-water samples taken at a variety of localities in the Porcupine Seabight and the Rockall Trough. Some of these samples were from hauls made near the surface over depths of 3000 m or more.
An analysis of these pelagic samples, and of benthic catches of D. thomsoni held by the Institute of Oceanographic Sciences and the British Museum (Natural History), indicate that most females and at least some males undergo the puberty prior to the third crab instar, these individuals therefore probably pass through a total of only three larval and three post-laval instars. There is at least a possibility that some individuals moult after the moult of puberty, unlike any other spider crabs.     

Reproductive biology of Hepatus pudibundus (Crustacea: Brachyura), the most abundant crab on the southeastern Brazilian coast

This study analyzed the size at sexual maturity and reproductive period of populations of Hepatus pudibundus in three bays on the northern coast of São Paulo, Brazil. Crabs were collected monthly and the bottom-water temperature was measured at each collection point. The animals were sexed, measured for carapace width (CW), and their gonadal stages were determined. A total of 8,674 specimens were collected (2,435 males and 6,239 females). Adult males showed the highest mean CW; the size at maturity for both sexes was 32.5 mm CW. Reproduction was continuous and peaked in spring and summer, because of the greater availability of plankton food for the larvae. This pattern is typical in tropical and subtropical regions, unlike the seasonal reproduction found in temperate regions. Reproductive activity of females was not significantly correlated with bottom-water temperatures. Immatures and individuals in all stages of gonadal development were found throughout the sampling period and at all depths, probably because the species completes its entire reproductive cycle in that area.     

Reproductive biology of the Suez Canal spider crab Schizophrys aspera (H. Milne Edwards, 1834: Crustacea: Brachyura: Majidae)

A reproductive biology study of the spider crab Schizophrys aspera (H. Milne Edwards, 1834) was conducted in the Suez Canal from July 2012 to June 2013. The annual sex ratio (Male:Female) of S. aspera was female biased with values of 1:1.25. Out of the four ovarian development stages of this crab, two stages were observed in the Suez Canal throughout the whole year. The ovigerous crab’s carapace width varied from 28 to 52 mm. This crab species can spawn during most of the year in the canal water, with a peak during late spring and early winter. The fecundity of ovigerous females ranged between 2349 and 13600 eggs with a mean of 5494 ± 1486 eggs. Female crabs that reached sexual maturity exhibited a minimum carapace width varying between 22 and 46 mm, and fifty percentage of all ovigerous females showed a carapace width of 36 mm.     

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).     

Population structure and reproductive biology of the fiddler crab Uca inversa (Hoffman, 1874) (Brachyura: Ocypodidae)

The population structure and reproductive biology of Uca inversa (Hoffman) were studied in Mozambique for the first time. Crabs were randomly sampled on monthly basis during low tide periods from January to December 2002 at Costa do Sol mangrove, Maputo Bay, southern Mozambique. A total of 1131 crabs was obtained, of which 518 (45.8%) were males, 322 non-ovigerous females (29.3%) and 281 (24.8%) ovigerous females, respectively. The present population presents non-normal size frequency distributions, with males reaching greater size than females. The overall sex ratio (M:F) (1:0.84) was significantly different from the 1:1 ratio. Ovigerous females were present throughout the year and the embryonic development showed synchrony with the gonadosomatic index, in which females carrying eggs close to hatching were more abundant when the gonadosomatic index reached minimum values in the population. Egg number increases with female size. Juvenile recruitment was also continuous with high proportion of young recruits being recorded in winter, probably due to the high reproductive activity displayed in summer. U. inversa exhibits a rapid embryonic cycle accompanied by a rapid larval development and settlement in the study area.     

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.     

Notes on the distribution and biology of the deep-sea crab Bathynectes maravigna (Brachyura: Portunidae) in the Mediterranean Sea

Data on the distribution and biology of the deep-sea portunid crab Bathynectes maravigna are reported for the Mediterranean Sea, based on several fisheries research surveys. Densities are low and, therefore, biological data are scarce. In the western Mediterranean, the species is much commoner in Alborán Sea than in the Catalano-Balearic Sea. Occurrences are also scarce in the southern Adriatic and northwestern Thyrrenian Sea, as well as in the Ionian Sea. The Alborán Sea and the seas surrounding the southern Italian peninsula are the areas where densities are the highest. The occurrence depth range was found to be 245–786 m, but most of the occurrences took place deeper than 500 m. Sizes ranged between 9 and 51 mm carapace length in males and between 12 and 51 mm in females. Ovigerous females have been only reported in October–December and March–May. Eighty three percent of both males and females are right-handed. Sexual dimorphism was present in cheliped length with males having longer chelae than females. The species appears to be much commoner in those areas where Atlantic influence is the highest.     

Reproductive biology of the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters

The reproductive activities of the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters were investigated from March 1996 to February 1998. Observations on the seasonal distribution of maturity stages and variations in seasonal fluctuations in the gonadosomatic index (GSI) confirmed recent findings that the spawning period begins in May. The species has a prolonged spawning period in the females extending from May to August, whereas the males mature in April and ripe specimens were encountered in monthly samples until September. The recruitment pattern confirmed the one breeding season. There are two spawning peaks, the first in May and the second in August. Variations in GSI relative to fish length indicated that females and males are most fecund at about 24.5–26.4 cm and 20.5–22.4 cm length classes, respectively. The males mature earlier than females, at a minimum size of 12.5–14.4 cm, while the females mature at 20.5–22.4 cm. The oocyte diameter‐frequency distribution suggests a serial rhythm of spawning. Fecundity ranged from 28 965 to 455 661 and correlated positively with: (a) standard length (P < 0.006); (b) ovary weight (P < 0.001); and (c) body weight (P < 0.001), and negatively with egg size (P < 0.003).     

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.     

Aspects of the biology of the big-handed crab,Heterozius rotundifrons (Decapoda: Brachyura), from Kaikoura,New Zealand

Abstract

From January 1975 to June 1976, samples of Heterozius rotundifrons A. Milne Edwards, 1867 were taken monthly from the intertidal zone at First Bay, Kaikoura Peninsula (42°25′S, 173°42′E). Small crabs (< 8 mm carapace width) were never common; they were either too cryptic to be collected in quantity, or have a different habitat from larger crabs. Ovigerous females were present in all months except February (in both 1975 and 1976), but generally formed less than 50% of the total sample of females each month. The number of newly deposited eggs (0.75×0.81 mm) carried by females increased with increase in carapace width according to the equation y = -1123.56+102.97x (r ² = 0.8213). Egg development lasted 3–5 months, and egg mortality during this period was almost 10%. The overall sex ratio for the 18-month sampling period was 1846 ♀ : 993 ♂, which suggests that females were approximately twice as numerous as males. However, when crabs were sorted into size classes it was evident that the sex ratio was not significantly different from 1:1 in crabs of 6–12 mm carapace width, whereas females significantly (P<0.001) outnumbered males in the 13–21 mm size range. The right and left chela were approximately equal in length in females of all sizes, but the right chela of large males was greatly enlarged compared with the left, and with the chelae of females of comparable carapace width. Increase in the growth rate of the males’ right chela commenced at a carapace width of approximately 11.0 mm. Since the smallest ovigerous female collected also had a carapace width of 11.0 mm, it is concluded that both males and females attain sexual maturity at this size.     

Reproductive biology of the shore crab Carcinus maenas (Decapoda,Portunidae): a macroscopic and histological view

A histological study of the reproductive cycle of male and female shore crabs, Carcinus maenas (Linnaeus), was performed monthly on the South West coast of Ireland (from December 2006 to July 2008). The calculated sex ratio deviated from equality, 1:0.53, revealing a strong male bias. A system was devised, based on screening of tissue sections, to describe and stage gametogenic development. Histological examinations revealed that ovarian development occurred biannually, with a primary winter cycle in which the larger crabs reproduced and a secondary summer cycle, when smaller crabs reproduced. An association was observed where more of the larger specimens were caught in the summer months and the smaller specimens in the winter months, which inversely correlated with the segregated breeding cycles. There was strong evidence that mature male crabs could potentially copulate year round since all mature specimens, collected throughout the year, contained viable spermatozoa. Developmental stages of oogenesis and spermatogenesis were described to develop a practical gonadal index for this portunid crab, providing information on the biology of this species, which will be of benefit for fisheries management.     

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.     

Reproductive biology and growth of bluestripe herring Herklotsichthys quadrimaculatus (Rüppell, 1837) in the northernmost waters

In order to examine the reproductive biology and growth of Herklotsichthys quadrimaculatus in the northernmost part of its reproductive range, the size frequency, gonadal development, and otolith daily increments of this species were collected from the coastal waters of Okinawa Island, southern Japan. Juveniles (<25 mm standard length, SL) were found from April to August. Their size increased to ca. 100 mm SL in November and subsequently remained unchanged. The gonadosomatic index of females was higher (>3.0) between March and August, which was the estimated spawning period. The modal hatching period back‐calculated from otolith daily increments was from April to May, which would be the peak of spawning. Because mature and spent ovaries also contained mature and immature oocytes, it was concluded that females spawn several times during the spawning season. Age determination from otolith increments showed logistic growth up to 97 mm (ca. 180 days post‐hatch), after which growth was almost stagnant. Maximum size and age were 121.6 mm SL and 384 days, respectively. The adult size decreased between August and September, indicating a change in the age cohort. Thus, the fish reached the end of their lifespans after spawning. Some of these ecological features were different from those of a previous study performed in southern areas; these differences suggest a flexible life history that could change to adapt to the surrounding environment.     

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.     

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.