Semi-terrestrial Crab Research Articles

Revision of the intertidal and semiterrestrial crab genera Chiromantes Gistel, 1848, and Pseudosesarma Serène & Soh, 1970 (Crustacea: Brachyura: Sesarmidae), using morphology and molecular phylogenetics, with the establishment of nine new genera and two new species

Revision of the intertidal and semiterrestrial crab genera Chiromantes Gistel, 1848, and Pseudosesarma Serène & Soh, 1970 (Crustacea: Brachyura: Sesarmidae), using morphology and molecular phylogenetics, with the establishment of nine new genera and two new species

Settlement patterns of two sesarmid megalopae in the Sai River Estuary, Ishikawa Prefecture, Japan

Two semi-terrestrial crab species, Chiromantes haematocheir and Chiromantes dehaani, are closely related and have a sympatric distribution. The ecological characteristics of these species, including habitat and behavior during the adult stage, have been investigated. However, the larval stage remains poorly understood because it is difficult to identify larvae morphologically. Our study objectives are to clarify the settlement patterns involved in recruitment of the two species of megalopae using genetic analysis and the effects of ecological factors on settlement, including 1) seasonal changes, 2) spatial variations (dominated by conspecific or heterospecific adults), and 3) tidal effects. The Chiromantes megalopae were collected in the lower reach of the Sai River during spring and neap tides from August to November 2017. Megalopa larvae were collected from three areas: one dominated by C. haematocheir adults, one dominated by C. dehaani adults, and a revetment area. Both species of megalopae showed seasonal and spatial variations in settlement, which also differed with tidal fluctuations. Chiromantes dehaani megalopae settled from mid-August to early October and C. haematocheir megalopae settled from early September to early November. Chiromantes haematocheir megalopae preferentially settled in the area dominated by conspecific adults over the area dominated by C. dehaani and the revetment area, while no difference in the settlement of C. dehaani megalopae was observed among areas. Chiromantes haematocheir megalopae returned on the spring tide; however, C. dehaani megalopae showed no tidal pattern.

Emersion behavior of the semi-terrestrial crab Neohelice granulata during hypoxic conditions: Lactate as a trigger

Climate changes affecting aquatic environments are increasing, and the resultant environmental challenges require animals to adopt alternative compensatory behavioral and physiological strategies. In particular, low levels of dissolved O2 are a regular problem for estuarine animals, leading to activation of a series of behavioral and physiological responses. This study on the semi-terrestrial crab Neohelice granulata examined patterns of emersion behavior under different levels of dissolved O2 availability and the role of lactate in this behavior. Emersion behavior was recorded for 4.5 h for crabs in water at four different levels of dissolved O2 (6, 3, 2, and 1 mg O2/L) and with free access to air. Oxygen consumption and hemolymphatic lactate levels were measured using the same experimental design. Emersion behavior was also recorded for 70 min in normoxic water after lactate or saline injections. Crabs increased their emersion behavior only in severe hypoxia (1 mg O2/L), and O2 consumption decreased under more severe hypoxic conditions. Despite the increase in emersion behavior, which leads to higher O2 availability, an increase in hemolymphatic lactate levels indicates that the animals still need to resort to anaerobic pathways to fulfill their metabolic demand. Furthermore, animals injected with lactate showed higher emersion behaviors than animals injected with a saline solution even in normoxia. These results suggest that the increase in hemolymphatic lactate can act directly or indirectly as a trigger for the increase in emersion behavior in the semi-terrestrial crab N. granulata.

Memory built in conjunction with a stressor is privileged: Reconsolidation-resistant memories in the crab Neohelice

The dynamics of memory processes are conserved throughout evolution, a feature based on the hypothesis of a common origin of the high-order memory centers in bilateral animals. Reconsolidation is just one example. The possibility to interfere with long-term memory expression during reconsolidation has been proposed as potentially useful in clinical application to treat traumatic memories. However, several pieces of evidence in rodents show that either robust fear memories or stressful events applied before acquisition promote reconsolidation-resistant memories, i.e., memories that are resistant to the interfering effect of drugs on memory reconsolidation. Conceivably, the generation of these reconsolidation-resistant fear memories also occurs in humans. Is the induction of reconsolidation-resistant memories part of the dynamics of memory processes conserved throughout evolution? In the semiterrestrial crab Neohelice granulata, memory reconsolidation is triggered by a short reminder without reinforcement. Here, we show that an increase in the salience of the aversive stimulus augmented the memory strength; nonetheless, the protein synthesis inhibitor cycloheximide still disrupted the reconsolidation process. However, crabs stressed by a water-deprivation episode before a strong training session built up a memory that was now reconsolidation-resistant. We tested whether these reconsolidation-resistant effects can be challenged by changing parametric conditions of memory-reminder sessions; multiple memory reactivations without reinforcement were not able to trigger the labilization-reconsolidation of this resistant memory. Overall, the present findings suggest that generation of reconsolidation-resistant memories can be another part of the dynamics of memory processes conserved throughout evolution that protects privileged information from change.

Geosesarmamirum, a new species of semi-terrestrial sesarmid crab (Crustacea, Decapoda, Brachyura) from central Taiwan.

A new species of semi-terrestrial sesarmid crab of the genus Geosesarma De Man, 1892, is described from central Taiwan. Geosesarmamirumsp. nov. is distinct in possessing a strong transverse crest on the inner surface of the male chela and a diagnostic male first gonopod which is relatively long and stout, with the distal chitinous part broad and spatuliform. Like most Geosesarma species, G.mirumsp. nov. has large eggs and direct development, contrasting with the only other species known from Taiwan, G.hednon Ng, Liu and Schubart, 2004, which has small eggs and planktotrophic larvae.

Underwater acoustic communication during the mating behaviour of the semi-terrestrial crab Neohelice granulata.

In semi-terrestrial crabs, the production of sounds has been recognized to be related to courtship communication dynamics. The present study aimed to assess if the crab Neohelice granulata (Varunidae) was able to emit acoustic signals and if they played a role in the crab's behaviour. We also assessed the locomotor behaviours to examine these parameters in different mating contexts of crabs. The study was divided into two different experimental conditions: 'solitary experiment' (consisting of three combination layouts with male, unreceptive and receptive females alone) and 'group experiment' (consisting of mixed combinations layouts of males, unreceptive, and receptive females). Synchronized acoustic and video monitoring systems were used to record the acoustic signals and locomotor behaviours of alone and grouped specimens. The greatest values of locomotor behavioural parameters were observed in layouts with receptive females alone and with 2 males plus 1 receptive female, probably related to courtship behaviour. N. granulata produced two distinct signals, a multi-pulse rasp signal (highest numbers were recorded in layouts with male alone and with 2 males plus 1 receptive female) and a single rasp signal. These results may suggest that males use the multi-rasp signal to advertise their presence to other males or to attract receptive females.

The sounds of fighting: contests between violet vinegar crabs, Episesarma versicolor (Tweedie, 1940) (Decapoda: Brachyura: Sesarmidae), are resolved through acoustic communication

Abstract Sound plays an important role in animal communication. Sesarmid crabs (family Sesarmidae) are semi-terrestrial crabs found in tropical and temperate regions, and are known to communicate through acoustic signals. The violet vinegar crab Episesarma versicolor (Tweedie, 1940) is a tree-climber known to possess sound-producing structures. The significance of sounds produced by E. versicolor during intraspecific contests, however, remains unknown. We investigated the context in which sound production occurs by staging 27 trials using male crabs. Three main types of acoustic behaviours were documented: rapping, leg stamping, and vibration. With the exception of vibration, these behaviours were also observed in female crabs. The air or the wood substrate was utilised to transmit acoustic signals, with each sound having unique spectral and temporal features serving different purposes. Rapping and leg stamping may be an advertisement of the sender’s resource-holding potential for territorial defence and asserting dominance during fights. Vibration is likely a victory display that discourages the contest loser as well as individuals in the vicinity from engaging the victor in another fight. Episesarma versicolor can therefore produce acoustic signals that may contain information about the sender, minimising costs associated with direct conflicts.

Combined effects of temperature and copper on oxygen consumption and antioxidant responses in the mudflat fiddler crab Minuca rapax (Brachyura, Ocypodidae)

This study investigates the combined effects of waterborne copper exposure and acute temperature change on oxygen consumption and the oxidative stress biomarkers, glutathione S-transferase (GST) and glutathione peroxidase (GPx), in the gills and hepatopancreas of the fiddler crab Minuca rapax. Crabs held at 25 °C were acclimated to 0 (control), 50, 250 or 500 μg Cu L−1 for 21 days, and were then subjected to 15, 25 and 35 °C for 24 h. Aerial oxygen consumption rates of crabs in copper free media increased with increasing temperature from 15 to 35 °C, Q10 values reaching ≈3. Crabs exposed to increasing copper concentrations exhibited variable responses, Q10 values falling to ≈1.5. Copper had no effect on oxygen consumption at 25 °C. However, at 35 °C, rates decreased in a clear concentration-response manner in the copper exposed crabs, revealing impaired aerobic capability. At 15 °C, oxygen consumption rates increased with copper concentration, except for a decrease at 500 μg Cu L−1. Gill GST activity was ≈2-fold that of the hepatopancreas, while hepatopancreas GPx activity was 3-fold that of the gills. Gill GST activities were reduced by copper exposure only at 25 °C while hepatopancreas GST activities were altered by copper at all temperatures. Hepatopancreas GST and GPx activities increased in crabs exposed to copper at 35 °C, revealing oxidative stress induction. Hepatopancreas GST and GPx activities were reduced in copper exposed crabs at 15 °C, suggesting a diminished capability to mitigate the effects of copper exposure at low temperature. These findings reveal that copper exposure increases oxygen consumption at low temperatures but decreases consumption at high temperature. Hepatopancreas GPx activities decreased at low temperature and increased at high temperature. These novel findings demonstrate that the interaction between copper exposure and temperature should be considered when evaluating biomarker activities in semi-terrestrial crabs.

Are semi-terrestrial crabs threatened by human noise? Assessment of behavioural and biochemical responses of Neohelice granulata (Brachyura, Varunidae) in tank

This study examined the effects of human lab-generated noise (sweep tone) on the behaviour and biochemistry of a semi-terrestrial crab (Neohelice granulata). The experiment was carried out in tanks equipped with video- and audio-recording systems on a total of seventy-eight specimens. In total, 42 experimental trials with sweep-tone exposure and control conditions were performed using crabs in single and group layouts. After a habituation period of 30 min, the locomotor and acoustic (sound signals emitted by the crabs) behaviours were monitored for 30 min. During this time, the animals in sweep-tone conditions were exposed to ascending sweeps in a bandwidth range of 2.5–25 kHz. Exposure to sweep-tone noise produced significant changes in the number of signals emitted, locomotor behaviours and plasma parameters, such as haemolymph total haemocyte count and glucose, lactate and total protein concentrations, revealing that human noise could represent a disturbance for this crustacean species.

Burrowing activity of the Neohelice granulata crab (Brachyura, Varunidae) in southwest Atlantic intertidal areas

The burrowing and semiterrestrial crab Neohelice granulata actively and constantly builds its burrows in the intertidal zone of the Bahía Blanca Estuary during low tide. Differences in structural morphology of N. granulata burrows and burrowing activities in contrasting microhabitats (saltmarsh and mudflat) were analyzed and related to several conditions, such as tide level, substrate type, sediment properties, and population density. In the mudflat the higher density of total burrows in autumn (172 burrows·m–2) was associated with molt timing, and the higher density of active burrows in summer (144 burrows·m–2) was associated with reproductive migration. Sediments from biogenic mounds (removed by crabs) showed higher water content and penetrability than surface sediments (control), suggesting that bioturbation increases the values of these parameters. Grain size distribution profiles and mineralogical composition did not vary between microhabitats or between seasons. Burrows were all tunnel-shaped and only those from the saltmarsh had chambers inside the tunnels, possibly used for reproductive purposes. Burrows from the saltmarsh had narrow entrances and deep tunnels, and burrows from the mudflat presented very narrow entrances and surface tunnels. Differences in burrow features and burrow activity of N. granulata between microhabitats were confirmed and associated with biotic and abiotic factors, indicating that this species has an adaptive burrowing behavior.

A new genus and new species of a semi-terrestrial freshwater crab from montane tropical rainforests in Java, Indonesia (Decapoda: Brachyura: Gecarcinucidae)

A new genus and new species of a semi-terrestrial freshwater crab from montane tropical rainforests in Java, Indonesia (Decapoda: Brachyura: Gecarcinucidae)

Thalamocyclops pachypes gen. nov., sp. nov. (Copepoda: Cyclopoida: Cyclopidae), a crevicular cyclopine from Socotra Island (Yemen): tale of a remarkable survival drive

ABSTRACTA new cyclopine copepod, Thalamocyclops pachypes sp. nov. was found to roam the crevicular residence of the semi-terrestrial brachyuran crab Socotra pseudocardisoma living on the Diksam limestone plateau of Socotra Island (Yemen). The remarkable morphology of the antennules, maxilliped and the inflated legs 4 and 5 justified the erection of a separate copepod genus, Thalamocyclops gen. nov. Re-examination of the previously described Bryocyclops soqotraensis revealed striking resemblances, which prompted the reallocation of it to the new genus: Thalamocyclops soqotraensis comb. nov. The description of the latter is emended. Besides the adult morphology, the copepod development of T. pachypes sp. nov. is described and some information on the naupliar stages is provided.The particular body shape, the highly specialized mouthparts and the uniquely engulfed metasomal somites and legs of T. pachypes sp. nov. appear to be related to its feeding and reproductive strategies in a most particular habitat in which drastic temporal and long-term changes occur.www.zoobank.org/urn:lsid/zoobank.org.pub:9ADC9001-1B11-4843-9A49-4B94675DFB33

Quaternary intertidal and supratidal crabs (Decapoda, Brachyura) from tropical America and the systematic affinities of fossil fiddler crabs

Concentrations of fully articulated crabs are rare in the fossil record, especially for terrestrial and semi-terrestrial taxa, which tend to be represented by scarce, fragmentary and poorly preserved fossils due to preservational biases. A newly discovered fossiliferous locality at Bahia Bique, west of Panama City, Panama, yielded a collection of supratidal, intertidal and shallow subtidal invertebrates and vertebrates of mid-Holocene age. Notable discoveries include the first fossils of the sally lightfoot crab Grapsus, the first for the land crab Cardisoma in the Eastern Pacific and, remarkably, the most complete and abundant collection of fossil fiddler crabs, Uca, yet discovered. The abundance and exceptional preservation of fossil male, female, juvenile and adult individuals of Uca aff. ornata in eroded burrow infills suggest that rapid entombment and early diagenesis were crucial for their preservation. The habitat preference of extant U. ornata for soft muds of open intertidal mudflats indicates that part of Bahía Bique must have been a large estuarine mudflat with close proximity to freshwater influx, in contrast to the present-day gravel field where the fossils are found as ex situ boulders, cobbles and gravel-sized clasts eroded from rocks of the poorly known Pacific Muck. We examine the systematic relationships of fossil fiddler crabs from Bahía Bique via synthetic and cladistic approaches, and conclude that they were from an extinct population of the extant Uca ornata. The fidelity of living–death assemblages between the Bique faunule and extant faunas of the tropical Eastern Pacific confirm the Quaternary age of the assemblage, and stimulate a detailed discussion of the preservation and palaeoecology of terrestrial and semi-terrestrial crabs in tropical assemblages.

Morphometric sexual maturity and allometric growth of the crab Sesarma rectum Randall, 1840 (Crustacea: Sesarmidae) in an impacted tropical mangrove in northeast Brazil

The size at sexual maturity and the allometric growth of the semi-terrestrial crab Sesarma rectum were studied in an impacted tropical mangrove in northeast Brazil. Crabs were monthly collected during spring low-tide periods, from October 2009 through September 2010. A catch-per-unit-effort (CPUE) technique was used to sample the crab population, with two-hour sampling periods, by two people. A total of 492 crabs were obtained, being 262 males and 230 females. The specimens were measured at carapace width (CW), the left and right propodus length and height (RPL, RPH, LPL and LPH), and the gonopod length of males (GL), and abdomen width (AW) of females. In males, the inflection point was at 27.14 mm CW in the relationship between CW and the length of right propodus (LRP), considering the morphological size at the onset of maturity. Based on the relationship between CW and AW, the size at sexual maturity in females was 22.97 mm. In spite of living in an impacted area, this population attained the maturity onset at a bigger size than other localities.

On the taxonomy of two poorly known species of Geosesarma De Man, 1892 (Crustacea: Brachyura: Sesarmidae) from the Philippines.

The identities of two poorly-known species of semiterrestrial crabs of the genus Geosesarma De Man, 1892, from the Philippines, are clarified. The types of Sesarma (Sesarma) vicentense Rathbun, 1914 (from Luzon), and Sesarma (Geosesarma) rathbunae Serène, 1968 (from Panay), are examined and both species are rediagnosed with detailed figures. Comparisons with allied congeners are also provided.

Phylogenetic patterns and the adaptive evolution of osmoregulation in fiddler crabs (Brachyura, Uca).

Salinity is the primary driver of osmoregulatory evolution in decapods, and may have influenced their diversification into different osmotic niches. In semi-terrestrial crabs, hyper-osmoregulatory ability favors sojourns into burrows and dilute media, and provides a safeguard against hemolymph dilution; hypo-osmoregulatory ability underlies emersion capability and a life more removed from water sources. However, most comparative studies have neglected the roles of the phylogenetic and environmental components of inter-specific physiological variation, hindering evaluation of phylogenetic patterns and the adaptive nature of osmoregulatory evolution. Semi-terrestrial fiddler crabs (Uca) inhabit fresh to hyper-saline waters, with species from the Americas occupying higher intertidal habitats than Indo-west Pacific species mainly found in the low intertidal zone. Here, we characterize numerous osmoregulatory traits in all ten fiddler crabs found along the Atlantic coast of Brazil, and we employ phylogenetic comparative methods using 24 species to test for: (i) similarities of osmoregulatory ability among closely related species; (ii) salinity as a driver of osmoregulatory evolution; (iii) correlation between salt uptake and secretion; and (iv) adaptive peaks in osmoregulatory ability in the high intertidal American lineages. Our findings reveal that osmoregulation in Uca exhibits strong phylogenetic patterns in salt uptake traits. Salinity does not correlate with hyper/hypo-regulatory abilities, but drives hemolymph osmolality at ambient salinities. Osmoregulatory traits have evolved towards three adaptive peaks, revealing a significant contribution of hyper/hypo-regulatory ability in the American clades. Thus, during the evolutionary history of fiddler crabs, salinity has driven some of the osmoregulatory transformations that underpin habitat diversification, although others are apparently constrained phylogenetically.

Genetic and Morphological Differentiation of the Semiterrestrial Crab Armases angustipes (Brachyura: Sesarmidae) along the Brazilian Coast.

The genetic and morphometric population structures of the semiterrestrial crab Armases angustipes from along the Brazilian coast were examined. The influence of the Central South Equatorial Current on larval dispersal of A. angustipes also was evaluated. Six populations were sampled from estuarine areas in São Luis do Maranhão, Maranhão; Natal, Rio Grande do Norte; Maceió, Alagoas; Ilhéus, Bahia; Aracruz, Espírito Santo; and Guaratuba, Paraná. Patterns of genetic differentiation were assessed using DNA sequence data corresponding to parts of the mitochondrial cytochrome c oxidase subunit 1. Geometric morphometric techniques were used to evaluate morphological variation in shape and size of the carapace and right cheliped propodus. Our results revealed low genetic variability and lack of phylogeographic structure; geometric morphometrics showed statistically significant morphological differentiation and geographic structuring. Our data indicate the absence of possible barriers to gene flow for this mobile species, and no clear correlation of morphological or genetic variation with ocean currents and/or geographic distance. Our results also suggest that historical geological and climatological events and/or possible bottleneck effects influenced the current low genetic variability among the populations of A. angustipes.

Moulting of the semi-terrestrial crab Chiromantes haematocheir (De Haan, 1833) (Decapoda, Sesarmidae) in Taiwan

Population structure and moulting of the semi-terrestrial crab Chiromantes haematocheir (De Haan, 1833) were studied in Taiwan. The crab moults nocturnally in small freshwater pools, and newly moulted crabs and cast integuments were used to assess moult increment. Males reached a larger size (max. CW 36 mm, ) than females (max. CW 33 mm, ): from 22 mm CW males increasingly dominated the population. Size at maturity was estimated at 17.5 mm CW. The percentage moult increment averaged 11.5% in males (5.5-19%, ) and 13.9% in females (7-23%, ). Female increment exceeded male increment for all overlapping size classes. The larger size of mature males, despite a smaller percentage increment, is explained by a higher post-puberty moult frequency. Of the moulting crabs, 25% of males and 38% of females had one or more missing or regenerating peraeopods. In both sexes this reduced the percentage increment, more so the larger number of limbs affected. The moulting conditions for C. haematocheir are not ideal, with constraints in relation to calcium supplies, and shelter. So the moult increments are unsurprisingly less than those of shallow water marine crabs moulting in an optimal environment, but larger than those of land crabs moulting without access to standing water.

A new species of semi-terrestrial freshwater crab (Crustacea: Decapoda: Brachyura: Potamidae) from the Central Highlands of Vietnam.

A new species of semi-terrestrial crab of the family Potamidae, Rathbunamon chumomrayense sp. nov. is described from Chu Mom Ray National Park, the Central Highlands of Vietnam. The new species can be distinguished from R. lacunifer (Rathbun, 1904), the only other species in the genus, by a suite of characters, including the slightly more rugose anterolateral regions, confluent epigastric and postorbital cristae that are sinuous, less convex anterolateral margins, relatively shorter fingers of the chelipeds, and the terminal segment of the male first gonopod being slightly curved outwards, with narrower dorsal flap.

A new genus and new species for an unusual semi-terrestrial potamid crab (Decapoda: Brachyura) with a bilobed mandibular palp from Peninsular Malaysia

Potamid freshwater crabs are characterised by mandibular palps possessing three segments with the terminal lobe simple. A new genus and new species of semi-terrestrial crab, Gempala bilobata , is here described from Peninsular Malaysia that possesses a 3-segmented mandibular palp having a bilobed terminal segment, a hitherto unknown condition. In addition, the carapace of the new genus is unusually high. Comparisons with allied potamid genera from Malaysia are also made and the affinities of the genus discussed.