Coenobita Research Articles

Chromosome-level assembly for the complex genome of land hermit crab Coenobita brevimanus

Land hermit crabs are a group of shell-carrying crabs that have evolved remarkable terrestrial adaptations in behavior, morphology, physiology, and biochemistry. However, the genetic mechanisms underlying these adaptations remain unclear. In addition, usually it is very difficult to get good genome assemblies for crustaceans. In this study, we managed to assemble the first chromosome-level genome for a land hermit crab (Coenobita brevimanus) with careful manual curation. The final assembly spans 4.74 Gb, with the contig N50 of 1.75 Mb and scaffold N50 of 42.95 Mb, encompassing 117 chromosomes that account for 96.54% of the genome. The evaluations including genome BUSCO (95.26%), Merqury qv (35.88) and the mapping ratio of pair-end short reads (99.48%) showed the high-continuity of C. brevimanus genome assembly, making it the genome with the highest quality in crustaceans with genome size bigger than 3 Gb. The availability of this chromosome-scale genome of crustaceans represents a valuable resource for the land hermit crab, which represents an independent water-to-land transition evolutionary event in the animal kingdom.

Evaluation of shrimp-associated species in abandoned ponds in Mati City, Philippines

This study aimed to identify, characterize, and evaluate the biodiversity of shrimp-associated species in abandoned shrimp ponds, specifically assessing the trophic levels of bycatch species in Barangay Dahican, Mati City. Using a scoop net, researchers collected macrobenthic samples from Maitum, Lahusan, and Butuasan, finding 1,528 individuals with varying species compositions namely: Oreochromis niloticus (Nile tilapia), Coenobita cavipes (Land hermit crab), Canarium labiatum (Plicate conch), Rochia nilotica (Commercial top), Clithon oualaniense (Guamanian nerite), Cerithium coralium (Coral cerith), and Callinectes sapidus (Blue crab). Cerithium coralium was the most abundant species with 70% relative abundance, followed by Clithon oualaniense, with 29%. In contrast, the least abundant species were the Oreochromis niloticus and Canarium labiatum, with 1% relative abundance. Moreover, biodiversity indices revealed that Lahusan 1 (H' = 0.731; D=0.46) and Butuasan (H' = 0.714; D = 0.5) had higher biodiversity, whereas Lahusan 2 had the lowest (H' = 0.318; D = 0.15). In contrast, Lahusan 2 appeared to be the least diverse (H' = 0.318; D = 0.15). There were significant differences in terms of species abundance (df = 6, MS = 34.18, F = 6.02, P = 0.000) and none in terms of site locations (df = 3, MS = 18.71, F=2.08, P= 0.188). The study results showed that these associated species were mainly benthic and came from the nearby environment. Providing good management for the abandoned shrimp ponds in the area could mean reverting them to their original state to provide a habitat for other organisms.

Seeing across variable ecological and social environments: comparative eye morphology of marine and terrestrial hermit crabs (Decapoda: Anomura: Coenobitidae, Paguridae)

Abstract Vision is a ubiquitous sensory modality adapted to vastly different environments, which place variable selection pressures on both macro- and microscopic dimensions of external eye morphology. The hermit crab clade (Crustacea: Decapoda: Anomura) spans environments from sea to land, yet, no systematic comparisons in eye morphology have been made between any species. We compared three species of hermit crabs inhabiting different ecological and social environments: two terrestrial species, one of which (Coenobita compressusH. Milne Edwards, 1837) is highly social and inhabits a flat, open diurnal habitat, and another (C. clypeatus Herbst, 1791) is its sister species that inhabits a rugged forested nocturnal habitat; and a third (Pagurus longicarpusSay, 1817) inhabits a marine intertidal habitat and is less social. We compared macroscopic eye morphology between species as well as microscopic differences in ommatidium-facet density and diameter within eyes. We found that eye dimensions (length, width, and thickness), but not overall volume, differed significantly between marine and terrestrial species. Furthermore, the highly social C. compressus had a significantly larger eye volume compared to its sister species, C. clypeatus, which is not as social. Larger eyes in C. compressus might be linked to its social lifestyle, where vision has been shown to be critical to finding conspecifics. All three species had a higher density of facets in the ventral compared to dorsal region of the eye. Our comparisons of external eye morphology revealed microscopic similarities but notable macroscopic variation between species, thus laying a foundation for future phylogenetically controlled tests within this species-rich clade, including comparisons of internal eye morphology.

An update on the incident involving illegal catching of land hermit crabs in Okinawa, Japan

An update on the incident involving illegal catching of land hermit crabs in Okinawa, Japan

The plastic homes of hermit crabs in the Anthropocene

Plastic is the most pervasive element of marine waste, with harmful impact on wildlife. By using iEcology (i.e., internet Ecology, use of online data sources as a new tool in ecological research), we report on the emergence of a novel behaviour in hermit crabs related to the use of plastic or other anthropogenic materials as protective shells. We analysed images posted on social media to identify 386 individuals with artificial shells — mainly plastic caps (85 %). We report that 10 of the world's 16 terrestrial hermit crabs use artificial shells, a behaviour observed on all of the Earth's tropical coasts. Four non-exclusive mechanisms may drive individual choice for artificial shells: sexual signaling, lightness of artificial shells, odour cues, and camouflage in a polluted environment. Further research is needed to determine the impact of this behaviour on hermit crab evolutionary trajectories.

Highlighting the urgency of conservation strategies for land hermit crabs in the light of current incidents

Highlighting the urgency of conservation strategies for land hermit crabs in the light of current incidents

Evidence of long-term allocentric spatial memory in the Terrestrial Hermit Crab Coenobita compressus.

Spatial learning is a complex cognitive skill and ecologically important trait scarcely studied in crustaceans. We investigated the ability of the Pacific (Ecuadorian) hermit crab Coenobita compressus, to learn an allocentric spatial task using a palatable novel food as reward. Crabs were trained to locate the reward in a single session of eleven consecutive trials and tested subsequently, for short- (5 min) and long-term memory 1, 3 and 7 days later. Our results indicate that crabs were able to learn the location of the reward as they showed a reduction in the time required to find the food whenever it was present, suggesting a visuo-spatial and olfactory cue-guided task resolution. Moreover, crabs also remember the location of the reward up to 7 days after training using spatial cues only (without the food), as evidenced by the longer investigation time they spent in the learned food location than in any other part of the experimental arena, suggesting a visuo-spatial memory formation. This study represents the first description of allocentric spatial long-term memory in a terrestrial hermit crab.

Correction to: New Record of Land Hermit Crab, Coenobita Perlatus H. Milne-Edwards, 1837, from Taiwan main Island

Correction to: New Record of Land Hermit Crab, Coenobita Perlatus H. Milne-Edwards, 1837, from Taiwan main Island

Seasonal variation in the land hermit crab, Coenobita rugosus H. Milne Edwards, 1837 (Decapoda, Anomura) and a preliminary study of land hermit crabs as a bioindicator of turtle nesting at Penghu County Wang-An Island green turtle nesting refuge, Taiwan

Abstract The present study surveyed the land hermit crab species, body size, shell type, and shell suitability, at five sites over four seasons in the Penghu County Wang-an Island Green Turtle Nesting Refuge. Coenobita rugosus H. Milne Edwards, 1837 was the only species recorded and found at three sites (Tiantai Hill, Xi’an Reservoir, and Tudigong). The density index of hermit crabs exhibited notable variations across the sites, showing no significant variation with the changing seasons. The bush habitat displayed a higher density index compared to the sand habitat. Additionally, the sites differed significantly in terms of the shell type and body size of the hermit crabs. Further, no significant relationship was established between abundance and weather factors or between crab abundance and sea turtle nesting. This investigation is a preliminary examination of the possibility of land hermit crabs being used as bioindicators for breeding of sea turtles.

Polarization vision in terrestrial hermit crabs.

Polarization vision is used by a wide range of animals for navigating, orienting, and detecting objects or areas of interest. Shallow marine and semi-terrestrial crustaceans are particularly well known for their abilities to detect predator-like or conspecific-like objects based on their polarization properties. On land, some terrestrial invertebrates use polarization vision for detecting suitable habitats, oviposition sites or conspecifics, but examples of threat detection in the polarization domain are less well known. To test whether this also applies to crustaceans that have evolved to occupy terrestrial habitats, we determined the sensitivity of two species of land and one species of marine hermit crab to predator-like visual stimuli varying in the degree of polarization. All three species showed an ability to detect these cues based on polarization contrasts alone. One terrestrial species, Coenobita rugosus, showed an increased sensitivity to objects with a higher degree of polarization than the background. This is the inverse of most animals studied to date, suggesting that the ecological drivers for polarization vision may be different in the terrestrial environment.

Morphological and Molecular Evidence for the Identity of Two Land Hermit Crabs Coenobita longitarsis De Man, 1902 and C. pseudorugosus Nakasone, 1988 (Crustacea: Decapoda: Anomura: Coenobitidae).

Two species of land hermit crabs, Coenobita longitarsis De Man, 1902 and C. pseudorugosus Nakasone, 1988 were described based on female specimens from Maluku, Indonesia and specimens from Cebu, the Philippines, respectively. However, no confirmed records of either species have been reported since their original descriptions. In this study, we examined specimens with typical morphological characters of C. longitarsis from Papua New Guinea and C. pseudorugosus from the Philippines and Indonesia, further supported by the analyses of the DNA barcoding marker, cytochrome oxidase subunit I (COI). The characters of male C. longitarsis are provided for the first time, with coxae of male fifth pereiopods subequal, without sexual tubes developed. Their slender morphology is suggested to be an adaptation to utilize native terrestrial snail shells in inland forests, which may also explain its rarity. Coenobita pseudorugosus is very similar to C. rugosus H. Milne Edwards, 1837, but can be distinguished by the adult sizes, as well as the morphology of sexual tubes of male fifth pereiopods and propodus of left third pereiopod. Morphological variation and the fresh coloration of C. longitarsis and C. pseudorugosus are also provided in this study.

First record of crab-eating mongoose (Herpestes urva formosanus) in coastal forest and use of anvils during predation on land hermit crabs in Taiwan

First record of crab-eating mongoose (Herpestes urva formosanus) in coastal forest and use of anvils during predation on land hermit crabs in Taiwan

Effect of salinity on survival and emigration behaviour during the sea-to-land transition of three terrestrial hermit crab species (Decapoda: Anomura: Coenobitidae) under laboratory conditions

Effect of salinity on survival and emigration behaviour during the sea-to-land transition of three terrestrial hermit crab species (Decapoda: Anomura: Coenobitidae) under laboratory conditions

Filling the knowledge gap in the reproductive biology of land hermit crabs (Decapoda: Anomura: Coenobitidae): captive breeding to explore incubation times and frequency

Abstract Land hermit crabs are widely distributed in tropical and subtropical regions, and play important roles in the coastal-forest ecosystem, such as contributing to seed dispersal and scavenging; however, they face serious threats such as habitat loss and smuggling for the exotic pet trade. Information on their reproductive biology is thus crucial for formulating and promoting conservation policies to their benefit. We conducted captive breeding for over 10 years, compiling records for four of the 10 years, and report the incubation times and frequency and the successful rate of release of larvae during captive breeding of five species of Coenobitidae: Coenobita brevimanusDana, 1852, C. cavipesStimpson, 1858, C. rugosus H. Milne Edwards, 1837, C. perlatus H. Milne Edwards, 1837, and C. purpureusStimpson, 1858. Results indicate that C. cavipes had the longest incubation period of more than 30 days and C. purpureus the shortest, approximately 20 days. Four of the species bred an average of 3.5 times per year, whereas C. cavipes bred once or twice per year. The success rate of larval release for all five species was 60%–70% over four years. Unsuccessful larval release may have been caused by human and environmental interference. Although further research is required because only small samples of each species were studied, the reported data may help to fill gaps in our knowledge on the reproductive biology of land hermit crabs.

Social conquest of land: Sea-to-land changes in shell architecture and body morphology, with consequences for social evolution

Architecture, like nests, burrows, and other types of fortresses, may have played an important role in the evolution of social life on land. However, few studies have examined architecture in organisms that transitioned from sea to land to test how and why architectural and morphological changes might have jointly impacted social evolution. Here I contrasted the shell architecture and body morphology of two of the phylogenetically most closely-related land versus sea species of hermit crab (the terrestrial hermit crab, Coenobita compressus, and the marine hermit crab, Calcinus obscurus), as well as the original builder of their shells (the gastropod, Nerita scabricosta). In contrast to the shells of gastropods and marine hermit crabs, only the shells of terrestrial hermit crabs were architecturally remodeled, with no columella inside for the occupants to grip upon to resist eviction. The bodies of terrestrial hermit crabs were also significantly more exposed outside the enlarged openings of their remodeled shells, whereas the substantially smaller-bodied marine hermit crabs were safeguarded deep within the recesses of their unremodeled shells. Ultimately, these changes in shell architecture and body morphology likely had consequences for social evolution on land, making conspecifics not only more dependent upon one another for homes, but also potentially easier to evict. Further changes in claw shape on land (with the claws of terrestrial hermit crabs becoming shorter, wider, and thicker) may have evolved to help offset their heightened danger of social eviction, acting as a more effective door against conspecifics.

Substrate-borne vibration and sound production by the land hermit crab Coenobita compressus during social interactions

Despite the diversity of sound production in crustacea, sounds produced by the land hermit crabs (Coenobitidae) are not well understood. Here, sound and substrate-borne vibration production by the tropical species Coenobita compressus was characterized in relation to shell architecture and social context. Sound production rates were compared between group and solitary conditions. Chirps were measurable in the air (peak frequency 800-8400 Hz) and within the sediment (40-1120 Hz). On average, chirp pulses were 0.08 s, spaced 0.41-0.92 s apart, and had trains composed of 4-6 pulses. There were significant correlations between the shell architecture and chirp vibroacoustics. Notably, a correlation between the substrate-borne peak frequency and shell wall thickness was found, indicating that the shell remodeling process which crabs undertake (shell wall thinning) impacts the vibroacoustics of the chirps. Chirp production was significantly linked to sociality during increased individual proximity and shell contests; hence, the function is hypothesized to be intraspecific communication relative to personal space and defense. Although there have been anecdotal observations of chirping in the Coenobitidae, this paper provides a full characterization of C. compressus, which produces chirps in two sensory modes, indicating the potential of being a seismic signaler.

Demography and shell use of the terrestrial hermit crab Coenobita clypeatus Fabricius, 1787 (Decapoda: Anomura: Coenobitidae) in two marine protected areas in Puerto Rico

Abstract Individuals of the terrestrial hermit crab Coenobita clypeatus Fabricius, 1787 use different gastropod shells for shelter during their life span. Availability of shells affects population traits, including density and size structure, influencing their fitness and survival. Locality and human presence can induce variation in the diversity and size of gastropod shells, influencing available shells for hermit crabs. We assessed how the diversity, size, and abundance of the occupied species of gastropod shells affect the density and demography of C. clypeatus in two marine protected areas (MPA) with different recreational use in Puerto Rico, Manatí (high) and Mona Island (low). We also evaluated the relationship between three shell traits (length, width, and aperture length) and the length of the crab chela as a size proxy. We did not find differences in the sex ratio. The density and median chela sizes were higher in crabs from Manatí. In Mona, however, they reached larger sizes. The diversity of occupied shell species was higher in Manatí than in Mona. Dimensions of occupied shells differed between genera and between study sites, and they scaled positively with hermit crab size. Differences in shells diversity, sizes, and abundance between MPAs might cause differences in density and demography of C. clypeatus. We only found large shells of Cittarium pica (Linnaeus, 1758), the only species occupied by larger individuals, occupied by hermit crabs in Mona. The low abundance of C. pica shells in Manatí might have affected the size of hermit crabs in this locality. Our in situ findings suggest that hermit crabs need larger shells to reach larger sizes as previously shown, and that location and the degree of human intervention might influence the availability of gastropod shells. Our study is the first attempt to characterize the demography and gastropod shells used by hermit crabs in Puerto Rico.

Presence and activity of endo-β-1,4-mannase, an important digestive carbohydrase within the digestive fluid of terrestrial crustaceans.

Within the midgut gland of the Christmas Island red crab, Gecarcoidea natalis, a single transcript for a GH5_10 endo-β-1,4-mannase had the highest expression out of all of the carbohydrase enzymes (Gan et al. in Mar Biotechnol 20:654-665, 2018). The activity, and potential digestive importance of this hemicellulase, compared with other carbohydrases, has yet to be established. The digestive fluid of G. natalis contained substantial endo-β-1,4-mannase activities (630 ± 55 (6) nmol reducing sugars. min-1. mg-1 protein). It was present as a single isozyme of 66.3 ± 0.7kDa (n = 6). Endo-β-1,4-mannase activities were higher than that for lichenase and endo-β-1,4-glucanase but lower than that for β-1,3-glucanase and amylase. The digestive fluid was able to hydrolyse, galactomannan, into its component monosaccharides. Hence, this confirms expression data that this enzyme is one of the most important digestive cellulases/ hemicellulases. Expression of GH5_10 endo-β-1,4-mannase mRNA was consistent with that of a digestive enzyme, as it was expressed in the digestive midgut gland but not in muscle and gill. Endo-β-1,4-mannase activities were also present within the digestive fluid of the terrestrial hermit crabs, Coenobita perlatus and Coenobita brevimanus. Endo-β-1,4-mannase activities (1351 ± 136 (n=3) nmol reducing sugars. min-1mg-1 protein for C. perlatus. 665 ± 32 n=(5) nmol reducing sugars. min-1mg-1 protein for C. brevimanus) were higher than that for endo-β-1,4-glucanase and amylase but were lower than β-1,3-glucanase activities. Animals within the terrestrial hermit crab family, Coenobitidae consume legume and palm seeds which contain substantial amounts of mannan. Hence, high endo-β-1,4-mannase activities suggest that digestion of mannan within these species may represent an important source of carbohydrate.

An ecological comparison of two populations of Coenobita purpureus in Japan ―Group for Terrestrial Hermit Crab Conservation―

An ecological comparison of two populations of Coenobita purpureus in Japan ―Group for Terrestrial Hermit Crab Conservation―

Gastropod shell use by the land hermit crabs <i>Coenobita brevimanus</i> and <i>C. cavipes</i> in an abandoned village on Iriomotejima Island, Japan

Gastropod shell use by the land hermit crabs <i>Coenobita brevimanus</i> and <i>C. cavipes</i> in an abandoned village on Iriomotejima Island, Japan