MARS: A protein family involved in the formation of vertical skeletal elements.

Vertical organizations of skeletal elements are found in various vertebrate teeth and invertebrate exoskeletons. The molecular mechanism behind the development of such structural organizations is poorly known, although it is generally held that organic matrix proteins play an essential role. While most crustacean cuticular organizations exhibit horizontal chitinous layering, a typical vertical organization is found towards the surface of the teeth in the mandibles of the crayfish Cherax quadricarinatus. Candidate genes encoding for mandible-forming structural proteins were mined in C. quadricarinatus molt-related transcriptomic libraries by using a binary patterning approach. A new protein family, termed the Mandible Alanine Rich Structural (MARS) protein family, with a modular sequence design predicted to form fibers, was found. Investigations of spatial and temporal expression of the different MARS genes suggested specific expression in the mandibular teeth-forming epithelium, particularly during the formation of the chitinous vertical organization. MARS loss-of-function RNAi experiments resulted in the collapse of the organization of the chitin fibers oriented vertically to the surface of the crayfish mandibular incisor tooth. A general search of transcriptomic libraries suggested conservation of MARS proteins across a wide array of crustaceans. Our results provide a first look into the molecular mechanism used to build the complex crustacean mandible and into the specialized vertical structural solution that has evolved in skeletal elements.

The chronic effects of terbuthylazine-2-hydroxy on early life stages of marbled crayfish (Procambarus fallax f. virginalis).

This study assessed the chronic effects of terbuthylazine-2-hydroxy (T2H), one of the main terbuthylazine degradation products, on early life stages of marbled crayfish (Procambarus fallax f. virginalis) by means of mortality, growth rate, early ontogeny, oxidative stress, antioxidant defence and histopathology. The crayfish were exposed to four concentrations of the tested substance as follows: 0.75µg/l (environmental concentration), 75, 375 and 750µg/l for 62days. Concentrations over 75µg/l caused lower weight compared to the control group. T2H at 750µg/l caused delay in ontogenetic development. Levels of thiobarbituric acid reactive substances and total superoxide dismutase activity were significantly (p<0.01) lower in groups exposed to 375 and 750µg/l T2H. Crayfish in these treatments also showed alteration of tubular system including disintegration of tubular epithelium with complete loss of structure in some places of hepatopancreas and wall thinning up to disintegration of branchial filaments with focal infiltrations of hemocytes. In conclusion, chronic terbuthylazine-2-hydroxy exposure in concentrations up 75µg/l (100 times higher than environmental concentration) affected growth, ontogenetic development, antioxidant system, caused oxidative stress and pathological changes in hepatopancreas of early life stages of marbled crayfish.

Recent Incidence of Paragonimus westermani Metacercariae in Freshwater Crayfish, Cambaroides similis, from Two Enzootic Sites in Jeollanam-do, Korea.

An epidemiological study was performed to know the recent infection status of Paragonimus westermani metacercariae (PwMc) in freshwater crayfish, Cambaroides similis, from 2 streams in Jeollanam-do, Republic of Korea. Crayfish were collected from creeks in Bogil-do (Island), Wando-gun, and in a creek near Daeheung Temple in Haenam-gun. The infection rate of crayfish with PwMc in Bogil-do was 89.8%, and the metacercarial burden was 37 PwMc per the infected crayfish. Crayfish in a creek near Daeheung Temple were larger and twice heavier than those in Bogil-do. Of them, 96.5% were infected with PwMc. An average of 140 metacercariae was found in the infected crayfish, almost quadruple to those of Bogil-do. There was a strong correlation between the number of PwMc and body weight of the crayfish. These results suggest that P. westermani metacercariae are still prevalent in crayfish of the 2 regions in Jeollanam-do, Korea.

High-resolution structural and elemental analyses of calcium storage structures synthesized by the noble crayfish Astacus astacus.

During premolt, crayfish develop deposits of calcium ions, called gastroliths, in their stomach wall. The stored calcium is used for the calcification of parts of the skeleton regularly renewed for allowing growth. Structural and molecular analyses of gastroliths have been primarily performed on three crayfish species, Orconectes virilis, Procambarus clarkii, and more recently, Cherax quadricarinatus. We have performed high-resolution analyses of gastroliths from the native noble crayfish, Astacus astacus, focusing on the microstructure, the mineralogical and elemental composition and distribution in a comparative perspective. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) observations showed a classical layered microstructure composed of 200-nm diameter granules aligned along fibers. These granules are themselves composed of agglomerated nanogranules of 50nm-mean diameters. Denser regions of bigger fused granules are also present. Micro-Raman spectroscopy show that if A. astacus gastroliths, similarly to the other analyzed gastroliths, are mainly composed of amorphous calcium carbonate (ACC), they are also rich in amorphous calcium phosphate (ACP). The presence of a carotenoid pigment is also observed in A. astacus gastrolith contrary to C. quadricarinatus. Energy-dispersive X-ray spectroscopy (EDX) analyses demonstrate the presence of minor elements such as Mg, Sr, Si and P. The distribution of this last element is particularly heterogeneous. X-ray absorption near edge structure spectroscopy (XANES) reveals an alternation of layers more or less rich in phosphorus evidenced in the mineral phase as well as in the organic matrix in different molecular forms. Putative functions of the different P-comprising molecules are discussed.

Histological changes and antioxidant enzyme activity in signal crayfish (Pacifastacus leniusculus) associated with sub-acute peracetic acid exposure.

Peracetic acid (PAA) is a powerful disinfectant recently adopted as a therapeutic agent in aquaculture. A concentration of 10 mg L(-1) PAA effectively suppresses zoospores of Aphanomyces astaci, the agent of crayfish plague. To aid in establishing safe therapeutic guideline, the effects of PAA on treated crayfish were investigated through assessment of histological changes and oxidative damage. Adult female signal crayfish Pacifastacus leniusculus (n = 135) were exposed to 2 mg L(-1) and 10 mg L(-1) of PAA for 7 days followed by a 7 day recovery period in clean water. Superoxide dismutase activity was significantly lower in gill and hepatopancreas after three days exposure to 10 mg L(1) PAA than in the group treated with 2 mg L(-1) PAA and a control in only clean water. Catalase activity in gill and hepatopancreas remained unaffected by both exposures. Glutathione reductase was significantly decreased in gill of 10 mg L(-1) PAA treated crayfish and increased in group exposed to 2 mg L(-1) compared to control after 7 days exposure. Antioxidant enzyme activity in exposed groups returned to control values after recovery period. Gill, hepatopancreas, and antennal gland showed slight damage in crayfish treated with 2 mg L(-1) of PAA compared to the control group. The extent and frequency of histological alterations were more pronounced in animals exposed to 10 mg L(-1). The gill was the most affected organ, infiltrated by granular hemocytes and displaying malformations of lamella tips and disorganization of epithelial cells. After a 7 day recovery period, the infiltrating cells in affected tissues of the exposed crayfish began to return to normal levels. Results suggested that the given concentrations could be applied to signal crayfish against crayfish plague agent in aquaculture; however, further studies are required for safe use.

Cloning and Expression of Ecdysone Receptor and Retinoid X Receptor from Procambarus clarkii: Induction by Eyestalk Ablation.

Ecdysone receptor and retinoid X receptor are key regulators in molting. Here, full length ecdysone receptor (PcEcR) and retinoid X receptor (PcRXR) cDNAs from Procambarus clarkii were cloned. Full length cDNA of PcEcR has 2500 bp, encoding 576 amino acid proteins, and full length cDNA of PcRXR has 2593 bp, in which a 15 bp and a 204 bp insert/deletion splice variant regions in DNA binding domain and hinge domain were identified. The two splice variant regions in PcRXR result four isoforms: PcRXR1-4, encoding 525, 520, 457 and 452 amino acids respectively. PcEcR was highly expressed in the hepatopancreas and eyestalk and PcRXR was highly expressed in the eyestalk among eight examined tissues. Both PcEcR and PcRXR had induced expression after eyestalk ablation (ESA) in the three examined tissues. In muscle, PcEcR and PcRXR were upregulated after ESA, PcEcR reached the highest level on day 3 after ESA and increased 33.5-fold relative to day 0, and PcRXR reached highest the level on day 1 after ESA and increased 2.7-fold relative to day 0. In the hepatopancreas, PcEcR and PcRXR dEcReased continuously after ESA, and the expression levels of PcEcR and PcRXR were only 0.7% and 1.7% on day 7 after ESA relative to day 0, respectively. In the ovaries, PcEcR was upregulated after ESA, reached the highest level on day 3 after ESA, increased 3.0-fold relative to day 0, and the expression level of PcRXR changed insignificantly after ESA (p > 0.05). The different responses of PcEcR and PcRXR after ESA indicates that different tissues play different roles (and coordinates their functions) in molting.

A crayfish molar tooth protein with putative mineralized exoskeletal chitinous matrix properties.

Some crustaceans possess exoskeletons that are reinforced with calcium carbonate. In the crayfish Cherax quadricarinatus, the molar tooth, which is part of the mandibular exoskeleton, contains an unusual crystalline enamel-like apatite layer. As this layer resembles vertebrate enamel in composition and function, it offers an interesting example of convergent evolution. Unlike other parts of the crayfish exoskeleton, which is periodically shed and regenerated during the molt cycle, molar mineral deposition takes place during the pre-molt stage. The molar mineral composition transforms continuously from fluorapatite through amorphous calcium phosphate to amorphous calcium carbonate and is mounted on chitin. The process of crayfish molar formation is entirely extracellular and presumably controlled by proteins, lipids, polysaccharides, low-molecular weight molecules and calcium salts. We have identified a novel molar protein termed Cq-M15 from C. quadricarinatus and cloned its transcript from the molar-forming epithelium. Its transcript and differential expression were confirmed by a next-generation sequencing library. The predicted acidic pI of Cq-M15 suggests its possible involvement in mineral arrangement. Cq-M15 is expressed in several exoskeletal tissues at pre-molt and its silencing is lethal. Like other arthropod cuticular proteins, Cq-M15 possesses a chitin-binding Rebers-Riddiford domain, with a recombinant version of the protein found to bind chitin. Cq-M15 was also found to interact with calcium ions in a concentration-dependent manner. This latter property might make Cq-M15 useful for bone and dental regenerative efforts. We suggest that, in the molar tooth, this protein might be involved in calcium phosphate and/or carbonate precipitation.

Cherax (Astaconephrops) gherardii, a new crayfish (Decapoda: Parastacidae) from West Papua, Indonesia.

Cherax (Astaconephrops) gherardii n. sp. is a moderate burrowing crayfish endemic to the Ajamaru Lakes of West Papua, Indonesia. This species is one of the crayfish species from this region that are exploited for ornamental purposes. Its commonly used commercial name in the pet trade is "Rainbow Crayfish" or "Blue Moon Crayfish", and its native name is "udang kuku biru". The new species is genetically and morphologically similar to Cherax boesemani, however, both species may be easily distinguished morphologically or by using sequence divergence, which is substantial for considering C. gherardii n. sp. to be a valid species.

Sedentary behavior as a factor in determining lateral line contributions to rheotaxis.

Rheotaxis is a robust, multisensory behavior with many potential benefits for fish and other aquatic animals. Visual (optic flow) cues appear to be sufficient for rheotaxis, but other sensory cues can clearly compensate for the loss of vision. The role of various non-visual sensory systems, in particular the flow-sensing lateral line, is poorly understood, largely because of widely varying methods and sensory conditions for studying rheotaxis. Here, we examine how sedentary behavior under visually deprived conditions affects the relative importance of lateral line cues in two species: one that is normally sedentary (the three-lined corydoras, Corydoras trilineatus) and one that normally swims continuously along the substrate (the blind cavefish, Astyanax mexicanus). No effect of lateral line disruption on rheotactic performance was found in blind cavefish, which were significantly more mobile than three-lined corydoras. By contrast, rheotaxis was significantly impaired at low, but not high, flow speeds in lateral-line-disabled corydoras. In addition, lateral-line-enabled corydoras were characterized by decreased mobility and increased rheotactic performance relative to lateral-line-disabled fish. Taken together, these results suggest that sedentary behavior is an important factor in promoting reliance on lateral line cues.

Modeling and predicting meat yield and growth performance using morphological features of narrow-clawed crayfish with machine learning techniques.

In recent studies, artificial intelligence and machine learning methods give higher accuracy than other prediction methods in large data sets with complex structures. Instead of statistical methods, artificial intelligence, and machine learning are used due to the difficulty of constructing mathematical models in multi-parameter and multivariate problems. In this study, predictions of length-weight relationships and meat productivity were generated by machine learning models using measurement data of male and female crayfish in the narrow-clawed crayfish population living in Apolyont Lake. The data set was created using the growth performance and morphometric characters from 1416 crayfish in different years to determine the length-weight relationship and length-meat yield. Statistical methods, artificial intelligence, and machine learning are used due to the difficulty of constructing mathematical models in multi-parameter and multivariate problems. The analysis results show that most models designed as an alternative to traditional estimation methods in future planning studies in sustainable fisheries, aquaculture, and natural sources management are valid for machine learning and artificial intelligence. Seven different machine learning algorithms were applied to the data set and the length-weight relationships and length-meat yields were evaluated for both male and female individuals. Support vector regression (SVR) has achieved the best prediction performance accuracy with 0.996 and 0.992 values for the length-weight of males and females, with 0.996 and 0.995 values for the length-meat yield of males and females. The results showed that the SVR outperforms the others for all scenarios regarding the accuracy, sensitivity, and specificity metrics.

Effects of antennule morphology and flicking kinematics on flow and odor sampling by the freshwater crayfish, Procambarus clarkii.

The flow structure around the lateral antennular flagellum of the freshwater crayfish, Procambarus clarkii, was quantified to determine how antennule morphology and flicking kinematics affect fine-scale flow surrounding their chemosensory sensilla, called aesthetascs. Particle image velocimetry was used to measure velocity and vorticity of flow between aesthetascs of dynamically scaled physical models of P. clarkii antennules. Results revealed that the spacing between aesthetascs and antennule flicking speed induces substantial changes in fluid flow near aesthetascs. The downstroke flicking motion of the antennule occurs at a peak speed of 2.7cm/s. The returnstroke occurs at approximately 70% of this speed, but the fluid velocity between aesthetascs during the returnstroke is approximately 15% compared with the downstroke. The significant decrease in fluid flow near aesthetascs results from the reduced antennule speed and from the coupled interaction of boundary layers of the aesthetascs and antennule during the returnstroke. Odorant-laden fluid captured during the downstroke is retained between the aesthetascs during the slower returnstroke, and sufficient time occurs for odorant molecules to molecularly diffuse to aesthetasc surfaces. In addition, locally generated vorticity was observed near the tip of the aesthetascs, which may induce odorant transport to aesthetasc surfaces and enhance olfactory response times to odors.

Crayfishes (Decapoda : Cambaridae) of Oklahoma: identification, distributions, and natural history.

We furnish an updated crayfish species list for the state of Oklahoma (United States of America), including an updated and illustrated dichotomous key. In addition, we include species accounts that summarize general characteristics, life coloration, similar species, distribution and habitat, life history, and syntopic species. Current and potential distributions were analyzed using ecological niche models to provide a critical resource for the identification of areas with conservation priorities and potential susceptibility to invasive species. Currently, Oklahoma harbors 30 species of crayfish, two of which were recently discovered. Eastern Oklahoma has the highest species diversity, as this area represents the western distribution extent for several species. The work herein provides baseline data for future work on crayfish biology and conservation in Oklahoma and surrounding states.

Cambarus (P) theepiensis, a new species of crayfish (Decapoda:Cambaridae) from the coalfields region of Eastern Kentucky and Southwestern West Virginia, USA.

Cambarus (Puncticambarus) theepiensis is a stream-dwelling crayfish that appears to be endemic to the junction of the Cumberland Mountains with the Appalachian Plateau in West Virginia and Kentucky. Within this region, it is prevalent in the Guyandotte and Twelvepole basins of West Virginia, the Little Sandy River and Levisa Fork basins of Kentucky, and tributaries of the Big Sandy River shared by both states. The new species is morphologically most similar to Cambarus robustus and Cambarus sciotensis. It can be differentiated from C. robustus by its broad rostrum, with subparallel, thick-ened margins compared to the narrow, converging rostrum with reduced rostral margins of C. robustus.; larger areola width/length ratio (26 %) than C. robustus (22 %); and mottled color pattern compared to the monotypic color pattern of C. robustus. Canibarus theepiensis can be differentiated from C. sciotensis by the presence of a distinct lateral impression on the chelae compared to the absence of a lateral impression in C. sciotensis; constant thickness of the rostral margin compared to the gradation of rostral thickness in C. sciotensis; greater rostrum width/ length ratio in C. theepiensis (63.1 %) compared to C. sciotensis (57.2 %); and a central projection on the gonopod that is the same length as the mesial process, compared to a central projection that extends past the tip of the mesial process in C. sciotensis.

Cambarus (C.) hatfieldi, a new species of crayfish (Decapoda:Cambaridae) from the Tug Fork River Basin of Kentucky, Virginia and West Virginia, USA.

Cambarus (Cambarus) hatfieldi is a stream-dwelling crayfish that appears to be endemic to the Tug Fork River system of West Virginia, Virginia, and Kentucky. Within this region, it is prevalent in all major tributaries in the basin as well as the Tug Fork River's mainstem. The new species is morphologically most similar to Cambarus sciotensis and Cambarus angularis. It can be differentiated from C. sciotensis by its squamous, subtrinagular chelae compared to the elongate triangular chelae of C. sciotensis; its shorter palm length/palm depth ratio (1.9) compared to C. sciotensis (2.3); and a smaller areola length/total carapace length ratio (30.4% vs.36.5% respectively). Cambarus hatfieldi can be differentiated from C. angularis by its smaller areola length/total carapace length ratio (30.4% vs. 36.7% respectively); a smaller rostrum width/rostral length ratio (59.4% vs. 67.2% respectively); its rounded abdominal pleura as compared to the subtruncated pleura of C. angularis; the length of the central projection and mesial process of C. hatfieldi which both extend to the margin of the gonopod shaft or slightly beyond the margin compared to the central projection of C. sciotensis and C. angularis where both extend well beyond the margin of the gonopod shaft. 

Reproductive season-based plasticity in the size and strength of female crayfish (Faxonius obscurus) claws.

Animal weapons are morphological traits that improve the fighting ability of the wielder and are associated with competition. These traits are typically sexually dimorphic, with males possessing weaponry and females lacking weaponry. However, in some cases, like in many crustaceans, both males and females wield enlarged claws, which may function as weapons. Further, animal weapons may vary in their size, shape, and performance, with theory predicting that selection pressure for weaponry should be the highest when the importance of fights is the greatest, such as during a reproductive season. However, the degree and direction of selection may vary based on sex and season, with females potentially benefiting from wielding larger weapons during nonreproductive seasons. Crayfishes offer an ideal system to investigate how weapon phenotypes change across reproductive seasons since both males and females undergo a form alteration associated with reproduction. Thus, we investigated whether female Allegheny crayfish, Faxonius obscurus, claws change in size, shape, or pinching strength based on whether a female is in a reproductive or nonreproductive form. We found that female F. obscurus claws are larger and stronger during the reproductive season. These findings align with previous research on males of the same species. We discuss how predictions about the relationship between seasonality and weapon investment may differ based on sex.

Differential uptake of MRI contrast agents indicates charge-selective blood-brain interface in the crayfish.

This study provides a new perspective on the long-standing problem of the nature of the decapod crustacean blood-brain interface. Previous studies of crustacean blood-brain interface permeability have relied on invasive histological, immunohistochemical and electrophysiological techniques, indicating a leaky non-selective blood-brain barrier. The present investigation involves the use of magnetic resonance imaging (MRI), a method for non-invasive longitudinal tracking of tracers in real-time. Differential uptake rates of two molecularly distinct MRI contrast agents, namely manganese (Mn(II)) and Magnevist® (Gd-DTPA), were observed and quantified in the crayfish, Cherax destructor. Contrast agents were injected into the pericardium and uptake was observed with longitudinal MRI for approximately 14.5 h. Mn(II) was taken up quickly into neural tissue (within 6.5 min), whereas Gd-DTPA was not taken up into neural tissue and was instead restricted to the intracerebral vasculature or excreted into nearby sinuses. Our results provide evidence for a charge-selective intracerebral blood-brain interface in the crustacean nervous system, a structural characteristic once considered too complex for a lower-order arthropod.

Development of agonistic encounters in dominance hierarchy formation in juvenile crayfish.

We have characterized the behavioural patterns of crayfish during agonistic bouts between groups of crayfish of four different body lengths (9-19, 20-32, 41-48 and 69-75 mm) to characterize changes in the patterns of agonistic encounter during development. The behaviour of both dominant and subordinate animals was analysed by single frame measurement of video recordings. Behavioural acts that occurred during agonistic bouts were categorized as one of seven types: capture, fight, contact, approach, retreat, tailflip and neutral. Dominant-subordinate relationships were formed between juvenile crayfish as early as the third stage of development. Patterns of agonistic bouts to determine social hierarchy became more aggressive during development. The dominant-subordinate relationship was usually determined after contact in crayfish of less than 20 mm and 20-32 mm in length, while several bouts of fights were necessary for crayfish of 41-48 and 69-75 mm in length. Furthermore, social hierarchy was formed more rapidly in small crayfish. In larger animals, the number of approaches by dominant animals that promoted retreat in subordinate animals increased after the establishment of the winner-loser relationship. In smaller crayfish, in contrast, no measurable changes in these behaviour patterns were observed before and after the establishment of the winner-loser relationship. With increasing body size, the probability of tailflips decreased while that of retreats increased as the submissive behavioural act of subordinate animals.

Interlocking of chelae is a key factor for dominance hierarchy formation in crayfish.

We characterized the role of chelae during agonistic encounters of the crayfish Procambarus clarkii. Physical asymmetries in body length, body mass and chelae size were directly related to dominance hierarchy formation. More than 80% of winning crayfish had longer body and chelae lengths, and winners were usually heavier in body mass, even if their differences were less than 3% compared with losing opponents. In mismatched pairings, large crayfish with short chelae were beaten by small crayfish with large chelae. Three physical elements of body length, body mass and chelae length equally affected the outcome of agonistic bouts. Chelae restriction, in which chelae were tightly closed using rubber bands, affected the outcome of agonistic bouts between large and small crayfish. Before chelae restriction, large crayfish won in all pairings. Following chelae restriction for at least 30 days from the first encounters, the winning rate of large crayfish that were previous winners decreased significantly in the second encounters against the same opponents that were previous losers. The handicap of chelae restriction significantly prolonged the time to formation of the winner-loser relationship. Individual fights escalated during agonistic bouts between large crayfish with one chela restricted and small crayfish with intact chelae, whereas the number of fights increased but the duration of individual fights did not increase in large crayfish with both chelae restricted. Furthermore, when the chelae of both large and small crayfish were disabled, the dominance order was frequently not formed during 30 min of agonistic bouts. Preventing chelae from interlocking prevented escalation of agonistic bouts. We show that interlocking of chelae acted as a key factor for the formation of dominance hierarchy.

Smelling, feeling, tasting and touching: behavioral and neural integration of antennular chemosensory and mechanosensory inputs in the crayfish.

Crustaceans possess two pairs of prominent, movable sense organs on the rostral aspect of their bodies termed antennae: (1) a relatively short, usually bifurcate pair, the 1st antennae, also referred to as antennules, and (2) a much longer, uniramous pair, the 2nd antennae, or just 'antennae'. The antennules are equipped with diverse arrays of six or more types of cuticular setae, most of which are believed to have a sensory function. Axons from these structures course within the antennular nerve to the deutocerebrum, a large middle brain region that is known to receive chemoreceptor and mechanoreceptor inputs. In crayfish, axons from two kinds of single sensory-function setae, the olfactory receptor aesthetasc sensilla and as yet unidentified hydrodynamic sensilla, on the lateral antennular flagellum terminate, respectively, within the ipsilateral olfactory lobe and the lateral antennular neuropil of the deutocerebrum, where their activity generates synaptic potentials in local interneurons having dendritic fields that span both of those regions. It has been suggested that the short-latency hydrodynamic input gates or otherwise supplements the olfactory input signals. Much less is known about the functional capabilities of the other sensillar types on the antennular flagella, including the bimodal sensilla: how their inputs are distributed to the various neuropils of the deutocerebrum, whether they target common or separate brain neurons, and the nature, if any, of their functional relationships to the aesthetasc and hydrodynamic sensilla. Integrated processing of chemical and hydrodynamic signals undoubtedly plays an important role in locating odorant sources, perhaps by detecting boundaries of odorant plumes (tropotactic discrimination); other less-plausible strategies include time averaging of turbulent odorant signals and determination of concentration slopes within turbulence-generated odorant patches. These gaps in our understanding present important, but surmountable, experimental challenges for the future.

Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons.

Animals commonly use their limbs as signals and weapons during territorial aggression. Asymmetries of limb performance that do not relate to asymmetries of limb size (cryptic asymmetry) could substantially affect disputes, but this phenomenon has not been considered beyond primates. We investigated cryptic asymmetry in male crayfish (Cherax dispar), which commonly use unreliable signals of strength during aggression. Although the strength of a chela can vary by an order of magnitude for a given size, we found repeatable asymmetries of strength that were only weakly related to asymmetries of size. Size-adjusted strength of chelae and the asymmetry of strength between chelae were highly repeatable between environmental conditions, suggesting that asymmetries of strength stemmed from variation in capacity rather than motivation. Cryptic asymmetry adds another dimension of uncertainty during conflict between animals, which could influence the evolution of unreliable signals and morphological asymmetry.