Larger Chelae Research Articles

Reproductive biology of the red swamp crayfish Procambarus clarkii (Girard, 1852) (Decapoda: Astacidea: Cambaridae): A review

Abstract The red swamp crayfish Procambarus clarkii (Girard, 1852) is an alien invasive species as well as a commercially exploited animal. The sterile-male-release technique (SMRT) using infertile but sexually active males has been an effective candidate measure to control this invasive crayfish. Additionally, the limited supply of juveniles due to females’ spawning seasonality hinders the further development of the P. clarkii aquaculture industry. Information on its reproductive biology, such mating strategies and factors affecting offspring production, is crucial for developing an effective SMRT and aquaculture systems for P. clarkii. We review the reproductive biology of this species in terms of 1) sexual dimorphism and reproductive status, 2) sex recognition, mating, and mate preferences, and 3) egg production, embryonic development, and hatching. Intra- and intersexual dimorphisms of chelae are evident in P. clarkii, and a reproductive morphotype (form I) with larger chelae and a non-reproductive morphotype (form II) with smaller chelae are detected in both females and males, allowing us to easily determine the reproductive status of both sexes. The crayfish exhibits mutual mate choice (i.e., preference for larger mates), and small-sized males reproductive potential is low. Female fitness (i.e., number of offspring) generally depends on their body size. Female brood care appears to promote early embryo development before the egg-nauplius stage. Further study is required to identify the maternal factors affecting early embryonic development, which may improve measures for controlling invasive populations and enhancing aquaculture productivity.

Morfologi dan Geometri Morfometri Holthuisana sp. (Crustacea, Decapoda, Gecarcinucidae) dari Danau Sentani, Papua

Holthuisana is a freshwater crab member of the family Gecarcinucidae which has a distribution in eastern Indonesia to Australia. This study was aimed to determine the variations in the shape of carapace and chelae within genus Holthuisana collected from Sentani Lake, Papua using analysis of geometric morphometric. The morphological characters confirmed the specimen examined belong to genus Holthuisana. The results showed that male crabs had slightly larger carapace length and width than females. The length and width of the large chelae in male crabs are greater than that of females. The ratio of carapace length and width to male is 6:5, and female is 5:4. The ratio of the length and width of the chelae (propodus) in male crabs is 9:5, and in females 2:1. Based on the 16 landmarks of carapace, there are no significant different between male and female crabs. Thus, based on 12 landmarks of chelae, the large right cheliped shows different variations between males and females. The large right cheliped of the males shows more convex on polex and propodus compare to the females. The large left cheliped shows variations that are not much different.Key words: freshwater crab; geometric morphometrics; morphological characters; New Guinea

Force and Boldness: Cumulative Assets of a Successful Crayfish Invader

Multiple causes can determine the disturbance of natural equilibrium in a population of a species, with a common one being the presence of invasive competitors. Invasives can drive native species to the resettlement of the trophic position, changing reproduction strategies or even daily normal behaviours. Here, we investigated the hypothesis that more effective anatomical features of an intruder (Faxonius limosus) come with increased boldness behaviour, contributing to their invasion success in competition against the native species (Pontastacus leptodactylus). We tested the boldness of specimens representing the two species by video-based assessment of crayfish individuals’ attempts to leave their settlement microenvironment. The experiment was followed by a series of measurements concerning chelae biometry, force and muscle energetics. The native species was less expressive in terms of boldness even if it had larger chelae and better muscular tissue performance. In contrast, because of better biomechanical construction of the chelae, the invasive species was capable of twice superior force achievements, which expectedly explained its bolder behaviour. These findings suggest that, in interspecific agonistic interactions, the behaviour strategy of the invasive crayfish species is based on sheer physical superiority, whereas the native crayfish relies on intimidation display.

Eocarcinus praecursor Withers, 1932 (Malacostraca, Decapoda, Meiura) is a stem group brachyuran

Beginning with the description by Withers in 1932, Eocarcinus praecursor from the Jurassic has long been considered the oldest representative of the Brachyura. In 2010 Feldmann and Schweitzer re-investigated the specimens of E. praecursor and expressed doubts about the brachyuran nature of this species. Among other characters, the suspected existence of small chelae in the 2nd or 3rd pereopods led them to the conclusion that E. praecursor must be removed from the Brachyura and rather be seen as a representative of the Anomala. However, Anomala also do not possess chelae on the 2nd and 3rd pereopods. This contradiction and other aspects initiated a new investigation of E. praecursor. It can be shown that neither the 2nd nor the 3rd pereopods of E. praecursor are chelate. Furthermore, there are no other derived characters shared with anomalans. By contrast, there are a number of apomorphies shared with Brachyura such as the shape and articulation of the large chelae and the attachment points of the last two pereopods. However, not all apomorphies of the crown group are present yet. Thus, E. praecursor is a stem group representative, which allows statements about individual steps in the evolution of the set of characters of the crown group Brachyura.

Sexual Dimorphism and Reproductive Status of the Red Swamp Crayfish Procambarus clarkii.

The red swamp crayfish Procambarus clarkii is native to northeastern Mexico and the south-central USA, and it has expanded its distribution worldwide and negatively impacted the ecosystems in the invaded regions. The dynamics of the P. clarkii populations have been studied as the basis for the development of effective control measures against this invasive alien species. Adult males of P. clarkii exhibit a cyclical dimorphism between two sexual morphotypes; reproductive form I has large chelae and non-reproductive form II has small chelae. However, whether P. clarkii females have two sexual morphotypes and exhibit form alternation has not been resolved, and little is known about the degree of intra-sexual dimorphism of the chelae, even among males. We employed allometric growth analysis on the chelae dimensions of P. clarkii females and males that were collected from a small pond in Yokohama, Japan. Our analysis demonstrated the existence of form I, which has larger chelae, and form II, which has smaller chelae, in P. clarkii females and highlighted the intra- and inter-sexual dimorphisms in the chelae of this species. The reproductive cycle of the population was successfully traced by the reproductive status of P. clarkii based on the occurrence patterns of each sexual morphotype; the form I crayfish occurred throughout the sampling period from April to December, while the occurrences of form I females and males were highly correlated, peaking in October. Our results suggested that alternation of sexual forms occurs in P. clarkii females. The ability to discriminate between the sexual morphotypes based on chelae allometric growth would allow us to evaluate the female reproductive status more easily and precisely in invasive P. clarkii populations.

Morphology, performance and fluid dynamics of the crayfish escape response.

Sexual selection can result in an exaggerated morphology that constrains locomotor performance. We studied the relationship between morphology and the tail-flip escape response in male and female rusty crayfish (Faxonius rusticus), a species in which males have enlarged claws (chelae). We found that females had wider abdomens and longer uropods (terminal appendage of the tail fan) than males, while males possessed deeper abdomens and larger chelae, relative to total length. Chelae size was negatively associated with escape velocity, whereas longer abdomens and uropods were positively associated with escape velocity. We found no sex-specific differences in maximum force generated during the tail flip, but uropod length was strongly, positively correlated with tail-flip force in males. Particle image velocimetry (PIV) revealed that the formation of a vortex, rather than the expulsion of fluid between two closing body surfaces, generates propulsion in rusty crayfish. PIV also revealed that the pleopods (ventral abdominal appendages) contribute to the momentum generated by the tail. To our knowledge, this is the first confirmation of vortex formation in a decapod crustacean.

The exoskeleton of scorpions’ pincers: Structure and micro-mechanical properties

Since scorpions exist almost all over the world, some expected body differences exist among the species: undoubtedly, the most evident is the shape and size of their pincers or chelae. The scorpion chela is a multifunctional body component (e.g. attack/defense, mating and protection from the environment) that leads to the development of different stresses in the cuticle. How such stresses in the cuticle are accommodated by different chelae shape and size is largely unknown. Here we provide new comparative data on the hierarchical structure and mechanical properties of the chela cuticle in two scorpion species: Scorpio Maurus Palmatus (SP) that has a large chela and Buthus Occitanus Israelis (BO), with a slender chela. We found that the SP exocuticle is composed of four different sublayers whereas the BO exocuticle displays only two sublayers. These structures are different from the exocuticle morphologies in crustaceans, where the Bouligand morphology is present throughout the entire layer. Moreover, the scorpion chela cuticle presents an exclusive structural layer made of unidirectional fibers arranged vertically towards the normal direction of the cuticle. Nanoindentation measurements were performed under dry conditions on transversal and longitudinal planes to evaluate the stiffness and hardness of the different chela cuticle layers in both scorpions. The chela cuticle structure is a key factor towards the decision of the scorpion whether to choose to sting or use the chela for other mechanical functions. Statement of SignificanceMany arthropods such as lobsters, crabs, stomatopods, isopods, and spiders have been the subject of research in recent years, and their hierarchical structure and mechanical properties extensively investigated. Yet, except for a limited number of pre-1980 publications, comparatively little work has been devoted to the terrestrial scorpion. The scorpion chela is a multifunctional part of the body (e.g. attack/defense, mating and protection from the environment) that involves the development of various stresses in the cuticle. How these stresses in the chela cuticle are managed by different chelae shape and size is still unknown. The lack of a single study that integrates morphological characterization of the entire hierarchical structure of the scorpion chela cuticle, and local mechanical properties, significantly affects the scientific knowledge regarding important structural approaches that can be used by nature to maximize functionality.

Sexual dimorphism in performance and muscle allocation in the western painted crayfish Faxonius palmeri longimanus (Faxon, 1898) (Decapoda: Astacidea: Cambaridae)

Multiple performance traits in animals can be affected by the same morphological feature. Armaments, or morphological weapons, and ornaments, morphological features used to attract mates, can have important influences on individual fitness. For example, ornaments of aquatic animals that improve fighting abilities or reproductive success can increase drag, resulting in decreased swimming performance. We investigated the effects of chela size on pinching force and escape performance in the western painted crayfish, Faxonius palmeri longimanus (Faxon, 1898). We predicted that individuals with larger chelae would swim more slowly than individuals with smaller chelae, and that males would be disproportionately affected because of male-biased sexual size dimorphism in chela size. We found support for our hypothesis that individuals with larger chelae would swim more slowly, but males and females were equally affected by large chela size, such that the differences in the scaling of chela growth did not correspond with differences in swimming performance for a given size. We also found that increased chela size in females corresponded strongly with increased strength. This was not necessarily the case for males, which exhibit three times as much variance in chela strength for a given chela size than females, potentially suggesting the use of dishonest signaling in this species. Muscle allocation differences between the sexes could also suggest that males can dishonestly signal their competitive abilities, such that weak males can have large chela. Our data support the idea of tradeoffs and lead us to further hypothesize about the roles of different life history strategies within the western painted crayfish.

Subterranean Invasion by Gapped Ringed Crayfish: Effectiveness of a Removal Effort and Barrier Installation

Non-native crayfish invasion is a major threat to many stream fauna; however, invasions in subterranean habitats are rarely documented. Our study objectives were to examine demographics and morphological and life-history traits of a gapped ringed crayfish Faxonius neglectus chaenodactylus population that invaded Tumbling Creek Cave and determine the effects of removal on the population. Crayfish were found throughout the cave though fewer individuals were observed upstream of an installed weir. Fecund females were collected in nearly all months, but were prevalent during spring (February–June). Males and females were of similar sizes. Males had larger chelae and chelae that were regenerated slightly more often than females. Removal of >4000 crayfish since 2011 resulted in reduced abundances, but the population persisted. Age estimates from counting bands on gastric mills indicated crayfish within the cave lived longer than populations in nearby Big Creek (6 vs. 4 years). Recent efforts to prevent upstream cave migrations included a barrier installation and since installation, few crayfish have been located upstream. We show that exploitation of new environments may lead to trait changes (i.e., reproduction and longevity). We also demonstrate that barriers reduce the spread of invasion at a comparable cost to removal. We hypothesize that increased reservoir elevation inundates springs hydrologically connected to the cave and this may be the invasion source.

Carapace asymmetries in crabs

AbstractThrough the geometric morphometric approach of the landmark-based method applied on adult right-handed specimens ofCarcinus aestuarii,Liocarcinus depuratorandPotamon fluviatile, statistical analyses showed significant outcomes for fluctuating asymmetry in the three studied species, and directional asymmetry only inP. fluviatile(that showed a less convex carapace shape on the right side, where larger chela occurred). Although these findings may be correlated to some environmental constraints, such as soil composition, refuge occurrence and predatory pressure, also other interpretations may be proposed.

Morphometric characterization of the freshwater crab Potamon elbursi Pretzmann, 1962 in the Caspian Sea and Namak Lake hydrographic systems

The freshwater crab Potamon elbursi Pretzmann, 1962 is widely distributed in northwestern Iran, occurring in two separate hydrographic systems, one draining into the Caspian Sea and a second into Namak Lake. A total of 192 specimens from the two drainage systems were analyzed: 122 specimens from the Caspian drainage and 70 specimens from the Namak Lake drainage. Fourteen measurements of body dimensions were taken for traditional morphometric analyses, and eight landmarks and two semi-landmarks from the carapace were used for geometric-morphometric analyses. Morphometric analyses were performed with the aid of SPSS ver. 22 and geometric analyses using PAST ver. 2.14 and MorphoJ ver. 1.06d software. Adults and juveniles were separated using the K-means method, and puberty-size calculations revealed females reach morphometric puberty at smaller sizes than males. Sexual size dimorphism (SSD) and allometric growth findings revealed that males have longer carapaces, higher body height, and larger chelae, probably due to optimizing mating with females, whereas females have broader pleonal somites and a wider posterior carapace, likely because of more energy investment in egg care and reproduction. Although separate comparison of sexes between the two drainages showed no significant differences between females (in traditional morphometry), population comparisons (excluding pleonal characters) provide evidence for a significant distinction with partial overlapping. Poor dispersal ability and philopatric behaviour, as often known to occur in freshwater crabs, is probably responsible for such intraspecific differentiation in P. elbursi.

Allometric sexual dimorphism in the river crab Potamon fluviatile (Herbst, 1785) (Brachyura: Potamidae)

We studied the ontogenetic allometry pattern in the freshwater brachyuran crab Potamon fluviatile (Herbst, 1785) to describe some new sexual dimorphic features on the ontogenic trajectories of the chelae. We surveyed carapace width, chela length and width, dactylus length, and propodus length of both chelae of 93 females and 114 males to the nearest 0.05 mm using a vernier caliper. Our main result was the identification of morphological biometry showing a variability of the chela linked to growth allometry, with some different between-sex ontogenic trajectories. Specifically, we emphasized how the morphometric features of the chelae change during body-size growth with different increasing rates. Particularly, the observed significant shape changes are mainly due to positive allometries in both sexes, although negative allometries (the latter visible only in the propodus length of females) and isometries were observed as well. Our study confirms that a form of sexual dimorphism exists in the ontogenetic allometric trajectories of P. fluviatile in both the large and small chelae, these trajectories being related to mechanical aspects in predation, food manipulation, mate acquisition, and between-sex differences in aggressiveness during antagonistic fights.

Intersex in the gonochoristic crustacean Tanais dulongii (Audouin, 1826) (Peracarida: Tanaidacea: Tanaididae): a comparison of external reproductive characteristics

Tanais dulongii (Audouin, 1826) is a small benthic crustacean with separate sexes and a marked sexual dimorphism characterized by a cephalothorax narrowed anteriorly, larger chelae (claws) and a pair of tiny genital cones in males, and ovisacs that form chambers for carrying embryos in females. Recent studies have described the existence of intersexual individuals with a cephalothorax similar to males, large chelae and ovisacs, but, due to their small size, it has not been possible to confirm the presence of genital cones under normal light microscopy. The present study analyses and compares external reproductive structures under scanning electron microscopy, of male and female T. dulongii, to corroborate the presence of both ovisacs and genital cones in potentially intersex individuals. The possible causes, such as hermaphroditism, environmental sex determination, parasitism, genetic aberration or endocrine-disrupting pollutants, are discussed.

Chela asymmetry in a durophagous crab: predominance of right-handedness and handedness reversal is linked to chela size and closing force.

The swimming crab Portunus trituberculatus is a durophagous brachyuran. Right-handed crabs are predominant, but left-handed crabs are also found in nature. Left-handedness may arise from loss of the right crusher. We examined whether heterochely (morphology) was correlated with differences in closing force (physical property) and handedness (behaviour). The closing force was stronger in larger chela with greater apodeme height and handedness resided in the chela with stronger closing force. With loss of the right chela (autotomy), handedness transitioned from the right to left chela, and all crabs were left-handed thereafter. Reversed handedness was accompanied with a reduction of size and closing force in the regenerated right chela, and growth of the original left chela. After handedness reversal, dentition on the left dactylus of the newly-converted crusher was close to that of the original right crusher, but did not attain the same shape, even after 10 moults. Left-handed crabs were significantly worse than right-handed crabs at crushing hard-shelled prey. Chela formation was symmetrical in the zoea, and heterochely and right-handedness started in the megalopa, regardless of maternal handedness. Since the left chela is capable of being the crusher, heterochely may be caused by differences in morphogenetic velocity between the right and left chelae, under a signal discriminating right from left. Right-handedness is an attribute of P. trituberculatus, that would be inheritable across generations. It is probable that right-handedness was used in the earliest durophagous crabs, and this trend has been succeeded to extant species.

First record of the reef lobster Enoplometopus occidentalis (Randall, 1840) from Indian waters

specimen of the reef lobster, Enoplometopus occidentalis measuring carapace length 57.0 mm, total length 127.0 mm and 46.7 g in weight was landed at Mandapam fish landing centre, on the southeast coast of India. The lobster was caught during the deep sea trawl fishing operations off Mandapam (08° 58' N lat. 79° 16' E long.). This is the first record of the species from Indian waters. The morphological characters along with colour pattern are described. The large chelae in the specimen were found missing.

Sex and Weapons: Contrasting Sexual Dimorphisms in Weaponry and Aggression in Snapping Shrimp

AbstractSexual dimorphisms in weaponry and aggression are common in species in which one sex (usually males) competes for access to mates or resources necessary for reproduction – sexually dimorphic weaponry and aggression, in other words, are frequently the result of intrasexual selection. In snapping shrimp, the major chela (snapping claw) can be a deadly weapon, and males of many species have larger chelae than females, a pattern readily interpreted as resulting from intrasexual selection. Thus, males might be expected to show more sex‐specific aggression than females, and be more aggressive overall. We tested these predictions in two species of snapping shrimp in a territorial defense context. Neither of these predictions was supported: in both species, females, but not males, engaged in sex‐specific aggression and females were more aggressive than males overall. These contrasting sexual dimorphisms – larger weaponry in males but higher aggression in females – highlight the importance of considering the function of weaponry and aggression in contexts other than direct competitions over mates. In addition, species differences in the degree of sexual dimorphism in chela size were due to differences in female, not male, chela size, and the species with greater sexual dimorphism in weaponry was significantly less aggressive overall; also, while paired and solitary males did not differ in residual chela size, for the species with greater sexual dimorphism, females carrying embryos had smaller residual chela sizes. These results suggest that understanding the sexual dimorphisms in weaponry and aggression in snapping shrimp requires understanding the relative costs and benefits of both in females as well as males.

Morphological characterization and molecular phylogeny of Portunoidea Rafinesque, 1815 (Crustacea Brachyura): Implications for understanding evolution of swimming capacity and revision of the family-level classification

Cheliped construction, in particular the teeth pattern on chelae fingers is considered as most important character suit (along with burrowing/swimming apparatus) for the diagnosis of Portunoidea. Heterochelic and heterodontic chelipeds with the molariform tooth in the larger chela and multi-lobed serial teeth are presumably ancestral and most common pattern for the group. New material (mostly species of Thalamitinae Paulson, 1875, Lupocyclus Adamd and White, 1848 and Portunus Weber, 1795 sensu lato) have been combined with the existing sequences from the GenBank to produce molecular phylogenetic reconstructions based on the histone H3 gene fragment and a multi-gene tree (for smaller set of species) based on partial sequences of H3, D1 region of 28S gene and mitochondrial COI gene. These reconstructions have not provided necessary support to the monophyly of Portunoidea sensu lato but indicated the presence of several monophyletic lineages, i.e. Portunidae sensu stricto, Polybiidae+Thiidae+Carcinidae+Pirimelidae, Benthochascon+Geryonidae (to lesser extent), and Ovalipes. Monophyly of the Portunidae sensu stricto is supported by both the H3 and multigene trees and morphological evidence. Swimming capacity probably evolves as a result of parallel evolution in at least three different lineages of portunoids. A new version of the family level classification of Portunoidea and a key to their families are provided with the following taxa: Geryonidae (Geryoninae+Benthochasconinae subfam. nov.), Ovalipidae fam. nov., Brusiniidae Števčić, 1991, Thiidae, Pirimelidae, Carcinidae McLeay, 1838 (Carcininae+Portumninae Ortmann, 1893), Polybiidae Ortmann, 1893, and Portunidae Rafinesque, 1815 sensu stricto. The most radical change in the systematics of Portunidae sensu stricto is the final recognition of the polyphyly of Portunus sensu lato and the need for revalidization and re-diagnozing of several taxa that were synonymized by Stephenson and Campbell (1959) and Stephenson (1972) under Portunus. While some subfamilies of the Portunidae (Podophthalminae Dana, 1851, Thalamitinae, and Lupocyclinae Alcock, 1895) are well supported by molecular phylogenies and the presence of morphological synapomorphies, the others need re-assessment.

Life history and physical observations of primary burrowing crayfish (Decapoda: Cambaridae) Cambarus (Lacunicambarus) diogenes and Cambarus (Tubericambarus) polychromatus

Primary burrowing crayfish make up 15% of total crayfish species, but account for 32% of those imperiled. Primary burrowers are also much less studied as compared to secondary and tertiary burrowers. The purpose of this study was to observe the annual life cycles, and morphometric and morphological characteristics of two primary burrowing crayfish species: Cambarus (Lacunicambarus) diogenes Girard, 1852 and C. (Tubericambarus) polychromatus Thoma et al., 2005. Sampling occurred adjacent to two streams near Troy, AL, using hand excavation at one-month intervals from February 2011 to March 2012. A total of 195 C. diogenes (sex ratio = 1.3) and 194 C. polychromatus (sex ratio = 0.85) were collected. For a given size, C. diogenes had a broader carapace than C. polychromatus ( p< 0.001), and males had larger chelae than females for both species (p = 0.01 and p = 0.001, respectively). Minimum carapace length at sexual maturity (smallest form I) was 32.7 mm for C. diogenes males, 41.2 mm for C. diogenes females, 27.4 mm for C. polychromatus males, and 32.2 for C. polychromatus females. The proportion of form I males for both species increased in summer and remained at an increased level through winter, though C. polychromatus males remained reproductively active longer than C. diogenes. Females of both species were reproductively active only in winter except for one form I C. polychromatus female. Four ovigerous C. diogenes and three ovigerous C. polychromatus were collected in March, and five young of the year of C. polychromatus were found in burrows in June, July, and September.

The male of the deep-living hyperiid Hyperoche shihi Gasca, 2005 (Peracarida: Amphipoda) and a new symbiotic association in the Gulf of California

From samples of deep-water zooplankton, obtained in the Gulf of California, female and male specimens of the rare deep-living amphipod Hyperoche shihi Gasca, 2005 were collected. The adult male is slightly larger than the female and it has the distinctly large chela of pereopod II. A full description of the male is provided to complement the morphological information of this unique hyperiid species. This is the only deep-living species of Hyperoche Bovallius, 1887 known. These specimens were found in a symbiotic association with the coronate scyphomedusa Nausithoe rubra Vanhöffen, a deep-living form. The female was previously reported from the bathypelagic hydromedusa Chromatonema erythrogonon (Bigelow); hence, the host range of H. shihi is expanded and includes a scyphomedusa. There are no previous records of hyperiids associated to species of Nausithoe Kölliker. The amphipods were found grasped to the medusan exumbrella and were moving to the inner part of the medusa.

FOR CRAYFISH CLAWS, SIZE ISN'T EVERYTHING

In a crayfish fight to the death, the combatant with the larger claws usually has better odds. In fact, many crayfish fights don't even make it to the death. After sizing up each other's claws, called chelae, the crayfish with the smaller chelae will often surrender before the fight even begins. This is a sound strategy: it keeps both parties from getting unnecessarily injured, and the stronger crayfish wins. Unless large chelae are not as strong as they appear. When size-based signals are used to determine the outcome of competition, deception can run rampant. Crayfish may gain an advantage merely by investing more in the size of a chela than in the muscle used to power it. Michael Angilletta Jr of Arizona State University, USA, and Robbie Wilson of the University of Queensland, Australia, set out to find whether chela size was an honest indicator of strength in male crayfish.The researchers collected wild male crayfish and measured the force produced as each chela clamped down on a sensor composed of metal plates. To be sure that they were measuring actual maximum force production, the researchers measured force production at different temperatures and multiple times for each crayfish.While the authors found that in general strength increased with chela size, larger chelae exhibited much greater variation in force production. This pattern held across temperatures, so differences in strength among chela are likely to be a product of real physiological differences, instead of the crayfish's motivation at that time.As a result of this variation in strength, the larger the chela, the more unreliable the chela size as a signal of potential force production. In some cases, larger chelae were weaker than slightly smaller counterparts. These asymmetries of size and strength suggest that deceptive signaling in crayfish is common. Angilletta and Wilson propose two explanations for this phenomenon: either the crayfish benefit tremendously from having deceptive chelae or, alternatively, crayfish pay tremendous costs for attempting to identify their opponents' deceptive chelae.Cryptic asymmetry between size and performance adds another dimension of uncertainty to the competitive interactions of crayfish. A crayfish may not be able to accurately account for the strength of his competitor, or even know which chela is most dangerous. Further study may elucidate some of the complexities of dominance and the evolution of deceptive signaling in crayfish, to find out why bigger isn't always better.