Chela Size Research Articles

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.

Some ecological aspects of the land hermit crab Coenobita scaevola (Coenobitidae) at Wadi El-Gemal protected area, Red Sea

Gastropod shells can be a limiting factor in allowing hermit crab populations to increase. The impact of this factor on population size of the land crab Coenobita scaevola (Forskal, 1775) was examined. Extensive and intensive works were conducted on a sandy beach of Wadi El-Gemal island and the protected area coast (35°04’0”E, 24°42’0”N). Activity, spatial and temporal distribution, food foraging, and impact of human tourism activities for this hermit crab were discussed. A total of 365 crab individuals were collected from the sandy beach of Wadi El-Gemal island during August 2007 to July 2008, among these 137 were used for frequency measurements of occupied shells by the land hermit crabs. The hermit crabs were found occupying seventeen species of gastropod shells. A significant regression and correlation were recorded between the shell aperture and chelae. However, our data showing no significant regression values between total body weight of crabs and for each of the shell weight and internal volume. From the other angle, the correlation relationship recorded high significant value for the same relationships. This may reflect that some smaller crabs tend to occupy larger shells than the preferred ones. Moreover, the shell species occupation as a function of chelar hermit crabs size. While the negative results between body weight of crab and both shell internal volume and weight it may be due to the variations behavior of some land hermit crab individuals within population. It is logical that fit the size of chelae with aperture of shell to achieve protection from predators while some members of the population that occupied shell is greater than the size of his body to the unavailability of appropriate shells.

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.

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.

Age and growth of Callinectes danae (Brachyura: Portunidae) in a tropical region

Some 2178 male and 2109 female Callinectes danae Smith, 1869 were caught in Northeastern Brazil, from March 2009 through February 2010; we reared 24 males and 24 females for 6 months. The relative growth (relation between weight and cephalothorax width) showed negative allometry, except in adult males. The females presented marked changes in relative size of the fifth pleomere as they matured, while the males showed changes in chela size. As rearing progressed, the females underwent ecdysis five times while the males underwent ecdysis six times. The puberal molt was the last to occur. The von Bertalanffy growth model (with t0) provided the best fit, when compared to the von Bertalanffy (with CW0), von Bertalanffy (with t0 = 0), Gompertz, and Richard models. The following growth functions for reared individuals were obtained: CW t = 9 . 88 ( 1 − exp ( − 0 . 0228 ( t + 14 . 27 ) ) ) and CW t = 8 . 02 ( 1 − exp ( − 0 . 0158 ( t + 26 . 23 ) ) ) . For wild individuals the growth functions were as follows: CW t = 12 . 12 ( 1 − exp ( − 0 . 0052 ( t + 29 . 36 ) ) ) and CW t = 9 . 48 ( 1 − exp ( − 0 . 0036 ( t + 59 . 04 ) ) ) , for males and females, respectively. The individuals reached smaller sizes in the rearing system; however, the growth rate was higher. The mean longevity ranged from 375 to 429 days for males and from 458 to 553 for females. The maximum longevity ranged from 550 to 860 and from 764 to 1205 days, for males and females, respectively.

Comparison of Mating Behavior and Copulation in Male Morphotypes of the Spider Crab Libinia spinosa (Brachyura: Majoidea: Epialtidae)

The mating behavior of the spider crab Libinia spinosa Milne Edwards 1834 was studied in the laboratory. Two male morphotypes as morphometrically immature (MI) with small chelae and morphometrically mature (MM) with large chelae were used in non competitive and competitive mating trials. The liberation of putative hormones by receptive females to attract males was studied. We examined whether male body or cheliped size influence mate acquisition and copulation. The liberation of putative hormones by receptive females could not be demonstrated because males did not behave differently among four treatments exposed to water from 1) ovigerous females, 2) non ovigerous females, 3) males, and 4) a control of water unexposed to crabs. Under non competitive and competitive scenarios, copulation occurred immediately after physical contact between partners, thus a contact pheromone could be involved. The copulatory behavior and the time of copulation were similar between both male morphotypes. In non-competitive mating trials, MI males copulated successfully with females, and immediately after the mating pairs decoupled. By contrast, MM males displayed a post-copulatory guarding behavior that consisted of holding the female with the major cheliped and carrying her around the aquarium. In a competitive scenario, MM males guarded females for several hours by either caging them within the legs, or holding them out of the water when MI males approached. MI males of larger sizes than MM males did not gain mates and avoided agonistic interactions with MM males; thus, large chelae size is a more decisive trait than large body size for mate acquisition.

Effects of androgenic gland ablation on growth and reproductive parameters of Cherax quadricarinatus males (Parastacidae, Decapoda)

This work investigates the effects of androgenic gland (AG) ablation on the structure of the reproductive system, development of secondary sexual characters and somatic growth in Cherax quadricarinatus males. The AG ablation, which was performed at an early developmental stage (initial weight: 1.85 ± 0.03 g), had no effect on the somatic growth parameters (specific growth rate and growth increment), but it prevented the re-formation of male gonopores and appendices masculinae. However, the red patch differentiation and chelae size were similar to those in control males. All the ablated animals developed a male reproductive system. Testis structure was macroscopically and histologically normal. The distal portion of the vas deferens (DVD) was enlarged in some animals, with histological alterations of the epithelium and the structure of the spermatophore. Results suggest that the higher growth in males than in females may be due to an indirect effect of the AG on energy investment in reproduction rather than to a direct effect of an androgen. This is the first report of a potential action of the AG on the secretory activity of the distal VD and the structural organization of the spermatophore. Although the AG may play a role in the development of male copulatory organs, its association with the red patch development deserves further research. The results obtained in the present study support and complement those from intersexes of the same species.

Population Structure of the Christmas Island Blue Crab, Discoplax hirtipes (Decapoda: Brachyura: Gecarcinidae) on Christmas Island, Indian Ocean

The population structure of the freshwater land crab Discoplax hirtipes (Gecarcinidae) was studied on Christmas Island, Indian Ocean, to which this species is endemic in its blue colour form. Despite previous overexploitation of this crab, this is the first such study to take place for this species on Christmas Island. Surveys were conducted in the dry (non-migration) season, at Ross Hill Gardens, which is one of several permanent ‘residential areas’ inhabited by D. hirtipes. The sex ratio was found to be skewed in favour of males 2:1. Similarly to other gecarcinid species, male crabs were found to grow larger than females in terms of body weight, carapace width and chelae size (length and width). During the survey, few juveniles were found, which could suggest an ageing population. Despite being protected by law on Christmas Island, this is potentially worrying for a species that due to its restricted distribution continues to be especially vulnerable to outside threats, including that of aggressive invasive species and long term habitat destruction.

Boldness as a consistent personality trait in the noble crayfish, Astacus astacus

Consistent individual differences in behavioural responses to perceived predation risk may have extensive ecological and evolutionary implications. We studied the repeatability of boldness across time and its relation to resource holding potential in the noble crayfish, Astacus astacus L., using predator-naive immature individuals. We followed individual’s shelter use both with and without exposure to the chemical and physical cues of predators, and with and without the presence of a conspecific. In addition, we examined if armament, i.e. relative chelae size, would be correlated with individual differences in behaviour. Individuals showed repeatable behaviours across time and context. Individuals that occupied the shelter in competitive dyadic tests also spent more time in the shelter during individual control observations, suggesting that boldness is a personality trait that does not necessarily relate positively to high resource holding potential in the noble crayfish. The relative size of chelae did not correlate with any of the measured behavioural variables. Our results suggest that boldness can be considered as individually consistent and ecologically important personality trait in the noble crayfish.

Aggressive Interactions of the Endangered Nashville Crayfish,Orconectes shoupi

Aggressive interactions, differences in chela size, and the effect of chela size on outcomes of aggressive interactions were studied in a laboratory setting using the federally protected (endangered) Orconectes shoupi (Nashville Crayfish), and two sympatric species, O. placidus (Bigclaw Crayfish) and O. durelli (Saddle Crayfish). Orconectes placidus and O. durelli are potential threats to O. shoupi through competitive or aggressive interactions. Understanding such interactions could help explain species distributions, provide insight on additional threats, and guide management decisions regarding Nashville Crayfish translocations. Aggressive interactions were examined with 30-min videotaped trials between body-size-matched hetero- and conspecific pairs. The predicted influence of chela size on outcomes of aggressive interactions was also analyzed. Our results demonstrated that O. shoupi males and females were significantly more aggressive than O. placidus. However, O. durelli females won more encounters and were slightly more aggressive than O. shoupi females. Significant differences in chela size were detected in some body-size-matched species and gender pairings: O. shoupi males had narrower chelae than O. durelli males; and O. shoupi females had longer and wider chelae than O. placidus females, and longer but narrower chelae than O. durelli females. Although chela size appeared to play a role in dominance, it was not the only factor influencing outcomes of aggressive interactions. Our laboratory results did not identify displacement threats to O. shoupi from O. placidus, and therefore do not preclude introduction of O. shoupi into habitat occupied by O. placidus to meet recovery plan objectives. However, interspecific aggression in the presence of a vital resource (e.g., food or shelter) was not tested here and should be investigated to provide a more comprehensive evaluation of possible threats to O. shoupi.

Comparison of chela size and pincer force in scorpions; getting a first grip

A key feature of the ancient body plan of scorpions is the pincer or chela. These multifunctional structures vary considerably in size and shape between different scorpion species. Here we provide the first comparative data on the pinching performance of the chelae of seven species of scorpions exemplifying the extremes of the shape range from slender to robust; Leiurus quinquestriatus, Androctonus amoreuxi, Androctonus australis, Hadogenes sp., Pandinus imperator, Scorpio maurus and Pandinus cavimanus (in the order of decreasing chela height to width ratio). Size-corrected chela height correlates highly with maximum pinch force. Independent contrasts suggest that the correlation of chela width, height and fixed finger length with maximum pinch force is independent of phylogeny, suggesting an adaptive component to the evolution of chela shape and performance.

Signal residuals and hermit crab displays: flaunt it if you have it!

In animal contests selection should favour information gathering regarding the likely costs and benefits of continued conflict, and displays may provide a means for contestants to gain information about the fighting ability or aggressive intent of competitors. However, there is debate over the reliability of such displays and low levels of deception may occur within otherwise honest signalling systems. Hermit crabs use displays involving the chelipeds during agonistic encounters. We examined how variation in chelae size in relation to body size, a determinant of fighting ability, affects their use in displays and the process and outcome of contests over gastropod shells. In accordance with deceptive use of an otherwise honest signal, we found that contestants with large chelipeds for their body size spent more time performing the cheliped presentation display. Moreover, cheliped residuals and displays influenced the escalation level of encounters. There was a positive association between cheliped displays and the occurrence of ‘grappling’, but a negative association between displays and the occurrence of shell fights, suggesting that displays may signal aggressive intent and a reluctance to back off or accept the more passive defender role in a fight. Furthermore, the smaller of the two contestants in shell fights had larger cheliped residuals compared to those smaller contestants not involved in shell fights, which is consistent with disrupted opponent assessment. This study adds to mounting evidence that when acting as a signaller, individuals for whom the display exaggerates competitive ability attempt to manipulate opponents, using the display more often.

Costs and benefits of increased weapon size differ between sexes of the slender crayfish,Cherax dispar

Unreliable signals of weapon strength are considered to be problematic for signalling theory and reliable signals are predicted to be the dominant form of signalling among conspecifics in nature. Previous studies have shown that males of the Australian freshwater crayfish (Cherax dispar) routinely use unreliable signals of strength whereas females use reliable signals of weapon strength. In this study, we examined the performance benefits of increased weapon (chela) size for both males and females of C. dispar. In addition, we investigated the possibility of functional trade-offs in weapon size by assessing the relationship between chela size and maximum escape swimming performance. We found males possessed larger and stronger chelae than females and the variance in chela force was greater for males than females. By contrast, females possessed greater absolute and body length-specific escape swimming speeds than males. Swimming speed was also negatively correlated with chela size for males but not females, suggesting that a functional trade-off exists for males only. Decreases in swimming speed with increases in weapon size suggest there could be important fitness costs associated with larger chelae. Larger weaponry of males may then act as a handicap ensuring large chelae are reliable signals of quality.

Differential Growth in Body and Chela Size Following Molts to Form I and Form II in the Crayfish, Orconectes Rusticus (Decapoda, Cambaridae)

The presence of two male morphs in crayfishes of the family Cambaridae is well established, but the selective value of this trait is unknown. Measurements of growth following molts to Form I and Form II were used to examine the hypothesis that alternating between the two molts may serve as an adaptation allowing animals to efficiently increase overall body size. The results revealed that the change in carapace length was significantly greater in animals molting to Form II, whereas changes in chela length and width were significantly greater in animals molting to Form I. These differences allow animals to maximally increase body length when molting to Form II and maximally increase chela size when molting to Form I. La presence de deux morphotypes chez les ecrevisses de la famille des cambarides est bien etablie, mais la valeur selective de ce trait est inconnue. Des mesures de croissance, suivant la mue de la Forme I a la Forme II ont ete utilisees pour examiner l'hypothese que l'alternance entre deux types de mues pourrait servir comme strategie adaptative permettant a l'animal d'accroitre efficacement sa taille generale. Les resultants revelent que les changements dans la longueur de la carapace ont ete significativement plus eleves chez les animaux qui muent en Forme II, alors que la longueur et largeur de la pince ont ete significativement plus elevees chez les animaux qui muent en Forme I. Ces differences permettent aux animaux de maximaliser l'accroissement de leur taille a la mue vers la Forme II, et celle de leur pince a la mue vers la Forme I.

Weapon size is a reliable indicator of strength and social dominance in female slender crayfish (Cherax dispar)

Weapons are specialized structures that are commonly used by animals to signal fighting ability and resource holding potential during agonistic encounters. Current theory predicts weapon size should reliably indicate weapon strength and unreliable signals should only occur at very low frequencies in nature. However, a recent study found weapon size was an unreliable signal of strength during agonistic interactions among males of the slender crayfish (Cherax dispar). In this study, we investigated the relationship between morphology, performance and social dominance in females of C. dispar. Based on current theory, we predicted chela size would reliably indicate chela strength and would relate indirectly to dominance via its influence on strength. We found females that possessed large chelae were more likely to possess stronger chelae, and those individuals with stronger chelae were more likely to win competitive bouts. The best predictive model of the relationships among morphology, performance and dominance indicated chela size indirectly affected social dominance via its influence on strength, thus demonstrating displays of weaponry are reliable signals of fighting ability. Reliable signals of strength among females of C. dispar supports current theory predicting stable signalling systems should largely consist of honest displays of strength. However, this contrasts with previous work demonstrating that male C. dispar routinely uses unreliable signals of weapon strength during agonistic encounters.

Pinching forces in crayfish and fiddler crabs, and comparisons with the closing forces of other animals

The pinching forces of crustaceans are in many respects analogous to the biting forces of vertebrates. We examined the effects of body size and chelae size and shape, on the closing forces of the fiddler crab, Uca pugilator, and the crayfish, Procambarus clarkii. We hypothesized that the allometric relationships would be similar among species, and comparable to those reported for other decapod crustaceans. We further hypothesized that the scaling of the closing forces of crustaceans, with respect to body size and with the geometry of the pinching or biting structures, would be similar to that of vertebrates. We found that pinching forces increased with body mass, claw dimensions, and claw mass in U. pugilator, but only with claw height and claw mass in P. clarkii. Contraction time increased with body mass for both species combined, whereas contraction speed decreased. Pooled data for these and 17 other species of decapod crustacean revealed a positive correlation between the pinching force and body mass with a scaling exponent of 0.71. These data are remarkably comparable to the values on closing forces of vertebrate jaws, with the pooled data having a scaling exponent of 0.58, slightly below the value of 0.67 predicted for geometric similarity. Maximum closing forces vary tremendously among both crustaceans and animals in general, with body size and food habits being among the most important determining factors.

Dishonest Signals of Strength in Male Slender Crayfish (Cherax dispar) during Agonistic Encounters

Many animals resolve disputes without combat by displaying signals of potential strength during threatening displays. Presumably, competitors use each other's displays to assess their relative strengths, and current theory predicts that these signals of strength should generally be honest. We tested this prediction by investigating the relationships among morphology, performance, and social dominance in males of the slender crayfish Cherax dispar. Crayfish routinely use their enlarged front claws (chelae) for both intimidation and fighting, making this species ideal for studying the honesty of weapon size. We evaluated five competing models relating morphological and physiological traits to dominance during paired competitive bouts. Based on the best model, larger chelae clearly resulted in greater dominance; however, chela strength had no bearing on dominance. Thus, displays of chela size were dishonest signals of strength, and the enlarged chelae of males seemingly function more for intimidation than for fighting. In addition, an analysis of the performance of isolated chela muscle showed that muscle from male crayfish produced only half the force that muscle from female crayfish produced (236.6+/-26.4 vs. 459.5+/-71.6 kN m(-2)), suggesting that males invest more in developing larger chelae than they do in producing high-quality chela muscle. From our studies of crayfish, we believe dishonest signaling could play a greater role in territorial disputes than previously imagined.

Gonopore sexing technique allows determination of sex ratios and helper composition in eusocial shrimps

An evaluation of the social organization and sexual system of eusocial species of Synalpheus has been hindered because it has not been possible to determine the sexual composition of colony helpers (workers). The external sexual characters typically used to sex caridean shrimps are lacking in Synalpheus. We used SEM sexing technique to determine the sexual composition of helpers in colonies of Synalpheus regalis, S. rathbunae, S. chacei, S. rathbunae A (see Morrison et al. Mol Phylogen Evol 30:563–568, 2004), and S. filidigitus. Colonies consisted of both sexes and sex ratios of helpers generally conformed to 50:50 female to male. Females were characterized by gonopores with U-shaped slits on the coxae of the third pereopods (first walking legs) while males had oval gonopore openings on the coxae of the fifth pereopods (third or last walking legs). In S. chacei, S. filidigitus, and S. rathbunae A, a few helpers were found that had both male and female gonopores (intersexes). All three reproductive females (queens) of S. filidigitus examined were intersexes. Sexing of helpers allowed us to test some hypotheses about sexual differences in helper morphology that might indicate task specialization (division of labor). Male helpers were not different from female ones in body size (except in S. regalis: males somewhat larger) and in fighting chela size. The lack of sexual dimorphism in these characters suggests no male–female specialization in colony tasks such as defense. The presence of male and female helpers similar in size suggests that the sexual system of these eusocial species is gonochoristic, although protandry of some sort in S. filidigitus can not be ruled out. The intersexuality observed in a few individuals may be due to developmental anomalies, protandry, or even simultaneous hermaphroditism. Finally, the sexing technique allowed us to establish that new colonizers of unoccupied sponges in S. rathbunae are a single male and female of helper size.

Female freshwater crayfish adjust egg and clutch size in relation to multiple male traits

Females may invest more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred partners may be fitter than offspring sired by non-preferred ones. In this study, we tested the differential maternal allocation hypothesis in the freshwater crayfish, Austropotamobius italicus, by means of a pairing experiment aimed at evaluating the effects of specific male traits (body size, chelae size and chelae asymmetry) on female primary reproductive effort. Our results showed that females laid larger but fewer eggs for relatively small-sized, large-clawed males, and smaller but more numerous eggs for relatively large-sized, small-clawed males. Chelae asymmetry had no effects on female reproductive investment. While the ultimate consequences of this pattern of female allocation remain unclear, females were nevertheless able to adjust their primary reproductive effort in relation to mate characteristics in a species where inter-male competition and sexual coercion may mask or obscure their sexual preferences. In addition, our results suggest that female allocation may differentially affect male characters, thus promoting a trade-off between the expression of different male traits.

Effect of Eyestalk-Ablation on Circulating Ecdysteroids in Hemolymph of Snow Crabs, Chionoecetes opilio: Physiological Evidence for a Terminal Molt

Bering Sea snow crabs (Chionoecetes opilio) are a commercially important crab harvested in the Bering Sea. Optimal management of this species requires an understanding of the biology of this crab that is currently incomplete. Fisheries managers apply a continuous growth model in their management of snow crab, which assumes that male crabs increase in size throughout their lifespan. Male snow crabs undergo a morphometric molt that leads to a disproportionate increase in chelae size and it is still debated whether this molt is associated with a terminal molt. This study was conducted to determine whether adult male C. opilio are anecdysic. Using current knowledge of the hormonal regulation of crustacean growth, snow crab physiology was manipulated to induce an increase in molting hormones (ecdysteroids). Since female snow crabs are known to undergo a terminal molt after attaining reproductive maturity, we compared ecdysteroid levels in eyestalk-ablated terminally molted females, small-clawed males and large-clawed males. Snow crabs were collected from the Bering Sea and maintained in circulating seawater at approximately 6°C. Animals were either eyestalk-ablated or left intact. Ecdysteroid levels in hemolymph were quantified using an enzyme-linked immunosorbant assay (ELISA). Circulating ecdysteroids were significantly higher in small-clawed male crabs when compared to large-clawed males or terminally molted females. Eyestalk-ablation increased circulating ecdysteroids in small-clawed males, but had no significant effect on circulating ecdysteroids in large-clawed males or in terminally molted females.