Crayfishes are both a highly imperiled invertebrate group as well as one that has produced many invasive species, which have negatively affected freshwater ecosystems throughout the world. We performed a trait analysis for 77 crayfishes from the southeastern United States in an attempt to understand which biological and ecological traits make these species prone to imperilment or invasion, and to predict which species may face extinction or become invasive in the future. We evaluated biological and ecological traits with principal coordinate analysis and classification trees. Invasive and imperiled crayfishes occupied dif- ferent positions in multivariate trait space, although crayfishes invasive at different scales (extraregional vs. extralimital) were also distinct. Extraregional crayfishes (large, high fecundity, habitat generalists) were most distinct from imperiled crayfishes (small, low fecundity, habitat specialists), thus supporting the "two sides of the same coin" hypothesis. Correct classification rates for assignment of crayfishes as invasive or imperiled were high (70-80%), even when excluding the highly predictive but potentially confounding trait of range size (75-90%). We identified a number of species that, although not currently listed as imperiled or found outside their native range, possess many of the life-history and ecological traits characteristic of currently invasive or imperiled taxa. Such species exhibit a high latent risk of extinction or invasion and consequently should be the focus of proactive conservation or management strategies. Our results illustrate the utility of trait-based approaches for taxonomic groups such as invertebrates, for which detailed species-specific data are rare and conservation resources are chronically limited.

http://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2013/03/ConservationBiology_2010.pdf

Latent Extinction and Invasion Risk of Crayfishes in the Southeastern United States

Solifugae are an understudied group of relatively large arachnids with well over 1000 species distributed on almost all major continents. These highly active predators utilize their large chelicerae for feeding, defense, burrowing and mating. We investigated the differences in cheliceral morphology and performance of two ecologically divergent species from North Africa; the cursorial Galeodes sp. and the burrowing Rhagodes melanus. Morphological data show differences in aspect ratio between the two species. Bite force measurements show Rhagodes (N=11) to be a much stronger biter than Galeodes (N=8), in terms of both absolute maximum force (Rhagodes 5.63 N, Galeodes 2.12 N) and force relative to cheliceral size. Synchrotron microtomographs of one specimen for each species reveal large differences in physiological cross-sectional area (PCSA) and estimated muscle stress, resulting in a much higher muscle stress in Rhagodes. This species also showed a longer muscle fiber length. Muscle volume and PCSA were found to differ between the two chelicerae in the two scanned specimens. Whereas Rhagodes reflects this morphological asymmetry in having a higher bite force in the right chelicera, Galeodes shows no such bias.

Functional morphology and bite performance of raptorial chelicerae of camel spiders (Solifugae)

Knowing the functionality and capabilities of masticatory apparatuses is essential for the ecological classification of jawed organisms. Nevertheless insects, especially with their outstanding high species number providing an overwhelming morphological diversity, are notoriously underexplored with respect to maximum bite forces and their dependency on the mandible opening angles. Aiming for a general understanding of insect biting, we examined the generalist feeding cockroach Periplaneta americana, characterized by its primitive chewing mouth parts. We measured active isometric bite forces and passive forces caused by joint resistance over the entire mandibular range with a custom-built 2D force transducer. The opening angle of the mandibles was quantified by using a video system. With respect to the effective mechanical advantage of the mandibles and the cross-section areas, we calculated the forces exerted by the mandible closer muscles and the corresponding muscle stress values. Comparisons with the scarce data available revealed close similarities of the cockroaches’ mandible closer stress values (58 N/cm2) to that of smaller specialist carnivorous ground beetles, but strikingly higher values than in larger stag beetles. In contrast to available datasets our results imply the activity of faster and slower muscle fibres, with the latter becoming active only when the animals chew on tough material which requires repetitive, hard biting. Under such circumstances the coactivity of fast and slow fibres provides a force boost which is not available during short-term activities, since long latencies prevent a specific effective employment of the slow fibres in this case.

/pdf/fast-and-powerful-biomechanics-and-bite-forces-of-the-3cdom9mfvj.pdf

Fast and Powerful: Biomechanics and Bite Forces of the Mandibles in the American Cockroach Periplaneta americana

Crustaceans can exert a greater force using their claws than many animals can with other appendages. Furthermore, in decapods, the chela is a notable organ with multifunctional roles. The coconut crab, Birgus latro, is the largest terrestrial crustacean and has a remarkable ability to lift weights up to approximately 30 kg. However, the pinching force of this crab’s chelae has not been previously investigated. In the present study, we measured the pinching force of the chelae in 29 wild coconut crabs (33–2,120 g in body weight). The maximum force ranged from 29.4 to 1,765.2 N, and showed a strong positive correlation with body mass. Based on the correlation between pinching force and body weight, the force potentially exerted by the largest crab (4 kg weight) reported in a previous study would be 3300 N, which greatly exceeds the pinching force of other crustaceans as well as the bite force of most terrestrial predators. The mighty claw is a terrestrial adaptation that is not only a weapon, which can be used to prevent predator attack and inhibit competitors, but is also a tool to hunt other terrestrial organisms with rigid exteriors, aiding in these organisms to be omnivores.

https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0166108&type=printable

A Mighty Claw: Pinching Force of the Coconut Crab, the Largest Terrestrial Crustacean.

SUMMARY 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.

/pdf/interlocking-of-chelae-is-a-key-factor-for-dominance-36zt60zayx.pdf

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

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.

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

Relative clutch mass (RCM), the ratio of total mass of a clutch to the postpartum body mass of the female, is considered by many a life history trait that indirectly quanti es reproductive e ort in snakes. e Northern Watersnake (Nerodia sipedon sipedon) is one of the most abundant and widespread species of snake within Ohio. Litter sizes of N. s. sipedon have been reported to range between four and 99 and RCM values typically fall between 0.20 and 0.38. Two gravid N. s. sipedon were hand collected from Collins Creek (Butler County, Ohio) and maintained in the laboratory until parturition. Females gave birth to three and six neonates with RCM values of 0.108 and 0.120, respectively. e extremely small litter sizes and RCM values are, by far, the lowest ever recorded for this species in Ohio and throughout their entire North American range. is local population should be investigated further to determine if and how reproductive output is being depressed at Collins Creek. OHIO J.SCI. 107 (4): 84-85, 2007 1Corresponding author: Gary W. Gerald, 212 Pearson Hall, Department of Zoology, Miami University, Oxford, OH 45056. Email: geraldgw@muohio.edu INTRODUCTION Relative clutch mass (RCM), which is the ratio of the total mass of a clutch to the postpartum body mass of the female, is considered by many an important life history trait that indirectly quanti es reproductive e ort in reptiles (Seigel and Fitch 1984; Shine 1992). Because a high RCM will likely reduce the locomotor abilities of females making them more vulnerable to predators, natural selection should favor individuals with an optimal RCM to maximize tness. Typical RCM values for snakes range from about 0.14 to 0.40 (Seigel and Fitch 1984). RCM values tend to be lower in viviparous snakes because they must carry their young for a longer period of time (Shine and Schwartzkopf 1992). Moreover, RCM values tend to be lower in species that frequently use aquatic locomotion since pregnancy disrupts stream-lining necessary for e cient swimming (Shine 1988). Ford and Seigel (1989) showed that clutch size and clutch mass are plastic in relation to resource levels (e.g. food intake) in the viviparous Checkered Gartersnake ( amnophis marcianus), with the reduction of RCM when resource levels are depressed. Arguably one of Ohio’s most abundant snakes is the Northern Watersnake (Nerodia sipedon sipedon), being found in all 88 counties (Wynn and Moody 2006). is viviparous species is found in a variety of lentic and lotic freshwater habitats across the state and feeds on a wide variety of prey (Gibbons and Dorcas 2004). e mean litter size for N. s. sipedon is 26 and litter sizes ranging from four to 99 have been reported throughout their entire North American range (Ernst and Ernst 2003; Gibbons and Dorcas 2004). Previous reports of RCM for N. s. sipedon range from 0.15 to 0.52 with typical values falling between 0.20 and 0.38 (Barron 1997). Herein, we provide a report of extremely small litter sizes and RCM values for two female N. s. sipedon originating from a small stream in southwestern Ohio. MATERIALS AND METHODS Two gravid females were hand collected less than 30 m from each other on 19 July 2006. Both females were basking in low lying riparian vegetation overhanging Collins Creek, a third order Fathead minnows (Pimephales promelas) daily until parturition. Females and newborns were measured to the nearest 0.1 cm and weighed to the nearest 0.1 g. is study was conducted in accordance with the Miami University Institutional Animal Care and Use Committee (Protocol # 634). RESULTS One female (A) gave birth to six o spring (combined weight = 15.5 g) on 17 August 2006 and the second female (B) gave birth to three o spring (combined weight = 14.7 g) on 18 August 2006 (Table 1). RCM values were 0.120 and 0.108 for females A and B, respectively. DISCUSSION Relative clutch masses reported here are the smallest ever reported for Nerodia sipedon sipedon within Ohio and throughout its entire range, and are among the smallest reported for the entire genus Nerodia in North America. Since o spring mass was very similar to those reported elsewhere for N. s. sipedon (Ernst and Ernst 2003; Gibbons and Dorcas 2004), the decrease in RCM is a direct result of the reduced litter sizes of both females. e observed litter sizes are extremely low compared to those reported for this species throughout the rest of their geographic range and, to our knowledge, the litter size of three is the smallest ever reported for N. s. sipedon. ese small litter sizes, and hence low RCM values, observed are likely due to decreased energy intake via consumption of low quality food or reduced food intake (Ford and Seigel 1989). Since these females were captured in the same stream within 30 m of each other, we cannot rule out that these individuals are closely related. However, the apparently high population density of Northern Watersnakes at Collins Creek (G.W. Gerald, personal observation) suggests that decreased litter sizes could be a result of intense intraspeci c competition for resources. is population should be investigated further to determine whether or not reduced litter sizes are characteristic of this population and, if so, ascertain precisely the factors depressing the reproductive output of female N. s. sipedon in this particular stream. stream located in Butler County, Ohio (39o29’52”N; 84o43’57”W). Snakes were transported to the laboratory where they were fed Acknowledgments. We would like to thank M. Kovach and C. Zematis for assistance in the eld. LITERATURE CITED Barron JN. 1997. Condition-adjusted estimator of reproductive output in snakes. Copeia 1997(2):306-318. Ernst CH, Ernst EM. 2003. Snakes of the United States and Canada. Washington D.C.: Smithsonian Books. 668 p. Ford NB, Seigel RA. 1989. Phenotypic plasticity in reproductive traits: evidence from a viviparous snake. Ecology 70(6):1768-1774. Gibbons JW, Dorcas ME. 2004. North American watersnakes: a natural history. Norman: University of Oklahoma Press. 438 p. Seigel RA, Fitch HS. 1984. Ecological patterns of relative clutch mass in snakes. Oecologia 61:293-301. Shine R. 1988. Constraints on reproductive investment: a comparison between aquatic and terrestrial snakes. Evolution 42(1):17-27. Shine R. 1992. Relative clutch mass and body shape in lizards and snakes: is reproductive investment constrained or optimized? Evolution 46(3):828833. Shine R, Schwarzkopf L. 1992. e evolution of reproductive e ort in lizards and snakes. Evolution 46(1):62-75. Wynn DE, Moody SM. 2006. Ohio turtle, lizard, and snake atlas. Columbus: Ohio Biological Survey. 80 p. Table 1 Summary of mass, snout-vent lengths (SVL), tail lengths, total lengths, and relative clutch mass (RCM) for two female Nerodia sipedon sipedon and their o spring. Each individual o spring, which are denoted by a letter (indicating the mother) and number, are listed directly under the mother. Individual Pre-birth mass (g) Post-birth mass (g) SVL (cm) Tail (cm) Total (cm) RCM Female A 159.2 129.4 65.7 17.9 83.6 0.1198 A1 3.0 14.3 3.8 18.1 A2 3.0 14.5 3.7 18.2 A3 1.6 11.3 3.7 15.0 A4 3.1 15.0 4.1 19.1 A5 3.2 15.2 4.7 19.9 A6 1.6 12.4 3.7 16.1 Female B 161.0 135.7 59.1 13.3 72.4 0.1083 B1 4.8 17.2 6.0 23.2 B2 5.3 17.9 4.9 22.8 B3 4.6 16.0 5.8 21.8 84 VOL. 107SMALL WATERSNAKE LITTER SIZES OHIO JOURNAL OF SCIENCE 85 G. W. GERALD AND C. A. MISKELL

Courtney A. Miskell

Papers

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

Small Litter Sizes and Relative Clutch Mass of Northern Watersnakes (Nerodia sipedon sipedon) in Southwestern Ohio