Handedness in wild chimpanzees

The debate over nonhuman primate precursors to human handedness is unsettled mainly due to lack of data, particularly on apes. Handedness in wild chimpanzees at the Taï National Park Côte d'Ivoire, has been monitored in four tasks. For the simple unimanual ones, reaching and grooming, adults use both hands equally (ambidextrous), while for the more complex unimanual wadge-dipping and the complex bimanual nut-cracking, adults are highly lateralized. These results support the hypothesis that lateralization increases with the complexity of the task. The lateralization is constant for years for each task but may vary in an individual with respect to different tasks. For nutcracking females are more lateralized than males. The ontogeny of handedness for nut-cracking shows many variations in the tendency to use one hand and in the side preferred, until at about 10 years of age, the individual achieves her adult handedness. No population bias toward one side exists in Taï chimpanzees. No heritability of handedness between mother and offspring was observed. Human and chimpanzees handedness are compared.     

Handedness in great apes: A review of findings

We present data on hand preference in great apes and discuss them in the context of theoretical models of hand preference in nonhuman primates presented by MacNeilageet al. (1987) and by Fagot and Vauclair (1991). We also discuss several methodological and statistical issues as they pertain to the assessment of hand preference in great apes and other primate species. Finally, we present a comparative framework for the study of hand preference, emphasizing the importance of studies with great apes in developing evolutionary models of hemispheric specialization.     

Winning and losing: causes for variability in outcome of fights in male Magellanic penguins (Spheniscus magellanicus)

Game theory models predict that fighting ability should be moreimportant in contest outcome when the payoffs of winning arehigh for both contestants, and ownership should be more importantwhen payoffs are low. Male Magellanic penguins (Spheniscusmagellanicus) provide an opportunity to test these predictionsin a natural setting because payoffs of winning are higher for penguins fighting before egg laying and lower for penguinsfighting after egg laying, allowing the prediction of differencesin who should win and lose. We watched an area of approximately2000 Magellanic penguin nests from 1992 to 1996 at Punta Tombobreeding colony, Argentina; we quantified fighting behavior,banded contestants, measured their body size (here used as anindex of fighting ability), determined ownership status whenpossible, and monitored their reproductive success. We determinedthat male Magellanic penguins fought for nests and mates. Astheory predicts, before egg laying, body size difference wasmore important than ownership as a predictor of contest outcome and fight duration. After egg laying, owners won fights, andsize did not predict who won or how long they fought. Our comparisonsof nest ownership, nest quality, and chicks fledged by winnersand losers suggested that our predictions on the change inbenefits of winning before and after egg laying were correct.We conclude that game theory models are useful in predictingwho won or lost fights in male Magellanic penguins and thatultimate benefits of winning fights are related to fitness.     

Factor Analysis of Multiple Measures of Hand Use in Captive Chimpanzees: An Alternative Approach to the Assessment of Handedness in Nonhuman Primates

We tested whether chimpanzee handedness could be characterized as either unidimensional or multidimensional when considered across multiple measures of hand use. We determined for each of 6 different tasks in a sample of 105 captive chimpanzees hand preferences, and subjected the individual hand preference scores to a factor analysis. Five of the 6 tasks loaded on two separate factors that accounted for 54% of the variance. To assess population-level handedness, we calculated handedness indices for the loadings on each factor, for the item loadings across all factors, and for all tasks including ones that did not load on any factor. There is significant population-level right handedness for all 4 indices, which suggests that chimpanzee handedness is multidimensional and not task specific.     

Does the handedness of the pebble crab Eriphia smithii influence its attack success on two dextral snail species?

The predaceous crab Eriphia smithii (Xanthidae) has one larger claw with molar teeth on either the right or the left cheliped, which it uses to crush the shell of prey. Whether the handedness of crabs affected successful predation on two snail species, Nerita albicilla (Neritidae) and Planaxis sulcatus (Planaxidae) was experimentally investigated. The fate of snails of each species was analysed by multiple logistic regression with three explanatory variables: handedness, shell-size index and individuality of crabs. No effect of handedness was detected in attacks on N. albicilla , probably as a result of the spherical and more symmetrical shell morphology of this species. In contrast, right-handedness contributed to greater attack success on P. sulcatus , which has more conical shells. Further investigation of how snail shells were broken revealed that left-handed crabs had more difficulty breaking the aperture of larger P. sulcatus , which was thought to cause the difference in attack success between right- and left-handed crabs. The advantages conferred by handedness are discussed.     

Visual shape discrimination in the fiddler crab,Uca pugilator

1. Research into the visual shape discrimination abilities of compound‐eyed animals has almost exclusively been limited to insects, the crustaceans having been virtually ignored. The two groups have many dissimilarities, having primarily adapted in different habitats to different lifestyles. Differences may exist in visual systems and visually mediated behavior.

2. Fiddler crabs (Uca pugilator), without training, differentially approached dissimilar silhouettes presented simultaneously, demonstrating visual discrimination between stationary, geometric shapes of equal‐area. The strength of response was ordered hierarchically: vertical rectangle, horizontal rectangle, triangle, square, circle.

3. Basic geometric shapes were used to facilitate replication and comparison with research findings from other species.

     

Population-Level Right Handedness for a Coordinated Bimanual Task in Chimpanzees: Replication and Extension in a Second Colony of Apes

The purpose of this study was to evaluate the reliability of previously published findings on hand preferences in chimpanzees by evaluating hand use in a second colony of captive chimpanzees. We assessed hand preferences for a coordinated bimanual task in 116 chimpanzees (Pan troglodytes) at the University of Texas M. D. Anderson Cancer Center and compared them to previously published findings in captive chimpanzees at the Yerkes National Primate Research Center. The new sample showed significant population-level right handedness, which is consistent with previously published findings in the Yerkes chimpanzees. Combined data on the 2 chimpanzee colonies, revealed a significant effect of rearing history on hand preference, with wild-caught chimpanzees showing less right-handedness than captive-born mother-reared chimpanzees. We discuss the results in terms of the role of early environment on the development of laterality.     

The fiddler crab Uca mjoebergi uses colour vision in mate choice

Although the role of colour in mate choice is well known, few tests of colour vision have been based on mating behaviour. Females of the fiddler crab Uca mjoebergi have recently been shown to use claw coloration to recognize conspecific males. In this study I demonstrate that the females use colour vision for this task; preferentially approaching yellow claws over grey claws regardless of their intensity while failing to discriminate between yellow claws differing in intensity. This is one of only a handful of studies confirming the involvement of colour vision in mate choice and the first conclusive evidence in fiddler crabs.     

Risk-taking behavior predicts aggression and mating success in a fiddler crab

Evidence is growing that an individual's propensity to takerisks in the presence of a predator is correlated to behaviorsthat can affect individual fitness. We examined whether risk-takingbehavior predicts aggression, surface activity levels, and matingsuccess in male fiddler crabs, Uca mjoebergi. Risk-taking behaviorwas highly consistent among individuals, remained stable overtime, and was unrelated to male size. We found that males thattook greater risks in the presence of a potential predator alsobehaved more aggressively when searching for a new territory.In addition, bold males exhibited higher surface activity levelsand spent more time courting females compared with their shycounterparts. Although risk-taking behavior was independentof other sexually selected traits, it accurately predicted malemating success in U. mjoebergi. We suggest nonsexually selectedtraits, such as risk taking, may represent important behavioralpredictors of success in other species.     

Neurosecretion in the sinus gland of the fiddler crab,Uca pugnax

The ultrastructure of the sinus gland of the fiddler crab, Uca pugnax, was investigated and found to be similar to that in other crustaceans. Five types of neurosecretory axon terminals were tentatively identified on the basis of the size, shape, and electron density of granules within the axons. Release of neuro-secretory material appears to be by exocytosis.     

RXR isoforms and endogenous retinoids in the fiddler crab, Uca pugilator

The pleiotropic effects of circulating ecdysteroids in the adult fiddler crab, Uca pugilator, during molting, regeneration, and reproduction are mediated by a limited number of receptor proteins. We hypothesize that hormonal effects in vivo may be the result of complex interactions between at least two receptor heterodimer conformations that differentially respond to multiple ecdysteroid/retinoid signals. Two splicing variants of the fiddler crab retinoid-X-receptor (UpRXR) differ from one another by the addition of a 33 amino acid insert in the ligand-binding domain. We show here that the ecdysteroid receptor in the fiddler crab (UpEcR) behaves differently depending upon the UpRXR isoform with which it is partnered. The two UpRXR variant partners for UpEcR confer slightly different responses in the binding of Ponasterone A (PA)—a naturally occurring ecdysteroid in the blood of Uca. UpRXR can bind 9-cis retinoic acid (9cRA) as well as terpenoids. 9cRA and the naturally occurring terpenoid, methyl farnesoate, influence the binding of PA to UpEcR/UpRXR dimers. Endogenous retinoids are found in the blastema of regenerating limbs of Uca and they (plus blood-borne terpenoids) may add additional levels of differential response by target tissues. Thus, the two sets of heterodimers tested here may represent different dynamic complexes whose properties are defined by the specific heterodimeric subunits involved and the specific ligands available.     

Heterochely and handedness in the shore crab Carcinus maenas (L.) (Crustacea: Brachyura)

A large sample ofadult male Carcinus maenas was 79% right-handed and 21% left-handed. A separate sample of 207 intact adult males was divided into left-handed and right-handed crabs and four measurements were taken from all major and minor chelae. Correlation and regression analyses against carapace width on log-transformed data showed that major chelae of right-handed crabs grow proportionately higher with increasing size and the ideal mechanical advantage increases; concurrently, the fingers of the minor chelae grow proportionately longer. The data for left-handed crabs showed greater variability, especially for minor chelae, providing evidence for the concept that left-handedness arises by reversal of handedness following loss of the major chela from the right-hand side. Records of handedness in large samples of non-ocypodid heterochelous brachyuran crabs show a preponderance of right-handedness.     

Multiple biomarker approach in the fiddler crab to assess anthropogenic pollution in tropical coastal environments

Context: Fiddler crabs are important to the ecology of estuarine systems around the world, however, few studies have incorporated them as bioindicators. Urias estuary represents one of the most urbanized lagoons in the Gulf of California region and received discharges from different sources: shrimp farm, thermoelectric plant, fish processing plants, and untreated domestic and sewage wastes.

Objective: Assess the effects on anthropogenic contamination on female fiddler crabs reproduction, survival and genetic stability.

Methods: Exposition of wild crabs from a less impacted (reference) site to naturally contaminated sediments on under controlled laboratory conditions. Reproductive parameters, levels of DNA damage and mortality rates were measured, together with chemical analyses of sediments.

Results: The most contaminated sediments corresponded to the site where fish processing plants were located and the integrated biomarker response analysis revealed that the most adverse effects were produced by exposure to sediments from this site; these crabs showed higher mortality (67%) and poorer ovarian development than those crabs exposed to sediments from other sites.

Conclusions: Female crabs under pollution stress are able to trade-off reproduction for survival, and surviving animals were able to restore genetic stability possibly by activating DNA repair mechanisms. Multiple biomarker approach discriminates different coastal contamination scenarios.