A developmental model for predicting handedness frequencies in crabs

Brachyuran crabs develop handedness in at least two different ways. Some crabs, such as Cancer productus, become heterochelous through use-induced differences in claw growth. Other crab species, for instance Carcinus maenas, appear to have a genetic predisposition towards right handedness. In this latter case, however, handedness reversal may take place following autotomy of the major claw. Thus, in C. maenas, and other species with this developmental strategy, younger cohorts are strongly biased towards right-handed individuals and the frequency of left-handedness increases with each subsequent moult. In the absence of differential mortality the ratio of left-handed to right-handed crabs in a given population should be predictable if the frequencies of right and left claw loss are known for different stages in the life history. Here, we develop a simple mathematical model for predicting handedness in crabs under the Carcinus-model of claw ontogeny and apply it to two species with very different ecologies and life histories; the green crab (Carcinus maenas (L.)) and the Trinidadian mountain crab (Eudaniela garmani (Rathburn)). The predicted and observed handedness frequencies were in complete concordance for the early intermoults of both species but significantly deviated in mature C. maenas where left-handed individuals were under-represented in the population. These results are discussed in the context of the evolution and functional significance of claw autotomy and handedness in crabs.     

Structure and function of the chelae and chela closer muscles of the shore crab Carcinus maenas (Crustacea: Brachyura)

Major and minor chelae of Carcinus maenas were investigated with respect to mechanical advantage, angles of pennation and sarcomere lengths of the closer muscle fibres, maximum pinching forces induced by nervous stimulation and maximum stress in the closer muscles. Major chelae differed from minor chelae in all these factors. Mean mechanical advantages of major and minor chelae were 0·36 and 0·26, respectively. Angles of pennation were greater at the distal ends of closer muscles and declined proximally: in half open major and minor chelae distal to proximal angles were about 35–26° and 29–19°, respectively. Mean sarcomere lengths in closer muscles of fully closed major and minor chelae were significantly different at 7·6 and 6·0 fim, respectively; there was great variation within chelae and between crabs. Major chelae pinched more strongly than minor chelae due to higher mechanical advantages, larger closer apodemes and greater stress in the muscle. Mean maximum stresses in major and minor chelae were 677 and 474 kN/m², respectively. The biggest stress recorded–1057 kN rrr²–was in a major chela. Pinching forces induced by injecting a high K⁺ and caffeine ringer were about 20% weaker than nervously stimulated pinches.     

Crab scars reveal survival advantage of left-handed snails

Biological asymmetries are important elements of the structure and function of many living organisms. Using the Plio-Pleistocene fossil record of crab predation on morphologically similar pairs of right- and left-handed snail species, we show here for the first time, contrary to traditional wisdom, that rare left-handed coiling promotes survival from attacks by right-handed crabs. This frequency-dependent result influences the balance of selection processes that maintain left-handedness at the species level and parallels some social interactions in human cultures, such as sports that involve dual contests between opponents of opposite handedness.     

On the handedness of Japanese monkeys

Forty-one monkeys living on the Koshima Island were tested for handedness by throwing a peanut 10 or 20 times toward each subject and recording which hand was used to pick it up. Handedness was judged at the 5% level of confidence. Animals showing no preference for the left or right hand after 20 trials were considered to be ambidextrous. The following distribution of handedness was found: left-handed, 17 (41%); right-handed, 8 (20%); ambidextrous, 16 (39%). These findings were compared with other studies on the handedness of Japanese monkeys. Handed monkeys outnumber the ambidextrous ones and the left-handed monkeys outnumber the right-handed ones. The characteristic distribution of handedness was shown to be irrespective of troop. By looking over the data from these different sources, the proportions of the left-handed, the ambidextrous, and the right-handed in Japanese monkeys were estimated at 39%, 33%, and 28% respectively. The method used in this study was compared withKawai's catching behavior and reasons for disagreement between judgments of handedness were discussed.     

Functional asymmetry in the face.

The possible existence of one-sided dominance in the face, similar to the phenomena of handedness and footedness, has been investigated by studying smiling pattern, movements of the angles of mouth, winking, platysma contraction, raising and everting the upper lip with dilatation of the nostril, and vertical wrinkling of the forehead, on 300 right-handed and 30 left-handed persons. The conclusions are as follows: 1. The large majority of persons investigated do not use the two sides of face equally. 2. Facial ambilaterality is a rare feature. 3. There is no clear-cut correlation between handedness and the dominant side of the face. 4. The greater percentage (58.66%) of right-handed persons show a left-sided smile and find it more convenient to perform almost all exercises with the left side of the face. A still greater percentage (73.33%) of left-handed persons shows a right-sided smile and a better performance of all exercises with the right side of the face. The contralateral relationship of handedness to the dominant side of the face is significant in the right-handed and more so, in the left-handed persons.     

Handedness in the common marmoset (Callithrix jacchus)

For about 20 months the development of hand preferences in 21 experimentally naive common marmosets (Callithrix jacchus) was examined in 15 different tests. Test preferences were compared with their spontaneous behavior preferences in such contexts as feeding, grooming, play, and others. In the spontaneous use of the hands, only eight animals showed a significant lateral preference (2 left-handed, 6 right-handed). During the test period, however, the number of handed marmosets increased to 19 (5 left-handed, 14 right-handed). Most of the animals fluctuated considerably in their preference levels, a situation which led to a remarkable test response inconsistency of handedness. When the test situation was changed, complete reversals of handedness were more frequent than weakening or strengthening of a particular preference. The animals' emotions during the test session and environmental variables affected handedness significantly. None of the tested marmosets showed an increase of hand preference from the first to the last test. Our results indicate that Callithrix is ambidextrous rather than handed.     

MORPHOLOGY AND BEHAVIOR OF CRABS AND GASTROPODS FROM LAKE TANGANYIKA,AFRICA: IMPLICATIONS FOR LACUSTRINE PREDATOR-PREY COEVOLUTION

The shells of most lacustrine gastropods are typically small, weakly calcified, and modestly ornamented to unornamented. Similarly, most lacustrine crabs are usually small detritivores with weak chelae. A number of invertebrate taxa in Lake Tanganyika, however, deviate from these generalities. This study explores a predator-prey coevolution model as an explanation for the large, heavily calcified, and ornate gastropods and the robust, durophagous crabs of Lake Tanganyika. The endemic thiarid and viviparid gastropods from Lake Tanganyika have significantly thicker shells and higher frequencies of terminal apertural lip thickening than closely related cosmopolitan taxa from outside the lake. Tanganyikan gastropods also display considerably higher incidence of shell repair, following nonlethal shell damage, than cosmopolitan taxa of the same families. There is a strong positive correlation between gastropod apertural lip thickness and shell repair frequency among all the gastropod species analyzed. The endemic Tanganyikan potamonautid crab Platytelphusa armata (a molluscivore) possesses larger, more robust crushing chelae than other African potamonautid or potamonid crabs. In contrast with the cosmopolitan African crabs, the Tanganyikan crabs display molariform, rather than serrate dentition on their crushing chelipeds. In shell-crushing experiments, the Tanganyikan gastropod shells were an order of magnitude stronger than typical lacustrine gastropod shells, many well within the range of tropical marine gastropod shell strengths. Predation experiments with the endemic gastropods Spekia, Neothauma, Lavigeria spp., Paramelania spp. and the crab Platytelphusa armata showed that increased size, apertural lip thickness or shell sculpture reduced the successful predation rate of P. armata. Crabs with large chelae have a greater ratio of successful: unsuccessful attacks than crabs with small chelae. Among cases of successful predation, crabs with large chelae employed predation methods that required less time and energy (such as crushing the shell in the cheliped) than the methods employed by crabs with small chelae (such as peeling the shell from the aperture or the spire). The morphological, shell-crushing, and aquarium experiment data, considered in concert, provide strong support for the idea that the endemic gastropods and crabs of Lake Tanganyika have coevolved over the past 7 million years.     

Handedness in comparison with the asymmetry of the upper extremities]

In 1990 221 males (88 children, age 3.5-7.25 years and 133 adults, age 20-44 years) were investigated. The sample was divided into two groups based on handedness; 140 individuals were right-handed and 81 left-handed. 10 measurements were taken at the upper limbs. In addition, marked handedness, handclasping and armfolding were determined. The last three traits showed no statistically significant connection. It was determined that measurements of length, breadth and circumference are more often significantly asymmetric in favor of the right side in right-handers than in left-handers. Further, skinfolds of right-handed individuals are larger on the left side. Partially reverse results were found for left-handers as a whole, however, the results are more irregular. A difference in the degree of asymmetry exists between children and adults. Asymmetries of breadth and circumference measurements as well as forearm skinfold are larger in adults. Taking into account the error of measurement, frequencies of R > L, R = L and L > R for right- and left-handed individuals were evaluated using the chi 2-test for significance. Preponderance of measurements on the dominant side could often be secured statistically.     

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.     

The enigma of reversed asymmetry in lithodid crabs: absence of evidence for heritability or induction of morphological handedness in Lopholithodes foraminatus

SUMMARY Mutations or environmental factors that result in reversal of conspicuous left–right asymmetries provide an opportunity to study developmental mechanisms. They may also provide insight into evolutionary changes in asymmetry states within and between species. King crabs (family Lithodidae) have a larger right claw and females typically exhibit a dextrally offset abdomen. Nevertheless, I observed a high incidence of left handedness in laboratory reared box crabs ( Lopholithodes foraminatus ) and captured the first known egg-bearing female lithodid to exhibit reversed asymmetry. This provided a unique opportunity to characterize the reversed phenotype and to compare the incidence of reversed asymmetry in the offspring of normal and reversed females. Asymmetry of the chelae became apparent in the first postzoeal stage (glaucothoe) and handedness was maintained through subsequent instars. Females with larger left claws developed reversed abdominal asymmetry by the fourth crab stage. No reversed asymmetry was observed in the mandibles of zoea larvae or juveniles of either handedness. The incidence of reversed asymmetry in glaucothoe reared from one reversed and three normal females was high (between 20% and 30%), and independent of maternity ( P =0.67). Removal of the right cheliped of fourth stage zoeae, and the major cheliped of glaucothoe, did not reverse the direction of asymmetry. Elevated larval rearing temperature also did not affect the frequency of reversed individuals. This lack of evidence for either heritability or induction of handedness is enigmatic. Further investigation of reversed asymmetry in lithodid crabs may provide valuable insights into the development and evolution of bilateral asymmetries.     

The influence of temperature,sex and chela size in the foraging strategy of the shore crab,Carcinus maenas (L.)

Foraging rate was highly variable among shore crabs of the same size category and for individual crabs from day to day. Possible physiological reasons for this variability are discussed. Shore crab foraging rate, both in terms of mussels eaten per day and energy intake per day, was estimated to be higher at 17°C than at 10°C. The shape of diet curves and their mode for male shore crabs at 17°C closely resembled those for 10°C, indicating that the temperature increase had no effect on their previously demonstrated optimal foraging strategy.

Female and certain male shore crabs showed a preference for prey smaller than for other equivalent sized males. These suboptimally feeding male and female crabs attained a relatively higher prédation rate (mussels day^‐1), although their energy intake (KJ day^‐1) remained lower than that of optimally feeding males. Preferred mussel size, number of mussels eaten per day and energy intake were strongly related to master chela height. The diet curves for female and suboptimally feeding male shore crabs could be explained by these crabs’ proportionately smaller master chelae.     

Temporal changes in the reproductive population structures and males’ secondary sexual character of the hermit crab <Emphasis Type="Italic">Diogenes nitidimanus</Emphasis>

We investigated the reproductive ecology of D. nitidimanus in the Waka-River estuary with special reference to temporal change in the relative size of chelae length for males, i.e., secondary sexual character. Ovigerous females were observed from April to October, peaking in June–July with over 90% of females being ovigerous. Adult female carapace size ranged from 3.5 to 8.5 mm, but with the majority of females falling between 5–6 mm. Male carapace length was more evenly distributed between 3.5 and 10 mm. Juvenile settlement occurred mostly in July, during which time the frequency of both large females (over 6.5 mm in carapace length) and large males (over 8.5 mm in carapace length) clearly decreased. The carapace length of precopulatory-guarded females varied from 4.8 to 8.0 mm, while guarding males were almost over 7 mm and always larger than their paired females. The relative growth of the major chelae differed significantly between small and large males during the early months of the year, including the reproductive peak months (April–June). During these early months, large males had relatively larger chelae for their body size than did small crabs. This difference, however, was not evident later in the year (July–September). Large males may grow their chelae relatively long in the early months in order to take advantage of the mating opportunities during April–June. This is the first report in animals, to our knowledge, that relative size of the secondary sexual character for males temporarily change during a single reproductive season.     

Determination of the spiral conformation of Aquaspirillum spp. by scanning electron microscopy of elongated cells induced by cephalexin treatment

The effect of the beta-lactam antibiotic cephalexin on the spiral conformation of cells of Aquaspirillum spp. was examined by scanning electron microscopy. A. itersonii and A. peregrinum, which are known to have a left-handed spiral shape, elongated and still showed left-handed spirals in medium containing cephalexin. The spiral conformation of the elongated cells is therefore considered to represent the natural condition. The spiral conformations of A. metamorphum and A. psychrophilum grown in ordinary cultures were difficult to determine because they have short cells without a complete spiral. After cephalexin treatment, the cells of these species elongated and displayed spiral forms, right-handed in A. metamorphum and left-handed in A. psychrophilum. This elongation method may be useful for checking and determination of the spiral handedness of short spiral or curved bacteria such as vibrios.     

Dynamics of Blood Serum Levels of Follicle-Stimulating Hormone, Luteinizing Hormone, Prolactin, Estradiol, and Progesterone in Right- and Left-Handed Women

The dynamics of follicle-stimulating hormone (FSH) luteinizing hormone (LH), prolactin (PRL), estradiol (E₂), and progesterone were studied in left- and right-handed women having a stable 28-day menstrual cycle. The hormones were determined by enzyme immunoassays on days 3, 8, 10, 13, 16, 22, 26, and 28 of the menstrual cycle. The data showed that bllod serum levels of FSH, LH, PRL, and E₂are higher in left-handed in comparison to right-handed women (p< 0.001). On days 10 through 28 of the cycle, the level of progesterone is also higher in left-handed women (p< 0.001). The dynamic of these hormones in left-handed and right-handed women appeared to remain within the normal limits. These findings indicate that the handedness correlates with the dynamucs of serum levels of these hormones. Higher serum levels of hormones in left-handed women suggests that they have higher levels of the functional activity of the hypophysis–ovarian axis and prolactin axis.     

Reversal in helix sense of copoly(beta-alkyl-L-aspartate-beta-benzyl-L-aspartate)

The conformation of copoly(beta-alkyl-L-aspartate-beta-benzyl-L-aspartate), in which the alkyl group is ethyl, propyl, butyl, hexyl, nonyl, dodecyl, or stearyl, was studied in solution and the solid state by optical rotatory dispersion and circular dichroism methods. The helix sense of the copolyaspartate studied here is transformed from a left-handed to right-handed alpha-helix as the degree of alkylation increases. Reversal in helix sense occurs, i.e., the left-handed alpha-helix based on the handedness of poly(beta-benzyl-L-aspartate) is transformed into a right-handed alpha-helix with increase in alkyl groups with right-handed nature. Reversal in helix sense is also observed for copolyaspartates with an intermediate or high degree of alkylation as temperature rises. Copolyaspartates with hexyl, nonyl, or dodecyl groups exhibit an induced circular dichroism around 230-238 nm and can form an ordered side chain structure which is broken down at high temperature. One has to consider the conformation of the omega-helix and beta-form of the copolyaspartates in the solid state in addition to the reversal in helix sense. Copolyaspartates with a low degree of alkylation are in the alpha-helical conformation over the low temperature range and adopt the omega-helical conformation in the high temperature range, indicative of a thermal alpha-omega transition. A small number of alkyl groups can be incorporated into the benzene ring stacking of the omega-helix, but not a large number. All the copolyaspartates can assume the beta-form at high temperatures. The helix conformation is not significantly affected by the formation of side chain crystals of the copolyaspartate with a large number of stearyl groups, in contrast to copolyglutamate.     

Morphogenetic variability and handedness in Montenegro and Serbia

This study tries to establish correlations between the types of handedness and several morphophysiological characteristics, controlled by one or a small number of genes with alternative dominant recessive manifestation. The population-genetic homozygosity degree study includes the analysis of the presence, distribution and individual traits combination in left-handed and right-handed persons. It was conducted at three localities in two states, Serbia (SRB) and Montenegro (MNE). Our hypothesis is that a possible genetic load due to increased recessive homozygosity, being a potential population-genetic parameter of left-handedness manifestation, may cause some change in other morpho-physiological characters. The average proportion of 23 studied homozygously-recessive characters (HRC’s) was similar among observed left-handed individuals in the studied localities. It varied from 10.5 ± 0.4 in Serbia to 10.7 ± 0.3 in MNE. The differences were somewhat bigger among right-handed persons, varying from 8.7 ± 0.3 in MNE to 9.1 ± 0.3 HRC’s in Serbia. However, in all localities the average homozygosity was significantly higher among left-handed school children. The number of HRC’s among 400 individuals varied from 2 to 16 among right-handed and from 4 to 19 among left-handed persons. There were no differences in scholar scores between left-handed and right-handed children, although small differences were found between two state samples.     

Development of the system of cognitive functions in right- and left-handed boys aged six to seven years: A study taking into consideration specific features of early ontogeny

Characteristics of early ontogeny and the formation of cognitive functions of left-and right-handed boys six to seven years of age have been studied with the genesis of handedness taken into account. A comparative analysis of cognition in right-and left-handed children has been performed using a unified approach to the history of early ontogeny with special emphasis on cognitive functions. The negative effect of pathological pregnancies and births, as well as disturbances in early ontogeny, on the development of cognitive functions in both left-and right-handed boys has been shown. The most “vulnerable” functions in right-handed boys with a history of various pathologies are the organization of activity and visuospatial perception; in left-handed boys, these are fine motor skills and speech development. In the absence of pathologies in the medical history, significantly higher indices of the organization of activity and visuomotor coordination have been found in right-handed boys and significantly higher indices of visuospatial perception, in left-handed boys.     

Influence of the task on hand preference: individual differences among gorillas (Gorilla gorilla gorilla)

The degree of task complexity and bimanual complementarity have been proposed as factors affecting lateralization strength in humans. However, a large number of studies have demonstrated group-level lateral hand bias for different manual activities in numerous non-human primate species. However, no study has tested the effects that a variety of tasks may have in inducing differences in hand preference. Here, we aim to test if 3 adult gorillas exhibited a greater hand preference bias performing 4 tasks of varying complexity: grasping small versus large foods, proto-tool use task and tool use task involving greater visuospatial requirements. We found that (1) the complexity of the task does not necessarily induce a right-handed bias and (2) a subject can be right-handed for a complex task and left-handed for another one. These results, complemented by many publications on hand preference in non-human primates, reveal a great variability in hand preference, which makes it very difficult to deduce any details of hominin handedness with artefacts.     

叶猴(Presbytis)、金丝猴(Rhinopithecus)、长臂猿(Hylobates)自由取食时的利手现象

本文报道叶猴、金丝猴、长臂猿自由取食时的利手现象。本研究共用金丝猴12只(雄性8只,雌性4只),叶猴25只(雄性16只、雌性9只),长臂猿5只(雄性3只,雌性2只)。对每个动物而言,总观察次数不少于30次,其结果显示:在雄性金丝猴中,62.5％的动物显示右利,25％显示主利,12.5％无利手现象。在雄性叶猴中,62.5％的动物显示右利,18.7％显示左利,18.7％无利手现象。在3只雄性长臂猿中,2只显示右利,一只无利手现象。 统计结果表明:雄性金丝猴有明显的右利手现象(P<0.05),雄性叶猴右利手现象接近显著(P=0.06),长臂猿因观察数量太少,未进行统计。 在上述三种动物中,雌性个体无利手现象。 木工作结果提示:(1)雄性金丝猴,叶猴在自由取食时具有右利手现象,长臂猿也可能有右利手现象,(2)大脑两半球的不对称性与性别有关。