Directional asymmetry and correlation of tail injury with left-side dominance occur in Serpentes (Sauropsida)

Assessment of the Orbital and Auricular Asymmetry in Italian and Sudanese Children: A Three-Dimensional Study

The evaluation of the symmetry of orbital and ear soft tissues is important for aesthetic and reconstructive surgery. However, little information is available for these facial regions, especially in children. We analyzed the orbital and auricular symmetry in 418 Italian and 206 Sudanese subadult males divided into three age groups (8–11, 12–15, and 16–19 years old). Orbital and auricular height and width were measured for calculating fluctuating and directional asymmetry indices. Differences in asymmetry indices according to ethnicity and age group were assessed through the two-way ANOVA test (p < 0.01), while differences in the prevalence of right or left asymmetry according to ethnicity were assessed through the chi-square test. On average, directional asymmetry indices ranged from −2.1% to 1.1%, while fluctuating asymmetry indices ranged between 2.9% and 5.4%, corresponding to a small effect size and to 1.06–2.34 mm actual dimensions. Sudanese subjects showed a greater asymmetry for all the indices except for the fluctuating asymmetry of orbital height (p < 0.01). The directional asymmetry of auricular width increased with age. A prevalent right-side asymmetry was found for all the orbital indices (p < 0.001) in both populations, although significantly more prevalent in Sudanese individuals (over 83% for both measures), while auricular measures showed a prevalent left asymmetry exclusively in the Sudanese but with lower percentages. Aside from the limited effect size, the results proved the ethnic variability of asymmetry of orbital and auricle regions in children and suggest the need to collect more population data.

Asymmetric Behavior in Ptyodactylus guttatus: Can a Digit Ratio Reflect Brain Laterality?

The digit ratio, an indicator of brain laterality, is the ratio of the second and fourth digits on the left (L24) or right foot (R24). Much of the research on the digit ratio and brain laterality focuses on primates, rather than other species such as reptiles. We tested whether the digit ratio in the gecko Ptyodactylus guttatus was associated with behaviors attributed to brain laterality. We examined risk-taking behavior (time spent under cover), foot preference (which foot was the first to start moving) and the side from which geckos bypassed an obstacle, in relation to the digit ratio. Geckos with longer fourth digits on their left hind foot (higher digit ratio) spent more time under cover. Geckos starting to move with their left leg were much more likely to bypass obstacles from the right side, and vice versa. This is the first evidence of laterality being associated with the digit ratio in reptiles. Comparisons among vertebrates are needed in order to decipher the evolutionary origin of the commonalities and peculiarities of brain asymmetry and disentangle the patterns and drivers of our evolutionary tree.

The causes and ecological correlates of head scale asymmetry and fragmentation in a tropical snake

The challenge of identifying the proximate causes and ecological consequences of phenotypic variation can be facilitated by studying traits that are usually but not always bilaterally symmetrical; deviations from symmetry likely reflect disrupted embryogenesis. Based on a 19-year mark-recapture study of >1300 slatey-grey snakes (Stegonotus cucullatus) in tropical Australia, and incubation of >700 eggs, we document developmental and ecological correlates of two morphological traits: asymmetry and fragmentation of head scales. Asymmetry was directional (more scales on the left side) and was higher in individuals with lower heterozygosity, but was not heritable. In contrast, fragmentation was heritable and was higher in females than males. Both scale asymmetry and fragmentation were increased by rapid embryogenesis but were not affected by hydric conditions during incubation. Snakes with asymmetry and fragmentation exhibited slightly lower survival and increased (sex-specific) movements, and females with more scale fragmentation produced smaller eggs. Counterintuitively, snakes with more asymmetry had higher growth rates (possibly reflecting trade-offs with other traits), and snakes with more fragmentation had fewer parasites (possibly due to lower feeding rates). Our data paint an unusually detailed picture of the complex genetic and environmental factors that, by disrupting early embryonic development, generate variations in morphology that have detectable correlations with ecological performance.

Foot-preference underlies bite-scar asymmetry in the gecko Ptyodactylus guttatus

Scar-asymmetry may reflect brain laterality because scar location may reflect behaviour when being attacked. This has been studied in a few organisms, but never in lizards. Wild geckos (Ptyodactylus guttatus) from Israel were examined for bite-scar numbers and their lateral asymmetry. Social status was documented in the field before capture. Foot-preference, for either the right (R-footed) or left (L-footed) hind leg was determined in six trials for each gecko on adults captured in Jerusalem. I studied 48 geckos: 15 R-footed, 6 ambidextrous and 9 L-footed females; 6 R-footed, 3 ambidextrous and 9 L-footed males. Adults showed significantly more bite-scars than juveniles. The proportion of L-footed males mirrored that of R-footed females. Ambidextrous and L-footed geckos had a higher social status. In males, R-footed individuals had more bite-scars on the right side of the body, while L-footed individuals had more on the left side. R-footed females had more bite-scars on the right side, while L-footed females had bite-scars equally on both sides. Bite-scar asymmetry correlated with hind-leg preference, clearly reflecting brain laterality. Since all ambidextrous males had high social status, that may be the driving factor behind the females' different bite-scar pattern.

Eye and pit size are inversely correlated in crotalinae: Implications for selection pressure relaxation

Mate, prey, and predator recognition often depend on the integration of information from multiple sensory modalities including visual, auditory, and/or olfactory inputs. In Crotalinae, the eyes sense visible light while the pit organs detect infrared (IR) radiation. Previous studies indicate that there is significant overlap between the eye and pit sensory fields and that both senses are involved in recognition processes. This study investigated the relationships between eye and pit sizes in this taxonomic group as a function of phylogeny and habitat. In view of the fact that pit orientation depends largely on snout shape, pit vipers were grouped as follows: 1) arboreal, 2) terrestrial with rounded snout, and 3) terrestrial with pointed snout. The pit orientations and habitant patterns were fully independent of the Crotalinae phylogenetic tree. The phylogenetic generalized least squares model showed that both eye and pit areas were not of significantly phylogenetic relatedness, implying alternatively a strong effect of adaptation on eye and pit sizes. Negative correlations between relative eye and pit areas in terrestrial (both pointed and rounded snouts) and arboreal species were statistically significant. Our results suggest that the eyes and pits function in a complementary fashion such that selection for IR-perception relaxes selection pressures on the visual system and selection for visual discrimination relaxes selection pressures acting on the IR-system.

Heritabilities of directional asymmetry in the fore- and hindlimbs of rabbit fetuses

Directional asymmetry (DA), where at the population level symmetry differs from zero, has been reported in a wide range of traits and taxa, even for traits in which symmetry is expected to be the target of selection such as limbs or wings. In invertebrates, DA has been suggested to be non-adaptive. In vertebrates, there has been a wealth of research linking morphological asymmetry to behavioural lateralisation. On the other hand, the prenatal expression of DA and evidences for quantitative genetic variation for asymmetry may suggest it is not solely induced by differences in mechanic loading between sides. We estimate quantitative genetic variation of fetal limb asymmetry in a large dataset of rabbits. Our results showed a low but highly significant level of DA that is partially under genetic control for all traits, with forelimbs displaying higher levels of asymmetry. Genetic correlations were positive within limbs, but negative across bones of fore and hind limbs. Environmental correlations were positive for all, but smaller across fore and hind limbs. We discuss our results in light of the existence and maintenance of DA in locomotory traits.