The functional morphology of lingual prey capture in a scincid lizard, Tiliqua scincoides (Reptilia: Squamata)

Ecological drivers of jaw morphological evolution in lepidosaurs

Ecology is a key driver of morphological evolution during adaptive radiations, but alternative factors like phylogeny and allometry can have a strong influence on morphology. Lepidosaurs, the most diverse clade of tetrapods, including lizards and snakes, have evolved a remarkable variety of forms and adapted to disparate ecological niches, representing an ideal case study to understand drivers of morphological evolution. Here, we quantify morphological variation in the lower jaw using three-dimensional geometric morphometrics on a broad sample of 153 lepidosaur species. Our results suggest that phylogeny has significantly influenced mandibular shape evolution, and snakes have diverged from a lizard-like jaw morphology during their evolution. Allometry and ecological factors like diet, foraging mode and substrate also appear to drive the diversification of mandibular forms. Ecological groups differ in patterns of disparity, convergence and rates of evolution, indicating that divergent evolutionary mechanisms are responsible for the acquisition of different diets and habitats. Our analyses support that lepidosaurs ancestrally use their jaws to capture prey, contrary to the traditional view favouring lingual prehension as ancestral. Specialized or ecologically diverse lineages show high rates of jaw shape evolution, suggesting that morphological innovation in the mandible has contributed to the spectacular ecomorphological diversification of lepidosaurs.

The role of cranial osteoderms on the mechanics of the skull in scincid lizards

Osteoderms (ODs) are calcified organs formed directly within the skin of most major extant tetrapod lineages. Lizards possibly show the greatest diversity in ODs morphology and distribution. ODs are commonly hypothesized to function as a defensive armor. Here we tested the hypothesis that cranial osteoderms also contribute to the mechanics of the skull during biting. A series of in vivo experiments were carried out on three specimens of Tiliqua gigas. Animals were induced to bite a force plate while a single cranial OD was strain gauged. A finite element (FE) model of a related species, Tiliqua scincoides, was developed and used to estimate the level of strain across the same OD as instrumented in the in vivo experiments. FE results were compared to the in vivo data and the FE model was modified to test two hypothetical scenarios in which all ODs were (i) removed from, and (ii) fused to, the skull. In vivo data demonstrated that the ODs were carrying load during biting. The hypothetical FE models showed that when cranial ODs were fused to the skull, the overall strain across the skull arising from biting was reduced. Removing the ODs showed an opposite effect. In summary, our findings suggest that cranial ODs contribute to the mechanics of the skull, even when they are loosely attached.

Studies of the Behavioral Sequences: The Neuroethological Morphology Concept Crossing Ethology and Functional Morphology

Simple Summary

Behavioral sequences analysis is a relevant method for quantifying the behavioral repertoire of animals to respond to the classical Tinbergen’s four questions. Research in ethology and functional morphology intercepts at the level of analysis of behaviors through the recording and interpretation of data from of movement sequence studies with various types of imaging and sensor systems. We propose the concept of Neuroethological morphology to build a holistic framework for understanding animal behavior. This concept integrates ethology (including behavioral ecology and neuroethology) with functional morphology (including biomechanics and physics) to provide a heuristic approach in behavioral biology.

Abstract

Postures and movements have been one of the major modes of human expression for understanding and depicting organisms in their environment. In ethology, behavioral sequence analysis is a relevant method to describe animal behavior and to answer Tinbergen’s four questions testing the causes of development, mechanism, adaptation, and evolution of behaviors. In functional morphology (and in biomechanics), the analysis of behavioral sequences establishes the motor pattern and opens the discussion on the links between “form” and “function”. We propose here the concept of neuroethological morphology in order to build a holistic framework for understanding animal behavior. This concept integrates ethology with functional morphology, and physics. Over the past hundred years, parallel developments in both disciplines have been rooted in the study of the sequential organization of animal behavior. This concept allows for testing genetic, epigenetic, and evo-devo predictions of phenotypic traits between structures, performances, behavior, and fitness in response to environmental constraints. Based on a review of the literature, we illustrate this concept with two behavioral cases: (i) capture behavior in squamates, and (ii) the ritualistic throat display in lizards.

A comparison of two techniques to identify the sex of the eastern blue-tongue skink (Tiliqua scincoides scincoides)

INTRODUCTION

The eastern blue-tongued skink (Tiliqua scincoides scincoides), native to eastern Australia, is commonly kept as both a pet and for breeding. As a sexually monomorphic species, it is important to develop reliable techniques for sex identification, both for breeding and health purposes. Numerous techniques have been developed for the identification of sex in other reptile species but, other than possibly morphometric analysis, none have proven to be reliable in this species. Two techniques showing promise are contrast radiography of the hemepenes/hemeclitores, and morphometrical analysis. This study looks at both techniques and compares them for accuracy.

METHODS AND MATERIALS

Twenty captive eastern blue-tongued skinks (of known sex) were sedated, contrast radiography of their hemepenes /hemeclitores was performed, and physical measurements were taken for morphometric analysis. The radiographs were examined by a panel of three researchers (blinded to the known sex) to identify sex. The morphometric data were statistically analysed, following a previously published methodology, and the individual sex identified. Again, the researchers were blinded to the known sex.

RESULTS

The contrast radiography technique was 100% accurate in correctly identifying the sex of all the skinks. Morphometric analysis was, by contrast, only 70% accurate.

CONCLUSION AND CLINICAL RELEVANCE

Physical differences between wild and captive skinks, as well as different environmental and nutritional factors, may have contributed to the lower accuracy of morphometric analysis in identifying the sex of eastern blue-tongued skinks. While contrast radiography was more accurate, the need for specialised equipment may render this technique impractical for field researchers, but more suitable for owned animals. More research is needed to assess the impact of captivity on eastern blue-tongued skinks' physical morphometrics.

Avoiding being stung or bitten - prey capture behaviors of the ant-eating Texas horned lizard (Phrynosoma cornutum)

Horned lizards (Phrynosoma) are specialized predators, including many species that primarily feed on seed harvester ants (Pogonomyrmex). Harvester ants have strong mandibles to husk seeds or defensively bite, and a venomous sting. Texas horned lizards possess a blood plasma factor that neutralizes harvester ant venom and produce copious mucus in the pharynx and esophagus, thus embedding and incapacitating swallowed ants. We used high-speed video recordings to investigate complexities of their lingual prey capture and handling behavior. Lizards primarily strike ants at their mesosoma (thorax plus propodeum of abdomen). They avoid the head and gaster, even if closer to the lizard, and if prey directional movement is reversed. Orientation of captured ants during retraction is with head first (rostral), thus providing initial mucus coating of the mandibles. Prey capture accuracy and precise handling illustrates the specificity of adaptations of horned lizards in avoiding harm, and the challenges lizards face when feeding on dangerous prey.

Summary: Horned lizards, primarily feeding on dangerous and venomous harvester ants, avoid being bitten or stung by striking ants mainly on the thorax, avoiding head and gaster.