Omnivory in lacertid lizards: adaptive evolution or constraint?

Abstract

Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade-offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade-offs.

Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource

“…4) in all individuals, including a hatchling (26.4-mm snout-vent length, umbilical scar present) and a very young juvenile (33.11-mm snout-vent length) examined from Pod Mrčaru. These valves are similar in overall appearance and structure to those found in herbivorous lacertid, agamid, and iguanid lizards (13,14) and are not found in other populations of P. sicula (13) or in P. melisellensis. Cecal valves slow down food passage and provide for fermenting chambers, allowing commensal microorganisms to convert cellulose to volatile fatty acids (15,16).…”

“…Indeed, in the lizards from Pod Mrčaru, nematodes were common in the hindgut but absent from individuals from Pod Kopište. The fact that Ͻ1% of all currently known species of squamates have cecal valves (13,14) illustrates the unusual nature of these structures in this population. The evolution of these structures has likely gone hand in hand with a novel association between P. sicula on Pod Mrčaru and a set of microorganisms assuring the digestion of cellulose as is suggested by the presence of nematodes in the hindgut of individuals from Pod Mrčaru.…”

A Sensitivity Analysis to the Role of the Fronto‐Parietal Suture in Lacerta Bilineata: A Preliminary Finite Element Study

“…However, as far as the objective of this sensitivity study is concerned, a simplified boundary condition was imposed on the skull. The skull was loaded under a 10 N vertical load, which represented the bite force (similar to the experimental data of Herrel et al, 2001Herrel et al, , 2004 via the most anterior teeth, while three nodes at the posterior part of the skull were fully constrained (occipital condyle; see Fig. 1c).…”

The Relationship Between Cephalic Scales and Bones in Lizards: A Preliminary Microtomographic Survey on Three Lacertid Species

“…Such changes are supposed to influence the biomechanical distribution of biting forces, characterizing the different figures recorded for small and large species (Herrel et al, 2004). Mechanical properties of the integument vary in different regions and can be modulated by the internal pressure exerted by the underlying structures (e.g., Wainwright et al, 1978;Hebrank, 1980;Gemballa and Bartsch, 2002;Rivera et al, 2005).…”

“…Under this scenario, applications of geometric modeling to study the morphology and the biomechanical dynamics of skull proved useful to quantify differences between species, providing helpful information on the structural organization of the skull (Hallgrimsson et al, 2007). Lacertids are one of the most diverse groups of lizards in terms of dietary specialization, and although they have been well described in the literature (e.g., Arnold, 1989;Barahona and Barbadillo, 1998;Herrel et al, 2004Herrel et al, , 2008Evans, 2008), the degree to which the mechanics of their skulls differs among species remains unexamined.…”