Anuran forelimb muscle tendinous structures and their relationship with locomotor modes and habitat use

The interaction between organisms and their environment is central in functional morphology.Differences in habitat usage may imply divergent morphology of locomotor systems;thus,detecting which morphological traits are conservative across lineages and which ones vary under environmental pressure is important in evolutionary studies.We studied internal and external morphology in 28 species of Neotropical anurans.Our aim was to determine if internal morphology(muscle and tendons)shows lower phylogenetic signal than external morphology.In addition,we wanted to know if morphology varies in relation to the habitat use and if there are different functional groups.We found differences in the degree of phylogenetic signal on the groups of traits.Interestingly,postaxial regions of the forelimb are evolutionarily more labile than the preaxial regions.Phylomorphospace plots show that arboreal(jumpers and graspers)and swimmer frogs cluster based on length of fingers and the lack of sesamoid,also reflected by the use of habitat.These functional clusters are also related to phylogeny.Sesamoid and flexor plate dimensions together with digit tendons showed to be important to discriminate functional groups as well as use of habitat classification.Our results allow us to identify a"grasping syndrome"in the hand of these frogs,where palmar sesamoid and flexor plate are absent and a third metacarpal with a bony knob are typical.Thus,a lighter skeleton,long fingers and a prensile hand may be key for arboreality.

When a general morphology allows many habitat uses

During the last decades the study of functional morphology received more attention incorporating more detailed data corresponding to the internal anatomy that together contribute for a better understanding of the functional basis in locomotion.Here we focus on 2 lizard families,Tropiduridae and Liolaemidae,and use information re­lated to muscle-tendinous and external morphology traits of hind legs.We investigate whether the value of the traits analyzed tend to exhibit a reduced phenotypic variation produced by stabilizing selection,and whether species showing specialization in their habitat use will also exhibit special morphological features related to it.As a result,we identified that evolution of hind limb traits is mainly explained by the Ornstein-Uhlenbeck mod­el,suggesting stabilizing selection.Liolaemids and tropidurids show clear ecomorphological trends in the vari­ables considered,with sand lizards presenting the most specialized morphological traits.Some ecomorphologi­cal trends differ between the 2 lineages,and traits of internal morphology tend to be more flexible than those of external morphology,restricting the ability to identify ecomorphs shared between these 2 lineages.Conservative traits of external morphology likely explain such restriction,as ecomorphs have been historically defined in oth­er lizard clades based on variation of external morphology.