Morphology, locomotor performance and habitat use in southern African agamids

Abstract

Understanding the relationships between form and function can help us to understand the evolution of phenotypic diversity in different ecological contexts. Locomotor traits are ecologically relevant as they reflect the ability of an organism to escape from predators, to catch prey or to defend territories. As such, locomotion provides a good model to investigate how environmental constraints may influence an organism’s performance. Here, we investigate the ecomorphological relationships between limb morphology, locomotor performance (sprint speed and endurance) and habitat use in six southern African agamid species. The investigated agamid species showed differences in hind limb and toe lengths. Both of these traits were further correlated with endurance capacity. This association was supported by stepwise multiple regression analyses. However, we demonstrate trade-offs in locomotor performance traits, suggesting that specialization towards speed comes at the detriment of endurance capacity. Overall, the single arboreal species studied had longer hind limbs, a higher exertion capacity and a higher mean speed. However, for a given hind limb length, the arboreal species was slower than the other habitat specialists. This study provides insights into the evolutionary mechanisms that have driven the morphological and functional evolution in southern African agamid lizards.

The Relationship Between Bite Force, Morphology, and Diet in Southern African Agamids.

“…They are thought to have undergone rapid diversi cation, radiating into multiple clades about 10 Mya [21]. A recent study has shown divergence in limb morphology and locomotor performance between southern African agamas utilising different habitats, suggesting ecological differentiation between these species [22]. Since habitat is likely an important factor shaping limb and locomotor variation in these agamas, we expect this to drive variation in cranial morphology, bite force, and possibly even diet.…”

“…A total of 147 individuals, including 51 Females, 51 males and 45 juveniles representing six species occupying different habitat types were sampled. We distinguish male agamas from females visually, based on the bulging of the hemipenes in males [22] (28°52′S, 31°28′E), KwaZulu-Natal, in February 2017. The GPS coordinates of each lizard were recorded upon capture.…”

“…Since habitat is likely an important factor shaping limb and locomotor variation in these agamas, we expect this to drive variation in cranial morphology, bite force, and possibly even diet. However, the ecomorphological relationships between habitat use, morphology, performance and diet remain poorly known in agamids (but see [22,23]). These lizards generally adopt a sit-and-wait foraging strategy, feeding predominantly on active prey such as ants, beetles and ying insects [24,25] which may impact how prey availability drives variation in head morphology and bite force.…”

“…In this study, we studied six species of agamas from contrasting habitat types, representing rock-dwelling (Agama atra, A. anchietae and A. aculeata distanti), ground-dwelling (A. aculeata aculeata and A. armata) and arboreal (Acanthocercus atricollis) habitats [22,26]. Although occupying very different habitats, A. a. aculeata and A. a. distanti are two subspecies of A. aculeata belonging to a species complex which has not been completely resolved.…”

Environmental correlates of morphological diversity in Australian geckos

“…It is thought that ground‐dwelling terrestrial species may encounter more obstacles with the potential to impede locomotion, and therefore, benefit from having shorter limbs (Foster et al., 2018; Melville & Swain, 2000). In contrast, climbing species occupying arboreal and saxicolous microhabitats would require greater stability and encounter fewer obstacles, allowing for faster rates of movement, and thus, evolve longer limbs (Foster et al., 2018; Goodman et al., 2008; Tan et al., 2020, but see Hagey et al., 2017 who showed that arboreal species had shorter femora, and Kaliontzopoulou et al, 2010 who showed terrestrial species had longer femora than scansorial species). Whilst these patterns have been observed within skinks (Foster et al., 2018; Goodman et al., 2008; Melville & Swain, 2000), attempts to link limb morphology and microhabitat use in non‐anoline lizards have often failed (e.g., Foster et al., 2018; Kulyomina et al., 2019; Olberding et al., 2016).…”