Body and skull morphometric variations between two shovel-headed species of Amphisbaenia (Reptilia: Squamata) with morphofunctional inferences on burrowing

Abstract

BackgroundMorphological descriptions comparing Leposternon microcephalum and L. scutigerum have been made previously. However, these taxa lack a formal quantitative morphological characterization, and comparative studies suggest that morphology and burrowing performance are be related. The excavatory movements of L. microcephalum have been described in detail. However, there is a lack of studies comparing locomotor patterns and/or performance among different amphisbaenids sharing the same skull shape. This paper presents the first study of comparative morphometric variations between two closely related amphisbaenid species, L. microcephalum and L. scutigerum, with functional inferences on fossorial locomotion efficiency.MethodsInter-specific morphometric variations were verified through statistical analyses of body and cranial measures of L. microcephalum and L. scutigerum specimens. Their burrowing activity was assessed through X-ray videofluoroscopy and then compared. The influence of morphological variation on the speed of digging was tested among Leposternon individuals.ResultsLeposternon microcephalum and L. scutigerum are morphometrically distinct species. The first is shorter and robust with a wider head while the other is more elongated and slim with a narrower head. They share the same excavatory movements. The animals analyzed reached relatively high speeds, but individuals with narrower skulls dug faster. A negative correlation between the speed and the width of skull was determined, but not with total length or diameter of the body.DiscussionThe morphometric differences between L. microcephalum and L. scutigerum are in accord with morphological variations previously described. Since these species performed the same excavation pattern, we may infer that closely related amphisbaenids with the same skull type would exhibit the same excavatory pattern. The negative correlation between head width and excavation speed is also observed in others fossorial squamates. The robustness of the skull is also related to compression force in L. microcephalum. Individuals with wider heads are stronger. Thus, we suggest trade-offs between excavation speed and compression force during burrowing in this species.

Skull variation in a shovel‐headed amphisbaenian genus, inferred from the geometric morphometric analysis of five South American Leposternon species

“…In the shovel-headed amphisbaenians, specifically L. microcephalum, even small variations in head width may have a major impact on burrowing compression force (Navas et al, 2004) and speed (Hohl et al, 2017). In this case, the analyses of the morphological configuration of the skull presented here indicate that the larger Leposternon specimens or species are able to exert a higher compression force, but dig more slowly, reflecting a trade-off between compression forces and burrowing speeds, as suggested by Hohl et al (2017).…”

“…tunnel floor. This cycle ends with the animal dropping its head to return to its initial static position (Barros-Filho, Hohl, & Rocha-Barbosa, 2008;Hohl et al, 2014;Hohl, Loguercio, Sicuro, Barros-Filho, & Rocha-Barbosa, 2017). The shovel-headed morphotype is considered to be the most specialized for digging, which allows these amphisbaenians to penetrate heavily compacted soils (Gans, 1974;Gans, 2005;Hohl et al, 2014;Kearney, 2003).…”

“…The characteristics of the amphisbaenian head are also useful for phylogenetic studies (Kearney, 2003), including those that discuss about homoplasy and adaptive convergence related to fossoriality (Gauthier, Kearney, Maisano, Rieppel, & Behlke, 2012;Mott & Vieites, 2009), and provide valuable insights into the ecology of these animals through studies on their fossorial locomotion (e.g., Barros-Filho, Hohl, & Rocha-Barbosa, 2008;Gans, 1960Gans, , 1974Hohl et al, 2014;Hohl et al, 2017;Kaiser, 1955;Navas et al, 2004) and masticatory biomechanics (e.g., Baeckens et al, 2017). For example, small variations in the width of the posterior skull segment may have a relatively large impact on burrowing compression force and speed (Hohl et al, 2017;Navas et al, 2004), as well as bite force (Baeckens et al, 2017).…”

Phylogenetic history influences convergence for a specialized ecology: comparative skull morphology of African burrowing skinks (Squamata; Scincidae)

“…Early work identified three specialized head shapes, in addition to the more generalized head shape, which are typically associated with different substrates [ 29 ]. More recent work has revealed that changes in skull width can impact burrowing performance between two closely related species [ 30 ] and that skull variation within the genus Leposternon is correlated with biogeographical variables related to soil type [ 31 ]. On the other hand, a study on Caribbean amphisbaenians found no relationship between skull shape and location (a proxy for soil type), and instead found a tight link with phylogenetic history and skull shape [ 18 ].…”

Food capture and escape behavior of Leposternon microcephalum Wagler, 1824 (Squamata: Amphisbaenia)

“…The present study describes the food capture behavior of L. microcephalum on the substrate surface in captivity. This species has the shovel-headed morphotype, considered the most specialized for digging (Gans, 1974;Hohl et al, 2017). Gans (1968) suggested that shovel-headed amphisbaenians are less efficient predators than species that share the rounded-headed morphotype.…”