The kinematics of locomotion in caecilians: effects of substrate and body shape

Abstract

Caecilians are limbless amphibians that have radiated extensively in the tropics, and have evolved distinct cranial and postcranial specializations associated with a burrowing lifestyle. Some species are recognized as being surface active, whereas others are dedicated burrowers. Previous authors have demonstrated that some caecilians use a hydrostatic mechanism to generate burrowing forces which is dependent on the existence of skin-vertebral independence. It has been hypothesized that skin-vertebral independence may be lost in extremely elongated species, thus affecting their ability to burrow. Here, we use X-ray video to study the kinematics of locomotion in five species of caecilian differing in their degree of body elongation. Animals were filmed moving in or across different substrates imposing different functional demands on the locomotor system. Our data demonstrate that all species have the ability to perform internal concertina locomotion, but indicate differences between species in the kinematics of locomotion with more elongate species showing a smaller degree of skin-vertebral independence. In all species, locomotion was dependent on the substrate and species switched from using lateral undulation on the surface substrates to the use of whole body or internal concertina in wide and narrow tunnels, respectively. When burrowing in soil, all species used a combination of whole-body and internal concertina locomotion. Additional studies on the ability of different species to generate forces are needed to test whether the reduced skin-vertebral independence in elongate forms has resulted in a decreased ability to generate burrows.

Head shape evolution in Gymnophthalmidae: does habitat use constrain the evolution of cranial design in fossorial lizards?

“…The association between burrowing performance, head shape and the microenvironment where the animal is digging has been previously reported in other taxa than squamates: for example, burrowing ability in different lineages of caecilians is directly affected by the soil characteristics (Ducey et al. , 1993; Herrel & Measey, 2010), and specifically in the species Schistometopum thomense , the males with larger and blunter heads tend to burrow slower (Teodecki et al. , 1998).…”

Evolution of Cranial Shape in Caecilians (Amphibia: Gymnophiona)

“…Yet attributing a direct, causal relationship is advised against at this time because the scanty available data do not demonstrate a clear correlation. For example, although comparative and experimental evidence suggest that Schistometopum thomense (with a relatively terminal mouth, perhaps secondarily) is a relatively poor burrower that prefers to use existing tunnels (Ducey et al 1993;Nussbaum and Pfrender 1998;Wollenberg and Measey 2009;Herrel and Measey 2010), many caecilians with strongly countersunk mouths (e.g. Scolecomorphus, Geotrypetes, Uraeotyphlus, Caecilia) have also been found in leaf litter rather than deeper soil (Burger et al 2004;Gower et al 2004;pers.…”

“…Burger et al 2004;Gower et al 2004Gower et al , 2010, although detailed ecological studies are lacking for most species. As far as is known, all adult caecilians practice some head-first burrowing, even the aquatic and semi-aquatic species (Moodie 1978), but burrowing ability differs among species (Ducey et al 1993;Herrel and Measey 2010).…”

Is solid always best? Cranial performance in solid and fenestrated caecilian skulls

“…The stegokrotaphic skull would, on casual inspection, appear better suited to burrowing than the zygokrotaphic skull with the large unroofed region and, for two caecilian groups with zygokrotaphic skulls, there might actually be an ecological link to poorer burrowing performance; rhinatrematids are considered to be poor burrowers that can be readily trapped during surface activity (Nussbaum, 1983;Gower et al, 2010); typhlonectids are mainly aquatic species and may therefore be relieved of the constraints of burrowing (Wilkinson and Nussbaum, 1997). However, the zygokrotaphic scolecomorphids are considered to be specialized burrowers (Nussbaum, 1977;Nussbaum, 1983); furthermore, the zygokrotaphic dermophiid caecilian Geotrypetes seraphini shows similar burrowing performance to other stegokrotaphic caecilians (Herrel and Measey, 2010).…”