Different selection regimes explain morphological evolution in fossorial lizards
Data files
Mar 13, 2024 version files 85.31 KB
Abstract
Independent origins of similar phenotypes are ubiquitous to the evolutionary process and evoke strong and recurrent environmental associations. Snakelike lizards evolved multiple times and are often portrayed as limb-reduced and body-elongated outcomes from shared selection associated with fossoriality. However, a refined evaluation including specific head traits and subtle differences in subterranean microhabitats unveils some degree of uniqueness even among lineages traditionally interpreted as phenotypically similar. Here we address regimes of selection in fossorial lizards accounting for differences in the burrowing substrate and emphasizing head shape in addition to body and limbs. We assembled an ecomorphological database comprising 213 species from all major lizard clades, and then characterized contemporary morphological diversity and modeled phenotypic evolution to test the hypothesis that fossoriality encompasses at least two distinct selection regimes. We identified two ecomorphological groups within the fossorial lizards: moist-soil fossorial and dry-soil fossorial. Both groups evolved towards distinct adaptive optima concerning head shape and limb size. Despite some degree of uniqueness, these groups also share similar patterns in specific traits. Dry-soil fossorial lizards present less morphological variation than moist-soil fossorial, possibly due to the combination of distinct sets of selective pressures with shared ancestry. Our study provides evidence that an often-interpreted general adaptive regime (e.g., fossoriality) may in fact comprise enough ecological and functional diversity to elicit several distinct ecomorphological associations despite overall convergence among phenotypic traits.
README: Different selection regimes explain morphological evolution in fossorial lizards
https://doi.org/10.5061/dryad.x95x69psc
Here we address regimes of selection in fossorial lizards accounting for differences in the burrowing substrate and emphasizing head shape in addition to body and limbs. We assembled an ecomorphological database comprising 213 species from all major lizard clades, and then characterized contemporary morphological diversity and modeled phenotypic evolution to test the hypothesis that fossoriality encompasses at least two distinct selection regimes. We identified two ecomorphological groups within the fossorial lizards: moist-soil fossorial and dry-soil fossorial. Both groups evolved towards distinct adaptive optima concerning head shape and limb size. Despite some degree of uniqueness, these groups also share similar patterns in specific traits. Dry-soil fossorial lizards present less morphological variation than moist-soil fossorial, possibly due to the combination of distinct sets of selective pressures with shared ancestry.
Description of the data and file structure
We assembled a morphological database comprising 213 species of lizards distributed worldwide, with 1932 specimens sampled (mean of 9 individuals per species) representing all major Squamate clades, except Serpentes. Most preserved animals were measured during visits to herpetological collections or obtained by loans. Both adult males and females were included in our study. Thirteen traits were obtained from direct measurements on preserved specimens by the same researcher using a digital caliper (Mitutoyo Inc., 0 – 200mm, precision 0.01mm). In a few species, metric tape was used to measure very long tails. Damaged or regenerated structures were not considered. Our database focused on functional traits of head shape (9 measurements) and also four post-cranial traits related to locomotion. We modeled phenotypic evolution by comparing different hypotheses of selection regimes to evaluate if limb reduction, body elongation and head shape evolved towards two distinct adaptive optima in fossorial lizards: dry-soil and moist-soil fossorial groups. We also characterized current morphological disparity within the fossorial lizards, as we predict that the dry-soil fossorial group encompasses less morphological diversity than moist-soil fossorial lizards, due to unique adaptations involved with headfirst burrowing in sand and dry soils. We also evaluated the profiles of morphological disparity through time, as we expect that historical processes associated with morphological diversity partitioning may reflect different combinations of shared ancestry and adaptation in distinct snakelike lineages.
List of abbreviations:
N = number of specimens sampled
HL = head length
HW = head width
HH = head height
ND = nostril distance
NH = nostril height
OD = orbital distance
SL = snout length
LJL = lower jaw length
QTL = quadrate-to-tip length
TrL = trunk length
Tal = tail length
FLL = forelimb length
HLL = hindlimb length
AH = Anthony Herrel's personal herpetological collection
MNHN = Muséum national d'Histoire naturelle (Paris, France)
MfN = Museum für Naturkund (Berlin, Germany)
NHM = Natural History Museum (London, England)
MZUSP = Museu de Zoologia da Unidade de São Paulo (São Paulo, Brazil)
CHRP = Coleção Herpetológica de Ribeirão Preto - USP (Ribeirão Preto, Brazil)
CHUNB = Coleção Herpetológica da Universidade de Brasília (Brasília, Brazil)
INPA = Instituto Nacional de Pesquisas da Amazônia (Manaus, Brazil)
MNRJ = Museu Nacional do Rio de Janeiro (Rio de Janeiro, Brazil)
Procedures for the morphological measurements were as described:
Head length: caliper tips are positioned at the tip of the snout and the posterior end of the parietal scale, in a dorsal view
Head width: caliper is positioned to measure the maximal distance between right and left sides of the head, in a dorsal view
Head height: caliper is positioned vertically in a lateral view; one tip of the caliper is on ventral edge of jaw, the other on the heighest point of parietal scale
Nasal height: caliper is positioned vertically in a lateral view; one tip at the right nostril opening, the other on the ventral edge of the jaw
Nasal distance: caliper is positioned in a dorsal view, one tip in each nostril opening
Orbital distance: caliper is positioned in a dorsal view horizontally at mid-eye direction; one tip in each lateral extremity of frontal scale
Rostral length: caliper is positioned in a lateral view; one tip at the tip of the rostral, the other at the postocular scale
Lower jaw length: caliper is positioned in a lateral view; one tip at the anterior extremity of lower jaw, the other gently positioned at the posterior extremity of the retroarticular process
Quadrate-to-tip length: caliper is positioned in a lateral view; one tip at the most anterior tip of the upper jaw, the other at the posterior edge of the quadrate and the squamosal
Trunk length: caliper is positioned in a ventral view; one tip at the cloaca, the other in mid-point between the two retroarticular processes, at neck height
Tail length: caliper is positioned in a ventral view; one tip at the cloaca, the other at tip of the tail (only intact tails; regenerated tails are not measured)
Forelim length: caliper is positioned in a ventral view, one tip at the proximal extremity of forelimb, the other at the tip of the longest forelimb digit; limb is gently stretched
Hindlimb length: caliper is positioned in a ventral view, one tip at the proximal extremity of hindlimb, the other at the tip of the longest hindlimb digit; limb is gently stretched
Methods
We assembled a large morphological database composed of all major lizard groups, focusing on snakelike lineages. We modeled phenotypic evolution by comparing different hypotheses of selection regimes to evaluate if limb reduction, body elongation and head shape evolved towards two distinct adaptive optima in fossorial lizards: dry-soil and moist-soil fossorial groups. We also characterized current morphological disparity within the fossorial lizards, as we predict that the dry-soil fossorial group encompasses less morphological diversity than moist-soil fossorial lizards, due to unique adaptations involved with headfirst burrowing in sand and dry soils. We also evaluated the profiles of morphological disparity through time, as we expect that historical processes associated with morphological diversity partitioning may reflect different combinations of shared ancestry and adaptation in distinct snakelike lineages.