Ecological specialization, rather than the island effect, explains morphological diversification in an ancient radiation of geckos

Abstract

Island colonists are often assumed to experience higher levels of phenotypic diversification than continental taxa. However, empirical evidence has uncovered exceptions to this ‘island effect’. Here, we tested this pattern using the geckos of the genus Pristurus from continental Arabia and Africa and the Socotra Archipelago. Using a recently published phylogeny and an extensive morphological dataset, we explore the differences in phenotypic evolution between Socotran and continental taxa. Moreover, we reconstructed ancestral habitat occupancy to examine if ecological specialization is correlated with morphological change, comparing phenotypic disparity and trait evolution between habitats. We found a heterogeneous outcome of island colonization. Namely, only one of the three colonization events resulted in a body size increase. However, in general, Socotran species do not present higher levels or rates of morphological diversification than continental groups. Instead, habitat specialization explains better the body size and shape evolution in Pristurus . Particularly, the colonization of ground habitats appears as the main driver of morphological change, producing the highest disparity and evolutionary rates. Additionally, arboreal species show very similar body size and head proportions. These results reveal a determinant role of ecological mechanisms in morphological evolution and corroborate the complexity of ecomorphological dynamics in continent–island systems.

A new species of feather-tailed leaf-toed gecko, Kolekanos Heinicke, Daza, Greenbaum, Jackman, Bauer, 2014 (Squamata, Gekkonidae) from the poorly explored savannah of western Angola

“…In addition, both species present a distinctive tail ornamentation that can be used as a clear morphological diagnostic feature between them. These findings seem to be consistent with the idea that habitat diversity leads to species and morphological diversification (Losos and Parent 2009;Tejero-Cicuéndez et al 2021).…”

Evolution along allometric lines of least resistance: Morphological differentiation inPristurusgeckos

“…We used a combination of phenotypic, phylogenetic, and ecological data to characterize and evaluate intra- and interspecific allometric trends. The data utilized here were obtained from our prior work on this system [30,31], and are briefly described here. First we used a time-dated, molecular phylogeny of squamates that included all members of the genus Pristurus, including several currently undescribed taxa.…”

“…The Afro-Arabian geckos in the genus Pristurus afford the opportunity to elucidate the inter-digitating effects of allometry and habitat specialization on clade-level patterns of phenotypic diversity. Prior work on this system [30] revealed that the colonization of ground habitats has been a trigger of morphological change, specifically reflected in an increase in body size and shape disparity. Interestingly, some ground-dwelling species are among the largest of the genus and also show increased relative head sizes and limb proportions, while some other species with this ecological specialization have evolved to be among the smallest of the group.…”

“…Interestingly, some ground-dwelling species are among the largest of the genus and also show increased relative head sizes and limb proportions, while some other species with this ecological specialization have evolved to be among the smallest of the group. Additionally, among the species exploiting rocky habitats (the most common ecological feature in Pristurus), there are also species with both considerably large and small body sizes [30]. What remains unexplored, however, is how the evolution of body shape is related to differences in body size and whether habitat specialization has an impact in this shape-size relationship.…”

Integrative Phylogenetics: Tools for Palaeontologists to Explore the Tree of Life

“…The most likely biogeographical scenarios at all internal nodes of a given time-calibrated evolutionary tree can be estimated using maximum likelihood or Bayesian approaches, notably with the dispersal–extinction–cladogenesis (DEC) model [ 85 , 89 , 90 , 91 , 92 ]. The DEC model and its derivatives [ 93 ] allow for investigation of time-calibrated phylogenies with extant and extinct taxa while considering tectonic evolution via the incorporation of time bins in which the connectivity between any two areas can change through time [ 94 , 95 ]. Geological connectivity can be coded as a matrix of connection/disconnection relying on the latest palaeogeographical scenarios (e.g., [ 96 ]) for a given region.…”