Anolis

Moreno-Arias, Rafael A. & Calderón-Espinosa, Martha L., 2016, Patterns of morphological diversification of mainland Anolis lizards from northwestern South America, Zoological Journal of the Linnean Society 176 (3), pp. 632-647 : 644-645

EVOLUTION OF ANOLIS MORPHOLOGICAL DIVERSITY OF NORTHWESTERN SOUTH AMERICA

A phylogenetic signal was present in the data analysed here for six traits (SVL, TLL, FLL, HLL, TRL and LN). Most morphological traits followed a trajectory influenced by the phylogenetic history of species. Nevertheless, Revell et al. (2008) showed that, in addition to genetic drift, high values of phylogenetic signal occur when evolution is not entirely neutral, such as in stabilizing selection at a constantly weak strength, highly fluctuating natural selection, or when the evolutionary rate or changes in adaptive shifts decrease through time. Evolution of morphological traits in anoles shows different intensities of phylogenetic signal; variables representing limbs and size features can have low or high Blomberg et al. K values, but always with significant values for phylogenetic signal ( Pinto et al., 2008; Hertz et al., 2013). In addition, convergent and deterministic evolution of morphology and ecology, bounded by ecological limits, is recognized as the main pattern of evolution of anole Caribbean radiation ( Losos et al., 1998; Mahler et al., 2010, 2013).

This pattern was the most frequently observed in our data, as most traits exhibited high phylogenetic signal without fitting neutral models, suggesting a deterministic morphological pattern of evolution for mainland anoles in northwestern South America.

Other traits, like head dimensions, which showed low Blomberg et al. K values, exhibited phylogenetic correlation. Low values for HW could be a result of punctuated divergent selection. Low values for HH and HL could be explained by a strong stabilizing selection or bounded phenotypic evolution under high mutation rates, as some theoretical models suggest for evolutionary processes that show low phylogenetic signal ( Revell et al., 2008). In relation to the tempo of evolution of morphological traits, the neutral model BM had high support compared with the variable rate of evolution model EB, suggesting that phylogeny best predicts the patterns and rates of evolution for these particular traits; this supports the stabilizing selection scenarios, which were more supported than the BM or EB, for explaining morphological evolution.

Although we cannot infer the magnitude of the fluctuation of selection across the phylogeny to make inferences of where the main changes occur, the links between (1) constant rates of evolution based on very poor support of EB (AICc = 57.6) compared with BM, (2) strength of selection towards a particular phenotypic peak, and (3) high values of phylogenetic signal in most traits, suggest that the main morphological shifts are concentrated near the root of the tree. It is likely that major morphological shifts in northwestern South America mainland anoles occurred early in their history. Therefore, the species to fill the same morphological peak increased their morphological covariance, with respect to species of other morphological peaks, more than expected by neutral evolution, which explains the high values of phylogenetic signal observed in most traits. Thus, the observed pattern of morphological evolution of mainland anoles from northwestern South America is similar to the niche occupancy ( Revell et al., 2008) and niche differentiation ( Price, 1997) models, which describe evolution following an adaptive radiation ( Schluter, 2000).

Both MORPHbwd and the comparison between the mainland and Caribbean anole species supported convergent evolution of morphology in at least six morphotypes. This finding is similar to the known convergence pattern of Caribbean anole radiation ( Losos et al., 1998; Mahler et al., 2010), which supports the theory that mainland radiation probably followed a similar pathway to the Caribbean radiation. Convergence between mainland and Caribbean anoles may have been rejected previously because different studies used different morphological variables ( Velasco & Herrel, 2007; Pinto et al., 2008; Schaad & Poe, 2010) to those used originally to define the ecomorphs, or because of the absence of a phylogenetic framework ( Irschick et al., 1997). Unlike these previous studies, we performed a comparison with the original variables used to define the ecomorphs under a phylogenetic framework to demonstrate that convergence between the radiations occurs in at least six of the 15 possible ecomorphs defined by island communities ( Mahler et al., 2013).