There is more to the picture than meets the eye: adaptation for crypsis blurs phylogeographical structure in a lizard

Abstract

Aim We examined dorsal coloration in and genetic relationships among Iberian populations of the lizard Psammodromus algirus to determine the extent to which the current distribution of phenotypic variation is correlated with phylogeographical history or local environmental conditions. Location Iberian Peninsula, western Palaearctic. MethodsWe sequenced mitochondrial DNA (ND4 and adjacent tRNAs genes) in 36 populations, and seven microsatellite loci in eight representative populations. In 23 populations, lizards were classified according to the presence and intensity of a dorsal striped pattern, the heritability of which was estimated by means of mother-offspring regressions. To determine whether colour pattern is an adaptation for crypsis, we compared the time taken by humans to detect striped and unstriped lizards in different environments.Results The analysis of mtDNA revealed an ancient split between a western clade, subdivided into south-and north-western haplogroups, and an eastern clade with central, south-eastern and eastern haplogroups. In contrast, nuclear markers showed a post-glacial admixture of central and western haplogroups, with the central haplogroup apparently isolated from the rest of its clade. This was consistent with variation in the dorsal striped pattern, a heritable phenotypic trait: central and western lizards were unstriped, whereas eastern lizards were striped. We then suggest that dorsal coloration promotes crypsis: in eastern locations detection times were longer for striped than for unstriped lizards, whereas the opposite was true in western and central locations. Main conclusionsOur results indicate that natural selection for crypsis may promote not only divergence within clades, as suggested by the apparent isolation between unstriped central lizards and striped members of eastern haplogroups, but also admixture between them. We conclude that ecologically driven selection is crucial for understanding the phylogeographical background of phenotypic variation, because recent adaptation to the environment can blur the effects of ancestral isolation.

Variation in field body temperature and total evaporative water loss along an environmental gradient in a diurnal ectotherm

“…Only a previous study reported the amount of water loss at low body temperature (~24°C) throughout a day from a single locality (Ferreira et al , ). The populations studied here (see below) all belong to the same clade and show both little genetic differentiation and high gene flow (Verdú‐Ricoy et al , ; Díaz et al , ). Consequently, we would expect to attribute variability among populations to acclimation to local conditions (i.e.…”

The combined use of raw and phylogenetically independent methods of outlier detection uncovers genome‐wide dynamics of local adaptation in a lizard

“…We used genotyping by sequencing (GBS; Elshire et al, ) and combined ROA and CIOA to explore how the fixation of ancestral genetic variation and genetic innovation underlie convergent local adaptation. To do so, we used as model species the most abundant and widespread lizard in the Mediterranean region of the Iberian Peninsula: the large Psammodromus Psammodromus algirus (Díaz et al, ; Figure ). This species shows consistent genetic and phenotypic divergence associated with environmental heterogeneity across its distribution range.…”

“…This species shows consistent genetic and phenotypic divergence associated with environmental heterogeneity across its distribution range. The northwest part of its range is more humid and temperate than the southeast, and this is mirrored by broad changes in the vegetation patterns, with forests dominating in the west and more open spaces in the east (Díaz et al, ). The genetic diversity of P. algirus is structured in two mtDNA lineages, eastern and western, separated ca.…”

“…3–3.5 Ma (Carranza, Harris, Arnold, Batista, & Gonzalez De La Vega, ). Each mtDNA lineage typically shows a distinct phenotype for a heritable trait that could be adaptively linked to crypsis: lizards that inhabit the eastern, more open and grassier regions tend to display a striped dorsal pattern absent among western lizards, which inhabit more vegetated forests (Díaz et al, ). However, striped and unstriped phenotypes do not perfectly match the eastern–western lineage dichotomy.…”

“…The phenotype of these lizards is unstriped, fitting what we would expect if they were locally adapted to the forests they live in. However, the analysis of their mtDNA places Lerma within the E2 clade of the eastern lineage, which is almost exclusively composed of striped lizards (Díaz et al, ). Therefore, the Lerma population provides an excellent opportunity to investigate the sources of variation that can be locally selected to generate phenotypic convergence after long periods of genetic divergence.…”