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Review
. 2019 Aug 26;10(9):646.
doi: 10.3390/genes10090646.

Patterns, Mechanisms and Genetics of Speciation in Reptiles and Amphibians

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Free PMC article
Review

Patterns, Mechanisms and Genetics of Speciation in Reptiles and Amphibians

Katharina C Wollenberg Valero et al. Genes (Basel). .
Free PMC article

Abstract

In this contribution, the aspects of reptile and amphibian speciation that emerged from research performed over the past decade are reviewed. First, this study assesses how patterns and processes of speciation depend on knowing the taxonomy of the group in question, and discuss how integrative taxonomy has contributed to speciation research in these groups. This study then reviews the research on different aspects of speciation in reptiles and amphibians, including biogeography and climatic niches, ecological speciation, the relationship between speciation rates and phenotypic traits, and genetics and genomics. Further, several case studies of speciation in reptiles and amphibians that exemplify many of these themes are discussed. These include studies of integrative taxonomy and biogeography in South American lizards, ecological speciation in European salamanders, speciation and phenotypic evolution in frogs and lizards. The final case study combines genomics and biogeography in tortoises. The field of amphibian and reptile speciation research has steadily moved forward from the assessment of geographic and ecological aspects, to incorporating other dimensions of speciation, such as genetic mechanisms and evolutionary forces. A higher degree of integration among all these dimensions emerges as a goal for future research.

Keywords: ecological speciation; genomics; integrative taxonomy; niche; phylogenetics; phylogeography; taxonomy; traits.

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
The distribution of the eastern South America dry diagonal biomes (top left) and the distribution of inferred Bayesian population clusters and ancestral distribution of P. pollicaris with respect to the inferred historical stability surface in yellow (stable areas obtained by overlapping predicted logistic outputs under four climatic scenarios: Current, 6, 21, and 120 kyr BP) and a digital elevation model for South America (brown represents higher altitudes). The pie charts represent the posterior probability that a given individual is assigned to a particular cluster. Alternative divergence models tested using an approximate Bayesian computation (ABC) framework (bottom left). STDF—Seasonal Tropical Dry Forest, T1—early divergence event, T2—recent divergence event, m—empirical relative mutation rates. Adapted from Werneck et al. (2012 [310]).
Figure 2
Figure 2
The geographic distribution of different clades within Salamandra salamandra across Europe derived from a population-based phylogeny of the mitochondrial D-loop [322]. The different shades of grey—the distribution of different phylogenetic clades. The distribution range of the subspecies S. s. gigliolii is uncertain (question mark). The dashed line—the approximate line of permafrost during the height of the last glaciation. Note that clade B shows an interrupted pattern by populations of clade C. (Modified after [322]).
Figure 3
Figure 3
The adaptive divergence of the Kottenforst fire salamander population according to pond- and stream larval habitat. The fine-scale spatial distribution of 2653 genotypes representing individual salamander larvae sampled from pond and stream habitats across the Kottenforst. Each dot represents a single individual displaying as a pie chart the percentage assignment assuming two genetic clusters (K = 2). The bar plot composed of individual genotypes (each line represents a single larva) shows the corresponding assignment as represented by the pie charts from west to east across the Kottenforst. (From Hendrix et al. [334]).
Figure 4
Figure 4
The importance of body size on amphibian diversification, from radiation to population. In Madagascar, the influence of body size on patterns and processes of evolution has been studied on several levels of the radiation, including (1) the complete radiation of mantellid frogs. Genera are abbreviated as follows: a, Aglyptodactylus; b, Laliostoma; c, Blommersia; d, Guibemantis; e, Mantella; f, Wakea; g, Spinomantis; h, Boehmantis; i, Gephyromantis; j, Mantidactylus; k, Tsingymantis; l, Boophis. SVL_ - Snout-vent length (2) The community level, comparing communities between sites of high diversity, Andasibe and Ranomafana, (3) A pair of mantellid sister species and (4) populations of one of these species. (1) Mantellid frogs of Madagascar constitute a species-rich amphibian radiation with high diversity of ecology and phenotype (tree). Young pairs of sister species are found in closer spatial proximity than older sister species pairs (top scatterplot), and sister species with different range sizes also differ in their body sizes (bottom scatterplot). (2) Mantellid divergence between sister species of two spatially separated communities is higher for smaller species indicating their more limited ability to disperse. (3) In a pair of ecologically similar mantellid sister species, Gephyromantis enki (smaller) and G. boulengeri (larger), the smaller species shows higher residual genetic variance across the same landscape than the larger species (box plot). Landscape resistance is lower for the larger species (inset maps; strength of landscape resistance is ranging from low—orange to high—red). (4) The population diversification for the small G. enki is influenced by barriers to dispersal such as the Namorona River (blue line) where localities on opposite sides of the river (yellow/green dots) are separated by a mutation in cytochrome b (indicated by the haplotype network with localities in corresponding colors). Figure references: Wollenberg et al., 2011 [34]; Pabijan et al., 2012 [348]; Wollenberg Valero, 2015 [199].
Figure 5
Figure 5
The covariation of rare allele frequencies of outlier RADseq SNPs with phenotypic adaptation to elevation (in meters above sea level). The transformed (residual to SVL and summarized via a principal component analysis) phenotypic variables (Wollenberg et al. [36]) representing body condition (relative body mass = snout-vent length/weight in g), and XPC1 (relative bone length, the variable shows shorter bones as larger values and is thus plotted inverse). The inset images show X-rays of typical lowland phenotypes of A. cybotes (left), and highland A. cybotes (right, own images). From Rodriguez et al. (2017) [391], under the Creative Commons license.
Figure 6
Figure 6
(A) The distribution of giant tortoises in the Galápagos Archipelago. The shaded and non-shaded islands indicate the presence of extant and extinct tortoise populations, respectively. The italicized names indicate current taxonomic designations. (B) A schematic of the proposed phylogeographic history of Galápagos giant tortoises modified from Poulakakis et al. (2012) [411]. The arrows represent dispersal and colonization events within Galápagos, with the numbers indicating approximate temporal order in millions of years. The short solid line segments indicate vicariance events. The solid black arrows are hypothesized natural colonization events, while the dashed arrows represent recent and likely human-induced translocations.
Figure 7
Figure 7
The different aspects contributing to speciation, modified after Butlin et al., 2012 [124].

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