Cryptic speciation patterns in Iranian rock lizards uncovered by integrative taxonomy

Abstract

While traditionally species recognition has been based solely on morphological differences either typological or quantitative, several newly developed methods can be used for a more objective and integrative approach on species delimitation. This may be especially relevant when dealing with cryptic species or species complexes, where high overall resemblance between species is coupled with comparatively high morphological variation within populations. Rock lizards, genus Darevskia, are such an example, as many of its members offer few diagnostic morphological features. Herein, we use a combination of genetic, morphological and ecological criteria to delimit cryptic species within two species complexes, D. chlorogaster and D. defilippii, both distributed in northern Iran. Our analyses are based on molecular information from two nuclear and two mitochondrial genes, morphological data (15 morphometric, 16 meristic and four categorical characters) and eleven newly calculated spatial environmental predictors. The phylogeny inferred for Darevskia confirmed monophyly of each species complex, with each of them comprising several highly divergent clades, especially when compared to other congeners. We identified seven candidate species within each complex, of which three and four species were supported by Bayesian species delimitation within D. chlorogaster and D. defilippii, respectively. Trained with genetically determined clades, Ecological Niche Modeling provided additional support for these cryptic species. Especially those within the D. defilippii-complex exhibit well-differentiated niches. Due to overall morphological resemblance, in a first approach PCA with mixed variables only showed the separation between the two complexes. However, MANCOVA and subsequent Discriminant Analysis performed separately for both complexes allowed for distinction of the species when sample size was large enough, namely within the D. chlorogaster-complex. In conclusion, the results support four new species, which are described herein.

Figure 1. The seven candidate species models for the Darevskia chlorogaster-complex (A) and the D. defilippii-complex (B) inferred with *BEAST using combined mitochondrial and nuclear DNA.

Values above branches are posterior probabilities, below branches are ML bootstrap values (support values below 0.95 and 50, respectively, are not shown). Bayesian species delimitation infers a speciation event at nodes marked by a solid circle and none at nodes with empty circles, numbers in parentheses refer to table 1 where detailed information on delimitation results is given. The geographic distribution of each candidate is shown in the maps, large points represent genetic sampling localities and small points are additional localities used for niche modeling. Supported species are encompassed by dashed lines.

Figure 2. The first two axes with largest explanatory power of the mixed variables PCA.

Multivariate analysis of specimens of the Darevskia chlorogaster- (empty symbols) and D. defilippii- (solid symbols) complexes was able to separate the two complexes, but not the species. Darevskia chlorogaster (squares); D. kamii sp. n. (diamonds); D. caspica sp. n. (circles); D. defilippii (solid squares); D. kopetdaghica sp. n. (upward triangles); D. schaekeli sp. n. (solid circles); and D. steineri (downward triangles).

Figure 3. Results of the Discriminant Analyses based on canonical scores for the Darevskia chlorogaster-complex performed separately for each sex.

Grouping according to genetically identified species: Darevskia chlorogaster (squares), D. caspica sp. n. (circles) and D. kamii sp. n. (diamonds).

Figure 4. Altitude of the study region (A) and ecological niche models for Darevskia chlorogaster (B), D. caspica sp. n. (C) and D. kamii sp. n. (D), D. defilippii (E), D. schaekeli sp. n. (F), D. kopetdaghica sp. n. (G) and D. steineri (H).

Predicted environmental suitability is indicated by colors, ranging from blue (i.e. areas with low predicted probabilities of occurrence) to red (i.e. areas with high predicted probabilities of occurrence), while dark gray shaded areas feature non-analogous environmental conditions (MESS).

Figure 5. Studied species of Darevskia in life: D. caspica sp. n. (A; photo by N. Moradi); D. chlorogaster (B; photo by M. Auer); D. kamii sp. n. (C; photo by O. Mozaffari); D. defilippii (D; photo by A. Shahrdari) D. kopetdaghica sp. n. (E; photo by O. Mozaffari); D. schaekeli sp. n. (F; photo by Barbod Safaei Mahroo); and D. steineri (G; photo by O. Mozaffari).

Figure 6. Dorsal view of the heads of the holotypes of the newly described Darevskia species (from left to right): D. caspica sp. n.; D. kamii sp. n.; D. kopetdaghica sp. n.; and D. schaekeli sp. n. Scale bar represents 5 mm.