Stenocereus pruinosus

Alvarado-Sizzo, Hernán, Casas, Alejandro, Parra, Fabiola, Arreola-Nava, Hilda Julieta, Terrazas, Teresa & Sánchez, Cristian, 2018, Species delimitation in the Stenocereus griseus (Cactaceae) species complex reveals a new species, S. huastecorum, PLoS ONE (e 0190385) 13 (1), pp. 1-25 : 19

Stenocereus pruinosus in central Mexico

Genetic delimitation fully supports the statements by Parra et al. [ 16] about population clusters in northern Mexico (the Huasteca group) and the eastern Tehuantepec Isthmus (the Chiapas group) as species different to S. pruinosus . Moreover, our study confirmed that the latter has a north-south substructure (green shades clusters in the Geneland column in Fig 2 ) which corresponds to the Tehuacán-Cuicatlán Valley and the Oaxaca Central Valleys .

S. pruinosus is separated from S. huastecorum by a genetic barrier, consistent with the TMVB, and is separated from S. laevigatus by a second barrier represented by the Isthmus of Tehuantepec, a well-known biogeographic barrier ( Fig 3 ). We did not observe genetic evidence of populations or individuals of S. pruinosus occurring in northern Mexico. Therefore, we do not consider a sympatric scenario between S. pruinosus and S. huastecorum in northern Mexico, but rather a long record of misidentified specimens.

Ecological evidence also provides clear distinction of S. pruinosus ENMs from those of S. huastecorum and S. laevigatus given that their comparisons ( Fig 5 , Table 2 ) suggest that these species have different ecological niches. Even though areolar morphology can easily distinguish S. pruinosus from S. huastecorum (every variable measured in Fig 6 ) only spine numbers ( Fig 6E and 6F ) were able to distinguish S. pruinosus from S. laevigatus . Areolar characters, however, may be confusing if developmental features are not taken into account because areolas may lose spines because of flowering events and branch age, or it may be simply deciduous as in central-left and right spines of S. laevigatus . Poor morphological differentiation is clearly related to the fact that this species pair shows the least interspecific genetic distance (Nei’s

D = 0.156). This suggests a recent divergence event, which involves the Isthmus of Tehuantepec constraining the distributional range of S. pruinosus to the Tehuacán-Cuicatlán and Oaxaca Central Valleys .

Figures

Fig 2. Kriging interpolation of individual Q-matrix by each clustering method. The first three maps columns (left to right) depict the interpolated assignment probability for each method (labeled in the heading) and K is the number of groups detected by each. Groups containing the same populations across methods (EGGs) are placed alongside and keep the same color hue, whereas the color gradient saturation represents higher probability:red = S. griseus-Mexico (here designated S. huastecorum); green = S. pruinosus and its subgroups (green shades in Geneland maps); blue = S. laevigatus and its subgroups (blue shades in Geneland maps), and dark gray = S. griseus. White bullets represent populations. EGGs populations are represented at the rightmost column by bullets which follow the color code before described. https://doi.org/10.1371/journal.pone.0190385.g002

Fig 3. Genetic clustering summary. Color gradients represent BC belonging probability starting from the 75% threshold value, purple bars with green types bootstrap values are the three genetic barriers detected by Barrier, at the left the UPGMA dendrogram following the color code used in the BC. https://doi.org/10.1371/journal.pone.0190385.g003

Fig 5. Niche suitability pairwise comparisons based on t-tests. Different letters represent levels of significant differences. https://doi.org/10.1371/journal.pone.0190385.g005

Fig 6. Areolar morphometrics t-tests. (A-D) areolar features lengths comparisons, (E-F) spines counts comparisons. Levels not connected by the same letter are significantly different. https://doi.org/10.1371/journal.pone.0190385.g006