Species Delimitation and Morphological Divergence in the Scorpion <i>Centruroides vittatus</i> (Say, 1821): Insights from Phylogeography

<div><p>Scorpion systematics and taxonomy have recently shown a need for revision, partially due to insights from molecular techniques. Scorpion taxonomy has been difficult with morphological characters as disagreement exists among researchers with character choice for adequate species delimitation in taxonomic studies. Within the family Buthidae, species identification and delimitation is particularly difficult due to the morphological similarity among species and extensive intraspecific morphological diversity. The genus <i>Centruroides</i> in the western hemisphere is a prime example of the difficulty in untangling the taxonomic complexity within buthid scorpions. In this paper, we present phylogeographic, Ecological Niche Modeling, and morphometric analyses to further understand how population diversification may have produced morphological diversity in <i>Centruroides vittatus</i> (Say, 1821). We show that <i>C. vittatus</i> populations in the Big Bend and Trans-Pecos region of Texas, USA are phylogeographically distinct and may predate the Last Glacial Maximum (LGM). In addition, we suggest the extended isolation of Big Bend region populations may have created the <i>C. vittatus</i> variant once known as <i>C. pantheriensis</i>.</p></div

Regional diversity indices for COI sequences.

<p>Significant values are noted for Northeastern and Big Bend populations for Fu's Fs and Tajima’s D.</p

MaxEnt results for <i>C. vittatus</i> Ecological Niche Modeling (ENM).

<p>Panel A represents current distribution modelling & panel B represents modelling for the Last Glacial Maximum (LGM), approximately 21,000 ybp. Warmer colors (red) represent more optimal climate, whereas cooler color (blue) represent suboptimal climate.</p

Bayes factor hypothesis testing for four alternate <i>C. vittatus</i> phylogenies.

<p>Bayes factor hypothesis testing for four alternate <i>C. vittatus</i> phylogenies.</p

Bayesian Phylogenetic tree for <i>C. vittatus</i> populations and outgroups.

<p>Numbers above nodes represent Bayesian posterior probabilities: bootstrap support values are shown below. Upper case letter designation of each clade represent networks produced in the TCS haplotype network analysis (see Fig. 4. and results for identification). Asterisked individuals (*) represent those identified as the <i>C. pantheriensis</i> variant with double asterisked clades (**) as those clades with all <i>C. pantheriensis</i> variants. Individuals or clades marked with a “+” symbol represent those specimens we identified as completely pale forms. Each color represents a general collection region: see results for further details. The inset box shows <i>C. vittatus</i> female morphologic diversity in four populations. The population designations are the same as in the Bayesian phylogenetic tree.</p

The haplotype network created from the nuclear 1075 locus.

<p>Each haplotype node is color coded to the geographic clade with the most represented individuals in the node: Green: northeastern populations, Blue: central Texas/eastern NM/CO/west KS/NE populations, Yellow: Big Bend and Transpecos populations, & Red: Falcon, Seminole Canyon, and Laredo populations. The largest nodes are lettered with all represented COI geographic clades in each node with bold letters representing the most frequent geographic clade. The three largest nodes contained these numbers of individuals: Green: 39, Yellow: 20, & Blue: 15.</p

All COI TCS networks overlaid on a geographic map to illustrate network boundaries.

<p>These networks are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068282#pone-0068282-g002" target="_blank">Figure 2:</a> A: Black Gap, B: Balmorhea Springs/Davis Mts., C: Independence Creek, D: Oliver Lee, E: central Texas/eastern NM/CO/west KS/NE populations, F: Big Bend populations, G: Chinati, H: Hueco Tanks, I: Aguirre Springs, J: Seminole Canyon, K: Laredo/Falcon Lake, L: Wichita Mts., & M: northeastern populations.</p

COI TCS networks for the three networks containing several population collection sites.

<p>The networks shown here are “E” central Texas/eastern NM/CO/west KS/NE populations, “F” Big Bend, & “M” northeastern populations. The node size represents individual number for each haplotype from singletons (smallest) to six individuals (largest). The large node in network “M” represents 18 individuals. The numbers next to each line break represent mutational steps connecting nodes.</p

Morphological classification of male scorpions with Discriminant Function Analysis (DFA) to show correctly classified versus misclassified groups.

<p>Each row represents actual groups whereas the columns represent predicted groups. Groups identified through the TCS analysis are shown in parentheses. The reduction in classification error (57.6%) shows the accuracy of the DFA compared to random classification. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068282#pone.0068282.s004" target="_blank">Protocol S1</a> for further information concerning population designations and statistical analyses.</p

Morphological classification of female scorpions with Discriminant Function Analysis (DFA) to show correctly classified versus misclassified groups.

<p>Each row represents actual groups whereas the columns represent predicted groups. Groups identified through the TCS analysis are shown in parentheses. The reduction in classification error (47.5%) shows the accuracy of the DFA compared to random classification. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068282#pone.0068282.s004" target="_blank">Protocol S1</a> for further information concerning population designations and statistical analyses.</p