The Utility of Molecular Hypotheses for Uncovering Morphological Diversity in the Notropis rubellus Species Complex (Cypriniformes: Cyprinidae)
When molecular phylogeography results in the discovery of hidden diversity, this diversity is often labeled as cryptic. Few studies have gone back to the morphology to determine whether or not this molecular diversity is in fact detectable at the morphological level. The Notropis rubellus species complex has a widespread distribution in freshwater streams of eastern North America. Recent molecular studies have identified up to seven allopatric clades, suggesting that there may be morphologically cryptic diversity within the group. This study uses traditional meristics and geometric morphometric methods to test molecular hypotheses of cryptic diversity within the species complex. Meristic data and a principal component analysis of geometric morphometric data supported the cryptic hypothesis. Canonical variates analyses (CVA), however, were able to detect statistically significant, clade-specific morphological variation, suggesting that in this case, cryptic diversity was an artifact of the detection method. CVA thus provided a useful tool for identifying subtle or complex shape variation. However, morphological variation within the N. rubellus species complex was undetectable without a pre-existing molecular hypothesis.Abstract
Topology of the Notropis rubellus species group based on mitochondrial cytochome b gene sequence data from Berendzen et al. (2008). Clade A = Notropis percobromus; clade B = N. rubellus; clade C = undescribed form; clade D = undescribed form; clade E = N. micropteryx; clade F = undescribed form; and clade G = N. suttkusi. Map of eastern North America with the approximate distribution of clades identified in the topology. White dots indicate approximate sampling localities in this study.
Morphometric landmarks: 1 = anterior part of head where premaxillary bones extend furthest; most anterior point where premaxillary bones come together; 2 = anterior border of epiphyseal bar at midline dorsal neurocranium; 3 = anterior dorsal fin insertion into body; 4 = posterior insertion of dorsal fin into body; 5 = base of caudal fin on dorsal midline; 6 = posterior termination of hypural bones of caudal fin where the muscle tissue extends to the ventral fin ray closest to the lateral line; 7 = base of caudal fin on ventral midline; 8 = posterior insertion of anal fin into body; 9 = anterior insertion of anal fin into body; 10 = insertion of pelvic fin into body; 11 = insertion of pectoral fin into underlying skeletal girdle dorsolateral to ventral midline; 12 = ventral side of articulation between quadrate and mandible, vertical to ventral midline; 13 = intersection of maxillary bone and infraorbital bone, the point lies well lateral to midline; 14 = most anterior portion of eye at midline; 15 = most posterior portion of eye at midline; 16 = most posterior point of bony opercle, usually coexists with lateral line. Illustration by J. W. Tamplin, University of Northern Iowa.
Plots of principal component scores 1 vs. 2. (A) All-individuals. (B) Males-only. Individuals are identified and grouped based on the hypothesis of Berendzen et al. (2008). Legends of symbols for each proposed group are to the right of the graphs.
Ordination of groups along the first two canonical variates (CV1 and CV2) based on the matrix of shape variables. (A) Grouping of all individuals based on the hypothesis of Berendzen et al. (2008). (B) Grouping of males-only based on the hypothesis of Berendzen et al. (2008). (C) Grouping of all individuals based on the hypothesis of Wood et al. (2002). Legends of symbols for each proposed group are to the right of each graph.
Ordination of sister clade comparisons based on the hypothesis of Berendzen et al. (2008) along the first two canonical variates (CV1 and CV2) based on the matrix of shape variables. (A) Clades A and B, all individuals. (B) Clades A and B, males-only. (C) Clades C and D, all individuals. (D) Clades C and D, males-only. (E) Clades E, F, and G, all individuals. (F) Clades E, F, and G, males-only. Legend of symbols for each proposed group is at bottom of figure.
Correlation graphs. (A) Genetic distance vs. geographic distance. (B) Full Procrustes distance vs. geographic distance. (C) Genetic distance vs. Full Procrustes distance. Lightly shaded squares indicate all clade comparisons with Notropis suttkusi; darkly shaded triangles indicate all other clade comparisons. Values for the graphs are listed in Table 7.
Contributor Notes
Associate Editor: D. Buth.