Historical Biogeography of the New-World Pupfish Genus Cyprinodon (Teleostei: Cyprinodontidae)
Analysis of mtDNA sequence variation (2,548 bp from ND2, cytb, and part of the control region) indicates that the genus Cyprinodon began diverging in the Late Miocene from a common ancestor with Megupsilon, a monotypic genus on the Mesa del Norte of Mexico. The geographic pattern of mtDNA variation, with estimates of divergence time, suggests that by the end of the Miocene Cyprinodon occurred from the Atlantic Coast and West Indies to near the western margin of North America via ancestral Rio Grande and Colorado River systems. Phylogeographic structure within the major mtDNA complexes supports a variety of hypotheses from geology and previous phylogenetic analyses for Late Neogene connections among basins in southwestern North America now separated by formidable barriers to dispersal. Comparison of the mtDNA tree with previous phylogenetic inferences from allozymes indicates that reticulate evolution involving divergent lineages probably was important in the history of Cyprinodon. El análisis de variación de secuencias de ADNmt (ND2, cytb, y parte de la región reguladora; 2,548 pb) indica que el género Cyprinodon empezó a divergir en el mioceno tardío de un antepasado común con Megupsilon, un género monotípico de la Mesa del Norte de México. El patrón geográfico de la variación de ADNmt, con estimadas de los tiempos divergencias, sugiere que al llegar al fin del mioceno Cyprinodon ocurrió desde la costa Atlántica y las Antillas hasta casi el margen oeste de Norteamérica por los sistemas pluviales antiguos del río Bravo y del río Colorado. La estructura filogeográfica entre los grupos principales de ADNmt apoya a una variedad de hipótesis de la geología y de los análisis filogenéticos anteriores para conexiones del neogeno tardío entre cuencas del suroeste de Norteamérica que ahora están separadas por barreras imponentes contra la dispersión. La comparación del árbol de ADNmt con deducciones filogenéticos anteriores de alozimas indica que la evolución reticulada que incluye líneas divergentes probablemente fue importante en la historia del Cyprinodon.Abstract
Resumen
Distribution of samples and basins. DV = Death Valley System, GB = Guzmán Basin, TB = Tularosa Basin, CC = Cuatro Ciénegas Basin, RM = Río Mezquital, SPB = Sandia and Potosi Basins. Basins not labeled are Devils River (7), Alamito Creek (8), Río Florido (9), and Laguna Santiaguillo (16). Localities 4 and 22 both comprise two sites in close proximity (Material Examined)
Strict consensus of maximum-parsimony trees. Terminal nodes with locality numbers in parentheses represent haplotypes generated in the present study. Taxa in boxes represent GenBank sequences. Weakly divergent (uncorrected p = 0.001–0.009) terminal nodes are collapsed to one except C. nevadensis, for which all are retained to show paraphyly with respect to C. diabolis, and the Lake Chichancanab/C. artifrons node, a polytomy of shared haplotypes. Numbers above branches = bootstrap support. Asterisks = Bayesian probabilities >95% (model = GTR + SS Γ); nodes uptree of arrows include GenBank sequences not subjected to Bayesian analysis. The node with a dashed line received Bayesian and bootstrap support but was not retained in the strict consensus of the shortest maximum-parsimony trees
Estimated timing of cladogenetic events. Ages indicated are as follows (20.3 Mya in Early Miocene) and the start of each of the following (from Berggren et al., 1995): Late Miocene (11.2), Pliocene (5.2), and Pleistocene (2.5 Mya). Based on the ultrametric, minimum-evolution tree, with timing based on the clock (2.8%/Mya) developed for Aphanius. Timing closely resembles that from the multidivtime approach (Table 1), but that approach does not produce an ultrametric tree in which all terminal nodes are at time zero
Geography and vicariance history of mtDNA clades in Cyprinodon: (A) Geographic distribution of the seven primary mtDNA-clades. 1 = Yucatan, 2A = maritime, 2B = southern Great Plains-northern Chihuahuan Desert, 3 = Sandia-Potosi, 4A = Río Conchos-middle Rio Grande, 4B = Old Río Nazas, 5 = western. Clade 2A is the maritime group, with a basal C. variegatus ovinus-C. bondi clade, and a clade with the following topology: (C. tularosa [C. dearborni {C. variegatus, C. sp. from Lake Enriquillo}]). (B) Some hypothetical paleosystems (arrows) and estimated times of vicariance for pupfish in each system. Basin abbreviations as in Fig. 1. Lettering in boxes = age of associated vicariance (average of the estimates in Table 1) and clades involved (labeled as in Fig. 2)
A synthesis of phylogenetic studies of mtDNA and allozymes in pupfishes. Nodes for mtDNA had >50% bootstrap support and, in the present study, >95% Bayesian probability. For allozymes, asterisks denote nodes supported by at least one synapomorphic allele; remaining allozyme nodes were in both the shortest allozyme trees and the mtDNA tree. Thick vertical lines denote conflicts between mtDNA and the best-supported allozyme inferences. Labeled boxes denote major mtDNA clades (Figs. 3 and 4). Letters on trees indicate sources other than this paper: A = Parker and Kornfield (1995) for placement of Cualac, Cyprinodon, and Megupsilon with Jordanella; B = Echelle et al. (1995) for monophyly of a group of species from Sandia and Potosí basins (C. veronicae and C. alvarezi here); C, D, E, and F = Echelle and Echelle (1992, 1993a, 1993b, and 1998) for, respectively, monophyly of the C. variegatus complex and the Death Valley System pupfishes and relationships among genera and among Mexican Plateau species and representatives of other lineages
Contributor Notes
(AAE, AFE, RAVDB) Zoology Department, Oklahoma State University, Stillwater, Oklahoma 74078; (EWC, TED) Department of Biology, Arizona State University, Tempe, Arizona 85287; (AM) Department of Biology, University of Konstanz, D-78457 Konstanz, Germany. (AAE) echelle@okstate.edu Send reprint requests to AAE.