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Night lizards (Xantusia) and their discoverers on the Baja California Peninsula
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The genus Nolina on the Baja California peninsula has not been critically studied. Most of the taxonomic literature dealing with this
group is older or incomplete in nature. Taxonomic problemswith this genus arise because it is not easy to make herbarium specimens from plants in
the field and the taxa are notwell represented in collections. Species in this genus are difficult because they are dioecious, generally have large rosettes
with many leaves, leaf margins that often cut skin, and the plants have large inflorescences. On older herbarium specimens, it is common to find
only a leaf and an inflorescence fragment, and labels often do not provide taxonomically important information such as the plant’s growth habit type.
Consequently, distinctive inflorescence characters are usually missing from the specimen or from the label data. It is rare to find a complete specimen
collection that includes all of the needed species-relevant data. Decisions for delimiting species in this genus are not easy, and in this case, were based
mostly upon their morphological character consistency, geographic distribution, and environmental factors. Five species of Nolina are now registered
for the Baja California peninsula: N. beldingii, N. bigelovii, N. interrata, N. palmeri, and the new nomenclatural combination N. brandegeei (Trelease) L.
Hern. This paper includes: a species identification key, species taxonomic descriptions, ecological and geographical information, common names,
taxonomic discussions of species, and pictures for species recognition of all taxa in the Baja California region.
Dos linajes de Xantusia presentes en el noroeste de México son muy divergentes en cuanto a su ADN mitochondrial y nuclear. Son mutuamente excluyentes con respecto a otros miembros del género y además diferenciables morfológicamente. Se describen aquí formalmente como especies nuevas. La especie de Sonora es parecido a sus pariente más cercana, Xantusia arizonae, en que las hembras no poseen poros femorales bien desarrollados, pero se diferencian en el número de escamas dorsales en el centro del cuerpo y por los patrones de color. Se encuentran cerca del Mar de Cortez en un microhábitat único, Pachycereus pringlei (cardón) caídos. Al contrario, X. arizonae se encuentra en grietas en las de piedras en Arizona central. La especie nueva de Baja California Sur se diferencia de su pariente más cercano, Xantusia gilberti, por su patrón de color y además por tener escamas pequeñas bordeando el labio detrás de la quinta infralabial. Esta especie se encuentra en el datilillo, Yucca valida, en las llanuras de Magdalena cerca de la costa Pacífica, mientras que X. gilberti se encuentra en los bosques de pino y roble de la Sierra de la Laguna, 350 kilómetros hacia el sur.
La singularidad biológica de la península de Baja California ha capturado el interés de los naturalistas por largo tiempo. Fruto de ello ha sido la publicación de una rica variedad de interpretaciones geográficas de su escenario ecológico y biogeográfico. Aunque coincidentes en un marco común general, presentan también numerosas discrepancias. En este trabajo se revisa exhaustivamente la literatura publicada sobre el tema con el objeto de identificar las fronteras o zonas de transición que presentan mayor diversidad o discrepancia. Se sometió el diagnóstico al examen y discusión de un taller de expertos, el cual contó con el apoyo de un sistema de información geográfica, generando decisiones consensuadas. Los resultados se presentan en un mapa de regiones ecológicas de la península de Baja California como una síntesis del estudio e interpretación sobre las ecorregiones naturales de la península de Baja California.
Identification of species in natural populations has recently received increased attention with a number of investigators proposing rigorous methods for species delimitation. Morphologically conservative species (or species complexes) with deep phylogenetic histories (and limited gene flow) are likely to pose particular problems when attempting to delimit species, yet this is crucial to comparative studies of the geography of speciation. We apply two methods of species delimitation to an ancient group of lizards (genus Xantusia) that occur throughout southwestern North America. Mitochondrial cytochrome b and nicotinamide adenine dinucleotide dehydrogenase subunit 4 gene sequences were generated from samples taken throughout the geographic range of Xantusia. Maximum likelihood, Bayesian, and nested cladogram analyses were used to estimate relationships among haplotypes and to infer evolutionary processes. We found multiple well-supported independent lineages within Xantusia, for which there is considerable discordance with the currently recognized taxonomy. High levels of sequence divergence (21.3%) suggest that the pattern in Xantusia may predate the vicariant events usually hypothesized for the fauna of the Baja California peninsula, and the existence of deeply divergent clades (18.8%-26.9%) elsewhere in the complex indicates the occurrence of ancient sundering events whose genetic signatures were not erased by the late Wisconsin vegetation changes. We present a revised taxonomic arrangement for this genus consistent with the distinct mtDNA lineages and discuss the phylogeographic history of this genus as a model system for studies of speciation in North American deserts.
An analysis of scalation, color pattern, and distribution of Eumeces skiltonianus and E. lagunensis in Baja California indicates that these taxa are discretely diagnosable from one another and allopatric. In the context of an evolutionary species concept, they are considered to be separate species. New records extend the range of E. lagunensis 220 km to the north in central Baja California. An erroneous report on the southern extent of E. skiltonianus in northern Baja California is corrected, restricting its southern distribution 145 km further north than previously reported.
We identify instances of parallel morphological evolution in North American scincid lizards of the Eumeces skiltonianus species group and provide evidence that this system is consistent with a model of ecological speciation. The group consists of three putative species divided among two morphotypes, the small-bodied and striped E. skiltonianus and E. lagunensis versus the large-bodied and typically uniform-colored E. gilberti. Members of the group pass through markedly similar phenotypic stages during early development, but differ with respect to where terminal morphology occurs along the developmental sequence. The morphotypes also differ in habitat preference, with the large-bodied gilberti form generally inhabiting lower elevations and drier environments than the smaller, striped morphs. We inferred the phylogenetic relationships of 53 skiltonianus group populations using mtDNA sequence data from the ND4 protein-coding gene and three flanking tRNAs (900 bp total). Sampling encompassed nearly the entire geographic range of the group, and all currently recognized species and subspecies were included. Our results provide strong evidence for parallel origins of three clades characterized by the gilberti morphotype, two of which are nested within the more geographically widespread E. skiltonianus. Eumeces lagunensis was also nested among populations of E. skiltonianus. Comparative analyses using independent contrasts show that evolutionary changes in body size are correlated with differences in adult color pattern. The independently derived association of gilberti morphology with warm, arid environments suggests that phenotypic divergence is the result of adaptation to contrasting selection regimes. We provide evidence that body size was likely the target of natural selection, and that divergences in color pattern and mate recognition are probable secondary consequences of evolving large body size.
The lizard genus Xantusia of southwestern North America has received recent attention in relation to delimiting species. Using more than 500 lizards from 156 localities, we further test hypothesized species boundaries and clarify phylogeographical patterns, particularly in regions of potential secondary contact. We sequenced the entire mitochondrial cytochrome b gene for every lizard in the study, plus a second mitochondrial DNA (mtDNA) region and two nuclear introns for subsets of the total sample. Phylogenetic analyses of the mtDNA recover a well-resolved, novel hypothesis for species in the Xantusia vigilis complex. The nuclear DNA (nDNA) data provide independent support for the recognition of X. arizonae, X. bezyi and X. wigginsi. Differences between the respective mtDNA and nDNA topologies result from either the effects of lineage sorting or ancient introgression. Nuclear data confirm the inference that some populations of X. vigilis in northwestern Arizona converged on rock-crevice-dwelling morphology and are not X. arizonae with an introgressed X. vigilis mtDNA genome. The historical independence of ancient cryptic lineages of Xantusia in southern California is also corroborated, though limited introgression is detected. Our proposed biogeographical scenario indicates that diversification of this group was driven by vicariance beginning in the late Miocene. Additionally, Pleistocene climatical changes influenced Xantusia distribution, and the now inhospitable Colorado Desert previously supported night lizard presence. The current taxonomy of the group likely underestimates species diversity within the group, and our results collectively show that while convergence on the rock-crevice-dwelling morphology is one hallmark of Xantusia evolution, morphological stasis is paradoxically another.
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