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Rattlesnakes!

Abstracts: Bradford D. Hollingsworth, Ph.D.


A REPORT ON THE HERPETOFAUNA OF THE VIZCAÍNO PENINSULA, BAJA CALIFORNIA, MÉXICO, WITH A DISCUSSION OF ITS BIOGEOGRAPHIC AND TAXONOMIC IMPLICATIONS

L. Lee Grismer, Jimmy A. McGuire, and Bradford D. Hollingsworth

Abstract -- The Sierra Vizcaíno and Sierra Santa Clara are located along the west coast of central Baja California and compose the continental portion of the Vizcaíno Peninsula. A survey of the herpetofauna of this region documented the presence of several previously unreported species. Three species (Gambelia wislizenii, Coleonyx variegatus, and Crotalus exsul) show a close morphological similarity to conspecifics of Isla de Cedros. The presence of a relict mesophilic species, Hyla regilla, in the Sierra Vizcaíno, suggests that this region was much more mesic in the past. It is hypothesized that the saxicolous taxa of the Sierra Vizcaíno and Sierra Santa Clara colonized these mountains from the Peninsular Ranges of Baja California while the former existed as Pacific islands during the last 10,000 years. Such habitat specialists would be unable to disperse across the flat, sandy, Vizcaíno Desert that currently separates these species from their peninsular counterparts.

Bulletin of the Southern California Academy of Sciences. 1994. 93(2):45-80


THE SYSTEMATICS OF CHUCKWALLAS (SAUROMALUS) WITH A PHYLOGENETIC ANALYSIS OF OTHER IGUANID LIZARDS

Bradford D. Hollingsworth

Abstract -- A systematic study of the chuckwallas (genus Sauromalus) is presented which combines a traditional monographic revision with a modern phylogenetic analysis. Included are a reassessment of alpha taxonomy and geographic variation, a hypothesis of evolutionary relationships, a reevaluation of the relationships of Sauromalus to other iguanid genera, and an examination of trends in morphology, biogeography, and natural history within Sauromalus in light of the recovered phylogeny.

Due to difficulties in diagnosing many of the chuckwalla species, geographically isolated populations were selected as operational taxonomic units (OTUs). This resulted in the designation of 31 insular and eight continental OTUs. These OTUs were included in a larger analysis with the other 23 species within Iguanini (the clade of iguanids above Dipsosaurus, Armandisaurus, and Brachylophus). A phylogenetic analysis was performed using 142 characters of scalation, coloration, soft tissues, and osteology; 93 of which came directly or were modified from the previous studies of de Queiroz (1987a, 1987b) and Norell and de Queiroz (1991). Two analyses were performed, each using different coding schemes for polymorphic characters. The first used the baseline method (polymorphisms coded as "0,1") and the second used the frequency bin method (Wiens, 1993, 1995). The monophyly of all currently recognized iguanid genera is supported in both analyses. Intergeneric relationships are resolved in the strict consensus tree using the frequency bin method (Ctenosaura ((Cyclura + Iguana) + (Sauromalus (Amblyrhynchus + Conolophus)))) and only partially resolved using the baseline method. Interspecific relationships are proposed for the genera Cyclura, Ctenosaura, and Sauromalus. Relationships among the 39 OTUs in Sauromalus are partly resolved using the frequency bin method, although some nodes are weakly supported. The results from the baseline method are consistent with the more strongly supported nodes from the frequency bin method. The strict consensus trees suggest the recognition of four insular endemics, hispidus, klauberi, slevini, and varius, while the OTUs recognized under obesus, australis, and ater yield an unresolved polytomy. Because the relationships between the obesus, australis, and ater OTUs are unresolved and these taxa cannot be diagnosed from each other using fixed character differences, obesus and australis are synonymized with ater. The phylogenetic relationships within Sauromalus are: (varius (hispidus (ater (klauberi + slevini)))).

Accounts of each species of Sauromalus include a synonymy, etymology, definition, diagnosis, detailed description of external morphology and color pattern, skeletal characterization, geographic variation, natural history, fossil record and distribution. A redescription of the type specimen of S. ater is provided and the type locality is restricted to southern coastal Sonora, México.

Herpetological Monographs. 1998. 11:38-191


WAR OF THE IGUANAS: CONFLICTING MOLECULAR AND MORPHOLOGICAL PHYLOGENIES AND LONG-BRANCH ATTRACTION IN IGUANID LIZARDS

John J. Wiens and Bradford D. Hollingsworth

Abstract -- Recent studies have found strongly conflicting phylogenies for the genera of iguanid lizards based on different types of data (i.e., morphology, molecules), but have been unable to explain the basis for this incongruence. We reanalyze published data from morphology and from the mitochondrial ND4, cytochrome b, 12S, and 16S genes to explore the sources of incongruence and resolve these conflicts. Much of the incongruence centers on the genus Cyclura, which is the sister taxon of Iguana based on morphology and the ribosomal genes but is the sister taxon of all other Iguanini according to the protein-coding genes. Maximum likelihood analyses show that there has been an increase in the rate of nucleotide substitution in Cyclura in the two protein coding genes (ND4 and cytochrome b), although this increase is not as clear when parsimony is used to estimate branch lengths. Parametric simulations suggest that Cyclura may be misplaced by the protein-coding genes due to long-branch attraction; even when Cyclura and Iguana are sister taxa in a simulated phylogeny, Cyclura is still placed as the basal member of the Iguanini by parsimony analysis in 55% of the replicates. A similar long-branch attraction problem may also exist in the morphological data involving the placement of Sauromalus with the Galápagos iguanas (Amblyrhynchus and Conolophus). The results have many implications for the analysis of diverse data sets, the impact of long branches on parsimony and likelihood methods, and the use of certain protein-coding genes in phylogeny reconstruction.

Systematic Biology. 1999-2000 (in press)