The peninsula of Baja California and associated regions in northwestern Mexico form one of the most geologically interesting areas in the world. Since early Miocene, intense tectonic plate interactions, volcanic activity, and sea level changes combined to form a remarkably diverse landscape (Carreño and Helenes, 2002). Undoubtedly, these forces have had a great effect on the evolution of the regional biota. Biologically, this affords the opportunity to investigate the genetic consequences of plate tectonics (Murphy, 1983).
Although the biogeography of Baja California is extremely complex, a better understanding of the history of the region is currently taking shape. Much of this resurgence in the history of the peninsula and associated islands owes to a genetic study of side-blotched lizards (Upton and Murphy, 1997), which reported a surprising break in mitochondrial DNA in the middle of the peninsula. Subsequent molecular studies based on mtDNA have also revealed deep intraspecific histories in a variety of vertebrates including reptiles, mammals, and birds (e.g., Zink et al., 1997; Riddle et al., 2000; Lawlor et al., 2002; Murphy and Aguirre-León, 2002). The geographic patterns of these genealogies are largely congruent in suggesting genetic breaks midway on the peninsula as well as across the Isthmus of La Paz. These patterns are consistent with a vicariant history of the peninsula (Lindell et al., 2006) when marine seaways temporarily severed the peninsula, creating a peninsular archipelago (Aguirre-León et al., 1999; Murphy and Aguirre-León, 2002). Following the disappearance of these seaways, isolated populations were reunited at secondary contact zones.
The doctoral research of Johan Lindell aims to further clarify the historical biogeography of Baja California and highlight the effects on the regional fauna as revealed by intraspecific patterns in mitochondrial and nuclear DNA. Lindell’s work focuses on three small, common phrynosomatid lizards: Callisaurus draconoides (zebra-tailed lizard), Urosaurus nigricaudus (black-tailed brush lizard), and Uta stansburiana (side-blotched lizard). His work explores the patterns of deep histories among maternal lineages in these lizards, and contrasts these common patterns with those derived from nuclear genes. In essence, although the maternal lineages are essentially parapatric, gene flow along the peninsula, as suggested by microsatellite DNA and allozyme loci, is free-flowing. For example, Lindell’s work on the mtDNA genealogy of C. draconoides (Lindell et al., 2005) revealed a deep genealogical history that strongly contrasts with a lack of population differentiation based on allozyme variation (Adest, 1987). Similar patterns are explored in U. nigricaudus and U. stansburiana (Lindell et al., submitted). The maintenance of cytonuclear discordance in narrow, secondary contact zones is also being explored. Lindell will be completing his doctoral thesis shortly and is currently exploring options for post-doctoral research.
In association with this work, we are completing an investigation of the phylogenetic relationships of Mexican leaf-toed geckos, genus Phyllodactylus. All described species have been samples, except for one on mainland Mexico which has eluded our capture.
The work in Mexico is being conducted in collaboration with Prof. Fausto Méndez de la Cruz and his students at UNAM. Check in link in “lab personnel.”
This research has been funded by grants to Lindell from the Theodore Roosevelt Foundation of the American Museum of Natural History, the Royal Swedish Academy of Sciences, and Sigma-Xi), which has enabled him to collect and analyze specimens of these three species from along the peninsula, in addition to specimens already available at the Herpetology frozen tissue collection at the Royal Ontario Museum. Funding was obtained by Murphy from NSERC (Discovery Grant A3148), the ROM Foundation, and private donations.
Adest, G.A., 1987. Genetic differentiation among populations of the zebratail lizard, Callisaurus draconoides (Sauria: Iguanidae). Copeia 1987, 854-859.
Aguirre-León, G., Morafka, D.J., Murphy, R.W., 1999. The peninsular archipelago of Baja California: a thousand kilometers of tree lizard genetics. Herpetologica 55, 369-381 (pdf).
Carreño, A.L., Helenes, J., 2002. Geology and ages of the islands. In: Case, T.J., Cody, M.L., Ezcurra, E. (Eds.), A New Island Biogeography of the Sea of Cortés. Oxford University Press, New York, pp. 14-40.
Lawlor, T.E., Hafner, D.J., Stapp, P., Riddle, B.R., Alvarez-Castañeda, S.T., 2002. The mammals. In: Case, T.J., Cody, M.L., Ezcurra, E. (Eds.), A New Island Biogeography of the Sea of Cortés. Oxford University Press, New York, pp. 326-361.
Lindell, J., Méndez-de la Cruz, F.R., Murphy, R.W., 2005. Deep genealogical history without population differentiation: Discordance between mtDNA and allozyme divergence in the zebra-tailed lizard (Callisaurus draconoides). Mol. Phylogenet. Evol. 36, 682-694 (pdf).
Lindell, J., Ngo, A., Murphy, R.W., 2006. In press. Deep genealogies and the mid-peninsular seaway of Baja California. J. Biogeogr.
Murphy, R.W. Paleobiogeography and genetic differentiation of the Baja California herpetofauna. Occ. Pap. California Acad. Sci. 1983. 137: 1-48 (pdf).
Murphy, R.W., Aguirre-León, G., 2002. The nonavian reptiles: origins and evolution. In: Case, T.J., Cody, M.L., Ezcurra, E. (Eds.), A New Island Biogeography of the Sea of Cortés. Oxford University Press, New York, pp. 181-220.
Riddle, B.R., Hafner, D.J., Alexander, L.F., Jaeger, J.R., 2000. Cryptic vicariance in the historical assembly of a Baja California peninsular desert biota. Proc. Natl. Acad. Sci. USA 97, 14438-14443.
Upton, D.E. and R.W. Murphy. 1997. Phylogeny of the side-blotched lizards (Phrynosomatidae: Uta) based on mtDNA sequences: Support for a midpeninsular seaway in Baja California. Mol. Phyl. Evol. 8:104-113 (pdf).
Zink, R.M., Blackwell, R., Rojas-Soto, O., 1997. Species limits on the Le Conte's Thrasher. Condor 99, 132-138.