Cryptic vicariance in the historical assembly of a Baja California Peninsular Desert biota

Abstract

We use analyses of phylogeographic population structure across a suite of 12 mammalian, avian, amphibian, and reptilian species and species-groups to assess the role of Late Miocene to Pleistocene geological history in the evolution of a distinct Baja California Peninsular Desert biota. Comparative examination of phylogroup distributions provides support for previously hypothesized vicariant events produced by: a middle Pleistocene midpeninsular seaway, a late Pliocene northward transgression of the Sea of Corté z, and a Pliocene seaway across the southern peninsular Isthmus of La Paz. Most of this phylogeographic architecture is cryptically embedded within widespread taxonomic species and speciesgroups, such that the unique evolutionary history of the Peninsular Desert has been obscured and ignored. The Peninsular Desert can no longer be considered a subset of the Sonoran Desert-it is a separate regional desert with its own unique evolutionary history, ecological arena, and conservation value.

Identifying cryptic diversity with predictive phylogeography

“…the training dataset) into those that harbour and those that lack cryptic diversity, our phylogeographic results agreed with those obtained from previous studies [33,40,44]. Indeed, we identified several species that harbour cryptic diversity in each biome (electronic supplementary material, tables S2 -S3).…”

“…Alternatively, it has been proposed that some disjunct species were isolated in the Baja Californian deserts and have only recently colonized the Sonoran region; this hypothesis is consistent with the observation of several xeric-adapted species that do not show genetic differentiation between the two areas, and thus do not display cryptic diversity (e.g. [40,43]; electronic supplementary material, table S1 [44]). …”

“…Although the area displays strong endemism, the Baja California-Sonoran areas share many species that are separated by the Colorado River and Gulf of California ( [40,41]; figure 1a). Geological data indicate that the Baja Californian desert became isolated from the Sonoran desert after the separation of the Baja Peninsula from the mainland Sonoran region.…”

Testing Species Boundaries in an Ancient Species Complex with Deep Phylogeographic History: GenusXantusia(Squamata: Xantusiidae)

“…The existence of deep divergences among the biota of regional deserts (e.g., Grismer and McGuire 1996;Hafner and Riddle 1997;Zamudio et al 1997;Orange et al 1999;Riddle et al 2000aRiddle et al , 2000bRiddle et al , 2000cRodríguez-Robles and De Jesú s-Escobar 2000) has been interpreted as a shared response across taxa to vicariant events (Riddle et al 2000c). However, the pattern in Xantusia does not match those summarized in Riddle et al (2000b), possibly due to the much older age of this group.…”

“…These life-history characteristics may make this genus particularly attractive as a model system for studies of the geography of speciation because historical range changes may have been sufficiently slow that the mode of speciation remains detectable (Barraclough and Vogler 2000;Losos and Glor 2003). This attribute is particularly attractive in view of the current interest in using multiple clades of vertebrates in comparative biogeographic studies of the Baja California peninsula and warm deserts of southwestern North America (Riddle et al 2000a(Riddle et al , 2000b(Riddle et al , 2000c.…”