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ABSTRACT Coalescent modelling of hybrid zones can provide novel insights into the historical demography of populations, including divergence times, population sizes, introgression proportions, migration rates and the timing of hybrid zone formation. We used coalescent analysis to determine whether the hybrid zone between phylogeographic lineages of the Plateau Fence Lizard (Sceloporus tristichus) in Arizona formed recently due to human‐induced landscape changes, or if it originated during Pleistocene climatic shifts. Given the presence of mitochondrial DNA from another species in the hybrid zone (Southwestern Fence Lizard,S. cowlesi), we tested for the presence ofS. cowlesinuclear DNA in the hybrid zone as well as reassessed the species boundary betweenS. tristichusandS. cowlesi. No evidence ofS. cowlesinuclear DNA is found in the hybrid zone, and the paraphyly of both species raises concerns about their taxonomic validity. Introgression analysis placed the divergence time between the parental hybrid zone populations at approximately 140 kya and their secondary contact and hybridization at approximately 11 kya at the end of the Pleistocene. Introgression proportions estimated for hybrid populations are correlated with their geographic distance from parental populations. The multispecies coalescent with migration provided significant support for unidirectional migration moving from south to north, which is consistent with spatial cline analyses that suggest a slow but steady northward shift of the centre of the hybrid zone over the last two decades. When analysing hybrid populations sampled along a linear transect, coalescent methods can provide novel insights into hybrid zone dynamics.
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This content will become publicly available on October 21, 2026
Comparative Phylogeography of Phrynosomatid Lizards in Baja California: Asynchronous Divergences and Expansion of Callisaurus draconoides Across the North American Deserts
ABSTRACT AimWe tested whether co‐distributed phrynosomatid lizards in the Baja California Peninsula (BCP) share synchronous phylogeographic discontinuities, as predicted by the “peninsular archipelago” hypothesis, and examined the diversification ofCallisaurus draconoidesthroughout its range. LocationThe BCP and the Great Basin, Mojave and Sonoran Deserts of southwestern North America. TaxaFive co‐distributed species complexes representing four genera within Phrynosomatidae:Callisaurus,Petrosaurus,UrosaurusandSceloporus. MethodsDouble‐digest restriction‐associated‐DNA (ddRAD) sequencing was used to collect genome‐wide sequence data for 309 lizards. We used phylogenetic analyses of concatenated loci and population admixture analysis of unlinked SNPs to identify lineages. To infer a species tree, we collected target sequence capture (TSC) data. Migration between adjacent peninsular lineages was estimated using the multispecies coalescent with migration (MSC‐M) in BPP. A full‐likelihood Bayesian comparative phylogeographic approach (ecoevolity) was used to test the simultaneous divergence hypothesis for the Isthmus of La Paz and Vizcaíno Desert. ResultsWe identified 24 potential lineages within the five co‐distributed complexes. Contact zones between lineages were observed at the Isthmus of La Paz in four of the five complexes, and in all five within the Vizcaíno Desert. The time‐calibrated species tree indicates that within each complex, divergences at the Isthmus of La Paz predate those across the Vizcaíno Desert. We found strong support for at least three independent divergence events at the Isthmus of La Paz and the Vizcaíno Desert, thereby rejecting the simultaneous divergence hypothesis. Inferred migration rates between adjacent peninsular populations were generally low (M << 1) to absent. Zebra‐tailed lizards (Callisaurus), in which the earliest diverging lineages are endemic to the southern BCP, exhibit a clear pattern of Pleistocene range expansion from the BCP into the deserts of the western United States and mainland Mexico. The most deeply nested populations inCallisaurusoccur at the northern, eastern and southeastern range limits in temperate, subtropical and tropical biomes, respectively. Main ConclusionsThese results support the BCP's tectonic isolation as a driver of peninsular endemism and a contributing factor to lineage diversification more broadly in the region. Taxonomic adjustments, including resurrectingUrosaurus microscutatus, are proposed to better reflect evolutionary history in taxonomy.
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- Award ID(s):
- 2023723
- PAR ID:
- 10652239
- Publisher / Repository:
- JBI
- Date Published:
- Journal Name:
- Journal of Biogeography
- ISSN:
- 0305-0270
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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