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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 February 1, 2026
Recent Range Expansion and Genomic Admixture in a Kleptoparasitic Spider, Argyrodes lanyuensis : A Case of Adaptive Introgression on Small, Isolated Islands of the Taiwan–Philippine Transition Zone?
ABSTRACT Adaptive introgression involves the acquisition of advantageous genetic variants through hybridisation, which are subsequently favoured by natural selection due to their association with beneficial traits. Here, we analysed speciation patterns of the kleptoparasitic spider,Argyrodes lanyuensis, through genomic analyses and tested for possible genetic evidence of adaptive introgression at the Taiwan–Philippines transition zone. Our study used highly polymorphic SNPs to demonstrate that speciation occurred when the Hualien (on Taiwan Island + Green Island) and Orchid Island + Philippine lineages separated during the early to mid‐Pleistocene. The best colonisation model suggested by approximate Bayesian computation and random forests and biogeographical analyses supported an inference of a bottleneck during speciation, an interpretation reinforced by observation of lowerFSTvalues and reduced genetic diversity of the Orchid Island + Philippines lineage. We also found the highest support for the occurrence of introgression on the youngest island (Green Island) of the Taiwan–Philippines transition zone based on the ABBA‐BABA test. Our study highlights the inference of two noteworthy species (Hualien + Green Island and Orchid Island + Philippines) based on our species delimitation tests, with gene flow between Green Island and Orchid Island that indicates introgression. The potential adaptive alleles in Green Island population, which are under balancing selection, provide initial evidence of possible rare case of adaptive introgression. This could represent an evolutionary response to a newly formed niche (or novel geographical context) lying between the tropical climate of the Philippines and the subtropical climate of Hualien, Taiwan.
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- Award ID(s):
- 1654388
- PAR ID:
- 10633115
- Publisher / Repository:
- Wiley & Sons
- Date Published:
- Journal Name:
- Molecular Ecology
- Volume:
- 34
- Issue:
- 3
- ISSN:
- 0962-1083
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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