Genomic Displacement and Shift of the Hybrid Zone in the Japanese Fire-Bellied Newt

Abstract

Hybridizations on a secondary contact zone between 2 diverged lineages can have various evolutionary consequences, including the genetic replacement of one lineage by another. We detected such a case between 2 lineages (the Central and Western lineages) of the Japanese fire-bellied newt, Cynops pyrrhogaster in the Chugoku district of western Japan. We genotyped 269 individuals from 30 localities using the mitochondrial cytochrome b gene and 11 microsatellite loci. The mitochondrial DNA (mtDNA) analysis revealed that the 2 lineages were mostly distributed parapatrically to each other but co-occurred around the contact zone, whereas the microsatellite analyses indicated the presence of a hybrid zone. Geographic cline analysis revealed that the cline width of mtDNA is wider than the width of the microsatellite loci. The migration rate estimation and the NewHybrids analysis revealed that the Central lineage has expanded their range into the range of the hybrid zone, suggesting the possibility of range displacement of the 2 lineages as a consequence of the shift of their hybrid zone. We explored the process of asymmetric gene flow associated with the invasion of the Central lineage to explain this pattern.

Structure and movement of the hybrid zone between two divergent lineages of the Japanese newt Cynops pyrrhogaster (Amphibia: Urodela) in central Japan

“…Recent studies revealed that STRUCTURE Q values could be strongly affected by sampling bias and drift (Kalinowski, 2011; Toyama et al, 2020); therefore, we calculated the hybrid index of each individual using INTROGRESS (Gompert & Buerkle, 2010). For comparison with the results of the present study, we also calculated the hybrid index for each individual in the western and central lineages hybrid zone examined by Tominaga et al (2018). The hybrid indices were used for the subsequent cline analyses and classification of modality of the hybrid zone.…”

“…The central mtDNA lineage populations surveyed in this study correspond to the intermediate morphological/behavioral group of Sawada (1963a,b), which shows mixture of the character states of other groups in terms of morphology and mating behavior characteristics (Figure 1a,c). The central mtDNA lineage populations studied by Tominaga et al (2018) correspond to the Sasayama group of Sawada (1963a,b) (Figure 1a,c). The Intermediate and Sasayama morphological/behavioral groups were not differentiated from each other by allozyme analyses, and thus, they are all together recognized as the intermediate allozyme group, which shows mixture of the allozyme characteristics of the other groups (Hayashi & Matsui, 1988, 1990; Matsui, 1996; Figure 1a,b).…”

“…We adopted the approach of Tominaga et al (2018), modified from Vähä and Primmer (2006) and Shurtliff et al (2014), to verify the adequacy of assigning the surveyed individuals to a particular genotypic class (pure or hybrids) in the STRUCTURE and NewHybrids analyses. We used HybridLab software (Nielsen et al, 2006) to generate simulated hybrid individuals from a subset of both parental genotypes in our dataset (28 individuals for pure‐N and 40 for pure‐C at Q > 99% and K = 2 in the STRUCTURE analysis).…”

“…Tominaga et al (2018) conducted population genetic analyses of the central and western lineages of C. pyrrhogaster in their contact zone and clarified the presence of a hybrid zone. They clarified the structure of this zone and showed that the two lineages formed a hybrid zone categorized as “tension zone” type.…”

“…They clarified the structure of this zone and showed that the two lineages formed a hybrid zone categorized as “tension zone” type. The study revealed that the westward movement of the hybrid zone caused by the asymmetric gene flow (Tominaga et al, 2018).…”