Repeated mitochondrial capture with limited genomic introgression in a lizard group

Mitochondrial introgression is common among animals and is often first identified through 34 mitonuclear discordance — discrepancies between evolutionary relationships inferred from 35 mitochondrial DNA (mtDNA) and nuclear DNA (nuDNA). Over recent decades, genomic data 36 have also revealed extensive nuclear introgression in many animal groups, with implications 37 for genetic and phenotypic diversity. However, the extent to which mtDNA introgression 38 corresponds to nuDNA introgression varies. Here, we investigated historical and recent 39 introgression in the Gehyra nana-occidentalis clade, a complex group of Australian geckos 40 with documented cases of mitonuclear discordance suggestive of repeated mtDNA 41 introgression. We hypothesised that mitonuclear discordance in this clade reflects mtDNA 42 introgression with substantial nuclear introgression. Despite evidence of repeated mtDNA 43 introgression, however, we found little to no evidence of historical nuDNA introgression using 44 exon capture and genome-wide single nucleotide polymorphism (SNP) data. We also found 45 no evidence of gene flow at modern contact zones and detected only a single early 46 generation hybrid. Unsurprising given these results, we found no evidence of transgressive, 47 intermediate, or more variable morphological phenotypes in taxa with introgressed mtDNA. 48 These findings suggest that hybridisation in this system has, at least in some cases, resulted 49 in repeated mitochondrial introgression with little or no nuclear introgression. This pattern 50 aligns with other studies showing limited nuDNA introgression in taxa with mitonuclear 51 discordance, highlighting a potentially broader trend in animal radiations.