Behavioral consequences of a rampant mitochondrial introgression in the Italian fire salamander Salamandra salamandra

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Andrea Chiocchio, Roberta Bisconti, Erica de Rysky, Claudio Carere and Daniele Canestrelli, Department of Ecological and Biological Sciences, Università della Tuscia, Viterbo, Italy

Background/Question/Methods
Mito-nuclear discordance across secondary contact zones have been widely reported in many taxa, including animal and plant species. It consists of a mismatch between nuclear and mitochondrial genomes in the geographic location and/or extension of the secondary contact zone between distinct lineages. Despite a large amount of theoretical and empirical studies on introgressive hybridization and pervasive introgression of genome portions, few data are available to understand the phenotypic underpinnings of rampant introgressions of the mitochondrial genome. In this study, we addressed the hypothesis that mtDNA variation across a contact zone could be associated with variation at phenotypic traits affecting dispersal propensity. This association might contribute to patterns of asymmetric introgression of specific mitotypes between resident lineages and colonizers after a range expansion. To address this hypothesis, we analyzed patterns of phenotypic and genetic variation across a mtDNAsecondary contact zone of the fire salamander Salamandra salamandra in central Italy, which is over 600 km displaced from its nuclear counterpart. We collected salamander larvae across the contact zone between the two mitochondrial lineages, and performed behavioral assays of individual personality in both larvae and post-metamorphic individuals.
Results/Conclusions
We found distinct behavioral profiles associated with the two mitotypes co-occurring in the mtDNA secondary contact zone. In particular, we found a ‘slow-thorough’ dispersal profile associated with the mitotype that introgressed into the colonizing lineage. This dispersal profile was characterized by exploratory, shy, fearful and prudent personality traits. Interestingly, this pattern was consistent across life-stages and contexts, i.e. aquatic larvae and terrestrial juveniles. Our results provide experimental evidence supporting the hypothesis that personality traits associated with distinct mitotypes could promote differential mitochondrial introgression within alternative nuclear backgrounds. Finally, we provide a framework to investigate the role of behavioral polymorphisms in shaping complex biogeographic patterns.