Predictors of Phylogeographic Structure among co-distributed taxa across the complex Australian Monsoonal Tropics

Differences in the geographic scale and depth of phylogeographic structure across co-distributed taxa can reveal how microevolutionary processes such as population isolation and persistence drive diversification. In turn, environmental heterogeneity, species’ traits and historical biogeographic barriers may influence the potential for isolation and persistence. Using extensive SNP data and a combination of population genetic summary statistics and landscape genomic analyses, we explore predictors of the scale and depth of phylogeographic structure in co-distributed lizard taxa from the topographically and climatically complex monsoonal tropics (AMT) of Australia. We first resolve intraspecific lineages and then test whether genetic divergence across space within lineages is related to isolation by distance, resistance and/or environment, and whether these factors differ across genera or between rock-related versus habitat generalist taxa. We then test whether microevolutionary processes within lineages explain differences in the geographic scale and depth of intraspecific phylogeographic lineages. Results indicate that landscape predictors of phylogeographic structure differ between taxa. Within lineages, there was prevalent isolation by distance, but the strength of isolation by distance is independent of the taxonomic family, habitat specialization and climate. Isolation by environment is the strongest predictor of landscape-scale genetic divergence for all taxa, with both temperature and precipitation acting as limiting factors. The strength of isolation by distance does not predict the geographic scale of phylogeographic structure. However localized lineages had higher mean individual heterozygosity and less negative Tajima’s D. This implies that finer-scale phylogeographic structuring within species is associated with larger and more stable populations and, hence, persistence.