The role of abiotic factors and competitive exclusion in the assembly patterns of two insular gecko radiations displaying ecomorphological convergence

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Adaptive radiation theory posits that speciation is largely driven by ecological opportunity with correlated morphological expansion in response to niche availability. We use a phylogenomic estimate of Australasian diplodactyloid geckos in combination with meristic and ecological data to infer patterns of ecological diversification and the factors associated with speciation processes. Specifically, we focus on two speciose and ecomorphologically diverse gecko lizard assemblages from the ancient continental islands of New Caledonia and New Zealand. We use these systems to infer historical patterns of community assembly and the relative importance of biotic and abiotic factors in shaping character diversification and the formation of adaptive radiations. Models accounting for stabilizing selection recover shifts in morphospace along many branches that also experienced shifts in ecological guild as inferred from ancestral state reconstructions. We find convergent evolution to be present between the two insular lineages as they independently transitioned to similar guilds from different ancestral ecologies. Bayesian and multiple regression analyses suggest that abiotic factors rather than interspecific competition have played a role in phenotypic divergence in both insular lineages. Species in both clades seem to diverge phenotypically in allopatry, not in sympatry as would be expected with character displacement. Subsequently, environmental factors, such as climate, in conjunction with competitive exclusion of phenotypically similar taxa dictate the degree of phenotypic similarity in secondary sympatry. This study provides an assessment of convergence in insular diplodactyloid geckos and provides compelling evidence indicating that similar selective pressures have shaped morphological diversity and community assembly in these disparate clades.