Geographic exploration within a highly niche-conserved moth in the Hawaiian archipelago

Abstract

For any lineage, colonization of a new habitat is dictated by the combined constraints of geography, or the ability to reach the new area through dispersal; the presence of other organisms; and the physiological ability to adapt to novel environmental conditions. Many studies have shown the importance of niche conservatism, although, in most of these, the geographical impediments have been relatively minor. Here, we examine the interplay between dispersal, biotic interactions, and adaptation in shaping the biogeography of a lineage in which both geography and environmental conditions in particular present substantial filters. Thyrocopa is a genus of generalist wood-feeding moths endemic to the Hawaiian Islands. Within the group, species are generally restricted to either wet forest, or dry, rocky, windy habitats. We sampled Thyrocopa from throughout the Hawaiian Islands, and performed phylogenetic analyses, likely ancestral area reconstruction, estimation of dates of divergence, and an ecological niche modeling analysis. We show that within the 'windswept' clade of Thyrocopa, species diversified between suitable habitats in the southeastern islands long after the northwestern Hawaiian Islands eroded to their current dry, rocky, windy state. Later, Thyrocopa back-colonized the northwestern islands despite having to cross long distances over open ocean. Dates of diversification are independently supported by two methods of dating nodes (a molecular clock as well as estimates based on calibration points). Our results suggest that, for Thyrocopa, neither dispersal ability nor biotic interactions play a major role in limiting present distributions. Instead, niche conservatism associated with the availability of suitable environmental conditions in a habitat appears to dictate the distribution of these moths.