Early Xanthochorema (Trichoptera, Insecta) radiations in New Caledonia originated on ultrabasic rocks

The toxic and nutrient poor ultrabasic rock substrate covering one-third of New Caledonia greatly influ- enced on the biogeography and diversity of plants in the island. Studies on the effect of ultrabasic sub- strate on fauna are almost entirely absent. In this paper we examine whether the diversification of Trichoptera of the New Caledonian endemic genus Xanthochorema Kimmins, 1953 was related to the presence of ultrabasic substrate. The analysis is based on data from a phylogeny derived from DNA sequences of mitochondrial COX1, COX2 and 16S, and nuclear EF1a genes. The study of the relationships between ancestral species and substrate was carried out using dispersal–vicariance analysis and tracing the history of substrate association with ultrabasic and non-ultrabasic distributions representing the ter- minals in the fully resolved phylogenetic tree. Our results show that (1) the ancestor of all Xanthochorema species was present on ultrabasic substrate, (2) early speciation events were restricted to ultrabasic sub- strate, (3) younger ancestral species dispersed into non-ultrabasic substrates, and (4) late speciation events were restricted to non-ultrabasic substrate. These results correspond to the hypothesis that New Caledonia once was more extensively covered by ultrabasic rocks than at present.