Climatic niche conservatism in a clade of disease vectors (Diptera: Phlebotominae)

Sandflies of the family Psychodidae show notable diversity in both disease
vector status and climatic niche. Psychodid species’ ranges can be solely
tropical, confined to the temperate zones, or span both. We obtained
observation site data, and associated climate data, for 223 psychodid
species to understand which aspects of climate most closely predict
distribution. Temperature and seasonality are strong determinants of
species occurrence within the clade. We built a mitochondrial DNA
phylogeny of Psychodidae, and found a positive relationship between
pairwise genetic distance and climate niche differentiation, which
indicates strong niche conservatism. This result is also supported by
strong phylogenetic signals of metrics of climate differentiation.
Finally, we used ancestral trait reconstruction to infer the tropicality
(i.e., proportion of latitudinal range in the tropics minus the proportion
of the latitudinal range in temperate areas) of ancestral species, and
counted transitions to and from tropicality states, finding that tropical
and temperate species respectively produced almost entirely tropical and
temperate descendant species, a result consistent for vector and
non-vector species. Taken together, these results imply that while vectors
of Leishmania can survive in a variety of climates, their climate niches
are strongly predicted by phylogeny.