Species New to Science

...

Biodiversity varies from place to place because the range of climates suitable for any one species tends to be limited. The giant hummingbird appears to defy this tendency, occurring across the broadest range of environments of any hummingbird. We asked whether its migration, physiology, or genetics explain its climate generalism, potentially illuminating mechanisms of niche breadth evolution. Microtracking devices revealed an epic migration from the Chilean coast to the Peruvian Andes, with an extreme, >4,100-m elevational shift and corresponding performance trade-offs. Genomes revealed that migrant and resident populations diverged in the Pliocene and have since evolved under phenotypic stasis. A migratory shift enabled climatic niche expansion, leading to speciation and niche subdivision, consistent with diversification by niche breadth oscillation.

The ecoevolutionary drivers of species niche expansion or contraction are critical for biodiversity but challenging to infer. Niche expansion may be promoted by local adaptation or constrained by physiological performance trade-offs. For birds, evolutionary shifts in migratory behavior permit the broadening of the climatic niche by expansion into varied, seasonal environments. Broader niches can be short-lived if diversifying selection and geography promote speciation and niche subdivision across climatic gradients. To illuminate niche breadth dynamics, we can ask how “outlier” species defy constraints. Of the 363 hummingbird species, the giant hummingbird (Patagona gigas) has the broadest climatic niche by a large margin. To test the roles of migratory behavior, performance trade-offs, and genetic structure in maintaining its exceptional niche breadth, we studied its movements, respiratory traits, and population genomics. Satellite and light-level geolocator tracks revealed an >8,300-km loop migration over the Central Andean Plateau. This migration included a 3-wk, ~4,100-m ascent punctuated by upward bursts and pauses, resembling the acclimatization routines of human mountain climbers, and accompanied by surging blood-hemoglobin concentrations. Extreme migration was accompanied by deep genomic divergence from high-elevation resident populations, with decisive postzygotic barriers to gene flow. The two forms occur side-by-side but differ almost imperceptibly in size, plumage, and respiratory traits. The high-elevation resident taxon is the world’s largest hummingbird, a previously undiscovered species that we describe and name here. The giant hummingbirds demonstrate evolutionary limits on niche breadth: when the ancestral niche expanded due to evolution (or loss) of an extreme migratory behavior, speciation followed.