Cryptic species diversity reveals biogeographic support for the ‘mountain passes are higher in the tropics’ hypothesis

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 283; no. 1832; p. 20160553
• Main Authors: Gill, B. A., Kondratieff, B. C., Casner, K. L., Encalada, A. C., Flecker, A. S., Gannon, D. G., Ghalambor, C. K., Guayasamin, J. M., Poff, N. L., Simmons, M. P., Thomas, S. A., Zamudio, K. R., Funk, W. C.
• Format: Journal Article
• Language: English
• Published: England The Royal Society 15-06-2016
• Subjects: Andes; Animals; Biodiversity; Climate; Colorado; Cryptic Species; DNA Barcoding, Taxonomic; Ecuador; Elevational Range; Ephemeroptera; Insecta - classification; Rocky Mountains; Species Richness; Species Specificity; elevational range; Andes; Rocky mountains; species richness; Ephemeroptera; cryptic species
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.2016.0553

The ‘mountain passes are higher in the tropics’ (MPHT) hypothesis posits that reduced climate variability at low latitudes should select for narrower thermal tolerances, lower dispersal and smaller elevational ranges compared with higher latitudes. These latitudinal differences could increase species richness at low latitudes, but that increase may be largely cryptic, because physiological and dispersal traits isolating populations might not correspond to morphological differences. Yet previous tests of the MPHT hypothesis have not addressed cryptic diversity. We use integrative taxonomy, combining morphology (6136 specimens) and DNA barcoding (1832 specimens) to compare the species richness, cryptic diversity and elevational ranges of mayflies (Ephemeroptera) in the Rocky Mountains (Colorado; approx. 40°N) and the Andes (Ecuador; approx. 0°). We find higher species richness and smaller elevational ranges in Ecuador than Colorado, but only after quantifying and accounting for cryptic diversity. The opposite pattern is found when comparing diversity based on morphology alone, underscoring the importance of uncovering cryptic species to understand global biodiversity patterns.