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

B A Gill; B C Kondratieff; K L Casner; A C Encalada; A S Flecker; D G Gannon; C K Ghalambor; J M Guayasamin; N L Poff; M P Simmons; S A Thomas; K R Zamudio; W C Funk

doi:10.1098/rspb.2016.0553

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

Proc Biol Sci. 2016 Jun 15;283(1832):20160553. doi: 10.1098/rspb.2016.0553.

Authors

B A Gill¹, B C Kondratieff², K L Casner³, A C Encalada⁴, A S Flecker⁵, D G Gannon³, C K Ghalambor⁶, J M Guayasamin⁷, N L Poff⁶, M P Simmons³, S A Thomas⁸, K R Zamudio⁵, W C Funk⁶

Affiliations

¹ Department of Biology, Colorado State University, Fort Collins, CO 80523, USA Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA gillbriana@gmail.com.
² Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523, USA.
³ Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
⁴ Colegio de Ciencias Biológicas y Ambientales, Universidad San Francisco de Quito, Diego de Robles y Vía Interoceánica, 17-1200-841 Quito, Ecuador.
⁵ Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA.
⁶ Department of Biology, Colorado State University, Fort Collins, CO 80523, USA Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA.
⁷ Colegio de Ciencias Biológicas y Ambientales, Universidad San Francisco de Quito, Diego de Robles y Vía Interoceánica, 17-1200-841 Quito, Ecuador Centro de Investigación de la Biodiversidad y Cambio Climático, Ingeniería en Biodiversidad y Recursos Genéticos, Facultad de Ciencias de Medio Ambiente, Universidad Tecnológica Indoamérica, Calle Machala y Sabanilla, Quito, Ecuador.
⁸ School of Natural Resources, University of Nebraska, Lincoln, NE 68583, USA.

Abstract

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.

Keywords: Andes; Ephemeroptera; Rocky mountains; cryptic species; elevational range; species richness.

MeSH terms

Animals
Biodiversity*
Climate
Colorado
DNA Barcoding, Taxonomic
Ecuador
Insecta / classification*
Species Specificity