Blood Variation Implicates Respiratory Limits on Elevational Ranges of Andean Birds

Linck E.B.; Williamson J.L.; Bautista E.; Beckman E.J.; Benham P.M.; Dubay S.G.; Flores L.M.; Gadek C.R.; Johnson A.B.; Jones M.R.; Núñez-Zapata J.; Quiñonez A.; Schmitt C.J.; Susanibar D.; Tiravanti C. J.; Verde-Guerra K.; Wright N.A.; Valqui T.; Storz J.F.; Witt C.C. · American Naturalist (2023) · DOI: 10.1086/723222

Resumen

The extent to which species ranges reflect intrinsic physiological tolerances is a major question in evolutionary ecology. To date, consensus has been hindered by the limited tractability of experimental approaches across most of the tree of life. Here, we apply a macrophysiological approach to understand how hematological traits related to oxygen transport shape elevational ranges in a tropical biodiversity hot spot. Along Andean elevational gradients, we measured traits that affect blood oxygen-carrying capacity—total and cellular hemoglobin concentration and hematocrit, the volume percentage of red blood cells—for 2,355 individuals of 136 bird species. We used these data to evaluate the influence of hematological traits on ele-vational ranges. First, we asked whether the sensitivity of hematolog-ical traits to changes in elevation is predictive of elevational range breadth. Second, we asked whether variance in hematological traits changed as a function of distance to the nearest elevational range limit. We found that birds showing greater hematological sensitivity had broader elevational ranges, consistent with the idea that a greater ac- climatization capacity facilitates elevational range expansion. We fur-ther found reduced variation in hematological traits in birds sampled near their elevational range limits and at high absolute elevations, patterns consistent with intensified natural selection, reduced effective population size, or compensatory changes in other cardiorespiratory traits. Our findings suggest that constraints on hematological sensitivity and local genetic adaptation to oxygen availability promote the evolution of the narrow elevational ranges that underpin tropical mon-tane biodiversity.

Instituciones: Universidad Nacional de Trujillo; Universidad Nacional Agraria La Molina