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Consistent responses by various organisms to common environmental pressures represent strong evidence of natural selection driving geographical variation. According to Bergmann's and Allen's rules, animals from colder habitats are larger and have smaller limbs than those from warmer habitats to minimize heat loss. Although evidence supporting both rules in different organisms exists, most studies have considered only elevational or latitudinal temperature gradients. We tested for the effects of temperature associated with both elevation and latitude on body and appendage size of torrent ducks (Merganetta armata), a widespread species in Andean rivers. We found a negative relationship between body size and temperature across latitude consistent with Bergmann's rule, whereas there was a positive relationship between these variables along replicate elevational gradients at different latitudes. Limb‐size variation did not support Allen's rule along latitude, nor along elevation. High‐elevation ducks were smaller and had longer wings than those inhabiting lower elevations within a river. We hypothesize that temperature is likely a major selective pressure acting on morphology across latitudes, although hypoxia or air density may be more important along elevational gradients. We conclude that the effect of temperature on morphology, and hence the likelihood of documenting ecogeographical ‘rules’, depends on the environmental context in which temperature variation is examined. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 850–862.

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We report on the use and efficiency of an active mist-net method for capturing 3 subspecies of torrent ducks (Merganetta armata), a territorial and specialized South American waterfowl, in fast-moving rivers of the Andes Mountains. As an active process, the execution of this methodology required the presence of a well-trained, 3-person team. During the austral winter and spring between 2010 and 2014, we captured 372 torrent ducks in 410 capture events on 8 different rivers in Colombia (n ¼ 1), Peru (n ¼ 5), and Argentina (n ¼ 2). Each captured torrent duck was banded and 38 opportunistic recaptures events were obtained using the same methodology in the same territories. We deployed the mist nets across fast-moving deep rivers, along elevational gradients (680-4,200 m). Males were more easily captured than females, because of their greater tendency to fly. Our data validated this capture method for torrent ducks, as we succeeded in capturing individuals of the 3 subspecies in different habitats at different elevations and latitudes. To avoid animal mortality, we recommend application of this method only when 3 minimal conditions are met: 1) each field crew has !3 people; 2) all of the crew members have hand-radios to enable continuous communication; and 3) each crew member has received prior training (e.g., installation, inspection, manipulation, and removal of the mist net, bird extraction, and familiarity with the behavior of the torrent ducks). Ó 2017 The Wildlife Society.

Background Complex organismal traits are often the result of multiple interacting genes and sub-organismal phenotypes, but how these interactions shape the evolutionary trajectories of adaptive traits is poorly understood. We examined how functional interactions between cardiorespiratory traits contribute to adaptive increases in the capacity for aerobic thermogenesis (maximal O2 consumption, V̇O2max, during acute cold exposure) in high-altitude deer mice (Peromyscus maniculatus). We crossed highland and lowland deer mice to produce F2 inter-population hybrids, which expressed genetically based variation in hemoglobin (Hb) O2 affinity on a mixed genetic background. We then combined physiological experiments and mathematical modeling of the O2 transport pathway to examine the links between cardiorespiratory traits and V̇O2max. Results Physiological experiments revealed that increases in Hb-O2 affinity of red blood cells improved blood oxygenation in hypoxia but were not associated with an enhancement in V̇O2max. Sensitivity analyses performed using mathematical modeling showed that the influence of Hb-O2 affinity on V̇O2max in hypoxia was contingent on the capacity for O2 diffusion in active tissues. Conclusions These results suggest that increases in Hb-O2 affinity would only have adaptive value in hypoxic conditions if concurrent with or preceded by increases in tissue O2 diffusing capacity. In high-altitude deer mice, the adaptive benefit of increasing Hb-O2 affinity is contingent on the capacity to extract O2 from the blood, which helps resolve controversies about the general role of hemoglobin function in hypoxia tolerance.

Complex organismal traits are often the result of multiple interacting genes and sub-organismal phenotypes, but how these interactions shape the evolutionary trajectories of adaptive traits is poorly understood. We examined how functional interactions between cardiorespiratory traits contribute to adaptive increases in the capacity for aerobic thermogenesis (maximal O2 consumption, V̇O2max, during acute cold exposure) in high-altitude deer mice (Peromyscus maniculatus). We crossed highland and lowland deer mice to produce F2 inter-population hybrids, which expressed genetically based variation in hemoglobin (Hb) O2 affinity on a mixed genetic background. We then combined physiological experiments and mathematical modeling of the O2 transport pathway to examine links between cardiorespiratory traits and V̇O2max. Physiological experiments revealed that increases in Hb-O2 affinity of red blood cells improved blood oxygenation in hypoxia, but were not associated with an enhancements in V̇O2max. Sensitivity analyses performed using mathematical modeling showed that the influence of Hb-O2 affinity on V̇O2max in hypoxia was contingent on the capacity for O2 diffusion in active tissues. These results suggest that increases in Hb-O2 affinity would only have adaptive value in hypoxic conditions if concurrent with or preceded by increases in tissue O2 diffusing capacity. In high-altitude deer mice, the adaptive benefit of increasing Hb-O2 affinity is contingent on the capacity to extract O2 from the blood, which helps resolve controversies about the general role of hemoglobin function in hypoxia tolerance.

The selection of species and individuals for molecular analyses critically affects inferences in various fields of systematic biology including phylogenetics, phylogeography, and species delimitation. Especially in areas like the Neotropical region where molecular analyses have recovered substantial within-species divergence and unexpected affinities of populations (Turchetto-Zolet et al. 2013), biases resulting from incomplete taxonomic or geographic sampling may compromise the understanding of phylogenetic relationships (Avendaño et al. 2017). Here we describe a case in which assessments of the validity of a potentially extinct species of Neotropical bird were likely compromised because within-species variation was not accounted for in phylogenetic analyses evaluating the alternative hypothesis that the only known specimen may represent a hybrid.