Phenotypic plasticity and genetic adaptation to high-altitude hypoxia in vertebrates

Abstract

SummaryHigh-altitude environments provide ideal testing grounds for investigations of mechanism and process in physiological adaptation. In vertebrates, much of our understanding of the acclimatization response to high-altitude hypoxia derives from studies of animal species that are native to lowland environments. Such studies can indicate whether phenotypic plasticity will generally facilitate or impede adaptation to high altitude. Here, we review general mechanisms of physiological acclimatization and genetic adaptation to high-altitude hypoxia in birds and mammals. We evaluate whether the acclimatization response to environmental hypoxia can be regarded generally as a mechanism of adaptive phenotypic plasticity, or whether it might sometimes represent a misdirected response that acts as a hindrance to genetic adaptation. In cases in which the acclimatization response to hypoxia is maladaptive, selection will favor an attenuation of the induced phenotypic change. This can result in a form of cryptic adaptive evolution in which phenotypic similarity between high-and low-altitude populations is attributable to directional selection on genetically based trait variation that offsets environmentally induced changes. The blunted erythropoietic and pulmonary vasoconstriction responses to hypoxia in Tibetan humans and numerous high-altitude birds and mammals provide possible examples of this phenomenon. When lowland animals colonize high-altitude environments, adaptive phenotypic plasticity can mitigate the costs of selection, thereby enhancing prospects for population establishment and persistence. By contrast, maladaptive plasticity has the opposite effect. Thus, insights into the acclimatization response of lowland animals to high-altitude hypoxia can provide a basis for predicting how altitudinal range limits might shift in response to climate change.

Regulatory changes contribute to the adaptive enhancement of thermogenic capacity in high-altitude deer mice

“…In contrast, both Sherpas and Andean Quechuas show evidence for enhanced cardiac glucose uptake at the tissue level (50), and in Sherpas, the decreased ratio of phosphocreatine to ATP in cardiac myocytes suggests a greater reliance on glucose for ATP production (51). However, neither Quechuas nor Sherpas exhibit enhanced maximal aerobic capacities compared with lowlanders at similar fitness levels (52,53), suggesting that human patterns of metabolic adjustment may be optimized to enhance O 2 economy rather than maximal aerobic capacity (54).…”

Genomic insights into adaptation to high-altitude environments

“…Consideration of the joint effects of these co-varying environmental stressors should be a priority for future work (Altschuler and Dudley, 2006;Storz et al, 2010b).…”

“…Tibetans differ from acclimatized lowlanders and other highaltitude human populations by maintaining sea-level hemoglobin (Hb) concentrations at elevations up to 4000 m (Beall et al, 1998;Beall, 2007). Although moderate increases in hematocrit and Hb concentration can improve aerobic capacity in normoxia (Ekblom and Hermansen, 1968;Kanstrup and Ekblom, 1984;Ekblom and Bergland, 1991), at high altitude, increased Hb concentration caused by excessive erythrocytosis can hinder tissue oxygenation by increasing blood viscosity and vascular resistance (Guyton and Richardson, 1961;Connes et al, 2006;Storz et al, 2010b). Correspondingly, theoretical studies have suggested that optimal Hb concentrations may be near the typical sea-level value (Villafuerte et al, 2004).…”

“…This is not intended to be a review of the physiological mechanisms of high-altitude adaptation, as this topic has been reviewed extensively elsewhere (see, for example, Moore and Regensteiner, 1983;Bouverot, 1985;Monge and Leon-Velarde, 1991;Hochachka, 1998;Moore et al, 1998;Beall, 2003;Scott and Milsom, 2006;Beall, 2007;Storz et al, 2010b), but we do draw on this body of work to make inferences about the adaptive significance of physiological variation in nature, and to identify candidate genes and biochemical pathways that may underlie physiological adaptations.…”

The Sixth Sense-Emotional Contagion; Review of Biophysical Mechanisms Influencing Information Transfer in Groups

“…Body plasticity implies the body responds to the environmental demands placed on it by continually modifying itself to better match environmental changes, [137]- [139].…”