Circulatory mechanisms underlying adaptive increases in thermogenic capacity in high-altitude deer mice

Abstract

We examined the circulatory mechanisms underlying adaptive increases in thermogenic capacity in deer mice () native to the cold hypoxic environment at high altitudes. Deer mice from high- and low-altitude populations were born and raised in captivity to adulthood, and then acclimated to normoxia or hypobaric hypoxia (simulating hypoxia at ∼4300 m). Thermogenic capacity [maximal O consumption (), during cold exposure] was measured in hypoxia, along with arterial O saturation (a ) and heart rate (). Hypoxia acclimation increased by a greater magnitude in highlanders than in lowlanders. Highlanders also had highera and extracted more O from the blood per heartbeat (O pulse=/). Hypoxia acclimation increased , O pulse and capillary density in the left ventricle of the heart. Our results suggest that adaptive increases in thermogenic capacity involve integrated functional changes across the O cascade that augment O circulation and extraction from the blood.

Botfly infections impair the aerobic performance and survival of montane populations of deer mice, Peromyscus maniculatus rufinus

“…Accordingly, across their range, different populations of deer mice display an array of habitat‐specific adaptations to biotic and abiotic factors. For instance, populations of the subspecies P. m. rufinus (hereafter: P. maniculatus or deer mice) at high elevations have evolved traits along the entire oxygen transport cascade that confer on individuals increased aerobic capacity and blood‐oxygen loading capabilities (Chappell et al, ; Scott, Elogio, Liu, Storz, & Cheviron, ; Tate et al, ). Given the importance of haematocrit and haemoglobin concentrations to an individual's blood‐oxygen carrying capacity, the known haematological effects imposed by botfly infections on P. maniculatus may have more pronounced consequences at higher elevations than in other contexts (Hayes & O'Connor, ).…”

Effects of chronic hypoxia on diaphragm function in deer mice native to high altitude

“…High‐altitude deer mice sustain high field metabolic rates in the wild, presumably to support the demands of thermogenesis in the colder environment at high altitudes (Hayes). There is strong directional selection at high altitudes that favours high aerobic capacity (VO 2 max) in hypoxia, and high‐altitude populations show an elevated VO 2 max in hypoxia compared to low‐altitude populations of deer mice and to low‐altitude white‐footed mice ( P. leucopus ) . High‐altitude populations also exhibit a more effective breathing pattern (higher tidal volumes and lower breathing frequencies) than low‐altitude populations in normoxia, and unlike lowlanders, highlanders change breathing very little in response to chronic hypoxia .…”

Maladaptive phenotypic plasticity in cardiac muscle growth is suppressed in high‐altitude deer mice

“…; Tate et al. ), which is under strong selection in the wild (Hayes and O'Conner ). Evolved increases in thermogenic capacity are associated with an increased ability to oxidize energy‐rich lipids under hypoxia (Cheviron et al.…”

“…; Chappell and Snyder ; Storz , ) and an enhanced ability to extract oxygen from each heart beat (Tate et al. ). These results suggest that evolved shifts in thermogenic capacity are associated with a modified capacity to obtain and circulate oxygen.…”

“…; Tate et al. ), though constitutive differences in aerobic performance suggest limits to phenotypic plasticity in both lowland P. maniculatus and P. leucopus (Cheviron et al. , ; Lui et al.…”