Contrasting response of haematological variables between long-term training and short exercise bouts in zebra finches (Taeniopygia guttata)

Abstract

Physical aerobic activity is oxygen demanding, butparticularly for birdsthere is still little understanding of how blood contributes to oxygen supply under various activity levels. In a two-factorial experimental design, we investigated the long-term effect of daily flight training and the immediate effect of a short exercise bout on a set of haematological variables: haemoglobin (Hb) content, haematocrit (Hct), and red blood cell number (RBC count) and size (RBC area) in zebra finches (Taeniopygia guttata). For a period of 6 weeks, birds were either trained daily for 3 h in a flight arena or remained untrained. Subsequently, half of each group was blood sampled either in the resting condition or after a 5 min exercise bout in a flight-hover wheel. We found significantly lower Hb content, Hct and RBC count compared with that in untrained controls in response to training, while RBC area did not differ between treatments. Response to an exercise bout revealed the opposite pattern, with significantly higher Hb content and Hct compared with that in non-exercised birds. Additionally, RBC area was significantly smaller immediately after exercise compared with that in non-exercised birds, and such short-term flexibility represents a novel finding for birds. This contrasting response in erythrocyte characteristics with respect to long-term training and short exercise bouts appears as a clear pattern, presumably underlain by changes in water balance. We infer alterations of blood flow to be involved in adequate oxygen supply. During an exercise bout, RBC area flexibility may not only enhance oxygen delivery through improved erythrocyte surface area to volume ratio but also improve blood flow through a compensatory effect on blood viscosity.

Hematocrit, age, and survival in a wild vertebrate population

“…2%–5%) in birds during endurance activities via an increase in blood plasma (hemodilution). In line with optimal hematocrit theory (Birchard, 1997), these authors suggest that hemodilution is an adaptive response to prolonged exercise, facilitating faster blood flow for less cardiovascular effort (Bury et al., 2019; Jenni et al., 2006; Yap et al., 2018). Thus, high hematocrit in young Seychelles warblers may reflect a failure to maintain optimal hematocrit, for example, due to dehydration.…”

“…Elevated hematocrit occurs via the production of new erythrocytes (erythropoiesis) and/or the release of reticulocytes (immature erythrocytes) from the bone marrow, which is triggered by hypothalamus–pituitary–adrenal‐mediated stress (see Voorhees et al., 2013). More rapid (<1 hr) increases in hematocrit can occur due to a reduction in blood plasma volume (hemoconcentration), which happens during exercise and dehydration (Bury et al., 2019; Kaltreider & Meneely, 1940). In some mammal species, splenic reservoirs of erythrocytes can also increase hematocrit at the onset of stress and exercise (Böning et al., 2011).…”

Haematocrit, age and survival in a vertebrate population

“…2-5%) in birds during endurance activities via an increase in blood plasma (haemodilution). In line with optimal haematocrit theory (Birchard, 1997), these authors suggest that haemodilution is an adaptive response to prolonged exercise; facilitating faster blood flow for less cardiovascular effort (Jenni et al, 2006;Yap et al, 2018;Bury et al, 2019). Thus, high haematocrit in young Seychelles warblers may reflect a failure to maintain optimal haematocrit, for example, due to dehydration.…”

“…Elevated haematocrit occurs via the production of new erythrocytes (erythropoiesis) and/or the release of reticulocytes (immature erythrocytes) from the bone marrow, which is triggered by hypothalamus-pituitary-adrenal mediated stress (see Voorhees et al, 2013). More rapid (< 1 hour) increases in haematocrit can occur due to a reduction in blood plasma volume (haemoconcentration), which happens during exercise and dehydration (Kaltreider and Meneely, 1940;Bury et al, 2019). In some mammal species, splenic reservoirs of erythrocytes can also increase haematocrit at the onset of stress and exercise (Böning, et al, 2011).…”

Recovery of hematocrit and fat deposits varies by cage size in food‐restricted captive red crossbills (Loxia curvirostra)

“…For example, higher hematocrits have been found when birds increase foraging behavior to feed nestlings (Dufva, 1996; Hõrak et al, 1998; Krause et al, 2016), invest in ornaments that increase flight costs (Saino, Cuervo, Ninni, et al, 1997), and prepare for migration during the spring and fall (deGraw et al, 1979; Krause et al, 2016; Morton, 1994; Piersma et al, 1996; Yap et al, 2019)—although acute effects of very‐intensive exercise typically cause reduced hematocrit in migrant birds (Jenni et al, 2006; Landys‐Ciannelli et al, 2002; Piersma et al, 1996). Acute hematocrit depression following intense or long‐bout exercise in birds (Bury et al, 2019; Carmi et al, 1993; Jenni et al, 2006) and mammals (Convertino, 2007; Santhiago et al, 2009; von Restorff et al, 1975) is thought to be the result of osmotic disturbance causing subsequent hemodilution (Steinach et al, 2019). Hemodilution may increase blood flow to working tissues by reducing blood viscosity, but cerebral oxygen delivery in mammals is still reduced during hemodilution compared with controls (Todd et al, 1994; von Restorff et al, 1975).…”