Use of erythrocyte indicators of health and condition in vertebrate ecophysiology: a review and appraisal

Abstract

We review evidence for and against the use of erythrocyte indicators of health status and condition, parasite infection level and physiological stress in free-living vertebrates. The use of indicators that are measured directly from the blood, such as haemoglobin concentration, haematocrit and erythrocyte sedimentation rate, and parameters that are calculated from multiple measured metrics, such as mean cell volume, mean cell haemoglobin content or mean cell haemoglobin concentration is evaluated. The evidence for or against the use of any given metric is equivocal when the relevant research is considered in total, although there is sometimes strong support for using a particular metric in a particular taxon. Possibly the usefulness of these metrics is taxon, environment or condition specific. Alternatively, in an uncontrolled environment where multiple factors are influencing a metric, its response to environmental change will sometimes, but not always, be predictable. We suggest that (i) researchers should validate a metric's utility before use, (ii) multiple metrics should be used to construct an overall erythrocyte profile for an individual or population, (iii) there is a need for researchers to compile reference ranges for free-living species, and (iv) some metrics which are useful under controlled, clinical conditions may not have the same utility or applicability for free-living vertebrates. Erythrocyte metrics provide useful information about health and condition that can be meaningfully interpreted in free-living vertebrates, but their use requires careful forethought about confounding factors.

Spatial variation in haemoglobin concentration of nestling Blue Tits (Cyanistes caeruleus): a long-term perspective

“…Data on the effects of blood parasites on the level of haemoglobin in nestlings are consistent for different study species and indicate negative effects of parasitism on the haematological condition of chicks and adult birds (Johnstone et al 2015;Minias 2015). Krams et al (2013) showed experimentally that in the absence of blood parasites, Great Tit nestlings had higher concentrations of haemoglobin.…”

“…The concentration of haemoglobin was shown to be a relatively simple biochemical indicator of bird metabolism and condition (Sergent et al 2004;Simmons and Lill 2006;Minias 2015;Johnstone et al 2015). It reflects the presence of pathogens and parasites, as well as the nutritional status of organism (a drop in haemoglobin concentration suggests nutritional deficiency ;Campbell 1995;Simon et al 2004;Kasprzyk et al 2006;Słomczyński et al 2006).…”

“…All those features support the use of the haemoglobin level as a relatively reliable indicator of physiological condition in field and experimental studies on birds (Stevens 1996;Kilgas et al 2006a;Kaliński et al 2009Kaliński et al , 2012Pyrke and Rollins 2012;Lill et al 2013;Minias 2014;Minias et al 2014;Glądalski et al 2015a). But it is important to emphasize that some recent studies recommend caution when using blood characteristics to evaluate physiological condition in some species (Fair et al 2007;Lill et al 2013;Minias 2015;Johnstone et al 2015). Also the use of haemoglobin concentration as a body condition index in a particular population should not be automatically extended to other populations (Fair et al 2007;Smith and Barber 2012;Lill et al 2013;Minias 2015;Glądalski et al 2015a).…”

Landscape context mediates the physiological stress response of birds to farmland diversification

“…Consequently, a positive association between haematocrit and condition is generally assumed. However, regenerative anaemia occurs when individuals respond to reductions in RBC or haemoglobin concentrations by stimulating the release of immature RBCs from bone marrow and/or increasing the generation of RBCs (erythropoiesis), leading to an increase in haematocrit (Johnstone, Lill, & Reina, 2017; Teague et al, 2007). Thus, over intermediate time‐scales (days–weeks), frequent or prolonged exposure to stressors can increase haematocrit.…”

“…We considered five broad categories of explanatory variables thought to influence the overall condition of birds in agricultural landscapes, including farm and landscape features of interest and potential confounding factors, such as climate, age, sex, season and time of day (Ellis et al, 2012; Johnstone et al, 2017; Table 1).…”