Experimental reduction of haematocrit affects reproductive performance in European starlings

Abstract

Summary Given the function of haemoglobin and observed increases in haematocrit during periods of increased energetic demands, haematocrit and haemoglobin are assumed to be related to aerobic capacity. Reductions in haematocrit and haemoglobin during reproduction are similar in magnitude to increases associated with aerobically demanding activities, and therefore, we sought to investigate whether these reductions in haematology have consequences for reproductive performance. We analysed associations between natural variation in haematology in free‐living European starlings (Sturnus vulgaris) and reproductive performance. To test whether transient reductions in haematology during different stages of reproduction (egg production and late incubation/early chick rearing) affected measures of reproductive performance, we also manipulated haematology using phenylhydrazine (PHZ), which lyses red blood cells. To investigate effects of reductions of haematology during egg‐laying, we treated females with PHZ or saline (control) upon completion of their unmanipulated first clutch and removed eggs to induce the production and rearing of a replacement clutch. To investigate effects of reductions of haematology during chick rearing, we treated females during incubation of the unmanipulated first clutch and then monitored the subsequent hatching and rearing of the clutch. Individuals with higher haematocrit and haemoglobin initiated nesting earlier. Furthermore, higher haemoglobin levels during incubation were associated with a greater number of chicks fledged. PHZ treatment prior to egg production resulted in a significant delay in the laying of replacement clutches, but had no effect on provisioning rate or the size or number of chicks fledged. PHZ treatment during incubation and early chick rearing resulted in decreased hatchling mass in all years and a decrease in the size and number of fledglings in one of 2 years. The year that the effect of PHZ was observed appeared to be a particularly difficult year, as hatchling mass, brood size at hatching and at fledging were low among control females compared to other years. Our results suggest that a reduction in haematology during reproduction can be functionally significant, but that these costs are context‐dependent.

Effects of experimental manipulation of hematocrit on avian flight performance in high and low altitude conditions

“…As noted earlier, while all six anti-EPO-treated birds attained the 3000 m simulated altitude, only four out of six vehicle-treated birds and one out of six EPO-treated birds reached 3000 m. The average flight duration at 3000 m for the anti-EPO group, EPO group and control group was 273.83 s, 50 s (n=1 only) and 188.5 s, respectively). These findings contrast with findings from other studies that manipulated Hct and investigated performance (Fronstin et al, 2016;Schuler et al, 2010), which generally found impaired performance with reductions in Hct. However, it is widely accepted that the relationship between Hct and oxygen carrying capacity is not linear, but rather parabolic in shape (Birchard, 1997;Petit and Vezina, 2014;Schuler et al, 2010).…”

An experimental test of the physiological consequences of avian malaria infection

“…Haematocrit and haemoglobin can be indicative of aerobic capacity and declines could limit individuals’ ability to perform energetically demanding tasks, like parental care or flight (Calbet, Lundby, Koskolou, & Boushel, ). Observational and experimental studies demonstrate that lower haematocrit and haemoglobin can be associated with lower reproductive effort and success (Fronstin et al., ; Minias, ). Therefore, the loss of red blood cells might be a mechanism for Plasmodium ‐caused reductions in reproductive success.…”

“…Here, we experimentally reduced parasitaemia in adult male red‐winged blackbirds ( Agelaius phoeniceus ) naturally experiencing haemosporidian infection to test if infection affects a suite of physiological traits that can be associated with fitness, including haematological measures (Fronstin, Christians, & Williams, ; Minias, ), a hormonal mediator of the stress response (Bonier & Martin, ; Bonier, Moore, Martin, & Robertson, ), oxidative status (Monaghan, Metcalfe, & Torres, ), immune function (Sheldon & Verhulst, ) and body condition (Milenkaya, Catlin, Legge, & Walters, ; Townsend, Clark, Mcgowan, Miller, & Buckles, ) (traits described in Table ). Thus, we aim to identify mechanisms that might underlie the haemosporidian‐caused reductions in survival and reproduction found in several studies of wild birds (Knowles, Palinauskas, et al., ; Martínez‐de la Puente et al., ; Marzal et al., ; Merino et al., ).…”

Physiological maturity at a critical life‐history transition and flight ability at fledging

“…). During the breeding season, haemoglobin concentration has been positively correlated with number of chicks fledged in female European starlings, and experimental decrease in haemoglobin decreased chick mass at fledging (Fronstin, Christians & Williams ). Given that fledglings are transitioning to a high activity, volant lifestyle, the development of physiological traits underlying aerobic capacity may be critical to surviving this transition.…”