The dynamics of health of wild field vole (Microtus agrestis) populations: a haematological perspective

BELDOMENICO,PM; TELFER,S; GEBERT,S; LUKOMSKI,L; BENNETT,M; BEGON,M

JOURNAL OF ANIMAL ECOLOGY

Año: 2008 vol. 77 p. 984 - 997

0021-8790

Pathogens have been proposed as potentially important drivers of population dynamics, but while a few studies have investigated the impact of specific pathogens, the wealth of information provided by general indices of health has hardly been exploited. By evaluating haematological parameters in wild populations, our knowledge of the dynamics of health and infection may be better understood. Here, haematological dynamics in natural populations of field voles are investigated to determine environmental and host factors associated with indicators of inflammatory response (counts of monocytes and neutrophils) and of condition: measures of immunological investment (lymphocyte counts) and aerobic capacity (red blood cell counts). Individuals from three field vole populations were sampled monthly for two years. Comparisons with individuals kept under controlled conditions facilitated interpretation of field data. Mixed effects models were developed for each cell type to separately evaluate the effects of various factors on post-juvenile voles and mature breeding females. There were three well characterised ‘physiological’ seasons. The immunological investment appeared lowest in winter (lowest lymphocyte counts), but red blood cells were at their highest levels and indices of inflammatory response at their lowest. Spring was characterised by a fall in red blood cell counts and peaks in indicators of inflammatory response. During the course of summer-autumn, red blood cell counts recovered, the immunological investment increased and the indicators of inflammatory response decreased. Poor body condition appeared to affect the inflammatory response (lower neutrophil and monocyte peaks) and the immunological investment (lower lymphocyte counts), providing evidence that the capacity to fight infection is dependent on host condition. Breeding early in the year was most likely in females in better condition (high lymphocyte and red blood cell counts). All the haematological parameters were adversely affected by high population densities.