%0 Journal Article
%T Effects of shortened host life span on the evolution of parasite life history and virulence in a microbial host-parasite system
%A Thibault Nidelet
%A Jacob C Koella
%A Oliver Kaltz
%J BMC Evolutionary Biology
%D 2009
%I BioMed Central
%R 10.1186/1471-2148-9-65
%X After 13 cycles (¡Ö 300 generations), parasites from the early-killing treatment were less infectious, but had shorter latency time and higher virulence than those from the late-killing treatment. Overall, shorter latency time was associated with higher parasite loads and thus presumably with more rapid within-host replication.The analysis of the means of the two treatments is thus consistent with theory, and suggests that evolution is constrained by trade-offs between virulence, transmission and within-host growth. In contrast, we found little evidence for such trade-offs across parasite selection lines within treatments; thus, to some extent, these traits may evolve independently. This study illustrates how environmental variation (experienced by the host) can lead to the evolution of distinct parasite strategies.Understanding the factors that shape the evolution of parasite life history and virulence is a major issue in evolutionary biology [1-4], with important implications in applied and medical contexts [5,6]. According to standard theory, a parasite needs to exploit the host to increase its rate of transmission. If exploitation harms the host, the parasite must therefore trade current for future transmission and evolution should lead to the balance between virulence and the rate of transmission that maximizes the parasite's life-time reproductive success. Where this balance lies may depend on genetic [7], epidemiological [8-11] or environmental factors [12,13].A general prediction concerning environmental factors is that increased extrinsic host mortality (i.e. the mortality that is not due to the parasite) selects for higher virulence [[11,14,16,16], but see [17]]. Because shorter host life span reduces future opportunities of transmission, the constraint to keep the host alive is relaxed. Rather, to compensate for the loss of future transmission, parasites should evolve to grow more rapidly within the host, start transmission earlier and, consequently, be mo
%U http://www.biomedcentral.com/1471-2148/9/65