Stress and Sex in Malaria Parasites: Why Does Commitment Vary?

By   Lucy M. Carter, Björn F.C. Kafsack, Manuel Llinás, Nicole Mideo, Laura C. Pollitt, and Sarah E. Reece

Evolution, Medicine, and Public Health  published 4 June 2013, 10.1093/emph/eot011     Open access, full text here

ABSTRACT: For vector-borne parasites such as malaria, how within- and between-host processes interact to shape transmission is poorly understood. In the host, malaria parasites replicate asexually but for transmission to occur, specialised sexual stages (gametocytes) must be produced. Despite the central role that gametocytes play in disease transmission, explanations of why parasites adjust gametocyte production in response to in-host factors remain controversial. We propose that evolutionary theory developed to explain variation in reproductive effort in multicellular organisms, provides a framework to understand gametocyte investment strategies. We examine why parasites adjust investment in gametocytes according to the impact of changing conditions on their in-host survival. We then outline experiments required to determine whether plasticity in gametocyte investment enables parasites to maintain fitness in a variable environment. Gametocytes are a target for anti-malarial transmission-blocking interventions so understanding plasticity in investment is central to maximising the success of control measures in the face of parasite evolution.