Résumé
Temporal variations in the activity of arthropod vectors can dramatically
affect the epidemiology and evolution of vector-borne pathogens. Here we
explore the “Hawking hypothesis” stating that these pathogens may evolve
the ability to time investment in transmission to match the activity of
their vectors. First, we use a theoretical model to identify the
conditions promoting the evolution of time-varying transmission strategies
in pathogens. Second, we experimentally test the “Hawking hypothesis” by
monitoring the within-host dynamics of Plasmodium relictum throughout the
acute and the chronic phases of the bird infection. We detect a periodic
increase of parasitaemia and mosquito infection in the late afternoon that
coincides with an increase in the biting activity of its natural vector.
We also detect a positive effect of mosquito bites on Plasmodium
replication in the birds both in the acute and in the chronic phases of
the infection. This study highlights that Plasmodium parasites use two
different strategies to increase the match between transmission potential
and vector availability. We discuss the adaptive nature of these
unconditional and plastic transmission strategies with respect to the
time-scale and the predictability of the fluctuations in the activity of
the vector.