Abstract:
Disease outbreaks are a consequence of interactions among the
three components of a host–parasite system: the infectious agent,
the host and the environment. While virulence and transmission
are widely investigated, most studies of parasite life-history
trade-offs are conducted with theoretical models or tractable
experimental systems where transmission is standardized
and the environment controlled. Yet, biotic and abiotic
environmental factors can strongly affect disease dynamics, and
ultimately, host–parasite coevolution. Here, we review research
on how environmental context alters virulence–transmission
relationships, focusing on the off-host portion of the parasite life
cycle, and how variation in parasite survival affects the evolution
of virulence and transmission. We review three inter-related
‘approaches’ that have dominated the study of the evolution of
virulence and transmission for different host–parasite systems:
(i) evolutionary trade-off theory, (ii) parasite local adaptation and
(iii) parasite phylodynamics. These approaches consider the role
of the environment in virulence and transmission evolution
from different angles, which entail different advantages and
potential biases. We suggest improvements to how to investigate virulence–transmission relationships, through conceptual and methodological developments and
taking environmental context into consideration. By combining developments in life-history
evolution, phylogenetics, adaptive dynamics and comparative genomics, we can improve our
understanding of virulence–transmission relationships across a diversity of host–parasite systems
that have eluded experimental study of parasite life history.
