Parasite Sex Determination
Parasite Sex Determination 10
R.E.L. Paul
Biochimie et Biologie Moléculaire des Insectes, Institut Pasteur,
25 Rue du Dr Roux, 75724 Paris Cedex 15, France
Introduction
The idea that organisms evolve strategies to achieve their life cycle is
purposefully teleological. The approach used in this chapter is that of
modern behavioural ecology, which attempts to understand the effects of
certain behaviours on the fitness of the individual: that is, can observed
behaviours be considered to be those that optimize the fitness of the
individual and hence be favoured by natural selection? Such an approach
is certainly open to discussion, but it has proved highly insightful in the
study of many evolutionary questions, most especially those pertaining to
sexuality. The chapter thus focuses on the behavioural strategies under-
lying sex determination, rather than molecular mechanisms (for a recent
review of molecular mechanisms, see Marin and Baker, 1998). The dis-
cussion will be largely based on parasites from the phyla Protozoa
(responsible for several of the most serious medical and veterinary
diseases), Platyhelminthes and Nematoda, and on insect parasitoids,
which have been used most extensively and successfully to explore
sex-determination strategies.
The environment that most organisms exploit is not homogeneous;
rather, it is a mosaic of habitats of varying quality. The colonization of a
habitat and the subsequent exploitation of its resources are among the
most basic interactions between the environment and any organism,
whether parasitic or free-living, enabling growth and replication. The
extent to which an organism successfully exploits a habitat for replication
represents its fitness and there will be selection for those mechanisms that
maximize fitness. Habitat resource exploitation will typically lead to a
deterioration in habitat quality, such that dispersal to new habitats is
necessary. In no other system is this basic concept of natural selection
CABInternational2002.The Behavioural Ecology of Parasites
(eds E.E. Lewis, J.F. Campbell and M.V.K. Sukhdeo) 199