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