Nematodes

Concluding remarks

Nematodes are greatly diverse in terms of species number but also in various kinds of life-cycle, modes of infection and life-history traits. This diversity is far for being completely known. Hence, recently, Clarke et al. (2004) presented evidence that an un-described nematode parasite of the very well investigated wood mouse Apodemus sylvaticus may be sexually transmitted. These authors found larval nematodes in the epididymides of males, which suggests that they would be transmitted to females during ejaculation.

In order to better understand the origins of all these facets of nematode biodiversity, we need a more detailed phylogenetic framework of this phylum. By mapping parasite traits onto the nematode phylogeny, we will better estimate the phylogenetical constraints and the ecological adaptation that may have shaped the diversity of nematodes, and particularly their interactions with small mammals.

Although rarely causing the death of their hosts, nematodes have the capacity to alter both the physiology and the behaviour of their hosts. Nematodes can regulate the population dynamics of their hosts, and this may contribute to the extinction spiral of small host populations (see Christe et al. in this volume), although much more experimental and theoretical work is needed. Finally, if nematodes are a threat to biodiversity, they are also of great concern with regards to human health (see Casanova and Ribas; Leirs and Singleton in this volume).