Interbreeding, monophyly and the genetic yardstick: species concepts in parasites.

The biological species concept defines species on the criterion of interbreeding. This may not be applicable to many parasites that are capable of self-fertilization and asexual reproduction. In this review, Alan Lymbery explores alternative concepts that may be applied to recognize species in such groups, using the cestode genus Echinococcus as an example. Two conclusions can be drawn. First, that the applicability of the biological species concept should not be dismissed without some knowledge o f the frequency of interbreeding in natural populations. Second, that where interbreeding is absent or rare, species should be delimited on the basis o f both monophyletic origin and genetic distinctness.