Do invading species have definable genedc characteristics?

Abstract

The search for general answers to this question dates at least from the seminal conference at Asilomar in 1964. It has included comparative surveys of a wide range of taxa, investigations within congeneric groups of why some species are successful invaders and others are not, and, at the intraspecific level, comparisons of genetic variability in colonist versus source populations. The relevant data are reviewed. They suggest that successful invading species have genetic characteristics (defined here as the set of attributes that collectively determine the form in which, and frequency with which, genetic information is passed from one generation to the next), which need only be sufficiently protean to ensure rapid expansion in the new environment. Generalizations attempting to relate colonizing ability to polyploidy, to levels of genetic variability, heterozygosity, or phenotypic plasticity, or to mating system types, ignore the interaction in individuals of these components of the genetic system, and rarely consider chromosomal and genic controls of recombination. The poor predictive power of such generalizations is emphasized by considering invaders into the British flora, which are drawn from a wide spectrum of families and life forms. They include only a few ‘colonizing species’, those that habitually invade and occupy transient habitats and from which most models of invaders have been derived. Analysis of the origin and spread of Spartina anglica emphasizes that serendipity is often an important element in successful invasions. Studies of the genetic consequences of invading, especially those that take an experimental approach, are more likely to throw light on current problems in evolutionary theory than those that analyse the shared attributes of past invaders.