POPULATION GENETIC STRUCTURING IN ISOPODS: HISTORICAL AND ECOLOGICAL DETERMINANTS

Isopods are crustaceans that show a wide adaptive radiation. They inhabit benthic marine and freshwater envi-ronments, are parasites of crustaceans and fishes, and have colonized terrestrial habitats. Isopods show an extraor¬dinary diversification in adaptations, coinciding with an equally diverse array of different degrees of stenoecy, char¬acterizing individual species. Among terrestrial isopods, trichoniscids show a very limited dispersal ability. This is mainly due to physiological constraints that necessitate them to inhabit humid edafic environments, and subterranean habitats. Results from genetic surveys have revealed that genetic variability in trichoniscids ranges in a wide spec¬trum, and a high degree of specific structure is often detectable (Gentile & Sbordoni, 1998; Gentile et al. 1998; Gentile & Allegrucci, submitted; Cobolli Sbordoni et al., 1997). Thus, trichoniscids are a valuable tool to study the inter- intrapopulation components of genetic variation, often allowing the researcher to detect the action of the different evolutionary factors as genetic drift, selection, and gene flow, separately. In this communication we discuss some case studies in which it has been possible to relate the genetic structure observed to historical and ecological factors. Centile. C. & V. Sbordoni. 1998. Evolution 52: in press. Gentile, G.. S. Sarbu, M. Menichetti 4 S. Galdenzi. 1998. In: H. Wilkens (ed.). Ecosystems of the World. In press. Cobolli Sbordoni, M.. V. Ketmaier. E. De Matthaeis & S. Taiti. 1997. Heredity. 79: 463-472