A complex genetic structure of Tetraclinis articulata (Cupressaceae) in the western Mediterranean

Abstract

Some tree species have distributions on both sides of the Strait of Gibraltar and the Strait of Sicily. It is a challenge to determine whether such distributions result from the Tertiary or Pleistocene or from more recent dispersal related to human activities. Tetraclinis articulata (Cupressaceae) is a gymnosperm that offers an ideal model to deal with this problem because it has a limited area of distribution and has been used only moderately by humans. Three hundred and twenty-three individuals from 30 populations covering the entire distribution of the species were analysed. A multiple approach was developed: (1) by assessing the genetic structure through two molecular techniques, AFLP and nSSR markers, which were used to evaluate the genetic diversity of these populations and the relationships among them and (2) by estimating past distributions. Four lineages of populations that are geographically intermixed to a certain extent are documented here. Results obtained are discussed in the context of palaeontological records and climatic models. There is evidence of an ancient widespread distribution, including Europe, and the subsequent appearance of four isolated lineages that, nowadays, are partially intermixed. Nevertheless, the origin of the current populations could not be fully ascertained through this work, although logical deductions are discussed that consider human activities or, much less probably, wind dispersal of seeds out of refugia in northern Africa-southern Europe during the Quaternary, including shore connections.