Molecular evolution, phylogenetics and biogeography in southern hemispheric bryophytes with special focus on Chilean taxa

Abstract

Researchers have long been fascinated by disjunct distribution patterns of plant and animal species. Especially the disjunctly distributed species occurring in the temperate Chilean and New Zealand rainforests of the southern hemisphere are considered interesting due to the common history these locations share. These areas were originally part of the former Gondwana landmass. There are also moss species from temperate forest habitats revealing such a disjunct distribution.<br /> The native moss flora of Chile comprises about 780 species. According to a study on the Chilean and New Zealand mosses 113 of these 780 species reveal a disjunct austral distribution pattern and also occur in New Zealand. The majority of the species common to both countries are inhabitants of temperate rainforests.<br /> This study investigates phylogenetic relationships within four southern hemispheric bryophyte taxa characteristic for the Chilean and New Zealand temperate rainforests. These taxa consisted of the families Lepyrodontaceae and Ptychomniaceae as well as the genera Acrocladium and Catagonium. The results are discussed within the context of historical and geological processes in order to test the hypothesis whether the distribution patterns can be attributed to a common Gondwanan origin or to long distance dispersal as an alternative explanation.<br /> Molecular phylogenetic analyses using molecular markers from nrDNA (ITS region, adk gene) and cpDNA (trnL-trnF region, rps4 gene) were conducted for a large number of specimens representing the taxa under study. Most of these specimens originated from the BryoAustral and the BryoTrop projects. The resulting molecular data set was used to reconstruct phylogenies. Additionally, genetic distances were determined to compliment the phylogenetic results.<br /> Firstly, phylogenetic relationships within the Ptychomniaceae and within a taxa group consisting of the Plagiotheciaceae, Lepyrodontaceae and related taxa were investigated. For this purpose phylogenetic analyses based on DNA sequence data were conducted for several data sets. Concerning the family Ptychomniaceae the results showed that the species Ptychomnion ptychocarpon, endemic to the Valdivian rainforest, does not belong to the genus Ptychomnion. In contrast to the other representatives of this genus Ptychomnion ptychocarpon occupies a basal position within the family showing no close relationship to any of the other genera within the family. Further results of this study placed the genus Dichelodontium in the family Ptychomniaceae. This genus was formerly considered a member of the Lepyrodontaceae.<br /> Further analyses were performed using specimens of the southern hemispheric genus Lepyrodon. This genus comprises seven species, two of which only occur in New Zealand and Australia and another four which are only found in southern Chile and southern Argentina. In contrast, Lepyrodon tomentosus has a distribution area which covers the southernmost tip of the American continents and expands northwards over Central America up to Mexico. The genetic analyses showed that the two New Zealand-Australian species form a common clade and that the most closely related species originate from Chile. Furthermore, based on the results of both phylogenetic analyses and genetic distances it is concluded that populations of Lepyrodon tomentosus occurring in southern and northern South America, respectively, probably already became separated during the tertiary.<br /> Analyses aimed at clarifying the phylogenetic relationships of the genus Acrocladium revealed a close relationship between this genus and the genus Lepyrodon. There has been much discussion on whether the genus Acrocladium comprises a single species or whether a distinction can be made between two species. In this study clear evidence was found for the existence of two genetically distinct species, a Chilean-Argentinian species (A. auriculatum) and a New Zealand-Australian species (A. chlamydophyllum).<br /> The genus Catagonium occupies a very basal position within the family Plagiotheciaceae. The study of this genus revealed a high genetic similarity between two species only occurring in northern South America on the one hand and a taxon only found in South Africa on the other hand. Based on this phylogenetic result the conclusion is made that the recent taxa had a common ancestor which occurred on the former Gondwana continent. When this landmass split apart the Catagonium populations found on today's African and South American continents were separated.<br /> Not all phylogenetic relationships resulting from analyses of molecular markers found in this study could be explained by vicariance events. Therefore, long distance dispersal is discussed as an explanation for the disjunct distribution of specific taxa.