Geomolecular divergence patterns of Gondwanan and Palaeoaustral bryophytes An overview Studies in austral temperate rain forest bryophytes 34
Frey, Wolfgang; Pfeiffer, Tanja; Stech, Michael
Continental drift led to the break-up of the ancient Southern Hemisphere supercontinent Gondwana and the Palaeoaustral region (Nothofagus region), is considered to be one of the most influential processes shaping both the earth's geosphere and biosphere, and it is still continuing today. Former southernmost Gondwanaland is supposed to be the “original locus of origin” of different plant groups, and its continental fragments are “floating Noah's arks” (Schuster 1982), on which a conspicuous number of palaeoendemics of Gondwanan and Palaeoaustral floras have survived. Vicariance is one main explanation for extant disjunct distributions of Gondwanan and Palaeoaustral taxa, which either underwent divergent evolution or remained (nearly) indistinguishable in the separated regions due to low rates of molecular and morphological evolution. Nowadays, however, such patterns are frequently explained by more recent or ongoing migration from one region to the other, probably through transoceanic dispersal of diaspores (dispersalist “counter-revolution”). A small number of extant bryophyte taxa still show a presumable Gondwanan distribution pattern, representing the Gondwanan genoelement, e.g., Haplomitrium blumei s.l. and species of the dendroid Symphyogyna-complex. More frequent are extant bryophyte species and genera with a southern Austral distribution pattern, a significant number of them representing the “Palaeoaustral genoelement”. Molecular investigations, especially in the BRYO AUSTRAL project (1997-2003), revealed new insights in the geomolecular divergence patterns of Gondwanan and Palaeoaustral taxa. The Palaeoaustral taxa can be divided into: (1) stenoevolutionary species with low rates of molecular and morphological evolution in the palaeoaustral region, and no means of long-range dispersal (e.g., Pallavicinia xiphoides, Hypopterygium didictyon, Lopidium concinnum), (2) species with no or little intraspecific genetic variation, but dispersal capabilities that make genetic homogenisation of disjunct populations by gene-flow possible (e.g., Leptotheca gaudichaudii, possibly Weymouthia spp., and (3) genera (or species) that have differentiated into species (or subspecies), indicating that a common ancestor evolved into separate taxa in the separated geographic regions (e.g., in Hymenophyton, Jensenia, Monoclea; Acrocladium, Dendroligotrichum, Dicranoloma, Lepyrodon, Polytrichadelphus, Pyrrhobryum; possibly Nothoceros). The present review summarizes the chorological and geomolecular knowledge on the distribution patterns and evolution of hitherto molecularly investigated southern Austral bryophytes. Dispersal behaviour is classified (transoceanic, long-range, short-range, shuttle, and non-dispersal) and the widely disputed scenarios of diaspore dispersal in the Southern Hemisphere are re-evaluated in a general geobotanical perspective. Morphological versus molecular divergence patterns of disjunct southern South Hemisphere taxa are compared for each taxon, from species that remained almost unchanged at both morphological and molecular levels for long geological periods (stenoevolutionary taxa) to independent evolution of taxa after the disruption of the land masses of Gondwana.