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Evolutionary processes behind morphological evolution and speciation: a phylogenetic approach

Final Report Summary - MOSSMORFOEVO (Evolutionary processes behind morphological evolution and speciation: a phylogenetic approach)

Aim of the project was to study evolutionary processes behind morphological evolution and speciation in mosses and to cast light on central questions in evolutionary biology on the role of natural selection, phenotypic plasticity, hybridisation, and biogeography in the speciation. I applied molecular systematic and phylogenetic comparative methods, population genetics and greenhouse experiments in series of case studies that deal with different evolutionary processes and their effect on morphological differentiation.

In aquatic Rhynchostegium parallel evolution of similar morphological character combinations in different populations were found to be rather result of repeated evolution of the same morphological traits than plasticity. Phylogeny revealed four independent lineages where very similar morphologies have evolved. No evidence on reticulate evolution due to hybridisation between lineages was found. Within an aquatic Euro-African Rhynchostegium lineage phylogeny and preliminary microsatellite analysis supported a clear genetic structure among populations. Some morphological differences appeared to follow genetic differentiation between populations. Growth experiments suggested them to be due to genetic isolation between populations rather than plasticity due to habitats. Results of population genetic study that aimed at detecting role of plasticity in morphologically and ecologically differentiated lake and river populations of R. riparioides, were somewhat surprising. Fennoscandian lake populations appeared to represent a species new to science that belonged genus Oxyrrhynchium and thus another subfamily of Brachytheciaceae. The final description of the taxon still waits for publication.

Polyphyletic lineages within Bryhnia also revealed to be genetically isolated, independent lineages. Molecular data did not support hybridisation between them but each lineage had some weak morphological charactersitics that enabled their identification. Geographical distribution of each lineage also shows a clear pattern of specialisation to certain environmental conditions. Polyphyly of the genus and species within it were thus due to poor taxonomical knowledge of the group. Based on new data and phylogenies we will provide a taxonomical revision of the genus and sum up morphological traits that allow identification of taxa.

Based on information that has accumulated during the project, it is clear that Brachytheciaceae, like many other families within the order Hypnales, is still in need for both traditional taxonomical and modern molecular systematic studies. When these methods are combined factors behind taxonomical problems can be evaluated. Morphological traits that tend to delimit evolutionary independent lineages are often difficult to interpret. Cryptic speciation and parallel evolution of morphologically very similar species appear to be common within a group, and genetic methods are needed for finding out hidden biodiversity within hypnalean mosses. Some of the taxonomical problems may be explained by young evolutionary age of the group, but some features in diversification of bryophytes may also be specific for the group. The haploid perennial life stage and relatively simple morphology but complex metabolic activity in these plants is in strong contrast with all other land plants. Both of these factors can affect on evolution potential and means of diversification in mosses.

Importance of further taxonomical work and studies on genetic diversity among hypnalean mosses increases a risk that need for nature conservation actions are underestimated. Even at areas where the taxonomical knowledge is the best in the world and bryophytes are the most thoroughly studied, such as Fennoscandia, new species are rather frequently found. The new taxon that was found in connection with this project has specialised aquatic habitats and due to its rarity treat status should be evaluated as soon as possible.