Skip to main content

Polypterids – development and evolution of a ’living fossil’

Final Report Summary - POLYPTERUS EVO-DEVO (Polypterids - development and evolution of a 'living fossil')

Placing the bichirs, of the polypteridae family, within the vertebrate tree of evolution was debated since their discovery at the beginning of the 19th century. They possessed several 'archaic' characters, known otherwise only from fossil fish, but at the same time they demonstrated many unique characters making a direct comparison to other fish groups difficult. At present bichirs are supposed to be the sister group of all other ray-finned fishes (actinopterygii). Despite their apparently important position within the vertebrate phylogeny few studies have tried to resolve the intrarelationships within this family. Solving these intrarelationships was the starting point for the project 'Polypterids - development and evolution of a living fossil'. The project addressed this issue with a unique combination of long-time established and modern approaches.

For the taxonomy approach almost 1 000 specimens of polypterids from museum collections all over Europe were studied in detail by taking meristic counts and morphometric measurements. It became clear that the present taxonomy within the studied group needed some revision and the status of several species, sub-species or colour-morphs needed to be adapted. A respective publication summarising these results and providing an updated taxonomy of the family polypteridae was in preparation by the time of the project completion.

Moreover, tissue samples from all known polypterid species and almost all sub-species were used in the molecular approach. Seven markers were chosen for further analyses, including two from the mitochondrial genome, namely barcode and 16S, and three nuclear markers, namely glyt, tbr and RAG1. Genes from all these markers were sequenced for 38 specimens and a phylogenetic analysis was performed using different approaches such as maximum parsimony, maximum likelihood and Bayesian analysis. As a further major focus molecular clock approaches were calculated for the data set and respective sub-sets. A publication summarising the phylogenetic analysis and molecular clock estimations for the age of the family polypteridae was also in preparation by the time of this report.

The biogeography approach planned to transfer the collection data of the museum specimens to detailed distribution maps, compatible with geographic information system (GIS), for all species. The resulting distribution patterns should have given additional insights in the evolutionary history of this family, particularly on the background of the taxonomic and molecular results.

The morphology approach aimed to record the polypterid skeletal anatomy in great detail by using skeletons as well as clearing and double staining techniques. It was planned to study representatives of several species, and at least of two species in great detail, using photographs, including techniques with extended focus, and drawings to compile a detailed atlas of the polypterid anatomy. This issue would have included a compilation of the different terminology for the skeletal elements of polypterids that were used so far in the literature.

Due to difficulties in the comparison of modern fish with polypterids the essential augmentation of the morphological approach would have been the ontogeny approach. The study aimed to provide detailed insights into the skeletal anatomy by following certain structures in their development. This additional pool of information often allows comparing structures between taxa in cases where adult situations differ too much to enable easy homologisation. As a combined result of the morphology and ontogeny approach it was planned to provide a hypothesis on the intrarelationships of bichirs based on morphological characters.

The POLYPTERUS EVO-DEVO project proceeded as planned and the expected objectives and goals where reached for the first half of the project. However, the project was prematurely terminated after 15 months. Therefore only parts of the herein given overview were realised, i.e. the taxonomy and the molecular approach. Several data for the other approaches had already been collected, but quitting the project 9 months before its planned termination did not allow concluding these parts.