AbstractsBiology & Animal Science

Evolutionary processes in mayflies (Ephemeroptera)

by Sereina Rutschmann

Institution: Freie Universität Berlin
Department: FB Biologie, Chemie, Pharmazie
Degree: PhD
Year: 2015
Record ID: 1108713
Full text PDF: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000098796


The field of molecular phylogenetics has benefited greatly from the recent advances of modern sequencing approaches that allow for the generation of large genomics data sets Nonetheless a lack of suitable genetic markers and incomplete taxon sampling remain common problems in studies of evolutionary relatedness. Most phylogenetic studies are based on mitochondrial DNA (mtDNA) because information about the nuclear genome and strategies to develop new genetic markers are often not available. The use of appropriate genetic markers and the inclusion of both a geographically and phylogenetically comprehensive taxon sampling are required for adequately reconstructing evolutionary histories among different taxa. This is particularly true for studies of recent diversification. Mayflies (Ephemeroptera) are ancient freshwater insects, dating back more than 300 million years, but at the same time have been reported to successfully colonize and diversify on recently formed Atlantic oceanic islands. This combination of ancient origin and recent diversification makes them a fascinating study system for molecular phylogenetics. In the first part of my thesis, I investigated the recent diversification and colonization history of mayflies on 13 Atlantic oceanic islands of the Azores, Madeira, and the Canary Islands. The island fauna provides an ideal setting to understand how speciation and dispersal shape present-day freshwater biodiversity. A first step in the research was an assessment of the species richness of the island fauna, because current taxonomic estimates are uncertain. Earlier research on mayflies in Europe, Africa, Madagascar, and North America has repeatedly uncovered otherwise cryptic diversity based on analysis of mtDNA. This suggests that past morphological estimates may underestimate species richness, and that a comprehensive understanding of island biodiversity and its evolution requires molecular-based taxonomy. In order to assess the biodiversity and date the origin of the island fauna, I used phylogenetic analyses based on universal mtDNA markers combined with a generalized mixed Yule- coalescent (gmyc) approach. In total, I found twelve island-endemic species within three species groups (Baetis canariensis s.l., B. pseudorhodani s.l., and Cloeon dipterum s.l.) that have diversified within the last 15 million years in parallel throughout the island archipelagos. While intriguing, the results also pointed out the limitations of mtDNA markers for the study of recent diversification events. The study clearly demonstrated a need for the development of new genetic markers that provide increased phylogenetic signal in order to resolve the relationships of closely related species groups. To investigate relationships among newly diverged species, many polymorphisms are needed, and these should ideally be derived from multiple unlinked markers. Since mayflies are a non-model organism i.e. no reference genome is available, I generated a whole genome draft and used these data to design 59 nuclear DNA (nDNA) markers…