| dc.description.abstracteng | Species are the fundamental units of comparison in all subfields of biology.
Moreover, species are the currency of biological classification and used to define areas of
conservation priority. Hence, central questions of evolutionary biology are “what is a
species?”, “how can we delimit species?”, “how many species exist?” and “how did
species evolve in space and time?”. These questions are the subject of this dissertation.
The first part of this thesis questions the use of the phylogenetic species concept to
delimit species via mtDNA-based methods, such as comparisons of intra- and interspecific
distances or diagnostic characters, in the lemurs of Madagascar. The number of lemur
species has almost tripled during the last two decades. Many of the newly described
species were solely delimited on the basis of mitochondrial DNA under the Phylogenetic
Species Concept (PSC) using the above-mentioned methods. We used published
sequence data collected from GenBank to compare intra- and interspecific distances
among lemur genera for different mtDNA loci. Fourteen out of 17 comparisons showed
overlapping intra- and interspecific genetic distances independent of the loci used. A
simulation of a fictive taxonomic study furthermore revealed that the minimum required
number of samples for the mitochondrial D-loop is 10 per population in order to avoid false
positives via Population Aggregation Analysis. The results indicate that both methods are
inappropriate to delimit species. We therefore recommend the use of nuclear and mtDNA
genetic loci as well as multiple independent datasets (e.g. morphological, acoustic,
ecological, etc.) to delimit species.
The second part of this thesis revisits the taxonomy of the brown lemur complex
endemic to Madagascar using several types of data. Seven species of the genus Eulemur
formerly treated as subspecies of the common brown lemur (Eulemur fulvus) and grouped
into the brown lemur complex (BLC) were previously elevated to species level without the
collection of new data. Between-group analyses of principal components revealed
significant heterogeneity in skull shape, pelage color variation and loud calls across all
seven populations. Furthermore, post hoc statistical tests between pairs of populations
revealed considerable discordance among different data sets for different dyads. Despite a
high degree of incomplete lineage sorting among nuclear genetic loci, significant exclusive
ancestry was found for all populations, except for E. cinereiceps, based on one
mitochondrial and three nuclear genetic loci. Under the general linage concept of species,
using several independent lines of evidence, our results confirmed the species status of
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the members of the BLC. More generally, this analysis highlights the importance and value
of integrating several types of evidence in delimiting recently evolved radiations.
In the third chapter we explored the evolution of the genus Eulemur in space and
time and the concordance of Eulemur diversification with major biogeographic hypotheses
proposed for Madagascar. Due to its remarkable species diversity and micro-endemsim,
Madagascar has recently been proposed as a biogeographic model region. However,
hypothesis-based tests of various diversification mechanisms that have been proposed for
the evolution of the island's micro-endemic lineages are still limited. Here, we tested the
concordance of several diversification hypotheses with new data on the broadly distributed
genus Eulemur using coalescent-based phylogeographic analyses. Time-calibrated
species tree analyses and population genetic clustering resolved the previously polytomic
relationships among eulemurs. The most recent common ancestor of eulemurs was dated
about 4.45 million years ago (mya). Estimates of divergence dates furthermore suggested
a very recent diversification among the members of the "brown lemur complex", i.e. former
subspecies of E. fulvus, during the Pleistocene (0.33-1.43 mya). Phylogeographic model
comparisons of past migration rates showed significant levels of gene flow between
lineages of neighboring river catchments as well as between eastern and western
populations of the redfronted lemur (E. rufifrons). Together, our results are concordant with
the centers of endemism hypothesis, underline the importance of watersheds for the
evolution of Madagascar's micro-endemic biota, and they highlight the utility of testing
diversification mechanisms using coalescent-based phylogeographic methods. | de |