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Why are difficulties so numerous in earthworm taxonomy and in the reconstruction of their phylogeny?
Anfiteatro da Física, Universidade do Minho, Campus de Gualtar, Braga terça-feira, 30-04-2013
Earthworms are regarded as a very important group of soil organisms affecting the biotic and abiotic properties of the soil. In many terrestrial ecosystems, they constitute the majority of the soil faunal biomass. They play a significant role in producing soil structure and increasing the ion base-exchange capacity and ion availability.
  Why are difficulties so numerous in earthworm taxonomy and in the reconstruction of their phylogeny?
 

SEMINÁRIO/ LECTURE - 30 de ABRIL, 2013; às 11 h

Under MESTRADO em ECOLOGIA/ CBMA organization





PAVLÍCEK Tomá¨
Institute of Evolution, University of Haifa, Haifa, Israel
e-mail: contact@tomas-pavlicek-biology.net

Why are difficulties so numerous in earthworm taxonomy and in the reconstruction of their phylogeny?

Earthworms are regarded as a very important group of soil organisms affecting the biotic and abiotic properties of the soil. In many terrestrial ecosystems, they constitute the majority of the soil faunal biomass. They play a significant role in producing soil structure and increasing the ion base-exchange capacity and ion availability.

Despite of their importance, the earthworm taxonomy and phylogeny is in a chaotic state. The period following the publication of the tenth volume of "Das Tierreich" (Michaelsen, 1900) deemed as "Triumph of as  earthworm taxonomy" (Stephenson, 1930), has been currently replaced by a period of "unequal chaos in earthworm taxonomy" (Briones, Morán, & Posada, 2009). The blind application of the taxonomic and phylogenetic methods developed for Deuterostomia and/or Ecdysozoa without considering the evolutionary peculiarities of earthworms, and possibly of all Lophotrochozoa, leads, among others, to the observed low statistical support splits, especially in the basal parts of the constructed bifurcating-like phylogenetic trees (Brigandt, 2001; James et al., 2010; Jamieson, 1988; Pop, Csuzdi, Cech, Wink, & Pop, 2007; Pop, Wink, & Pop, 2003).

The failure of the traditional phylogenetic approaches that are using averaging of taxonomic characters and/or the classical bifurcating-like phylogenetic tree like analyses, is, in our opinion, due to the hybrid origin of earthworm species (Pavlícek, Hadid, & Csuzdi, 2012), and possibly of other annelids. Also, the use of mtDNA for phylogenetic analyses (and for barcoding) in earthworms is problematic. It seems that the existing barrier protects nuclear genes or at least part of the nuclear genes, but not the mtDNA genes, from the effect of gene flow during hybridization events. The documented rare cases of biclitellate homeosis producing "nsters"(Gates, 1956) indicate the potentially disastrous effects (Pavlí?ek et al., 2012) of inter-lineage hybridizations.

At the end of 19th century, two conflicting theories of evolution had been proposed: the first based on the concept of continuous variation and the second on the concept of discontinuous (saltational) variation. W. Bateson concluded that continuous and discontinuous variation are distinct essentially ... that they are manifestation of different process". Scientists like De Vries, R. Goldschmidt, N. Eldredge and S. J. Gould would agree with the content of this quote, but it would be dismissed, together with all the concept of the saltational evolution, by the majority of influential evolutionary biologists such as E. Mayr, and T. Dobzhansky. The discontinuous variability in body size in a population of earthworms is a sign of saltational evolution resulting from the autohomoploid hybridization process in earthworms. The autohomoploid hybridization and other processes, some of them unique for annelida or clitellata, during embryogenesis and cytogenesis have a determining role on speciation, population differentiation, and probably account for the discordance between nuclear and mtDNA evolution. The proposed model of evolution can also explain, among others, the problems experienced during phylogeny reconstruction by means of bifurcating phylogenetic trees, and failures to delineate some species by means of morphological or genetic (molecular) distances.

Dr. PAVLÍCEK Tomá¨
Senior researcher at the Institute of Evolution, University of Haifa, Israel

Fields of specialization: Evolutionary genetics, population genetics, ecology, zoogeography, entomology, earthworm biology.

Convenor of the 3th, 4th, 5th and 6th , International Oligochaete Taxonomy Meetings (Cyprus, Turkey, Switzerland, Portugal)
 
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