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SUMMARY: The taxonomical status and distribution of the Westpalearctic Sericostoma species complex (Trichoptera: Sericostomatidae) is subject of controversial debate. Species descriptions are based in general on minor morphological differences of the male genitalia. In this work, species boundaries of these taxa, mainly the Central European ‘species’ couple S. personatum (SPENCE in Kirby & Spence, 1826) and S. schneideri KOLENATI, 1848, are reconsidered using autecological, chemotaxonomic, and molecular genetic methods.
Autecological analyses focused on differences concerning emergence period, diurnal activity as well as swelling of the egg masses and temperature dependence of embryogenesis. The chemotaxonomic approach focused on identification of compounds of the pheromone glands to detect differences concerning the communication system. For molecular genetic investigations two mitochondrial genes (16S rDNA, cytochrom oxidase I) and one nuclear gene fragment (ITS-1, 5.8S rDNA, ITS-2) were used. Members of all Westpalearctic sericostomatid genera were investigated, especially specimens of the S. personatum and S. schneideri ‘group’.
Autecological investigations revealed differences concerning the emergence period and diurnal activity between the two populations. No differences concerning the swelling of egg masses were observed. All but one of the egg masses remained partially developed diapausing at all incubation temperatures thus limiting the interpretation. Maternal induction of diapause by means of diapause hormones due to unfavourable environmental conditions simulated in the laboratory during development of last instar larva and pupa seems most likely to explain this phenomenon.
No components directly related to pheromones could be identified from male and female pheromone glands.
Molecular genetic investigations do not support a division of S. personatum and S. schneideri into two distinct groups or potentially sibling species. Mitochondrial haplotypes thus exhibited a unique geographical pattern with one group primarily found in Eastern European regions (including Finland), one in Central Europe (including Norway and Sweden), and one group predominantly located in the Alps. Specimens morphologically described as S. flavicorne SCHNEIDER, 1845 from Turkey and S. vittatum RAMBUR, 1842 from Spain were distinct from the European S. personatum / schneideri complex. The haplotype pattern can be explained with the Quaternary ice ages and the resulting glaciation of major parts of Europe.
Morphological characters frequently used for the identification of species may be polymorphisms or the result of phenotypic plasticity and were therefore considered as not useful to resolve systematical questions. The division of the Central European Sericostoma ‘species’ into S. personatum and S. schneideri seems to be questionable.
An alternative hypothesis supports the division of S. personatum and S. schneideri populations and explains overlapping haplotype data with introgression before speciation. In this case, both distinct species received the same mitochondria from different ancestral populations. This hypothesis is well supported by activity patterns.
From the available data, a phylogeny hypothesis of the four European sericostomatid genera Notidobia, Oecismus, Schizoplex and Sericostoma was deduced. While some methods resolved a basal position of the genera Notidobia, most methods resolved solely polytomic relationships.
