Master's Defensio Laura Koch

Advisor: Harald Ahnelt

Congratulations to Laura Koch for successfully defending her Master's Degree on "Get small if it gets uncomfortable. Character shift and phenotypic plasticity of Ninnigobius canestrinii Ninni, 1883) introduced in a shallow freshwater lake." on June 9th 2022!


Ninnigobius canestrinii (formerly Pomatoschistus canestrinii) is an epibenthic, euryhaline sand goby inhabiting brackish and freshwater habitats along the Adriatic coast. Past morphological studies revealed that sand gobies which face the same environmental conditions like a similar habitat and life history combined with a low dispersal rate tend to exhibit the same morphological features: a reduction of head canals, squamation and body size. In this study, a natural population from river Jadro (Croatia) was compared to a recently introduced population of lake Trasimeno (Italy) regarding these three morphological traits. This offered the opportunity to assess (1) the phenotypic diversity between natural and introduced populations and (2) how the squamation and the head lateral line canal system of this benthic species responds to a shift along a hydrodynamic gradient (lake vs. stream). Because both traits are key taxonomic tools, the introduction offered also the opportunity to assess (3) the strength of these two morphological traits as taxonomic tools. Specimens from the introduced population showed a smaller body size, a higher variability and more reductions in head canal and squamation types than the natural population of river Jadro. The reason seems to be adaptation to a new habitat and consequently to different environmental and hydrodynamic conditions. Since recent phylogenetic studies revealed cryptic diversity in Adriatic sand gobies, these morphological results could perhaps be used for future species identification.