NEUROECOLOGY OF CYPRINIDS - COMPARATIVE, QUANTITATIVE HISTOLOGY REVEALS DIVERSE BRAIN PATTERNS

Brain patterns are compared by quantitative histology in 28 native and introduced mid-European cyprinid species, considering 17 primary sensory and higher order brain areas. Cluster analysis (CLA) and principal component analysis (PCA) based on relative volumes of these brain areas indicate that cyprinid brains are diversified into four major groups, basic cyprinid, abramine, octavo-lateralis and chemosensory. PCA recognizes the brain of Phoxinus phoxinus as a fifth group. Interspecific differences in brain morphology are mainly caused by variability in relative sizes of the brain stem lobes for external and internal taste (lobus facialis and lobus vagus), as well as of octavo-lateralis and visual areas. Higher order brain areas show little interspecific variation in relative size, and were grouped by PCA according to inter- and intraspecific allometries. Hypotheses on brain functions are based on brain area correlations. We propose that the processing of external taste information in the valvula cerebelli may be particularly important for benthivorous cyprinids, whereas the integration of octavo-lateralis input with visual information via the torus longitudinalis - stratum marginale system may play a key role in the planktivores. Brain patterns suggest two major pathways of cyprinid evolutionary and ecological radiation, one leading from the basic cyprinids towards octavo-lateralis dominated midwater and surface planktivores, the second towards taste-dominated benthivores.