Nervous and sensory system correlates of an epibenthic evolutionary radiation in Antarctic notothenioid fishes, genus Trematomus (Perciformes; Nototheniidae)

The perciform suborder Notothenioidei consists of 120 species, with 94 conf ined to the Antarctic Region of the Southern Ocean. On the Antarctic shelf, this phyletic radiation has been accompanied by a substantial morphologica l and ecological diversification towards a pelagic existence. For example, the primarily benthic genus Trematomus contains an epibenthic radiation tha t includes T. loennbergii, T. lepidorhinus, and T. eulepidotus. By comparin g these epibenthic species with three congeneric benthic species (T. scotti , T. pennellii, and T. bernachii) we tested three null hypotheses regarding brain variation in Antarctic trematomids: 1) that there is no difference i n brain morphology among the six species; 2) that phylogenetic and ecologic al factors do not influence brain morphology; and 3) that peripheral sensor y structures do not influence brain morphology. We rejected each of these h ypotheses, leading us to conclude that Trematomus brains vary interspecific ally, between benthic and epibenthic species, and with a species' depth dis tribution. Further, we conclude that brain variation is correlated with dif ferences in peripheral sensory systems and motor activity. Specifically, ep ibenthic Trematomus have larger percentages of their brain volume devoted t o lateral line mechanoreceptive and motor (cerebellar) structures. Species living at greater depths have low ratios of cones:rods in the retina and la rger olfactory structures. J. Morphol. 245:67-79, 2000. (C) 2000 Wiley-Liss , Inc.