Divergence of brain and retinal anatomy and histology in pelagic antarctic notothenioid fishes of the sister taxa Dissostichus and Pleuragramma

• Published in: Journal of Morphology
• Main Authors: Eastman, Joseph T., Lannoo, Michael J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2011
• Subjects: Antarctic; Southern Ocean; Antarc*
• Online Access: http://dx.doi.org/10.1002/jmor.10926; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjmor.10926; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmor.10926

Abstract The neutrally buoyant Antarctic fishes of the sister taxa Dissostichus ( D. eleginoides and D. mawsoni ) and Pleuragramma antarcticum diverged early in the notothenioid radiation and filled different niches in the pelagic realm of the developing Southern Ocean. To assess the influence of phylogenetic and ecological factors in shaping neural morphology in these taxa, we studied the anatomy and histology of the brains and retinae, and determined the proportional weights of brain regions. With the brain of the non‐Antarctic sister taxon Eleginops maclovinus as plesiomorphic, statistically significant departures in the brains of the two Antarctic taxa include reduction of the corpus cerebelli and expansion of the mesencephalon and medulla. Compared to Eleginops , both species also have a relatively smaller telencephalon, although this is significant only in Dissostichus . There are a number of apomorphic features in the brain of Pleuragramma including reduced olfactory nerves and bulbs, an extremely small corpus cerebelli and an expanded mesencephalon. Although there is not a significant difference in the relative weights of the medulla in the two taxa, the prominence of the eminentia granularis and bulging cap‐like appearance of the crista cerebellaris are distinctive in Pleuragramma . Brain histology of Dissostichus and Pleuragramma reflects typical perciform patterns and the two species of Dissostichus are histologically identical. Lateral compression in Pleuragramma and notable lobation in Dissostichus also contribute to differences between the taxa. Compression in Pleuragramma is attributable to convergence on an anchovy/herring body shape and to the relatively large brain in this small fish. The less prominent pattern of lobation of the telencephalon, inferior lobes and corpus cerebelli in Pleuragramma probably reflects underlying histology, specifically a reduction in cellularity of the neuropil in the nuclei and lobes. The retinal histology of Dissostichus and Pleuragramma encompasses the extremes ...