The buoyancy-based biotope axis of the evolutionary radiation of Antarctic cryonotothenioid fishes
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ORIGINAL PAPER
The buoyancy‑based biotope axis of the evolutionary radiation of Antarctic cryonotothenioid fishes Joseph T. Eastman1 Received: 30 October 2019 / Revised: 8 June 2020 / Accepted: 16 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In the absence of any prior comprehensive analysis, I evaluate divergence along the biotope axis in the habitat stage of the evolutionary radiation of Antarctic cryonotothenioids. I utilize the available percentage buoyancy (%B) measurements as habitat proxies for recognition of the pelagic, semipelagic, demersal, and benthic biotopes that include, respectively, 5%, 10%, 73%, and 12% of the 59 species and 1749 specimens in the study. The majority of species retain the ancestral demersal biotope of Eleginops maclovinus, and this probably enhances ecological plasticity. Divergence into the pelagic biotope is the most distinctive organismal feature of the radiation and, although only 5% of species are pelagic, this biotope is not depauperate in global comparisons. Pelagic or potentially pelagic species are Dissostichus mawsoni, D. eleginoides, Pleuragramma antarctica, Aethotaxis mitopteryx, and Gvozdarus svetovidovi. Small ontogenetic changes in %B with growth are typical; however, this is extensive in D. mawsoni, a species with the potential to transition through benthic to pelagic biotopes over ontogeny. Occupation of the pelagic biotope by large D. mawsoni may be impermanent as it is lipid-dependent, a contingency reliant on the availability of P. antarctica as prey. In unusual conditions, the specialized sacs of P. antarctica can also yield their lipid for metabolism with possible loss of buoyancy. Pelagic species are inordinately important in the food web. In the southwestern Ross Sea a guild of large mammalian and avian predators, which includes D. mawsoni, is reliant on lipid-rich, energy-dense cryonotothenioid prey. This includes asymmetrical intraguild predation on D. mawsoni, with P. antarctica as a basal resource for the guild. Keywords Pelagic biotope · Ecological plasticity · Ross Sea · Intraguild predation
Introduction The array of habitats occupied by notothenioid fishes is a distinctive feature of the evolutionary radiation of this group in the waters around Antarctica. Vertebrate radiations are hypothesized to progress through similar stages, diverging sequentially in habitat utilization, morphology and, sometimes, sensory communication as represented by sexual selection (Streelman et al. 2002; Streelman and Danley 2003; Gavrilets and Losos 2009). Notothenioid fishes are among the foremost examples of evolutionary radiation and species flock formation in the marine realm (Eastman and McCune 2000; Eastman 2005; Near et al. 2012; Lecointre et al. 2013; Bowen et al. 2020) and there is now sufficient * Joseph T. Eastman [email protected] 1
Department of Biomedical Sciences, Ohio University, Athens, OH 45701, USA
information about their biology that the essential process of identifying the axes of the radiation is in progres
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