Parallel ecological diversification in Antarctic notothenioid fishes as evidence for adaptive radiation

Abstract

Antarctic notothenioid fishes represent a rare example of a marine species flock. They evolved special adaptations to the extreme environment of the Southern Ocean including antifreeze glycoproteins. Although lacking a swim bladder, notothenioids have diversified from their benthic ancestor into a wide array of water column niches, such as epibenthic, semipelagic, cryopelagic and pelagic habitats. Applying stable carbon (C) and nitrogen (N) isotope analyses to gain information on feeding ecology and foraging habitats, we tested whether ecological diversification along the benthic-pelagic axis followed a single directional trend in notothenioids, or whether it evolved independently in several lineages. Population samples of 25 different notothenioid species were collected around the Antarctic Peninsula, the South Orkneys and the South Sandwich Islands. The C and N stable isotope signatures span a broad range (mean δ(13) C and δ(15) N values between -25.4‰ and -21.9‰ and between 8.5‰ and 13.8‰, respectively), and pairwise niche overlap between four notothenioid families was highly significant. Analysis of isotopic disparity-through-time on the basis of Bayesian inference and maximum-likelihood phylogenies, performed on a concatenated mitochondrial (cyt b) and nuclear gene (myh6, Ptr and tbr1) data set (3148 bp), showed that ecological diversification into overlapping feeding niches has occurred multiple times in parallel in different notothenioid families. This convergent diversification in habitat and trophic ecology is a sign of interspecific competition and characteristic for adaptive radiations.

Comparative population genetics of seven notothenioid fish species reveals high levels of gene flow along ocean currents in the southern Scotia Arc, Antarctica

“…Their life histories diVer in a variety of traits (Table 1): C. aceratus, G. gibberifrons, and L. squamifrons are benthic species of which the two former ones spend most of their time resting on the bottom (Fanta et al 1994;Kock and Jones 2005). C. gunnari, C. rastrospinosus, and T. eulepidotus show a benthopelagic lifestyle preying for food in the water column (Rutschmann et al 2011). Vertical migrations between near bottom layers during the day and sub-surface waters during the night are known from several notothenioids including C. gunnari (Kock and Everson 1997).…”

Tracking the elusive monophyly of nototheniid fishes (Teleostei) with multiple mitochondrial and nuclear markers

“…Notothenioids represent approximately 76% of the fish species of the Antarctic shelf, and more than 91% for both abundance and biomass (Eastman, 2005). These fishes possess unique physiological attributes and adaptations to their environment (Chen et al, 1997;Cheng et al, 2006;Rutschmann et al, 2011), including antifreeze glycoproteins in five out of eight of the families (except in Bovichthidae, Pseudaphritidae, and Eleginopidae), to the complete loss of hemoglobin in the Channichtyidae.…”

Iterative Ecological Radiation and Convergence during the Evolutionary History of Damselfishes (Pomacentridae)

“…The gray shaded area indicates the 95% range for the simulated data. or lakes (Losos and Ricklefs 2009), but damselfishes and Antartic notothenioids (Rutschmann et al 2011) illustrate the first cases of repeated adaptive radiations occurring in the oceans. In coral reef ecosystems, repeated radiations might be expected during events of regionalization or geographic expansion allowing the colonization of new reefs.…”