Antarctic teleosts with and without hemoglobin behaviorally mitigate deleterious effects of acute environmental warming

Recent studies forecast that many ectothermic animals, especially aquatic stenotherms, may not be able to thrive or even survive predicted climate change. These projections, however, generally do not call much attention to the role of behavior, an essential thermoregulatory mechanism of many ectotherms. Here we characterize species-specific locomotor and respiratory responses to acute ambient warming in two highly stenothermic Antarctic Notothenioid fishes, one of which (Chaenocephalus aceratus) lacks hemoglobin and appears to be less tolerant to thermal stress as compared to the other (Notothenia coriiceps), which expresses hemoglobin. At the onset of ambient warming, both species perform distinct locomotor maneuvers that appear to include avoidance reactions. In response to unavoidable progressive hyperthermia, fishes demonstrate a range of species-specific maneuvers, all of which appear to provide some mitigation of the deleterious effects of obligatory thermoconformation and to compensate for increasing metabolic demand by enhancing the efficacy of branchial respiration. As temperature continues to rise, Chaenocephalus aceratus supplements these behaviors with intensive pectoral fin fanning which may facilitate cutaneous respiration through its scaleless integument, and Notothenia coriiceps manifests respiratory-locomotor coupling during repetitive startle-like maneuvers which may further augment gill ventilation. The latter behaviors, found only in Notothenia coriiceps, have highly stereotyped appearance resembling Fixed Action Pattern sequences. Altogether, this behavioral flexibility could contribute to the reduction of the detrimental effects of acute thermal stress within a limited thermal range. In an ecologically relevant setting, this may enable efficient thermoregulation of fishes by habitat selection, thus facilitating their resilience in persistent environmental change.

Antarctic Teleosts With and Without Haemoglobin Behaviourally Mitigate Deleterious Effects of Acute Environmental Warming

Recent studies forecast that many ectothermic animals, especially aquatic stenotherms, may not be able to thrive or even survive predicted climate change. These projections, however, generally do not call much attention to the role of behaviour, an essential thermoregulatory mechanism of many ectotherms. Here we characterize species-specific locomotor and respiratory responses to acute ambient warming in two highly stenothermic Antarctic Notothenioid fishes, one of which (Chaenocephalus aceratus) lacks haemoglobin and appears to be less tolerant to thermal stress as compared to the other (Notothenia coriiceps), which expresses haemoglobin. At the onset of ambient warming, both species perform distinct locomotor manoeuvres that appear to include avoidance reactions. In response to unavoidable progressive hyperthermia, fishes demonstrate a range of species-specific manoeuvres, all of which appear to provide some mitigation of the deleterious effects of obligatory thermoconformation and to compensate for increasing metabolic demand by enhancing the efficacy of branchial respiration. As temperature continues to rise, Chaenocephalus aceratus supplements these behaviours with intensive pectoral fin fanning which may facilitate cutaneous respiration through its scaleless integument, and Notothenia coriiceps manifests respiratory-locomotor coupling during repetitive startle-like manoeuvres which may further augment gill ventilation. The latter behaviours, found only in Notothenia coriiceps, have highly stereotyped appearance resembling Fixed Action Pattern sequences. Altogether, this behavioural flexibility could contribute to the reduction of the detrimental effects of acute thermal stress within a limited thermal range. In an ecologically relevant setting, this may enable efficient thermoregulation of fishes by habitat selection, thus facilitating their resilience in persistent environmental change.

Expansion of capacities for iron transport and sequestration reflects plasma volumes and heart mass among white-blooded notothenioid fishes

The family Channichthyidae or “icefishes” (suborder Notothenioidei) represents the only vertebrates lacking hemoglobin (Hb) as adults. Several icefish species also do not express cardiac myoglobin (Mb). We address how levels of proteins involved in iron (Fe) processing (transport, sequestration, and export) vary among white- and red-blooded notothenioids, and whether absence of Hb and/or Mb in channichthyids is accompanied by expansion of contents of Fe-binding proteins to protect against unchaperoned Fe. Levels of transferrin (Tf), ferritin (Ft), ceruloplasmin (Cp), and non-heme Fe were quantified in plasma, serum, and/or nonhematopoietic tissues (cardiac ventricle, skeletal muscle, and liver) from species of white-blooded ( Chaenocephalus aceratus, Champsocephalus gunnari, Chionodraco rastrospinosus, Pseudochaenichthys georgianus) (the first two species not expressing Mb) and red-blooded ( Notothenia coriiceps, Gobionotothen gibberifrons) notothenioids. We also measured levels of ascorbate (Asc), a mediator of Fe uptake. While plasma concentrations of Tf and tissue levels of Asc are similar among species, concentrations of plasma Asc are lower in white-blooded species. Concentrations of Ft and non-heme Fe and activities of Cp are also generally reduced in icefishes compared with red-blooded notothenioids. The presence of cardiac Mb in some icefish species does not appear to influence levels of proteins involved in Fe processing. To address further the question of Fe sequestration within a physiological context, we account for well-characterized differences in blood volume and heart mass among white- and red-blooded notothenioids. We report that total contents of plasma Tf are greater, while ventricle non-heme Fe is at least at parity in white- vs. red-blooded species.