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Leukocyte counts in three sympatric pack-ice seal species from the western Antarctic Peninsula

Abstract

Global warming, and its consequences, constitute one of the main stressors for organisms worldwide, affecting different factors such as the geographic distribution and the abundance of parasites, which in turn can affect the immune system of their hosts, and vice versa. Therefore, it is important to have baseline information on immune parameters of organisms in order to make future comparisons within this changing ecological context. Here, we report on the leukocyte counts of the Antarctic pack ice seals, the crabeater (Lobodon carcinophaga), Weddell (Leptonychotes weddellii) and leopard (Hydrurga leptonyx) seals, sampled off the western Antarctic Peninsula. We captured and sampled seals in the pack ice off the Danco Coast, Antarctica in the austral summers, January to March, of 2015 and 2016. The leukocyte counts, along with the counts of each different leukocyte (e.g., basophil, neutrophil, eosinophil, lymphocyte and monocyte), were made from blood smears viewed under the light microscope. As a potential stress indicator, we examined whether seals with lice, so presumably under greater physiological stress, had changes in leukocyte counts, including higher ratios of neutrophil-to-lymphocytes (N/L ratio). Leukocyte counts were different among the seal species. While crabeater and Weddell seals had higher neutrophil counts, followed by lymphocyte counts, leopard seals had the reverse pattern. Basophil, eosinophil, and lymphocyte counts were higher in the leopard seal, while the N/L ratio, as well as the neutrophil counts, were higher for the crabeater seal. We show, for the Weddell seal, that the animals with lice were more likely to have higher N/L ratios. This suggests that future research into the potential of the N/L index as a stress indicator, that incorporates additional stress parameters including cortisol concentrations, oxidative damage, as well as other measures of immune function, is warranted for the pack ice seals. Our results are a first step towards establishing leukocyte count baselines for the Antarctic pack ice seals off the western Antarctic Peninsula.

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Acknowledgements

The study was financially and logistically supported by the Dirección Nacional del Antártico, Instituto Antártico Argentino. The permit for this work was granted by the Dirección Nacional del Antártico (Environmental Office). This research was funded by the Agencia de Promoción Científica y Tecnológica (PICT 2015-0082) and Lerner-Grey Fund for Marine Research. The authors express their support to the Argentinean scientific program, and thank the public politics during the period 2003–2015 that made possible this research. Field work was supported and funded by the Dirección Nacional del Antártico, Instituto Antártico Argentino PICTA 01–2010.

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Correspondence to María Soledad Leonardi.

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The immobilisation and sampling of leopard, crabeater and Weddell seals within the Antarctic Specially Protected Area No. 134 were approved by the Dirección Nacional del Antártico, Program of Environmental Management and Tourism (PGAyT), Buenos, Aires, Argentina (Permit No. 8). Research procedures were reviewed and approved by the University of New South Wales’ Animal Care and Ethics Committee protocol numbers 08/103B and 11/112A to TR.

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Leonardi, M.S., D’Amico, V.L., Márquez, M.E. et al. Leukocyte counts in three sympatric pack-ice seal species from the western Antarctic Peninsula. Polar Biol 42, 1801–1809 (2019). https://doi.org/10.1007/s00300-019-02551-y

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Keywords

  • Antarctica
  • Crabeater seal
  • Health status
  • Leopard seal
  • Leukocyte counts
  • Weddell seal