Leukocyte counts in blood smears of Antarctic seals and penguins: a new less time-consuming method

Research on immune response in polar fauna is gaining great importance due to different scenarios of environmental change. Total leukocyte counts in blood smears are one of the most widespread practices and provide useful information about the health status of individuals. However, there is no methodological agreement for these analyses. Total leukocyte counts can be performed at ×400 magnification in optical microscopy using 10,000 erythrocytes for standardizing. However, counting such number of erythrocytes is costly and time-consuming. Here, we describe a new technique to simplify leukocyte counts in blood smears from Antarctic wildlife based on the number of microscope fields instead of the number of erythrocytes which reduces considerably the time spent. We have counted total leukocytes using both methods in the three penguin species of the genus Pygoscelis —Adélie ( P. adeliae ) , gentoo ( P. papua ), and chinstrap penguin ( P. antarcticus )—and four Antarctic mammal species: crabeater seal ( Lobodon carcinophaga ), leopard seal ( Hydrurga leptonyx ), weddell seal ( Leptonychotes weddellii ), and southern elephant seal ( Mirounga leonina ) for validation. Our results show a high correlation between the total leukocyte counts using 10,000 erythrocytes or 10 microscope fields for standardizing. These results show the reliability of the latter method for counting the total number of leukocytes in different species of birds and mammals saving time and effort.