Trade-off between aerobic performance and egg production in migratory macaroni penguins

• Published in: Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
• Main Authors: Jubinville, Isabelle, Williams, Tony D., Trathan, Phil N., Crossin, Glenn T.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2020
• Subjects: Eudyptes chrysolophus
• Online Access: http://nora.nerc.ac.uk/id/eprint/527975/; https://www.sciencedirect.com/science/article/pii/S1095643320300945

When successive stages of an organism's life-history overlap, conflicts and trade-offs can emerge due to competition among physiological pathways. For example, long periods of sustained locomotion in migrating birds are supported by the androgenic up-regulation of aerobic factors, such as new red blood cell production and hematocrit. However, towards the end of migration, many female birds begin up-regulating 17ß-estradiol (E2) to support vitellogenesis and egg production, but E2 secretion is known to have suppressive effects on red blood cell production (anti-erythropoiesis). We explored potential trade-offs between factors related to aerobic performance (hematocrit, reticulocyte index) and the expression of factors related to E2-mediated vitellogenesis (i.e. yolk precursor production) in female macaroni penguins (Eudyptes chrysolophus), a species in which the physiologies controlling egg production and migratory activity run simultaneously (e.g. females experience a migratory conflict). We collected blood samples from penguins immediately upon their return to the colony, prior to egg laying. Hematocrit was elevated when the penguins returned to the colony (50.05% ± 3.40 SD), which is similar to pre-laying values observed in other migratory bird species. Furthermore, mean reticulocyte levels were elevated (34.87% ± 2.34), which is the highest level yet recorded in birds. Similarly, both plasma vitellogenin and yolk-targeted very low density lipoprotein levels were upregulated (2.30 ± 0.06 μg Zn ml−1, and 9.70 ± 0.19 mmol l−1, respectively), indicating that penguins were reproductively active and producing eggs during migration and upon arrival on land. As predicted, a negative relationship between hematocrit and plasma vitellogenin was found, but we found no evidence to suggest that birds were experiencing reproductive anemia. Alternatively, we attribute the negative relationship to a hemodilution effect of yolk precursor secretion into circulation. It appears that female macaroni penguins are able to preserve ...