Climate-induced divergence in breeding population dynamics among Pygoscelis penguins: Nutritional-physiological mechanisms and evolutionary consequences
The southwestern Atlantic sector of the Southern Ocean, including the Bellingshausen Sea west of the Antarctica Peninsula (AP), is now strongly influenced by ocean-climate warming. Average winter air temperature has increased ~6°C in association with a notable reduction in regional winter sea-ice formation, particularly within the northern sector of the western AP. Marine community responses to regional warming are now evident. Especially marked are breeding population responses by Pygoscelis penguins including the sea ice-obligate Adélie penguin (P. adeliae), in addition to the sea ice-intolerant chinstrap (P. antarctica) and gentoo (P. papua) penguins, all of which are demonstrating pole-ward shifts in bio-geographic range mediated by environmental effects on demographic parameters. Using data collected over the 2008-2010 austral summers, we examine nutritional and physiological correlates of within and among species variation in individual reproductive performance of Pygoscelis penguins nesting near Anvers Island; an ecotone now shifting from a cold, dry polar climate to a warm, moist sub-Antarctic system. Also, we consider latitudinal variation in reproductive performance among Adélie penguins nesting at Anvers Island, as well as 400 km south at Avian Island and 700 km south at Charcot Island, regions where sea ice remains a prominent physical feature.
Analyses utilize naturally occurring ratios of carbon (d13C) and nitrogen (d15N) stable isotopes of penguin red blood cells as proxies of foraging niche and marine trophic structure, in addition to circulating levels of corticosterone, a primary glucocorticoid in avian homeostatic energetic balance. Using information-theoretic methods, we show that among Pygoscelis penguins breeding at Anvers Island, egg production is driven by divergent nutrient sources across species, however, chick production is associated with similar nutrient sources by 5-weeks of age, suggesting that sea ice-obligate Adélie penguins rear chicks using the same nutrient sources as their sub-Antarctic congeners. Adélie penguin chicks reared at southern rookeries, where sea ice remains a prominent physical feature, are isotopically enriched relative to Anvers Island chicks, which is associated with higher size-corrected body mass and lower corticosterone levels suggesting southern Adélie penguin chicks are in better condition prior to fledge than their northern conspecifics. Variation in marine trophic structure suggests that key sea ice-associated prey drive latitudinal variation in Adélie penguin chick isotope signature and body condition, and may represent a critical environmental factor linking climate-driven sea ice change, predator demography, and community structure.