Resumen de Ecophysiological factors affecting oxidative balance in penguins
The relationship between oxidative balance and life history has been in the spotlight of evolutionary ecologists during the last decade. Ecological as well as physiological factors can affect such balance and hence, oxidative stress is defined as the imbalance between pro-oxidants and antioxidant defences. If such imbalance is in favour of the former, leading oxidative damage (i.e.: oxidative destruction of biomolecules such as lipids, proteins, and DNA), oxidative stress would increase. However, the way animals adjust their oxidative balance in relation to those ecological (e.g. diet, foraging strategies or parasitism) and physiological (e.g. breeding or moulting) factors in free-ranging animals remained either unstudied or with the need of further research. Therefore, this thesis aims to increase the knowledge between oxidative balance and life history at different ecophysiological levels in the wild, using penguins as our model species.
Diet as well as feeding strategies might influence the antioxidant defenses or the production of reactive oxygen species (ROS) of several organisms. The way free-ranging animals adjust their oxidative balance in relation to their diet, feeding strategies and dietary antioxidants remained unstudied as far as we know. Penguins are an interesting biological model to assess such comparison because their diet based on krill and/or fish present marked differences in terms of dietary antioxidant absorption depending on their habitat. Therefore, we investigated by means of stable isotopes, diet and foraging strategies (15N and 13C respectively); dietary antioxidants ( , α-tocopherol and astaxanthin) and oxidative balance, antioxidant capacity (OXY) and oxidative damage (ROMs) of four penguin species, the three Pygoscelid penguins (Pygoscelis antarcticus, P. papua and P. adeliae) breeding in Antarctica and the Magellanic penguin (Spheniscus magellanicus) in Valdés Peninsula, Argentina. We found interspecific differences for all variables analysed x p f α-tocopherol. Whereas Magellanic penguins would feed on anchovies foraged at inshore locations, Pygoscelids would caught mainly krill in off-shore and pelagic places, although Gentoo penguins appear to exploit lesser krill in favour to fish in more coastal and benthic waters. Magellanic penguins showed the highest retinol levels and the best oxidative status. In contrast, Gentoo penguins presented the worse oxidative status even showing the highest astaxanthin values, a compound with high antioxidant capacities. F h , p g m gh α-tocopherol similarly. Overall, no common pattern appears among species. More studies are necessary to understand the interplay between all pieces in wild animals including animal movement at sea and potential changes in the environment including long-term comparisons.
Penguins breed colonially and their breeding cycle comprised different periods (courtship and nest building, incubation, guard phase and crèche) which have different energy requirements as occurs in several species. Energy use has been related with oxidative balance. It is then expected that activities which require a high use of energy could generate higher oxidative stress. Thus, we have compared two breeding periods (incubation and chick rearing) in a Magellanic penguin colony at Valdés Peninsula, Argentina. Our results showed that incubating adults unbalanced their oxidative status showing significantly lower antioxidant levels than those rearing chicks. However, oxidative damage did not show a significant variation between breeding periods. Further, we did not find differences in oxidative status between sexes. Our results suggest that incubation is a highly demanding activity compared to chick rearing in terms of oxidative balance since antioxidants have probably depleted to limit oxidative damage by ROS. Differential foraging effort could explain such results as Magellanic penguins adjust their foraging location to prey availability performing longer foraging trips during incubation than during chick rearing which increases the energy costs and therefore imbalance penguins oxidative status.
The oxidative cost of reproduction has been another matter of debate in recent years presumably because of the lack of proper experimental studies. Based on the hypothesis that different brood sizes produce differential reproductive costs, an experimental manipulation during breeding of Adélie penguins was conducted at Hope Bay, Antarctica, to study oxidative status and stress. We randomly assigned nests with two chicks to a control reproductive effort group (CRE), and by removing one chick from some nests with two chicks, formed a second, low reproductive effort group (LRE). Our nest manipulation showed significant differences in offspring total biomass, which was lower in the LRE group. As predicted, the LRE group had higher antioxidant capacity than individuals in the CRE group. We also found, although marginally significant, interactions between sex and treatment in the three variables analysed. Females had higher antioxidant capacity (OXY), lower oxidative damage (ROMs) and lower heterophil/lymphocyte ratio (H/L), another measure of stress, when rearing one chick, whereas males did so when rearing two except for OXY which was high regardless of treatment. Moreover, there was a significant negative correlation between the H/L ratio and OXY in females. Finally, we found a negative and significant relationship between the duration of the experiment and OXY and ROMs and positive with H/L ratio which shows that indeed breeding penguins are paying an effort in physiological terms in relation to the duration of the chick rearing. Overall, a reduction of the reproductive effort decreased oxidative stress in this long-lived bird meaning that a link exists between breeding effort and oxidative stress. However, our findings suggest different sex strategies which results in opposite physiological responses presumably depending on different life-history strategies in males and females.
As mentioned for different breeding periods (incubation and chick rearing), energy use has been related with oxidative balance. Therefore, other life history events apart from reproduction such as moult which is costly for several bird species could unbalance homeostasis as well. Both oxidative balance and stress are related to energy expenditure. Thus, we examined these two very costly events (breeding and moult) in the life history of wild birds to find out whether they compromise homeostasis using an Antarctic marine top predator in which these two activities do not overlap, the Chinstrap Penguin. Our results show that the H/L ratio was significantly higher during breeding, but no significant differences were found in oxidative balance. A significant negative relationship was found between oxidative damage and total antioxidant capacity. These findings suggest that breeding is a more stressful period than moult in the Chinstrap Penguin, although the oxidative imbalance seems to be similar in both critical periods, thus resulting in similar oxidative costs.
Other environmental factors which impact oxidative balance a part from those already mentioned (e.g. diet, foraging strategies or prey availability) are parasites. Ectoparasites are organisms which inhabit the skin or its outgrowths of another organism (the host) for various periods, and several are vectors of many zoonoses. At present, there is very few information about the presence of ectoparasites and their effects on the Antarctic fauna, although their association to seabird colonies is known. In the Antarctic Peninsula region one of the most prevalent ectoparasites are ticks of the species Ixodes uriae although, no consideration has been given to their effects and its tick-borne pathogens on the health status of seabirds in Antarctica. Therefore, we show for the first time the effects of I. uriae on Chinstrap penguins in the Antarctic region. Ticks produce a greater mortality and hence, a lesser survival rate, when chicks grew on a high tick density area. The presence of ticks increases the immunoglobulin levels in adults, but not in chicks suggesting that surviving chicks are better individuals with an excellent immunity. Moreover, it has been also reported for the first time B. burgdorferi s.l. in Antarctica as well as its consequences when present (higher values of OXY, IgY and lymphocytes, and lower values of heterophils and H/L ratio). Further, adults had a significantly higher prevalence than chick. The influence of Babesia sp. has been also assessed for the first time in the Antarctic region, reducing penguin immunoglobulin levels when present. Finally, three cases of coinfection with B. burgdorferi s.l. and Babesia sp. have been reported. Consequences due to climate change on this region (e.g.: greater proportions of fed ticks when temperatures are higher) might deteriorate the host-(ecto)parasite system described in this thesis. Thus, ticks could be used as climate change indicators and hence, more knowledge (physiology, breeding biology, population status...) is needed to disentangle future implications under a warmer scenario.
