Karin Maldonado

Osmoregulatory capacity and the ability to use marine food sources in two coastal songbirds (Cinclodes: Furnariidae) along a latitudinal gradient

Cinclodes nigrofumosus and C. oustaleti are two closely related songbirds that inhabit the northern Chilean coast during the austral fall and winter.This stretch spans a dramatic north to south latitudinal gradient in rainfall and temperature. Whereas C. nigrofumosus lives exclusively on coastal environments, C. oustaleti shifts seasonally from coastal environments to inland freshwater ones. We used the δ13C of these two species’ tissues to investigate whether the reliance on marine versus terrestrial sources varied from the hyper-arid north to the wet south. We also investigated latitudinal variation in the renal traits that mediate how these birds cope with dehydration and a salty marine diet. Both species increased the incorporation of terrestrial carbon, as measured by δ13C, as terrestrial productivity increased southwards. However, C. nigrofumosus had consistently more positive (i.e. more marine) and less variable δ13C values than C. oustaleti. The osmoregulatory traits of both species varied with latitude as well. Urine osmolality decreased from extremely high values in the north to moderate values in the south, while C. nigrofumosus produced more concentrated urine than C. oustaleti. In both species, the proportion of kidney devoted to medullary tissue decreased from north to south, and kidney size increased significantly with latitude. Cinclodes nigrofumosus had larger kidneys with larger proportions of medullary tissue than C. oustaleti. C. nigrofumosus and C. oustaleti are terrestrial organisms subsidized by a rich marine environment where it is adjacent to an unproductive terrestrial. Variation in the reliance on marine food sources seems to be accompanied by adjustments in the osmoregulatory mechanisms used by these birds to cope with salt and dehydration.

Within-Species Digestive Tract Flexibility in Rufous-Collared Sparrows and the Climatic Variability Hypothesis

The climatic variability hypothesis (CVH) states that species are geographically more widespread at higher latitudes because individuals have a broader range of physiological tolerance or phenotypic flexibility as latitude and climatic variability increase. However, it remains unclear to what extent climatic variability or latitude, acting on the phenotype, account for any observed geographical gradient in mean range size. In this study, we analyzed the physiological flexibility within the CVH framework by using an intraspecific population experimental approach. We tested for a positive relationship between digestive-tract flexibility (i.e., morphology and enzyme activities) and latitude and climatic and natural diet variability in populations of rufous-collared sparrows (Zonotrichia capensis) captured in desert (27°S), Mediterranean (33°S), and cold-temperate (41°S) sites in Chile. In accordance with the CVH, we observed a positive relationship between the magnitude of digestive-tract flexibility and environmental variability but not latitude. The greatest digestive flexibility was observed in birds at middle latitudes, which experience the most environmental variability (a Mediterranean climate), whereas individuals from the most stable climates (desert and cold-temperate) exhibited little or no digestive-tract flexibility in response to experimental diets. Our findings support the idea that latitudinal gradients in geographical ranges may be strongly affected by the action of regional features, which makes it difficult to find general patterns in the distribution of species.

Geographic Variation in the Association between Exploratory Behavior and Physiology in Rufous-Collared Sparrows*

Increasing research has attempted to clarify the links between animal personality and physiology. However, the mechanisms driving this association remain largely unknown, and knowledge of how ecological factors may affect its direction and strength is scant. In this study, we quantified variation in the association between exploratory behavior, basal metabolic rate (BMR), and total evaporative water loss (TEWL) in rufous-collared sparrows (Zonotrichia capensis) inhabiting desert, Mediterranean, and cold-temperate climates. We found that the exploratory behavior score was highest in birds from the cold-temperate site, which was characterized by a moderate level of ecological variability (seasonality). Moreover, the association between exploratory behavior and physiological variables differed among localities. Only birds from the Mediterranean site showed a positive correlation between exploratory behavior and BMR. We found no association between exploration and TEWL at any study site. Our findings suggest that differences in the ecological conditions experienced by each sparrow population result in a particular combination of behavioral and physiological traits. An understanding of this intraspecific variation along ecological gradients provides unique insights into how specific ecological conditions affect the coupling of behavioral and physiological traits and the mechanisms underlying that relationship.

Between-population differences in digestive flexibility in the olivaceous field mouse

The flexibility of digestive traits characterizes a standard model of physiological flexibility, demonstrating that animals adjust their digestive attributes in order to maximize overall energy return. Using an intraspecific experimental study, we evaluated the amount of flexibility in digestive tract mass and length in individuals from field mouse populations inhabiting semi-arid and temperate rain forest habitats and acclimated for six months to diets of different qualities. In accordance with the predictions of the theory of digestion, we observed a highly significant relationship between dietary variability and digestive flexibility in both specific digestive chambers and in the total digestive tract mass and length. Specifically, we found higher digestive plasticity in response to diet quality in rodents inhabiting southern temperate ecosystems with higher dietary variability in comparison to individuals from northern semi-arid habitats.

Temporal variation in isotopic composition of Pygoscelis penguins at Ardley Island, Antarctic: Are foraging habits impacted by environmental change?

Several studies have suggested that penguins are undergoing a major restructuring of their feeding habits and distribution after drastic climatic changes in the Antarctic Peninsula region. With the objective of estimating potential medium-term and inter-annual variations in trophic niche, we measured δ15N and δ13C in feather samples of pygoscelid penguins from museum specimens (1982–1984) and in blood and feather samples from 2009/10–2011 collected from animals on Ardley Island. Current penguin feathers had lower δ13C and δ15N values and were more similar to Antarctic krill values, than feathers in 1982–1984 and blood from 2009/10-2011. Moreover, δ13C and δ15N values from museum feathers and modern samples occupied a larger isotopic space in Gentoo Penguins (Pygoscelis papua), compared to Adélie Penguins (Pygoscelis adeliae) and Chinstrap Penguins (Pygoscelis antarctica). Our results from feathers samples indicated that penguins have decreased their consumption of fish and other prey of higher trophic levels in the early interbreeding period (EIBP), while increasing the amount of euphausiids (Antarctic krill Euphausia superba) taken. The isotopic values of the species suggest that foraging sites varied significantly over time and seasonally. We suggest that environmental changes may have modified the feeding habits of pygoscelid penguins, resulting in changed foraging behaviour in the EIBP, and altering the secondary prey consumption. Prey choice in breeding pygoscelid species is probably limited by the foraging range around the breeding colony and competitive exclusion between congeners.

Coping with Salt Water Habitats: Metabolic and Oxidative Responses to Salt Intake in the Rufous-Collared Sparrow

Many physiological adjustments occur in response to salt intake in several marine taxa, which manifest at different scales from changes in the concentration of individual molecules to physical traits of whole organisms. Little is known about the influence of salinity on the distribution, physiological performance, and ecology of passerines; specifically, the impact of drinking water salinity on the oxidative status of birds has been largely ignored. In this study, we evaluated whether experimental variations in the salt intake of a widely-distributed passerine (Zontotrichia capensis) could generate differences in basal (BMR) and maximum metabolic rates (Msum), as well as affect metabolic enzyme activity and oxidative status. We measured rates of energy expenditure of birds after 30-d acclimation to drink salt (SW) or tap (fresh) water (TW) and assessed changes in the activity of mitochondrial enzymes (cytochrome c oxidase and citrate synthase) in skeletal muscle, heart, and kidney. Finally, we evaluated the oxidative status of bird tissues by means of total antioxidant capacity (TAC) and superoxide dismutase activities and lipid oxidative damage (Malondialdehyde, MDA). The results revealed a significant increase in BMR but not Msum, which resulted in a reduction in factorial aerobic scope in SW- vs. TW-acclimated birds. These changes were paralleled with increased kidney and intestine masses and catabolic activities in tissues, especially in pectoralis muscle. We also found that TAC and MDA concentrations were ~120 and ~400% higher, respectively in the liver of animals acclimated to the SW- vs. TW-treatment. Our study is the first to document changes in the oxidative status in birds that persistently drink saltwater, and shows that they undergo several physiological adjustments that range that range in scale from biochemical capacities (e.g., TAC and MDA) to whole organism traits (e.g., metabolic rates). We propose that the physiological changes observed in Z. capensis acclimated to saltwater could be common phenomena in birds and likely explain selection of prey containing little salt and habitats associated with low salinity.

Testing the niche variation hypothesis in a community of passerine birds

The niche variation hypothesis (NVH) predicts that populations with broader niches should exhibit greater between-individual diet variation or individual specialization (IS) relative to populations with narrower niches. Most studies that quantify population niche widths and associated levels of IS typically focus on a single or few species, but studies examining NVH in a phylogenetically informed comparative analysis among species are lacking. Here we use nitrogen isotope (δ15 N) analysis to measure population niche widths and IS in a single bird community composed of 12 passerine species representing different foraging guilds. We found support for the NVH at the interspecific level; species with broader population niche widths were comprised of more individual specialists. Moreover, our results suggest that this relationship is influenced by foraging guild; specifically, omnivores have higher degrees of IS for a given population niche width than insectivores. Finally, the levels of IS among passerine species, in contrast to population niche width, were associated with their relatedness, suggesting that the potential phylogenetic effect on the prevalence of IS is higher than previously recognized.