ALTITUDINAL EFFECTS ON ENERGY ACQUISITION ABILITY IN A SMALL MAMMAL (Phyllotis xanthopygus, Rodentia: Muridae)

PAOLA L. SASSI

Ottawa

Congreso; 1st Joint Congress on Evolutionary Biology; 2012

ALTITUDINAL EFFECTS ON ENERGY ACQUISITION ABILITY IN A SMALL MAMMAL (Phyllotis xanthopygus, Rodentia: Muridae) Paola L. Sassi  Biodiversity Investigations Group GIB, IADIZA, Mendoza - CONICET, Argentina. psassi@mendoza-conicet.gob.ar Physiological ecology provides the framework to study the diversity of responses of organisms to the environment. Desert mammals have been models for different investigations in this field, in the search for adaptive traits. This study addresses physiological traits relevant for the ability of P. xanthopygus to acclimate to spatial and temporal variability in the arid highlands of Argentina. This species presents a wide distribution along the Andes Mountains. A broad temperature and rainfall gradient affects vegetation resources, that in addition to the species’ small size and herbivorous habits, imply possible trade-offs in its energetic and nutritional balance. The objective of this study was to test for differences in ability for acquisition of dry matter by populations of P. xanthopygus across an altitudinal cline. Hypothesis:digestive strategies that maximize nutritional balance are favored by natural selection. P. xanthopygus would display a plastic response in resource-acquisition traits to face environmental variability, with high altitude populations being more efficient. Study area: Central Andes, Mendoza, Argentina. Individuals were collected at three sites along an altitudinal transect: 1750, 2300, and 3100 m a.s.l. Variation in dry matter intake (DMI) and digestibility (DMD) among 10 individuals from each altitude was analyzed. Measurements were taken under three experimental treatments: at 25ºC when arrived from the field, after two-month acclimation to 25ºC, and after two-month acclimation to 16ºC. Factorial ANOVA was used to analyze data (body weight as covariable).The results show no effect of altitude, while effects of experimental treatment on DMI (F=29.9, d.f.=2, p<0.01) and DMD (F=6.32, d.f.=2, p<0.01) were significant. Interactions between altitude and treatment were significant for DMI (F=9.37, d.f.=4, p<0.01) and DMD(F=3.37, d.f.=4, p<0.05). Altitudinal trends varied among treatments, revealing population-specific strategies. Under the inertia of each origin site’s conditions, data suggest different compensatory responses in the species at different altitudes. With acclimation to less challenging temperature conditions (25ºC), intake decreased and digestibility pattern changed. After acclimation to cold conditions (16ºC), adjustment responses were evident in mid and low altitude populations, resulting in a completely different pattern. In conclusion, there are at least partially fixed attributes to deal with energy trade-offs, that vary among populations according to the site they inhabit and could be due to local adaptation or ontogeny. In any case, the species shows a plastic strategy covering the high variation in ecological conditions along the altitudinal cline under study. Our results contribute to explain the great range of distribution of P. xanthopygus, and pose it as a good model to investigate potential responses to environmental changes. This study was financially supported by Agencia Nacional de Promoción Científica y Tecnológica (PICT 2010-0892, PICT 25778) and Consejo Nacional de Investigaciones Científicas y Técnicas.