31.3. Acclimation to hydric stress in birds: A field and a laboratory study

31.3. Acclimation to hydric stress in birds: A field and alaboratory study

Sabat, P.Departamento deCiencias Ecológicas, Universidad deChile, Chile

psabat@uchile.cl

Carbon stable isotope ratios can be used as indicators of diet(marine vs. terrestrial) and as indirect indices of the salt loadsexperienced by birds consuming marine and terrestrial inverte-brates. We compared the carbon isotopic composition andosmoregulatory capacities of field caught individuals of fiveCinclodes (Passerine, Furnariidae) species in Chile. Thedifferences in carbon isotopic composition among these specieswere paralleled by differences in osmoregulatory character-istics. Birds consuming marine invertebrates exhibits moreconcentrated blood plasma and produce more concentrate urinein the field. We also investigated latitudinal variation in therenal traits that mediate how these birds cope with dehydrationand a salty marine diet. The species increased the incorporationof terrestrial carbon, as measured by 13C, as terrestrialproductivity increased southwards. The osmoregulatory traitsof both species varied with latitude as well. Urine's osmolalitydecreased from extremely high values in the north to moderatevalues in the south. In both species, the proportion of kidneydevoted to medullary tissue decreased from north to south, andkidney size increased significantly with latitude. Variation in thereliance on marine food sources at inter- and intraspecific scaleseems to be accompanied by adjustments in the osmoregulatorymechanisms used by these birds to cope with salt anddehydration. However, differences in kidney morphologyalong the gradient may be the result of phenotypic plasticityor population differentiation. Hence, we investigated theresponse of three Cinclodes species to acclimation experimentsto two regimes of salinity for 15 days. Our results indicate thatspecies of Cinclodes are able to modify the proportion ofmedullary tissue and the Umax. The effect of exposure to fresh-or saltwater on medullary size, however, was relatively small(22%) and smaller than the differences found along theextremes of the latitudinal gradient and among species(120%). These experiments suggest that phenotypic flexibilityin adult birds is unlikely to explain all the variation in renal traitsobserved along the latitudinal gradient and among Cinclodesspecies. However, we cannot yet discount the possibility thatexposure to different environments during early developmentcontributes to latitudinal variation in renal traits.

doi:10.1016/j.cbpa.2007.06.334

31.4. Diet and energetics in mammals: Phenotypic integrationand flexibility

Cruz-Neto, A.Department of Zoology, UNESP – Rio Claro, SP, Brazil

neto@rc.unesp.br

The food-habit hypothesis attempts to explain in an evolu-tionary time-scale the effects of diet quality, availability andpredictability on basal metabolic rate (BMR). Albeit attrac-tive, there are several problems and ambiguities in the resultsthat attempted to test this hypothesis. Ambiguities surround-ing diet categorization and the use of coarse classificationsbased on aridity or continuous measures of climate variablesof the species' habitat of origin as a proxy to infer theproductivity of the habitat can potentially confounds inter-pretations from interspecific analysis of the food-habithypothesis. Finally, and superimposed on these problems,interspecific analysis, by assuming that species are fixedentities, neglect the role played by phenotypic flexibility inproviding a fine-tuned adjustment of BMR to changes in dietquality, availability of predictability. In this review, I willpresent three intraspecific studies carried out with bats,rodents and marsupials where specific aspects of the food-habit hypothesis were tested. Such studies, besides solvingsome of the problems mentioned, allow for direct analyses ofhow BMR changes as a function of diet quality, availabilityand predictability and, thus, may provide a more thoroughtest of this hypothesis. These results also shows thatrelationship between diet quality and BMR at the proximatelevel can not be easily predicted from interspecific analysis,as the outcomes depends on a complex integration of thephenotypic plasticity observed in behavioral, morphologicaland physiological traits.

doi:10.1016/j.cbpa.2007.06.335

31.P1. Gut size flexibility in laboratory mice and rats: A meta-analysis

Naya, D.E., Karasov, W.H., and Bozinovic, F.Pontif ícia Universidad Católica de Chile, Chile

dnaya@bio.puc.cl

Gut flexibility has been suggested as one of the mostimportant physiological adjustments to changes in environ-mental conditions. Here we demonstrate, through a quantita-tive review of the evidence for laboratory mice and rats, thatgut length flexibility is highly significant for adjustment topregnancy, lactation, and change in diet quality, while gut drymass flexibility is highly significant for adjustments to thesefactors plus changes in environmental temperature. Inagreement with previous ideas, we observed that lactationcauses larger adjustments in small intestine size than doespregnancy and adjustment to lower temperature. We alsodemonstrate that flexibility in hindgut length is greater forchange in diet quality than it is for changes in energydemanding factors such as pregnancy and low environmentaltemperature. In addition, we found a clear positive relation-ship between the amount of increase in small intestine size

S133Abstracts / Comparative Biochemistry and Physiology, Part A 148 (2007) S132–S137