FOOD CONSUMPTION AND ENERGY ASSIMILATION IN THE CABRERA VOLE MICROTUS CABRERAE (RODENTIA)

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FOOD CONSUMPTION AND ENERGY

ASSIMILATION IN THE CABRERA VOLE

MICROTUS CABRERAE (RODENTIA)

S Santos, M Klunder, M Mathias

To cite this version:

S Santos, M Klunder, M Mathias. FOOD CONSUMPTION AND ENERGY ASSIMILATION IN THE

CABRERA VOLE MICROTUS CABRERAE (RODENTIA). Vie et Milieu / Life & Environment,

Observatoire Océanologique - Laboratoire Arago, 2004, pp.27-30. �hal-03217985�

FOOD CONSUMPTION AND ENERGY ASSIMILATION

IN THE CABRERA VOLE MICROTUS CABRERAE (RODENTIA)

S. SANTOS

_{, M. KLUNDER}

_{, M.L. MATHIAS}

Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

2_{Department of Tropical Nature Conservation and Vertebrate Ecology, Wageningen University,}

Bornsesteeg 69, 6708 PD Wageningen, The Netherlands Corresponding author: mmathias@fc.ul.pt

RODENTIA MICROTINE MICROTUS CABRERAE FOOD CONSUMPTION ENERGY INTAKE

ABSTRACT. – Energy intake was studied for the first time in Cabrera voles (Mi-crotus cabrerae Thomas, 1906). Experiments were carried out between June and September. Under a composite diet of carrots, apples, corn and sunflower seeds, average food consumption was 4.88 g dry mass/day, which was equivalent to 75.95 kJ/day (1.82 kJ/g/day). This corresponded to 11.7% of vole’s body mass. Vo-les defecated around 0.36 g dry mass/day or 6.65 kJ/day (0.16 kJ/g/day). Digestibi-lity values averaged 92.50% of dry matter and 91.15% of energy.

RODENTIA MICROTINAE MICROTUS CABRERAE INGESTION ÉNERGIE INGÉRÉE

RÉSUMÉ. – L’énergie ingérée par le Campagnol de Cabrera, Microtus cabrerae (Thomas, 1906) a été étudiée pour la première fois. Pour un régime alimentaire composite de carottes, de pommes, de blé et de graines de tournesol, la moyenne de la nourriture consommée a été de 4,88 g poids sec/jour, soit l’équivalent de 75,95 kJ/jour (1,82kJ/g/jour). Ces valeurs correspondent à 11,7 % du poids du corps du Campagnol. Les déjections représentent 0,36 g de masse sèche/jour ou 6,65kJ/jour (0,16 kJ/g/jour). Les valeurs de digestibilité atteignent 92,50 % de ma-tière sèche et 91,15 % en énergie.

INTRODUCTION

The Cabrera vole (Microtus cabrerae Thomas, 1906) is an endemic and threatened species (Cabral et al. 1990, Blanco & González 1992), distributed over the supra and mesomediterranean bioclimatic zones of the Iberian Peninsula (Rivas-Martinez 1981), from Central Portugal to the Iberian Prepyrenees (Ventura et al. 1998, Mathias 1999). This vole is one of the less known rodents in Eu-rope. Available literature on the species is very scarce, except for a few studies on its distribution (e.g. San Miguel 1992, Mathias 1999), biology (Fernández-Salvador 1998, Ventura et al. 1998, Fernández-Salvador et al. 2001) and population dy-namics (Landete-Castillejos et al. 2000). In partic-ular, no data have ever been published on the en-ergy requirements of Cabrera voles, and on the relationships between digestible energy or nutrient availability and the amount of food intake.

The present study, which is part of a larger one on the energetics of the Cabrera vole, provides the first information on the daily energy intake of non-reproductive adults, measured under experi-mental conditions. We are hoping that the mea-sures on the species basic physiological needs can

be used as indicators in indirectly assessing adapta-tion of voles to their habitat.

MATERIALS AND METHODS

Nine adult non-reproductive voles (five females and four males) were captured in Alentejo, Central Portugal, between June and September 2001, in two different sites: Alandroal (38º40’N, 7º23’W) and Grândola (38º05’N, 8º35’W), both associated to temporary watercourses. At capture, body mass of voles ranged from 32.9 to 55.4 g (43.0±6.8 g).

Voles were housed in individual cages (0.41×0.30× 0.20 m) under natural light conditions and natural am-bient temperature, averaging 24 ºC during the period of captivity. A composite diet, including carrot, apple, corn and sunflower seeds in weight proportions of respective-ly 3:3:1:1, and water ad libitum were provided throug-hout this period. Food items selection was based on preferences of voles, as judged by previous studies on bait attraction (S Santos, unpubl data, J Ventura pers comm).

At the beginning of experiments voles were weighed (to an accuracy of 0.1g) and received water and food in excess. The following day, and repeatedly for six conse-cutive days, at the same hour, voles were reweighed,

uneaten food and faeces were collected and weighted, and fresh food was again supplied in excess. Afterwards, the uneaten food and faeces were dried at 60 ºC to cons-tant weight (24 h) and then samples were combusted in a semi-micro adiabatic calorimeter PARR 1425 for the calculation of energy contents, according to the standard techniques described in the PARR reference manual. This procedure allowed the estimation of the energy consumption (C), the energy loss in faeces (F) and the coefficient of digestibility [D=(C-F)/C×100] (e.g. Woo-dall 1989, Veloso & Bozinovic 1993, Speakman & McQueenie 1996). Energy assimilation [A=C – (F+U)] was also calculated considering 3% of energy loss in urine (U) (Grodzinski & Wunder 1975).

Water percentage in food items was calculated through the relation between fresh and dried food, while the amounts of protein and fiber were obtained from food composition tables (Ferreira & Graça 1977, Hol-land et al. 1991, HolHol-land et al. 1992). Although different food composition tables may indicate distinct values for the same measure, values are here included mainly as in-dicators of the relative differences in food consumption.

Differences between intakes of food items were as-sessed by one-way ANOVA and least significance diffe-rence tests (LSD) for post-hoc comparisons, while differences in water percentage between food items were assessed by a Kruskal-Wallis non-parametric test. The relationship between food intake and food contents was tested by the Pearson correlation coefficient (Sokal & Rohlf 1995).

All feeding experiments were carried out from June to September. Each vole was tested within a period up to 14 days since capture. All specimens were released at the end of experiments.

RESULTS

Cabrera voles consumed differently the four items available in terms of food mass (F=4.21, p<0.05). Apple was more consumed than corn (p<0.05) and sunflower seeds (p<0.01), and carrot was preferred to sunflower seeds (p<0.05). In aver-age, the most consumed items were apple and car-rot and the less consumed were corn and sunflower seeds (Table I), although among individuals a marked variability in the intake of corn and sun-flower seeds has occurred. There were no signifi-cant differences in energy consumption among the items ingested (F=1.46, p>0.05). In addition, no significant changes in individual body mass were recorded during experiments (paired t test, t=–0.62; p>0.05).

A significant positive correlation was found be-tween dry mass intake and water content of food (n=36, r=0.510, p<0.05), while a significant nega-tive correlation was found with protein (r=–0.48, p<0.05) and fiber contents (r=–0.41, p<0.05), indi-cating that the most consumed food items con-tained more water (H=36.00; df=3; p<0.0001) and less protein and fiber (Table I).

During the 6-day feeding experiment, average daily food consumption was 75.95 kJ/day (1.82 kJ/g/day). Voles defecated 6.65 kJ/day (0.16 kJ/g/day). The coefficient of food digestibility amounted in aver-age to 92.50%, in terms of dry matter, and to

28 S. SANTOS, M. KLUNDER, M. L. MATHIAS

Table I. – Mean values of dry mass (g/day), energy intake (kJ/day) and contents of water (%), protein and fiber (g/100 g of food) of food items consumed by Cabrera voles (minimum and maximum values within brackets).

91.15%, in terms of energy. Energy assimilation was 67.22 kJ/day (1.61 kJ/g/day) (Table II).

DISCUSSION

Most consumed food items by voles were, in general terms, rich in water and poor in protein and fiber.

Daily food intake of Cabrera voles, maintaining constant body mass, represented 11.7% of body mass. Derting & Bogue (1993) reported a food in-take of 15% of body mass in non-reproducing M. pennsylvanicus. Similarly, Gross et al. (1985) re-ferred a corresponding value of 11% in M. ochrogaster fed with a high-quality diet (low fiber) at favourable ambient temperature, a value increas-ing to 19% when a low-quality diet (high fiber) is offered instead, while under a high-fiber diet and at low temperatures, food intake increased to 33% of voles mass, suggesting the influence of both energy availability (diet quality) and energy needs (cold exposure) on rates of food intake.

Furthermore, values of digestibility measured were 92.50% and 91.15% for dry matter and en-ergy, respectively, which are clearly above the range values (52.4%-73.7%) reported for wild M. cabrerae under a natural low-quality diet, mostly constituted by leaves and stems of grasses and ana-lyzed from May to December (Soriguer & Amat 1988). However, values are similar to those found in Microtus pinetorum fed on a low-fiber diet of apples – 91.6% (dry matter) and 90.1% (energy) (Servello et al. 1983). Identically, Gebczynski & Gebczynska (1984) found values of 89.2% of di-gestibility in M. subterraneus fed on oat grain, car-rot and parsnip and Yahav et al. (1988) referred to values of 95.6% of dry matter digestibility in xeric populations of the subterranean mole rat Spalax ehrenbergi, fed on carrots.

Increased digestibility may also allow conserve water (e.g. Kronfeld & Shkolnik 1996). This mech-anism may be relevant during summer, when the availability of preferred food and water are ex-pected to decrease.

Considering that 3% of the energy digested was loss in urine (Grodzynski & Wunder 1975), energy assimilation in M. cabrerae averaged around 3xRMR – resting metabolic rate at the lower limit

of the thermoneutral zone (approximately 33.5 ºC): 1.13 ml O₂/g/h (0.55 kJ/g/day) – in association with a conductance value of 0.16 ml O2/g/h/ºC

(Mathias et al. 2003). In many rodents, costs of maintenance are referred as twice or three times the basal metabolic rate (e.g. Wunder 1985), which means that energy requirements of Cabrera voles fall within these standard values. However, RMR at thermoneutrality is low while conductance is high, in comparison with other rodents, confirming a physiological ability of voles for both energy and water economy in a mediterranean environment characterised by high ambient temperatures and drough during the summer (e.g. Yahav et al. 1988, Veloso & Bozinovic 1993, Mathias et al. 2003 and references therein).

ACKNOWLEDGEMENTS. – Authors are indebted to A C Nunes for laboratory support and to C Figeiredo and M J Santos for fieldwork assistance. Thanks are also due to A Almeida and M Alfredo of the Laboratório Marítimo da Guia (Faculty of Science of Lisbon) for facilities in obtaining calorimetric data. This work was partly deve-loped under the Internship of MK in the Centro de Biolo-gia Ambiental (Faculty of Science, University of Lisbon), supported by the University of Wageningen and the Dutch Government.

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Reçu le 10 juin 2003; received June 10, 2003 Accepté le 16 janvier 2004; accepted January 16, 2004