Evaluating body condition in small mammals

Abstract

Body condition (energy reserves) can have important fitness consequences. Measuring condition of live animals is typically done by regressing body mass on measures of body size and using the residuals as an index of condition. The validity of this condition index was evaluated by determining whether it reflected measured fat content of five species of small mammals (yellow-pine chipmunks (Tamias amoenus Allen), bushy-tailed wood rats (Neotoma cinerea Ord), deer mice (Peromyscus maniculatus Ord), red-backed voles (Clethrionomys gapperi Vigors), and meadow voles (Microtus pennsylvanicus Ord)). We also determined whether body water could predict fat content, enabling the use of hydrogen-isotope dilution for estimating condition. For all five species, condition estimates weakly predicted fat content and more accurately predicted variation in lean dry mass and water content. The relationship between body water and fat content was inconsistent among the five species, discouraging against the general use of isotope dilution in these animals. Although ecologically important, these indices are best interpreted as explaining variation in all constituents of body composition.Résumé : La condition physique (réserves énergétiques) peut avoir une influence importante sur le fitness. La mesure de la condition physique d'animaux vivants se fait généralement par une régression de la masse du corps en fonction de mesures de la taille du corps, les résidus servant de coefficient de condition. La validité de ce coefficient de condition a été évaluée en déterminant s'il reflète bien le contenu lipidique mesuré chez cinq petits mammifères (le Tamia amène (Tamias amoenus Allen), le Néotoma à queue touffue (Neotoma cinerea Ord), la Souris à pattes blanches (Peromyscus maniculatus Ord), le Campagnol-à-dos-roux de Gapper (Clethrionomys gapperi Vigors) et le Campagnol des champs (Microtus pennsylvanicus Ord). Nous avons également tenté de déterminer si le contenu hydrique du corps permet de prédire le contenu lipidique, ce qui justifierait l'utilisation d'une dilution des isotopes d'hydrogène pour estimer la condition physique. Chez les cinq espèces, les indices de la condition physique se sont révélés des indicateurs mé-diocres du contenu lipidique; ils permettent toutefois de prédire plus exactement la masse du corps sans les graisses, la masse sèche et le contenu en eau. La relation entre le contenu hydrique et le contenu lipidique n'est pas la même chez les cinq espèces, ce qui nous empêche de recommander la méthode de dilution des isotopes chez ces animaux. Malgré leur intérêt écologique, c'est comme facteurs explicatifs de la variation de toutes les composantes du corps que ces indices semblent le plus utiles.[Traduit par la Rédaction] 1029Schulte-Hostedde et al.

Food provisioning alters infection dynamics in populations of a wild rodent

“…The effect of food supplementation on population density (F 3,28 foodÂtrapping occasion ¼ 6:80, p ¼ 0.001; figure 1) and growth rates (F 3,28 foodÂtrapping occasion ¼ 4:02, p ¼ 0.024; figure 2) changed with time. All populations declined in size from October until January.…”

“…Densities declined considerably in FþBþ populations in the initial two-week period following B. bronchiseptica introduction, while densities in the other treatment group remained relatively stable. Food supplemented populations, especially those without B. bronchiseptica introduction, increased in size during the latter two weeks (F 2,28 foodÂtrapping occasion ¼ 3:77, p ¼ 0.04; figure 1). Higher population growth rates were observed in FþB2 populations than in the other three treatment groups, and food supplementation similarly had an increasingly positive influence on population growth during the latter two weeks of the post-B.…”

“…Studentized residuals of a linear regression of body mass on head width were employed as an index of body condition [28]. Identity of the head width measurer was entered as a random factor in the model to adjust for possible systematic measurement error.…”

Body condition changes arising from natural factors and fishing gear entanglements in North Atlantic right whales Eubalaena glacialis

“…Body condition, a metric used to estimate relative energetic reserves, has been correlated with survival and reproductive success of both terrestrial (Young 1976, Schulte-Hostedde et al 2001) and marine mam -mals (Lockyer 1986, 1993, Pitcher et al 1998, Hall et al 2001, Pettis et al 2004, Rolland et al 2007b, Miller et al 2011 and is often used to assess and monitor the overall health of animal populations (Beck et al 1993, Gerhart et al 1996, Pitcher et al 1998, Bradford et al 2012, Williams et al 2013. In large whale species, energetic reserves are stored in, and mobilized from, the blubber layer, visceral tissues, and muscles (Lockyer et al 1985, Aguilar & Borrell 1990, Niaess et al 1998, and thus characteristics of these tissues, including thickness and chemical composition, are considered to be primary indicators of overall body condition (Lockyer et al 1985, Miller et al 2011.…”

Physiological Factors Affecting the Bactericidal Activity of the Western Fence Lizard (Sceloporus Occidentalis) for the Lyme Disease Spirochete, Borrelia Burgdorferi

“…With a larger sample size, we could have sampled lizards of much lower and higher body conditions, and possibly clarify the role of body condition in borreliacidal capacity. Recently, calculating body condition accurately in vertebrates has come into debate with many methods being described (Stevenson and Woods, 2006;Murphy et al, 1991;LeCren, 1951;Schulte-Hostedde et al, 2001, Garcia-Berthou, 2001). Peig and Green (2010) reviewed and provided critical comments on these methods, suggesting the use of a scaled mass index method because it accounts for the changing relationship between mass and length as body size changes and growth occurs.…”