Body condition is a metric that ecologists and conservation biologists often use to assess the amount of energy reserves an animal has. An individual in good body condition is thought to have more energy reserves, like fat, than one with a poorer body condition. This metric – body condition – is valuable because it directly influences an animal’s survival and reproductive potential. It has also been found to relate to numerous aspects of animal biology and ecology, including being associated with foraging success, advantageous behaviour, increased immune function, and the ability to persist in physiologically challenging environments. Thus, knowledge of body condition and how it impacts a species’ fitness can aid current and future conservation efforts.

There are a few common ways to study body condition; each with their own advantages and disadvantages. Sometimes we use measures of the overall body length and weight of an animal and compare the relationship between these measurements to others from the population to approximate the amount of fat reserves they have (i.e., body condition indices). Yet, the use and suitability of this method for amphibians is questionable, as their weight can change drastically over short periods depending on their level of hydration. This means that body condition indices based on an amphibian’s weight are often an inaccurate way to quantify energy reserves. An alternative is measuring body composition, which involves measuring the amount of fat, lean muscle tissue, and water that makes up an animal’s body. This is a much more direct measure of an individual’s fat reserves. Traditionally, this has required the animal to be euthanized, and then a series of chemical methods are used to measure the various tissues; a process known as chemical carcass analysis (CCA). However, there is a new, non-lethal technology being used to quantify an animal’s energy reserves without these issues, called Quantitative Magnetic Resonance (QMR). The QMR works on the same basic principle as an MRI machine, but instead of generating a picture – like what you’d see in a hospital – this machine simply provides readings on how much fat, lean muscle mass, and water are in the individual. But, a limitation of this method is that QMR machines were originally built for mammals and medical research.

Yet, this method is being applied more and more in wildlife ecology and conservation. In this study, we are testing to see whether using a QMR machine, a non-invasive way to measure body composition, is a viable method for amphibians. Specifically, we studied mole salamanders (Ambystoma maculatum and A. laterale) and American toads (Anaxyrus americanus). Before being used to study new taxa, the QMR method requires validation and potentially calibration against traditional measures of body composition quantification, like CCA. So, in this study, after scanning each amphibian specimen in the QMR machine (these specimens were donated from other studies across Canada to minimize our impact), we then also completed CCA so that we can compare the measures of fat, lean, and water mass between the new and traditional methods. From this comparison, we can then assess whether this novel method accurately measures the body composition of amphibians.