Student Research – Misha Rowell

Melomys

Misha Rowell – Bachelor of Science (Honours) at James Cook University.

Exploring the nexus between environment, emotion and spatial cognition; a test using Melomys Cervinipes.

The Wet Tropics is a world heritage biodiversity hotspot. However, human pressures and environmental change is increasing and animals are predicted to be highly impacted by these novel, unpredictable conditions. The ability of an animal to cope with changed environments is reliant on the complex interactions between behaviour and physiology, which collectively impacts spatial navigation abilities.

Over nine months, I investigated the influence of changed microclimatic conditions on the anxiety behaviour, physiology and spatial cognition of a native Australian tropical rainforest rodent, the fawn-footed melomys (Melomys cervinipes). I observed 20 males that were collected from the rainforest surrounding James Cook University, Cairns in the Wet Tropics World Heritage area. These males were allocated to two environmental treatments, namely simple (no access to climbing equipment and only standard rodent food) and complex (access to climbing equipment and high quality food). I tested males in an open field test and a modified Barnes maze to determine if anxiety and spatial cognition were impacted by the environmental conditions in which the animals were housed. I also assessed whether environmental conditions impacted the physiology of individuals, as behaviour and cognition are, to a large extent, also driven by the individual’s physiology. I measured blood concentrations of two hormones, namely corticosterone and dopamine, both of which are known to impact behaviour and cognition. Corticosterone is mobilised after exposure to stress and dopamine is linked with reward-seeking and motivation. I also measured glucose concentrations as corticosterone mobilises glucose to provide energy for behavioural expression. These hormones were measured at a basal level before allocation to environmental treatments and again after acclimation for 5 days in the environmental treatment. After testing and blood collection, males were then randomly allocated to either remain in their same treatment (complex:complex or simple:simple) or were switched to the opposite environmental category (complex:simple or simple:complex). This allowed me to test for the effect of prior experience and length of time in an environmental category. Testing and blood collection was then repeated.

Melomys2

Melomy by Misha Rowell

I found that individual M. cervinipes housed in a complex environment, which allowed them to express natural behaviours, were initially more bold than males housed in a simple environment. However, over time, environmental treatment had no effect on anxiety, suggesting males were habituating to the open field. Interestingly, in the short-term, I found no effect of environmental treatment on cognition (memory and motivation). However, increasing time spent in the simple environment, or switching from a complex to a simple environment, impacted memory retention and motivation to escape. While environmental treatment did not appear to impact corticosterone, dopamine or glucose concentrations in a predictable manner, individuals with higher concentrations of dopamine appeared to demonstrate greater motivation to escape. This is the first study to investigate the interactions between micro-environmental changes, physiology, behaviour and cognition in a wild species. In addition, this is one of the first studies to systematically test spatial cognition in an Australian mammal.

Interestingly, my results provide further support for a decoupling of behavioural and physiological traits, and suggest that M. cervinipes may be capable of coping with short-term, small-scale environmental change. This provides an interesting avenue for future research to understand what may occur when changes are of a larger magnitude or longer duration.

The novelty of this study, and the findings, provide us with a greater understanding of the complex relationships between environmental conditions, physiological mechanisms, and behavioural and cognitive responses.

Student funding was released by the Skyrail Rainforest Foundation for the purpose of rainforest research, preservation and education.