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Worth a Thousand Words

This week’s featured PLoS ONE image is taken from an article entitled, ECG Response of Koalas to Tourists Proximity: A Preliminary Study, by Yan Ropert-Coudert of the Institut Pluridisciplinaire Hubert Curien, France, and colleagues in Australia and Japan.

Koalas (Phascolarctos cinereus) are listed by the IUCN as a vulnerable species and their distribution is now limited to the east of Australia. In their study, Ropert-Coudert and colleagues measured the physiological response (heart rate and autonomic nervous system) throughout the day of three female koalas and studied the effects of tourists approaching them from a boardwalk at the Koala Conservation Centre in Victoria, Australia.

This image forms Figure 2 of PLoS ONE article e7378; any reuse should cite the authors and journal.
This image forms Figure 2 of PLoS ONE article e7378; any reuse should cite the authors and journal.

They attached a mini electrocardiogram (ECG) recorder to each koala, externally, and recorded the heart rate of each animal between 1 PM to 6 PM (“day”) and 6 PM to 10 PM (“evening”). One of the animals (Nemo) was kept in a tourist-free area, while the other two (Crimson and Nugget) were in separate exhibit areas where they could be approached from a boardwalk by tourists.

The image is Figure 2 from the published paper and shows the heart rates of Crimson (red), Nugget (orange) and Nemo (blue), averaged every 5 minutes (dots) over the whole recording periods. The arrows show the time when an experimenter walked around the trees of Crimson and Nugget. Of note is the substantial change in heart rate around 6:30 PM for all three.

The results suggest that the presence of tourists has a non-negligible effect on the koalas’ metabolic activity despite them not showing external signs of weariness. The researchers found evidence of a circadian rhythm in the koalas’ cardiac activity with a synchronised change in the average rate and variability of the heart rate of the animals occurring at the end of the afternoon, which corresponds to the fact that koalas tend to be mainly inactive during the day and show peak of activities (usually for feeding) between 5 PM and 12 AM.

Ropert-Coudert and colleagues conclude that more research is needed to determine whether the presence of tourists increases the average heart rate of koalas—for example, by comparing the heart rate of each koala both throughout a day spent in the display area and one spent in a tourist-free area, although ethical and logistical factors prevented a larger sample size here. Similarly by measuring stress hormone levels, future research could help to quantify the stress imposed by tourist proximity.

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