Beyond the Holarctic comfort zone: Thermoregulation in a Sundaland Rodent

Expedition Dates:  May 31 – August 11, 2019

Field Team Members:

Ana M. Breit1,2, Tal Kleinhause-Goldman Gedalyahou3, Khairul Ikhwan4, Marcellinus Isaac Stia Dominic4, Andrew Alec Tuen4, Danielle L. Levesque 1,2

1 School of Biology and Ecology, University of Maine, USA

2 Climate Change Institute, University of Maine, USA

3 Department of Wildlife, Fisheries and Conservation Biology, University of Maine, USA

Institute of Biodiversity and Environmental Conservation, Universiti Malaysia- Sarawak

Expedition Location:   Sarawak, Malaysia


Expedition Funding: 

Maine Space Grant Consortium graduate summer fellowship to AMB and UMaine start-up funding to DLL.


Project Overview:

Endothermy, the ability to regulate body temperature through internal heat production, evolved in mammals in the tropics under warm and humid conditions. Yet, most thermophysiological research has been done in temperate zones and despite the immense biodiversity of the Indo-Malayan region, biological studies in the area have been scarce and the physiology of the local fauna is understudied. While the Indo-Malayan region contains 954 mammalian species, to our knowledge, only 21 peer-reviewed studies have been published. This imbalance contributes to the already-skewed representation in physiological data, where the bias towards taxa with a Holarctic distribution can lead to incorrect conclusions. In addition to adjusting the misconceptions of thermoregulation that result from biased research, the legacy of our Holarctic approach could have repercussions on how we interpret climate change risk for tropical species. Although the polar regions are warming faster than anywhere else on earth, equatorial regions are predicted to experience a 0.3-4.4° increase between 2081 and 2100. The effect of these fluctuations on animals could be dire, as they are adapted to relatively steady temperature regimes due to the low seasonality of temperature in the tropical regions.

Photo of Field Site in Mount Singai.
Figure 1: A view from our field site on the slopes of Mount Singai.

In 2019 we returned to Borneo to study the body temperature regulation of tropical mammals. Borneo, the world’s third-largest island, is considered one of the most biologically diverse places in the world. This equatorial island is home to an estimated 282 mammals, 44 of which are endemic. Located directly over the equator, this island is located in the center of Sundaland, a biodiversity hotspot with a complex biogeographical history. During the Pleistocene glacial periods, Sundaland was a continuous continental landmass due to lower sea levels, allowing periodic species migrations. Today, the partial submersion of Sundaland divides the region in the Malay peninsula and the islands of Sumatra, Java, Sulawesi, and Borneo. Borneo has a relatively constant climate, with the photoperiod fluctuating by only 17 minutes over the course of the year. Additionally, Borneo has slight seasonality: a wet season generally spanning from November to March, and a dry season spanning from April to October. Generally, conditions are hot and humid (29°C-34°C, 70%-85% humidity.)

Equatorial Borneo.
Figure 2: The warm, humid climate of equatorial Borneo fosters dense jungle habitat for an abundance of endemic species.

My objective was to quantify the thermal profile of the nocturnal murid rodent, Sundamys muelleri, by acquiring accurate subcutaneous temperatures and resting metabolic rate measurements at a range of set ambient temperatures. These data were then used to determine the lower critical and upper critical temperatures, beyond which they would need to expend more energy to maintain stable body temperature. We predicted that the small and nocturnal S. muelleri should have similar metabolic rates to other small mammals, and maintain lower body temperatures compared to diurnal tropical mammals We also expected the Sundamys rats to be more thermally flexible than small mammals found at higher latitudes.

Photo of nocturnal rat.
Figure 3: A nocturnal Sundamys muelleri rat caught in a locally-made trap placed on the jungle floor.

Data Collection

In collaboration with Dr. Andrew Alec Tuen from the local Univeristi Malaysia-Sarawak, we set up our field lab in the  Bidayuh community forests of Kampung Tanjong Bowang (1.505°N, 110.154°E) in the district of Bau, Sarawak, Malaysia. There, we stayed with our gracious hosts, Lucia Upang and her family, where they run a weekend café for people climbing Mt. Singai. The jungle at the base of Mt. Singai is a secondary agroforest used for hiking and hunting.

Photo of Ribuo Uong Cafe.
Figure 4: Ribuo Uong Café in the village of Kampung Tanjong Bowang caters to hikers of Mount Singai.


Photo of Ribuo Uong Cafe.
Figure 5: Ribuo Uong Café is run by Lucia Upang and her family, where she serves homecooked meals made from fruits and vegetables from her garden.

Together with two Unimas students, we set transects of traps throughout the local rainforest and baited each trap with a slice of pineapple or banana. We caught nocturnal species in the morning after the traps had been left open overnight. When we caught our species of interest, the Sundamys rat, we would take the individual back to our field lab and conduct flow-through respirometry. Respirometry is the measurement of the rate of oxygen used and carbon dioxide and water vapor produced by an individual that can then be used to calculate metabolic rate. By conducting respirometry experiments across a range of ambient temperatures and calculating the corresponding metabolic rates, we were able to find the lower critical temperature of the thermoneutral zone of Sundamys rats. Below the lower critical limit of between 32°C and 33°C, we found rats increased their metabolic rate,  evaporative water loss, and thermal conductance (the inverse of insulation).

Transects of traps set in forest.
Figure 6: Transects of traps were set off the trail through the forest. Each trap was baited with either banana or pineapple and left open overnight.


Photo of respirometry station.
Figure 7: Our respirometry station was set up in our local field laboratory, where Sundamys rats were put in a temperature-controlled chamber and their rates of oxygen consumption and carbon dioxide expiration were measured during their rest phase before being released back at their capture site.


Group photo of research members.
Figure 8: This project was a collaboration between the University of Maine and the Universiti of Malaysia Sarawak.
Back row: Marcellinus Isaac Stia Dominic, Gertrude Upang, Lucia Upang, and Dr. Andrew Alek Tuen.
Front row: Khairul Ikhwan, Ana Breit, Tal Kleinhause-Goldman Gedalyahou, and Babai the dog.


Photo fo Kuching, Malaysia
Figure 9: Kuching, the capital of Sarawak, Malaysia.