Study subjects and fecal sample collection.

We collected 35 fecal samples and 29 blood samples over 3 months between November 2021 and January 2022 from captive koalas (the largest koala population outside Australia) living in the Guangzhou Chimelong Safari Park in China (23°00′N, 113°33′E). A controlled environment with a temperature range of 15 to 26°C and a relative humidity range of 40 to 70% was used to keep all koalas. The koalas shared the same assigned diet. Various forms of data, such as identification, sex, body mass, reproductive status, and food information, were gathered for each sample taken from captive koalas. A total of 35 fecal samples were collected from different ages, sex, living environments, and reproductive states captive koalas. These groups included subadults (1 to 3 years old, 5 females and 4 males, n = 9), adults (4 to 7 years old, 5 females and 5 males, n = 10), older animals (9 to 13 years old, 5 females and 5 males, n = 10), and lactating females (3 to 7 years old, n = 6). Fecal samples were transported at 4°C and kept at −80°C in the lab until DNA extraction was performed. We collected 29 blood samples from different-aged animals, including subadults (1 to 3 years old, n = 9), adults (4 to 7 years old, n = 10), and aged animals (9 to 13 years old, n = 10). To prevent causing stress in lactating female koalas, we did not collect blood from them. Portions (500 to 1,000 μL) of blood were collected and stored at 4°C until RNA extraction and cDNA synthesis on the same day. This study was performed in accordance with the protocols of the Chimelong Safari Park and South China Agriculture University.