Study population
Our study population consisted of 519 koalas that were monitored between
2013 and 2017 as part of a management program associated with a 13km
rail infrastructure project in Moreton Bay Council, Queensland,
Australia (area centroid: -27.234°; 153.036°), and described in detail
in . During the five-year program, most of the population
(>95% of individuals in the study area) was intensively
monitored. Individuals were first captured between 13/03/2013 and
02/02/2017 using either live traps or flagging pole methods, and were
fitted with VHF collars. After their first capture, individuals were
then periodically re-caught at least every six months for routine
veterinary exams, or earlier if they were observed with visible signs of
disease (see below) or injury. Tissue samples were taken and ear tags
fitted at first capture, and blood samples were taken during routine
veterinary examinations, at first capture and at subsequent check-ups.
Blood samples were stored at -20°C, and tissue samples were stored in
70% ethanol. Individuals were given a comprehensive veterinary
examination each time they were caught, which included recording of sex,
age, and presence of a joey (offspring) for females (either through the
female having a back-riding or pouch joey or an elongated teat, or
through a pregnancy observed by sonogram). Ageing of koalas relied on
examination of their tooth wear . They were then tested for the presence
of chlamydia bacterium and inspected for visible signs of chlamydial
disease (see below for full details). During the project, individuals
were treated for any illness (including chlamydial disease, see below)
or injury, and some individuals were also included in a chlamydia
vaccination trial, which involved a subset of individuals being
vaccinated for chlamydia at their first capture (see ). VHF tracking of
individuals took place approximately twice a week. By identifying the
time of the year in which joeys were born, and accounting for the
gestation period (one month), based on the birth of 350 joeys between
2013 and 2016, we determined the breeding season to occur from September
to December in this population. The analyses presented here used data
from those individuals for which we had complete genetic, spatial and
disease status data (described below), a total of N = 342. The dataset
included some joeys (N = 4), because dependent joeys have been found to
be infected by chlamydia as young as nine months old (Nyari et al. 2017)
and the youngest dependent joey sampled in this survey was 10 months
old.
The monitoring program was conducted under animal ethics approvals
(Queensland Department of Agriculture and Fisheries CA 2012/03/597, CA
2013/09/719, CA 2014/06/777, CA 2015/03/852, and CA 2016/03/950) and
scientific purposes permits (Queensland Department of Environment and
Heritage Protection WISP 11525212, WISP 16125415, WISP 13661313, WITK
14173714 and WISP 17273716).