Ying-Yi Ho

Date of Award


Degree Type


Degree Name

Doctor of Philosophy




Dr. Brock Fenton


Group living is widespread among animals. Theory predicts that animals should aggregateifthebenefitsassociatedwithgrouplivingoutweighthecosts. Benefits associated with group living could arise passively (e.g. aggregate independently to exploit a patchily distributed resource) or actively (e.g. cooperation).

Some forest-dwelling bat species switch roosts frequently, but maintain an association among specific individuals, and therefore are fission-fusion societies, the temporary splitting ofcolonies into several subgroups. Normally, movements between alternative roosts are costly. Fission-fusion societies might overcome the costs by providingbenefitsassociatedwithlargesubgroupsizeorcooperation. Inaddition, sociality could influence the movements of individuals within and between social groups andaffectthegeneflow. However,ourunderstandingabouttheunderlyingcausesand effects of fission-fusion behaviour is still lacking.

I used both direct behavioural observation and indirect molecular analysis to study the roosting behaviour and sociality of Myotis formosus. In my study area, M.

formosus used two different types of day roosts in summer, houses and foliage, which wereextremelydifferentinavailability,permanency,andspace. Ifoundtheroosttype affected roosting behaviour of bats. In general, roost switching frequency of foliage­ roosting Myotis formosus was high and associated with intrinsic and environmental factors. Myotisformosus in large subgroups switched roosts less frequently than those living in smaller subgroups. Bats were faithful to specific roosting areas, and the nonrandom association between individuals indicated that they live in a fission-fusion society and switched roosts to enhance social interaction. Reproductive status also


affected the association pattern and roost switching frequency offoliage-roosting M. formosus while the similarity in genetic relatedness or matrilineal relationship did not

facilitateassociationbetweenindividuals. Benefitsassociatedwithcooperationor clustering as well as female philopatry are possible reasons for the fission-fusion society ofM.formosus. Themoleculardatabasedonthecontrastedpatternfoundfromthe biparentally inherited nuclear microsatellite markers and maternally inherited mitochondrial DNA markers also suggest that gene flow between colonies is male- mediated, while females appeared to show high fidelity to a small roosting area. Behaviourally, the male-mediated gene flow among bat colonies might occur by male dispersal and/or mating outside the colony, including swarming sites, hibernacula, or on the migration route. However, the details about the mating ofthis species are still unknown



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