During summer the brown long-eared bat Plecotus auritus (Vespertilionidae)
forms stable colonies, comprised of both adult females and males and young
of the year. A long-term ringing study conducted in north-east Scotland has
established that little movement occurs among colonies and that both sexes
are recruited into their natal colony. The aim of the present study was to
investigate, using microsatellite DNA markers, if genetic structure within
the population reflects the spatial structure indicated by ringing. Inter-
colony F(ST)estimates obtained for all colony members, and for females and
males separately, were low (0.019, 0.026 and 0.011, respectively), but all
values differed significantly from zero. These data indicate high gene flow
between colonies, although some coancestry among colony members is evident
in both sexes. On combining the ringing and genetic data, it is concluded
chat gene flow occurs via extracolony copulation, rather than natal dispers
al, and that each colony behaves as a distinct subpopulation. Microgeograph
ical genetic isolation by distance was demonstrated for, to our knowledge,
the first time in a bat species, and found to be apparent both across the e
ntire study area and along one river valley. The results suggest that exten
sive macrogeographical population genetic structure may be evident across t
he species' range.