Data from: Contrasting patterns of population structure at large and fine scales in an avian disturbance specialist of braided river ecosystems

Aim: To understand the population structure and its potential drivers at
different spatial scales in a migratory bird, the black-fronted tern
(Chlidonias albostriatus); a specialist of the spatially and temporally
dynamic environments of braided rivers. Location: New Zealand Methods: We
used a three-pronged approach based on 17 microsatellites, two
mitochondrial loci (cytochrome b / control region), and phenotypic data
(head-bill length, bill depth, wing length, weight). We determined
large-scale genetic structure throughout the whole breeding range (approx.
150,000 km2), calculated genetic divergence of breeding populations, and
tested for isolation-by-distance between populations. We investigated the
level of fine-scale genetic structure based on spatial autocorrelation
analyses and assessed the presence of a body size cline based on
phenotypic data. Lastly, we compared phenotypic divergence (PST) and the
level of divergence by genetic drift (FST) among breeding populations to
test for underlying mechanisms of population differentiation. Results:
Nuclear and mitochondrial DNA showed that across their range black-fronted
terns were effectively panmictic, with low genetic divergence between
breeding colonies overall and no isolation-by-distance. However, at fine
geographical scales black-fronted terns accrued significant genetic
structure for distances up to 75 km, primarily driven by males, indicating
more frequent female dispersal. Furthermore, a phenotypic cline in
accordance with Bergmann’s rule was evident. PST exceeded FST in three
traits, suggestive of local adaptation. Main conclusions: Significant
fine-scale structure can be present in highly mobile, specialist species
while not affecting spatial structures at larger scales. Hence,
methodologies applied to both whole landscapes and local scales are
important to appropriately estimate connectivity in dynamic
metapopulations and investigate the processes behind connectivity.
Conservation management will need to include protecting currently
uninhabited patches to facilitate natural colonisation of suitable
habitat. For black-fronted terns, managing whole catchments throughout the
entire breeding range would be preferable to managing single patches.