Genetic differentiation and historical demography of wood stork populations in brazilian wetlands

Wood stork, Mycteria americana (Linnaeus 1758), is a key bioindicator of environmental changes and an effective target for conservation-directed monitoring in wetlands where it inhabits and reproduces. We investigated past and contemporary levels of genetic diversity, genetic differentiation and demographic processes in wood stork populations from two major wetlands in Brazil, using nine microsatellite loci and a 237-bp fragment of mtDNA. Amapá populations (northern region) showed slightly higher levels of genetic diversity than Pantanal populations (central-western region) and both populations had a low number of effective breeders. Assignment tests, F-statistics, AMOVA and Bayesian clustering analyses suggested ongoing gene flow among colonies within regions, but significant differentiation between regions. Bayesian coalescent analyses based on both markers indicated that the northern population exchanged migrants with unsampled populations, and that the central-western population was founded by individuals from the north. Mitochondrial estimates revealed that the timing of population divergence broadly overlapped the Last Glacial Maximum (LGM; ~20,000 YBP) and that the central-western population expanded more recently. The results support that the coastal wetlands in northern Brazil remained stable enough to shelter large wood stork populations during the LGM, and that the storks colonized freshwater wetlands in the central-western region following deglacial warming. Conservation policies should consider Amapá and Pantanal wood stork populations as genetically differentiated units and priority should be given to Amapá populations which represent the source gene pool. Continuous genetic monitoring of wood storks could help detect signs of demographic trends that could reflect alterations or degradation in wetlands.