Data from: Demographic collapse and low genetic diversity of the Irrawaddy dolphin population inhabiting the Mekong River

In threatened wildlife populations, it is important to determine whether
observed low genetic diversity may be due to recent anthropogenic pressure
or the consequence of historic events. Historical size of the Irrawaddy
dolphin (Orcaella brevirostris) population inhabiting the Mekong River is
unknown and there is significant concern for long-term survival of the
remaining population as a result of low abundance, slow reproduction rate,
high neonatal mortality, and continuing anthropogenic threats. We
investigated population structure and reconstructed the demographic
history based on 60 Irrawaddy dolphins samples collected between 2001 and
2009. The phylogenetic analysis indicated reciprocal monophyly of Mekong
River Orcaella haplotypes with respect to haplotypes from other
populations, suggesting long-standing isolation of the Mekong dolphin
population from other Orcaella populations. We found that at least 85% of
all individuals in the two main study areas: Kratie and Stung Treng, bore
the same mitochondrial haplotype. Out of the 21 microsatellite loci
tested, only ten were polymorphic and exhibited very low levels of genetic
diversity. Both individual and frequency-based approaches suggest very low
and non-significant genetic differentiation of the Mekong dolphin
population. Evidence for recent bottlenecks was equivocal. Some results
suggested a recent exponential decline in the Mekong dolphin population,
with the current size being only 5.2% of the ancestral population. In
order for the Mekong dolphin population to have any potential for
long-term survival, it is imperative that management priorities focus on
preventing any further population fragmentation or genetic loss, reducing
or eliminating anthropogenic threats, and promoting connectivity between
all subpopulations.