Monitoring genetic diversity with new indicators applied to an alpine freshwater top predator

Genetic diversity is the basis for population adaptation and long-term
survival, yet rarely considered in biodiversity monitoring. One key issue
is the need for useful and straightforward indicators of genetic
diversity. We monitored genetic diversity over 40 years (1970-2010) in
metapopulations of brown trout (Salmo trutta) inhabiting 27 small mountain
lakes representing 10 lake systems in central Sweden using >1200
fish per time point. We tested six newly proposed indicators; three were
designed for broad, international use in the UN Convention on Biological
Diversity (CBD and are currently applied in several countries. The other
three were recently elaborated for national use by a Swedish
science-management effort and applied for the first time here. The Swedish
indicators use molecular genetic data to monitor genetic diversity within
and between populations (indicators ΔH and ΔFST, respectively) and assess
the effective population size (Ne-indicator). We identified 29 genetically
distinct populations, all retained over time. Twelve of the 27 lakes
harbored more than one population indicating that brown trout biodiversity
hidden as cryptic, sympatric populations are more common than recognized.
The Ne indicator showed values below the threshold (Ne≤500) in 20
populations with five showing Ne<100. Statistically significant
genetic diversity reductions occurred in several populations.
Metapopulation structure appears to buffer against diversity loss;
applying the indicators to metapopulations suggest mostly acceptable rates
of change in all but one system. The CBD indicators agreed with the
Swedish ones but provided less detail. All these indicators are
appropriate for managers to initiate monitoring of genetic biodiversity.