4.7 Further developments of indicators
For the indicator ΔH, recommendations for threshold values are
based on the general guideline of retention of 95% heterozygosity over
100 years (Allendorf & Ryman, 2002). It should be noted, however, that
this guiding principle refers to short term genetic conservation and may
need to be revised for long term genetic resilience. Further, detecting
changes of the magnitude proposed – i.e. a reduction of 5% over 100
years – can be statistically challenging. Sampling over extended
periods (several generations) is warranted, but even then, it may be
difficult to obtain a reasonable statistical power for detecting
statistically significant changes.
Further work is needed to refine the indicators. The statistical power
for detecting various levels of heterozygosity change from typically
used sets of markers are needed. Also, N eestimation in non-isolated populations is complex. For instance, no
method for assessing inbreeding effective population size
(N eI) from genotypic data is currently available
for structured populations. In such situations, different types ofN e differ - N eV andN eLD reflect inbreeding rates of local population
in isolation, but fail to provide estimates of inbreeding rates for
populations in the face of migration (Ryman et al., 2019). If we are
able to sample a full metapopulation with all subpopulations at
proportions reflecting their contribution to the total system, we can
use N eV to get a good estimate of inbreedingN eI. However, if we fail in identifying the full
metapopulation, estimates of N eV will
underestimate the N eI of the metapopulation
(Ryman et al., 2019). As discussed above, we do not think we have been
able to completely identify all subpopulations in the present case.
Further, to implement the ΔF ST indicator we used
the simplifying assumption of an island model in migration-drift
equilibrium to translate temporal changes of F STamong subpopulations into migration rates. Clearly, important future
work includes investigating the effects of violating this assumption.
The limiting values used here are also highly subjective, and it is
unclear if they are sufficient to detect biologically important changes
of connectivity. A temporal aspect of the change is also missing. The
national indicators are now being applied to more species in Sweden
including herring, cod, salmon, and eelgrass (Maria Jansson, SwAM, pers.
comm.) and this work will provide more empirical information that can
aid in modifying and improving the indicators and limiting values
applied for them.