2.4 Indicators
In general, by mapping genetic diversity within and between populations
we can identify populations with particularly low levels of genetic
diversity in relation to other populations of the same species, and/or
populations that appears isolated from other population at one point in
time. Mapping data can thus tell us something about the genetic status,
but monitoring over time is needed to understand if the observations are
temporally stable.
To quantify changes in genetic diversity over time we used three
indicators suggested for national monitoring and management of genetic
resources in aquatic environments in Sweden (Johannesson & Laikre,
2020). We also applied the three indicators proposed for the CBD context
by Laikre et al. (2020) and elaborated by Hoban et al. (2020, 2021b) and
Laikre et al. (2021; Figure 2). These indicators are pragmatic and
designed to be applicable at a global scale by all nations with
indicators 1 and 2 possible to apply using proxies in the absence of
genetic data (Figure 2; Hoban et al., 2020, 2021b; Laikre et al., 2021).
The three indicators suggested by Johannesson & Laikre (2020) all
represent application of proposed CBD indicator 3 (Figure 2) – i.e.
they are based on genetic data. They have only been presented in Swedish
(a peer-reviewed report to SwAM; Johannesson & Laikre, 2020), so we
present those indicators in more detail here. Indicator 1, denotedΔH, reflects changes of within population genetic
diversity, measured as changes in expected heterozygosity
(H E) between two points in time (Figure 3). Other
measures of intrapopulation genetic diversity are also considered in
this indicator such as potential changes in observed heterozygosity
(H O), allelic richness
(A R), number of alleles per locus
(N A), and proportion of polymorphic loci
(P L).
Indicator 2 concerns the effective population size,Ne , and is quantified
for single isolated populations, subpopulations within metapopulations,
full metapopulations, or for species with a continuous distribution for
subareas over the distribution range (cf. Hoban et al., 2021b).
Indicator 3 is used to monitor between population genetic diversity. We
call this indicator ΔFST and it
quantifies the change of genetic differentiation among populations
between points in time. It applies to systems of more or less
genetically connected populations. However,ΔFST also addresses the degree of
population retention over time (Figure 3).
Clearly, there is overlap and close connection between the CBD
indicators and the Swedish
national indicators (Figure 2). All national indicators represent
application of CBD indicator 3 and all national indicators provide
information that can be used feed into CBD indicators 1 and 2 (Figure
2). It should be noted that none of these indicators explain the
underlying causes of potential changes of within and between population
genetic diversity. They only inform about change, and depending on the
degree of detected change (below; Figure 3) they call for more or less
rapid measures to investigate what the causes are.