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.