4.2 Metabarcoding without taxonomic identification
Metabarcoding can provide ecological information even if reference
databases are not available, as molecular taxonomic units can allow the
comparison of communities among sites with environmental differences (Jiet al. 2013; Apothéloz-Perret-Gentil et al. 2017). The
taxonomy-free approach allows overcoming the fact that, despite
intensive efforts, databases remain incomplete for many taxa (Fig. 3).
Primers with high taxonomic coverage and resolution are essential also
in this case. High taxonomic coverage is needed to avoid
under-representation of some taxa, while resolution allows teasing apart
related taxa. Related taxa can have very different ecological
properties, and some widespread taxa, tolerant to human disturbance, can
be closely related to highly sensitive specialists (Caro et al.2005). Therefore, ecological responses of communities can remain
obscured if metabarcodes are not able to resolve related taxa with
different ecology. Our study focused on European taxa, where taxonomic
knowledge is particularly good (Moustakas & Karakassis 2005; Rodrigueset al. 2010; Brewer et al. 2012) and, with targeted
studies, we could envisage an improvement of database completeness in
the next years. However, our results on primer performance can be also
useful in megadiverse, tropical areas, where taxonomy-free biomonitoring
can be a viable option (Andersen et al. 2019).