3. Drivers of island arthropod speciation
Traditional approaches to speciation research typically analyse a
limited number of species with great detail, necessitating accurate
estimation of population and phylogenetic histories, and the limitations
of single-locus markers for such purposes are well recognized (e.g.
Bazin, Glémin, & Galtier, 2006; Toussaint et al., 2015). However it has
been shown that, across multi-species comparisons, potentially
idiosyncratic single marker signals within a subset of arthropod species
may be outweighed by common community level signatures (e.g.
Salces-Castellano et al., 2020; Scalercio et al., 2020). As the
histories of individual species complexes may themselves be
idiosyncratic, having noisy data across hundreds or even thousands of
species may, in some cases, be more revealing of general patterns and
processes in a region than deeper sequencing of a more limited number.
With the ability to now obtain reliable haplotype-level data from
metabarcode sequence output (Andújar et al., 2021), it is possible to
implement both multiplex barcode and wocDNA metabarcoding to explore
both the patterns and drivers of diversification and speciation across
arthropod assemblages. Andújar et al. (2022, this issue) demonstrate the
implementation of such a metaphylogeographic approach with wocDNA
barcoding to understand the relative roles of ecological and
geographical drivers for diversification among soil arthropods within a
single oceanic island. Extending such an approach across multiple
islands within archipelagos can provide baseline data on the relative
importance of ecological and geographical speciation within many as yet
largely unstudied fractions of arthropod diversity. When contrasted with
existing data for plants, vertebrates, and more easily studied
invertebrate groups, a fuller understanding of: (i) dispersal dynamics
within and among islands; (ii) the role of environment in structuring
genetic variation within species, and; (iii) their implications for
speciation, will emerge. Recent work also demonstrates how a single
locus community-level approach can inform about the relative importance
of specific traits for diversification within islands (Salces-Castellano
et al., 2021). In conjunction with barcode reference libraries with
trait data (e.g. body size, dispersal ability, niche) multiplex
barcoding and wocDNA metabarcoding can be used to scale up both
geographic and taxonomic sampling to identify functional traits
associated with arthropod diversification within and across island
systems.