Results:
Most of the 104 time-series (i.e. 96) were composed of sequences having
mainly been sampled in inland locations rather than in coastal
environments, suggesting that sequences from dispersal-limited
populations (i.e. living in different inland water bodies) may have been
sampled at the considered spatial scale. The median number of
independent drainage basins sampled across time-series was 3, ranging
from 0 (for Sebastes auriculatus andCoryphopterus
venezuelae, the only two strictly marine species; Table A1) to 15 (forSqualius cephalus , a common freshwater species in European
watersheds; Table A1 and Figure A1-C for an example). Overall, most fish
time-series (84/104) grouped sequences sampled at locations situated
within at least 2 different drainage basins, hence resulting in
time-series representing non-biologically-meaningful groups of sequences
originating from potentially non-interbreeding,
demographically-independent populations.
The median number of different sampling locations per time-series
was high (12), with a quite variable range (between 3-98 different
locations). This, combined with the variable number of locations sampledper year, and the variable, but generally low number of sequences
sampled per year and per year per location across
time-series (see Table A1) illustrates the scattered nature of samples
in the time-series included in Millette et al. (2020). Figure 1 in the
main text, as well as Figure A1 A-D below, provide visual examples of
the spatial distribution of sequences for five time-series. For
instance, for Astyanax bimaculatus (see Figure A1 A below),
sequences sampled at locations situated within 11 different
South-American drainage basins (including the Amazon and the Orinoco
river basins) were pooled together. This example, and all other examples
in Figure A1 A-D, also show that the clustering algorithm used to build
‘populations’ in Millette et al (2020) may result in ‘daisy chaining’,
with sequences from locations far greater than the considered clustering
distance (here, 1,000 km) being grouped together.
Finally, the time-span covered by time-series in years was low (7.9
years), and represented an average of just 2.2 generations for the 33
species with generation time estimates available in FishBase, which is
an insufficient time-span for most evolutionary changes in IGD.