Figure captions:
Figure 1. a) Number of Daphnia studies that examine geographic, ecological and non-ecological isolating barriers, associated with the type of method used in the study. The height of the bar indicates the total number of studies in the group, while the width of each line represents the number of studies corresponding to geographic, ecological or non-ecological isolating barriers. Each line is coloured by the type of study: experimental (red), genetic (blue), or phylogenetic (green) evidence. b) The number of geographic, ecological/ non-ecological studies that examine multiple species pairs in the subgenus Ctenodaphnia , Daphnia , or species pairs in the species complex level.
Figure 2. The maximum likelihood phylogeny of the genusDaphnia based on mitochondrial markers 12S rRNA, 16S rRNA, and cytochrome oxidase subunit I (COI) obtained from Adamowicz and colleagues (2009). The subgenera Daphnia , Ctenodaphnia , and Australodaphnia are shown in black bars on the right. Mitochondrial markers were individually aligned using CLUSTAL-W (Thompson, Higgins, & Gibson, 1994), trimmed, and concatenated into a 1737 nt alignment. A best fit GTR model and partitioning scheme was estimated using PartitionFinder2 (Lanfear, Calcott, Kainer, Mayer, & Stamatakis, 2014). Phylogeny reconstruction was based on RAxML-ng (Kozlov, Darriba, Flouri, Morel, & Stamatakis, 2019) with convergence at 500 bootstrap replicates. Bootstrap support is indicated at the nodes. Indicated in arrows at the nodes are the possible intracontinental splits, and labels in red show the species capable of intercontinental dispersal. Branch colours signify the geographic distribution of each species: North America (red), Eurasia (blue), South America (green), Australia (orange), Africa (purple), Tibet (pink), Antarctica (grey).
Figure 3. Strengths of the components of reproductive isolation (RIi ) plotted against divergence time (Mya) based on metrics from Sobel and Chen (2014) from 17 experimental studies. We show the relationship of reproductive isolation against divergence time for (a) prezygotic reproductive isolating barriers, and (b) postzygotic reproductive isolating barriers. Divergence time estimates were based on mitochondrial markers (Table 2).