Molecular diet studies of water mites reveal prey biodiversity

were abundant in both species, albeit in higher proportion in L. davidcooki (median = 89% of sequences) than in L. quinquemaculosa (median = 47%; Fig 5A). Conversely, oligochaete sequences (Fig 5B) were present more often in the mite L. quinquemaculosa (17 of 20 animals; median = 47% of sequences) than in L. davidcooki (10 of 29 animals; median = 0%). Even for the ten specimens of L. davidcooki with measurable oligochaete DNA the median abundance was only 5%, much lower than for L. quinquemaculosa. A preliminary statistical analysis of these data using the non-parametric Mann-Whitney test indicated that the higher percentage of chironomids in the diet of L. davidcooki v. L. quin- quemaculosa and oligochaetes in the diet of L. quinquemaculosa v. L. davidcooki was signifi- cant (p<0.00001 for both comparisons). However, this difference might be attributable to seasonal differences in the presence of the two species of mites and their prey. As illustrated in Fig 8, L. quinquemaculosa accounted for 90% of the Lebertia specimens collected in the fall of 2016 but only 15% of the Lebertia collected in late winter and early spring 2017 (significantly different from L. davidcooki, p<0.0001, Fisher exact test). Due to unequal variances in the dis- tribution of prey organism sequences in their diets, a parametric test was inappropriate. Analy- sis of the data using Yuen’s method [31], (with Winsorized standard errors and symmetric Fig 7. Histograms of frequency of percent abundances of sequences. (A) chironomid, (B) oligochaete, and (C) mosquito (Culex pipiens)

OTUs in 20 L. quinquemaculosa (Lq, black bars) and 29 L. davidcooki (Ldc, white bars). The frequency of “no mosquito sequence” (bin “0”, not shown in (C)) was 16 L. quinquemaculosa and 27 L. davidcooki. Bins are 10% wide for A & B, 1% wide for C. Abundances are significantly different between L. quinquemaculosa and L. davidcooki for chironomids (p<0.00001, Mann-Whitney U test) and oligochaetes (p<0.00001, Mann-Whitney U test) but not mosquitoes (p>0.05). https://doi.org/10.1371/journal.pone.0254598.g007 Fig 8. Seasonal distribution of water mite species and the percent abundances of sequences of (A) chironomid and (B) oligochaete in 20 L. quinquemaculosa (Lq, orange points) and 29 L. davidcooki (Ldc, blue points). Some points are not visible where others are superimposed on them. Differences over time analyzed by the seasonal Mann-Kendall test for trend were significant for oligochaetes in L. quinquemaculosa (p = 0.031) but not for other comparisons. In (A) L. davidcooki had a higher percentage of chironomid sequences than L. quinquemaculosa (Yuen’s test, p = 0.00001). In (B), L. quinquemaculosa had a higher percentage of oligochaete sequences than L. davidcooki (Yuen’s test, p = 0.0002). https://doi.org/10.1371/journal.pone.0254598.g008 PLOS ONE Prey DNA diversity in water mites PLOS ONE | https://doi.org/10.1371/journal.pone.0254598 July 29, 2021 12 / 18