Molecular diet studies of water mites reveal prey biodiversity

may feed on oligochaetes [37]. The present study showed highly diverse oligochaete sequences including many whose percent identities to known sequences in GenBank are less than 90% (see Figs 3B and 3C); these sequences could potentially represent new previously unidentified or cryptic species. Erseus et al. [38] have suggested that morphospecies with intraspecific COI barcodes differing by > 9% are likely to comprise cryptic species. We interpret this to mean that we have scarcely scratched the “benthic surface” in understanding the full extent of varia- tion and diversity among oligochaete species in Blue Heron Lagoon and that the study of water mite diets may be an excellent method for discovering oligochaete diversity and unravel- ling benthic food web trophic dynamics. The ingestion of chironomids, cladocerans, and oligochaetes in the diet of water mites may be in direct competition with fish, of which many secondary consumers favor these small invertebrates as part of their diets. Previous studies showed that various species of water mites can reduce the standing crop of chironomids by 50% [6] and to equal the amount of predation of cladocerans by fish [9]. By far, the most abundant prey item found in Lebertia water mites was chironomids. We also show that Lebertia preys on two cladocerans namely Chydorus bre- vilabris (see Fig 6D, preyed by L. quinquemaculosa) and Diaphanosoma (see Fig 6A and 6E, preyed by both L. davidcooki and L. quinquemaculosa). Cladoceran Chydorus brevilabris is a

species complex with high biodiversity that is an important food source for many aquatic organisms [39]. This is just one of several prey items our study has identified which play key roles in food web dynamics. One of the crucial questions that arise from our study. Could Lebertia and other water mites be adding to the top down effect on zooplankton prey availability? This paper also demonstrates seasonal changes in the occurrence of the two Lebertia species in Blue Heron Lagoon and differences between the two water mite species in their diets (see Fig 8 and S1 Table). Differences between the diets of L. quinquemaculosa and L. davidcooki may reflect seasonal differences in the presence of the two species of Lebertia and prey avail- ability. Most specimens of L. quinquemaculosa (15 out of 20) were collected in October and November 2016, while 20 out of 29 specimens of L. davidcooki were collected from February to April 2017, and only four of Lebertia sp. were collected in October and November 2016. The partial allochrony of these two species may be the mechanism by which these two sympatric species survive in the same geographic area. The quantitative and qualitative differences in both species of Lebertia (significant differences in proportions of chironomids and oligo- chaetes and appearance of ostracod Podocopida respectively) may be another mechanism enabling this sympatric relationship. We have previously noted that significant seasonal differ- ences in richness and diversity of water mites in Blue Heron Lagoon may occur as an adaptive

response to an intermediate seasonal disturbance [20]; maintenance of sympatry may be another explanation for these seasonal variations. Sympatry may also be maintained by the size difference between the two Lebertia species as predator size (see Fig 1) may mediate niche partitioning among various prey choices [20]. The novel observation that adult Lebertia prey upon mosquito larvae is supported by both laboratory experiments (Fig 2) and molecular data (Fig 4). The observed mosquito species, Culex pipiens, is a known vector of West Nile virus [40]. Both species of Lebertia were shown here to ingest C. pipiens, but as a percentage of the sequences and of all specimens examined, the amount of C. pipiens in their diets is low (Fig 7). However, Blue Heron Lagoon is less than ideal habitat for mosquitoes, which favor fish-free stagnant waters [41], compared to the lentic habitat but nevertheless wind-affected fishery habitat. An important study, which we have started, is to test the effect of Lebertia water mites or other water mite genera found in tempo- rary pools where mosquitoes are generally found [12]. As opportunistic feeders, Lebertia in Blue Heron Lagoon may simply not have had many mosquito larvae to choose from compared PLOS ONE Prey DNA diversity in water mites PLOS ONE | https://doi.org/10.1371/journal.pone.0254598 July 29, 2021 14 / 18