Molecular diet studies of water mites reveal prey biodiversity

Abstract

Water mites are diverse aquatic invertebrates that provide potentially important ecosystem and economic services as bioindicators and mosquito biocontrol; however, little is known about water mite digestive physiology, including their diet in nature. Water mites, much like their spider relatives, liquefy their prey upon consumption. This results in the absence of morphologically identifiable prey in water mite mid-gut. Previous studies have reported associations in the field of water mites with presumed prey and laboratory observations of water mites feeding on specific organisms offered for ingestion; however, the present work aims to determine what water mites have ingested in nature based on molecular studies of gut contents from freshly collected organisms from the field. To elucidate water mite prey, we used next-generation sequencing to detect diverse cytochrome oxidase I DNA barcode sequences of putative prey in the guts of 54 specimens comprising two species of Lebertia and a few specimens of Arrenurus (2) and Limnesia (1). To our knowledge this is the first molecular study of the diets of water mites as they feed in nature. While the presence of chironomid DNA confirmed previous observations of midge larvae as part of the diets of Lebertia, we also found the DNA of diverse organisms in all four species of water mites, including the DNA of mosquitoes in 6 specimens of Lebertia and a large number of previously unknown prey, especially from oligochaete worms. These studies thereby reveal a greater diversity of prey and a potentially broader significance than previously appreciated for water mites in aquatic food webs. Molecular studies like this can detect water mite predators of mosquito larvae and add knowledge of water mite predatory contributions to freshwater food webs.

Improved Chironomid Barcode Database Enhances Identification of Water Mite Dietary Content

“…Adult chironomid flies were collected from bushes and other structures-such as spider webs, surfaces of cars, boats, leaves and buildings-with 250 µm mesh sweep nets directly into vials containing either isopropanol or ethanol. We sampled for water mites from Blue Heron Lagoon, Detroit, MI, using a 250 µm circular net followed by washing on a 250 µm sieve and preservation in ethanol, as described in Vasquez, Mohiddin, Li, Bonnici, Gurdziel and Ram [15]. Specimens were transported to the laboratory for morphological identification.…”

“…The keys of Townes [23], Saether [24], Saether [25], Epler [26], Dendy and Sublette [27], Cranston et al [28], Roback [29], and Heyn [30] were used. Water mite genera studied for this work were Lebertia, Limnesia and Arrenurus and were the same specimens described in Vasquez, Mohiddin, Li, Bonnici, Gurdziel and Ram [15].…”

“…For water mites, a sterile minutien pin was used to puncture each water mite. The mites were then transferred to lysis buffer, where DNA was extracted using the Qiagen DNeasy kits similarly to the chironomid extraction-with the exception that the water mites were lysed overnight rather than homogenized-to more completely extract the DNA from the gut of the punctured water mite, as described in Vasquez, Mohiddin, Li, Bonnici, Gurdziel and Ram [15]. For chironomid specimens, DNA barcodes were generated by PCR as reported in Failla, Vasquez, Hudson, Fujimoto and Ram [18], amplifying the COI gene (658 bases in length) with the Folmer primers [19].…”

“…The PCR products were sequenced using Sanger sequencing by Genewiz company (South Plainfield, NJ, USA). For water mites, COI barcodes were generated using Folmer primers to verify the mite identity and a second set of primers (modified mLEP and Folmer LCOI primers, which amplify insect sequences but not arachnids (and hence are able to amplify chironomid sequences but not the DNA from the water mite host)) [15]. The mLEP:FolmerLCOI primer set amplifies a somewhat shorter (332 bases) region of the COI gene than the Folmer primers and were modified with adapters for next-generation sequencing on a MiSeq V2 Illumina platform at the Michigan State University RTSF Genomics Core, as described by Vasquez, Mohiddin, Li, Bonnici, Gurdziel and Ram [15].…”

“…However, the DNA of ingested organisms, like chironomids, remains sufficiently intact so that their DNA sequences can be detected up to 24 h after ingestion [14]. Application of next-generation sequencing (NGS) to analyze DNA fragments of ingested prey in water mites freshly collected from the field revealed many chironomid taxa as prey items [15]. The identification of the species level of many of these prey organisms was difficult because many reference sequences in barcode databases were not identified for chironomids beyond generic or family-level classification.…”