title: iDNA from terrestrial haematophagous leeches as a wildlife surveying and monitoring tool - prospects, pitfalls and avenues to be developed.
abstract: Invertebrate-derived DNA (iDNA) from terrestrial haematophagous leeches has recently been proposed as a powerful non-invasive tool with which to detect vertebrate species and thus to survey their populations. However, to date little attention has been given to whether and how this, or indeed any other iDNA-derived data, can be combined with state-of-the-art analytical tools to estimate wildlife abundances, population dynamics and distributions. In this review, we discuss the challenges that face the application of existing analytical methods such as site-occupancy and spatial capture-recapture (SCR) models to terrestrial leech iDNA, in particular, possible violations of key assumptions arising from factors intrinsic to invertebrate parasite biology. Specifically, we review the advantages and disadvantages of terrestrial leeches as a source of iDNA and summarize the utility of leeches for presence, occupancy, and spatial capture-recapture models. The main source of uncertainty that attends species detections derived from leech gut contents is attributable to uncertainty about the spatio-temporal sampling frame, since leeches retain host-blood for months and can move after feeding. Subsequently, we briefly address how the analytical challenges associated with leeches may apply to other sources of iDNA. Our review highlights that despite the considerable potential of leech (and indeed any) iDNA as a new survey tool, further pilot studies are needed to assess how analytical methods can overcome or not the potential biases and assumption violations of the new field of iDNA. Specifically we argue that studies to compare iDNA sampling with standard survey methods such as camera trapping, and those to improve our knowledge on leech (and other invertebrate parasite) physiology, taxonomy, and ecology will be of immense future value.
authors.affiliation: Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark ; Center for Zoo and Wild Animal Health, Copenhagen Zoo, Frederiksberg, Denmark.
authors.forename: Ida Bærholm
authors.initials: IB
authors.lastname: Schnell
authors.affiliation: Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany ; Department of Forestry and Environmental Resources, North Carolina State University, North Carolina, Raleigh USA ; Present address: US Forest Service, Pacific Southwest 17 Research Station, 1731 Research Park Drive, Davis, CA 95618 USA.
authors.forename: Rahel
authors.initials: R
authors.lastname: Sollmann
authors.affiliation: Epidemiology of highly pathogenic microorganisms, Robert Koch Institute, Berlin, Germany.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Calvignac-Spencer
authors.affiliation: Sackler Institute of Comparative Genomics and Division of Invertebrate Zoology, American Museum of Natural History, New York, USA.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Siddall
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, UK ; State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan China.
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Yu
authors.affiliation: Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wilting
authors.affiliation: Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark ; Trace and Environmental DNA Laboratory, Department of Environment and Agriculture, Curtin University, Perth, Western Australia Australia.
authors.forename: M Thomas P
authors.initials: MT
authors.lastname: Gilbert