DOI: 10.5061/dryad.q573n5tnn
title: An invasive appetite: Combining molecular and stable isotope analyses to reveal the diet of introduced house mice (Mus musculus) on a small, subtropical island

description: House mice (Mus musculus) pose a conservation threat on islands, where
 they adversely affect native species’ distributions, densities, and
 persistence. On Sand Island of Kuaihelani, mice recently began to
 depredate nesting adult mōlī (Laysan Albatross, Phoebastria immutabilis).
 Efforts are underway to eradicate mice from Sand Island, but knowledge of
 mouse diet is needed to predict ecosystem response and recovery following
 mouse removal. We used next-generation sequencing to identify what mice
 eat on Sand Island, followed by stable isotope analysis to estimate the
 proportions contributed by taxa to mouse diet. We collected paired fecal
 and hair samples from 318 mice between April 2018 to May 2019; mice were
 trapped approximately every eight weeks among four distinct habitat types
 to provide insight into temporal and spatial variation. Sand Island’s mice
 mainly consume arthropods, with nearly equal (but substantially smaller)
 contributions of C3 plants, C4 plants, and mōlī. Although seabird tissue
 is a small portion of mouse diet, mice consume many detrital-feeding
 arthropods in and around seabird carcasses, such as isopods, flesh flies,
 ants, and cockroaches. Additionally, most arthropods and plants eaten by
 mice are non-native. Mouse diet composition differs among habitat types
 but changes minimally throughout the year, indicating that mice are not
 necessarily limited by food source availability or accessibility.
 Eradication of house mice may benefit seabirds on Sand Island, but it is
 unclear how arthropod and plant communities may respond and change.
 Non-native and invasive arthropods and plants previously consumed (and
 possibly suppressed) by mice may be released post-eradication, which could
 prevent recovery of native taxa. Comprehensive knowledge of target
 species’ diet is a critical component of eradication planning. Dietary
 information should be used both to identify and to monitor which taxa may
 respond most strongly to invasive species removal and to assess if
 proactive, pre-eradication management activities are warranted.
description: House mouse metadata includes house mouse samples as rows and
 columns include data related to the date collected, location, and habitat
 type as well as the sex and age of each mouse specimen. The mouse metadata
 set contains data from mice captured on Sand Island from April 2018 to May
 2019. We used eight existing traplines across Sand Island to capture mice
 and account for differences in food source composition, availability, and
 accessibility. Each trapline consisted of five pre-baited traps with
 peanut butter and oats spaced 10 m apart, for a total of 40 traps
 (<em>n</em> = 40). We trapped mice across four habitat types:
 forest, herbland, shrub, and wetland. We conducted seven trapping
 sessions; each averaged 6.1 (± 0.7 SD) trapping days (or 5.1 ± 0.7 SD trap
 nights), and intervals between trapping sessions averaged 55.8 (± 15.0 SD)
 days. For each mouse captured, we determined sex (female, male, unknown),
 reproductive condition (if female), and age (juvenile, adult, unknown).
 Mice were humanely euthanized to remove colon contents and hair (which was
 collected from the lower abdomen area) in a sterilized lab setting. Colon
 samples were individually stored in vials of 70% isopropyl alcohol,
 labelled, and placed in a -20°C freezer until shipment to the mainland for
 further preparation; hairs were kept in dry, individually-sealed vials at
 room temperature. Mouse metadata includes information for 318 house mouse
 samples (both colon and hair samples) used for next-generation sequencing
 (NGS) and stable isotope analysis (SIA).<br>Molecular data includes
 house mouse fecal samples as rows and raw read counts of plant and
 arthropod ASVs as columns. Each column is an ASV, and the assigned
 taxonomy is included in the first row. Data have not been normalized by
 total read counts per sample. The ASV tables contain data from mouse fecal
 samples, from which DNA was extracted, amplified, and sequenced. DNA
 extraction, library preparation, pooling, and sequencing were performed at
 the University of Illinois at Chicago Genome Research Core within the
 Research Resources Center. For plant amplicons, DNA sequencing was
 performed on an Illumina MiSeq instrument employing V3 chemistry. For
 arthropod amplicons, DNA sequencing took place on an Illumina NovaSeq
 instrument owing to high host DNA amplification. Stable
 isotope data includes house mouse hair tissue samples as rows and the
 carbon and nitrogen elemental composition (C:N ratio) and carbon and
 nitrogen isotopes (δ13<sup>C</sup> and
 δ15<sup>N</sup>) data as columns. The stable isotope tables
 contain data from mouse hair and diet item samples. All samples were
 processed in isotope-ratio mass spectrometers (Delta Plus Advantage Mass
 Spectrometer and Delta Plus XL Mass Spectrometer, Thermo Fisher
 Scientific, Waltham, USA) at Northern Illinois University and the
 University of Tennessee – Knoxville to obtain carbon and nitrogen
 elemental composition (C:N ratio) and carbon and nitrogen isotopes
 (δ13<sup>C </sup>and δ15<sup>N</sup>).
description: <strong>For house mouse metadata</strong>: Variables
 include "SIA ID" and "NGS ID" (both of which identify
 a specific hair sample [for stable isotope analysis] and a colon sample
 [for next-generation sequencing]); "Scientific Name";
 "Order"; "Date Collected" (between April 2018 to May
 2019); "Sex" (male or female); "Age" (only adult);
 "Trap" (trap ID where mouse was captured); "Trapline
 ID" (trapline ID where mouse was captured); "Habitat" (one
 of four habitat types in which traplines were located: forest, herbland,
 shrub, wetland); "Trapping Session" (trapping session when mouse
 was captured: 1 through 7); "Latitude" and "Longitude"
 (coordinates of mouse capture). <strong>For ASV
 data</strong>: For plant ASVs, we filtered out all ASVs assigned to
 any phylum other than Streptophyta (land plants and all green algae except
 Chlorophyta). Similarly, for arthropod ASVs, we filtered out all ASVs
 assigned to any phylum other than Arthropoda. For both plants and
 arthropods, we used only ASVs identified at least to genus in subsequent
 analyses. Because these data include read counts per ASV by sample, we
 have included taxa here that did not pass our minimum read threshold to be
 included in further analyses. Data have not been normalized by total read
 counts per sample.  <strong>For stable isotope
 data</strong>: For both mice and diet items, we provide sample ID,
 mass (in milligrams), carbon and nitrogen elemental composition (C:N
 ratio), and carbon and nitrogen isotopes (δ13C and δ15N). In addition, for
 diet item data, variables include "Scientific Name";
 "Order"; "Group (8-source model)" (the name of the
 source group that a diet item was assigned for our SIA model with eight
 source groups); "Group (4-source model)" (the name of the source
 group that a diet item was assigned for our SIA model with four source
 groups); "Date Collected" (between April 2018 to November 2021);
 "Location Collection" (description of location where diet item
 was collected, if available); "Latitude" and
 "Longitude" (coordinates where diet item was collected, if
 available); and "Tissue" (specifies which part[s] of the diet
 item sample were used for SIA).