DNA metabarcoding reveals diet composition of invasive rats and mice in Hawaiian forests

Abstract

Rodents are among the most widespread and problematic invasive animals on islands worldwide contributing to declining endemic island biota through predation and disruption of mutualisms. Identifying what rodents eat is critically important to understanding their effects on ecosystems. We used DNA metabarcoding to identify the diets of three invasive rodents in Hawaiian forests: house mouse (Mus musculus), black rat (Rattus rattus), and Pacific rat (Rattus exulans). These rodents primarily eat invertebrates and plants, but previous diet studies have provided only a limited understanding of the diet breadth by relying on morphological identification methods. We opportunistically collected fecal samples from rodents trapped at seven forest sites across Oʻahu, Hawaiʻi for two years. Plant and invertebrate diet items were identified from DNA extracted from fecal samples using rbcL and COI primers, respectively. Intact seeds were identified using a dissecting microscope to quantify potential contributions to seed dispersal. All rodent species ate primarily plants and invertebrates of introduced species. However, some native taxa of conservation importance were identified. Neither the rodent species nor the sites drove patterns of diet composition, suggesting that diet variation may be determined by opportunistic foraging or intraspecific variation. Black rat fecal samples contained intact seeds more frequently than house mouse samples, but surprisingly, when samples contained seeds, black rats and house mice both defecated hundreds of introduced seeds, likely contributing to seed dispersal. Conservation efforts targeting invasive rodent control should specifically include house mice and should monitor introduced prey items to prevent predation release of unwanted introduced species.

Appendix

See Table 1.

Table 1 List of plant taxa found in fecal samples of all rodents at all sites on Oʻahu, Hawaiʻi, from 2014 to 2016. The number of samples (N) within which each taxa was identified, species of rodent and site (EKA, ʻĒkahanui; KAH, Kahanahāiki; MOA, Moanalua Valley; MTK, Mt. Kaʻala; PAH, Pahole; TAN, Tantalus; WAI, Waimea Valley) where the sample was identified are noted. Nativity of the taxon is noted if taxon was identified to a level at which its status can be concluded, otherwise unknown (unk). Whether the species produces fleshy fruit (FF) and if the seeds of that species were found intact in any samples are noted. Sequences identified as phylum Magnoliophyta were found in 379 samples in all rodent species at all sites

Table 2 List of invertebrate taxa in fecal samples of all rodents at all sites on Oʻahu, Hawaiʻi from 2014 to 2016. The number of samples (N) within which each invertebrate taxa was identified, species of rodent and site (EKA, ʻĒkahanui; KAH, Kahanahāiki; MOA, Moanalua Valley; MTK, Mt. Kaʻala; PAH, Pahole; TAN, Tantalus; WAI, Waimea Valley) where the sample was identified are noted. Nativity of the taxon is noted if identified to a level at which its status can be concluded, otherwise unknown (unk). Sequences assigned to kingdom Animalia were found in 16 samples in all rodent species at six of the seven sites