Dietary competition between the alien Asian Musk Shrew (Suncus murinus) and a re‐introduced population of Telfair's Skink (Leiolopisma telfairii)

Abstract

Re-introduction of rare species to parts of their historical range is becoming increasingly important as a conservation strategy. Telfair's Skinks (Leiolopisma telfairii), once widespread on Mauritius, were until recently found only on Round Island. There it is vulnerable to stochastic events, including the introduction of alien predators that may either prey upon it or compete for food resources. Consequently, skinks have been introduced to Ile aux Aigrettes, another small Mauritian island that has been cleared of rats. However, the island has been invaded by Asian Musk Shrews (Suncus murinus), a commensal species spread by man well beyond its natural Asian range. Our aim was to use next-generation sequencing to analyse the diets of the shrews and skinks to look for niche competition. DNA was extracted from skink faeces and from the stomach contents of shrews. Application of shrew- and skink-specific primers revealed no mutual predation. The DNA was then amplified using general invertebrate primers with tags to identify individual predators, and then sequenced by 454 pyrosequencing. 119 prey MOTUs (molecular taxonomic units) were isolated, although none could be identified to species. Seeding of cladograms with known sequences allowed higher taxonomic assignments in some cases. Although most MOTUs were not shared by shrews and skinks, Pianka's niche overlap test showed significant prey overlap, suggesting potentially strong competition where food resources are limited. These results suggest that removal of the shrews from the island should remain a priority.

The effects of parameter choice on defining molecular operational taxonomic units and resulting ecological analyses of metabarcoding data

“…Although jMOTU is too computationally intensive for many of the larger datasets now produced, it offers a conservative approach by disregarding gaps that can be legitimate taxonomic characters particularly in ribosomal or intron data (Jones et al 2011). The original authors (Brown et al 2014) determined the presence of an apparent "barcode gap" (Meyer andPaulay 2005, Ratnasingham andHebert 2013) using 4-bp differences to define separate MOTU to conform as closely as possible to actual species.…”

“…We analysed two cases, one where all data are retained (all-MOTU analysis) and one where rare MOTU found only once in the entire dataset are removed (common-MOTU analysis). This approach was used in the original paper (Brown et al 2014) to remove MOTU that may be the result of sequencing error or may represent rare prey not contributing substantially to the diet of either predator. See Fig.…”

“…The data used were taken from an analysis of dietary overlap by skinks and shrews on Ile Aux Aigrettes, Mauritius (Brown et al 2014). In this system, endemic Telfair's skinks (Leiolopisma telfairii) are thought to be under threat from invasive Asian musk shrews (Suncus murinus).…”

“…The original paper analysing the diet overlap of skinks and shrews (Brown et al 2014) used jMOTU (Jones et al 2011) to describe the MOTU richness. Although jMOTU is too computationally intensive for many of the larger datasets now produced, it offers a conservative approach by disregarding gaps that can be legitimate taxonomic characters particularly in ribosomal or intron data (Jones et al 2011).…”

“…In this investigation we take a real dataset, an analysis of dietary niche overlap by predatory skinks and shrews (Brown et al 2014), and measure the effect of increasing and decreasing MOTU estimates by using different sequence clustering programmes and parameters (Fig. 1).…”