Abstract
BackgroundDetermination of seabird diet usually relies on the analysis of stomach-content remains obtained through stomach flushing; this technique is both invasive and logistically difficult. We evaluate the usefulness of DNA-based faecal analysis in a dietary study on chick-rearing macaroni penguins (Eudyptes chrysolophus) at Heard Island. Conventional stomach-content data was also collected, allowing comparison of the approaches.Methodology/Principal FindingsPrey-specific PCR tests were used to detect dietary DNA in faecal samples and amplified prey DNA was cloned and sequenced. Of the 88 faecal samples collected, 39 contained detectable DNA from one or more of the prey groups targeted with PCR tests. Euphausiid DNA was most commonly detected in the early (guard) stage of chick-rearing, and detection of DNA from the myctophid fish Krefftichthys anderssoni and amphipods became more common in samples collected in the later (crèche) stage. These trends followed those observed in the penguins' stomach contents. In euphausiid-specific clone libraries the proportion of sequences from the two dominant euphausiid prey species (Euphausia vallentini and Thysanoessa macrura) changed over the sampling period; again, this reflected the trend in the stomach content data. Analysis of prey sequences in universal clone libraries revealed a higher diversity of fish prey than identified in the stomachs, but non-fish prey were not well represented.Conclusions/SignificanceThe present study is one of the first to examine the full breadth of a predator's diet using DNA-based faecal analysis. We discuss methodological difficulties encountered and suggest possible refinements. Overall, the ability of the DNA-based approach to detect temporal variation in the diet of macaroni penguins indicates this non-invasive method will be generally useful for monitoring population-level dietary trends in seabirds.
Highlights
Information on predator-prey interactions is essential for understanding everything from animal behaviour and population dynamics to the direct and collateral impacts that humans have on ecosystems
The data we present on the diet of macaroni penguins at Heard Island will provide information crucial for informed management of this remote World Heritage listed area
The stomach content data we collected present a picture of macaroni penguin diet that is generally consistent with the results obtained in two previous diet studies carried out at Heard Island [4,30]
Summary
Information on predator-prey interactions is essential for understanding everything from animal behaviour and population dynamics to the direct and collateral impacts that humans have on ecosystems. While stomach flushing is certainly an improvement ethically, the procedure requires animal capture and can have adverse effects on the sampled birds and/or their offspring [e.g. 7] This means that the number of stomach samples that can be obtained during a study is often limited due to ethical concerns and that the approach may not be appropriate for studies of threatened species. Euphausiid DNA was most commonly detected in the early (guard) stage of chick-rearing, and detection of DNA from the myctophid fish Krefftichthys anderssoni and amphipods became more common in samples collected in the later (creche) stage These trends followed those observed in the penguins’ stomach contents. The ability of the DNA-based approach to detect temporal variation in the diet of macaroni penguins indicates this non-invasive method will be generally useful for monitoring population-level dietary trends in seabirds
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