Summary
For many species trophic interactions are difficult to study because of their cryptic habits and/or the unfavourable characteristics of samples for traditional diet techniques. DNA-based diet techniques are sensitive, can identify prey to a species level and are applicable to samples not useful for hard-parts analysis. This talk will discuss basics of DNA-based diet techniques, present results from some study systems where they have been applied and discuss future work using next-generation sequencing technologies. These techniques have been applied to scat samples from both captive bottlenose dolphins (Tursiops truncatus) fed a known diet and from wild free-ranging individuals. Results from captive dolphins suggest that prey can be detected within 4-7 hours of feeding and signals persist for at least 12-19 hours since the last ingestion. After first detection around ¾ of samples are positive for prey items, which is a lower detection rate than previous studies and reasons for this are discussed. Up to six prey species were detected in a single sample (range 0-6, mean 3.1 +/- 1.7 (S.D)) and all but one prey species consisting of 2% wet weight of the total diet were detected across all samples. In free-ranging dolphins, up to 7 prey items were identified in a single sample (range 0-7, mean 3.3 +/- 1.7 (S.D)) and 26 prey operational taxonomic units consisting of 22 species level identifications were identified across all samples. The results gained from the free-ranging samples showed a remarkable congruence to diet data gathered from this population via traditional hard-parts analysis, allowing for the first time a comparison of hard parts analysis from stranded individuals with data from healthy free-ranging individuals. These techniques have also been applied to some nearshore generalist Antarctic teleost taxa. At a course taxonomic level, preliminary results show some spatial differences in diet within species and some evidence for niche partitioning between species. This summer an ecosystem scale study was initiated using field collections and laboratory depurations from a diverse array of taxa representing a broad trophic spread in the Antarctic nearshore ecosystem. Field results and laboratory strategies using next generation sequencing technologies will be presented and discussed, to illustrate the potential to upscale these methods using new sequencing technologies.