Can sex-specific consumption of prey be determined from DNA in predator scat?
Sex-biased predation, a predator’s bias for one prey sex over the other, can have important demographic impacts on prey species of conservation concern. Yet, it is difficult to measure in the wild. Molecular scatology has been used to indirectly determine the proportion of prey items consumed in the diet, and it may be possible to apply similar approaches to determine the sex-biased consumption of prey items. We developed a molecular method to indirectly examine sex-specific predation employing scat, focusing on predator–prey interactions between Chinook salmon (Oncorhynchus tshawytscha) and harbor seals (Phoca vitulina richardii). We established that the proportions of male and female Chinook DNA can be determined in a controlled sample by measuring a Y-linked marker, growth hormone pseudogene, using qPCR. We then applied the assay to harbor seal scat samples. Although the assay amplified in 83% of scat samples, 27% of samples quantified had an estimated male proportion > 1, which may have been due to a lack of robustness of the PCR assay in samples. Lastly, we constructed a biomass calibration curve to determine whether DNA measurements could estimate the proportions of male and female biomass consumed. The calibration curve was skewed by high male DNA density precluding our ability to quantify the relative amounts. We demonstrated that nuclear prey markers can be amplified in predator scat, however, contamination and extreme DNA density differences between the prey sexes may pose practical difficulties to estimate the relative amounts of male to female biomass consumed.
KeywordsSex-biased predation Molecular scatology qPCR Scat Phoca vitulina richardii Oncorhynchus tshawytscha
We would like to thank Dr. Craig Moyer and Dr. Alejandro Acevedo for their feedback on experimental design and helpful comments on the manuscript. Thanks to Dionne Sakhrani and Krista Woodward at Fisheries and Oceans Canada for assistance with the sex-determining assay. Special thanks to the Cowlitz Fish Hatchery (WDFW) and Dr. Katherine Haman who provided Coho salmon. Thanks to Allegra La Ferr, Ashlyn Teather, Jenna Brooks, and Ryan Mclaughlin who assisted in fish homogenization. This project was funded by the Coastal Fish and Wildlife Compensation Program, the Pacific Salmon Foundation, WWU Biology Graduate Summer Scholarship, and the WWU Research and Sponsored Programs.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The harbour seal scats were collected under Fisheries and Oceans Canada Marine Mammal Research License (MML 2011-10) and a University of British Columbia Animal Care Permit (A11-0072).
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