Reading Mammal Diversity from Flies

According to the Global Mammal Assessment (2008), information on the distribution and abundance of most tropical mammal species remains data-deficient, and thus some species appear to be disproportionately threatened. Lack of data on tropical mammal species can be associated with limitations of the existing monitoring approaches. Field-trapping techniques vary in efficiency and are often a biased representation of diversity. For example, identification of animal signs is laborious, requiring the input of specialists over an extended time period, and can be imprecise. Likewise, expensive camera traps cannot identify individuals to species lacking easily observed diagnostic markings. Impediments also include the challenge posed by cryptic species, which are not always morphologically distinct, and are more easily recognised by molecular techniques. Considering that the current monitoring approaches are challenged by ethics, precision, and accuracy, a new approach is urgently needed.

One alternative for monitoring mammal populations could be the analysis of non-invasively sampled vertebrate DNA. For instance, environmental DNA extracted from sediments, soil, or water samples could permit the assessment of a broad range of vertebrate diversity in a given area, for a relatively minimal sampling effort. Alternative sources are naturally shed or otherwise deposited samples, including feces, hair, and feathers. 

Perhaps there is an even more elegant solution to this. Recent studies (here and here) already suggested that mammal genetic material ingested by invertebrates (iDNA) can be used to investigate mammal biodiversity. Colleagues from Malaysia now tested the utility of blowfly-derived DNA as an effective method for local mammal monitoring. Their objectives were (i) to determine the persistence period of amplifiable mammal mtDNA in blowfly guts through a laboratory feeding experiment, and (ii) to design and test primers that can selectively amplify mammal DNA mini-barcodes in the presence of high concentrations of blowfly DNA. The animal of their choice was the oriental latrine fly (Chrysomya megacephala).

The results of this study are quite promising. The feeding experiments established that amplifiable mammal mtDNA persists in the guts of adult Chrysomya megacephala for 24 h—96 h post-feeding (89% at 48 h). The researchers also established a new primer set for DNA mini-barcodes that worked very well across all mammal groups. Actually the 205 bp COI fragment was so successful in distinguishing mammal species that it could also separating some so called “dark” bat taxa, previously recognised species that lack formal taxonomic status. This would potentially allow for the detection of cryptic taxa overlooked by other methods. The authors conclude:

Our findings suggest our new DNA mini-barcode target and a standardized trapping protocol with retrieval of blowflies every 24 h could point the way forward in the development of blowfly-derived DNA as an effective method for mammal monitoring in Peninsular Malaysia. The next step would be a comprehensive comparison of diversity measures for mammals produced by the blowfly-derived DNA approach and by traditional monitoring approaches such as cage traps, mist nets, hair traps, camera traps, or scat samples.