With the next lot of roadkill fieldwork to start at the end of May, I am currently busy analyzing the data collected over the last two ecological seasons. During the next season of fieldwork, the Roadkill Research and Mitigation Project will collaborate with Isabel Collett, a Master’s degree student from the Department of Zoology and Entomology at Rhodes University. Isabel is conducting her study on the DNA of beetles and in particular ‘carrion beetles’. Through collecting beetles from the carcasses of roadkilled animals, our project will enable her to examine the DNA of beetle species from a different area of the country.
Below is a great piece written by Isabel about carrion beetles and how they assist forensic entomology. If you can assist Isabel with collecting carrion beetles or would like to know more about her work, then contact her on: 082 828 9892 / email@example.com.
CSI: Beetles in forensics
“If one could conclude as to the nature of the Creator from a study of creation, it would appear that God has an inordinate fondness for stars and beetles.”
Generations of entomologists have realised that not only the flies, but also the beetles found on corpses tell a story. The investigation of carrion beetles (Figure 1) in forensic science has enabled scientists to determine the time of death of a corpse (also known as the post-mortem interval or PMI) and to draw conclusions regarding infestations of stored organic matter. As their name suggests, carrion beetles feed on the flesh of dead animals, but they are also known to feed on stored products such as grain and furniture, and as such, feature in insurance claims for damaged produce.
To calculate a PMI, forensic entomologists observes the life stage that beetles are in at the time of discovery and, by using previously drawn up developmental charts, they are able to work out how long a body has been dead and exposed to the elements – a kind of biological clock. The diversity of beetles found on a body changes over time and can therefore provide evidence of ecological succession, which provides a second clock. These sources of evidence all require the beetles to be identified, because the growth rates and ecological requirements of each species are different. This is a difficult challenge if they are still eggs, pupae or larvae (Figure 2). Up to now, morphologists have made these identifications based on their external features, a time-consuming exercise which requires a level of expertise. Throughout the world, the identification of the immature and adult stages of many species is difficult because of our lack of knowledge coupled with the lack of research. Molecular taxonomy can overcome this problem.
Figure 2: Dermestes maculatus larvae cleaning the skull of a deer – a method employed by museums to prepare specimens for preservation.
DNA barcoding is a new method of identification based on a fragment of a mitochondrial gene, cytochrome oxidase 1 (CO1), which is common to every species (Figure 3). This fragment varies between different species but remains similar within species. This is why it is known as the ‘barcode’, comparable to those used in supermarkets, and it may be the answer to problems in identifying carrion beetles. Sequences of the barcoding region of COI are useful to forensic entomologists because they can identify specimens found on carcasses. By analysing the genetic make-up of an organism, rather than the morphology (which can require an expert and time-consuming preparation and still destroy evidence), nondescript specimens of juveniles and even unrecognisable fragments of specimens can be identified.
Figure 3: Outline of barcoding protocol (adapted from http://www.dna-sequencing-service.com)
My project concerns the sequencing of barcodes from populations of southern African carrion beetles. These sequences will be submitted to GenBank (the online database of all DNA sequences) and used as straightforward comparisons for other identifications. In addition, I will also see how the sequences vary within and between populations. Species from different regions probably have population-specific differences, as beetles do not disperse as successfully as other flying insects and their genetic makeup remains similar within common areas of movement. Because of these slight differences, it will be possible to determine the geographical origin of specimens. This would allow an investigator to tell where a product was infested, or whether a body has been moved substantial distances since death. However, DNA barcodes have not always been successful for various reasons including hybridisation. I will therefore try to cross-validate the COI barcodes using a rapidly-evolving nuclear gene (Elongation Factor 1 alpha) as a means of quality control. Because many species of carrion beetle occur across whole continents, research done in South Africa will be relevant to forensic science and biosecurity worldwide. As yet, I have collected and barcoded a number of beetles collected in the Eastern Cape, but I still need more from other areas in the country to be able to make these comparisons and fulfil the objectives of my thesis.
Isabel Collett: MSc candidate, Department of Zoology and Entomology, Rhodes University.