Despite intense conservation efforts, there are fewer than 3,200 tigers (Panthera tigris) in the wild, living in less than seven percent of their historical range. When a population is confined to small islands of wilderness, as are tigers, there is a higher risk of inbreeding and loss of genetic diversity, leaving the species with weaker young. To combat this, the American Museum of Natural History has been working with the global wild-cat conservation organization Panthera to establish genetic corridors that allow tigers to seek new territory for prey and new populations for breeding. Tracking individual cats by using genetic markers lets researchers map movement within and between populations.
Genetic tracking has traditionally relied on extracting DNA from scat collected in the wild. But in humid, tropical landscapes--like those in Sumatra, where a number of tigers live--scat often degrades before researchers can find it. Scent sprays left by tigers on trees and overhanging leaves degrade less quickly, and can be detected between two and eight times as frequently as scat. So, to boost the effectiveness of genetic monitoring of tigers in warm regions, the colleagues questioned whether DNA could be extracted from sprays.
For a proof of concept study researchers collected spray samples from three captive tigers in Ontario (I guess those are Sumatran Tigers from the Toronto Zoo) with cotton swabs that were then stored in tubes of buffer to help preserve the DNA. Tiger spray is a combination of anal gland secretions -said, surprisingly, to have a floral scent like citrus -and urine, which contains DNA in the form of cells from the urethra. The researchers were able to amplify microsatellite loci, providing enough information to fingerprint individual tigers, and portions of the sex chromosome to determine whether they are male or female. They also confirmed the species identity by using a mtDNA marker. However, why they chose cytb instead of COI remains a mystery to me.
The results show that DNA taken from tiger spray is just as good or even better than scat in identifying individual tigers and their gender.
Genetic monitoring of tiger source populations is a conservation priority. The utility of this new method is really impactful because it will let us dramatically build upon the number of tigers that can be surveyed and, consequently, increase our understanding of these elusive animals--hopefully before they are gone. We recently spent weeks looking for tiger scat in the field with very little luck. Although this new spray technique wouldn't replace scat studies entirely, we now know that we can use both methods in conjunction to drastically increase our monitoring abilities.