Get them before they get you

Haemadipsa sp, Credit: AMNH/M. Siddall

Southern Asia is a biodiversity hotspot both for terrestrial mammals and for leeches. Many small-mammal groups are under-studied in this region, while other mammals are of known conservation concern. In addition to standard methods for surveying mammals, it has recently been demonstrated that residual bloodmeals within leeches can be sequenced to find mammals in a given area. While these invertebrate-parasite-derived DNA (iDNA) methods are promising, most of the leech species utilized for this type of survey remain unevaluated, notwithstanding that their diversity varies substantially.

Researchers at the American Museum of Natural History, conducted a broad survey across southern Asia to reinforce the idea that the mammal biodiversity of an area can be determined by looking at the DNA found in leeches' blood meals. 

The usefulness of iDNA was first shown in an earlier study on about two dozen leeches found in Vietnam. This new survey collected and genetically analyzed about 750 terrestrial leeches in the genus Haemadipsa from the forests of Bangladesh, Cambodia, and China. The colleagues found that the leeches feed at least somewhat indiscriminately on a large variety of mammals, including small deer called muntjacs, macaque monkeys, wildcats, rodents like porcupines and rats, as well as a vulnerable species in the area, a gaur, or Indian bison. They also recovered DNA from three types of ground-dwelling birds and one species of bat. So far there were only a few previous and somewhat anecdotal reports of those animals being targeted by Haemadipsa leeches.

This work is turning out to be an extremely useful tool for conservation purposes, and it's quick and easy to survey a park in this way as you don't really need to search for the leeches-they come to you looking for a meal. You just go on a casual hike and make sure you get the leeches before they get you. A snapshot of the vertebrates in an area can be taken with just one day's worth of sampling; the current standard for surveys, camera traps, takes months or longer.