Using Stable Isotope Analysis to Identify Tick Hosts

Lyme disease is a pervasive illness caused by the transmission of the spirochete Borrelia burgdorferi from the bite of an infected black-legged tick, Ixodes scapularis. Ticks obtain the spirochete by feeding on an infected animal host.Ticks feed on a broad range of hosts, but some host species are more competent carriers of Lyme disease and more readily transmit B. burgdorferi to feeding ticks.Thus, knowing what host species a tick has fed on could provide valuable information in studying the transmission of Lyme disease. However, studying the relationships between ticks and their hosts has proved challenging. One possible option for determining a tick’s prior host is Stable Isotope Analysis (SIA), a technique often used for food web studies that provides unique signatures based on the concentration of stable isotopes found in the analyzed subject. The animal being tested and the diet they consumed largely determine these signatures. I built on previous SIA work by testing how isotopic signatures of ticks varied when Eastern chipmunk hosts, Tamias striatus, were fed different diets. Prior studies using a carbon tracer suggested that incorporation of carbon stable isotopes is quick and sensitive.This led to concern that brief diet changes may significantly distort isotopic signature in ticks and reduce its use as an indicator. To follow up, chipmunks were captured in Reist Sanctuary and held in the animal care facility. Upon their arrival nymphal ticks were placed on the chipmunks to feed. Meanwhile the animals were fed a variety of regimented diets. After tick feeding, animals were released. Adult ticks were processed and submitted for SIA along with samples of diets for comparison.The results from the stable isotope analysis showed little variation among diet groups and signatures from ticks did not match the corresponding host diets. It appears that nitrogen from short term dietary changes was not as readily incorporated in ticks as the carbon tracer was, suggesting that SIA could provide insight to understanding tick-host interactions without being sensitive to short-term dietary changes. Although the study did not yield significant results, it provided valuable insight into how tick physiology may impact nitrogen isotopic signature and suggests that the nitrogen isotope could potentially be a valuable indicator of tick-host relations.