Stable Isotope Project


exuvia-A_Carlton The Stable Isotope Project investigates patterns of reproduction, emergence, and movement among migrant species at different latitudes. Participants will help us assess connectivity of migratory dragonfly populations using stable isotope signatures.

Stable isotopes of hydrogen in the dragonfly wings and exuviae (cast off skin of the final stage nymph left behind when an adult emerges) are being analyzed to investigate patterns of movement north and south in North America. Contributing specimens to the Stable Isotope Project will help inform research into a dragonfly’s travels from the site where it developed and emerged.

The first round of analysis for the isotope project was successful! Thank you to all the citizen scientists who collected and submitted specimens. After analyzing specimens collected by dragonfly enthusiasts around the region, the Partnership has developed a snapshot of Common Green Darner (Anax junius) spring migration across the eastern half of North America. Based on the information gathered, the Partnership’s Isotope Project will soon be changing direction. Please stay tuned for updates to this project regarding specimen collection and information on where to send any new specimens.

Focal Species


Isoscape Map

Isoscape map shows different hydrogen isotope ratios that occur naturally and vary latitudinally throughout North America. (Map from www.waterisotopes.org.)

isoscape-map


Frequently Asked Questions

What are isotopes?

Isotopes are different forms of one chemical element, each with a slight variation in atomic structure. These isotopic forms vary characteristically with latitude. For dragonflies, an isotopic signature can be generated by measuring the ratio between stable isotopes of hydrogen, a component of the waters in which the nymphs live during development, traces of which remain locked into the wing tissue of the adult after emergence.

What is the Stable Isotope Project?

MDP partners at the Vermont Center for Ecostudies and the Smithsonian Conservation Biology Institute are using stable isotopes of hydrogen to help understand migratory connectivity among dragonfly populations and the geographic scale of migration. The Stable Isotope Project analyzes H2:H1 in dragonfly tissue to assign a geographic region of origin to migratory individuals.

How are stable isotopes used to understand migration?

By comparing the hydrogen isotope ratio in its wings to that of the water body where the insect was captured, researchers can get an indication of how far a captured dragonfly has moved from its emergence site. Isotope data will increase our understanding of the points of origin of dragonflies in a mass flight, better delineate southern and northern endpoints of migration, and help distinguish migratory individuals from residents.

Why use isotopes to study migration instead of radio transmitters?

Small radio transmitters have been used to track migratory movements of Common Green Darners, but this technology is of limited use for studying migratory connectivity as only a small number of dragonflies could be tracked, the transmitter load is ~25% of the dragonflies’ body mass, and individuals can’t be tracked more than 100-200 km (60-120 miles) from the release point. Also, this technique does not provide information about broad-scale origins of newly-arriving migrants in spring. A different and more promising approach takes advantage of a well-documented north/south gradient in the hydrogen isotope ratios (H2:H1) that occurs naturally in fresh waters. This hydrogen isotope ratio is incorporated into the aquatic animals living in these waters, including odonate nymphs, and is preserved in the wings of the adults thereafter. Thus, regardless of how far from its emergence site an adult dragonfly is captured, the hydrogen isotope ratio in its wing tissue will be that of the water in which it developed as a nymph.

Do I have to collect live specimens?

Volunteers can participate in the Stable Isotope Project by collecting dragonfly exuviae (the cast-off skins of dragonfly nymphs emerging from the water). Dead adults may also be found and picked up around lights, houses, and ponds.

Who can participate?

Anyone who has an interest in dragonfly ecology and would like to contribute to our growing knowledge about dragonfly migration in North America.

How can I get involved?

This project is currently changing direction. If you are interested in contributing specimens, please stay tuned for details on which species to collect and where to send your specimens.

Do I need experience to participate?

No prior experience with dragonflies is needed–recognizing these five species is easy to learn! Check out the MDP field guide to start learning how to identify these species. Protocols regarding data collection and information on where to send specimens will be updated soon in the protocols booklet. Please stay tuned for these changes. Click on the above photos of the five focal species to learn more about each and visit the photo gallery at OdonataCentral to see an array of photos of Common Green Darner, Black Saddlebags, Wandering Glider, Spot-winged Glider, and Variegated Meadowhawk.

How do I know what species an exuvia is?

Exuviae are harder to identify, but it can be done, and the MDP is developing a field guide to migratory species exivuae to help you. Stay tuned!


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