29 August 2011

Striped Saddlebags and the value of vouchers

Craves, J. A., and D. S. O’Brien. 2011. Tramea calverti (Odonata: Libellulidae): new for Michigan with notes on other new reports from the Great Lakes region (pdf). Great Lakes Entomologist 44:78-82.

Our paper on Striped Saddlebags appears in the most recent issue of the Great Lakes Entomologist. As the title implies, it not only describes our first state record for Michigan in 2010, but also includes reports from the Great Lakes region, all over the eastern U.S., and background on previous northward movements of this species.

In late 2010, this southern species was reported from eight states and Canada north of 38°N. It had never been reported in five of those states and Canada. Some of the locations had multiple sightings over multiple days. Quite a few were photographed. 

But the voucher we obtained was the only one obtained in 2010 in this incursion. Not just in Michigan, but anywhere in the eastern U.S., as far as we were able to determine.

We've talked before about the pitfalls of trying to identify Odonata from photographs, one reason most states require a voucher specimen to confirm county or state level records.  Of course, many species, including Striped Saddlebags, can be identified from a photo. But concrete ID is only one aspect of the value of specimens, and the lack of vouchers of Striped Saddlebags from 2010 is a good example.

Ohio, for instance, had multiple sightings of Striped Saddlebags in 2010 in at least two locations. However, this wasn't the first time this species had been seen and photographed there. There were reports from 2006, 2007, and 2008. No vouchers have been submitted for this species in Ohio.

There are a number of fundamental questions that cannot be answered by the photographs of Striped Saddlebags in Ohio, such as whether or not this is a breeding population, or if they are repeatedly colonizing the same spots year after year. Nor can we determine where they came from. Because there are no vouchers from Ohio or other states (except ours in Michigan), we can't see if these saddlebags all originated from a particular region or population. Or if there is some subtle morphological difference in these far-wandering saddlebags -- wing shape, flight musculature, etc. -- that helped them make the trip north. And, if breeding populations are being established from such individuals, whether these traits being maintained in the population, representing evolution at work.

Specimens could help answer these questions (and others I have not considered, I'm sure). Molecular work on insects is widely used to look at dispersal, routes of expansion, and colonization; delineate genetic populations and gene flow; and examine evolutionary divergence. Measurements of morphological traits obviously cannot be performed without a physical specimen.

When our paper went through informal and formal peer review, several referees did not want sight or photo reports included at all because they are generally not accepted by the scientific community. Obviously this removed a great deal of context for our record. In the end, we came to the conclusion that describing all the sightings would at least provide some published historical record, given that specimen material is not available.

And publication in some sort of formal journal is important. Usually these are archived in libraries as hard copy and are therefore available to researchers for the long haul. About 70% of the Striped Saddlebags records we referenced in this paper were found on local Internet forums, listservs, or personal web sites. These sources are far too ephemeral and difficult to find to act as historical documentation. Fortunately, quite a few of the records were also submitted to Odonata Central. This is extremely helpful, but does not replace vouchers as valid records in every state, and as a site that relies on donations, it's future is not guaranteed.

For significant records of Odonata, please consider collecting voucher specimens. If you would rather not do it yourself, please let someone who is willing to do so know about your observations.


Patrick B. said...

Do you have a good reference on the best method for collecting the voucher?

JAC said...

Pat, the Michigan Odonata Survey has a collecting guide. Here's the relevant page:

Very simple and straightforward. The article mentions creating paper triangles, but we use those glassine envelopes used by stamp collectors. We carry a supply with us that have one corner snipped off - those go right in the acetone. Then we transfer the specimen to a fresh intact envelope with a paper tag inside for submission to the museum.

I think we will do an illustrated post on how to collect and prepare a voucher.

Darrin OBrien said...

Yes, I am delinquent on the "How to" post.