Monthly Archives: December 2013

What’s in a name? A previously unrecognized species of North American black fly from Baffin Island

Biting flies are a scourge at northern latitudes. Nearly every early explorer made reference to the tenacity and voracity of these tiny insects. Not surprisingly, biting flies reach their peak abundances in northern environments, with mosquito densities reaching a staggering 12.5 million individuals per hectare in the Hudson Bay Lowlands. Similarly, black fly larvae can reach densities of 1.2 million per square meter of stream substrate under optimal conditions. Given their abundances, and economic importance (through blood feeding and transmission of parasitic diseases), it is not surprising that biting flies are among the best known insects in North America.

Black flies are an especially well known as they were the subject of a monumental revision of the North American simuliid fauna by Adler et al. (2004).  In fact, no new North American species have been described since that book was published 9 years ago. Consequently, I was amazed to discover a hitherto unknown species near Iqaluit, NU on southern Baffin Island (Figure 1). It is a member of the circumpolar genus Stegopterna (Enderlein 1930) which includes 8 North American species.  However, only one species — St. emergens (Stone 1952) — is known to be distributed widely at northern latitudes.

This previously unknown species was overlooked during initial sorting and counting. However, subsequent DNA barcoding, revealed >10% sequence divergence between this species and Stegopterna emergens, the species it was initially mistaken for. This prompted a closer examination of the morphology of the Iqaluit population, which differed from St. emergens in 2 important ways. The first relates to the length of the pupal gill trunk (Figure 2). Pupal gills are often used for species level identification of black flies, and this difference was consistent in all specimens examined. However, a more striking and ecologically significant difference is that the Iqaluit species has mouthparts adapted for blood feeding. Distributional records reveal that, of the 9 black fly species previously recorded from the Canadian Arctic Archipelago, only 2 had biting mouthparts. The other species were arctic-adapted (i.e., non-bloodsucking) species that use nutrients from their larval stages to develop their eggs. Interestingly, the two biting species were both found only on southernmost Baffin Island.

The discovery of this previously unknown species of bloodsucking black fly raises important ecological and evolutionary questions. Historical records suggest that St. emergens was present on southern Baffin Island during the 1950s; however, contemporary collections yielded only this previously unrecognized one. Were historically collected specimens simply mistaken for this undescribed species, or was St. emergens supplanted by this new one on southern Baffin Island? Reexamination of historically collected material in the Canadian National Collection of Insects is needed to select from these alternative hypotheses. DNA barcoding may again prove useful should the diagnostic life stages (i.e., adult females, pupae) prove unavailable for study.

Another important question is why southern Baffin Island was the only region in the Canadian Arctic Archipelago to historically support bloodsucking black flies. The recent discovery of yet another blood feeding species on the Island (Schaefer 2011) further reinforces the suitability of conditions for this feeding habit. A more favorable climatic regime seems a likely explanation; however, further analyses are required.

Finally, this undescribed species was not present at any other Arctic or Boreal site sampled by the NBP. This raises the question of how widely distributed this species is. There have been no records of morphological or chromosomal differences between mainland and continental island populations, nor have any continental island endemic black flies have ever been found in North America. This makes it extremely unlikely that this new species is restricted to Baffin Island and suggests its distribution likely extends southward into northern Quebec or westward across Nunavut (albeit in potentially low numbers).

The process of assigning a name to this previously unrecognized species is not particularly straightforward. While it’s possible that the southern Baffin Island Stegopterna is an undescribed (i.e., is a new to science) species, we can’t rule out the possibility that it’s actually a Holarctic species that already carries a valid scientific name.  Unfortunately, Stegopterna species are notoriously difficult to identify morphologically, and there are at least 7 candidate names to consider from the northern Palearctic Region (all members of the St. trigonium species complex). We must now begin the process of poring over species descriptions to determine whether any of the available names could reasonably be applied to the southern Baffin Island population. But however this exercise turns out, it’s gratifying to know that there are still new and exciting discoveries to be made in northern Canada.

References

Adler, P.H., D.C. Currie and D.M. Wood. 2004. The Black Flies (Simuliidae) of North America. Cornell University Press. Ithaca, NY.

Schaefer, P. 2011. Update on the biting fly component (Diptera: Simuliidae, Culicidae and Tabanidae) of the Northern Biodiversity Program. Newsletter of the Biological Society of Canada 30: 41-49.

“Mastering” northern flies: another student crosses the finish line

By Terry Wheeler (originally posted at http://lymanmuseum.wordpress.com/2013/06/08/mastering-northern-flies-another-student-crosses-the-finish-line/)

I’ve written previously about our work on the flies from the Northern Biodiversity Program (the joys of collecting them, and the challenge of processing them). Three years, tons of travel, a mind-boggling number of hours in the lab, and more than a hundred thousand specimens into the project, we are starting to see the first wave of student projects wrapped up. And it’s a great feeling.

I’m delighted to report that my M.Sc. student Meagan Blair has joined the list of NBP grad students who have finished their thesis. Meagan’s thesis on spatial patterns and long-term change in northern scathophagid flies has been awarded a Pass. So, huge congratulations to Meagan for successfully steering an ambitious project on a large and difficult group of flies through to completion. Meagan was part of the first wave of students who joined the NBP in the first year of sampling in 2010 and she was one of the few students who was in the field from start to finish in both the 2010 and 2011 field seasons. That’s a lot of northern time! Meagan was also one of the stalwarts in the NBP “sorting room” in the Lyman Museum, cleaning, sorting and processing vast amounts of material before she could start in on the long hours of microscope time needed to identify her flies.

Scathophagids, also known by the unflattering common name of “dung flies” are probably most familiar to many people through the big fuzzy yellow dung fly Scathophaga stercoraria, which seems to be fond of sitting on fresh piles of cow manure (hence the name). They don’t eat the manure though; they eat the insects that feed on the manure. But that yellow dung fly is only one member of this morphologically and ecologically diverse family of flies, a family that has some very sleek, colourful and, yes, very attractive species. Many scathophagids are predators, others are scavengers and many feed on live plants. They are also interesting from the perspective of our NBP project because they are one of the few families of flies (and indeed one of the few families of insects) that becomes more diverse as you move north into the arctic.

Meagan found high species richness and high abundance of scathophagids at our NBP sampling sites from the northern edge of the boreal forest right up to the high arctic islands. And there is a significant change in the species found from site to site. Our late colleague Dick Vockeroth had a great interest in northern Scathophagidae and in 1958 Dick proposed what some of us informally call “Vockeroth’s Rule”. Dick hypothesized that tree line is a strong filter for scathophagid distributions, with species found either north of, or south of, tree line, but not both. Meagan’s work added several species to Vockeroth’s initial data set from his 1958 paper and in most cases confirmed that strong split at tree line (although what it is about tree line that actually limits the distribution of generalist scavengers and predators is another question).

Meagan’s work on documenting the current patterns of distribution of northern scathophagids will provide a valuable starting point for tracking change in distributions in the future as climate change causes the north to warm up. Will these flies track tree line north, or will a more complex set of interactions drive future patterns? Will the species that are dominant now remain dominant at the same sites into the future?

Meagan also reached back into time to compare our NBP specimens to specimens of the same species collected at the same sites in the early 1950′s. Her question was simple: “have northern flies themselves changed over the past half-century?”. The answer was “yes”, and in an interesting way. It’s not just the composition of the insect communities that are being affected by a changing north, there are evolutionary changes in the species themselves.

I won’t give away any more details of Meagan’s results here. A finished thesis is a very satisfying milestone along the academic journey, but it’s the published papers that matter most — those are the products that are read by the broader scientific community. We’re working on those now and you’ll be hearing more about Meagan’s results in the future.

The joys of arctic fieldwork: Meagan hunting flies on Ellesmere Island (photo: Donna Giberson)

The joys of arctic fieldwork: Meagan hunting flies on Ellesmere Island (photo: Donna Giberson)