Barcodes and bristles, keys and trees

Much has been written about DNA barcoding, ranging from evangelically PRO to fundamentalist CON. I must confess that my early reactions were negative, not because of the inherent science involved, but because of some unfortunate marketing tactics in the early days of the movement. As a taxonomist, one gets a bit weary of being told we can all be replaced by an, as yet, non-existent tricorder that will identify any species instantly and accurately in the field. DNA barcoding is a tool – nothing more, nothing less – and a tool that I have recently added to my toolbox of Ways to Discover Biodiversity. And ironically, it has given me the opportunity to spend a lot of time on the microscope looking at specimens.

I am involved in a project, spearheaded by the Biodiversity Institute of Ontario and the Polar Barcode of Life, on barcoding the biota of a single subarctic site – Churchill, Manitoba, on the shore of Hudson Bay. My role, along with some of the other people in my lab (Stéphanie Boucher, Chris Borkent, Anna Solecki) and several colleagues in Canada and around the world, is to document the Diptera species diversity at the site by comparing the results of DNA barcode identifications with species limits based on morphology, as determined by taxonomic specialists.

I was very keen to take on the Chloropidae (in collaboration with Anna Solecki, as well as Jinjing Wang and Ding Yang from China) because initial results suggested very high species diversity at Churchill. In the end, there has been a pleasing agreement between DNA barcodes and morphology in the nearly 50 species of chloropids in the collections (more on the areas of disagreement, as well as several new species, in some coming publications).

I also agreed to make an effort, with no guarantee of completeness, to do some initial sorting in the other families of acalyptrate flies that had not been spoken for by other collaborators. We have taxonomic expertise and experience in the lab on some of these families, but others are more of a challenge, for a variety of reasons. Fortunately, our reference collection is a good one. A good insect collection provides verification and taxonomic resolution that time spent with keys alone simply can’t replace.

Some acalyptrate families are species-rich at Churchill (Sciomyzidae, Ephydridae, Sphaeroceridae, Agromyzidae, Piophilidae), while several others were represented by only one or a few species. As with the Chloropidae, there will be greater detail on the diversity in these families, the recognition of some new species, and the fit between DNA barcodes and morphology, in some publications now in preparation. Stay tuned . . .

Beyond the goal to help document our own Canadian Diptera diversity, our involvement in the Diptera of Churchill project has another significant benefit – our ongoing research in the Northern Biodiversity Program is yielding extremely rich collections of Diptera from across Canada’s north from treeline to the high arctic, and from Labrador to the Yukon. Having a reference library of barcoded arctic species, confirmed by Diptera specialists, will give us a valuable baseline from which to describe Diptera diversity across the north on a much larger spatial scale.

In the process of sorting these several hundred acalyptrate specimens, I have had a few assorted realizations:

1. I dislike sorting specimens in ethanol. I realize that some of my colleagues swear by fluid-preserved material, but I find it SO much more convenient to work from dried, mounted specimens (not to mention the long-term preservation issues). Time constraints have conspired against me in this instance – chemically drying, mounting and labelling several hundred specimens takes time, so I resolved to try it in ethanol. My conclusion – I still dislike sorting specimens in ethanol.

2. Our knowledge of our own Diptera diversity is fragmentary compared to regions such as western Europe. I am envious of my European colleagues who can, often, not only put names on many acalyptrate species, but access information on the occurrence of species X in region Y of country Z. Compare this to Canada, where we have estimated that well over half of our Diptera fauna remains undescribed or unrecorded, and our knowledge of their actual geographic distribution, phylogenetic relationships and natural history is, well, often abysmal.

3. The Manual of Nearctic Diptera, rightfully regarded as a model of how to write an identification manual, is great (mostly) in getting a fly to genus (although some of the chapters are now, more than 20 years on, in need of updates), but things can break down at the species level. In many cases, identification to species is virtually impossible because keys either have never been written, or date from the 1920s or earlier, or are incomplete. Admittedly, there are only so many of us to get the work done, and we are stretched very thin. I, myself, have spent more time in recent years documenting and describing the Central American chloropid fauna while our own species remain unknown and unidentifiable. It is a source of frustration (and embarrassment!) that I still cannot put names on some local common chloropid species. I obviously need to shift my priorities, and recruit more good students

Clearly, we, as a community, have much to do to make the Nearctic Diptera fauna identifiable and accessible. There are many tools we can use as we move forward and there has never been a better time for taxonomists and ecologists to take advantage of the power of this array of techniques – high resolution photography for morphological characters, efficient molecular techniques, new approaches in data management and publication, powerful mapping tools, web-based methods for collaboration – to get the job done.

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About terry wheeler

professor, museum director, entomologist, ecologist, naturalist
This entry was posted in Research News and tagged , , , , , , . Bookmark the permalink.

9 Responses to Barcodes and bristles, keys and trees

  1. phoridae says:

    Terry – Central American chloropids vs those from Canada- which advance science more and which are worth more of your valuable time? You can’t do everything (life is too short), so how do you prioritize? I grapple with this constantly, and would be interested in your take.

    From Brian, currently voting with his feet in Costa Rica.

  2. Hi Brian – great questions, and some tough ones. To answer the first, and easiest, one – I would argue that working on the fauna of either region advances science equally. If the goal of taxonomy is to describe biodiversity and make that knowledge accessible to other branches of science, then anything we can do to document the understudied fauna of any region is a significant contribution. How do I allocate my time and effort? Now THAT is a response that warrants a separate blog post, and it’s something I’ve thought about a bit over the past few years. I think it’s a great conversation to get started.

  3. Gunnar says:

    An argument for concentrating on central America is that tropical insect biodiversity both is much greater in magnitude and less well-known than temperate faunas. You say that about 50% of Canadian Diptera are yet to be identified. This is certainly believable, but what is the corresponding figure for Costa Rica? Brazil? Indonesia? Congo? We have very little of an idea of what to expect to be the total species numbers in the countries where the majority of biodiversity is to be found. Is it also in these countries where the infrastructure and the legal framework is worst suited for maintaining and managing said biodiversity, so the species that abund there today may not be there when your graduate students start considering this dilemma…

    However, in Canada it is not inconceivable that you can actually reach a fairly complete picture of what you have within your lifetime. Because of both the lower species richness and the physical proximity to the fauna you can get more specimens of each species and thus learn more about each of them. Furthermore the physical proximity makes it easier to do detailed natural history observations and understand what your animals actually do in terms of host plants, predators, parasites, life cycles, phenologies etc.

    I tend to think that tropical biodiversity is more important to study because of its size and our immense ignorance, but those factors also make it much harder to study. For convenience, the majority of my own work is on West Palearctic animals…

  4. Gunnar – I think you’ve summarized the temperate/tropical dichotomy, and described my dilemma, perfectly. I wear two hats in research – one taxonomist, one ecologist. If I were solely involved in taxonomic work, I think I would be much more excited to work on the tropical fauna – so much to discover, so much to describe, and a lot of it in peril (I will resist the temptation in this post to address Canada’s shameful record of protecting our own biodiversity). I could easily, and happily, spend the rest of my career describing and revising new Chloropidae from Central America or Australia or other tropical regions.

    On the other hand, I do research in community ecology of Diptera with my students and with other collaborators. In such studies, species-level resolution is very helpful, especially in ecologically diverse groups such as Diptera, and so there is a need for taxonomic expertise to inform the ecological analyses. There are many advantages to doing such research closer to home – the diversity and ecological structure of the systems is more manageable, more of the species can be identified, and more of their ecological interactions are known. This makes study design, analysis and interpretation easier (usually).

    The interests of our collaborators can also play a role in my choice of systems and localities. If someone offers me the opportunity to become part of a study in the Canadian arctic, or the prairies, or an eastern deciduous forest and there are both good research questions for my students, and a source of funding, then it only makes sense to collaborate. Plus it gives us the opportunity to show ecologists how much better their work can be when they work with taxonomists! (of course, I would jump at the opportunity to get involved with more such collaborative work in Costa Rica, or Australia, or . . . )

  5. Pingback: Setting priorities – so many questions, so little time | Lyman Entomological Museum

  6. fetalrainbow says:

    I’m wondering if your education in this area can help me. I’m working on an art project centered on the notion of flies playing a central role in the cyclic nature of life. its exciting to see all the flies here, and they enthusiasm to contrast the conventional cultural connotations of flies! I’ve been glueing them with an acrylic painting medium that goes on in a kind of mayonnaise consistency, and then I place the fly on top and it dries clear, locking the fly down. but I’m wondering, how long will they last left like that, and if they do decompose is there anything, like shellac or other lacquer I could use that would preserve them delicately? they appear completely dried out, and I’ve had some sitting this way for over a year and haven’t noticed a change, but i know nothing lasts forever (hence, the cycle of life, hah)

    also, by the nature of the piece and the amount I’m using I’m not able to enclose them in epoxy blocks, as some people have done for jewelry and such, it would need to be much thinner – as I said, like shellac possibly? I experimented with hairspray, to poor results.

    anyways, apologies for the peculiar question, and many thanks in advance for any suggestions
    -Richard

    • Hi Richard. An interesting question (and yes, I suppose some might find it peculiar . . . ). The good news is that the nature of an insect exoskeleton means that once the specimen is dried, they can potentially last, visibly unchanged, for hundreds of years. Many insect collections, for example, have pinned insects more than 200 years old that still look freshly collected. If they’re exposed they will accumulate dust, and if exposed to UV light they’ll fade, eventually. The main enemy of dried insects is, ironically, another insect – larval carpet beetles or larder beetles (dermestids). The larvae will crawl up the pin and eat their way through the dried specimen, potentially reducing it to dust (that whole cycle of life thing again). We keep dermestids out of collections by making sure the drawers and cabinets are well-sealed (some fumigants will help too), but that may or may not be a possibility, depending on the nature of your project. Dermestids may be less of a problem if the works with the flies are hung, for example.

      Sealing the flies with spray-on shellac (also derived from insects, of course), lacquer or another sealer might protect them slightly from dust, light and dermestids, but the trade-off is that even with a light spray you run the risk of gumming up the specimens as the finish fills in tiny spaces between bristles and the body. May not have the desired effect.

      If you’re gluing flies into the medium, I would also be careful to glue them by the body, and not just legs or wings. Even in our collection, if flies are only glued to their pin by a leg or two, there’s a good chance they’ll eventually get broken and blown off by breezes.

      Hope this helps. I’m definitely PRO flies in art.

      • fetalrainbow says:

        thanks so much! glad i found you, I’ve been pondering these questions for a good while now, and thats exactly what i needed to hear. back to work.

  7. fetalrainbow says:

    so, one of the pieces did have an issue with what i presume is the carpet beetle larvae. if they have been on it, is the whole thing compromised? there are thousands of flies in the piece itself, and only a number have been eaten away, but presumably laid eggs etc. is it at all possible to combat this?

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