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Dung beetles in high mountain landscapes of Oaxaca

By Matthias Rös, Alfonsina Arriaga-Jimenez, Bert Kohlmann

 

Dung beetles (Scarabaeidae) belong, besides ants and butterflies, to the best-studied insect groups in tropical ecosystems. Three subfamilies are considered as true dung beetles: Scarabaeinae, Geotrupinae, and Aphodiinae. There are about 10,000 species of dung beetles around the world known to science, although that number is still rising; montane areas in the tropics are exceedingly rich in species, and new species are regularly discovered. 

High mountain ecosystems in the American tropics have been less studied than the diversity-rich lowland rain forests, which have received greater attention and efforts for conservation purposes. Nevertheless, the significance of temperate ecosystems within the tropics may have been underestimated regarding their importance to explain species distribution patterns in various biodiversity hotspots of the Earth. Mexico, and particularly the state of Oaxaca, will serve us here as an example to explain why. 

Oaxaca is one of the most (if not the most) biodiverse states of Mexico. One reason is the rugged orography, shaped by different geological events, which, accompanied by changing climate, separated and connected animal and plant populations several times, and so turned Oaxaca into a laboratory of species evolution. Oaxaca is situated in the southeast of Mexico and is dominated by three major montane areas (Sierra Norte, Sierra Sur, Mixteca Shield). Eighteen percent of the state has an elevation higher than 2000 m, and around four percent is situated between 2500m and 3700m. 

Typical land-use patterns in Oaxacan mountains. Forest dominated landscapes with traditional milpa system (corn, beans, squash). El Rosario Temextitlan, Chinantla, Sierra Norte de Oaxaca at elevations between 2000 and 2700 m. Photo by Matthias Rös.

In the last two years, we have collected and described new dung beetle species from Oaxaca. All of them were not collected in pristine or remote places, but in mountain forests close to the capital city of Oaxaca. Whereas the state has few large reserves, Oaxaca is known for its high number of community-conserved areas (CCA), and the new species were collected in the CCA La Mesita, in San Pablo Etla, a 3000 ha community-managed forest at altitudes between 1800 and 3200 m, which provides firewood, clean water to the entire watershed, and offers small scale sustainable tourism. In Oaxaca, at lower altitudes, there exists an oak forest, with mostly small trees that lose all their leaves during the dry season, reminiscent of the familiar chaparral vegetation. In Oaxaca, this oak forest is a typical vegetation type of piedmont, mostly surrounding the Central Valley. We named Canthidium quercetorum after this forest type, only known at present from La Mesita. Onthophagus etlaensis, named after the Nahuatl word for bean-fields, sampled by us in the same reserve, had already been collected in the 1970s but was erroneously identified because of its closeness to another, more common species. This is a very typical pattern found in Oaxaca: there abound many endemic sister species of common and more widespread taxa, and they have a small distribution range in the mountains of Oaxaca, which indicates their speciation in situ.  Finally, Phanaeus dionysius, a veritable jewel of a beetle, was also found in this CCA.

Onthophagus etlaensis (left) and Phanaeus dionysius (right), two dung beetle species of the subfamily Scarabaeinae, described from the community-conserved area of La Mesita, San Pablo Etla, near the city of Oaxaca.

Oaxaca belongs to the Mexican Transition Zone, a region ranging between the southern USA down to the Nicaraguan lakes. Its outstanding characteristic is the overlap of Nearctic and Neotropical species distributed here, the former more often at higher elevations with the latter at lower elevations. Both Neotropic and Nearctic faunas have generated a high number of endemic species in Mexican mountains. 

Besides its rich biodiversity, Oaxaca is also one of the most understudied states in Mexico, and regarding plant or animal groups we have only little information. This  might explain why we also found, in addition to the recently described species, some species which were last collected 45 years ago. 

This map shows Oaxaca as depicted by a 3D Digital Elevation Model. Black dots represent sampling sites for Onthophagus anthracinus, the red dot Canthidium quercetorum, and the blue dot Phanaeus dionysius.

AAJ started to work on dung beetle diversity at high-altitude mountains ten years ago when she collected insect material from the alpine prairies of the Trans-Mexican Volcanic Belt (TMVB). For her Ph.D. project, she moved up to high elevations between 2500 and 3500 at four volcanos. One of the most interesting results was that a high variability of diversity patterns between the volcanoes existed. We also found an unexpectedly high diversity, coupled with low abundances and detection probabilities, that in three years of sampling, abundances were still lower than what you collect in one rainy season in a cloud forest. Our next step shall be to compare diversity patterns between the mountains of Oaxaca and the Trans-Mexican Volcanic Belt. Bert Kohlmann has studied for almost three decades the dung beetle communities in the high altitude-mountains of Costa Rica and Mexico, where interesting evolutionary phenomena have been discovered associated with the Last Glacial Maximum. Nevertheless, to detect and understand processes which determine diversity patterns at high altitude mountains in the tropics, more attention, longer sampling periods, and deeper taxonomic knowledge of the species and their phylogenetic relationships covering the whole Neotropics is needed. Matthias Rös studies diversity patterns in natural and human-modified landscapes, looking for biodiversity-friendly land-use patterns. Oaxaca seems to have plenty of these biodiversity-friendly land-use patterns in its mountain landscapes, despite or even because of a human-induced modification history dating millennia. Our research of describing new species is the baseline for further investigations. How can we protect the outstanding biodiversity under scenarios of climate change and land-use intensification? Oaxaca might suggest very interesting answers to many questions related to this topic. Oaxaca and its mountains still have many secrets to unfold, and we want to explore and reveal them.

 

Arriaga-Jiménez, A., Escobar-Hernández, F., Rös, M., & Kohlmann, B. (2020). The establishment of the Onthophagus anthracinus (Coleoptera: Scarabaeidae) species complex and the description of a new species. The Canadian Entomologist, 152:1-17. https://doi:10.4039/tce.2019.62. (Paper made available to read for FREE until March 24, 2020 in cooperation with Cambridge University Press)

 

Related research to dung beetles in high mountains:

Kohlmann B., Arriaga-Jiménez, A., Rös, M. 2018. Dung beetle vicariant speciation in the mountains of Oaxaca, Mexico, with a description of a new species of Phanaeus (Coleoptera, Geotrupidae, Scarabaeidae). ZooKeys743:67-93. https://zookeys.pensoft.net/articles.php?id=23029

Arriaga-Jiménez, A., Rös, M. & Halffter.G. 2018. High variability of dung beetle diversity patterns at four mountains of the trans-Mexican volcanic belt. PeerJ 6:e4468. https://doi.org/10.7717/peerj.4468

Kohlmann, B., Arriaga-Jimenez, A., & Rös, M. 2018. An unusual new species of Canthidium (Coleoptera: Scarabaeidae: Scarabaeinae) from Oaxaca, Mexico. Zootaxa 4378 (2): 273–278. https://doi.org/10.11646/zootaxa.4378.2.7

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Spiders with an identity crisis: a new taxonomy paper

The following is a guest post by Terry Wheeler, from the Lyman  Entomological Museum at McGill University. It is re-posted from the Lyman Museum Blog, where it originally appeared. 

Two wolf spiders, whose names are Pardosa lapponica and Pardosa concinna, run across open ground all over northern Canada. Here’s the problem: these two species of spiders live in a lot of the same places, and they look very similar. Katie Sim, a grad student working with Chris Buddle and me here at McGill, asked the obvious question: are these spiders really separate species? Katie’s insights on that question were just published in the journal Zootaxa.

As taxonomists, we can use multiple kinds of evidence to determine species limits. This includes things like morphology, genetic sequence data, geographic distribution, and ecology. These two species were originally described from widely separated areas: P. lapponica from Lapland, and P. concinna from Colorado. But since then they’ve been found in many more sites and we now know that their ranges overlap in northern North America.

The other long-accepted way of distinguishing between these two species was a small morphological difference between their reproductive structures (many closely related arthropods look very similar externally, but if there are differences, we often see them in the genitalia. “Why?” is a topic for another post).

As Katie collected spiders as part of our Northern Biodiversity Program fieldwork in northern Canada, she realized that the morphological differences between the two species weren’t that clear-cut, once you take variation into account. Based on careful measurements of specimens from all across the north, Katie found overlap in almost all morphological characters, even genitalic characters that had been used in the past. There was only one small piece of the complex male mating structures (the terminal apophysis, for the spider fans reading along) that seemed to hold up as a difference between the species (and only the males, obviously). Question marks started to appear.

sim-et-al-fig-3

Katie’s next step was to delve into the genetic differences between the two species. Even though species can look very similar externally, DNA sequence data sometimes uncovers fine differences between them. This is especially helpful with closely related, or recently diverged species. Katie used the DNA barcode, a section of the mitochondrial gene CO1, which has proven pretty useful for distinguishing animal species. And the DNA results showed some interesting patterns, some of which were unexpected.

sim-et-al-fig-5

The figure above is a haplotype network. Each circle is a little island of genetic similarity, connected to other islands by the lines. We’d expect different species to be part of separate “islands”, but that didn’t happen here. Pardosa lapponica (in light gray) and P. concinna(in black) sometimes share the same haplotype, and each of the two has multiple haplotypes. That means there’s more genetic variation within a “species” than between them. But wait! There’s more!

After a suggestion from one of the reviewers on an earlier version of the paper (this back-and-forth of suggestions is one of the strengths of peer-reviewed science), Katie looked at the CO1 barcode sequences of P. lapponica specimens from northern Europe, where it was originally described. Unexpectedly, the Russian specimens (the dark gray circles without numbers in the figure above) were genetically distinct, by a good margin, from the North American specimens of P. lapponica.

So what does this all mean, taxonomically? First, the spider we call “Pardosa lapponica” in North America seems not to be the same species as “Pardosa lapponica” from northern Europe (which “owns” the name, because it was described from there first). Our North American P. lapponica may, in fact, be the same species as the spider we’ve been callingPardosa concinna, but before we can make the final decision on that, it would be necessary to study additional North American specimens, especially from Colorado (the “type locality”, or collection site of the original P. concinna), to confirm this.

And that’s how taxonomy often works: good, careful research will answer one question, and in the process, new questions pop up. Sometimes, you think you know a spider, and sometimes, you realize you really don’t.

Reference

Sim, K.A., C.M. Buddle, and T.A. Wheeler. 2014. Species boundaries of Pardosa concinna and P. lapponica (Araneae: Lycosidae) in the northern Nearctic: morphology and DNA barcodes. Zootaxa: 3884: 169–178.

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Myrmica brevispinosa, the short-spined ant
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The trouble with common names

By Dr. Staffan Lindgren, University of Northern British Columbia

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When teaching Invertebrate zoology, entomology or forest entomology, I am regularly asked by students if they can use common names. Mostly this request is precipitated by the perceived difficulty of memorizing, let alone pronouncing, Latin names. I am fairly relaxed about these things, particularly with forestry students, who are quite unlikely to become entomologists no matter how you define that term.  It should be clarified that forest entomology is taught within a Disturbance Ecology and Forest Health course at my institution (UNBC), with diagnostics in half of a separate lab course. My stock answer is thus that they may use common names as long as the name clearly defines the species they are referring to.

Foresters are prone to colloquial terms, whether with respect to insects, trees or other organisms. For example, subalpine fir (Abies lasiocarpa) is called balsam by many, if not most foresters in BC, even though it is a distinct species from balsam fir (Abies balsamea) of eastern North America. Similarly, Pissodes strobi, the white pine weevil, is called spruce weevil (a legacy of the days when this weevil was considered three separate species, two of which primarily infest different spruce species in the west) or simply leader weevil.  The reason, supposedly, is that it is the wood quality that matters in terms of trees, and the type of damage with respect to insects. The consequences of being a bit loose with the taxonomy of a particular species may therefore seem fairly inconsequential in forestry.

Incidentally, our forestry students have even more to worry about when it comes to pathology, which they have to learn at the same time, as the same biological organism often has two completely different Latin names (including genera) depending on whether it is the sexual or asexual form (why this remains an accepted practice is beyond me), and they often do not have common names. Add the fact that fungal species seem to change name more often than I change vehicles (I was going to write ‘shirt’, but didn’t want to gross anyone out making you think that I wear the same shirt for years), and it becomes rather a nightmarish proposition for the poor students.

When it comes to entomology in general, however, common names are most commonly used in casual conversation, particularly with members of the public. For entomologists this is usually not a problem, but for non-entomologists it can be very confusing.  For example, colloquial use of ‘bug’ is pretty much anything that is small and crawls or flies around. Taxonomically it is quite specific (Hemiptera: Heteroptera). Ladybugs (Coleoptera: Coccinellidae) are perhaps the most recognizable insects to people in general, but they are clearly not bugs. Plant lice (Aphidoidea and Phylloxeroidea), bark lice (Psocoptera) and body lice (Phthiraptera) represent three vastly different taxonomic groups. In addition, if the non-louse groups above were to be correctly written to show that they are not Phthirapterans, there should be no space – however for these common names that principle is never applied as far as I can tell. It is to differentiate dragonflies, damselflies, stoneflies, mayflies, whiteflies etc. from the true flies. For example, a dragon fly, if there were such a thing (and probably there is somewhere – perhaps a decapitating fly (Phoridae) comes close enough to earn that epithet!) would be a dipteran, whereas a dragonfly is not. How is a non-entomologist supposed to know that (assuming that it is important to anyone except us entomophiles)? Then we can go on to more obvious misnomers such as ‘white ants’, which aren’t ants (Hymenoptera: Formicidae) at all, but termites (Isoptera).

Going back to forest entomology, one can have all kinds of fun with some common names, the origin of some could serve as fodder for endless speculation. For example, when discussing the problems with common names, I ask my students what they think a sequoia pitch moth (Synanthedon sequoiae)(Lepidoptera: Sesiidae) would attack. The correct answer is naturally “mostly lodgepole pine, but not sequoia”. Similarly, the Douglas-fir pitch moth (Synanthedon novaroensis) commonly breeds in lodgepole pine, but as far as I know not in Douglas-fir. I then go on to western spruce budworm, which as the name does not imply primarily attacks Douglas-fir.

Myrmica brevispinosa, the short-spined ant

Myrmica brevispinosa, the short-spined ant

Clearly one cannot expect members of the public to keep track of Latin names of insects, so common names are here to stay. I was interested to find in a book I recently purchased (Ellison et al. 2012) that the authors had invented common names for every species by essentially translating the Latin species epithet. That creates an interesting situation vis-à-vis the attempt of entomological societies to standardize common names (http://www.esc-sec.ca/ee/index.php/cndb; http://www.entsoc.org/common-names). Nevertheless, some ants simply retained their genus name, e.g., Harpagoxenus canadenis became “The Canadian Harpagoxenus” (not sure why, as they named the genus “The robber guest ants”), Formica hewitti became “Hewitt’s ant”,  Myrmica brevispinosa (the species in the photo accompanying this article) is called “The short-spined ant”, and perhaps my favourite Lasius subglaber was named “The somewhat hairy fuzzy ant”. Common names aren’t generally that innovative, but Latin names certainly can be.

Many years ago May Berenbaum (1993) wrote a column on this topic. If students would all read Dr. Berenbaum’s eminently humorous take on how insects get named, they would without a doubt get a new appreciation for both Latin names and their creators, and perhaps feel less trepidation about memorizing them. Then not only true blue entomologists would be tempted to buy a bumper sticker that read “Sona si Latine loqueris” (Honk if you speak Latin) (Unverified from http://www.latinsayings.info/).

Berenbaum, M. 1993. “Apis, Apis, Bobapis….”, American Entomologist 39: 133-134.

Ellison, A.M., N.J. Gotelli, E.J. Farnsworth, and G.D. Alpert. 2012. A field guide to the ants of New England. Yale University Press, New Haven and London, 398 pp.

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Female of Polistes parametricus Buck Vespidae Wasp
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Taxonomic adventures in the world of paper wasps (Polistes, Vespidae)

By Matthias Buck, Royal Alberta Museum, Edmonton

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For many of us who are working as taxonomists, describing new species has become somewhat of a routine. Sometimes it can even become a burdensome chore: I am thinking about those of us who work on hyperdiverse groups of insects in the tropics where almost every species is undescribed (case in point: one of my former lab mates recently described 170 new species of a single genus of Diptera in one paper!). However, the feeling is very different when new species unexpectedly show up in iconic groups that were thought to be well-known. Suddenly, common and familiar creatures turn into an exciting new research frontier, providing a fresh rush of adrenaline!

Mug shot of a female of Polistes hirsuticornis Buck. Vespidae Wasp

Mug shot of a female of Polistes hirsuticornis Buck. The hairs on the basal articles of the flagellum are longer than in related species (Photo credit D.K.B. Cheung & M. Buck).

This is what happened a few years ago when I started working on the vespids of the northeast. The family Vespidae (which includes mason wasps, paper wasps, yellowjackets and hornets) is most diverse in warmer parts of the World, as is the majority of stinging wasps. Doing a review of the northeastern Nearctic fauna therefore didn’t seem to be a very promising project for taxonomic novelty. Especially considering that the fauna of the eastern half of the continent is significantly less diverse and far better known than that of the west.

To my utmost surprise the study (published 2008 in the Canadian Journal of Arthropod Identification) not only turned up four new species of mason wasps but also two new paper wasps (Polistes). As you know, paper wasps are some of the most iconic species in the world of wasps, almost as much as their odious relatives, the yellowjackets. Further to that, they have received great attention as model organisms for the study of social behaviour and its evolution in insects. Finding not only one, but two new species in a group like this was beyond what I expected in my wildest dreams.

So how did it come to pass? As a novice to paper wasps I expected that reviewing the taxonomy of such a high-profile group would be like a walk in the park. Weren’t there scores of scientists before me who seemingly had no difficulties in identifying these sizeable and handsome insects for their behavioral studies, filling up cabinets of specimens in collections across the continent? Or so I thought! After months of fruitless staring through the microscope my nonchalant attitude gradually turned into frustration. One of the species, the common and widespread Northern Paper Wasp (Polistes fuscatus), was so variable that it blended virtually into almost every other species in the same subgenus. Previously published keys gave me a pretty clear sense of what typical specimens of each species look like, but where were the objective criteria that would allow me to identify the numerous intermediate forms? Truly, I found myself in a taxonomic quagmire!

Aedeagus of Polistes parametricus Buck. Vespidae Wasp

Aedeagus (penis) of Polistes parametricus Buck. The size, shape and position of teeth is diagnostic with regard to P. fuscatus and P. metricus, with which this species was previously confused (Photo credit D.K.B. Cheung & M. Buck).

Grasping for straws I turned to three taxonomic methods that had not been applied to Polistes before: DNA barcoding, detailed study of male genitalic features and morphometric analysis. During the previous months, I had rounded up a number of puzzling specimens which represented the spearhead of my taxonomic headaches, and submitted them for sequencing. The results came back like a thunderclap, turning my anguish into cautious excitement: the DNA barcodes of these troublemakerswere clearly different from any of the described species. With renewed energy I launched into a detailed morphological study which led to the discovery of several new diagnostic characters, confirming the distinctness of these wasps beyond a doubt. A lot of hard work had finally paid off, and I was looking at the first newly discovered species of paper wasps in eastern North America since 1836 when Amédée Louis Michel Lepeletier de Saint-Fargeau described Polistes rubiginosus!

Female of Polistes parametricus Buck Vespidae Wasp

Female of Polistes parametricus Buck nectaring on goldenrod in West Virginia (Photo credit: Donna Race).

Since molecular methods, and in particular DNA barcoding, have received a lot of attention in recent years, it seems opportune to share some of my experiences working on Polistes. Unlike a few other taxa (such as spider wasps, Pompilidae), vespids sequence nicely and easily from pinned specimens, which makes them an ideal group for this kind of study. I found the sequence data extremely helpful but they certainly did not provide the cure of all taxonomic confusion. Barcoding uncovered an unexpected genetic diversity below the species level, which proved to be hard to interpret in the absence of other data. In Polistes there is no hint of a “barcoding gap”, which postulates that genetic distances between individuals of the same species are (nearly) always greater than those between conspecific individuals. In fact, some of the species were genetically so similar that they differed by a mere 2 base pairs (out of 658). Nonetheless, the combination of molecular data with fine-scale morphology resulted in a quantum leap forward for Polistes taxonomy. Just days ago, I found out that a group of researchers in Germany and Switzerland are making similar progress on European paper wasps using a nearly identical approach.

My research paper on eastern Nearctic Polistes, including formal descriptions of Polistes hirsuticornis Buck and P. parametricus Buck, was published in the journal Zootaxa on October 1st.
Matthias Buck, Tyler P. Cobb, Julie K. Stahlhut, & Robert H. Hanner (2012). Unravelling cryptic species diversity in eastern Nearctic paper wasps, Polistes (Fuscopolistes), using male genitalia, morphometrics and DNA barcoding, with descriptions of two new species (Hymenoptera: Vespidae) Zootaxa, 3502, 1-48 Other: urn:lsid:zoobank.org:pub:6126D769-A131-49DD-B07F-0386E62FF5B9

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