A blog post highlighting the article  by Yong, Matile-Ferrero and Peeters in Insectes Sociaux.

By Christian Peeters

Many ant genera obtain honeydew from a variety of scale insects feeding on the sap of tropical trees. However, the most advanced and speciose scale insects – family Diaspididae – do not excrete honeydew, but build a protective shield made of wax and proteins and are known to associate with only one ant genus in Africa and Madagascar. The minute workers of Melissotarsus chew an extensive network of tunnels under living bark, and these are inhabited by vast numbers of diaspidids. Typically, these do not secrete the trademark shield when defended by ants, unlike free-living forms. Melissotarsus workers have extremely modified legs and cannot walk outside host trees, it is therefore assumed that they obtain all their food from the scale insects.

The Asian genus Rhopalomastix is strikingly similar in morphology to Melissotarsus, especially the bullet-shaped head of workers with the antennal sockets touching each other (in all other Myrmicinae, the antennal sockets are widely separated), and silk glands inside the head of adult females. However, the legs are normal, and a sting is retained. Molecular data confirm these are sister genera, sitting together on a separate branch. Rhopalomastix is widely distributed (India to eastern Australia), yet its biology was undocumented until Gordon Yong located it in Singapore. Four species nested in seven genera of living trees, together with five genera (one new) of diaspidids. Large numbers of naked diaspidids occurred in all ant nests, with only few shields.

Heads of Melissotarsus and Rhopalomastix workers, showing how the antennal sockets meet in the center of the face (SEMs by Roberto Keller). Note that the Melissotarsus mandibles are strikingly abraded, indicating an old individual. The ventral expansion of the head accommodates large opener mandible muscles, a novel adaptation for chewing through healthy wood (Khalife et al. 2018). Image: Roberto A. Keller/AMNH

This mutualism is distinct from others involving ants and scale insects because of striking differences in the biology of diaspidids: (i) they feed on parenchyma cells, not the sap; (ii) adults are strictly sessile. First instars (‘crawlers’) disperse but once they have selected a feeding spot and insert their stylets, the legs and antennae degenerate. Thus, ants cannot regulate the distribution of diaspidids within their tunnels, instead the crawlers decide! Ant eggs are distributed throughout the tunnels and larvae feed autonomously, a character also found in attine ants where larvae feed on the cultivated fungus. We lack direct observations of feeding behaviour because the ants switch to other tasks once we exposed the tunnels. Do they eat the flesh of diaspidids? Or their milk (secretions of wax and proteins normally used to build the shield)? Probably both. Diaspidid exuviae are not found in the tunnels, suggesting that they are also eaten by the ants.

Naked diaspidids (Andaspis numerata) and a few shields (green arrows) inside Rhopalomastix tunnels.

Trees hosting ants and scale insects generally benefit because the cost incurred from the ingestion of sap is compensated by the protection given by ants against leaf herbivores. This is not so in the mutualisms involving diaspidids with Melissotarsus and Rhopalomastix, because these ants are unsuited to be guards. Indeed, after removing bark and exposing tunnels, we observed that both workers and brood were preyed upon by Pheidole and Crematogaster ants. Field studies need to determine what is the impact on host trees, especially in fruit plantations (mangoes, durians, …) that are often preferred. Because only older trees are infested, we assume that these are more tolerant of the diaspidid exactions. Of special note is the host tree Aquilaria that is harvested commercially to produce an extremely valuable resin used for perfumes.

Numerous naked diaspidids in galleries of Rhopalomastix from Thailand. Ant larvae are scattered along the tunnels.

Rhopalomastix is likely to be widespread throughout tropical Asia but it is necessary to scrape tree bark with a knife in order to locate nests. Previous collection events were restricted to pyrethroid spraying of tree trunks, and soil pit traps (hence they are often classified as ‘litter ants’). We have recently found their arboreal nests in Thailand, Borneo and the southerly Japanese island of Okinawa.

Gordon Yong investigating a nest of Rhopalomastix on mango tree (Pulau Tekukor island, off Singapore).

References

Khalife A, Keller R, Billen J, Hita Garcia F, Economo E & Peeters C (2018) Skeletomuscular adaptations of head and legs of Melissotarsus ants for tunnelling through living wood. Frontiers in Zoology 15: 30.

 

Every day, thousands of papers in various research fields are published. Some of them receive lots of attention, while others remain unnoticed. Simultaneously, thousands of studies are not even submitted to journals because the results are insignificant or the authors think the work does not add sufficient new knowledge to their research field. In these joint interviews by Insectes Sociaux and Myrmecological News, Bert Hölldobler and Robert E. Page Jr. share some interesting insight about their own research and why some studies did not result in papers. Here, you will read the interview with Dr. Robert Page. Also, check out the corresponding interview with Dr. Bert Hölldobler!

IS: Dr. Page, as you look back on (and are still proceeding with) a fantastic career in social insect research, roughly how many papers have you published so far?

RP: I have published about 250 papers so far, including reviews and book chapters.

IS: Which of your papers received the most widespread attention? Did you expect this?

RP: The honey bee genome sequence paper in Nature in 2006 is by far the most cited, but I was one of a million authors, and it is basically a resource paper. I expected it to be the most cited.   Next is the Cell paper I published with Martin Beye in 2003.  I also expected it to be cited a lot because it is probably the most important paper I’ve been a part of.  It also represents a long hard struggle in my lab and Martin’s spanning about 7 years, and a question I actually started working on in 1980.  My 4^thmost cited paper is one I published in Experimental Gerontology with Christine Peng in 2001.  It was a review article on a subject I knew little about but was picked up and has been cited 300 times.  I never would have figured that.

IS: Have you published any papers that you think received insufficient attention from the scientific community? If so, can you give us an example?

RP: I have several, but I know why they didn’t receive the attention I thought they should.  I tend to undersell my work.  I don’t go for high impact journals, just because they are high impact.  I try to publish in the journal that is appropriate for the audience I am trying to reach.  Often that is an audience of specialists.  I also tend to publish places that let me present all of the data and methods.  In the long run, the ability to repeat someone else’s work is the hallmark of science, and you need to provide your data.  And, hypotheses and current trends in what is perceived as exciting science come and go, but bad data stand forever.  So, I try to present all of the data as best I can so they can stand whether my ideas do or not.

IS: What do you think is the main reason well-designed studies go unnoticed by the scientific community?

RP: Science today is like a collection of infomercials.  If you don’t package it right and sell it in the right venue, it goes unnoticed.  I guess I am an old fogey about this, but I believe it.

IS: Have you completed studies of which you have not published the results even though you consider them relevant? To how many projects or datasets does this apply over your career, approximately?

RP: Yes of course. I don’t believe in “do an experiment, write a paper.”  The objective of science in my mind is to contribute to an understanding of something. Sometimes experimental results obfuscate our understanding, not improve it.  Usually, more experimentation will fit the pieces together and lead to an understanding, but sometimes you don’t get back to it, so it sits in the filing cabinet, or in an electronic file on your computer desktop.  I have many incomplete studies sitting there.

IS: Do your unpublished datasets have anything in common? Why did you not publish them? Was it ever due to a lack of statistical significance?

RP: As I said in the previous question, it is usually because I can’t figure out how the results fit into a bigger understanding.

IS: Does the field of social insect research generally suffer from gaps due to data not being published?

RP: No, I think too much is published too soon.  We would be better off with fewer papers that actually resolve something.

IS: What do you think is the general trend over time concerning the amount of unpublished data? Stable, decreasing, increasing?

RP: I really don’t know about other people.  I think mine increased over time because as I got older and had more of a focus on specific questions that I wanted to answer, I became more demanding that each paper contributed to an understanding.

IS: Would you be willing to share any or all of these unpublished data so that others could learn from them or profit in any other way? If so, what might be a good platform for this? Do you think that, for example, a database could be set up for such data?

RP: That is a difficult question.  My idea about bad data lasting forever actually came from Darwin.  Often there are reasons data don’t get published, often it is a lack of confidence in them.  Something peculiar in the methods, or an environmental anomaly when the experiment was conducted.  I don’t think any data should be shared on a public platform that isn’t completely reliable and carefully screened.  If you do that, you should write the paper.

By Heike Feldhaar (University of Bayreuth, Germany)

Many people are fascinated by ants and their behaviour. Even children will often recognize these little busy-bodies that always seem to be determined to pursue their work. Ants have captured the attention of many hobby entomologists. At least in temperate regions of the world, they are an attractive and manageable group in terms of species number. However, species identification of ants is often difficult; in comparison to other insects, ants have seemingly fewer characters for easy identification, such as colour patterns of butterflies or bumblebees. Several ant genera, such as the Holarctic Lasius, Myrmica, or Formica, contain species that even professional myrmecologists have trouble identifying. Only a few very conspicuous ant species, such as Dolichoderus quadripunctatus or Lasius fuliginosus can be identified easily without magnifying glasses; many require some type of optical equipment. In the field, notes on the structure of nests or habitat features help to narrow down species identity.

A good guidebook should, therefore, include a workable key for species identification as well as an informative natural history section with detailed pictures. Bernhard Seifert’s The Ants of Central and North Europe (2018) provides precisely that. The book is divided into two major parts: a “General Part“ with an overview of ant natural history and ecology, and a “Special Part” with a key to all 180 species (for gynes and workers) occurring outdoors in Central and Northern Europe (and a few more that may expand their range into the region) and detailed natural history information for every species. Here, I describe the contents of these two parts in more detail.

The “General Part” (translated into English by Elva Robinson) comprises short chapters on the general morphology of ants, ecological aspects such as their habitats and nests, colony foundation and life cycles of colonies, social parasitism, natural enemies of ants, and feeding strategies. These feeding strategies include interactions of ants with trophobionts for honeydew consumption and seed dispersal by ants. This general part may be skipped by professional myrmecologists that are familiar with the general biology of ants and the corresponding terminology. For beginners, it lays the foundation for understanding the “Special Part” in which Seifert provides natural history details for every species.

The “Special Part” begins with a short introduction to ant determination and mounting, a list of the covered ant species (with a focus on Germany, Switzerland, Austria and South Tyrolia), a checklist of German ants with information on their distribution within Germany (occurrence in federal states, vulnerability and broad ecological niche), and an overview of their ecological preferences and tolerances. This table covers ~ 90 of the 180 ant species and is based on over 200 plots studied by Seifert in Central Europe during the years 1979–2015. It provides detailed information on temperature and humidity preferences and occurrence patterns with respect to plant cover. Thus, the three tables focus on the area where Seifert was most active himself, and less information is available on other areas of the geographic range covered in the book, such as Fennoscandia, Great Britain or Northern France. However, Seifert lists occurrences and ecology of species in these areas in the detailed species accounts. This part is followed by three short chapters where Seifert discusses methods of taxonomic delimitation of species (morphology vs. genetics), justifies the method used by him, numeric morphology-based alpha-taxonomy (NUMOBAT), and defends Linnean binomial nomenclature. These three chapters are part of an ongoing debate among taxonomists, and amateur myrmecologists will most likely skip these four pages.

Seifert then provides an identification key from subfamily to species level (for gynes and workers) for the 180 ant species with outdoor occurrence and nine Mediterranean species that will likely expand their range into Central and Northern Europe due to climate warming. Tramp species are also included, which are mostly found in warm buildings such as larger greenhouses. The key is illustrated with line drawings for many characters that allow for easy comparison of different character states. These drawings might be challenging for beginners, such as the detailed drawings of antennal scapes viewed from different angles of Myrmica workers, but once the reader has grasped the concept, these drawings are very helpful and allow identification to species level. The key works well for slightly advanced ant enthusiasts for the majority of species. For a few species, optical equipment with a micrometer is required; this will not be available to most amateurs, but this is a hurdle in all insect groups and not a failing of this book.

The key is followed by a detailed description of the life histories and profiles of all ant species covered in the book. Bernhard Seifert provides detailed information on the geographic range, habitat and ecology, abundance and nest structure, colony demography and population structure, as well as nutrition and behavior of all species (if known!). These natural history notes are beneficial to beginners and professionals alike. They contain most of the basic information known for each species and are referenced very well, which allows an interested reader to quickly find more details for each species (the reference section contains more than 1,000 references!). Thus, the book is a great starting point for myrmecologists who want to know about the natural history of a particular ant species. The life history and reference sections are substantially extended in comparison to the German book Die Ameisen Mittel- und Nordeuropas, which appeared in 2007 (Lutra Verlags- und Vertriebsgesellschaft), making it not a mere translation of the former.

Students, amateur myrmecologists, and specialists will appreciate Bernhard Seifert’s The Ants of Central and North Europe. The “General Part” provides an excellent overview of general ant ecology and natural history to enthuse amateur myrmecologists, whereas the keys might be challenging for beginners but are very helpful for specialists as they allow the identification of most ant species occurring in Central and North Europe. The extensive information on each ant species makes it an essential reference about ants in this geographic region for all interested readers – from beginners wanting to know more about ants to professional myrmecologists.

 

 

Reference

Seifert, B. 2018. The Ants of Central and North Europe. – lutra Verlags – und Vertriebsgesellschaft, Tauer, Germany, 408 pp; ISBN 9783936412079 (hardcover), EU € 64.00.