Highlighting the article by Mitra et al. in the May 2015 issue of Insectes Sociaux

Written by Aniruddha Mitra

Mate recognition is a vital aspect of communication, essential for survival of the species, as in nature males and females have to find each other and recognize the sex of the partner before engaging in reproduction related behaviors and mating. Sensing chemicals form a major part of the sensory world of insects, and chemical signals (pheromones) released by an individual are perceived by others, following which, the kind of signal received alters the behavior and decision making of the receiver.

Chemical signals called sex pheromones play an important role in attracting mates, sex recognition and mating related behaviors in the majority of insects. In many insects, sex pheromones are volatile chemicals that serve to attract mates from a distance. In some insects non-volatile chemicals like hydrocarbons present on the body surface have been implicated as sex pheromones. The external body surface (cuticle) of insects is covered by a waxy layer of hydrocarbons, which primarily serves to provide protection from dessication and pathogens. However in some insects, especially the social Hymenoptera (ants, social wasps and social bees), the cuticular hydrocarbons (CHCs) also play a role in communication.

CHCs can provide several types of information about an individual ant, bee or wasp. Variations in the composition of CHCs, allow workers to identify their queen, distinguish members of their own nest from those of other nests as well as obtain other forms of information about an individual. CHCs may also function as sex pheromones, and differences in CHC profiles of males and females (sexual dimorphism in CHCs) have been discovered in diverse groups of insects (more than 100 species from 7 different orders).

The social hymenopteran insects have been the focus of numerous studies of CHCs and their role in communication. However, few studies have looked at sexual dimorphism of CHCs or role of CHCs in mate recognition in social hymenopterans. Also sex pheromones (including CHCs as well as other volatile chemicals) remain a relatively less known area in the biology of Hymenoptera. Hence to generate more knowledge in this area, we investigated the question of whether sexual dimorphism of CHCs exists in our study species, a social wasp from southern India. We also tried to detect potential volatile cues that may attract mates from a distance.

The wasp Ropalidia marginata has been studied over more than two decades, and only in the last 5 years have we uncovered aspects of chemical communication in this species. We have discovered that the queen signals her presence to workers through a gland secretion and that through CHCs, workers can differentiate their own nest members from members of other nests. In our work detailed in Insectes Sociaux, we investigated another aspect of possible chemical communication in this species – mate recognition through chemical cues.

R. marginata wasps live in colonies comprising of a queen and several workers and build nests of paper from cellulose from plants. There is no seasonal variation in colony cycle, and all females can mate and have the potential to become a queen. Males stay on the nest for about a week and then leave the colony to live a solitary nomadic life. Mating is believed to occur on trees and other areas where females go out to collect food and building material, and has never been seen on the nest. Before mating, males approach females and touch them with their antennae, following which the male mounts the female and grasps her antennae with his antennae, finally culminating in mating.

Since the male and female touch each other with their antennae before mating, we looked for any non-volatile cue that may be present on the cuticle and be perceived by touching with antennae. We analyzed the chemical composition of non-volatile CHCs by gas chromatography (see Fig. 2). For a CHC to act as sex pheromone, there should be some consistent difference between the CHC profiles of males and females, otherwise the wasps would not be able to differentiate between the two. We did not find any significant differences in CHC composition between males and females, therefore we ruled out the involvement of any non-volatile CHC as a mate recognition cue.

Next, we explored the possibility that there are volatile cues that may act as sex attractants. We then further analysed the CHCs in order to detect chemicals that may be volatile. This analysis showed that volatile chemicals are absent in the CHCs. Finally we did a behavioral assay to see if males and females are attracted towards each other from a distance. By doing this, we could test for any volatile compound from the cuticle that may have been missed in the chemical analysis, and would also cover volatile cues from sources other than CHCs. Wasps were introduced at the center of a T-tube maze (see Fig. 3), and a female and a male were kept at either end of the T-tube (separated from the test wasp by a mesh). We found that males did not spend more time towards the side of the T-tube containing a female, compared to the side that had a male. The same held true for females, who did not spend more time towards the male side, compared to the female side. Thus we failed to find evidence of any volatile cues that may attract members of the opposite sex towards each other.

It remains unclear whether any sex pheromone exists in this species. In Hymenoptera, apart from CHCs, sex pheromones have been reported from various glands, so it is possible that some glandular secretion that is released after the male and female come in contact with each other plays a role in mate recognition. Compounds other than hydrocarbons like peptides and proteins are also reported to be present on the cuticle, and these may have a role in mate attraction. Finally it may also be possible that mate recognition in this species does not involve chemical cues and involves visual cues instead. Some social wasps have the ability to recognize faces (see, for example, here) and since the face of males is yellow, while those of females is brown (see Fig. 1), it is possible that they might use this visual cue to recognize members of the opposite sex, but we still need to search for the answer to how male and female R. marginata manage to find and recognize each other in a large and complex environments.

About the author: Aniruddha Mitra is a researcher at Laboratoire Evolution, Génomes, Comportement, Ecologie, CNRS, Gif sur Yvette, France. He can be reached by email at mitra.aniruddha@gmail.com.

Editorial

Insectes Sociaux now has a strategy for engaging the IUSSI community of scholar/scientists in a faster-paced and less formal mode of scientific conversation. Through our Facebook page, Twitter feed @InsSociaux, and blog, we aim to bring life to the often difficult to penetrate world of scientific publication and to connect our community in a new and dynamic way.

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Traditional scientific publication forms an extended and very slow-paced conversation. The segments of the conversation include citations of older publications, the interchange among authors, editors and reviewers during the publication process. Readers react to a publication, and ultimately may join the conversation by continuing the cycle by publishing work that adds another layer of citations to the conversation. The traditional conversation has tremendous advantages in providing a filtering system, via editors and reviewers, for quality-checking work prior to publication.

The traditional system also has enormous disadvantages in favoring a writing style that is compact, unexpressive of emotion, and very restrained. This means that an author’s passion for their work is left unexpressed. Opinions about interpretations are typically self-suppressed because they are likely to incite negative reviews. Sometimes—perhaps often!— jargon and cryptic writing cloak the significance of piece of scientific work so that it is only apparent to a small circle of colleagues who possess very specific expertise related to the topic of the article.

The blog gives authors and editors an opportunity to express their passion for their work in less formal terms. We can try to write clearly, to explain the history behind their scientific choices, and to articulate opinions about findings. We can argue for the significance of a piece of work and why the community should pay attention to that work. In other words, we add an element of excitement to the framework of our journal. By presenting our work in this way, we also make it accessible to wider audiences, who can (potentially) get as excited about our work as we do!

Our honest intent is to elevate Insectes Sociaux in the collective mind of our community so that we remain an important outlet for scientific publication. By providing immediacy, non-traditional outlets for expression, and a conversation that extends beyond the pages of the journal we hope to bolster the significance of Insectes Sociaux.

Michael Breed, Editor-in-Chief

Marianne Peso, Social Media Editor

Highlighting the article by Helms and Kaspari in the May 2015 issue of Insectes Sociaux

Written by Jackson A. Helms IV

When most people think of ants they probably picture a colony of wingless workers. Seen this way, it is easy to forget that ants are really just an odd family of wasps. Most ant queens, on the other hand, are indeed wasp-like, possessing wings and the ability to fly.

After maturation, virgin queens leave their birth nests and fly out into the world to mate, find a place to live, and start their own colonies. These aerial explorers—the mothers of the ant world—fascinate me. While most ant enthusiasts spend their time looking down at what worker ants do on the Earth’s surface, I spend my time looking up at what their elusive queens do in the atmosphere.

In our most recent paper, just out in Insectes Sociaux, my coauthor and I take a comprehensive look at queens from across the ant family to answer some questions about ant flight. How well do different species fly? Does flight vary depending on whether a queen hunts, farms, or acts as a social parasite that invades the nests of other species? How and why do some ant species lose the ability to fly?

To investigate these questions we compared queens of twenty-one ant species from Panama, ranging from the tiny Pheidole christopherseni (weighing in at less than a third of a milligram) to the grape-sized leafcutter ant Atta colombica (about 700 times as heavy). First we captured the queens on their mating flights using light traps hung in the forest. We then dissected them and examined their wings, flight muscles and abdomens to get some insight into how they fly based on their body size and shape.

We find that just as there is seemingly infinite variation in ant morphology, physiology and behaviour, (over 12,000 known species and counting), each species likewise varies in how it flies. Based on our analyses of the 21 species we collected in Panama, we found that tiny species are nimble flyers and able to stay aloft for a long time, while large species fly faster. Queens from the subfamily Ponerinae (which are primarily hunting species), have agile athletic bodies and large flight muscles, making them decent all-around flyers. Soft-bodied tree-dwelling ants (subfamily Dolichoderinae) appear to have short, fast flights—probably just long enough to find a suitable hollow branch or snag to settle in. Socially parasitic queens, who take over or make their homes inside other ant or termite nests, can probably fly longer and farther than queens who go through the trouble of starting a colony from scratch. Leafcutter ant queens, who plant and tend fungus gardens, likely get a similar boost in flight ability.

On the other hand, those hardworking queens who grow their own colonies through sheer individual effort, without the help of crops or a manipulated host species, have evolved the ability to carry extreme loads of fat and protein to fuel them as they start their massive families. In fact, we believe they can fly with more weight than any other known insect. The flight muscles of some species can carry nearly nine times their own mass! Not only do ants fly, but, by this measure at least, some of them are actually really good at it.

As for those species that have lost the ability to fly, permanently abandoning the skies of their ancestors and cousins, they may have done so in exchange for the ability to become extra fat and nutritious, thus ensuring they are productive mothers for the next generation. Tradeoffs like these are a pervasive theme in evolutionary biology (and pretty much everywhere else too).

As exciting as these insights are, they are based on only a tiny fraction of the world’s ant diversity. And we’ve conspicuously ignored male ants, which are also winged and wasp-like. What about them? How do they fly?

There’s still a lot of work to do before we come to a full understanding of flight ability in ants. We have, after all, only just begun to explore the hidden ant world above our heads.

About the author: Jackson A. Helms IV is a researcher at the University of Oklahoma. He can be reached by email at Jackson.a.helms-1@ou.edu or on Twitter @Marine_Ants.