A blog post highlighting the article by N. Tsvetkov, B. Madani, L. Krimus, S. E. MacDonald, and A. Zayed in Insectes Sociaux

By Armo Zayed

 

 

As central place foragers, honey bees have an amazing ability to fly several kilometers away from their colony to forage and then beeline back to their home without getting lost. Honeybee foragers can perceive and communicate spatial information via the famous waggle dance. But how are these traits encoded in the honey bee genome?

When Nadia Tsvetkov joined my lab in 2012, she was keenly interested in studying the genetics of spatial learning and memory in bees. She spent several months training bees to fly through mazes. The maze experiments were fun but took too long, and our sample sizes were far fewer than the hundreds of bees needed to tease out the likely subtle genetic effects on learning and memory. What we needed was an assay that was as fast and as easy to standardize as the proboscis extension reflex assay – the workhorse of insect olfactory learning and memory studies. We tried some different approaches (one involved a very beautiful but unwieldy maze constructed out of Christmas balls) until colleague Dr. Suzanne MacDonald, a vertebrate biologist at York University’s Department of Psychology, suggested that we try the food search task paradigm. The paradigm is commonly used to study spatial learning and memory in primates and rodents. A common protocol entails hiding toys or food in boxes within a testing arena that animals are allowed to explore. Over time, the animals learn and can recall the location of boxes that contain rewards.

So we set out to try a similar assay on bees. For prototyping, we used some common and inexpensive items; we made the testing arena of clear Tupperware containers and we employed several artificial flowers made out of Q-tips. After a few pilot assays, we decided that a small arena containing four flowers was the best compromise between complexity and length of the experiment. Nadia worked out the testing protocol that involved placing bees into the arena where one of the artificial flowers had a sucrose reward. Once a bee found and fed from the rewarding flower, it was removed and tested again for a total of three training trials. Finally, the bee entered the arena where none of the flowers had a sugar reward. This time, the bee had to rely solely on its memory to find the focal flower. Our data analysis showed that bees subjected to this test exhibited two telltale signs of learning and memory: they improved their ability to find the rewarding flower during training, and they were able to recall the location of the rewarding flower after training. The Food Search Box (FSB) was born.

We carried out two more experiments to test the utility of the FSB for studying spatial learning and memory in bees. We first compared the performance of nurses (young honeybee workers that nurse the brood) and foragers (older workers that forage outside the colony) in the FSB paradigm. While both nurses and foragers did equally well in the training trials, foragers did substantially better than nurses in the memory test. So, is it age (young vs. old) or behavioral state (nurse vs. forager) that is influencing spatial memory in the FSB? To answer this question, we carried out another study on same-aged workers. We treated these workers with either cGMP, which causes precocious foraging, or cAMP, which does not alter behavioral state. The cGMP-treated bees performed similarly to foragers in the FSB, while cAMP and the control bees performed like nurses in the assay. Taken together, the results of these two experiments indicate that behavioural state (nurse vs. foragers) is primarily associated with differences in spatial memory in the FSB.

We are very excited by the results of the FSB; we were able to test bees quickly without much attrition. It is feasible to screen hundreds of bees within a short period, opening up the door for genetic and genomic studies of spatial learning and memory in honeybees. While it is certainly possible to improve on the design to enhance automation (i.e., RFID readers or tactile sensors to passively record visits to artificial flowers), the low-tech version presented in the paper is very easy to set up and perform. We are looking forward to feedback from the community on the test, and we hope it will provide a useful tool for studying spatial learning and memory in honeybees and other insects.

A blog post highlighting the article by M. Maziarz, R. K. Broughton, G. Hebda, and T. Wesołowski in Insectes Sociaux

By Marta Maziarz

As an ornithologist, I have focused on the reproduction of birds but often overlooked the fact that bird nests can also be home to many invertebrates that find shelter, food or a suitable microclimate within them. When we discovered ant workers and their larvae inside nests of the wood warbler Phylloscopus sibilatrix, curiosity drove us to study this phenomenon.

An initial literature review revealed just a handful of published records of ant broods found inside bird nests, including blue tits Cyanistes caeruleus breeding in nest-boxes in Corsica (Lambrechts et al. 2008), and great tits Parus major and marsh tits Poecile palustris occupying tree cavities in primeval stands of the Białowieża Forest, Poland (Mitrus et al. 2015). Blem and Blem (1994) reported ant colonies on the side of nests in nest-boxes used by prothonotary warblers Protonotaria citre but gave no further details. This surprising scarcity of observations of ants in songbird nests suggested that this phenomenon may be exceptional and occur only among cavity-nesting species.

Our discovery of ant workers and their larvae in wood warbler nests, which are domed structures composed of dry grass, moss, and leaves and situated on the forest floor, challenged this view. We made the original finding during long-term studies of wood warbler ecology in 2004-2015 in Białowieża Forest (Eastern Poland), which prompted us to document this phenomenon systematically during 2016-2017. In 2017, we also contacted researchers in Switzerland and the UK to ask them to inspect nests for the presence of ants and their broods. We wanted to find the frequency of ants colonising wood warbler nests, and whether ants are present in wood warbler nests elsewhere in the species’ breeding range.

During our systematic observations in 2016-2017, we found adult ants in 43% of warbler nests, and one-third of nests also contained ant larvae or pupae. These ant broods were situated within the sidewalls of the nests, at or just above ground level. The most frequent species were Myrmica ruginodisor M. rubra, and occasionally Lasius niger, L. platythoraxor L. brunneus. These numbers, compared to 30% of nests containing adult ants and 20% containing broods during the earlier (2004-2015) period, indicated a long-term association between the ants and the birds. The findings from Białowieża Forest contrasted with those from Switzerland and the UK, where we only found single cases of adult ants and their broods. The different frequencies of ant presence between regions could be due to varying densities of bird or ant nests between woodlands transformed by humans to a different degree, but further studies would be necessary to confirm this.

These first records of adult ants and their broods in wood warbler nests showed that occupation of bird nests by ants can be a locally common phenomenon, which may have been overlooked previously in this and other songbirds. Systematic examination of nests belonging to different bird species would be valuable in understanding this further.

Furthermore, the occurrence of ant broods in the walls of wood warbler nests showed that ants colonised these structures following their construction by birds. Why they do this remains unclear; are the ants attracted to the nests by their structure, the presence of other invertebrates as a source of protein, or by heat generated by the birds? More work is underway to answer these questions, but it seems that these potential ant-bird interactions could be much more widespread than has been suspected.

References

Blem CR, Blem LB (1994) Composition and microclimate of Prothonotary warbler nests. Auk 111:197–200.

Lambrechts MM, Schatz B, Bourgault P (2008) Interactions between ants and breeding Paridae in two distinct Corsican oak habitats. Folia Zool 57:264–268.

Mitrus S, Hebda G, Wesołowski T (2015) Cohabitation of tree holes by ants and breeding birds in a temperate deciduous forest. Scand J For Res 31:135–139.

Highlighting the article written by J. C. Jones et al. in Insectes Sociaux

Written by Insectes Sociaux Editor-in-Chief, Michael Breed

Molecular techniques for identifying microbial community composition have created a
true biological revolution. Recent discoveries lead us to understand the bacteria as an
evolutionarily complex and diverse domain, and this in turn has sparked interest in
characterizing microbiota from a large number of contexts. Of particular significance has been the exploration of gut microbiomes, which vary dramatically among species, and developmentally within species. Gut microbiomes interact strongly with diet and health, giving added interest to studies focusing on this subset of communities (Dunn 2011, DeSalle and Perkins 2016).

We have long understood the importance of the gut microbiome in social insect species. In termites, some components of the microbiota reduce cellulose to usable sugars while in other species, members of the microbiota fix nitrogen. More recent studies of ant and bee gut microbiomes have shown some level of intraspecific consistency even over broad geographic ranges, but also variation associated with diet and to a certain extent differences among colonies.

In this issue of Insectes Sociaux, Jones and her colleagues (Jones et al 2018) focus on
differences in the gut microbiota based on task group in honeybee (Apis mellifera) colonies. This is a question previously addressed by Kapheim et al (2015) but Jones and colleagues add critical dimensions by age-matching the worker bees in their study and collecting gut samples from bees observed performing specific tasks.

Each of five experimental colonies consisted of 1500 workers of the same age and from
the same source colony (400 of which Jones and colleagues individually marked). They
observed worker behavior in ten to fourteen-day old bees. Nurses, food receivers/handlers and foragers were noted and collected. This approach allowed assessment of diet and task-related differences in microbiomes independent of age-related developmental effects.

Jones et al (2018) found that Firm-4 (Lactobacillus mellis), one of the characteristic
bacteria of the honeybee microbiome, was more prevalent in nurse and food handling bees than in foragers. This pattern was also seen with quite a few other bacteria species, which had higher presences in nurses and/or food handlers than in foragers. One species, Lactobacillus kunkeei, was more common in forager guts, although they found it less commonly there, so this result is more provisional. Of particular note in the guts of food processing bees was Bartonella apis, as this species expresses genes that may be involved in the degradation of secondary plant metabolites.

Globally, the microbiomes of nurses and food handlers were more diverse than the
microbiome of foragers. Jones et al (2018) suggest that the needs for carbohydrate metabolism are higher for nurses and food handlers and that perhaps this drives functional differences in the gut microbiome between these task groups and foragers.

Concerns over bee health, responses of bees to diseases or parasites, and the impact on bees of the agricultural use of antimicrobials have generated much of attention given to bee microbiomes (Napflin and Schmid-Hempel 2018, Raymann and Moran 2018). While these topics are important, the microbiomes of social insects existed long before humans started to impact social species, and social insect microbiomes must have evolved alongside sociality. How might gut microbiomes facilitate worker task performance? Do they determine workers’ roles within colonies? The cause and effect relationship between task group and microbiome could go in either direction, with task environment driving the microbiota or the nature of the microbiological community feeding back into the task choice of bees. This study presents these alternatives as tantalizing avenues to pursue in future research.

References

DeSalle R, Perkins SL (2016) Welcome to the microbiome: Getting to know the trillions of bacteria and other microbes in, on, and around you. Yale University Press 264pp.

Dunn R (2011) The wild life of our bodies: Predators, parasites, and partners that shape who we are today. Harper 304pp

Jones JC, Fruciano C, Marchant J, Hildebrand F, Forslund S, Bork P, Engel P, Hughes WOH (2018) The gut microbiome is associated with behavioural task in honey bees. Insect Soc https://doi.org/10.1007/s00040-018-0624-9

Kapheim, KM, Rao VD, Yeoman CJ, Wilson BA, White BA, Goldenfeld N, Robinson GE (2015) Caste-specific differences in hindgut microbial communities of honey bees (Apis mellifera). PLoS ONE 10: e0123911

Napflin K, Schmid-Hempel P (2018) Host effects on microbiota community assembly. J Anim Ecol 87: 331-340

Raymann K, Moran NA (2018) The role of the gut microbiome in health and disease of adult honey bee workers. Current Opinion in Insect Science 26: 97-104

A blog post highlighting the article by R. Palavalli-Nettimi and A. Narendra in Insectes Sociaux

By Ravindra Palavalli-Nettimi and Ajay Narendra

Imagine finding a location in a new city without any map. How would you navigate toward your destination?

If you were an ant, you could use celestial cues such as the position of the sun or the polarised skylight pattern (Wehner and Strasser 1985; Zeil et al. 2014) as a compass to navigate in the direction of your destination (e.g., nest). The compound eye of an ant has a few special ommatidia that are sensitive to polarised skylight (light waves oscillating in one orientation). However, the eye size and also the total number of ommatidia in the ants’ eyes decrease with their body size. Some ants have close to 4,100 ommatidia (Gigantiops destructor) in their eyes while a miniature ant has a mere 20 ommatidia (Pheidole sp.). However, it is not clear how this variation affects their ability to navigate.

 

 

In this study, we investigated how size variation affects ants’ ability to use celestial cues to navigate towards their nest.

To test this, we captured ants on their way to their nest and displaced them to a circular platform. The displacement site was at least 500-1,000 m from the ants’ nest and was surrounded by a creek. Thus, the ants had never foraged there and could not use landmark cues to navigate, but instead, they had to rely on celestial compass cues to walk towards their nest. We filmed the paths taken by the ants using a video camera and later digitized their head position frame by frame.

We found that having fewer ommatidia does not affect the ants’ ability to use celestial cues. The ants’ heading direction on the platform did not significantly differ from the fictive next direction. Since larger ants have greater strides and thus travel more distance for the same number of strides, we also analyzed their heading direction at a distance on the platform scaled to the body size of the ants.

We also found that the smaller ants were slower and had less-straight paths than the larger ants, even after controlling for differences in leg size (correlated with body size and head width) and stride length. This finding means that a reduced ability of the smaller ants to access celestial compass information results in a less straight path and reduced walking speed. However, the overall ability to initially orient towards the nest using a celestial compass is retained in miniature ants. Thus, while miniaturization in ants can affect their behavioral precision, it may not always lead to a loss of vital behavioral capability such as using celestial cues to navigate.

 

 

In conclusion, finding a destination in a new city might be a lot easier if we were ants—of any size—and could use celestial cues!

References

Wehner R, Strasser S (1985) The POL area of the honey bee’s eye: behavioural evidence. Physiol Entomol10:337–349.

Zeil J, Ribi WA, Narendra A (2014) Polarisation vision in ants, bees, and wasps. In: G Horváth (ed) Polarized light and polarization vision in animal sciences, Springer, Heidelberg, pp 41–60.