Light intensity during evening twilight triggers Bullant activity

After having spent several days of nocturnal lifestyle studying the Bull ant, Myrmecia pyriformis in Canberra, I am quite pleased to report that one of our findings has been published¹. Our earlier discovery² that these ants exhibit strong bursts of inbound and outbound activity in evening and morning twilight respectively in the summer, prompted us to ask whether the onset activity of these ants is restricted to the twilight period for the whole year and if so how do they determine the time of the day in such a dim-lit temporal niche.

By regular monitoring of activity schedules at different nests it became clear that temperature does not play a major role in this – a factor thought to play a major role in regulating ant foraging. Of course when surface temperature dropped to 6.5°C the ants decided to take a break (thankfully for us!), which indicated that this might be close to their critical minima – that’s another story.

The interesting bit here was that in overcast conditions (determined by measuring light levels) ants began their activity much earlier relative to sunset time and conversely under clear skies began activity much later. This indicated that light intensity might play a role in the timing of foraging and that the setting sun alone was not a cue to begin activity.

Inspired by Edward Hodgson’s observations in 1955 on leaf cutter ants³ we set about modifying light intensity during twilight. The challenge of was to make the twilight brighter ensuring no point light sources would be available for orientation. We did this by using a dome shaped diffuser and suspending it above the nest entrance. This also ensured that if the ants came close to the nest entrance the visual panorama was still available for them to navigate. Keeping the lights on for the first 60 minutes of the twilight did not result in ant activity. As soon as the lights were turned off, activity began within a few minutes. The necessary controls were carried out and replication at three nests provided very similar results.

Publications in Proceedings B is currently available for free download as they are celebrating their 350^th anniversary. So go on and download this paper.

¹Narendra A, Reid SF & Hemmi JM. 2010. The twilight zone: light intensity triggers activity in primitive ants. Proceedings of the Royal Society, Biological Sciences. doi: 10.1098/rspb.2009.2324

^{2Greiner B, Narendra A, Reid SF, Dacke M, Ribi WA & Zeil J. 2007. Eye structure correlates with distinct foraging-bout timing in primitive ants. Current Biology 17, R879–R880.}

³Hodgson ES 1955. An ecological study of the behaviour of the leaf-cutting ant Atta cephalotes. Ecology 36: 293-304

Animal navigation summer school

I just got back from a fantastic summer school on animal navigation. This was the 8th consecutive year of this school and was organised by Allen Cheung at The University of Queensland, QBI, Brisbane. The summer school has always maintained a high teacher to student ratio & was no different this time around. We had several fantastic lectures and tours to labs. Here are a few highlights:

• Magnetoreception in birds from Roswitha Wiltschko and Wolfgang Wiltschko. They gave a stunning overview of the field, the current controversies, and ideas of how to determine if your favourite animal uses magnetic field for orientation or positional information.
• Medium-scale navigation of bats by Nachum Ulanovsky. The route following behaviour these bats from Israel exhibit is very different from what we currently know from birds. This was easily the most hotly discussed/debated talk over the whole week. Keep an eye out when this gets published sometime next year!
• Janet Wiles, Director of Thinking Systems introduced us to her work on how they get robots to associate spaces with languages. Very cool!
• Mandyam Srinivasan took us along the journey of the discovery of use of optic flow for distance estimation by honeybees. Also highlighted were the challenges bees face in making the perfect landing on vertical or horizontal surfaces.
• Some pretty cool virtual reality work by Dan Angus and Allen Cheung where they created 3-D arenas and got us to think about image differences in a multitude of situations. This will be very crucial in light of the recent work on image differences in panoramic images in several animals.
• Jochen Zeil gave us an overview of knowledge base of insects with great emphasis on the the different ways insects use landmarks.
• Justin Marshall explained to us know why we know very little about navigation in marine environments, while we drooled over his study sites and study species (mantis shrimp, cuttlefish).

Jochen and I got two practical sessions running:

• from the human navigation experiments using differential GPS all of us became acutely aware of the difficulty of walking in a straight line while blindfolded and ears plugged. Kudos to the desert ants!
• in the ant navigation practical we discovered that Rhytidoponera metallica mostly rely on visual landmark information for homing but in certain contexts path integrates using a celestial compass.

I am already looking forward for the next year's summer school!

Use of panoramic skyline for navigation: Melophorus bagoti

Ants use vector or visual information to head to a particular goal. To cope with disturbances or 'errors' arising from their global vector, they use landmarks either as familiar beacons to guide their entire journey or/and to pinpoint a specific location. Studies on Formica and Melophorus bagoti have shown the ants correct for any local displacements along the route which led several authors (me included!) to predict that ants use panoramic cues for homing.

Till date, however, no studies have explicitly tested this. Paul and Ken do exactly this in their recent article in Current Biology. By mimicking the skyline profile using walls of differing dimensions, they provide the best experimental evidence for the use of panoramic skyline not only for ants, but also for any insect. They show the ant's orientation in the natural scene is similar to the skyline profile they provided. They then rotated the skyline profile and found the ants change their orientation to match the rotation of the panorama.

Further reading:

Paul Graham & Ken Cheng. 2009. Ants use the panoramic skyline as a visual cue during navigation. Current Biology 19: R935 - R937

Asexuality in ants

Eukaryotic organisms mostly reproduce sexually. Since no males were collected in the Neotropical ant fungus growing ant Mycocepurus smithii, Himler and colleagues tested if M. smithii is asexual using different strategies: genetic tools, morphological measures and experimental analyses. Read this paper and check out the neat images of the reproductive tracts.

Abstract: Asexual reproduction imposes evolutionary handicaps on asexual species, rendering them prone to extinction, because asexual reproduction generates novel genotypes and purges deleterious mutations at lower rates than sexual reproduction. Here, we report the first case of complete asexuality in ants, the fungus- growing ant Mycocepurus smithii, where queens reproduce asexually but workers are sterile, which is doubly enigmatic because the clonal colonies of M. smithii also depend on clonal fungi for food. Degenerate female mating anatomy, extensive field and laboratory surveys, and DNA fingerprinting implicate complete asexuality in this widespread ant species. Maternally inherited bacteria (e.g. Wolbachia, Cardinium) and the fungal cultivars can be ruled out as agents inducing asexuality. M. smithii societies of clonal females provide a unique system to test theories of parent–offspring conflict and reproductive policing in social insects. Asexuality of both ant farmer and fungal crop challenges traditional views proposing that sexual farmer ants outpace coevolving sexual crop pathogens, and thus compensate for vulnerabilities of their asexual crops. Either the double asexuality of both farmer and crop may permit the host to fully exploit advantages of asexuality for unknown reasons or frequent switching between crops (symbiont reassociation) generates novel ant–fungus combinations, which may compensate for any evolutionary handicaps of asexuality in M. smithii.

From: Anna G. Himler, Eric J. Caldera, Boris C. Baer, Hermógenes Fernández-Marín and Ulrich G. Mueller. 2009. No sex in fungus-farming ants or their crops. Proc. R. Soc. B. DOI 10.1098/rspb.2009.0313.

Cane toads: ants to the rescue

Cane toad, Bufo marinus, are large toxic animals that are native to Central and South America and were introduced to Australia in 1935 to eradicate sugarcane beetles. These toads however have had detrimental effects on native Australian fauna - including marsupials, snakes & lizards. Checking the spread of these toads has been a task next to impossible. Recent work from Rick Shine's lab shows that the diurnal toads somehow fail to detect approaching Iridomyrmex reburrus ants, and the ants kill and feed on the toads. Read more about this latest research where the authors report their findings and discuss the possibility of using these ants to control cane toad spread.

Reference: Ward-Fear G et al., 2009. Maladaptive traits in invasive species: in Australia cane toads are more vulnerable to predatory ants than are native frogs. Functional Ecology: DOI 10.1111/j.1365-2435.2009.01556.x

Updates: Cataulacus

Cataulacus ants are the cute and cuddly in the ant world! This is an arboreal genus distributed across the Indomalayan, Afrotropical and Madagascar region. They nest within cavities of plants and branches of trees. They play dead when disturbed and camouflage extremely well with the tree barks. Pictures of Cataulacus taprobanae from South India are up at the Ant Gallery.

When & Where do ants do it

In some ant species males are known to aggregate and wait to attract females, while in others females stay put at a particular place & attract males. However, there is surprisingly little known about where and when ants prefer to mate and hence this recent article is a welcome addition. In this article Noordijk & others set up window traps in 3 locations: open field, forest edge and in the forest to capture flying ants. They set up pitfall traps to identify the ants that occupy these 3 regions. They studied six ant species Lasius umbratus, Lasius niger, Myrmica rubra, Myrmcia ruginodis, Stenamma debile and Temnothorax nylanderi. By regularly checking the window traps from April to December, they were able to identify specific duration of nuptial flights for each ant species. 

The really interesting bit is that though nesting habitats of Temnothorax nylanderi, Myrmica rubra & Myrmcia ruginodis were located in forests, maximum alates were captured in the forest edges. Though nesting locations of Lasius niger was in the open field, alates were captured not only in the the open field, but also along forest edges & in the forest. The pitfall traps failed to capture Stenamma debile and Lasius umbratus, but alates of these two species were captured in the window traps. And guess where the maximum alates were found – forest edges! The authors suggest that preference of forests edges might have something do with specific micro-climate the ants require. But they think it could be more to do with the edges acting as a conspicuous landmark which ants use to find mates. For now, I am leaning towards the second possibility.

Read this article here:

Noordijk et al. How ants find each other; temporal and spatial patterns in nuptial flights. Insect Soc. DOI 10.1007/s00040-008-1002-9

Temporal niches & sympatric ants

For the past few weeks I have been ardently trying to catch up on what's known about ants segregating their niche temporally for foraging. Turns out that there are several studies that address temporal shifts in ants, mostly at the community level, and very few that actually address temporal foraging patterns. Interestingly, I learnt that two Camponotus species, C. socius and C. floridanus exploit the same honeydew sources with socius being diurnal and floridanus nocturnal. However heartening it was to learn this, its frustrating that there is no more information [ex: seasonal differences, variation in castes, facet count, competition] available about this observation from Central Florida, USA which is reported in 4 lines in The Ants [p-383], as 'we made similar observations'. This more so, because temporal niche partitioning in foraging was recently shown in four species of Australian bull ants, Myrmecia species where all four species of ants rely on the same carbohydrate source (plant sap) produced by the same tree.

For what its worth, here are the two Camponotus species:

The diurnal Camponotus socius

Source [Mississippi Entomological Museum]

The nocturnal Camponotus floridanus 

[source: Mississippi Entomological Museum]

Updates

A new genus page on Dolichoderus is up. Yet to find a key to identify these ants to the species level. 

No such issues with Polyrhachis though!! With some fantastic help from Rudy Kohout all species of Polyrhachis at the ant gallery have been identified to the species. The latest addition has been Polyrhachis australis which was found during a recent trip to Coffs Harbour. 

Further, two species of the shield ants Meranoplus (M. diversoides and one from the fenestratus sp gp) have been added. I found Stefan Schoedl's 2007 publication extremely helpful to identify Australian Meranoplus. Here is the reference: Schoedl S 2007. Revision of the Australian Meranoplus: the Meranoplus diversus group, pp. 370-424. In Snelling R, Fisher BL & Ward PS (eds). Advances in ant systematics (Hymenoptera: Formicidae): homage to EO Wilson - 50 years of contributions. Memoirs of the American Entomological Institute, 80 [pdf].

Argentine ant or not?

For all of us who are unsure if the ant we have in hand is the Argentine ant, Linepithema humile or not, Alex Wild gives us a clear idea of what to look for. Even if you do not have this ant in your hand or where you come from (lucky you!), give it a read to see its distribution and key morphological features.

Shooting in the dark

Lighting plays a crucial role in making an picture look presentable both technically and aesthetically. So what if the animal is nocturnal and hates light but is loved by the camera??

Here is a ant called Rhytidoponera which I found while I was at Nadgee nature reserve, a few kilometers south of Eden on the east coast of Australia. I found a nest of these ants so close to where my tent was pitched that I could watch them by actually lying down on the sleeping mat with half of me jutting outside the tent! One of those days, by late in the evening, after finishing off some experiments with solitary wasps, I set up the sleeping mat, flicked on the torch and lay there watching these fellows go about their work. They became active just before sunset and continued activity all through the night, till sunrise. They regularly returned to the nest with dead insects. I tried taking some pictures but with light levels being very low, it was proving to be a challenge. The twin lite flash I use comes with a lamp but the light was just too bright and almost always scared the ants away. So after having taken pictures for a couple of hours with no luck, I gave up and decided that just watching them may be a better option. Soon I realised that I could predict where an ant returning to its nest would be say after 5 secs. I decided to see if this would allow me to take some pictures which meant clicking in completing darkness. It turned out that in a matter of 30 mins I actually had a few nice pictures [see one below]. A gentle drizzle in the night led to a rain drop on the ant also being captured.
More and some new images of Rhytidoponera here.

A Rhytidoponera species returns to its nest carrying parts of a bull ant, Myrmecia pyriformis.

Photographed at 0215 hrs; Nadgee Nature Reserve, NSW, Australia

Restructuring & some additions

The ant gallery has just undergone some major file restructuring and this now lets me add new images with less hassle. A new page on the shield ants Meranoplus is up and running. Next set of additions will be Meranoplus bicolor, Meranoplus diversoides and Meranoplus fenestratus sp gp.

Link to the Ant gallery has changed to: http://web.mac.com/ajaynarendra/Ants

With help from Dinesh Rao, a new spider gallery is up and running with live feed. The tricky ones have been Salticidae and Lycoidae members and we are in the middle of tackling these. Will post here of any additions, but thats unlikely to happpen till the end of the next week: juggling with some lecturing, running experiments and moving houses!

Back from Alice

Been absconding for almost a month now! The most significant bit during this period was a visit to Alice to watch Melophorus bagoti. Here we began an ambitious project of trying to determine what is that the ants see while returning to the nest. While watching Melophorus, by sheer luck I ended up finding the Muscle-man ants Podomyrma species (pictured) in this site, a species which I hadn't seen here since 2003! So, yes in short that was really exciting!

Updates: Pheidole

A genus that is hard not to get excited about, a genus in which most species exhibit distinct dimorphism in the worker caste, a genus renowned for having several specialist seed harvesters, a genus present in both the New and Old World and often not merely present but ecologically dominant - the ant genus Pheidole. I have just added some images of Pheidole in a valient attempt towards clearing up space on the hard drive.

Asian Myrmecology

Just heard from the Editors of the Journal, that all articles in the first issue of Asian Myrmecology are available for free download. Kudos to them!