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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

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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 doublyenigmatic 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.

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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

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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 

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Ever wondered about what goes on in the enormous eyes of Bullants? Yup we did too, and we ended up finding that the diameter of the photoreceptor, the optical sensitivity, the number of facets and the facet sizes, all increase gradually from diurnal to diurnal/crepuscular, crepuscular/nocturnal and nocturnal species. Such adaptations in eye structure within a single genus, the primitive ant genus Myrmecia especially, is truly remarkable.
Read more here:
Greiner 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 (20): R879-R880.

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