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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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