Search

Current opinion in insect navigation assumes that animals need to align with the goal direction to recognize familiar views and approach it. Yet, ants sometimes drag heavy food items backwards to the nest and it is still unclear to what extent they rely on visual memories while doing so. In this study displacement experiments and alterations of the visual scenery revealed that ants indeed recognized and used the learnt visual scenery to guide their path towards the nest while walking backwards. In addition, the occurrence of forward-peeking behaviours revealed that backward-walking ants continually estimated their directional uncertainty by integrating multiple cues such as visual familiarity, the state of their path integrator and the time spent backwards. A simple mechanical model based on repulsive and attractive visual memories captured the results and explained how visual navigation can be performed backwards. • Backward-walking ants can steer using learnt terrestrial visual cues. • Steering does not require forward body alignment. • Steering may be based on the integration of attractive and repulsive views. • Peeking behaviour is triggered in periods of low directional certainty. • Directional certainty is built on multiple sources of current and past information. [ABSTRACT FROM AUTHOR]

In some social insects, workers can produce females asexually through thelytokous parthenogenesis. This allows them to produce replacement queens (i.e. requeening) if the queen has died, but also to compete with the queen to produce females (i.e. reproductive cheating). For the first time, we experimentally tested the role of worker thelytoky under quasinatural conditions in the ant Cataglyphis cursor , where the queen uses both sexual and thelytokous reproduction. We reared pairs of orphaned and queenright colonies in enclosures for almost 3 months, during which they competed for resources. Orphaned colonies lost more workers than queenright colonies over the course of the experiment, presumably because of the costs of reproductive conflicts between workers. Nevertheless, they produced new queens through worker thelytoky and new colonies through colony fission. This is the first unambiguous demonstration that worker thelytoky allows requeening under natural conditions in this species. We further showed that worker thelytoky results in reproductive cheating in the form of a few workers reproducing in the presence of the queen (in queenright colonies) and a few worker lineages producing more new queens than other lineages (in orphaned colonies). In addition, it also results in rare instances of social parasitism, that is, workers entering and reproducing in foreign colonies. These benefits to workers seem too occasional and too low to drive the evolution of thelytoky in this species. We argue that thelytoky probably evolved in the queen caste, where it allows the production of young queens and confers frequent and large benefits by increasing gene transmission, but is also expressed in workers because of genetic correlations between the two castes. [ABSTRACT FROM AUTHOR]

How parents invest resources in offspring is a central aspect of life history. While investment strategies have been well studied in solitary organisms, comparatively little has been done on social species, including the many that reproduce by fission. Under colony fission, a parent colony divides resources (individuals) to form two or more offspring colonies. Because individuals differ in characteristics (e.g. size), there is opportunity for both quantitative and qualitative bias in their allocation. In this study we investigated the qualitative aspect of offspring investment during colony fission. Colonies of the ant Cataglyphis cursor fission into multiple offspring colonies as part of their lifecycle, and the distribution of workers is quantitatively biased. We found that investment is also qualitatively biased in terms of worker size and worker genetic characteristics (patrilines). This bias was mainly between the offspring colony that inherited the original nest and offspring colonies that dispersed to new nesting sites. In 74% of cases, dispersing colonies contained larger workers, and the distribution of genetic patrilines was biased in two of six cases in a manner that cannot be explained by the observed variation in worker size between patrilines. Fission also led to a reduction in diversity in offspring colonies compared to the parent colony, in terms of both worker size (70% of cases) and genetic diversity (40% of cases). These patterns are probably the result of differing dispersal probability between workers of different patrilines and of different size. This differential allocation may be adaptive because larger workers may be of disproportionate value to dispersing colonies, and their loss an acceptable cost to the colony inheriting the nest. [ABSTRACT FROM AUTHOR]

Desert ants, Cataglyphis fortis , forage for dead arthropods in the Tunisian salt pans. Both the unpredictable food distribution and the high surface temperatures might account for the fact that the ants do not use any pheromone trails. However, Cataglyphis has been shown to still use olfactory cues for navigation. For instance, the ants locate sparsely distributed food or pinpoint their inconspicuous nest entrance by following odour plumes. In this study we found that, as well as using odours to pinpoint a target, the ants might use environmental odours as olfactory landmarks when following habitual routes. When analysing odours collected at 100 positions in the desert, we found spatially distinct gradients of a range of different environmental odorants. Furthermore we confirm that individual foragers followed forager-specific routes when leaving the nest. Therefore these ants could potentially learn such olfactory landscape features along their stable routes. We, hence, asked whether ants could learn and use olfactory cues for route guidance. We trained ants to visit a stable feeder and presented them with a sequence of four different odours along the way. Homing ants that had already passed the odour alley on their way back were displaced to a remote test field and released at the starting point of an identical alley. Control ants that experienced the alley only during the test situation focused their search on the release point. Ants that had experienced the odours during training, however, biased their nest search towards the odour alley and performed straight walking segments along the alley. Hence, we found that ants learnt the olfactory cues along their homeward route and used these cues in the absence of other navigational information. Hence, desert ants seem to be able to use odour information to follow routes. [ABSTRACT FROM AUTHOR]