Three-dimensional orientation in desert ants: context-independent memorisation and recall of sloped path segments

Desert ants (Cataglyphis fortis) navigate by a combination of path integration and landmark-based route memories. Their ability to correct sloped path segments to their ground distances enables them to orientate accurately even in undulating terrain. In this study, we tested whether or not ants incorporate vertical components of an itinerary into their route memory in similar ways as they do with visual landmarks and horizontal changes of direction. In two separate experiments, we trained desert ants to walk over artificial hills and later tested their acceptance of slopes within novel contexts. In the first paradigm, ants had to traverse a hill only on their outbound run, but not on their homebound trip. In a follow-up experiment, we confronted ramp-trained animals with descents in a completely new temporal and spatial context. The animals transferred their newly acquired acceptance of slopes from the outbound to the homebound run as well as to novel foraging trips. Cataglyphis obviously dissociates the experience of sloped path segments from the original context in which they appeared, thus reducing their significance as a navigational aid.     

Soil texture as an influence on the distribution of the desert seed-harvester ants Pogonomyrmex rugosus and Messor pergandei

Summary Pogonomyrmex rugosus and Messor pergandei are ecologically similar species of desert seed-harvester ants that coexist in numerous areas throughout the Sonoran and Mohave Deserts. However, these two species also commonly segregate along physical gradients, with each species predominating in areas that differ in soil texture and/or topographic relief. Along gradients that included bajada and alluvial flat habitats, P. rugosus occurred alone in coarse-textured soils near mountains, while M. pergandei occurred alone in finer-textured soils further away. Conversely, along a vegetation gradient that included creosote bush and saltbush habitats, P. rugosus occurred alone in finer-textured soils than those occupied by either M. pergandei alone or both species in coexistence. However, in both situations clay content was significantly higher in areas occupied by P. rugosus alone, and at the latter site clay content was correlated with relative abundance of each species. Moreover, local distribution pattern of these two species may be related to the effects of clay on water retention, with retention being highest in areas occupied by P. rugosus alone. Differences in reproductive ecology may also affect these patterns as P. rugosus reproductive flights follow summer monsoon rains, while those of M. pergandei occur during the milder winter and spring.     

The hidden spiral: systematic search and path integration in desert ants,Cataglyphis fortis

The main navigational mechanism used by foraging desert ants of the genus Cataglyphis is path integration (dead reckoning). Any such egocentric system of navigation is prone to cumulative navigational errors. Hence, while homing Cataglyphis might have reset its path integration system and yet not arrived at the start of its foraging excursion, the nest entrance. Then it resorts to piloting or performs a systematic search for the nest. The search pattern consists of a system of loops of ever increasing size centred about the origin, i.e. the start of the search. Here we show that underlying the system of loops is a spiral search programme that gets transformed into the observed pattern of loops by the ant's idiosyncratic path-integration algorithm. The ant starts to follow a spiral course, then breaks off this course and walks towards the centre, i.e. to what its path-integration system has computed to be the origin of the search. This reset episode is followed by another spiral course, which is terminated by the next reset, and so forth. After each reset, the spiral gets wider, so that the whole pattern expands. Futhermore, every now and then the spiral might change its sign. Computer simulations based on these simple rules lead to search patterns of the kind actually recorded in Cataglyphis ants. These patterns ensure that those parts of the area in which the target (nest entrance) is most likely to be located are searched most heavily; in other words: the search density profile is adapted to the probability density function of the target.     

Visual cue learning and odometry in guiding the search behavior of desert ants, Melophorus bagoti, in artificial channels

Terrestrial panoramic cues, path integration and search behavior are the main navigational strategies used by ants to locate food and find their way back to the nest. Searching becomes important when the other navigational cues are either not available or cannot provide sufficient information to pinpoint the goal. When searching in one-dimensional channels Melophorus bagoti ants exhibit a systematic drift in the starting-point-to-goal direction as they turn back and forth, sometimes past the goal location ( Narendra et al., 2008). Here we show that this drift in channels is not a stereotypical part of the search behavior in these ants. It rather depends on the conditions of training. In experiments in which the nest entrance is located not at the end but at the side of the channel, forward drift is not always part of the nest search. Experiments on food searches showed that with the food source at the end of the channel, ants performed a linear drift in the starting-point-to-food direction. With food at the side of the channel, they showed a less pronounced drift toward the food source. In this constrained environment, especially with the goal at the end of the channel, ants seem to learn a routine such as ‘run along the channel’, and mix this routine with their usual strategy of turning back and forth in search.     

An updated checklist of the ants of India with their specific distributions in Indian states (Hymenoptera,Formicidae)

As one of the 17 megadiverse countries of the world and with four biodiversity hotspots represented in its borders, India is home to an impressive diversity of life forms. However, much work remains to document and catalogue the species of India and their geographic distributions, especially for diverse invertebrate groups. In the present study, a comprehensive and critical list of Indian ant species is provided with up-to-date state-wise distribution. A total of 828 valid species and subspecies names belonging to 100 genera are listed from India. Potential erroneous data, misidentifications and dubious distributional records that may exist in the literature are also identified. The present exhaustive listing of Indian ants will provide a holistic view about diversity and distribution and will also help to identify major undersampled areas where future sampling and taxonomic efforts should be directed.