Nocturnal orientation in the black carpenter antCamponotus pennsylvanicus (DeGeer) (Hymenoptera: Formicidae)

Summary The black carpenter antCamponotus pennsylvanicus (DeGeer), a predominantly nocturnal Formicine ant, responds to a hierarchy of visual and tactile cues when orienting along odor trails at night. Under illumination from moonlight or artificial light, workers rely upon these beacons to mediate phototactic orientation. In the absence of moonlight or artificial lights, ants were able to orient visually to terrestrial landmarks. In the absence of all landmarks, save for overhanging tree branches, ants could negotiate shortcuts or make directional changes in response to visual landmarks presented within the tree canopy on a moonless night. When experimental manipulations placed the ants in total darkness, they could no longer negotiate shortcuts and would resort to thigmotactic orientation along structural guidelines to reach a food source. The hierachical organization of these diverse cues in a foraging strategy is discussed, as well as their adaptive significance toC. pennsyhanicus.     

Ant navigation en route to the goal: signature routes facilitate way-finding of Gigantiops destructor

We investigated in laboratory conditions how foragers of the tropical ant Gigantiops destructor develop individually distinctive landmark routes. Way-finding along a familiar route involved the recognition of at least two locations, nest and feeding site, and the representation of spatial relations between these places. Familiar visual landmarks were important both at the beginning and at the end of the foraging journey. A motor routine guided the ants at the start of their foraging path towards the first landmarks, which they learnt to pass consistently on the same side, before taking the next direction. At the last stage of the route, landmark recognition allowed them to pinpoint their preferred feeding site without using distant cues or odometric information. By contrast, ants en route to the goal were not systematically guided by a stereotyped sequence of snapshots recalled at each corresponding stage of the route. Each ant slalomed in an idiosyncratic distinctive way around different midway landmarks from a foraging excursion to the next, which induced a variability of the path shapes in their intermediate parts. By reducing the number of landmark recognition-triggered responses, this economical visuomotor strategy may be helpful in the Amazonian forest where many prominent landmarks are alike.     

Local vectors in desert ants: context-dependent landmark learning during outbound and homebound runs

Desert ants, Cataglyphis fortis, associate nestward-directed vector memories (local vectors) with the sight of landmarks along a familiar route. This view-based navigational strategy works in parallel to the self-centred path integration system. In the present study we ask at what temporal stage during a foraging journey does the ant acquire nestward-directed local vector information from feeder-associated landmarks: during its outbound run to a feeding site or during its homebound run to the nest. Tests performed after two reversed-image training paradigms revealed that the ants associated such vectors exclusively with landmarks present during their homebound runs.     

Visual landmarks and route following in desert ants

Summary Little is known about the way in which animals far from home use familiar landmarks to guide their homeward path. Desert ants, Cataglyphis spp., which forage individually over long distances are beginning to provide some answers. We find that ants running 30 m from a feeding place to their nest memorise the visual characteristics of prominent landmarks which lie close to their path. Although remembered visual features are used for identifying a landmark and for deciding whether to go to its left or right, they are not responsible for the detailed steering of an ant's path. The form of the trajectory as an ant approaches and detours around a landmark seems to be controlled by the latter's immediate retinal size; the larger it is, the greater the ant's turning velocity away from the landmark.     

Mapping the navigational knowledge of individually foraging ants,Myrmecia croslandi

Ants are efficient navigators, guided by path integration and visual landmarks. Path integration is the primary strategy in landmark-poor habitats, but landmarks are readily used when available. The landmark panorama provides reliable information about heading direction, routes and specific location. Visual memories for guidance are often acquired along routes or near to significant places. Over what area can such locally acquired memories provide information for reaching a place? This question is unusually approachable in the solitary foraging Australian jack jumper ant, since individual foragers typically travel to one or two nest-specific foraging trees. We find that within 10 m from the nest, ants both with and without home vector information available from path integration return directly to the nest from all compass directions, after briefly scanning the panorama. By reconstructing panoramic views within the successful homing range, we show that in the open woodland habitat of these ants, snapshot memories acquired close to the nest provide sufficient navigational information to determine nest-directed heading direction over a surprisingly large area, including areas that animals may have not visited previously.     

Sex-inducing effect of a hydrophilic fraction on reproductive switching in the planarian Dugesia ryukyuensis (Seriata, Tricladida)

Background

Insects are known to rely on terrestrial landmarks for navigation. Landmarks are used to chart a route or pinpoint a goal. The distant panorama, however, is often thought not to guide navigation directly during a familiar journey, but to act as a contextual cue that primes the correct memory of the landmarks.

Results

We provided Melophorus bagoti ants with a huge artificial landmark located right near the nest entrance to find out whether navigating ants focus on such a prominent visual landmark for homing guidance. When the landmark was displaced by small or large distances, ant routes were affected differently. Certain behaviours appeared inconsistent with the hypothesis that guidance was based on the landmark only. Instead, comparisons of panoramic images recorded on the field, encompassing both landmark and distal panorama, could explain most aspects of the ant behaviours.

Conclusion

Ants navigating along a familiar route do not focus on obvious landmarks or filter out distal panoramic cues, but appear to be guided by cues covering a large area of their panoramic visual field, including both landmarks and distal panorama. Using panoramic views seems an appropriate strategy to cope with the complexity of natural scenes and the poor resolution of insects' eyes. The ability to isolate landmarks from the rest of a scene may be beyond the capacity of animals that do not possess a dedicated object-perception visual stream like primates.     

Host-Specific Myrmecophily and Myrmecophagy in the Tropical Coccinellid Diomus thoracicus in French Guiana

A variety of arthropods, particularly insects, have developed myrmecophilous interactions with ants to gain access to resources and/or for protection. Among these myrmecophiles, only a few examples have been documented in the Coccinellidae, most of them involving species able to feed on ant-tended Hemiptera. We report here a new case of obligate myrmecophily in the coccinellid Diomus thoracicus. Larvae are invariably and exclusively found in the nests of the ant Wasmannia auropunctata and seem to rely on ant brood as their only food source. Not only do ant workers show no aggressiveness toward the D. thoracicus larvae in their behavioral interactions at the colonial level, but also at the species level; while coccinellid adults are always attacked. The integration of the larvae inside of the ant nests is based on their chemical mimicry of the host's cuticular cues. Therefore, given the presence of the D. thoracicus larvae inside of the ant's nest, their predation on Wasmannia brood and their chemical mimicry, this species can be considered a specific parasite of W. auropunctata. Overall, this new case of myrmecophily not only specifically involves a highly invasive ant species, but also provides insights into the evolution of myrmecophily and myrmecophagy in coccinellids.     

Comparing inclined locomotion in a ground-living and a climbing ant species: sagittal plane kinematics

Formicine ants are able to detect slopes in the substrates they crawl on. It was assumed that hair fields between the main segments of the body and between the proximal leg segments contribute to graviception which triggers a change of posture in response to substrate slopes. The sagittal kinematics of two ant species were investigated and compared on different slopes. Cataglyphis fortis, a North African desert ant, is well known for its extraordinary sense of orientation in texturally almost uniform habitats, while Formica pratensis, a common central-European species, primarily uses landmarks and pheromone traces for orientation. A comparison of these two species reveals differences in postural adaptations during inclined locomotion. Only minor slope-dependent angular adjustments were observed. The largest is a 25° head rotation for Cataglyphis, even if the slope is changed by 150°, suggesting dramatic changes in the field of vision. The trunk’s pitch adjustment towards the increasing slope is low in both species. On all slopes Cataglyphis achieves higher running speeds than Formica and displays greater slope-dependent variation in body height. This indicates different strategies for coping with changing slopes. These specific aspects have to be reflected in the ants’ respective mode of slope perception.     

How do insects use path integration for their navigation?

 We combine experimental findings on ants and bees, and build on earlier models, to give an account of how these insects navigate using path integration, and how path integration interacts with other modes of navigation. At the core of path integration is an accumulator. This is set to an initial state at the nest and is updated as the insect moves so that it always reports the insect's current position relative to the nest. Navigation that uses path integration requires, in addition, a way of storing states of the accumulator at significant places for subsequent recall as goals, and a means of computing the direction to such goals. We discuss three models of how path integration might be used for this process, which we call vector navigation. Vector navigation is the principal means of navigating over unfamiliar terrain, or when landmarks are unavailable. Under other conditions, insects often navigate by landmarks, and ignore the output of the vector navigation system. Landmark navigation does not interfere with the updating of the accumulator. There is an interesting symmetry in the use of landmarks and path integration. In the short term, vector navigation can be independent of landmarks, and landmark navigation needs no assistance from path integration. In the longer term, visual landmarks help keep path vector navigation calibrated, and the learning of visual landmarks is guided by path integration. Received: 6 June 1999 / Accepted in revised form: 20 March 2000     

Views,landmarks, and routes: how do desert ants negotiate an obstacle course?

The Australian desert ant Melophorus bagoti often follows stereotypical routes through a cluttered landscape containing both distant panoramic views and obstacles (plants) to navigate around. We created an artificial obstacle course for the ants between a feeder and their nest. Landmarks comprised natural objects in the landscape such as logs, branches, and tussocks. Many ants travelled stereotypical routes home through the obstacle course in training, threading repeatedly the same gaps in the landmarks. Manipulations altering the relations between the landmarks and the surrounding panorama, however, affected the routes in two major ways. Both interchanging the positions of landmarks (transpositions) and displacing the entire landmark set along with the starting position of the ants (translations) (1) reduced the stereotypicality of the route, and (2) increased turns and meanders during travel. The ants might have used the entire panorama in view-based travel, or the distal panorama might prime the identification and use of landmarks en route. Despite the large data set, both options (not mutually exclusive) remain viable.     

Polyrhachis lama, a parasitic ant with an exceptional mode of social integration

Social parasitism is a common phenomenon amongst ants that occurs in manifold variations with differing levels of parasite–host integration. Particularly, high levels of social integration occur amongst closely related species (Emery’s rule), which form mixed colonies with their hosts and comprise the vast majority of social parasites. Considerable lower levels of integration are typically found amongst unrelated species that live in clearly separated colonies. The formicine ant Polyrhachis lama, however, parasitises a phylogenetically distant host species, Diacamma sp. of the subfamily Ponerinae, but lives spatially mixed with the host colonies. Studies on integration and communication have indicated that P. lama shows a high degree of host integration. However, the allocation of brood care behaviour, a central aspect of parasite integration, has not been studied. Because all known ant social parasites that are fully mixed with their host colonies are also true brood parasites, we investigated the integration of P. lama brood. Our results demonstrate that the parasite brood has a high degree of spatial integration, although it remains functionally separated regarding nutritive brood care. This can be attributed to behavioural and morphological differences between the phylogenetically distant species. The observed spatial confinement of parasite brood, however, is most likely due to an unusual method of chemical host integration. The parasite brood remains accepted in the Diacamma colonies only under the presence of adult parasites. Altogether, this suggests an active mechanism of chemical integration based on the acceptance allomones originating from P. lama workers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Use of Long-Term Stored Vector Information in the Neotropical Ant <Emphasis Type="BoldItalic">Gigantiops destructor</Emphasis>

We investigated how the formicine ant Gigantiops destructor can use vector information to navigate within the cluttered environment of the rain forest. Displaced foragers use skylight information to move in the theoretical feeder-to-nest direction, whether they are prevented from updating their path-integrator during foraging or captured at the departure from their nest, i.e. with a current accumulator state very close to zero. Only ants that have collected food are able to download a long-term stored reference vector pointing in the nest direction, irrespective of the current accumulator state of their path-integrator stored in a working memory and independent of familiar landmarks. Depending on the release sites, ants that became lost at a maximum distance of 50 cm could still hit and recognize their familiar route, or they engaged in a systematic search for it centered on the release sites. In contrast to Cataglyphis desert ants, Gigantiops ants do not rely primarily on the current accumulator state of their egocentric path integrator. Such a long-term vector-based navigation primed by food capture is well adapted for a tropical ant foraging during periods spanning several hours. This could prevent the numerous cumulative errors in the evaluation of the angles steered that might result from a continuously running path-integrator operating during complex foraging patterns performed at ground or arboreal levels and during passive displacement in response to heavy rain.     

Which portion of the natural panorama is used for view-based navigation in the Australian desert ant?

Ants that forage in visually rich environments often develop idiosyncratic routes between their nest and a profitable foraging ground. Such route knowledge is underpinned by an ability to use visual landmarks for guidance and place recognition. Here we ask which portions of natural visual scenes are essential for visually guided navigation in the Australian desert ant Melophorus bagoti whose foragers navigate through a habitat containing grass tussocks, shrubs and trees. We captured M. bagoti foragers after they had returned to their nest from a feeder, but before they had entered their nest, and tested their ability to home accurately from a series of release locations. We used this simple release paradigm to investigate visually guided navigation by monitoring the accuracy of nestwards orientation when parts of the ants’ visual field were obscured. Results show that the lower portion of the visual panorama is more important for visually guided homing than upper portions. Analysis of panoramic images captured from the release and nest locations support the hypothesis that the important visual information is provided by the panoramic contour, where terrestrial objects contrast against sky, rather than by a limited number of salient landmarks such as tall trees.     

Path integration controls nest-plume following in desert ants

The desert ant Cataglyphis fortis is equipped with sophisticated navigational skills for returning to its nest after foraging. The ant's primary means for long-distance navigation is path integration, which provides a continuous readout of the ant's approximate distance and direction from the nest. The nest is pinpointed with the aid of visual and olfactory landmarks. Similar landmark cues help ants locate familiar food sites. Ants on their outward trip will position themselves so that they can move upwind using odor cues to find food. Here we show that homing ants also move upwind along nest-derived odor plumes to approach their nest. The ants only respond to odor plumes if the state of their path integrator tells them that they are near the nest. This influence of path integration is important because we could experimentally provoke ants to follow odor plumes from a foreign, conspecific nest and enter that nest. We identified CO(2) as one nest-plume component that can by itself induce plume following in homing ants. Taken together, the results suggest that path-integration information enables ants to avoid entering the wrong nest, where they would inevitably be killed by resident ants.     

Path integration in insects

The most notable advance in our knowledge of path integration in insects is a new understanding of how the honeybee measures the distance that it travels during its foraging trips. Data from two groups show that the bee's odometer records distance in terms of the net amount of image motion over the retina that is accumulated during a flight. Progress has also been made in clarifying the relation between path integration and other navigational strategies. On unfamiliar ground, path integration is the only available means of navigation. In familiar surroundings, however, guidance by landmarks may override guidance by path integration. Path integration then becomes a back-up strategy that is used primarily when landmarks fail.     

Sex matters in echoacoustic orientation: gender differences in the use of acoustic landmarks in <Emphasis Type="Italic">Phyllostomus discolor</Emphasis> (lesser spear-nosed bat)

Sex-specific differences in orientation strategies are well known for several rodent and primate species with females relying more on landmarks when it comes to visually guided orientation, whereas males preferentially use Euclidean cues. We used the echolocating bat Phyllostomus discolor for a behavioural study on gender differences in the use of acoustic landmarks. The experimental animals (6 males, 6 females) had to learn and perform a simple orientational task, firstly in the absence of landmarks and subsequently in the presence of four acoustic landmarks of which one was occasionally removed during the critical experiment. The results presented here show that gender differences in the use of acoustic landmarks exist in P. discolor, which supports our hypothesis that the phenomenon is independent of the modality that is used to sense the environment during orientation. Therefore, our findings allow for the prediction of similar phenomena in other acoustically orienting mammals. Interestingly, due to the specific ecology of P. discolor, our results partially contradict the evolutionary theories on gender-specific orientation, as will be discussed. Finally, we consider our finding as being one of several important steps toward establishing bats as a new model organism in neuroscientific studies on allocentric spatial cognition in mammals.     

Learning and time‐dependent cue choice in the desert ant,Melophorus bagoti

Foraging ants are known to use multiple sources of information to return to the nest. These cue sets are employed by independent navigational systems including path integration in the case of celestial cues and vision‐based learning in the case of terrestrial landmarks and the panorama. When cue sets are presented in conflict, the Australian desert ant species, Melophorus bagoti, will choose a compromise heading between the directions dictated by the cues or, when navigating on well‐known routes, foragers choose the direction indicated by the terrestrial cues of the panorama against the dictates of celestial cues. Here, we explore the roles of learning terrestrial cues and delays since cue exposure in these navigational decisions by testing restricted foragers with differing levels of terrestrial cue experience with the maximum (180°) cue conflict. Restricted foragers appear unable to extrapolate landmark information from the nest to a displacement site 8 m away. Given only one homeward experience, foragers can successfully orient using terrestrial cues, but this experience is not sufficient to override a conflicting vector. Terrestrial cue strength increases with multiple experiences and eventually overrides the celestial cues. This appears to be a dynamic choice as foragers discount the reliability of the terrestrial cues over time, reverting back to preferring the celestial vector when the forager has an immediate vector, but the forager's last exposure to the terrestrial cues was 24 hr in the past. Foragers may be employing navigational decision making that can be predicted by the temporal weighting rule.     

The significance of visual landmarks for navigation of the giant tropical ant,Paraponera clavata (Formicidae,Ponerinae)

Summary Workers of the giant tropical ant,Paraponera clavata, use trail pheromones for orientation and recruitment of nestmates. However, chemical markings may not always be sufficient for successful navigation in complex three-dimensional terrain, and additional orientation cues may be required. Behavioral field experiments were performed to investigate the significance of visual landmarks for homing foragers. Animals which were prevented from seeing the canopy were unable to navigate back to the nest, even though trail pheromones were still present. In contrast, foragers found their way back to the nest after their trail pheromones had been abolished but their visual scenes remained unchanged. This emphasizes the important role of visual landmarks during spatial orientation in homingP. clavata foragers. Individually foraging scouts were discovered in the understory of the forest floor up to 30 m away from their nest. They were rewarded, and displaced between 0.8 m and 13.6 m. Fifteen out of 16 animals had no difficulties in finding the nest entrance despite the altered appearance of local and distant landmarks at the release site. Apparently the scouts were able to recognize the visual scenes at the release site, and used them for reference to locate the nest entrance. In contrast, ants displaced from their nest to sites around 4 m away had more difficulties to re-find the nest.     

Hierarchy of sun,beach slope,and landmarks as cues for Y-axis orientation of the supratidal amphipod Talorchestia longicornis (Say)

The semi-terrestrial amphipod Talorchestia longicornis (Say) undergoes Y-axis orientation and has a hierarchy among orientation cues. A previous study found that they used sun compass orientation and moved in the onshore direction of the home beach in both air and water. The present study determined whether this species could also use local landmarks and beach slope as orientation cues. They oriented upslope in simulated darkness in the laboratory on both dry and wet sand with threshold slopes of 2° and 4°, respectively. When tested outside in an arena in air on wet sand, they were disoriented when sun, slope, and landmarks were absent as cues. If presented with single cues, they moved upslope, toward landmarks and in the up-beach direction of the home beach during sun compass orientation. Using paired cues, sun was dominant over slope and landmarks, while slope was dominant over landmarks. In the presence of all three cues, amphipods displayed sun compass orientation in all test combinations except when slope and landmarks were paired together against the sun, which evoked a bimodal response. Thus, the hierarchy of cues for up-beach movement of T. longicornis during Y-axis orientation is the sun, then the slope, and finally the landmarks.     

Development of parasitic <Emphasis Type="Italic">Maculinea teleius</Emphasis> (Lepidoptera,Lycaenidae) larvae in laboratory nests of four <Emphasis Type="Italic">Myrmica</Emphasis> ant host species

Maculinea butterflies are social parasites of Myrmica ants. Methods to study the strength of host ant specificity in the Maculinea–Myrmica association include research on chemical and acoustic mimicry as well as experiments on ant adoption and rearing behaviour of Maculinea larvae. Here we present results of laboratory experiments on adoption, survival, development and integration of M. teleius larvae within the nests of different Myrmica host species, with the objective of quantifying the degree of specialization of this Maculinea species. In the laboratory, a total of 94 nests of four Myrmica species: M. scabrinodis, M. rubra, M. ruginodis and M. rugulosa were used. Nests of M. rubra and M. rugulosa adopted M. teleius larvae more readily and quickly than M. ruginodis colonies. No significant differences were found in the survival rates of M. teleius larvae reared by different ant species. Early larval growth of M. teleius larvae differed slightly among nests of four Myrmica host species. Larvae reared by colonies of M. rugulosa which were the heaviest at the beginning of larval development had the lowest mean larval body mass after 18 weeks compared to those reared by other Myrmica species. None of the M. teleius larvae was carried by M. scabrinodis or M. rubra workers after ant nests were destroyed, which suggests a lack of integration with host colonies. Results indicate that Myrmica species coming from the same site differ in their ability to adopt and rear M. teleius larvae but there was no obvious adaptation of this butterfly species to one of the host ant species. This may explain why, under natural conditions, all four ants can be used as hosts of this butterfly species. Slight advantages of particular Myrmica species as hosts at certain points in butterfly larval development can be explained by the ant species biology and colony structure rather than by specialization of M. teleius.