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.     

Nest relocation and prey specialization in the antLeptogenys propefalcigera Roger (Formicidae: Ponerinae) in an urban area in southeastern Brazil

Summary Leptogenys propefalcigera Roger in southeastern Brazil feeds exclusively on oniscid isopods, showing a strong preference for one of two species. The ant shows a conspicuous nomadic behavior, with frequent nest relocations. The significance of these features is compared with other species ofLeptogenys and specialized predatory ants.     

Individual constancy of local search strategies in the giant tropical ant,Paraponera clavata (Hymenoptera: Formicidae)

Paraponera clavata workers engage in a period of local search after encountering a small amount of artificial nectar. Giving-up times from local search are not distributed normally; there is a strong skew to longer times. There is no statistically significant relationship between the amount of time required to collect the food and the subsequent search time. Giving-up time in response to the first reward presented to an ant is positively correlated with that ant's response to a second such reward. However, giving-up times diminish when an ant is presented with a series of rewards. Local search is a function of individual strategies, which remain relatively constant in the short term.     

Social structure and nestmate discrimination in two species of Brachyponera ants distributed in Japan

The ponerine ant Brachyponera chinensis was introduced to the USA, where it has become invasive. Although various ecological data have been collected for B. chinensis populations in the USA, most aspects concerning the biology and ecology of native populations in Japan, a presumed origin, remain unknown. Here we investigated the social structure and nestmate discrimination in native populations of B. chinensis and a closely related species, B. nakasujii. Both species showed functional polygyny over seasons. Only in B. nakasujii was there a seasonal change in the numbers of queens and workers per nest. In arena tests, workers of neither species showed aggressive behaviors to conspecific non‐nestmates from the same population, and the mean aggression score did not increase with the distance between nests. However, some differences in non‐aggressive responses were detected between nestmate and non‐nestmate pairs in both species. In an experiment to introduce a single worker into a nest, B. chinensis accepted non‐nestmates with a high probability just like nestmates, whereas in B. nakasujii non‐nestmates were less accepted than nestmates. These findings suggest that native populations of B. chinensis already possess some of the key characteristics shared by many invasive exotic ants in introduced ranges, such as stable polygyny, weak internest aggression and acceptance of non‐nestmates. These tendencies are remarkable in comparison to the closely related B. nakasujii.     

Vertebrate Fruit Removal and Ant Seed Dispersal in the Neotropical Ginger Renealmia alpinia (Zingiberaceae)*

Plants frequently display fruit characteristics that support multiple seed‐dispersal syndromes. These ambiguous characteristics may reflect the fact that seed dispersal is usually a complex process involving multiple dispersers. This is the case for the Neotropical ginger Renealmia alpinia (Zingiberaceae). It was originally suggested that the aromatic fruits of R. alpinia located at the base of the plant are adapted for terrestrial mammal seed dispersal. However, the dark‐purple coloration of the fruits and bright orange aril surrounding the seeds suggest that birds may play a role in R. alpinia seed dispersal. At La Selva Biological Station, Costa Rica, we used camera traps to record vertebrate visits to infructescences of R. alpinia. Most visitors were toucans and aracaris (Ramphastidae). However fruits were also removed by terrestrial mammals (coatis and armadillos). In addition to vertebrate fruit removal, some of the fruits dehisce and the seeds that fall on the ground are dispersed by ants. Fruitfall traps showed that 77 percent of fruits are removed by vertebrates. However, 15 percent of fruits fall to the base of parent plants to be potentially dispersed by ants. Experiments using a laboratory ant colony showed that ants are effective seed dispersers of R. alpinia. Ant seed manipulation increased germination success and reduced time to germination. In conclusion, primary seed dispersal in the Neotropical ginger R. alpinia is mostly performed by birds, additionally ants are effective dispersers at short distances. Seed dispersal in R. alpinia is a complex process involving a diverse array of dispersal agents.     

Pliocene and Pleistocene events shaping the genetic diversity within the central corridor of the Brazilian Atlantic Forest

Dinoponera lucida (Formicidae; Ponerinae) is an extinction‐threatened species of ant which is endemic in the central corridor of the Atlantic Forest. We used mitochondrial sequences of the Cox1, Cox2 and Cytb genes in order to infer some aspects of the evolutionary history and phylogeography of this ant. High genetic divergence and population structure were observed for the whole species. The current pattern of D. lucida diversity seems to be shaped during different geological times: middle Pliocene, early Pleistocene and mainly late Pleistocene, when the reduction of populations generated a structure pattern of the genetic variation of this species. Our data show that this structure results from the maintenance of populations of D. lucida within very small putative refuges to the south of the central Bahia refugium. We thus argue that, for some Atlantic forest endemic species, especially those resistant to very small fragments of forest, such as D. lucida, the small putative refuges were as important as, or even more important than, larger and stable refuges for the creation and maintenance of diversity, adding another piece to the puzzle of the mechanisms underlying local endemism. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 949–960.     

Patterns in foraging and nesting ecology in the neotropical ant, <Emphasis Type="Italic">Gnamptogenys moelleri</Emphasis> (Formicidae,Ponerinae)

Summary This study provides quantitative field data on the natural history and foraging behaviour of the Neotropical bromeliad-nesting ant Gnamptogenys moelleri (Ponerinae) in a sandy plain forest in Southeast Brazil. The ant nested on different bromeliad species and the nests were more frequently found in bigger bromeliads. The species used a wide array of invertebrates in its diet, hunting for live prey and scavenging the majority of the items from dead animals. The food items varied greatly in size (1 to 26 mm). Hunting was always performed by solitary workers. Retrieving was performed by solitary workers (small items), or by a group of 3 to 12 workers recruited to the food source (large items). Almost all G. moelleri foraging activity was restricted to the nest bromeliad. In the warm period more ants left the nest to forage, and foraging trips achieved greater distances compared to the cool season. Trap data revealed that overall availability of arthropod prey is higher in the summer than in the winter. The opportunism in nest site use and in foraging behaviour, the small foraging area, as well as the seasonal differences in foraging activity are discussed and compared with other tropical ants.Received 30 May 2003; revised 22 September 2003; accepted 3 October 2003.     

Interspecific Trail Following and Commensalism Between the Ponerine Ant Gnamptogenys menadensis and the Formicine Ant Polyrhachis rufipes

Gnamptogenys menadensis (subfamily Ponerinae) foragers use chemical trails to home to their nests. Although prey capture and retrieval are generally performed solitarily, trails seem to enhance foraging to areas rich in prey or to sugar sources. Trail laying and following are most conspicuous during nest migration. These trails are laid down by tapping the sting onto the substrate. In laboratory tests, only extracts from the Dufour's gland were readily followed. Workers of Polyrhachis rufipes (Formicinae) use the trails of G. menadensis to gain access to otherwise nonavailable sugar sources. When they encounter Gnamptogenys foragers, P. rufipes workers show a typical aggressive antennal boxing, to which Gnamptogenys reacts with a submissive behavior. This is the first report of commensalism between a ponerine and a formicine ant.     

Reproductive conflict among ant workers inDiacamma sp. from Japan: dominance and oviposition in the absence of the gamergate

Summary Queens do not exist inDiacamma sp. from Japan, and a single worker (gamergate) mates and monopolizes reproduction in each colony. We isolated small groups of workers without the gamergate, and confirmed that after 7–15 days many workers were able to oviposit (Tab. 1). These egg-laying individuals engage in stereotyped attacks towards each other. In six groups of individually marked workers (Tabs. 3 to 7), the pattern of aggressive interactions always indicated that one worker was dominant. She usually initiated a large number of attacks, but was herself never attacked. This dominant worker (alpha) also ate the eggs just laid by others. There was no linear dominance hierarchy, although a second highest-ranking worker could be recognized (she was only attacked by alpha). When these workers were dissected 4–6 weeks after being orphaned, only the alpha worker had active ovaries; other individuals that had been observed to oviposit earlier exhibited resorbed ovaries. Dissection of another 12 orphaned groups, kept together for different periods of time (Tab. 2), confirmed that one dominant worker is able to suppress the ovarian activity of all others in her group. We discuss how these aggressive interactions also function to regulate the production of males in other contexts, even when the gamergate is present. This aggression is separate, however, from another competitive interaction, mutilation of the gemmae, that functions as a control of mating activity in this species.     

Tandem running by foraging Pachycondyla striata workers in field conditions vary in response to food type,food distance,and environmental conditions

Ants show collective and individual behavioral flexibility in their response to immediate context, choosing for example between different foraging strategies. In Pachycondyla striata, workers can forage solitarily or recruit and guide nestmates to larger food sources through tandem running. Although considered more ancestral and less efficient than pheromone trail-laying, this strategy is common especially in species with small colony size. What is not known is how the decision to recruit or follow varies according to the immediate context. That is, how fine adjustments in information transfer affect immediate foraging decisions at the colony level. Here, we studied individually marked workers and evaluated their foraging decisions when food items varied in nature (protein versus carbohydrate), size, and distance from the nest at different temperatures and humidity levels. Our results show that tandem run leaders and potential followers adjust their behavior according to a combination of external factors. While 84.2% of trips were solitary, most ants (81%) performed at least 1 tandem run. However, tandem runs were more frequent for nearby resources and at higher relative humidity. Interestingly, when food items were located far away, tandem runs were more successful when heading to protein sources (75%) compared with carbohydrate sources (42%). Our results suggest that the social information transfer between leaders and followers conveys more information than previously thought, and also relies on their experience and motivation.