Christoph von Beeren

Multiroute memories in desert ants

When offered a permanent food source, central Australian desert ants, Melophorus bagoti, develop individually distinct, view-based foraging routes, which they retrace with amazing accuracy during each foraging trip. Using a particular channel setup connected to an artificial feeder, we trained M. bagoti ants to either two or three inward routes that led through different parts of their maze-like foraging grounds. Here, we show that ants are able to adopt multiple habitual paths in succession and that they preserve initially acquired route memories even after they have been trained to new routes. Individual ants differ in the consistency with which they run along habitual pathways. However, those ants that follow constant paths retain their route-specific memories for at least 5 days of suspended foraging, which suggests that even multiple route memories, once acquired, are preserved over the entire lifetime of a forager.

Differential host defense against multiple parasites in ants

Host–parasite interactions are ideal systems for the study of coevolutionary processes. Although infections with multiple parasite species are presumably common in nature, most studies focus on the interactions of a single host and a single parasite. To the best of our knowledge, we present here the first study on the dependency of parasite virulence and host resistance in a multiple parasite system. We evaluated whether the strength of host defense depends on the potential fitness cost of parasites in a system of two Southeast Asian army ant hosts and five parasitic staphylinid beetle species. The potential fitness costs of the parasites were evaluated by their predation behavior on host larvae in isolation experiments. The host defense was assessed by the ants’ aggressiveness towards parasitic beetle species in behavioral studies. We found clear differences among the beetle species in both host–parasite interactions. Particular beetle species attacked and killed the host larvae, while others did not. Importantly, the ants’ aggressiveness was significantly elevated against predatory beetle species, while non-predatory beetle species received almost no aggression. As a consequence of this defensive behavior, less costly parasites are more likely to achieve high levels of integration in the ant society. We conclude that the selection pressure on the host to evolve counter-defenses is higher for costly parasites and, thus, a hierarchical host defense strategy has evolved that depends on the parasites’ impact.

Acquisition of chemical recognition cues facilitates integration into ant societies

BackgroundSocial insects maintain the integrity of their societies by discriminating between colony members and foreigners through cuticular hydrocarbon (CHC) signatures. Nevertheless, parasites frequently get access to social resources, for example through mimicry of host CHCs among other mechanisms. The origin of mimetic compounds, however, remains unknown in the majority of studies (biosynthesis vs. acquisition). Additionally, direct evidence is scarce that chemical mimicry is indeed beneficial to the parasites (e.g., by improving social acceptance).ResultsIn the present study we demonstrated that the kleptoparasitic silverfish Malayatelura ponerophila most likely acquires CHCs directly from its host ant Leptogenys distinguenda by evaluating the transfer of a stable-isotope label from the cuticle of workers to the silverfish. In a second experiment, we prevented CHC pilfering by separating silverfish from their host for six or nine days. Chemical host resemblance as well as aggressive rejection behaviour by host ants was then quantified for unmanipulated and previously separated individuals. Separated individuals showed reduced chemical host resemblance and they received significantly more aggressive rejection behaviour than unmanipulated individuals.ConclusionOur study clarifies the mechanism of chemical mimicry in a social insect parasite in great detail. It shows empirically for the first time that social insect parasites are able to acquire CHCs from their host. Furthermore, it demonstrates that the accuracy of chemical mimicry can be crucial for social insect parasites by enhancing social acceptance and, thus, allowing successful exploitation. We discuss the results in the light of coevolutionary arms races between parasites and hosts.

The Social Integration of a Myrmecophilous Spider Does Not Depend Exclusively on Chemical Mimicry

Numerous animals have evolved effective mechanisms to integrate into and exploit ant societies. Chemical integration strategies are particularly widespread among ant symbionts (myrmecophiles), probably because social insect nestmate recognition is predominantly mediated by cuticular hydrocarbons (CHCs). The importance of an accurate chemical mimicry of host CHCs for social acceptance recently has been demonstrated in a myrmecophilous silverfish. In the present study, we investigated the role of chemical mimicry in the myrmecophilous spider Gamasomorpha maschwitzi that co-occurs in the same host, Leptogenys distinguenda, as the silverfish. To test whether spiders acquire mimetic CHCs from their host or not, we transferred a stable isotope-labeled hydrocarbon to the cuticle of workers and analyzed the adoption of this label by the spiders. We also isolated spiders from hosts in order to study whether this affects: 1) their chemical host resemblance, and 2) their social integration. If spiders acquired host CHCs, rather than biosynthesizing them, they would be expected to lose these compounds during isolation. Spiders acquired the labeled CHC from their host, suggesting that they also acquire mimetic CHCs, most likely through physical contact. Furthermore, isolated spiders lost considerable quantities of their CHCs, indicating that they do not biosynthesize them. However, spiders remained socially well integrated despite significantly reduced chemical host similarity. We conclude that G. maschwitzi depends less on chemical mimicry to avoid recognition and aggressive rejection than the silverfish previously studied, suggesting that the two myrmecophiles possess different adaptations to achieve social integration.

On the use of adaptive resemblance terms in chemical ecology

Many organisms (mimics) show adaptive resemblance to an element of their environment (model) in order to dupe another organism (operator) for their own benefit. We noted that the terms for adaptive resemblance are used inconsistently within chemical ecology and with respect to the usage in general biology. Here we first describe how resemblance terms are used in general biology and then comparatively examine the use in chemical ecology. As a result we suggest the following consistent terminology: “chemical crypsis” occurs when the operator does not detect the mimic as a discrete entity (background matching). “Chemical masquerade” occurs when the operator detects the mimic but misidentifies it as an uninteresting entity, as opposed to “chemical mimicry” in which an organism is detected as an interesting entity by the operator. The additional terms “acquired” and “innate” may be used to specify the origins of mimetic cues.

Collective exploitation of a temporally unpredictable food source: mushroom harvesting by the ant Euprenolepis procera

Foraging on spatiotemporally unpredictable food sources is widespread among animals. Locating unpredictable food is, however, expected to pose specific challenges to an animal’s foraging strategy. Primarily exploiting wild-growing mushrooms, the ant Euprenolepis procera represents a remarkable example of an animal that relies on ephemeral resources. In the present study we investigated how the ant’s foraging system has adapted to this challenging diet. We tested feeding preferences of E. procera, monitored spatiotemporal growth patterns of mushrooms and analysed the ant’s foraging trail system. The growth patterns of mushrooms turned out to be more predictable than commonly believed, since they reappeared frequently (up to 15 times in 1 month) in close vicinity of former growth locations. Generally, such spatially fixed and periodically regrowing resources can be utilized effectively by revisiting them. While many animals rely on idiosyncratic spatial memory to accomplish this task, we found that E. procera established a wide-ranging, stable trail network that served as an external colony memory. Subsections of the trail network were used only periodically. Inactive trail sections persisted and served as the external colony memory allowing the ants to check growing sites periodically and eventually harvest regrowing mushrooms collectively. We conclude that this unusual foraging behaviour, which features permanence (route fidelity over time) as well as flexibility (activation/deactivation of trail sections), is well adapted to the growth pattern of mushrooms, underlining the high potential of collective behaviour for an efficient exploitation of ephemeral food sources.

Aleocharine rove beetles (Coleoptera, Staphylinidae) associated with Leptogenys Roger, 1861 (Hymenoptera, Formicidae) II. Two new genera and two new species associated with L. borneensis Wheeler, 1919.

Abstract Two new genera and two new species of Aleocharinae (Staphylinidae) from Malaysia are described: Parawroughtonilla Maruyama, gen. n. (type species: Parawroughtonilla hirsutaMaruyama, sp. n.), Leptogenonia Maruyama, gen. n. (type species: Leptogenonia roslii Maruyama, sp. n.), which are associated with Leptogenys borneensis Wheeler, 1919. They are closely related and share a unique character state of the aedeagus.

Sicariomorpha, a New Myrmecophilous Goblin Spider Genus (Araneae, Oonopidae) Associated with Asian Army Ants

ABSTRACT A new genus of oonopid spider, Sicariomorpha Ott and Harvey, is named for the type and only known species, Gamasomorpha maschwitzi Wunderlich from Malaysia. The most striking feature of the spider is the eyes, which are arranged in two widely separated triads. Besides taxonomic description, we summarize the biology of Sicarimorpha maschwitzi, which is a kleptoparasite of the Southeast Asian army ant Leptogenys distinguenda (Emery) and one among only few well-studied myrmecophilous spiders. Its morphology, behavior and life history seem to be well adapted for the life with its predatory army ant host.