Abel Bernadou

Effect of fipronil on side-specific antennal tactile learning in the honeybee.

In the honeybee, the conditioning of the proboscis extension response using tactile antennal stimulations is well suited for studying the side-specificity of learning including the possible bilateral transfer of memory traces in the brain, and the role of inhibitory networks. A tactile stimulus was presented to one antenna in association with a sucrose reward to the proboscis. The other antenna was either not stimulated (A+/0 training), stimulated with a non-reinforced tactile stimulus B (A+/B- training) or stimulated with B reinforced with sucrose to the proboscis (A+/B+ training). Memory tests performed 3 and 24h after training showed in all situations that a tactile stimulus learnt on one side was only retrieved ipsilaterally, indicating no bilateral transfer of information. In all these groups, we investigated the effect of the phenylpyrazole insecticide fipronil by applying a sublethal dose (0.5 ng/bee) on the thorax 15 min before training. This treatment decreased acquisition success and the subsequent memory performances were lowered but the distribution of responses to the tactile stimuli between sides was not affected. These results underline the role of the inhibitory networks targeted by fipronil on tactile learning and memory processes.

Diversity in identity: behavioral flexibility, dominance, and age polyethism in a clonal ant

In many species of social insects, division of non-reproductive labor is to some extent affected by age, in that younger individuals engage in activities in the nest, whereas older individuals forage. While the link between age and task is less robust than originally thought, the transition from nursing to foraging is associated with large changes in gene expression, neuroanatomy, and physiology and therefore seems largely irreversible. Here, we investigate division of labor in the thelytokous ant Platythyrea punctata. Since it forms clonal colonies, it is an ideal model to investigate the behavioral flexibility of individuals and the proximate mechanisms underlying division of labor, while avoiding confounding factors, such as variation in genotype or morphology. We found that nurses and foragers of P. punctata differ in residual life span, fat content, fecundity, and the propensity to engage in dominance interactions. However, age-based division of labor appears to be flexible: foragers can revert to nursing and egg laying, even though they appear less fecund than original nurse workers. Interestingly, the transition from foraging to nursing seemed to slow down aging and senescence.

Effect of substrate roughness on load selection in the seed-harvester ant Messor barbarus L. (Hymenoptera, Formicidae)

We investigated the effect of substrate roughness on load selection in the seed-harvester ant Messor barbarus. Ants were forced to travel either on sand or on gravel to reach a seed patch containing seed fragments of different weights. We hypothesized that foragers travelling on a rough substrate could either increase their load as a result of the increased distance travelled (due to a more sinuous path and an increase in the vertical component of the path) or decrease their load because of the anticipated difficulty of moving with a heavy load on a rough surface. Our results were consistent with neither of these hypotheses: Load selection by ants did not depend on the roughness of the substrate encountered during their outbound trip. The main effect of substrate roughness was to slow down the progression of the ants and increase their probability of dropping or transferring heavy seeds on their way back to the nest, thus resulting in an overall reduction of the rate of seed return to the nest.

The effects of fungal infection and physiological condition on the locomotory behaviour of the ant Myrmica scabrinodis

Parasite infection often results in alterations in host behaviour. These changes vary greatly in their magnitude, from slight shifts in the time spent by the host performing a given activity to the appearance of novel behaviours. The effects of parasites can differ with the age and the physiological condition of the host. Rickia wasmannii is an ectoparasitic fungal symbiont in Myrmica ants that covers the whole body surface of the host and reduces its lifespan. The fungus is present in both young and old individuals, making it an optimal subject for the study of age-related parasitic effects. We tested the effect of fungal infection on the locomotory activity of the Myrmica scabrinodis ant in different age categories. The fat content of workers was measured as a proxy for their physiological status. Based on our findings, old workers bore more thalli and were leaner than young individuals, while they tended to move at higher speeds and with a lower degree of meandering. Young individuals covered smaller distances, at slower speeds and with a higher degree of meandering. Contrary to our expectations, the infection intensity of R. wasmannii affected neither the fat content nor the locomotory activity of ant workers. However, the two age classes seem to have different strategies with regards to the relationship between fat content and distance covered. Our results suggest that characteristics of locomotory activity differ between the age classes in many respects, and are also influenced by their physiological status, but parasitism by R. wasmannii does not seem to have a straightforward effect on any of the variables studied.

First come, first served: the first-emerging queen monopolizes reproduction in the ant Cardiocondyla “ argyrotricha ”

While colonies of most tropical species of the ant genus Cardiocondyla regularly contain multiple egg-laying queens (polygyny), single-queening (monogyny) evolved convergently in a Palearctic clade of Cardiocondyla and in Southeast Asian C. “argyrotricha.” In the latter species, monogyny is probably an adaptation to patchily distributed but highly stable nest sites. In experimentally orphaned colonies of C. “argyrotricha,” the first emerging queen shed its wings, began to lay eggs, and stayed mostly on the brood pile. Queens that emerged later remained in the peripheral areas of the nest without dispersing but retained their wings even after mating in the nest. Aggressive interactions among queens and between workers and queens were occasionally observed, but it appears that the order of queen emergence determines which of them will become reproductive and inherit the nest. We conclude that young queens commonly compete for nest inheritance in some species of Cardiocondyla and that queen–queen antagonism does not necessarily involve lethal fighting.

The Caucaso-Anatolian slave-making ant Myrmoxenus tamarae (Arnoldi, 1968) and its more widely distributed congener Myrmoxenus ravouxi (André, 1896): a multidisciplinary comparison (Hymenoptera: Formicidae)

A small minority of the presently recognized ∼12,500 species of ants are slave-makers, which permanently depend on the help of “slave workers,” that is workers of other ant species, which they pillage as brood from their nests in well-organized slave raids. The genus Myrmoxenus is one of the most species-rich taxa of slave-making ants, but individual species are often not well-delimited. Here, we compare behavior, morphometry, and nuclear and mtDNA sequences between two taxa of Myrmoxenus: Myrmoxenus tamarae (Arnoldi, 1968), known only from its type locality in Georgia, and the wide-spread M. ravouxi (André, 1896) to determine if the former might simply represent a Caucasian variant of the latter. Workers of the two taxa differed clearly in locomotor activity and slightly also in morphometry, while genetic investigations with nuclear and mitochondrial genes revealed only a weak differentiation. Given that Myrmoxenus appears to be a genus with a relatively recent radiation, we suggest to conservatively keep the present taxonomic situation with M. ravouxi and M. tamarae as separate species. The latter would then include specimens from Eastern Turkey and probably also Ukraine. Further studies, in particular in Greece and Turkey, might help to clarify the status of these endangered ants.

Ergonomics of load transport in the seed harvesting ant Messor barbarus: morphology influences transportation method and efficiency.

ABSTRACT We studied in the field the load transport behavior of workers of the polymorphic Mediterranean seed harvester ant Messor barbarus. Individual ants used two different methods to transport food items: carrying and dragging. The probability of dragging instead of carrying varied significantly with both the mass of the item transported and its linear dimension. Moreover, the values of item mass and length at which dragging began to occur increased with increasing size of the workers. However, larger ants began dragging at decreasing values of the relative mass represented by the items transported, which reflects different biomechanical constraints resulting from allometric relationships between the different parts of their body. Transport rate was significantly higher in large ants but varied in the same way for workers of different sizes with the relative mass of the item transported. Nevertheless, although large ants were individually more efficient than small ants in transporting food items, the relative transport rate, defined as the ratio of transport rate to the mass of the ant, was higher for small ants than for large ants. Colonies should thus have a greater benefit in investing in small ants than in large ants for the transport of food items. This may explain why the proportion of large ants is so small on the foraging columns of M. barbarus and why large ants are most often employed in colonies for tasks other than transporting food items. Summary: Investigation of load transportation efficiency in ants shows that it depends on both their morphology and the transportation method they use, i.e. carrying or dragging.

Avoid mistakes when choosing a new home: Nest choice and adoption of Leptothorax ant queens

In ants, mating and colony founding are critical steps in the life of ant queens. Outside of their nests, young queens are exposed to intense predation. Therefore, they are expected to have evolved behavior to accurately and quickly locate a nesting place. However, data on the early life history of female reproductives are still lacking. Leptothorax gredleri is a suitable model organism to study the behavior of young queens. Reproductives can be reared under artificial conditions and readily mate in the laboratory. After mating, L. gredleri queens have the options to found solitarily, seek adoption into another colony, or return into their natal nest. In this study, we investigated the decision-making processes of female sexuals before and after mating. In particular, we tested whether female sexuals use chemical cues to find their way back to the nest, studied if they prefer their own nest over other nesting sites and followed the adoption dynamics of mated queens over 8 weeks (plus hibernation and spring). We showed that female sexuals and freshly mated queens spent more time on substrate previously used by workers from their own colony and from another colony than on a blank substrate. This discriminatory capability of queens appears to be lost in old, reproductive queens. Nest choice experiments showed that female sexuals and freshly mated queens can distinguish their own nest while old mated queens do not. When reintroduced in their maternal colony, young queens were readily adopted, but a few weeks later aggression against young queens led to their emigration from the maternal nest and eventually also death.

Body size but not colony size increases with altitude in the holarctic ant, Leptothorax acervorum

1. Bergmanns rule states that organisms inhabiting colder environments show an increase in body size or mass in comparison to their conspecifics living in warmer climates. Although originally proposed for homoeothermic vertebrates, this rule was later extended to ectotherms. In social insects, only a few studies have tested this rule and the results were ambiguous. Here, ‘body size’ can be considered at two different levels (the size of the individual workers or the size of the colony).

A preliminary checklist of the ants (Hymenoptera, Formicidae) of Andorra

Abstract Within the last decade, checklists of the ant fauna of several European countries have been published or updated. Nevertheless, no ant checklists have hitherto been published for the principality of Andorra, a small landlocked country located in the eastern part of the Pyrenees. This work presents a critical list of the ant species of Andorra based on a review of the literature and on the biological material we collected during several field campaigns conducted in Andorra since the year 2005. Seventy-five species belonging to 21 genera of Formicidae were recorded. Nine species were recorded for the first time in Andorra: Aphaenogaster gibbosa (Latreille, 1798), Camponotus lateralis (Olivier, 1792), Camponotus piceus (Leach, 1825), Formica exsecta Nylander, 1846, Lasius piliferus Seifert, 1992, Tapinoma madeirense Forel, 1895, Temnothorax lichtensteini (Bondroit, 1918), Temnothorax niger (Forel, 1894), Temnothorax nigriceps (Mayr, 1855). The most speciose genera were Formica Linnaeus, 1758 and Temnothorax Forel, 1890 with 14 and 12 species, respectively. The ant fauna of Andorra is mostly dominated by Central European species (some are typical cold climate specialists); however species belonging to the Mediterranean ant fauna were also found. This can be explained by the particular geographic situation of Andorra which is characterized by a high mountain Mediterranean climate.