Cristina Castracani

The ant fauna of Castelporziano Presidential Reserve (Rome, Italy) as a model for the analysis of ant community structure in relation to environmental variation in Mediterranean ecosystems

Ants are often used as ecological indicators in environmental monitoring programs, but rarely in Europe, probably because of a lack of baseline knowledge on the relationship between ant community structure and environmental variation. We present this baseline knowledge for Italian ecosystems that are typical of the Mediterranean climate, in order to assess the value of ants as ecological indicators in this biogeographic zone. Sampling areas were selected inside the Castelporziano Natural Reserve (Rome, Italy). The elevated variety of habitats and diverse ecological conditions, as well as the different levels of human impact in the Reserve, make this area a suitable location to develop and test biological indicators of environmental quality. The ant community structure was compared among several Mediterranean ecosystems using pitfall trapping, multidimensional scaling, the indicator species analysis and the Functional Groups Approach. Key factors for differences in ant community structure seem to be the presence/absence of water, the level of light and microhabitat diversity. Our results suggest that Castelporziano is an informative area in order to develop a study model for the Italian ant fauna and the Functional Group Approach is a promising procedure to associate differences in ant community structures with differences in habitat stress and disturbance.

Mandible associated glands in queens of the slave-making ant Polyergus rufescens (Hymenoptera, Formicidae)

SummaryA first description of the structural organization of two exocrine glands associated with the mandibles of queens of the obligatory slave-making ant Polyergus rufescens is reported. The mandibular gland consists of clustered bicellular secretory units connected by means of cuticular ducts to a big reservoir. The reservoir continues in a duct that opens proximally on the mandible cuticle. Intramandibular glands are isolated bicellular secretory units connected to the external pores through a cuticular duct. No reservoir has been observed. In both cases the secretory cells belong to the 3rd class. Functional aspects of the investigated glands are discussed taking also into account for the parasitic habit of this slave-making species.

Climate mediates the effects of disturbance on ant assemblage structure

Many studies have focused on the impacts of climate change on biological assemblages, yet little is known about how climate interacts with other major anthropogenic influences on biodiversity, such as habitat disturbance. Using a unique global database of 1128 local ant assemblages, we examined whether climate mediates the effects of habitat disturbance on assemblage structure at a global scale. Species richness and evenness were associated positively with temperature, and negatively with disturbance. However, the interaction among temperature, precipitation and disturbance shaped species richness and evenness. The effect was manifested through a failure of species richness to increase substantially with temperature in transformed habitats at low precipitation. At low precipitation levels, evenness increased with temperature in undisturbed sites, peaked at medium temperatures in disturbed sites and remained low in transformed sites. In warmer climates with lower rainfall, the effects of increasing disturbance on species richness and evenness were akin to decreases in temperature of up to 9°C. Anthropogenic disturbance and ongoing climate change may interact in complicated ways to shape the structure of assemblages, with hot, arid environments likely to be at greatest risk.

Glandular sources of recruitment, trail, and propaganda semiochemicals in the slave-making ant Polyergus rufescens

The chemical sources involved in raiding activities of the slave-making ant Polyergus rufescens were investigated in the laboratory. In particular, we identified the sources of substances the raiding workers employ to convey information to nestmates and to disrupt reactions by defending workers during host nest invasion. Different secretions were offered to the dulotic ants on the tip of a blotting paper strip inserted a few centimetres into the nest entrance. The Dufours gland secretion induced the characteristic mass exit from the nest and is likely the source of a recruitment signal. Moreover, laboratory tests with secretions from different anatomical structures revealed that the trail signals for homing raiding workers are conveyed by their hindgut contents released during the outbound trip. Finally, to ascertain if P. rufescens raiding workers use “propaganda” pheromones, the behavioural response of the Formica (Serviformica) cunicularia host workers to different secretions of the slave-makers was investigated. Only mandibular secretions caused the typical panic reactions shown by residents at the moment of nest invasion. This probably facilitates both nest invasion and brood sacking by raiding workers.

Ecologists, educators, and writers collaborate with the public to assess backyard diversity in The School of Ants Project

Citizen science can generate data that would not exist otherwise while increasing public scientific literacy. However, the quality and use of citizen science data have been criticized in the recent ecological literature. We need an approach that advances eco-evolutionary understanding, achieves education goals and incorporates public participation into as many aspects of the scientific process as possible. We collaborated with public participants to make new discoveries about the distribution and ecology of ants while informing the next studies that participants and scientists might perform together. We implemented the School of Ants (SoA) program in which participants sample ants that are identified by taxonomic experts. Using a comprehensive framework that meets the needs of multiple agents, we also developed outreach materials about ant biology, collaborated with educators to incorporate SoA into classroom science, and launched an international SoA module in Italy. In the first 17 months, SoA volunteers collected ants at 500 unique sites across the USA-including all 50 states and Washington, D.C. To address concerns about the validity of citizen scientist-derived data, we conducted a ground truthing trial that confirmed that trained and untrained volunteers were equally effective at collecting ants. Data from SoA samples indicate that ant diversity varies across wide geographic scales and that there can be high levels of native ant diversity where people live. SoA volunteers collected 7 exotic and 107 native ant species. Although exotic ants were common, ants native to North America occurred in ∼70% of all sites. Many of the ants common in backyards were species that tend to be very poorly studied. For example, citizen scientists documented a range extension of more than 2000 miles for the Asian Needle Ant, Pachycondyla chinensis. Using SoA data as a starting point, we collaborated with a science writer to produce a free, interactive iBook about the common ants in North America; the book included distribution maps such as that for P. chinensis informed by participant collections. Moving forward, we plan to leverage this existing framework to address more complex ecological and evolutionary questions in partnership with our public participants.

The mandibular glands as a source of sexual pheromones in virgin queens of Polyergus rufescens (Hymenoptera, Formicidae)

Abstract> ‘Female‐calling syndrome’ is the reproductive strategy adopted by the European slave‐making ant Polyergus rufescens, where a winged female disperses a short distance from the nest, ascends to an elevated position (at the top of a blade of grass) and is joined shortly thereafter by conspecific males. This suggests the probable use of very effective sexual calling pheromones by females. Here, the role of the mandibular glands of winged females is demonstrated to be a source of sexual pheromones. The secretion of these glands (among the structures tested: the mandibular, Dufour, poison and pygidial glands and the head without mandibular glands) appears to have a strong attractive effect on males and also elicits male copulatory behaviour.

Chemical communication in mating behaviour of the slave-making ant Polyergus rufescens (Hymenoptera, Formicidae): 3-ethyl-4-methylpentanol as a critical component of the queen sex pheromone

Abstract.The aim of the research reported here was to determine whether 3-ethyl-4-methylpentanol, a minor but crucial component of the sex pheromone of the North American slave-making ant species Polyergus breviceps, was also a component of the sex pheromone of the European congener Polyergus rufescens. Thus, the contents of mandibular glands of P. rufescens virgin queen were extracted and analysed. The main component of the extracts was methyl 6-methylsalicylate and 3-ethyl-4-methylpentanol was identified as one of several minor components. Further analyses showed that the insects produce mainly the (R)-enantiomer of the alcohol. Males’ responses to various blends of methyl 6-methylsalicylate with the racemate or the pure enantiomers of 3-ethyl-4- methylpentanol were tested in field behavioural bioassays. The data showed that blends of methyl 6- methylsalicylate and 3-ethyl-4-methylpentanol were strongly synergistic, with the most active ratios being biased toward the first component. The addition of other minor components to the binary blend neither increased nor decreased responses by males. Only the (R)-enantiomer of the alcohol was biologically active; its antipode did not inhibit attraction. The results are discussed in terms of the evolution of signals, and are compared with the results previously obtained for the allopatric species Polyergus breviceps.

A global database of ant species abundances

What forces structure ecological assemblages? A key limitation to general insights about assemblage structure is the availability of data that are collected at a small spatial grain (local assemblages) and a large spatial extent (global coverage). Here, we present published and unpublished data from 51 ,388 ant abundance and occurrence records of more than 2,693 species and 7,953 morphospecies from local assemblages collected at 4,212 locations around the world. Ants were selected because they are diverse and abundant globally, comprise a large fraction of animal biomass in most terrestrial communities, and are key contributors to a range of ecosystem functions. Data were collected between 1949 and 2014, and include, for each geo-referenced sampling site, both the identity of the ants collected and details of sampling design, habitat type, and degree of disturbance. The aim of compiling this data set was to provide comprehensive species abundance data in order to test relationships between assemblage structure and environmental and biogeographic factors. Data were collected using a variety of standardized methods, such as pitfall and Winkler traps, and will be valuable for studies investigating large-scale forces structuring local assemblages. Understanding such relationships is particularly critical under current rates of global change. We encourage authors holding additional data on systematically collected ant assemblages, especially those in dry and cold, and remote areas, to contact us and contribute their data to this growing data set.

Behavioral bioassays testing the methyl 6-methylsalicylate as a component of the female sex pheromone in the slave-making ant Polyergus rufescens (Hymenoptera, Formicidae)

The mating behavior of the slave-making ant Polyergus rufescens is an example of “Female-calling Syndrome” as defined by Hölldobler and Bartz (1985). In this species, in fact, nuptial flights are inconspicuous and not well synchronized between sexes. Moreover, females typically call for males, do not disperse widely, and remain near their natal nest or return to a dulotic colony after mating. Lastly, the virgin queen usually mates only with the first male that is able to locate her and after mating she cuts off her wings and hides in the vegetation surrounding the nest (Mori et al., 2001). Two main aspects of P. rufescens ecology could explain the mating strategy adopted by this species: the relative low density of both sexes and its parasitic nature. As suggested by Bourke and Franks (1995), female calling could be advantageous for species that do not produce a large amount of sexuals: through this mating strategy, females probably maximize their chances of finding a mate. Moreover, female calling is suitable for scattered colonies, like those

Daily activity patterns and food preferences in an alpine ant community

Species may reduce competitive interactions by temporal separation in activity times. Similarly to other animals, ants also partition their niches by being active during specific periods of the year or at specific times of the day. However, if several species share the same temporal niches, interspecific competition may give rise to behavioural dominance hierarchies, territoriality or spatial mosaics. Thus, our first aim was to study daily activity patterns of alpine communities to investigate their temporal dynamics at both general and specific levels. Due to short distances among different ecosystems, montane systems are ideal models to study the effect of geographic variation on community structure. On the other hand, ants represent an excellent model to analyze beta-diversity because they are one of the most ecologically significant components of many ecosystems. Nevertheless, there is a lack of ecological studies on ant communities in Italy and, in particular, on alpine ants. Therefore, the second aim of this work was to study ant species richness and distribution in order to update information on alpine ant fauna. As ants can simultaneously exhibit multiple trophic roles, assessing the feeding habits of an ant community may help to clarify how these insects can influence their ecosystem. Thus, the third aim of this research was to evaluate ant food preferences in alpine environments. Samplings were conducted in Soana Valley, inside the Gran Paradiso National Park, during summer 2011: pitfall traps and food baits were placed in order to collect data on species richness, abundances and food preferences. The acquired results on activity patterns showed that ants were more active in the late morning. The analysis of food preferences revealed that sugary solutions were the favourite resources. Finally, concerning species spatial distribution, there was a higher level of biodiversity at intermediate elevations, probably due to an increase of temperature and spatial heterogeneity.