Luca Pietro Casacci

Ant Pupae Employ Acoustics to Communicate Social Status in Their Colony’s Hierarchy

The possession of an efficient communication system and an ability to distinguish between young stages are essential attributes that enable eusocial insects to live in complex integrated societies. Although ants communicate primarily via chemicals, it is increasingly clear that acoustical signals also convey important information, including status, between adults in many species. However, all immature stages were believed to be mute. We confirm that larvae and recently formed pupae of Myrmica ants are mute, yet once they are sclerotized, the pupae possess a fully functioning stridulatory organ. The sounds generated by worker pupae were similar to those of workers but were emitted as single pulses rather than in the long sequences characteristic of adults; both induced the same range and intensity of benevolent behaviors when played back to unstressed workers. Both white and sclerotized pupae have a higher social status than larvae within Myrmica colonies, but the latters status fell significantly after they were made mute. Our results suggest that acoustical signals supplant semiochemicals as a means of identification in sclerotized pupae, perhaps because their hardened integuments block the secretion of brood pheromones or because their developing adult secretions initially differ from overall colony odors.

The “Evolutionarily Significant Unit” concept and its applicability in biological conservation

Abstract Although most conservationists claim to protect “species”, the conservation unit actually and practically managed is the individual population. As resources are not unlimited, we need to focus on a restricted number of populations. But how can we select them? The Evolutionarily Significant Unit (ESU), first conceptualised by Ryder in 1986, may offer some answer. Several definitions have been proposed for the ESU, but all make reference to units “whose divergence can be measured or evaluated by putting differential emphasis on the role of evolutionary forces at varied temporal scales”. Thus, an ESU might be fully identical with a “species”, or a “species” could be composed of multiple ESUs. On the other hand, an ESU might comprise single/multiple populations exchanging a degree of gene flow, such as meta-populations. In an attempt to show strengths and weaknesses of ESU concepts, we present here, among several others, some case studies on the myrmecophilous butterflies of the genus Maculinea. In particular, we analyse the apparently everlasting debate about Maculinea alcon and M. rebeli, whose separation into separate species has been accepted by many authors, on mainly ecological criteria, but has not been fully supported by molecular analyses. We also discuss how the tight association with host ants may have driven selection for increasingly more strictly adapted Maculinea populations, arguably deserving specific taxonomic identity. Finally we discuss how current DNA analyses may fail to detect critical information on differences between taxa recently originated by the action of separate adaptive processes, which non-molecular studies can sometimes reveal. We conclude by discussing some current and often conflicting taxonomic trends, in their relationships with conservation policies.

Plant defences against ants provide a pathway to social parasitism in butterflies

Understanding the chemical cues and gene expressions that mediate herbivore–host-plant and parasite–host interactions can elucidate the ecological costs and benefits accruing to different partners in tight-knit community modules, and may reveal unexpected complexities. We investigated the exploitation of sequential hosts by the phytophagous–predaceous butterfly Maculinea arion, whose larvae initially feed on Origanum vulgare flowerheads before switching to parasitize Myrmica ant colonies for their main period of growth. Gravid female butterflies were attracted to Origanum plants that emitted high levels of the monoterpenoid volatile carvacrol, a condition that occurred when ants disturbed their roots: we also found that Origanum expressed four genes involved in monoterpene formation when ants were present, accompanied by a significant induction of jasmonates. When exposed to carvacrol, Myrmica workers upregulated five genes whose products bind and detoxify this biocide, and their colonies were more tolerant of it than other common ant genera, consistent with an observed ability to occupy the competitor-free spaces surrounding Origanum. A cost is potential colony destruction by Ma. arion, which in turn may benefit infested Origanum plants by relieving their roots of further damage. Our results suggest a new pathway, whereby social parasites can detect successive resources by employing plant volatiles to simultaneously select their initial plant food and a suitable sequential host.

Butterflies that trick ants with sound

Larvae of parasitic Maculinea butterflies use acoustic mimicry to induce host ants to adopt and care for them.

The acoustic repertoire of lycaenid butterfly larvae

Abstract Sounds and vibrations play vital roles in intra- and inter-specific communication of many insect taxa, for sexual display, defence and social recruitment. In Lepidoptera, sound production occurs in larvae, pupae and adults and has evolved in response to selection of sexual or defensive traits. About 75% of the 6000 estimated lycaenid butterflies are associated with ants (termed “myrmecophilous species”) and many species produce acoustic emissions during pre-imaginal development. It was initially believed that these acoustic emissions were only produced by myrmecophilous species, but later studies showed that the ability to produce sounds may be universal among this butterfly family. The acoustic repertoire of the late-instar larvae of 12 lycaenid species (Polyommatinae and Lycaeninae), showing different degrees of interaction with ants, was analysed by investigating 12 acoustic parameters measured on the call fundamental unit (pulse). All samples produced species-specific calls whose spectra were characterized by harmonic frequency components. The inter-specific call diversity better reflects the level of association with ants than the taxonomic relationships between species. Our results support the hypothesis that the ability to emit acoustic signals is widespread in lycaenids, and that these emissions play a role in myrmecophilous interactions.

Lock-picks: fungal infection facilitates the intrusion of strangers into ant colonies

Studies investigating host-parasite systems rarely deal with multispecies interactions, and mostly explore impacts on hosts as individuals. Much less is known about the effects at colony level, when parasitism involves host organisms that form societies. We surveyed the effect of an ectoparasitic fungus, Rickia wasmannii, on kin-discrimination abilities of its host ant, Myrmica scabrinodis, identifying potential consequences at social level and subsequent changes in colony infiltration success of other organisms. Analyses of cuticular hydrocarbons (CHCs), known to be involved in insects’ discrimination processes, revealed variations in chemical profiles correlated with the infection status of the ants, that could not be explained by genetic variation tested by microsatellites. In behavioural assays, fungus-infected workers were less aggressive towards both non-nestmates and unrelated queens, enhancing the probability of polygyny. Likewise, parasitic larvae of Maculinea butterflies had a higher chance of adoption by infected colonies. Our study indicates that pathogens can modify host recognition abilities, making the society more prone to accept both conspecific and allospecific organisms.

The first red list of Italian butterflies

The Italian biodiversity is among the richest in Europe. In particular, the Italian butterfly fauna includes almost 300 native species, and within the Euro‐Mediterranean area is second in species richness only to Turkey. Italy, however, has suffered from the lack of suitable instruments to evaluate the extinction risk of individual butterfly species on the basis of internationally recognised standards. We have been working to create the first Italian Red List for butterflies. The achievement of this goal was divided into three actions: (i) the institution of a network of experts on butterfly conservation; (ii) the evaluation of the extinction risk for all Italian butterfly species; (iii) the integration of the baseline information provided by the Italian Red Lists of other taxa crucial for future evaluations of biodiversity trends in Italy. Assessments of extinction risks were based on the IUCN Red List Categories and Criteria following their most updated guidelines and were discussed during workshops involving experts from different Italian regions. All native Italian butterflies were included in the evaluation. The whole national population of each species was evaluated, including those on large and small islands. Of 289 butterfly species assessed, one has become Regionally Extinct recently. Threatened species are 18 in total, corresponding to 6.3% of the species assessed. The majority of Italian butterfly populations are stable. The main threats to Italian butterflies are natural reforestation, as a consequence of rural land abandonment, agricultural intensification and climate change for species living at high altitude.

Acoustic communication within ant societies and its mimicry by mutualistic and socially parasitic myrmecophiles

This review focuses on the main acoustic adaptations that have evolved to enhance social communication in ants. We also describe how other invertebrates mimic these acoustic signals in order to coexist with ants in the case of mutualistic myrmecophiles, or, in the case of social parasites, corrupt them in order to infiltrate ant societies and exploit their resources. New data suggest that the strength of each ant–myrmecophile interaction leads to distinctive sound profiles and may be a better predictor of the similarity of sound between different myrmecophilous species than their phylogenetic distance. Finally, we discuss the evolutionary significance of vibrations produced by specialized myrmecophiles in the context of ant multimodal communication involving the use of chemical and acoustic signals in combination and identify future challenges for research including how new technology might allow a better understanding of the study systems.

Habitat preferences of Papilio alexanor Esper, [1800]: implications for habitat management in the Italian Maritime Alps

ABSTRACT Papilio alexanor Esper, [1800] is a threatened European butterfly species listed in Annex IV of the Habitats Directive and in Appendix II of the Bern Convention, being considered extremely vulnerable to climate change. According to some projections (e.g., Bambu, a scenario of moderate climate change), it would be expected to lose 63% of its European climatic niche by the year 2050 and 77% by 2080. The few remaining populations are expected to become concentrated in the Maritime Alps. In 2009 and 2010, we studied what is probably the densest P. alexanor population in the Italian part of this area. It occurs in a series of dry, xerothermic grasslands, also partially occupied by an abandoned limestone quarry, where the larval food plant is Ptychotis saxifraga (L.) Loret & Barrandon. Females lay eggs in July, choosing patches where the food plants are higher and more abundant. The habitat preference, conservation status and survival of the early instars larvae of P. alexanor have been investigated in order to draw up conservation strategies for this species in the Italian Maritime Alps.

Butterfly Diversity in a Changing Scenario

For many historical and ecological reasons, Italy is characterized by extremely high biodiversity level, which we can observe in virtually all animal and plant groups. This occurs in concomitance with relatively low levels of anthropic disturbance, at least in comparison to most areas of central Europe. The elongate shape and mountainous nature of Italy, together with its vast littoral areas, contribute to generate very diverse ecological conditions, all along a series of latitudinal and altitudinal habitat gradients. The Mediterranean basin, where Italy has centre-stage position, is among the 25 world biodiversity hotspots identified in Myers’ seminal paper (Myers et al., 2000). Whatever will happen to, or affect the, Italian biodiversity will be reflected on a world-wide scale. This chapter describes animal diversity as a dynamic functional system, now increasingly threatened by various kinds of anthropogenic threats and pressures. We describe how and to what extent biodiversity is changing, taking as an example a particularly well-known animal group, such as butterflies, within an area of focal importance, such as the Mediterranean basin. We mainly discuss data that we, and our research group, have personally obtained in the course of the past several years, and even though we mainly worked in Italy, we discuss them in the more general framework of a pan-European scientific scenario.