Emilio Balletto

Is the partial Mantel test inadequate

Abstract.— A publication by Raufaste and Rousset (2001) questioned the effectiveness of the partial Mantel test, a nonparametric statistical test for association among three distance matrices. By repeated simulations, we calculated the cumulative density functions of the null‐hypothesis probability of no correlation, within an explicit model of causal relationships. Results do not support the criticism: in conditions of moderate correlation between the independent matrices, the actual error rate is closely associated to the intended type‐I error a.

Queen ants make distinctive sounds that are mimicked by a butterfly social parasite.

Ants dominate terrestrial ecosystems through living in complex societies whose organization is maintained via sophisticated communication systems. The role of acoustics in information exchange may be underestimated. We show that Myrmica schencki queens generate distinctive sounds that elicit increased benevolent responses from workers, reinforcing their supreme social status. Although fiercely defended by workers, ant societies are infiltrated by specialist insects that exploit their resources. Sounds produced by pupae and larvae of the parasitic butterfly Maculinea rebeli mimic those of queen ants more closely than those of workers, enabling them to achieve high status within ant societies. We conclude that acoustical mimicry provides another route for infiltration for ∼10,000 species of social parasites that cheat ant societies.

Relative importance of density-dependent regulation and environmental stochasticity for butterfly population dynamics

The relative contribution of density-dependent regulation and environmental stochasticity to the temporal dynamics of animal populations is one of the central issues of ecology. In insects, the primary role of the latter factor, typically represented by weather patterns, is widely accepted. We have evaluated the impact of density dependence as well as density-independent factors, including weather and mowing regime, on annual fluctuations of butterfly populations. As model species, we used Maculinea alcon and M. teleius living in sympatry and, consequently, we also analysed the effect of their potential competition. Density dependence alone explained 62 and 42% of the variation in the year-to-year trends of M. alcon and M. teleius, respectively. The cumulative Akaike weight of models with density dependence, which can be interpreted as the probability that this factor should be contained in the most appropriate population dynamics model, exceeded 0.97 for both species. In contrast, the impacts of inter-specific competition, mowing regime and weather were much weaker, with their cumulative weights being in the range of 0.08–0.21; in addition, each of these factors explained only 2–5% of additional variation in Maculinea population trends. Our results provide strong evidence for density-dependent regulation in Maculinea, while the influence of environmental stochasticity is rather minor. In the light of several recent studies on other butterflies that detected significant density-dependent effects, it would appear that density-dependent regulation may be more widespread in this group than previously thought, while the role of environmental stochasticity has probably been overestimated. We suggest that this misconception is the result of deficiencies in the design of most butterfly population studies in the past, including (1) a strong focus on adults and a neglect of the larval stage in which density-dependent effects are most likely to occur; (2) an almost exclusive reliance on transect count results that may confound the impact of environmental stochasticity on butterfly numbers with its impact on adult longevity.

Acoustical mimicry in a predatory social parasite of ants.

SUMMARY Rapid, effective communication between colony members is a key attribute that enables ants to live in dominant, fiercely protected societies. Their signals, however, may be mimicked by other insects that coexist as commensals with ants or interact with them as mutualists or social parasites. We consider the role of acoustics in ant communication and its exploitation by social parasites. Social parasitism has been studied mainly in the butterfly genus Maculinea, the final instar larvae of which are host-specific parasites of Myrmica ants, preying either on ant grubs (predatory Maculinea) or being fed by trophallaxis (cuckoo Maculinea). We found similar significant differences between the stridulations of model queen and worker ant castes in both Myrmica sabuleti and Myrmica scabrinodis to that previously reported for Myrmica schencki. However, the sounds made by queens of all three Myrmica species were indistinguishable, and among workers, stridulations did not differ significantly in two of three species-pairs tested. Sounds recorded from the predatory caterpillars and pupae of Maculinea arion had similar or closer patterns to the acoustics of their host Myrmica sabuleti than those previously reported for the cuckoo Maculinea rebeli and its host Myrmica schencki, even though Maculinea rebeli caterpillars live more intimately with their host. We conclude that chemical mimicry enables Maculinea larvae to be accepted as colony members by worker ants, but that caterpillars and pupae of both predatory and cuckoo butterflies employ acoustical mimicry of queen ant calls to elevate their status towards the highest attainable position within their hosts social hierarchy.

Phylogeny of the salamandrid genus Triturus

Abstract The Salamandrid genus Triturus and its allies have attracted a considerable amount of interest for many years. As a consequence, much evidence has accumulated on a number of aspects on their karyology, allozymic variation, reproductive behaviour, taxonomy, osteology and even paleontology. Few of these studies, however, have made use of modern and more disciplined methods of phylo‐genetic reconstruction, and none have so far attempted to evaluate all the available evidence in a single analysis. This paper attempts to synthesize current knowledge into a comprehensive, multidimensional picture of the evolutionary relationships of Triturus, and to integrate it in a single phylogenetic tree. Mate recognition systems and environmental constraints were superimposed to the cla‐dogram and employed to generate a broader evolutionary scenario. All species of ≪bigger newts≫ (T. cristatus complex, T. vittatus) are characterized by a higly developed sexual dimorphism, based mainly on visual characters. In cont...

Population extinctions in the Italian diurnal lepidoptera: an analysis of possible causes

In depth studies of patterns of extinction are fundamental to understand species vulnerability, in particular when population extinctions are not driven by habitat loss, but related to subtle changes in habitat quality and are due to ‘unknown causes’. We used a dataset containing over 160,000 non-duplicate individual records of occurrence (referred to 280 butterflies and 43 zygenid moths), and their relative extinction data, to carry out a twofold analysis. We identified ecological preferences that influence extinction probability, and we analysed if all species were equally vulnerable to the same factors. Our analyses revealed that extinctions were non-randomly distributed in space and time, as well as across species. Most of the extinctions were recorded in 1901–1950 and, as expected, populations at their range edges were more prone to become extinct for non-habitat-related causes. Ecological traits were not only unequally distributed between extinction and non-extinction events, but also not all ecological features had the same importance in driving population vulnerability. Hygrophilous and nemoral species were the most likely to experience population losses and the most prone to disappear even when their habitat remained apparently unchanged. Species vulnerability depends on both ecological requirements and threat type: in fact, each species showed a distinct pattern of vulnerability, depending on threats. We concluded that the analysis may be an important step to prevent butterfly declines: species that are strongly suffering due to ‘unknown changes’ are in clear and urgent need of more detailed auto-ecological studies.

When the Rule Becomes the Exception. No Evidence of Gene Flow between Two Zerynthia Cryptic Butterflies Suggests the Emergence of a New Model Group

There is increasing evidence that most parapatric cryptic/sister taxa are reproductively compatible across their areas of contact. Consequently, the biological species concept, which assumes absence of interbreeding, is becoming a not so effective criterion in evolutionary ecology. Nevertheless, the few parapatric sister taxa showing complete reproductive barriers represent interesting models to study speciation processes and the evolution of reproductive isolation. In this study, we examined contact populations in northwestern Italy of two butterfly species, Zerynthia polyxena and Z. cassandra, characterized by different genitalic morphotypes. We studied levels of divergence among 21 populations distributed from Sicily to France using three genetic markers (the mitochondrial COI and ND1 genes and the nuclear wingless gene) and genitalic geometric morphometrics. Moreover, we performed species distribution modelling to estimate different climatic requirements of Z. polyxena and Z. cassandra. We projected climatic data into glacial maximum scenarios in order to verify if and to which extent glacial cycles could have contributed to speciation processes. Genetic and morphometric analyses identified two main groups. All specimens showed a concordant pattern of diversification, including those individuals sampled in the contact area. Haplotype distribution and climatic models showed that during glacial maxima both species experienced a strong range contraction and presumably remained separated into different microrefugia in southern France, in the Italian Peninsula and on the islands of Elba and Sicily. Long term separation was probably favoured by reduced dispersal ability and high phylopatry, while genitalic diversification probably favoured interbreeding avoidance. Conversely, the aposematic wing pattern remained almost identical. We compared our results with those obtained in other species and concluded that Z. polyxena and Z. cassandra represent a valuable model in the study of speciation.

Evidence for chromosome and Pst I satellite DNA family evolutionary stasis in the Bufo viridis group (Amphibia, Anura).

The West Palearctic green toads, Bufo viridis, represent a species complex. Apart from tetraploid populations, which form at least one separate species, evidence exists for relevant differentiation among diploid populations. We present the results of a chromosomal (C-, Ag-NOR-, Replication pattern, DAPI and CMA3 banding) and molecular study (isolation and characterization of a satellite DNA family) carried out on a number of Central Asian, European and North African populations. For comparative purposes, our molecular analysis was also extended to specimens of three additional Bufo species (B. bufo, B. mauritanicus and B. cf. regularis), as well as two rare African bufonids (Werneria mertensis and Wolterstoffina sp.). Our results demonstrate a remarkable karyological and molecular evolutionary stasis in the Bufo viridis complex. In fact, all chromatinic markers showed the same pattern and/or composition in all specimens, independently of their origin and ploidy levels. Even the NOR loci were invariably two and located on the telomeric regions of two chromosomes of the sixth pair, or quartet. Furthermore, very similar patterns of genomic hybridization of a monomeric unit of the Pst I satellite DNA family (named pBv) were observed in all diploid and tetraploid populations, as well as in B. bufo and B. mauritanicus. Finally, pBv hybridizes with monomeric units of Pst I satellite DNA in all species studied, including Werneria and Wolterstorffina, which are thought to have separated from Bufo as early as in the Mesozoic.

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.

Loggerhead turtle (Caretta caretta) by catches on long‐lines: The importance of olfactory stimuli

Abstract In order to reduce sea turtle by‐catches on surface drifting long‐lines during professional swordfish (Xiphias gladius) fishing, the relevance of olfactory stimuli in eliciting predation by loggerhead sea turtles (Caretta caretta) was investigated. Choice experiments were run in captivity. Squid‐shaped plastic lures having or lacking scomber odour were presented to 27 specimens (22 immatures and 5 adults). The turtles’ behavioural responses highlighted the importance of chemical clues in eliciting approaching and biting behaviours. This study was carried out within the framework of the EU‐Life Project ‘Urgent conservation measures for C. caretta in the Pelagie islands’ (LIFE 99 NAT/IT/006271).