Populations inhabiting Mediterranean islands often show contrasting genetic lineages, even on islands that were connected to the mainland during glacial maxima. This pattern is generated by forces acting in historical and contemporary times. Understanding these phenomena requires comparative studies integrating genetic structure, functional traits and dispersal constraints. Using as a model the butterfly species living across the Messina strait (3 km wide) separating Sicily from the Italian Peninsula, we aimed to unravel the mechanisms limiting the dispersal of matrilines and generating genetic differentiation across a narrow sea strait. We analysed the mitochondrial COI gene of 84 butterfly species out of 90 documented in Sicily and compared them with populations from the neighbouring southern Italian Peninsula (1,398 sequences) and from the entire Palaearctic region (8,093 sequences). For each species, we regressed 13 functional traits and 2 ecological constraints to dispersal (winds experienced at the strait and climatic suitability) against genetic differentiation between Sicily and Italian Peninsula to understand the factors limiting dispersal. More than a third of the species showed different haplogroups across the strait and most of them also represented endemic haplogroups for this island. One fifth of Sicilian populations (and 32.3% of endemic lineages) had their closest relatives in distant areas, instead of the neighbouring Italian Peninsula, which suggests high relictuality. Haplotype diversity was significantly explained by the length of the flight period, an intrinsic phenology trait, while genetic differentiation was explained by both intrinsic traits (wingspan and degree of generalism) and contemporary local constraints (winds experienced at the strait and climatic suitability). A relatively narrow sea strait can produce considerable differentiation among butterfly matrilines and this phenomenon showed a largely deterministic fingerprint. Because of unfavourable winds, populations of the less dispersive Sicilian butterflies tended to differentiate into endemic variants or to maintain relict populations. Understanding these phenomena required the integration of DNA sequences, species traits and physical constraints for a large taxon at continental scale. Future studies may reveal if the patterns here shown for mitochondrial DNA are also reflected in the nuclear genome or, alternatively, are the product of limited female dispersal.
Understanding host plant preference and the relative quality of resource provided by cooccurring host plants is a key step to predict butterfly species abundance and responses to environmental changes, and, consequently, to plan management measures. Zerynthia cassandra is an Italian endemic species strongly dependent on the availability of its host plants, Aristolochia rotunda and A. lutea. The insular population occurring on Elba island (Tuscan Archipelago) is highly threatened, because of limited host plant distribution, small population size and apparent lack of gene flow with the mainland. In 2017, we carried out field surveys and rearing experiments to i) identify the characteristics of the host plants (vegetative status) and the site characteristics (aspect, irradiation, distance from other patches) correlated with the number of eggs occurring on individual plants, ii) compare larval growth, food-conversions rate and larval and adult survivorship on the two host plants species. Egg occurrence depends on patch irradiation, the number of leaves and flowers occurring on individual plants and the occurrence of nearby patches. These findings allowed to identify the optimal Aristolochia patch features for egg laying and development.Laboratory rearing success was higher than 50% and although plant species did not show a significant effect on oviposition, we found that larval and adult survival was higher on A. rotunda. Our results suggest habitat management aimed at increasing resource availability for Z. cassandra and possible ex-situ conservation actions aimed at recovering the population in case of potential catastrophic events.
Trans-generational immunization is defined as the transmission of an enhanced resistance to a pathogen from parents to offspring. By using the host-parasite system of the ant and the entomopathogenic fungus, we describe this phenomenon for the first time in ants. We exposed four groups of hibernating queens to different treatments (i) a non-lethal dose of live conidiospores in Triton, (ii) a dose of heat-killed conidiospores in Triton, (iii) a control Triton solution, and (iv) a naive control. We exposed their first workers to a high dose of conidiospores and measured mortality rates Workers produced by queens exposed to live conidiospores survived longer than those belonging to the other groups, while exposure to Triton and dead spores had no effect. Starved workers showed a significantly higher mortality. The treatments did not influence queen mortality, nor the number of offspring they produced at the emergence of the first worker, showing no evidence of immunization costs-at least for these parameters in the first year of colony development. We propose that trans-generational immunization represents an important component of social immunity that could affect colony success, particularly during the critical phase of claustral foundation.
The abandonment of agricultural land and the afforestation of grassland habitats represent major threats for butterflies in European and Mediterranean areas. A crucial goal for Lepidoptera conservation is to maintain and/or restore habitat quality by targeted management. Nevertheless, there are few experimental studies allowing to derive data‐driven strategies to protect butterflies of open grasslands in the Mediterranean region. We developed a habitat management strategy for the conservation of the Italian endemic butterfly Zerynthia cassandra by adopting a three‐step procedure: (i) characterising which environmental and host plant features influence oviposition on plants; (ii) identifying and testing the effect of a data‐driven habitat management intervention; (iii) understanding which micro‐habitat features promote Z. cassandra oviposition in restored places to optimise the intervention. Both patch (areas of 1 m radius hosting Aristolochia shoots) and plant features affect oviposition, with the strongest positive effects showed by high irradiation of the patch and plant quality (high number of flowers and leaves). Accordingly, the management consisted in vegetation cuts to increase irradiation, and 2 years of monitoring demonstrated that this procedure significantly increased oviposition (average increase of about 2 eggs per plant) and larval presence. Micro‐habitat sampling demonstrated that the maximum oviposition differed between vegetation structures, highlighting the importance of a local fine‐tuning before the intervention. We provided a data‐driven, effective, and sustainable management strategy to increase habitat suitability and oviposition for an endemic and endangered Mediterranean butterfly. Our framework can drive management strategies for other species with similar ecological requirements and subjected to similar threats.
The significant risk of disease transmission has selected for effective immune-defense strategies in insect societies. Division of labour, with individuals specialized in immunity-related tasks, strongly contributes to prevent the spread of diseases. A trade-off, however, may exist between phenotypic specialization to increase task efficiency and maintenance of plasticity to cope with variable colony demands. We investigated the extent of phenotypic specialization associated with a specific task by using allogrooming in the honeybee, Apis mellifera, where worker behaviour might lower ectoparasites load. We adopted an integrated approach to characterize the behavioural and physiological phenotype of allogroomers, by analyzing their behavior (both at individual and social network level), their immunocompetence (bacterial clearance tests) and their chemosensory specialization (proteomics of olfactory organs). We found that allogroomers have higher immune capacity compared to control bees, while they do not differ in chemosensory proteomic profiles. Behaviourally, they do not show differences in the tasks performed (other than allogrooming), while they clearly differ in connectivity within the colonial social network, having a higher centrality than control bees. This demonstrates the presence of an immune-specific physiological and social behavioural specialization in individuals involved in a social immunity related task, thus linking individual to social immunity, and it shows how phenotypes may be specialized in the task performed while maintaining an overall plasticity.
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