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Evolutionarily Significant Unit, G8 & G9, host specificity pattern in…

- - - - Inhabit very distinct biotopes
      - Sometimes considered one of the best example of “ecological races” among cuckoo species
      - Show distinct ecological preferences
      - suggested to be undergoing rapid ecological divergence
        
        The populations use as hosts more than 10 Myrmica species all across their European distribution
        
        Large number of host switches. Individual populations are typically highly species-specific with respect to ant association
    - - Subspecies or Formenkreis of a single species with indistinguishable adult morphologies and genitalic characters.
    - - Separation of species based on ecological criteria (host ant species, habitat, initial larval food plant) and behavioural criteria (caterpillar’s growth rate & adult phenology)
        
        ASPECT
        
        Ecological
        
        Habitat
        
        M. alcon
        ➜ Wet meadows
        
        M. rebeli
        ➜ Adults inhabit dry grasslands
        
        Initial larval food plant
        
        M. alcon
        ➜ Molinia caerulea (L.) Moench
        ➜Females primarily oviposit on Gentiana pneumonanthe L.
        
        M. rebeli
        ➜ Gentiana cruciata L.
        
        Behavioural
        
        Variations in caterpillar’s growth rate & adult phenology
        
        M. alcon
        ➜ Gain most of their weight in the late spring of the following year.
        ➜ Accelerate their development after diapause to obtain the optimal timing of adult emergence of G. pneumonanthe.
        
        M. rebeli
        ➜ Acquire G. cruciata about half of their final body mass before
        overwintering.
    - - Italian population of M. rebeli and M. alcon indicate distinct phenological differences between them based on:
        
        Note: Phenology is the scientific study of periodic biological phenomena, in relation to climatic conditions
        
        On the wing (from mid-June till mid-July and end of July to end of August)
        
        Choices made by adult butterflies during oviposition
        
        Host ant species
    - - Are they from separate clade?
        
        Some unpublished data from larval epicuticular hydrocarbons support their differentiation, however other molecular studies based on sequence data of nuclear and mtDNA or on allozymes unable to separate them.
        
        From recent molecular research in Poland and Lithunia, the issue on their conservation status is reopened again.
        
        The analysis of nuclear EF1-a gene was insufficient for taxonomic classification.
        
        Combining EF1-a gene and the microsatellite information manifest three ESUs.
        
        corresponding to population of M. alcon and two geographically separated of M. rebeli.
        
        Each species deserve specific conservation measures.
      - Are they severely threatened?
        
        Yes, habitat patches of these species are becoming more isolated due to:
        
        Abandonment of previous agricultural practices.
        
        Light grazing in controlling soil erosion.
        
        Deforestation.
        
        Climate change.
        
        M. alcon is more threatened at southern limits of its range, especially in Italy.
        
        Environmental fragmentation.
        
        Sinking water table.
        
        M. rebeli needs more conservation actions in northern Europe compared to M. alcon.
      - What is the status in the Appendixes and Annexes to the Bern Convention and to the EU Habitats Directive?
        
        Due to unresolved taxonomic status:
        
        Not listed as threatened species with extinction in Europe.
        
        Failed to find evidence for clade-level separation between M. alcon and M. rebeli.
- - - - M. arion, M. teleius, M. nausithous, M. alcon, M. rebeli
      - obligate social parasites
      - model system for studies in the field of evolutionary ecology
    - - "cuckoo feeders"
        
        larvae being fed by worker ants by trophallaxis)
        
        M. alcon & M. rebeli
      - "predatory species"
        
        prey on ant brood
        
        M. arion & M. teleius
      - M. nausithous (not fully clarified)
        
        coexistence of "cuckoo" and "predatory" strategies
        
        predominance of "cuckoo" behaviour
    - - Gained wide public attention due to
        
        endangered status
        
        extraordinary life history
      - Listed in Annexes II & IV of European Habitats Directive
- - - - Extinction in UK:
        
        Shows that comprehensive ecological, demographic & genetic understanding of (threatened) species is necessary for an effective conservation strategy (Thomas et al.,2009).
    - - Maculinea arion ligurica (Wagner, 1904)
        
        Taxon was described in northwest Italy
        
        Flight occurs from end-June to mid-August
        
        Usually in xerothermic areas
        
        Lay eggs on Origanum flowerhead (Patricelli et al., 2011).
      - Maculinea arion arion (Linnaeus, 1758)
        
        Fly from mid-May to mid-June
        
        Favours short-grass dry fields
        
        Initial food plant is mostly Thymus spp.
        
        Despite having different habitat preferences, the two ecotypes can locally co-occur while being phenologically isolated.
        
        Differentiation in phenology and habitat preference constitutes conservation value despite not considered as separate ESUs
    - - Poland population - Occupy xerothermic grasslands on the southerly exposed slopes and exploit Thymus spp
        
        There is almost no mtDNA polymorphism found.
        
        Posglacial re-colonisation area
      - Italy population - Three morpho-ecotypes are present and colonised high-altitude pastures and exploit Thymus spp.
        
        There is genetic differentiation in both COI and EF-1 alpha nuclear gene.
        
        High degree of polymorphism & divergence
        
        Able to survive glaciations
        
        Relevance in the context of biodiversity conservation
- - - - Butterflies possess well-known ecological preferences and react much more strongly and more rapidly to the behaviour of the drivers of change than other well-studied taxa.
      - Some butterflies have been found extinct even though have enough resources to survive.
- - - - • Definitions by some other authors (Waples 1991; Dizon et al. 1992; Vogler & Desalle 1994; Bowen 1998) tend to overlap with subspecies concepts.
      - • Some recent works, considering the ever-increasing availability of genetic data, have suggested, or sometimes even tended to force, the adoption of criteria exclusively based on molecular phylogenies, while largely ignoring all other otherwise measurable adaptive components (Avise 1994; Moritz 1994a,b).
      - • Traditionally, judgements on how distinctive a population should be, before it becomes eligible for being recognised as an ESU, were based on ecological as well as on variously measurable genetic information, thereby trying to take into account its effective evolutionary distinctness (see definitions by Ryder 1986 but also Crandall et al. 2000 in Table I).
      - • Here we have a theoretical issue, because although mainstream notions of speciation mechanisms include evolution of separate adaptations in allopatric or peripatric conditions (see Mayr 1963; Provine 2004 for reviews), the ESU concept, which implies demonstrable adaptation, does not necessarily overlap, or cannot necessarily be applied, to every separate segment in a phylogenetic tree, whose divergence may be a consequence of other genetic mechanisms, unless otherwise demonstrated.
      - • All ESU definitions possess both strengths and bits of weakness, authors have argued that differing approaches may work more efficiently than others, depending on cases and circumstances. This implies that designating ESUs should be done flexibly, on a case-by-case basis (Fraser & Bernatchez 2001).
      - • Strictly speaking, populations or taxa apparently characterized only by genetic divergence should better be considered Conservation Significant Units (CSUs) (see Yuan et al. 2011) rather than ESUs.
      - • Some authors have suggested that obtaining a fixed and universal definition of ESU, valid across all species, may not be feasible (e.g. Fraser & Bernatchez 2001).
      - ESU: conservation unit below the species level, theoretically applicable to various taxa
        
        ESU Conception: design to provide a theoretical background for prioritizing taxa
        
        Field: conservation management, economic, genetic diversity
        
        ESU might be fully identical with a "species". A "species" could be compose of multiple ESU. ESU lineage include single or multiple population and exchanging a degree of gene flow
        "Species" concept was adapting in ESU
        
        Aim : To define an identical "entity" whose divergence can be measured or assessed by placing differential emphasis on the role of evolutionary forces at different time scales
    - - Ryder (1986) - state basic definitions: Population units presenting significant adaptive variation based on concordance between sets of data derived by different techniques (life history information, morphometric, range and distribution data, and genetic data)
        
        Definitions stressing the importance of molecular data
        
        Dizon et al. (1992) - Populations exhibiting discontinuous genetic divergence patterns, geographic isolation and significant genetic distances
        
        Moritz (1994a,b) - Populations that are reciprocally monophyletic for mtDNA alleles and demonstrate significant divergence of allele frequencies at nuclear loci
        
        Bowen (1998) - Populations which show evidence of long-term isolation
        
        Fraser and Bernatchez (2001) - A lineage demonstrating highly restricted gene flow from other such lineages within the higher organizational level of the species
        
        Definitions stressing the importance of using molecular analysis and ecological data
        
        Vogler and Desalle (1994) - Groups that are diagnosed by characters which cluster individuals or populations to the exclusion of other such clusters
        
        Waples (1991) - A population or group of populations that: is substantially reproductively isolated from other conspecific population units; represents an important component of the evolutionary legacy of the species
        
        Crandall et al. (2000) - Prefer identification of distinct populations characterized by genetic and ecological inexchangeabilities over recent and historical times
        
        De Guia and Saitoh (2007) - Full ESUs can be defined solely when information about both neutral genetic variation and adaptive variation is available; otherwise the taxa are ascribed to partial ESU
    - - Some countries are trying to protect so-called Independent Conservation Unit (ICU) instead of species
      - USA: Endangered Species Act makes references to "species" in Distinct Population Segments (DPS) that is applying pragmatic basis
        
        DPS should be reproductively at least partially isolated by some physical barrier
        
        Some authors/state agencies make reference of DPS respect to ill-defined ESUs
        
        Can encompass all conservation needs such as protect population of harvested species and prevent extinction
- - - - increased specialization restricts each social parasite
        to a smaller, regional part of its host range.
        
        extremely complex, as a consequence of local adaptations
  - - - Evolution between European form of M. alcon (that exploits Myrmica scabrinodis) and
        that of Scandinavia and Netherlands, which is adapted to Myrmica rubra/M. ruginodis had similar differentation.
  - - - Case of Maculinea arion in United Kingdom
        
        Species went extinct (1979)
        
        Due to the host ant was replaced by unsuitable congener species, unable to support the caterpillars of the parasite with modest changes in grazing regimes and vegetation structure (Thomas et al. 2009)