A molecular study of the butterfly fauna from the Alps to Sicily showed that the long-assumed single 'Italian refugium' actually contains two distinct functional refugia: an ecological centre of endemicity (ECOc) in the Alps, assembling old paleoendemic lineages that co-occur through shared ecological tolerances, and an evolutionary centre (EVOc) in the Italian Peninsula and Sicily, generated by in-situ Pleistocene divergence of neoendemics. Whether this functional dichotomy is a general property of other West Palearctic refugial hotspots, and how the two endemic assemblages will differentially respond to ongoing climate change, remains unresolved. The problem asks whether the dichotomy recurs in the other West Palearctic hotspots named by the source, and what differential responses to ongoing climate change the two functionally different endemic assemblages show; multilocus or genomic validation of the single-mitochondrial-marker delimitations on which the dichotomy rests, finer key-biodiversity-area delineation within the two large Italian centres, and the incorporation of entity-level lineages into IUCN-type conservation planning are source-suggested future directions and implications of the result rather than parts of the open question itself.

Background

A refugium is a region where lineages persisted through the climatic oscillations of the Quaternary ice ages while more northern areas became uninhabitable. Southern European peninsulas are classic glacial refugia, and the Alps and Apennines have often been treated together as a single 'Italian refugium'. Endemic species (those restricted to a region) can co-occur in an area for two very different reasons: they either evolved in situ and persisted regionally, producing an evolutionary centre of endemicity, or they evolved elsewhere and later dispersed into shared habitats, producing an ecological centre. An influential conceptual precursor distinguished 'evolutionary refugia' from 'ecological refuges' for Australian arid-zone freshwater biodiversity (Davis et al. 2013, doi:10.1111/gcb.12203).

Menchetti et al. (2021, Molecular Ecology 30(5):1297–1310, doi:10.1111/mec.15795) tested this distinction for the butterflies of the Alps–Apennines–Sicily region. They analysed 27,123 occurrence records of 269 species together with 26,557 sequences of the mitochondrial DNA barcode COI (cytochrome c oxidase subunit I, a ~658-base-pair gene segment widely used to identify and delimit animal lineages). Species delimitation used the GMYC model (Generalized Mixed Yule–Coalescent), which fits a threshold between intra-species coalescent branching and inter-species Yule branching on a time-calibrated gene tree; the resulting clusters are treated as evolutionary significant units (ESUs, lineage-level units below or across the species rank). Combining taxonomic species and GMYC ESUs into 369 'operational entities', of which 69 were regionally restricted endemics, they produced a biogeographic regionalisation from turnover in 0.5° × 0.5° grid cells. Two centres emerged: the Alps versus the Italian Peninsula plus Sicily. Alpine endemics are phylogenetically clustered (about 38% belong to one butterfly genus, Erebia), are on average older paleoendemics, and occupy an ecological centre (ECOc); Peninsula–Sicily endemics diverged mostly since the onset of the Pleistocene around 2 million years ago, forming an evolutionary centre (EVOc) of neoendemics. The regionalisation itself depended on entity-level resolution: without intraspecific ESUs the Peninsula–Sicily centre would not have been detected, while 18 endemic entities recognized as good species were 'lumped' by COI, a signature of possible mitochondrial introgression (movement of mitochondrial DNA across species boundaries by hybridization, which can mask true species boundaries).

Comparable COI barcode infrastructure exists for Iberia (Dincă et al. 2015, doi:10.1038/srep12395) and, since, for the whole West Palearctic (Dapporto et al. 2022, doi:10.1111/geb.13579), and a continental-scale COI regionalisation of the West Palearctic has identified seven bioregions including Maghreb, Iberia and Balkans–Anatolia (Dapporto et al. 2024, doi:10.1126/sciadv.adm8596). However, all community-scale work remains single-locus, and no analysis has tested whether the ECOc/EVOc functional dichotomy of endemic assemblages recurs in the other West Palearctic hotspots named by the source (Iberia–Pyrenees–Sierra Nevada, the Balkan Peninsula–Balkans–Carpathians, Turkey and the mountain systems therein, Maghreb–Atlas, and most areas of Iran), nor has any study modelled the differential response of the two Italian endemic assemblages to climate change.

Problem Statement

The source problem asks whether the functional dichotomy of endemicity centres documented for the butterflies of the Alps–Apennines–Sicily region — an ecological centre of endemicity (ECOc) in the Alps, where old paleoendemic lineages co-occur through ecological assembly, and an evolutionary centre of endemicity (EVOc) in the Italian Peninsula and Sicily, generated by in-situ Pleistocene divergence — is a general property of West Palearctic refugial hotspots, and what it implies for the conservation of endemic assemblages under climate change. As formulated in the source's Conclusions, the open question comprises two forward components. (1) Generalisation: whether similar mechanisms have acted on the other West Palearctic diversity hotspots named by the source — Iberia–Pyrenees–Sierra Nevada, the Balkan Peninsula–Balkans–Carpathians, Turkey and the mountain systems therein, Maghreb–Atlas, and most areas of Iran. Whether the ECOc/EVOc dichotomy recurs in those hotspots, with which relative roles of in-situ speciation and ecological assembly, or fails to generalise, is unresolved. (2) Differential climate response: what contrasting responses to ongoing climate change the two functionally different endemic assemblages show. The source states a hedged, simplified-scenario expectation — possible range contractions of Alpine endemics to higher-altitude areas versus poleward expansions of the Peninsula–Sicily endemics — while noting that the outcome can be affected by the quality of the habitat taxa will track, which could be better for mountain species than for lowland ones and thus determine unpredictable trends; a divergent or habitat-modified result therefore also answers this component, and projections resolved at the level of habitat quality are a natural refinement, habitat quality being the source's only stated modelling consideration.

Beyond the open question itself, the source points to three further directions and implications of the result, which are not conditions for answering it: (a) multilocus or genomic validation of the entity delimitations on which the dichotomy rests — all delimitations and divergence-time estimates derive from the single mitochondrial COI marker, so cases of mitochondrial introgression versus true species boundaries, and the timing of the endemic splits, would be resolved by multilocus or genomic data sets, which the source expects will provide higher resolution to phylogenetic assessments of endemic taxa; (b) identification of smaller portions of the two large Italian centres (roughly 210,000 and 270,000 km²) representing key biodiversity areas (sites identified against the KBA Standard for their irreplaceable biodiversity) for potential conservation actions; and (c) inclusion of entity-level ESUs in conservation plans such as the IUCN Red List and protected-area planning, for which no protocols currently exist.

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