Identifying zones of phenetic compression in West Mediterranean butterflies (Satyrinae): refugia, invasion and hybridization

Abstract

Aim Distinct insular populations are generally considered important units for conservation. In island–mainland situations, unidirectional introgressive gene flow from the most abundant, typically continental, populations into the smaller island populations can erase native insular genetic units. As an indication of threat, the concept of phenetic slope is developed, a measure proportional to differentiation and to geographical proximity. Location The Western Mediterranean, including the following islands: Sardinia, Sicily, Corsica, Balearics, circum‐Italian, circum‐Sicilian and circum‐Sardo‐Corsican archipelagos. Eastern Europe is included for comparison. Methods Geometric morphometrics was applied to 2392 male genitalia of seven butterfly species groups. Geographic Information System techniques were used to depict the pattern in the distribution of morphotypes. The slope of variation in genital shape was computed to highlight geographical areas showing abrupt morphological changes. Correlation analyses were performed between the mean slope values across sea straits separating islands and nearest sources and ecological traits of the species that underlie their colonization and migration capacity. Results Phenetic slope analysis has revealed that the strait of Messina and the northern Tyrrhenian Sea support particularly contrasting populations. In these areas, mean slopes for species also correlated with certain ecological traits of the species. Sardinia emerges as the most stable refugium for ancestral mediterranean populations. Main conclusions There is strong support for the hypothesis that Italy has experienced invasion by populations from Eastern Europe with postglacial expansion of these populations across Italy. However, propagules are impeded from invading islands by the expanse of sea straits. Even so, sea straits are not invariably barriers. Our results suggest that wind direction in combination with habitat occupancy may have maintained ancestral insular populations in key locations distinguished by phenetic compression. We conclude that native insular populations acting as barriers to introgression in the areas showing particularly steep phenetic slopes deserve attention in conservation programmes.

Integrating three comprehensive data sets shows that mitochondrial DNA variation is linked to species traits and paleogeographic events in European butterflies

“…The fourth cluster recognised Sardinia and the Balearics as a unit, according to a well‐known and still largely unexplained similarity between these areas that may be explained by a refugium hypothesis (Dincă et al, ; Vodă et al, ; Figure d). The fifth cluster separated the Alps and Pyrenees from the Italian peninsula, with Corsica and circum‐Italian islands resembling more the Pyrenees‐Alps, reflecting a recurrent phylogeographic pattern found in several butterfly species (Dapporto et al, ; Figure e). The sixth cluster produced the expected division between the Alps and Pyrenees with Corsica, Elba and Giglio resembling more the Pyrenees than the spatially closer Alps (Dapporto et al, ; Figure f).…”

“…The first node separated Iberia (except for Catalonia), the Balearics and Sardinia from the other areas (Figure b). A solution with three clusters divided Sicily from the Pyrenees, Alps and Italian peninsula, according to a well‐known efficient barrier to dispersal represented by the narrow Messina strait (Dapporto, Bruschini, Dincă, Vila, & Dennis, ; Vodă, Dapporto, Dincă, & Vila, ; Figure c). The fourth cluster recognised Sardinia and the Balearics as a unit, according to a well‐known and still largely unexplained similarity between these areas that may be explained by a refugium hypothesis (Dincă et al, ; Vodă et al, ; Figure d).…”

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

“…Such pattern was followed by expansion and marginal contacts with Z. polyxena during interglacial periods. The presence of a single haplotype endemic to Elba Island suggests that island colonization may have been hindered by sea level rise at the end of the last Ice Age, while genetic structure of mainland populations changed following complex and recurrent colonization events, as shown for other butterfly species from the same region [57], [58].…”

Phylogeography of the rare velvety tree ant Liometopum microcephalum (Formicidae: Dolichoderinae)

“…Thus, winged females could have crossed that distance carried by strong wind. Similarly, Satyrinae butterflies probably entered the peninsula from south‐eastern Europe (Dapporto et al ., ). Three different haplotypes found within a small geographical area covering eastern Slovenia and Croatia (h19 and h23 from the Western clade, h24 from the Northern clade) suggest that another refugium could have been situated at the south‐eastern margin of the Alps.…”