DOI: 10.5061/dryad.5qfttdz1x
title: How long is 3 kilometres for a butterfly? Ecological constraints and functional traits explain high mitochondrial genetic diversity between Sicily and the Italian Peninsula

description: 1. 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 relating genetic structure, functional traits and
 dispersal constraints. 2. Using as a model the butterfly species living
 across the Messina strait separating Sicily from the Italian Peninsula (3
 km wide), we aimed to unravel the mechanisms limiting the dispersal of
 matrilines across a narrow sea strait and producing genetic
 differentiation.  3. 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 (1398
 sequences) and from the entire Palearctic region (8093 sequences). For
 each species, we regressed 13 functional traits and two 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. 4. 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 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). 5. 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.
description: All the script to carry out the analysis are available in the
 Appendix S2.R script. The table of sequences belonging
 to the study area is available in the "sequences_Sic_Cal.txt"
 file and fasta sequences in the "sequences_Sic_Cal.fas" fasta
 file The table of reference sequences belonging to the
 Palaearctic area is available in the
 "reference_sequences_r1.txt" file and fasta sequences in the
 "reference_sequences_r1.fas" fasta file
 Species traits are available in
 the "butterfly_data.txt" file