Habitat Fragmentation Accelerates Butterfly Evolution — And Extinction

Glanville fritillary butterfly (Melitaea cinxia), adult male, underside. (Credit: Tari Haahtela/University of Helsinki)
Figure 1A: Map of the Baltic region. The Åland Islands in Finland, Uppland in Sweden, and SW Finland (extinct populations) represent highly fragmented landscapes, whereas Öland in Sweden and Saaremaa in Estonia have much more continuous grassland habitat. (Bottom Right) A more detailed map of the Åland Islands, indicating the region in Åland (Saltvik) from which the contemporary samples are available and the island of Sottunga, where a metapopulation was introduced in 1991. Museum samples are in blue and contemporary samples are in red. (doi:10.1073/pnas.1600951113)
Museum butterfly collections. (Credit: Toby Fountain/University of Helsinki/doi:10.1073/pnas.1600951113)

Extinct populations became increasingly distinct from extant populations over time

Figure 2: DAPC ordination based on 222 SNPs with samples aggregated in space and time: Åland1905 (1889–1921), Åland1945 (1936–1949), and Åland1965 (1957– 1974) for museum samples from the Åland Islands and SW Finland1900 (1880– 1920), SW Finland1950 (1945–1954), and SW Finland1960 (1962–1968) for museum samples from the now extinct populations in SW Finland, and contemporary samples from the mainland Åland and the 24-y-old introduced metapopulation in Sottunga (see Figure 1 for locations). FST values calculated for the different groups show that the SW Finnish samples become increasingly differentiated from the Åland samples over time. (doi:10.1073/pnas.1600951113)

Different populations show similar allelic shifts to habitat fragmentation

Figure 3: Allele frequency differences of outlier loci (n = 12; excluding two loci on the sex chromosome and Mc1:4593:27912, which is known to be associated with host plant preference) between samples from now extinct populations in SW Finland (black) and the recently introduced metapopulation in Sottunga (white), compared with old, well-connected local populations in Saltvik. (doi:10.1073/pnas.1600951113)

Alleles associated with flight showed strong selective pressure, even in extinct populations

Figure 4: Allele frequency changes in the outlier loci (n = 12) in (A) the introduced Sottunga metapopulation and (B) the extinct SW Finnish populations from the contemporary Saltvik reference (old local populations), plotted against the allele frequency difference between newly established versus old local populations in the contemporary metapopulation. Allele frequencies have shifted in the same direction in Sottunga and SW Finland as newly colonized populations differ from old local populations (Sottunga, R2 = 0.14, P = 0.13; SW Finland, R2 = 0.36, P = 0.02). (doi:10.1073/pnas.1600951113)

Museums can shed light on extinct populations

Glanville fritillary butterfly (Melitaea cinxia), adult male. (Credit: Tari Haahtela/University of Helsinki)

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𝐆𝐫𝐫𝐥𝐒𝐜𝐢𝐞𝐧𝐭𝐢𝐬𝐭

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Evolutionary ecologist & ornithologist, science journalist. Freelance, job hunting. Writes about science for Forbes. Formerly: The Guardian. Always: Ravenclaw.

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