Variation at range margins across multiple spatial scales: environmental temperature, population genetics and metabolomic phenotype

Abstract

Range margins are spatially complex, with environmental, genetic and phenotypic variations occurring across a range of spatial scales. We examine variation in temperature, genes and metabolomic profiles within and between populations of the subalpine perennial plant Arabidopsis lyrata ssp. petraea from across its northwest European range. Our surveys cover a gradient of fragmentation from largely continuous populations in Iceland, through more fragmented Scandinavian populations, to increasingly widely scattered populations at the range margin in Scotland, Wales and Ireland. Temperature regimes vary substantially within some populations, but within-population variation represents a larger fraction of genetic and especially metabolomic variances. Both physical distance and temperature differences between sites are found to be associated with genetic profiles, but not metabolomic profiles, and no relationship was found between genetic and metabolomic population structures in any region. Genetic similarity between plants within populations is the highest in the fragmented populations at the range margin, but differentiation across space is the highest there as well, suggesting that regional patterns of genetic diversity may be scale dependent.

Figure 1

PCA ordination of temperature data from our field sites. This figure shows axes 1 and 2, which together represent 74.5% of the total variation. Ovals indicate variation in each region (turquoise, Iceland (circles, Ice_1; filled squares, Ice_2; uptriangles, Ice_3; diamonds, Ice_4; asterisks, Ice_5; pluses, Ice_6; open squares, Ice_7; crosses, Ice_8); light green, Ireland (circles, Ire_1; diamonds, Ire_2); red, Norway (circles, Nor_1; filled squares, Nor_2; triangles, Nor_3; diamonds, Nor_4; asterisks, Nor_5; pluses, Nor_6; open squares, Nor_7; crosses, Nor_8); dark blue, Scotland (circles, Sco_1; uptriangles, Sco_2; downtriangles, Sco_3; diamonds, Sco_4; asterisks, Sco_5; pluses, Sco_6; squares, Sco_7; crosses, Sco_8); orange, Sweden (circles, Swe_1; filled squares, Swe_2; uptriangles, Swe_3; diamonds, Swe_4; asterisks, Swe_5; pluses, Swe_6; open squares, Swe_7; crosses, Swe_8); dark green, Wales (circles, Wal_1; squares, Wal_2)). Details are given in the electronic supplementary materials.

Figure 2

Decline in pairwise genetic similarity (Loiselle kinship coefficient) with distance, in each of the focal regions considered. (a) Ireland and Wales, (b) Scotland, (c) Norway, (d) Sweden and (e) Iceland. (f) The fitted relationships (Mantel tests, genetic similarity×log (distance)) of the regions together for comparison are provided (solid line, Ireland and Wales; long-dashed line, Scotland; medium-dashed line, Norway; small-dashed line, Sweden; dotted line, Iceland).

Figure 3

Score scatter plot from PCA (PC axes 4 and 5) of m/z values (binned to 0.2 Da) obtained by metabolic fingerprinting of A. lyrata spp. petraea populations from Iceland, Sweden, Norway, Ireland, Scotland and Wales. Fingerprints were obtained from direct injection mass spectrometry of the aqueous phase (methanol : water) in negative ionization. All data were Pareto scaled prior to PCA (turquoise, Iceland (circles, Ice_1; squares, Ice_2; uptriangles, Ice_3; diamonds, Ice_4; asterisks, Ice_5; pluses, Ice_6; downtriangles, Ice_7; crosses, Ice_8); light green, Ireland (circles, Ire_2); red, Norway (circles, Nor_1; squares, Nor_2; uptriangles, Nor_3; diamonds, Nor_4; asterisks, Nor_5; pluses, Nor_6; downtriangles, Nor_7; crosses, Nor_8); dark blue, Scotland (circles, Sco_5; squares, Sco_7); orange, Sweden (circles, Swe_1; squares, Swe_2; uptriangles, Swe_3; diamonds, Swe_4; asterisks, Swe_5; pluses, Swe_6; downtriangles, Swe_7; crosses, Swe_8) dark green, Wales (circles, Wal_1)).