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Results
Habitat preference
next sectionAlong the synthetic environmental axis (PCA-1) C. australis has a highly significant (R2 = 0.599, F1,33 = 49.20, P < 0.001) positive relation to PCA-1 whereas C. hyale has a highly significant (R2 = 0.599, F1,33 = 49.24, P < 0.001) negative relation (Fig. 1). Of the six environmental variables, vegetation and altitude were positively correlated with PCA-1, aspect and humidity negatively correlated, and date and weather uncorrelated. Humidity is thus probably the most important environmental determinant of both species since there is an obvious relation (e.g., exposed ridges tend to be drier than valley bottoms) between humidity and the other three variables that had high loadings for PCA-1 (vegetation, altitude, and aspect).
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Fig. 1. Regression of C. alfacariensis and C. hyale onto the first Principal component axis (PCA-1). The slope of both lines is highly significant (P < 0.001). |
Population analysis
Four of the loci (ald, mdh1, ck2, and got1) are monomorphically fixed for the same allele in the populations of both species. The remaining set of 12 allozyme loci did not contain loci that were diagnostic between C. alfacariensis and C. hyale (Appendix I). Four loci (got2, mpi, pgi, and pgm) show a very high degree of genetic polymorphism, but got2 is monomorphic in all populations of C. hyale.An intermediate level of genetic polymorphism is found among the loci hk, idh1, and me. Low levels of genetic variability are present in the remaining loci (Appendix 1).
In general, C. alfacariensis tends to have both a higher mean number of alleles and percentage of polymorphic loci (Table 2). Consequently, Colias alfacariensis also has a significantly higher heterozygosity (range: 0.148-0.194) than C. hyale (range: 0.084-0.094) (F1,11 = 72.70, P < 0.001). Heterozygosity is highest for C. alfacariensis populations in the geographically complex Alps and drops off towards the lower-lying regions to the South (Provence and Italy) and the North (Metz and Seine), with the lowest values occurring in Northern Europe. Within C. alfacariensis, the Alpine/Italian on the one hand and the Provence/Northern populations on the other hand consistently differ at the PGI locus (Fig. 2).
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Fig. 2. Map of the localities where the populations of C. alfacariensis were sampled. Five main localities are shown, representing a single population with the exception of the Alps and Provence where three and four populations, respectively, were sampled. Within each circle average heterozygosity of 12 loci and the frequency of the pgi-b allele are given. For the Provence and Alps the values are means of the three populations. H = heterozygosity of a single populations, Hm = mean heterozygosity from more than one population. |
In C. alfacariensis, estimated single locus FIS significantly differs from zero at me (Table 3). In C. hyale the PGM locus significantly differs from zero. FIS values were generally slightly positive in both species indicating a small deficiency of heterozygotes. In both species total genetic diversity (FIT ) was mainly the result of inbreeding (FIS ), among population variation (FST ) being less important. Within populations of both species the most common allele at a locus is usually the same (Appendix 1). Within C. hyale none of the loci have a FST value significantly different from zero indicating that, at least until recently, there was a panmictic population structure with high levels of gene flow. Over the same geographic range, C. alfacariensis has an estimated Ne M of less than 10. The difference here though is solely due to the PGI locus, which effectively divides the species into a Northern-Provence and Alpen-Italian component. Excluding this locus gives a panmictic population structure, since none of the other loci differ significantly from zero, quite similar to its sister species.
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