Heavy metal tolerance in plants

Heavy metal tolerance in plants - Hypothesis = predation...

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Heavy metal tolerance in plants. Selection inferred: mine populations have evolved resistance to high concentrations of copper, zinc and lead. Test : for selection of genetic basis: transplant plants across boundary and the "pasture" form cannot grow on the heavy metal soil: implies true genetic response. Pattern of distribution: cline in frequency of resistant forms as one moves across boundary. Suggests gene flow between tolerant and non-tolerant forms, but despite gene flow divergence is maintained: must be strong selection to overcome effects of gene flow. Examine patterns carefully: both the presence of a cline (frequency transition) and the "steepness " of the cline can say thing about process. Shell polymorphism in Cepaea nemoralis : find different colors (pink, yellow, brown) and different banding pattern (five banded, two-banded, unbanded, etc.). Genetics worked out pretty well: one locus for color, another for banding number and other modifier loci. Pattern: find different morphs in different habitats. Is it selection or not?
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Unformatted text preview: Hypothesis? = predation. Test=? look at so called "thrush-anvils" stones where the song thrush who preys on the snails breaks them open to eat. Look at the frequency of types of shells around thrush anvils and compare these frequencies to the frequencies in the general population. Apparent that there is differential predation by habitat: pink and unbanded snails more common in woods; yellow and banded snails more common in fields and hedgerows. Implies that visual predation is important character. Allele frequency clines : Alcohol dehydrogenase locus (Adh) and α-glycero-phosphate dehydrogenase locus ( α-GPDH) have cline along the east coast of N. America. Hypothesis=? selection differs with latitude. Test=? compare southern hemisphere: get same cline in opposite direction implies selection but difficult to identify a specific mechanism...
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