To investigate the genetic mechanisms that underlie morphological evolution in natural populations, we employed QTL mapping to dissect the inheritance of leaf sheath characters that distinguish Chalco from Balsas teosinte. Abundant macrohairs (trichomes) and intense anthocyanin accumulation are found in Chalco teosinte sheaths whereas Balsas teosinte leaf sheaths are green and glabrous. These character states may represent adaptations to the cooler highland (Chalco) vs. warmer middle-elevation (Balsas) climates. QTL mapping in multiple populations revealed a mix of major-and minor-effect QTL affecting both sheath color (anthocyanin) and macrohair abundance. The major QTL for macrohairs accounts for 52% of the parental difference. Epistatic interactions were detected between the major-effect QTL and multiple other QTL for both traits, accounting for substantial portions of phenotypic variance. Developmental analyses suggest that regulatory program changes underlie the phenotypic differences. Sheath anthocyanin QTL are clearly associated with b1 and a3, both of which are regulators of anthocyanin biosynthesis. Our findings suggest that changes in a small number of QTL can lead to morphological evolution by modulating existing developmental programs.

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Summary• The effects of Ni and Mg, two factors involved in the infertility of serpentine soils, were studied in the alpine plant Cerastium alpinum . Root growth of plants from adjacent serpentine and non-serpentine populations in Scandinavia, representing an eastern and western postglacial immigration lineage and the hybrid zone between them, were compared to study the adaptation of C. alpinum populations.• Seedlings were placed in solutions with low or high concentrations of Ni and Mg in a full factorial experiment according to a randomized block design. The growth of roots was analyzed and discussed in relation to the soil content.• The serpentine populations showed higher tolerance to Ni and Mg stress than nonserpentine populations. The degree of metal tolerance differed among the serpentine populations and was related to the effective concentrations of Ni and Mg in the soil at each site.• The results suggest that serpentine tolerance is locally evolved in C. alpinum and that tolerance has arisen in parallel during the postglacial colonization of Scandinavia on serpentine soils with similar composition.

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Westerbergh, A. 2004. An interaction between a specialized seed predator moth and its dioecious host plant shifting from parasitism to mutualism. Á/ Oikos 105: 564 Á/574. Seed predator/pollinator and host plant interactions, which may be considered as antagonistic, have the potential to provide good model systems for the study of the early stages of evolution towards mutualism. I describe a relationship between a seed predator, the geometrid moth Perizoma affinitatum , and the dioecious plant Silene dioica . The moth is an obligate seed predator on its host plant. The searching and ovipositing behaviour of the female moths, number of eggs deposited per flower, the pollinating ability of the moths and the seed consumption by the larvae are described as different parameters and studied in two Finnish coastal populations. A high pollinating ability and limited seed consumption by the predator was found and discussed in relation to fitness models of P. affinitatum and S. dioica . In a mutualistic relationship there must be a balance between the costs and benefits so that the seed production by the moths is larger than the seed consumption by the larvae, given a net seed output larger than zero. The data of the parameters included in a seed production/ consumption model give a positive seed output when the proportion of S. dioica flowers pollinated by other non-predating insects is less than 60%. Accordingly, even if P. affinitatum would become the exclusive pollinator it would not endanger the survival of the host plant and both partners would benefit from this interaction. Limited seed consumption, high pollinating ability and host specificity as seen in the P. affinitatum and S. dioica interaction are considered to have been important pre-existing qualities in the evolution of the obligate mutualisms between yucca and yucca moths and fig and fig wasps. In isolated serpentine populations where the gene flow is restricted and copollinators are rare the interaction between P. affinitatum and S. dioica has the potential to shift from parasitism to mutualism.