As a result of natural hybridization and human selection over millennia, the skin colors of grapes have become greatly diversified. The color is determined by the quantity and composition of anthocyanins. Color-skinned cultivars accumulate anthocyanins in their skins, whereas white-skinned cultivars do not. Myb-related transcription-factor genes such as VvmybA1 regulate anthocyanin biosynthesis. VvMYBA2r, VlmybA1-1, VlmybA1-2, and VlmybA2, which are homologs of VvmybA1, also regulate anthocyanin biosynthesis. In this study, we isolated a novel Myb-related sequence, VlmybA1-3, from cultivars of Vitis labruscana (Vitis vinifera x Vitis labrusca) by means of inverse PCR, and confirmed by means of transient gene expression assay that the gene regulates anthocyanin biosynthesis in grape berry skin. Seedlings of V. labruscana with two functional haplotypes at a region of berry color loci accumulated more anthocyanins than seedlings with a single functional haplotype. In addition, we investigated the haplotypes at the region in 35 cultivars (both V. vinifera and V. labruscana), and found certain typical characteristics. These findings will contribute to the selection of seedlings with high anthocyanin quantities in breeding programs for wine and table grapes, and will help elucidate the origin and evolution of Vitis species.
Charnov's host-size model explains parasitoid host-size-dependent sex ratio as an adaptive consequence when there is a differential effect of host size on the offspring fitness of parasitoid males versus females. This article tests the predictions and the assumptions of the host-size model. The parasitoid wasp Pimpla nipponica Uchida (Hymenoptera: Ichneumonidae) laid more female eggs in larger or fresher host pupae when choice among hosts of different sizes or ages was allowed. Then, whether an asymmetrical effect of host size and age on the fitness of females versus males existed in P. nipponica was examined. Larger or fresher host pupae yielded larger wasps. Larger females lived longer, whereas male size did not influence male longevity. Large males mated successfully with relatively large females but failed with small females, whereas small males could mate successfully either with small or with large females. Thus, small-male advantages were found, and this held true even under male-male competition. Ovariole and egg numbers at any one time did not differ among females of different sizes. Larger females attained higher oviposition success and spent less time and energy for oviposition in hosts. Larger females produced more eggs from a single host meal. Taken together, females gained more, and males lost more, by being large. Host size and age thus asymmetrically affected the fitness of offspring males versus females through the relationships between host size or hast age and wasp size, which means the basic assumption of the hostsize model was satisfied. Therefore, sex ratio control by P. nipponica in response to host size and age is adaptive.
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