Animal-mediated pollination is essential in plant reproductive biology and is often associated with pollination syndromes, sets of floral traits, such as color, scent, shape, or nectar content. Selection by pollinators is often considered a key factor in floral evolution and plant speciation. Our aim is the identification and characterization of the genetic changes that caused the evolution of divergent pollination syndromes in closely related plant species. We focus on ANTHOCYANIN2 (AN2), a welldefined myb-type transcription factor that is a major determinant of flower color variation between Petunia integrifolia and Petunia axillaris. Analysis of sequence variation in AN2 in wild P. axillaris accessions showed that loss-of-function alleles arose at least five times independently. DNA sequence analysis was complemented by functional assays for pollinator preference using genetic introgressions and transgenics. These results show that AN2 is a major determinant of pollinator attraction. Therefore, changes in a single gene cause a major shift in pollination biology and support the notion that the adaptation of a flowering plant to a new pollinator type may involve a limited number of genes of large effect. Gene identification and analysis of molecular evolution in combination with behavioral and ecological studies can ultimately unravel the evolutionary genetics of pollination syndromes.

No abstract

No abstract

A major innovation in angiosperms is the recruitment of animal pollinators as a means to enhance the efficiency and specificity of pollen transfer. The implementation of this reproductive strategy involved the rapid and presumably coordinated evolution of multiple floral traits. A major question concerns the molecular identity of the genetic polymorphisms that specify the phenotypic differences between distinct pollination syndromes. Here, we report on our work with Petunia, an attractive model system for quantitative plant genetics and genomics. From interspecific crosses, we obtained F2 plants that differed in the length of the floral tube or the size of the limb. We used these plants to study the behaviour of the hawkmoth pollinator, Manduca sexta. Plants with larger limbs were preferentially visited, consistent with the notion that flower size affects visibility under low light conditions. The moths also displayed an innate preference for shorter tubes. However, in those cases that flowers with long tubes were chosen, the animals fed for equal time. Thus, the perception of tube length may help the moths, early on, to avoid those plants that are more difficult to handle.

We all appreciate the beauty of flowers, but we seldom consider their function in the life cycle of the plant. The function of beautiful flowers is to advertise the presence of nectar. Floral nectar is the key component in the mutualism between flowering plants and their pollinators. Plants offer nectar as a reward for the transport of pollen by animal vectors. Studying nectar is challenging because of its complex physiology, complex polygenetic structure, and strong environmental variability. Recent advances set the stage for exciting future research that combines genetics and physiology to study ecological and evolutionary questions. IntroductionFloral nectar is a key innovation of angiosperms that evolved as a reward to visitors that transport pollen in return. It is a sugar-rich fluid dominated by the hexoses glucose and fructose, and the disaccharide sucrose. Nectar allows flowers to 'outsource' the pollination business to animal vectors, which assure a directional, accurate, and efficient transfer of pollen compared to wind pollination. The establishment of animal-mediated pollination not only solves a problem but also creates new ones. First, nectar production is costly in terms of seed production and photoassimilate allocation [1,2]. Second, the sugar solution does not only attract pollinators. Nectar robbers and microbes may consume the reward without transferring pollen. Third, pollen may be deposited at the wrong recipient, that is, a different plant species. While this latter problem can be reduced with the evolution of more exclusive relationships with few or even only one pollinator species, plants using this strategy limit their potential distribution to the distribution of their pollinators, which may increase extinction risk (Figure 1).Most floral traits are likely to be genetically complex, and few of the genes involved have been isolated so far. The identification of such genes will allow a genetic analysis of floral traits involved in plant-pollinator interactions. Downregulation of relevant genes can give information about the effect of single gene mutations on pollinator behavior [3,4,5 ,6 ]. Marker-assisted breeding (near isogenic lines) and transgenic plants can provide useful material for field assays [7 ,8 ].We will briefly present the recent key advances in nectar research related to the following topics: first, the physiology of nectar sugar production; second, nectar composition, in particular the functions of primary and secondary compounds; and third, the genetics of nectar production. We will conclude with suggestions for important future research questions on nectar.

No abstract

No abstract

Although it has been hypothesised that cis-regulatory mutations contribute significantly to natural evolution, clear demonstration of a causative mutation has proven to be challenging.Here we demonstrate how cis-regulatory mutations can contribute to pelvic reduction in three-spined sticklebacks. Pelvic reduction is a major skeletal alteration that has evolved repeatedly in different animals, and is genetically tractable in sticklebacks. Previous genetic and expression studies have linked pelvic reduction to unknown regulatory changes near the major developmental control gene Pitx1. Here we have characterised its molecular basis using both laboratory crosses and natural stickleback populations. We conducted association mapping in a natural population segregating pelvic reduction using microsatellite markers flanking Pitx1. We identified a conserved non-coding region consistently associated with pelvic reduction. Functional transgenic assays demonstrated tissue-specific enhancer function: it drives reporter gene expression specifically in the developing pelvis of stickleback larvae. Introduction of a transgene containing the pelvic-complete enhancer driving a Pitx1 coding region restores pelvic formation in pelvic-reduced sticklebacks. Identification of this key region allows detailed comparison of the molecular basis of pelvic reduction in different populations. Genotyping and sequencing studies revealed distinct deletions occurring on different pelvic-reduced haplotypes. Together, these haplotypes defined a 481bp interval and show patterns consistent with fixation following selective sweeps in the same region. The current work identifies how parallel mutations in cis-regulatory sequences can contribute to evolution through inactivation of a tissue specific enhancer of the Pitx1 gene, giving rise to a major adaptive alteration in the vertebrate skeleton. The faces of vertebrates are often readily recognizable as they display a number of species-specific characteristics. It is likely that this stunning diversity of cranial morphology in vertebrates was generated by alterations in craniofacial development. We are employing a combination of genetic, genomic, molecular, bioinformatic, 2D and 3D imaging and modeling approaches to understand evolution of craniofacial structures, such as highly adaptive beak morphologies in such species as Darwin's Finches (a classic example of species multiplication and diversification caused by natural selection) and their relatives, the African Seedcrackers Pyrenestes ostrinus (textbook example of adaptive polymorphism), and other avian and reptilian species. The major goal of these studies is to use both novel approaches on well-studied evolutionary systems to address some of the long-standing questions in animal development and evolution. Animal-mediated pollination is essential in the reproductive biology of many flowering plants and tends to be associated with pollination syndromes, sets of floral traits that are adapted to particular groups of pollinators. The complexity and fun...