ABSTRACT
We analyzed the global genetic variation pattern of Capsella bursa-pastoris (Brassicaceae) as expressed in allozymic (within-locus) diversity and isozymic (between-locus) diversity. Results are based on a global sampling of more than 20,000 C. bursa-pastoris individuals randomly taken from 1,469 natural provenances in the native and introduced range, covering a broad spectrum of the species' geographic distribution. We evaluated data for population genetic parameters and F-statistics, and Mantel tests and AMOVA were performed. Geographical distribution patterns of alleles and multilocus genotypes are shown in maps and tables. Genetic diversity of introduced populations is only moderately reduced in comparison with native populations. Global population structure was analyzed with structure, and the obtained cluster affiliation was tested independently with classification approaches and macroclimatic data using species distribution modeling. Analyses revealed two main clusters: one distributed predominantly in warm arid to semiarid climate regions and the other predominantly in more temperate humid to semihumid climate regions. We observed admixture between the two lineages predominantly in regions with intermediate humidity in both the native and non-native ranges. The genetically derived clusters are strongly supported in macroclimatic data space. The worldwide distribution patterns of genetic variation in the range of C. bursa-pastoris can be explained by intensive intra- and intercontinental migration, but environmental filtering due to climate preadaption seems also involved. Multiple independent introductions of genotypes from different source regions are obvious. "Endemic" genotypes might be the outcome of admixture or of de novo mutation. We conclude that today's successfully established Capsella genotypes were preadapted and found matching niche conditions in the colonized range parts.
ABSTRACT
For almost 100 years now, ecotypic differentiation of plant species has been a major topic of research. In changing environments, the question needs to be answered as to how long it takes to adapt, and which parameters are subject to this fast adaptation. Short-living colonizing plant species are excellent examples, especially when they are selfing. Shepherd's Purse Capsella bursa-pastoris (Brassicaceae) is one of the most wide-spread flowering species on earth and avoids only the hot and humid tropics. Many studies demonstrated the ecotypic differentiation of C. bursa-pastoris in various regions of the world but ecotypic differentiation regarding adaptability of anatomy and physiology of rosette leaves so far remained less recognized. However, the leaves are relevant for subsequent seed set; in particular, winter-annual accessions require a robust rosette to survive adverse conditions. Leaf-related traits such as the thickness of the mesophyll and epidermis, stomatal density, photosynthetic capacity and the ability to withstand and even use high light conditions were therefore analysed in provenances from various climatic zones. Photosynthetic capacity depends on leaf anatomy and cellular physiological parameters. In particular, the ability to dynamically adjust the photosynthetic capacity to changing environmental conditions results in higher fitness. Here, we attempt to relate these results to the four Mendelian leaf types according to Shull.
ABSTRACT
During the last years DNA barcoding has become a popular method of choice for molecular specimen identification. Here we present a comprehensive DNA barcode library of various crustacean taxa found in the North Sea, one of the most extensively studied marine regions of the world. Our data set includes 1,332 barcodes covering 205 species, including taxa of the Amphipoda, Copepoda, Decapoda, Isopoda, Thecostraca, and others. This dataset represents the most extensive DNA barcode library of the Crustacea in terms of species number to date. By using the Barcode of Life Data Systems (BOLD), unique BINs were identified for 198 (96.6%) of the analyzed species. Six species were characterized by two BINs (2.9%), and three BINs were found for the amphipod species Gammarus salinus Spooner, 1947 (0.4%). Intraspecific distances with values higher than 2.2% were revealed for 13 species (6.3%). Exceptionally high distances of up to 14.87% between two distinct but monophyletic clusters were found for the parasitic copepod Caligus elongatus Nordmann, 1832, supporting the results of previous studies that indicated the existence of an overlooked sea louse species. In contrast to these high distances, haplotype-sharing was observed for two decapod spider crab species, Macropodia parva Van Noort & Adema, 1985 and Macropodia rostrata (Linnaeus, 1761), underlining the need for a taxonomic revision of both species. Summarizing the results, our study confirms the application of DNA barcodes as highly effective identification system for the analyzed marine crustaceans of the North Sea and represents an important milestone for modern biodiversity assessment studies using barcode sequences.
