Multiple introductions,admixture and bridgehead invasion characterize the introduction history of Ambrosia artemisiifolia in Europe and Australia

Admixture between differentiated populations is considered to be a powerful mechanism stimulating the invasive success of some introduced species. It is generally facilitated through multiple introductions; however, the importance of admixture prior to introduction has rarely been considered. We assess the likelihood that the invasive Ambrosia artemisiifolia populations of Europe and Australia developed through multiple introductions or were sourced from a historical admixture zone within native North America. To do this, we combine large genomic and sampling data sets analysed with approximate Bayesian computation and random forest scenario evaluation to compare single and multiple invasion scenarios with pre‐ and postintroduction admixture simultaneously. We show the historical admixture zone within native North America originated before global invasion of this weed and could act as a potential source of introduced populations. We provide evidence supporting the hypothesis that the invasive populations established through multiple introductions from the native range into Europe and subsequent bridgehead invasion into Australia. We discuss the evolutionary mechanisms that could promote invasiveness and evolutionary potential of alien species from bridgehead invasions and admixed source populations.     

GENETIC DATA HINT AT A COMMON DONOR REGION FOR INVASIVE ATLANTIC AND PACIFIC POPULATIONS OF GRACILARIA VERMICULOPHYLLA (GRACILARIALES,RHODOPHYTA)1

Gracilaria vermiculophylla (Ohmi) Papenf., an agar‐producing red alga introduced from northeast Asia to Europe and North America, is often highly abundant in invaded areas. To assay its genetic diversity and identify the putative source of invasive populations, we analyzed the mitochondrial cytochrome c oxidase subunit I (cox1) gene from 312 individuals of G. vermiculophylla collected in 37 native and 32 introduced locations. A total of 19 haplotypes were detected: 17 in northeast Asia and three in Europe and eastern and western North America, with only one shared among all regions. The shared haplotype was present in all introduced populations and in ～99% of individuals in the introduced areas. This haplotype was also found at three native locations in east Korea, west Japan, and eastern Russia. Both haplotype and nucleotide diversities were extremely low in Europe and North America compared to northeast Asia. Our study indicates that the East Sea/Sea of Japan is a likely donor region of the invasive populations of G. vermiculophylla in the east and west Atlantic and the east Pacific.     

Genetic examination of the type specimen of Ulva australis suggests that it was introduced to Australia

‘Ana‐aosa’, one of the most common marine green algae in Japan, was described as Ulva pertusa Kjellman in 1897 from Hakodate in northern Japan. Ulva pertusa was considered to be a temperate species, with its native distributional range restricted to northeastern Asia. Although this species has been reported from various regions outside northeastern Asia, these records have been explained as non‐indigenous populations. Recently, on the basis of genetic data and nomenclatural priority, U. pertusa was synonymized with U. australis Areschoug, a species described in 1851 from specimens collected in South Australia. Based on genetic studies, Australian populations identified as U. pertusa had been considered to have originated from Japan. However, the published genetic data on U. australis in Australia have been based only on recent collections and no historical specimens have been examined. We tested the hypothesis that native (true) U. australis is an independent species of very similar morphology to U. pertusa, but that its natural domination of shoreline habitats has been suppressed by introduced populations of U. pertusa from Asia. In the present study, we extracted DNA from the type specimen of U. australis housed in the Swedish Museum of Natural History (S) and obtained DNA sequences of the chloroplast rbcL gene and the nuclear rDNA ITS2 region. Our results show that U. australis and U. pertusa are genetically virtually identical, confirming that U. pertusa is a synonym of U. australis. This suggests that the introduction of U. australis to Australia occurred by the middle of the 19th century, when the type was collected and before there was a direct shipping route between Japan and Australia. We speculate that the introduction of U. australis to Australia occurred as a secondary introduction from non‐indigenous populations in northeastern Asia, but not directly from Japan.     

Introgression of exotic Cervus (nippon and canadensis) into red deer (Cervus elaphus) populations in Scotland and the English Lake District

Since the mid‐19th century, multiple introductions of Japanese sika deer (Cervus nippon nippon) and North American wapiti (C. canadensis) have taken place in the British Isles. While wapiti have generally been unsuccessful, sika have been very successful, especially in Scotland where they now overlap at least 40% of the range of native red deer (C. elaphus). Hybridization between these two species and red deer has been demonstrated in captivity and in the wild. Using a panel of 22 microsatellite loci that are highly diagnostic between red deer and sika, and moderately diagnostic between red deer and wapiti, we investigated the extent of introgression between these species in 2,943 deer sampled from around Scotland and from the English Lake District using the Bayesian clustering software STRUCTURE. We also used a diagnostic mitochondrial marker for red deer and sika. Our survey extends previous studies indicating little introgression of wapiti nuclear alleles into red deer, in particular in Northern Scotland, Kintyre, and the Lake District. We found a new area of extensive sika introgression in South Kintyre. In the North Highlands, we show for the first time geographically scattered evidence of past hybridization followed by extensive backcrossing, including one red‐like individual with sika introgression, two sika‐like individuals with red deer introgression, and six individuals that were apparently pure sika at the nuclear markers assessed but which carried red deer mitochondria. However, there has not been a collapse of assortative mating in this region. Similarly, in the English Lake District red deer, we found only traces of past sika introgression. No sika alleles were detected in the Central Highlands or the Hebridean red deer refugia. We make suggestions for management to prevent further spread of sika alleles into red deer and vice versa.     

Evidence from mtDNA RFLP analysis for the introduction of Fundulus heteroclitus to southwestern Spain

Restriction analysis of mitochondrial DNA confirmed the taxonomic status of a southwestern Iberian Peninsula population of Fundulus heteroclitus and its probable origin in North America.     

山东省引种乌桕的生态适应性分析

山东省引种乌桕的生态适应性分析王华田杨锦（山东农业大学,泰安２７１０１８）（山东日照港务局,２７６８２６）ＡｎａｌｙｓｉｓｏｆＥｃｏｌｏｇｉｃａｌＡｄａｐｔａｔｉｏｎｏｆＳａｐｉｕｍｓａｂｉｆｅｒｕｍＩｎｔｒｏｄｕｃｅｄｔｏＳｈａｎｄｏｎｇＰｒｏｖｉ...     

小麦抗锈变异体的RAPD分子验证

将长穗偃麦草DNA导入普通小麦甘麦8号,在其后代出现广泛变异,并从中选育出两个优良的抗条锈病的姊妹变异体。本实验以原供体和受体作为对照,对两个变异体进行了RAPD分子验证,其主要结果为：两个变异体的大多数引物扩增产物带型类同于受体,而与供体带型差异显著;在81个引物中有2个引物检测出了DNA的多态生,主要表现为变异体90001-17中1条带活性不仅超过受体,而且也远超过90001-1的相应带活性,同时两个变异体都出现了1条供体和受体都没有的新带,分子量约为1044bp;另一引物扩增后,变异体90001-17和90001-1分别出现了2条和1条特异性带,分子量约为1073bp和1020bp,此外在两个变异体阳极端带明显被激活,而受体中1条分子量约为968bp的带在变异体中活性降低或消失等。从而表明抗锈变异体9001-17和90001-1的形成是供体的DNA片段进入受体基因组的结果。     

沙地植物柄扁桃的生物学特性及引种栽培的研究

通过研究发现柄扁桃具有典型旱生植物的形态结构特征。同时,在生理特征上也与旱生环境相适应。因此,在沙区引种栽培柄扁桃是可行的。柄扁桃的繁殖主要采用播种法,利用沙藏催芽法处理种子,树苗当年可出圃造林。沙地造林采用植前造林法,将株高４０—１００ｃｍ的健壮苗在春季栽植于平缓的沙地、沙丘迎风坡下部或丘间地等风蚀轻、水分条件好的沙地。     

From richer to poorer: successful invasion by freshwater fishes depends on species richness of donor and recipient basins

Evidence for the theory of biotic resistance is equivocal, with experiments often finding a negative relationship between invasion success and native species richness, and large‐scale comparative studies finding a positive relationship. Biotic resistance derives from local species interactions, yet global and regional studies often analyze data at coarse spatial grains. In addition, differences in competitive environments across regions may confound tests of biotic resistance based solely on native species richness of the invaded community. Using global and regional data sets for fishes in river and stream reaches, we ask two questions: (1) does a negative relationship exist between native and non‐native species richness and (2) do non‐native species originate from higher diversity systems. A negative relationship between native and non‐native species richness in local assemblages was found at the global scale, while regional patterns revealed the opposite trend. At both spatial scales, however, nearly all non‐native species originated from river basins with higher native species richness than the basin of the invaded community. Together, these findings imply that coevolved ecological interactions in species‐rich systems inhibit establishment of generalist non‐native species from less diverse communities. Consideration of both the ecological and evolutionary aspects of community assembly is critical to understanding invasion patterns. Distinct evolutionary histories in different regions strongly influence invasion of intact communities that are relatively unimpacted by human actions, and may explain the conflicting relationship between native and non‐native species richness found at different spatial scales.