Genetic Structure Of Invasive Populations Research Articles

Population genetics of invasive and native Nymphaea mexicana Zuccarini: Taking the first steps to initiate a biological control programme in South Africa

Nymphaea mexicana Zuccarini (Nympheaceae) (Mexican waterlily) is a rooted floating-leaved aquatic plant native to southern USA and Mexico that has become a problematic invasive alien plant in South Africa. Biological control is considered a desirable management strategy for the plant in South Africa. A good understanding of the genetic structure of invasive populations has been useful in other biological control programmes because taxonomic uncertainty about the target plant can result in natural enemies that are not adapted to the invasive populations being considered as potential agents. For N. mexicana, hybrids exist in the wild and horticultural trade, but identification is difficult, so understanding the genetic structure of populations is required to ensure that potential agents are collected off plants similar to invasive populations in South Africa. ISSR (inter-simple sequence repeats) analysis was used to determine whether invasive N. mexicana populations from South Africa were genetically similar to native range populations from USA or whether they were hybrids. Results from these analyses were matched with the morphotypes of each population based on petal colour, shape, and size. The genotypes suggested by the ISSR analyses corroborated the presence of both hybrid and pure forms of N. mexicana in South Africa. Populations of N. mexicana in the invaded range that are genetically similar to native range populations are more likely to be suitable for biological control, while other populations are likely to be hybrids formed by crossing of parents from the native range or within the horticultural trade, which may present difficulties for management using biocontrol.

Rapid Genetic Divergence of an Invasive Species, Spartina alterniflora, in China.

Hundreds of plants and half a kilogram of seeds of Spartina alterniflora, which were collected from Morehead City in North Carolina, Sapelo Island in Georgia, and Tampa Bay in Florida, were introduced to China in 1979. However, according to documented records, S. alterniflora from different origins were introduced to different areas when the species was first introduced to the coastal areas of China in the 1980s. In order to understand the relationship between the invasive S. alterniflora populations of China and the native S. alterniflora populations of the United States, and whether the genetic structure and genetic diversity of the invasive populations of China were affected by different introductions in the 1980s, molecular markers were used to determine the levels of gene flow and its effect on population differentiation. A total of 715 samples of S. alterniflora were collected from nine invasive populations in China and nine native populations from the United States. The genetic diversity and genetic structure of invasive and native populations were compared using microsatellite markers. The heterozygosity of Chinese invasive populations of S. alterniflora (HO = 0.538, HE = 0.725) were similar with those of native populations (HO = 0.530, HE = 0.744), which may attribute to its multiple introductions with the multisource populations from different geographic areas of the United States. However, the lower allelic diversities of Chinese invasive populations were detected, which may be due to the founder effect, or the bottleneck, which supports the theory that the allelic diversity is more sensitive to population bottlenecks than heterozygosity. The results of the STRUCTURE analysis among all sampling sites showed that the value of ΔK was largest when K = 2, which indicated that the invasive S. alterniflora populations in China had completed differentiated from the native populations of the United States. This may be because of admixture and hybridization of three non-overlapping original populations, or the postintroduction rapid evolution in China, and reproductive isolation under long-term geographic isolation. There was significant differentiation among invasive populations, which was mainly affected by different human-mediated introductions in 1980s. Significant genetic structure (K = 7) and high genetic differentiation (Fst = 0.30193) were detected in Chinese invasive populations, which may due to the low natural gene flow among populations. The genetic structure of the invasive populations in China was still affected by the human-mediated introductions in the 1980s, and the different initial introductions might promote differentiation among the invasive populations. In fact, the human-mediated long-distance dispersal should take the most of responsibility for the rapid spread of S. alterniflora along the coast of China. Multisource introductions of S. alterniflora are perhaps helpful for local adaptation but itself cannot cause rapid spread along the whole coast of China. Meanwhile, we suggest that the prevention of gene exchange among populations of S. alterniflora is the first and most important step in the control of the species on the coast of China, because admixture and hybridization of isolated populations might generate new heterosis and increase the difficulty of managing S. alterniflora in China.

Microsatellite primer development for the invasive perennial herb Gypsophila paniculata (Caryophyllaceae).

Premise of the Study Gypsophila paniculata (baby's breath; Caryophyllaceae) is a herbaceous perennial that has invaded much of northern and western United States and Canada, outcompeting and crowding out native and endemic species. Microsatellite primers were developed to analyze the genetic structure of invasive populations.Methods and ResultsWe identified 16 polymorphic nuclear microsatellite loci for G. paniculata out of 73 loci that successfully amplified from a primer library created using Illumina sequencing technology. Microsatellite primers were developed to amplify di‐, tri‐, and tetranucleotide repeats and tested in three invasive populations in Michigan.ConclusionsThese markers will be useful in characterizing the genetic structure of invasive populations throughout North America to aid targeted management efforts, and in native Eurasian populations to better understand invasion history. Five of these developed primers also amplified in G. elegans.

Mitochondrial Polymorphism of Native and Invasive Populations of Harmonia axyridis (Coleoptera, Coccinellidae)

Ladybird Harmonia axyridis is a widespread polyphage and forms stable populations in East Asia and spreading invasive populations in Europe and other regions with temperate and subtropical climate. A characteristic of haplotype diversity of native and invasive populations of H. axyridis at the atp6 gene is given. The characteristic differences in the composition and quantitative ratio of mitochondrial haplotypes between the western and eastern groups of populations of the native range are revealed. The genetic structure of invasive populations is uniform across the whole range in Europe, from the Atlantic coast to the Black Sea coast of the Caucasus, which is indicative of the spread of H. axyridis invasive populations in Europe from one center. In Europe, the mitochondrial gene pool of invasive populations is formed by two major haplotypes. This mitochondrial haplotype composition remains unchanged in the process of the invasion expansion. The possible role of mixed origin of invasive populations of H. axyridis in the formation of the invasive ability is discussed.

An evaluation of the genetic structure and post-introduction dispersal of a non-native invasive fish to the North Island of New Zealand

The efficacy of invasive species management is dependent on a thorough understanding of the size, origin, and genetic structure of invasive populations. We evaluated the genetic diversity and structure of the western mosquitofish, Gambusia affinis, across the North Island of New Zealand in an effort to better understand the genetic structure and post-introduction dispersal mechanisms of this highly invasive estuarine species. We found clear evidence of founder effects and significant genetic structure for populations derived from populations initially established in New Zealand in the 1930s. Our findings indicate that G. affinis populations have succeeded through a combination of localized dispersal and human-assisted colonization. Additionally, we identify a series of populations in one region that are apparently genetically isolated from the other regions. This area could thus represent a “significant eradication unit” where re-colonization is unlikely. Our results highlight the utility and value of molecular tools as an efficient method to facilitate a richer understanding of the nature and condition of invasive species while identifying definitive management objectives.

Different Habitats Show Similar Genetic Structure of <i>Bunias orientalis</i> L. (Brassicaceae)in Lithuania

We studied genetic diversity within and among populations of warty cabbage (Bunias orientalis L.), which is an alien species in Lithuania and other Baltic countries. In Lithuania, this weed colonises two main types of habitats: railway/roadsides and meadows on riversides. The aim of this study was to assess the genetic structure of invasive populations of B. orientalis in Lithuania and consider the impact of diverse habitats on the partitioning of genetic diversity using inter-simple sequence repeat (ISSR) markers. An analysis of molecular variance (AMOVA) carried out on the basis of ISSR showed that there is high genetic differentiation (46%) among populations of B. orientalis, which is probably caused by the founder effect and limited gene flow. However, we observed no impact of habitat on the genetic difference among populations. Similar levels of ISSR polymorphic loci were observed in riverside (P = 31.67%) and railway/roadsides (P = 30.51%) populations. UPGMA cluster analysis and principal coordinate analysis (PCoA) also did not show grouping of studied populations according to habitat type. High genetic differentiation among populations, as indicated by ISSR markers, confirm multiple independent introductions of this species in Lithuania.

Genetic and chemical variation of Tanacetum vulgare in plants of native and invasive origin

High genetic diversity of introduced plant populations may pose a key advantage under changed selection pressures but may also have important implications for biological control of such plants. However, molecular markers employed to measure genetic variation do not necessarily reflect variations in phenotypic traits such as plant chemical composition, which may be similarly important for both the invasion success of a plant and the establishment of biological control agents. The Asteraceae species Tanacetum vulgare is of Eurasian origin, but was introduced to North America, where it became invasive in some areas. This species varies greatly in terpene composition, forming different chemotypes. To assess the genetic diversity of T. vulgare in relation to its chemical diversity, we grew populations originating from different sources of the native and introduced ranges under standardized conditions. Using inter simple sequence repeat markers, we found indications for an increased genetic diversity in plants of the introduced compared to the native range. Analyses of volatile profiles of these individuals indicated similarly high chemical diversities in native and introduced populations. Clustering analyses revealed a considerable amount of unique geno- and chemo-types on both continents. No significant relation between the genetic and chemical data could be detected, demonstrating that the genetic structure of invasive populations does not necessarily offer information on its chemical diversity and vice versa. Knowledge of both the genetic structure and the actual variation in plant chemistry allows biological control research to consider factors potentially interfering with the success of biocontrol agents prior to release.

Looking at both sides of the invasion: patterns of colonization in the violet tunicate Botrylloides violaceus

Understanding the ecological and evolutionary forces that shape the genetic structure of invasive populations and facilitate their expansion across a large spectrum of environments is critical for the prediction of spread and management of ongoing invasions. Here, we study the dynamics of postestablishment colonization in the colonial ascidian Botrylloides violaceus, a notorious marine invader. After its initial introduction from the Northwest Pacific, B. violaceus spread rapidly along the Pacific and Atlantic coasts of North America, impacting both aquaculture facilities and natural ecosystems. We compare genetic diversity and patterns of gene flow among 25 populations (N=679) from the West and East coasts, and evaluate the contribution of sexual vs. asexual reproduction to this species' invasion success using data from the mitochondrial cytochrome c oxidase subunit I (COI) gene and 13 nuclear polymorphic microsatellite loci. Our results reveal contrasting patterns of spread in the coastal waters of North America. While the West coast was colonized by noncontiguous (long-distance) dispersal, the East coast invasion appears to have occurred through contiguous (stepping-stone) spread. Molecular data further indicate that although dispersal in colonial ascidians is predominantly achieved through sexually produced propagules, aquaculture practices such as high-pressure washing can facilitate fragmentation and potentially exacerbate infestations and spread via asexual propagules. The results presented here suggest that caution should be used against the general assumption that all invasions, even within a single species, exhibit similar patterns of colonization, as highly contrasting dynamics may transpire in different invaded ranges.

Comparative phylogeography of two colonial ascidians reveals contrasting invasion histories in North America

Surveys of genetic structure of introduced populations of nonindigenous species may reveal the source(s) of introduction, the number of introduction events, and total inoculum size. Here we use the mitochondrial cytochrome c oxidase subunit 1 (COI) gene to explore genetic structure and contrast invasion histories of two ecologically similar and highly invasive colonial ascidians, the golden star tunicate Botryllus schlosseri and the violet tunicate Botrylloides violaceus, in their global and introduced North American ranges. Haplotype and nucleotide diversities for B. schlosseri were significantly higher than for B. violaceus both globally (h = 0.872; π = 0.054 and h = 0.461; π = 0.007, respectively) and in their overlapping North American ranges (h = 0.874; π = 0.012 and h = 0.384; π = 0.006, respectively). Comparative population genetics and phylogenetic analyses revealed clear differences in patterns of invasion for these two species. B. schlosseri populations on the west and east coasts of North America were seeded from the Pacific and Mediterranean regions, respectively, whereas all North American B. violaceus populations were founded by one or more introduction events from Japan. Differences in genetic structure of invasive populations for these species in North America are consistent with their contrasting probable introduction vectors. B. schlosseri invasions most likely resulted from vessel hull fouling, whereas B. violaceus was likely introduced as a ‘fellow traveler’ in the shellfish aquaculture trade.

Patterns of genetic variation in invasive populations of Gunnera tinctoria: an analysis at three spatial scales

While there is evidence that the genetic structure of invasive populations may be distinct from native populations, it has proved difficult to establish the causes of any variation owing in part to the range of evolutionary processes involved. In order to assess differences in the genetic structure of invasive populations of Gunnera tinctoria, five native populations were compared to 23 geographically widely dispersed invasive populations using amplified fragment length polymorphic markers (AFLPs). In total, 221 individuals were sampled at three spatial scales: inter-regional, within-region, and at a high-resolution local scale. It was observed that there were high levels of genetic variation between most populations, that invasive populations were generally distinct from both native populations and from each other and that genetic variation away from founding populations can occur relatively quickly and within a small geographic area. Changes in the pattern of genetic variation observed in invasive populations strongly indicated that founder effects and genetic drift played a significant role in shaping their genetic structure. It was further concluded that gene flow had a homogenizing effect on the structure of invasive populations occurring in close proximity, increasing their allele content and potentially contributing to their successful establishment.

Patterns of invasion and colonization of the sea lamprey (Petromyzon marinus) in North America as revealed by microsatellite genotypes

Invasions by exotic organisms have had devastating affects on aquatic ecosystems, both ecologically and economically. One striking example of a successful invader that has dramatically affected fish community structure in freshwater lakes of North America is the sea lamprey (Petromyzon marinus). We used eight microsatellite loci and multiple analytical techniques to examine competing hypotheses concerning the origins and colonization history of sea lamprey (n = 741). Analyses were based on replicated invasive populations from Lakes Erie, Huron, Michigan, and Superior, populations of unknown origins from Lakes Ontario, Champlain, and Cayuga, and populations of anadromous putative progenitor populations in North America and Europe. Populations in recently colonized lakes were each established by few colonists through a series of genetic bottlenecks which resulted in lower allelic diversity in more recently established populations. The spatial genetic structure of invasive populations differed from that of native populations on the Atlantic coast, reflecting founder events and connectivity of invaded habitats. Anadromous populations were found to be panmictic (theta(P) = 0.002; 95% CI = -0.003-0.006; P > 0.05). In contrast, there was significant genetic differentiation between populations in the lower and upper Great Lakes (theta(P) = 0.007; P < 0.05; 95% CI = 0.003-0.009). Populations in Lakes Ontario, Champlain, and Cayuga are native. Alternative models that describe different routes and timing of colonization of freshwater habitats were examined using coalescent-based analyses, and demonstrated that populations likely originated from natural migrations via the St Lawrence River.

CHARACTERIZATION OF ISOZYME DIVERSITY WITHIN AND AMONG PURPLE LOOSESTRIFE POPULATIONS (LYTHRUM SPP.).

Purple loosestrife populations have developed into a highly aggressive and invasive weed in several Northern states (MN, NY, NJ etc.). How these populations arose is a key question in developing control strategies. Therefore, we initiated a study to elucidate the origin and genetic structure of invasive populations using isozyme analysis. The germplasm examined included invasive populations found in MN, NY, NJ, WI and MD, populations of Lythrum alatum, populations of L. virgatum and 22 cultivars of L. salicaria, the suspected progenitor of the invasive populations. Unique isozyme patterns for most cultivars was observed and these were consistently indicative of that clone over repeated sampling. Clones of putative “salicaria” origin could not be distinguish from those of putative “virgatum” origin.Significant isozyme polymorphism was observed within and among the 26 Lythrum populations. Indicating that isozymes can be an important tool in studies on the structure and evolution of invasive loosestrife populations. To date, our isozyme analysis indicates that L. salicaria and L. virgatum are not distinct species. It appears that the decision by the MN Department of Agriculture to add all horticultural lines to the noxious weeds list regardless of origin was a prudent decision.