Geographic Population Structure of the Sugarcane Borer,Diatraea saccharalis (F.) (Lepidoptera: Crambidae), in the Southern United States

The sugarcane borer moth, Diatraea saccharalis, is widespread throughout the Western Hemisphere, and is considered an introduced species in the southern United States. Although this moth has a wide distribution and is a pest of many crop plants including sugarcane, corn, sorghum and rice, it is considered one species. The objective was to investigate whether more than one introduction of D. saccharalis had occurred in the southern United States and whether any cryptic species were present. We field collected D. saccharalis in Texas, Louisiana and Florida in the southern United States. Two molecular markers, AFLPs and mitochondrial COI, were used to examine genetic variation among these regional populations and to compare the sequences with those available in GenBank and BOLD. We found geographic population structure in the southern United States which suggests two introductions and the presence of a previously unknown cryptic species. Management of D. saccharalis would likely benefit from further investigation of population genetics throughout the range of this species.     

Origin of the invasive Arundo donax (Poaceae): a trans-Asian expedition in herbaria

Background and Aims

The hypothesis of an ancient introduction, i.e. archaeophyte origin, is one of the most challenging questions in phylogeography. Arundo donax (Poaceae) is currently considered to be one of the worst invasive species globally, but it has also been widely utilzed by man across Eurasia for millennia. Despite a lack of phylogenetic data, recent literature has often speculated on its introduction to the Mediterranean region.

Methods

This study tests the hypothesis of its ancient introduction from Asia to the Mediterranean by using plastid DNA sequencing and morphometric analysis on 127 herbarium specimens collected across sub-tropical Eurasia. In addition, a bioclimatic species distribution model calibrated on 1221 Mediterranean localities was used to identify similar ecological niches in Asia.

Key Results

Despite analysis of several plastid DNA hypervariable sites and the identification of 13 haplotypes, A. donax was represented by a single haplotype from the Mediterranean to the Middle East. This haplotype is shared with invasive samples worldwide, and its nearest phylogenetic relatives are located in the Middle East. Morphometric data characterized this invasive clone by a robust morphotype distinguishable from all other Asian samples. The ecological niche modelling designated the southern Caspian Sea, southern Iran and the Indus Valley as the most suitable regions of origin in Asia for the invasive clone of A. donax.

Conclusions

Using an integrative approach, an ancient dispersion of this robust, polyploid and non-fruiting clone is hypothesized from the Middle East to the west, leading to its invasion throughout the Mediterranean Basin.     

Genetic diversity does not affect the invasiveness of fountain grass (Pennisetum setaceum) in Arizona, California and Hawaii

Pennisetum setaceum (Poaceae) is a perennial bunch grass that invaded the United States during the 20th century and is highly invasive in Hawaii, moderately invasive in Arizona, and not yet invasive in southern California. Pennisetum setaceum is apomictic, a condition that is normally associated with low genetic variation within populations, but even moderate levels of genetic variation among populations could account for differences in invasiveness. To determine whether genetic factors are causing the variable invasion success, we used Inter‐Simple Sequence Repeat markers (ISSRs) to examine genetic variation in populations from the three areas. Screening of 16 primers revealed no genetic variation within any population or between any geographical areas, a pattern consistent with complete apomixis. Variation in invasion success appears unrelated to genetic differences among populations. Differences in the seasonal timing of rainfall among the regions may be the cause of variable invasiveness of fountain grass. Alternatively, differences in timing of introduction or duration of lag phase may have limited invasiveness in Arizona and southern California.     

Evidence for an invasive aphid "superclone": extremely low genetic diversity in Oleander aphid (Aphis nerii) populations in the southern United States

Background

The importance of genetic diversity in successful biological invasions is unclear. In animals, but not necessarily plants, increased genetic diversity is generally associated with successful colonization and establishment of novel habitats. The Oleander aphid, Aphis nerii, though native to the Mediterranean region, is an invasive pest species throughout much of the world. Feeding primarily on Oleander (Nerium oleander) and Milkweed (Asclepias spp.) under natural conditions, these plants are unlikely to support aphid populations year round in the southern US. The objective of this study was to describe the genetic variation within and among US populations of A. nerii, during extinction/recolonization events, to better understand the population ecology of this invasive species.

Methodology/Principal Findings

We used five microsatellite markers to assess genetic diversity over a two year period within and among three aphid populations separated by small (100 km) and large (3,700 km) geographic distances on two host plant species. Here we provide evidence for A. nerii “superclones”. Genotypic variation was absent in all populations (i.e., each population consisted of a single multilocus genotype (MLG) or “clone”) and the genetic composition of only one population completely changed across years. There was no evidence of sexual reproduction or host races on different plant species.

Conclusions/Significance

Aphis nerii is a well established invasive species despite having extremely low genetic diversity. As this aphid appears to be obligatorily asexual, it may share more similarities with clonally reproducing invasive plants, than with other animals. Patterns of temporal and geographic genetic variation, viewed in the context of its population dynamics, have important implications for the management of invasive pests and the evolutionary biology of asexual species.     

Genetic and allelopathic differences between populations of daisy fleabane Erigeron annuus (L.) Pers. (Asteraceae) from disturbed and stable habitats

The interactions between invasive plants and their habitats may vary at different phases of the invasion process and depend on the phenotypic plasticity or local adaptations of each species. In this study, we investigated whether habitat changes during the invasion process are related to variations in the physiological traits (allelopathic properties) and genetic differentiation of daisy fleabane (Erigeron annuus (L.) Pers.). E. annuus is a winter annual invasive species that originated in North America and is now distributed throughout Europe. Genetic and genotypic diversity analyses were performed for 37 populations of E. annuus based on inter simple sequence repeat (ISSR) polymorphisms. In total, 684 plants were analyzed; 342 were from stable habitats and 342 were from disturbed habitats. The genetic differences among the populations from the different habitats were studied using a Bayesian cluster analysis and an analysis of molecular variance (AMOVA) and by calculating the genetic and genotypic diversity parameters. A germination test using the juglone index was employed to examine the potential allelopathic properties of the plants from the different habitats. Bayesian cluster analysis, AMOVA and allelopathic effects evaluation revealed differences in the allelopathic potential and genetic structure of the E. annuus populations from the disturbed and stable habitats. This differentiation of populations could be associated with founder effects or with different selection pressures among habitats.     

Inferring the invasion history of coral berry Ardisia crenata from China to the USA using molecular markers

Genetic comparisons between native and invasive populations of a species can provide insights into its invasion history information, which is useful for guiding management and control strategies. The coral berry Ardisia crenata was introduced to Florida last century as a cultivated ornament plant, and has since spread widely throughout the southern regions of the USA. Previously, the genetic variation among 20 natural populations of A. crenata across its distribution center in southern China was quantified using seven microsatellite markers. Here we expand on that work by additionally sampling individuals from four other native populations in Taiwan and Japan, and from five invasive populations in the USA. We also examined the results from one chloroplast intergenic spacer region (trnF-trnL) in all 29 populations. Our aim is to identify the invasion source and subsequent history of the species?? spread throughout the southern USA. We observed lower genetic diversity in the invasive populations based on both microsatellite and chloroplast markers. Our data show that the invasive populations can be clustered with native populations in southeastern China, inferring this region as the geographic origin of A. crenata cultivars invading the USA. We further classified invasive individuals into invasive I and invasive II clusters. Nantou in Taiwan and Xihu in mainland China are the most closely related populations to those, which identify the former as potential sources for host-specific control agents. Our results, combined with the known introduction records, suggest that A. crenata was first multiply introduced into Florida and then secondarily colonized Louisiana and Texas from Florida.     

Rooting Out Genetic Structure of Invasive Wild Pigs in Texas

Invasive wild pigs (Sus scrofa), also called feral swine or wild hogs, are recognized as among the most destructive invasive species in the world. Throughout the United States, invasive wild pigs have expanded rapidly over the past 40 years with populations now established in 38 states. Of the estimated 6.9 million wild pigs distributed throughout the United States, Texas supports approximately 40% of the population and similarly bears disproportionate ecological and economic costs. Genetic analyses are an effective tool for understanding invasion pathways and tracking dispersal of invasive species such as wild pigs and have been used recently in California and Florida, USA, which have similarly long-established populations and high densities of wild pigs. Our goals were to use molecular approaches to elucidate invasion and migration processes shaping wild pig populations throughout Texas, compare our results with patterns of genetic structure observed in California and Florida, and provide insights for effective management of this invasive species. We used a high-density single nucleotide polymorphism (SNP) array to evaluate population genetic structure. Genetic clusters of wild pigs throughout Texas demonstrate 2 distinct patterns: weakly resolved, spatially dispersed clusters and well-resolved, spatially localized clusters. The disparity in patterns of genetic structure suggests disparate processes are differentially shaping wild pig populations in various localities throughout the state. Our results differed from the patterns of genetic structure observed in California and Florida, which were characterized by localized genetic clusters. These differences suggest distinct biological and perhaps anthropogenic processes are shaping genetic structure in Texas. Further, these disparities demonstrate the need for location-specific management strategies for controlling wild pig populations and mitigating associated ecological and economic costs. © 2021 The Wildlife Society. This article has been contributed to by US Government employees and their work is in the public domain in the USA.     

Skewed adult sex ratios observed early in the North American invasion of Lycorma delicatula (Hemiptera: Fulgoridae)

The spotted lanternfly, Lycorma delicatula, (Hemiptera Fulgoridae) is an invasive pest in Korea and the United States, but originating from mainland Asia. Both tree of heaven, Ailanthus altissima, and grapevine (Vitis) are known to be preferred hosts of adults. However, much is unknown about its adult behavior with respect to mating or dispersal patterns. In 2015, just after it was discovered in the United States, we performed an observational study to elucidate movement by adults in relation to host plants. We noted weekly changes in their presence and sex ratio on host plants at four sites in a quarantine zone in Berks County, PA. Just after adult emergence, the trunks of large (>15 cm diameter at breast height) A. altissima hosted nearly exclusively females, while smaller A. altissima, Vitis, Salix nigra, and other less commonly inhabited tree species, had high proportions of males. By October 1st, greater proportions of males were observed on the trunks of the larger A. altissima trees. Pairings of males and females were observed most frequently on the smaller A. altissima and Vitis. At the very end of the season, a large mixed-sex population was found on Salix nigra, which was the only deciduous tree species in the area still bearing green leaves.     

Haplotype diversity of mt<Emphasis Type="Italic">COI</Emphasis> in the fall webworm <Emphasis Type="Italic">Hyphantria cunea</Emphasis> (Lepidoptera: Arctiidae) in introduced regions in China,Iran, Japan,Korea, and its homeland,the United States

Hyphantria cunea (Drury) has colonized many countries outside its native range of North America and has become a model species for studies of the colonization and subsequent adaptation of agricultural pests. Molecular genetic analyses can clarify the origin and subsequent adaptations to non-native habitats. Using the mitochondrial COI gene, we examined the genetic relationships between invasive populations (China, Iran, Japan, and Korea) and native populations (i.e., the United States). The Jilin (China) and Guilan (Iran) populations showed nine previously unknown haplotypes that differed from those found in the south–central United States, suggesting multiple colonization events and different regions of invasion. A dominant mtDNA haplotype in populations in the United States was shared by all of the populations investigated, suggesting that H. cunea with that haplotype have successfully colonized China, Iran, Japan, and Korea.     

Analysis of genetic relations and evaluation of medicinal value among Hedera plants in China by sequence related amplified polymorphism markers and high performance liquid chromatography detection

Hedera plants are ornamental vines which are regarded as traditional medicinal plants. These plants are widely cultivated worldwide; moreover, new species and varieties have been discovered. For the first time, molecular markers based on sequence-related amplified polymorphism (SRAP) were used in this study to classify species and to analyse the genetic relationship of 21 Hedera plant varieties which are commonly cultivated in China. We also employed high-performance liquid chromatography (HPLC) to evaluate the medicinal value of these plants by measuring their hederacoside C contents. Results of SRAP–PCR and cluster analyses show that the SRAP molecular markers can successfully be applied in Hedera plants and are available. In addition, HPLC detection results indicate that the Chinese wild species in group I contain less than 30 mg/g hederacoside C and do not comply with the European Pharmacopoeia standards. By contrast, groups II and III exhibit high medicinal value and accord with these standards.     

Host specificity of different populations of the leaf beetle Diorhabda elongata (Coleoptera: Chrysomelidae), a biological control agent of saltcedar (Tamarix spp.)

The leaf beetle, Diorhabda elongata (Brullé) sensu lato, was released in 2001 for the classical biological control of exotic saltcedars, a complex of invasive Tamarix species and hybrids. It did not establish at sites south of 37°N latitude where summer daylengths are below the critical photoperiod of the northern-adapted populations of the beetle that were released. Therefore, we assessed the host specificity of four D. elongata populations collected from more southern latitudes in the Old World (Tunisia, Crete, Uzbekistan, and Turpan, China). All populations were similar to each other and the previously released populations of D. elongata in their host specificity. Larval/pupal survival for all populations was 34–100% on Tamarix test plants, 0–76% on native Frankenia plants (both in the order Tamaricales), and 0% on the remaining 28 species of plants on which all the larvae died as 1st instars. D. elongata laid high numbers of eggs on saltcedar, generally fewer eggs on athel (a moderately valued evergreen species of Tamarix) except for Uzbekistan beetles, and few to no eggs on three species of Frankenia. Few to no adults were found on Frankenia plants which also were poor maintenance hosts. The release of any of the four D. elongata populations in the southern US and northern Mexico should pose no risk to plants outside the order Tamaricales and a low risk to native, non-target Frankenia plants. Athel may be less damaged than saltcedar.     

Genetic diversity in native and introduced populations of the amethyst gem clam Gemma gemma (Totten, 1834) from the U.S. east and west coasts

Reduced genetic diversity due to founder effects often is expected for invasive populations. The present study examined two nuclear gene regions and one mitochondrial gene to evaluate the origins and genetic diversity of Gemma gemma, a ‘stow-away’ that was introduced to California more than 100 years ago with the importation of the Eastern oyster, Crassostrea virginica, from the United States’ Atlantic coast. A previous investigation involving mitochondrial DNA cytochrome-c-oxidase subunit I sequences reported no significant difference in haplotype diversity between the native and introduced populations; however, estimates of allelic (or haplotypic) variability are insensitive to losses of rare alleles that may accompany founder events and population bottlenecks. Estimates of allele richness and the distribution of rare alleles provide more sensitive indicators of such events. The present investigation of introduced and potential source populations identified lower allele richness and number of singleton alleles in California samples. Atlantic coast Gemma exhibit a sharp phylogeographic transition between northeastern (New York through New England) and mid-Atlantic (southern New Jersey through Virginia) subpopulations, which appear latitudinally inverted for the California Gemma populations. These genetic results, and information from the transportation history of the Eastern oyster, help to clarify processes involved in the introduction of this invasive species.     

Sunshine versus gold: The effect of population age on genetic structure of an invasive mosquito

The genetic diversity and structure of invasive species are affected by the time since invasion, but it is not well understood how. We compare likely the oldest populations of Aedes aegypti in continental North America with some of the newest to illuminate the range of genetic diversity and structure that can be found within the invasive range of this important disease vector. Aedes aegypti populations in Florida have probably persisted since the 1600‐1700s, while populations in southern California derive from new invasions that occurred in the last 10 years. For this comparison, we genotyped 1,193 individuals from 28 sites at 12 highly variable microsatellites and a subset of these individuals at 23,961 single nucleotide polymorphisms (SNPs). This is the largest sample analyzed for genetic structure for either region, and it doubles the number of southern California populations previously analyzed. As predicted, the older populations (Florida) showed fewer indicators of recent founder effect and bottlenecks; in particular, these populations have dramatically higher genetic diversity and lower genetic structure. Geographic distance and driving distance were not good predictors of genetic distance in either region, especially southern California. Additionally, southern California had higher levels of genetic differentiation than any comparably sized documented region throughout the worldwide distribution of the species. Although population age and demographic history are likely driving these differences, differences in climate and transportation practices could also play a role.     

Global genetic analysis reveals the putative native source of the invasive termite,Reticulitermes flavipes,in France

Biological invasions are recognized as a major threat to both natural and managed ecosystems. Phylogeographic and population genetic analyses can provide information about the geographical origins and patterns of introduction and explain the causes and mechanisms by which introduced species have become successful invaders. Reticulitermes flavipes is a North American subterranean termite that has been introduced into several areas, including France where introduced populations have become invasive. To identify likely source populations in the USA and to compare the genetic diversity of both native and introduced populations, an extensive molecular genetic study was undertaken using the COII region of mtDNA and 15 microsatellite loci. Our results showed that native northern US populations appeared well differentiated from those of the southern part of the US range. Phylogenetic analysis of both mitochondrial and nuclear markers showed that French populations probably originated from southeastern US populations, and more specifically from Louisiana. All of the mtDNA haplotypes shared between the United States and France were found in Louisiana. Compared to native populations in Louisiana, French populations show lower genetic diversity at both mtDNA and microsatellite markers. These findings are discussed along with the invasion routes of R. flavipes as well as the possible mechanisms by which French populations have evolved after their introduction.     

Cryptic speciation, habitat differentiation, and geography in Hamatocaulis vernicosus (Calliergonaceae, Bryophyta)

A molecular study of the wetland pleurocarpous moss Hamatocaulis vernicosus (Mitt.) Hedenäs, based on the ITS region, the trnL-trnF region, and rpl16 revealed two cryptic species. One of these is widespread in Europe, and was also sampled from several localities in Minnesota (United States). The other cryptic species occurs only south of the boreal zone in Europe, and was in addition sampled from single localities in Peru and northernmost Asiatic Russian Federation. Although it seems likely that the southern species colonized parts of Europe from southern refugia after the last glaciation, its wide distribution outside Europe indicates that the speciation event is unrelated to the European glacial history. No correlations could be found between variation in habitat preferences (pH and electric conductivity) and molecular variation.     

Invasion by the marine gastropod Ocinebrellus inornatus in France: I. Scenario for the source of introduction

The rate of introduction of exotic marine species has dramatically increased during the 19th and 20th centuries. Exemplifying this trend, the marine gastropod Ocinebrellus inornatus was first detected outside its native range in 1924 on the American Pacific coast, then in 1995 on the French Atlantic coast. To determine the origin of the French populations of this invasive species, we compared a French population with populations collected in Asia—the native range—and with a population collected in the United States. Analyses of mitochondrial DNA and allozyme polymorphism revealed that the French and American populations were closely related and substantially differentiated from the Asian populations. According to our results, the most likely scenario is that the source population of the French Atlantic coast populations was located in the United States. Indeed, taken altogether, the genetic structure of Asian populations, the time lag separating the introduction on the American Pacific coast from the introduction on the French Atlantic coast and the high level of genetic diversity in the two introduced areas (indicating an absence of major founder events) are hardly compatible with a scenario in which French population resulting only from primary introduction events from the native area. Finally, although similar, the French and American populations were not identical. Thus, even if the main source population of the French populations was located in the United States, the genetic structure of French populations may have been modified by cryptic and recurrent introduction events directly from Asia.     

The Hoosier cavefish,a new and endangered species (Amblyopsidae,Amblyopsis) from the caves of southern Indiana

We describe a new species of amblyopsid cavefish (Percopsiformes: Amblyopsidae) in the genus Amblyopsis from subterranean habitats of southern Indiana, USA. The Hoosier Cavefish, Amblyopsis hoosieri sp. n., is distinguished from A. spelaea, its only congener, based on genetic, geographic, and morphological evidence. Several morphological features distinguish the new species, including a much plumper, Bibendum-like wrinkled body with rounded fins, and the absence of a premature stop codon in the gene rhodopsin. This is the first new cavefish species described from the United States in 40 years and exemplifies how molecular data can alert us to the presence of otherwise cryptic biodiversity.     

Analysis of chromosome number and speculations on the origin of Arundo donax L. (Giant Reed)

Arundo donax (commonly called Giant Reed) is a perennial rhizomatous grass native to Asia, nowadays diffused all over the world. Due to its high biomass production and great adaptability to marginal land, interest in this species is increasing. In fact A. donax could represent an important and promising energy crop for heat and bioethanol second generation production. The propagation of A. donax is strictly agamic by rhizome fragmentation and cane node germination, strongly limiting the possibility of genetic improvement by breeding. The sterility could be caused by the fact that A. donax is a hybrid with uneven ploidy or a triploid species. It is difficult to propose an explanation for its sterility, because the chromosome number of A. donax is still a matter of debate, due to the high number and small size of the chromosomes; in the bibliography different counts ranging from 40 to 110 are reported. With the aim of establishing the chromosome number of A. donax we selected and counted 17 metaphase plates prepared from root tips obtained by hydroponic cultivation of cane nodes; our counts showed that A. donax most probably has 110 chromosomes. Our results suggested us two possible hypotheses, also based on SSR molecular marker results, concerning the evolutionary processes involved in the origins of A. Donax.     

Multiple introductions boosted genetic diversity in the invasive range of black cherry (Prunus serotina; Rosaceae)

Background and Aims

Black cherry (Prunus serotina) is a North American tree that is rapidly invading European forests. This species was introduced first as an ornamental plant then it was massively planted by foresters in many countries but its origins and the process of invasion remain poorly documented. Based on a genetic survey of both native and invasive ranges, the invasion history of black cherry was investigated by identifying putative source populations and then assessing the importance of multiple introductions on the maintenance of gene diversity.

Methods

Genetic variability and structure of 23 populations from the invasive range and 22 populations from the native range were analysed using eight nuclear microsatellite loci and five chloroplast DNA regions.

Key Results

Chloroplast DNA diversity suggests there were multiple introductions from a single geographic region (the north-eastern United States). A low reduction of genetic diversity was observed in the invasive range for both nuclear and plastid genomes. High propagule pressure including both the size and number of introductions shaped the genetic structure in Europe and boosted genetic diversity. Populations from Denmark, The Netherlands, Belgium and Germany showed high genetic diversity and low differentiation among populations, supporting the hypothesis that numerous introduction events, including multiple individuals and exchanges between sites, have taken place during two centuries of plantation.

Conclusions

This study postulates that the invasive black cherry has originated from east of the Appalachian Mountains (mainly the Allegheny plateau) and its invasiveness in north-western Europe is mainly due to multiple introductions containing high numbers of individuals.     

New microsatellite markers for the ectomycorrhizal fungus Pisolithus tinctorius sensu stricto reveal the genetic structure of US and Puerto Rican populations

The ectomycorrhizal fungus Pisolithus tinctorius has been introduced to many areas around the world as a source of inoculum for pine plantations. However, little is known about the genetic structure of fungal populations in their introduced habitats. To study the genetics of exotic P. tinctorius populations, we developed and employed seven new microsatellite markers and compared samples from Puerto Rico (exotic range) and the eastern United States (native range). Bayesian cluster analysis, neighbor joining analysis and F_ST values all strongly separated Puerto Rican populations from North American populations. Consistent with a founder effect, populations from Puerto Rico had reduced allelic richness when compared to samples from the United States. The genetic structure of P. tinctorius populations in Puerto Rico is weak to modest and is not correlated with geographic distance reflecting anthropogenic movement of inoculum with forestry practices.