Population genetic history of the dreissenid mussel invasions: expansion patterns across North America

This study tests population genetic patterns across the Eurasian dreissenid mussel invasions of North America—encompassing the zebra mussel Dreissena polymorpha (1986 detection) and the quagga mussel D. rostriformis bugensis (detected in 1990, which now has largely displaced the former in the Great Lakes). We evaluate their source-spread relationships and invasion genetics using 9–11 nuclear microsatellite loci for 583 zebra mussels (21 sites) and 269 quagga mussels (12 sites) from Eurasian and North American range locations, with the latter including the Great Lakes, Mississippi River basin, Atlantic coastal waterways, Colorado River system, and California reservoirs. Additionally, mtDNA cytochrome b gene sequences are used to verify species identity. Our results indicate that North American zebra mussels originate from multiple non-native northern European populations, whereas North American quagga mussels trace to native estuaries in the Southern Bug and Dnieper Rivers. Invasive populations of both species show considerable genetic diversity and structure (zebra F _ST = 0.006–0.263, quagga F _ST = 0.008–0.267), without founder effects. Most newer zebra mussel populations have appreciable genetic diversity, whereas quagga mussel populations from the Colorado River and California show some founder effects. The population genetic composition of both species changed over time at given sites; with some adding alleles from adjacent populations, some losing them, and all retaining closest similarity to their original composition. Zebra mussels from Kansas and California appear genetically similar and assign to a possible origin from the St. Lawrence River, whereas quagga mussels from Nevada and California assign to a possible origin from Lake Ontario. These assignments suggest that overland colonization pathways via recreational boats do not necessarily reflect the most proximate connections. In conclusion, our microsatellite results comprise a valuable baseline for resolving present and future dreissenid mussel invasion pathways.     

Zebra mussels (Dreissena polymorpha) in Ireland, AFLP-fingerprinting and boat traffic both indicate an origin from Britain

1. The zebra mussel (Dreissena polymorpha) is an aquatic nuisance species that invaded Ireland around 1994. We studied the invasion of the zebra mussel combining field surveys and genetic studies, to determine the origin of invasion and the vector of introduction. 2. Field surveys showed that live zebra mussels, attached to the hulls of pleasure boats, were transported from Britain to Ireland. These boats were lifted from British waters onto trailers, transported to Ireland by ferry and lifted into Irish waters within a day. Length‐frequency distributions of dead and living mussels on one vessel imported 3 months earlier revealed a traumatic occurrence caused by the overland, air‐exposed transportation. Results show that a large number of individuals survived after re‐immersion in Irish waters and continued to grow. 3. Zebra mussels from populations in Ireland, Great Britain, the Netherlands, France and North America, were analysed using amplified fragment length polymorphisms (AFLP)‐fingerprinting to determine the origin of the Irish invasion. Phylogenetic analysis revealed that Irish and British mussels clustered closely together, suggesting an introduction from Britain. 4. Ireland remained un‐invaded by the zebra mussel for more than 150 year. The introduction of the zebra mussel to Ireland occurred following the abolition of value added tax in January 1993 on imported second‐hand boats from the European Union (UK and continental Europe). This, together with a favourable monetary exchange rate at that time, may have increased the risk of invasion of the zebra mussel.     

Zebra Mussel Infestation of Unionid Bivalves (Unionidae) in North America

SYNOPSIS. In 1989, zebra mussels received national attentionin North America when they reached densities exceeding 750,000/m2in a water withdrawal facility along the shore of western LakeErie of the Laurentian Great Lakes. Although water withdrawalproblems caused by zebra mussels have been of immediate concern,ecological impacts attributed to mussels are likely to be themore important long-term issue for surface waters in North America.To date, the epizoic colonization (i.e., infestation) of unionidbivalve mollusks by zebra mussels has caused the most directand severe ecological impact. Infestation of and resulting impactscaused by zebra mussels on unionids in the Great Lakes beganin 1988. By 1990, mortality of unionids was occurring at somelocations; by 1991, extant populations of unionids in westernLake Erie were nearly extirpated; by 1992, unionid populationsin the southern half of Lake St. Clair were extirpated; by 1993,unionids in widely separated geographic areas of the Great Lakesand the Mississippi River showed high mortality due to musselinfestation. All infested unionid species in the Great Lakes(23) have become infested and exhibited mortality within twoto four years after heavy infestation began. Data indicate thatmean zebra mussel densities >5,000–6,000/m² and infestationintensities >100-200/unionid in the presence of heavy zebramussel recruitment results in near total mortality of unionids.At present, all unionid species in rivers, streams, and akesthat sympatrically occur with zebra mussels have been infestedand, in many locations, negatively impacted by zebra mussels.We do not know the potential consequences of infestation onthe 297 unionid species found in North America, but believezebra mussels pose an immediate threat to the abundance anddiversity of unionids.     

Genetic variability in Irish populations of the invasive zebra mussel, Dreissena polymorpha: discordant estimates of population differentiation from allozymes and microsatellites

1. The recent arrival and explosive spread of the zebra mussel, Dreissena polymorpha (Pallas), in Ireland provided a rare opportunity to study the population genetics of an invasive species.
2. Eight polymorphic allozyme loci ( ACO-1, ACO-2 , EST-D, GPI, IDH-2, MDH, OPDH and PGM ) were used to investigate genetic diversity and population structure in five Irish populations, and the results were compared with those from a previous microsatellite study on the same samples.
3. The mean number of alleles per locus (2.7 ± 0.1) was similar to the mean for the same loci in European populations, suggesting that Irish founder populations were large and/or multiple colonization events took place after foundation. A deficiency of heterozygotes was observed in all populations, but was uneven across loci.
4. Pairwise comparisons, using Fisher's exact tests and F _ST values, revealed significant genetic differentiation among populations. The overall multilocus F _ST estimate was 0.118 ± 0.045, which contrasted with an estimate of 0.015 ± 0.007 from five microsatellite loci on the same samples in a previous study.
5. Assuming that microsatellites can be used as a neutral baseline, the discordant results from allozymes and microsatellites suggest that selection may be acting on some allozyme loci, specifically ACO-1, ACO-2 , IDH-2 and MDH, which contributed most to the significant differentiation between samples.     

Molecular ecology of zebra mussel invasions

The invasion of the zebra mussel, Dreissena polymorpha, into North American waters has resulted in profound ecological disturbances and large monetary losses. This study examined the invasion history and patterns of genetic diversity among endemic and invading populations of zebra mussels using DNA sequences from the mitochondrial cytochrome oxidase I (COI) gene. Patterns of haplotype frequency indicate that all invasive populations of zebra mussels from North America and Europe originated from the Ponto-Caspian Sea region. The distribution of haplotypes was consistent with invasive populations arising from the Black Sea drainage, but could not exclude the possibility of an origin from the Caspian Sea drainage. Similar haplotype frequencies among North American populations of D. polymorpha suggest colonization by a single founding population. There was no evidence of invasive populations arising from tectonic lakes in Turkey, while lakes in Greece and Macedonia contained only Dreissena stankovici. Populations in Turkey might be members of a sibling species complex of D. polymorpha. Ponto-Caspian derived populations of D. polymorpha (theta = 0.0011) and Dreissena bugensis (one haplotype) exhibited low levels of genetic diversity at the COI gene, perhaps as a result of repeated population bottlenecks. In contrast, geographically isolated tectonic lake populations exhibited relatively high levels of genetic diversity (theta = 0.0032 to 0.0134). It is possible that the fluctuating environment of the Ponto-Caspian basin facilitated the colonizing habit of invasive populations of D. polymorpha and D. bugensis. Our findings were concordant with the general trend of destructive freshwater invaders in the Great Lakes arising from the Ponto-Caspian Sea basin.     

Conservation of the Lake Kasumigaura population of Nymphoides indica (L.) Kuntze based on genetic evaluation using microsatellite markers

We compared the genetic diversity of the Lake Kasumigaura population of Nymphoides indica with that of pond populations in Hyogo and Kagawa Prefectures, which are thought to maintain high genetic diversity, to elucidate the current genetic diversity and occurrence of distinctive alleles in the Lake Kasumigaura population. The genetic diversity, as measured by the mean number of alleles per polymorphic locus, effective number of alleles per locus, mean observed heterozygosity, mean expected heterozygosities, total gene diversity, and number of multilocus genotypes was lower in the Lake Kasumigaura population than in the Hyogo and Kagawa populations. In addition, the inbreeding coefficient suggests that random mating does not occur in the Lake Kasumigaura population. The degree of genetic differentiation between the Lake Kasumigaura population and the Hyogo and Kagawa populations suggests that the Lake Kasumigaura population is largely genetically distinct. We found five genotypes in the Lake Kasumigaura population that were absent from the Hyogo and Kagawa populations. These results demonstrate that the Lake Kasumigaura population is an important component of the overall genetic diversity of N. indica in Japan.     

Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22-mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer-based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.     

Exploration of Nuclear DNA Markers for Population Structure Assessment in the Desmid Micrasterias rotata (Zygnematophyceae,Streptophyta)

Freshwater green microalgae are diverse and widely distributed across the globe, yet the population structuring of these organisms is poorly understood. We assessed the degree of genetic diversity and differentiation of the desmid species, Micrasterias rotata. First, we compared the sequences of four nuclear regions (actin, gapC1, gapC2, and oee1) in 25 strains and selected the gapC1 and actin regions as the most appropriate markers for population structure assessment in this species. Population genetic structure was subsequently analyzed, based on seven populations from the Czech Republic and Ireland. Hudson's Snn statistics indicated that nearest‐neighbor sequences occurred significantly more frequently within geographical populations than within the wider panmictic population. Moreover, Irish populations consistently showed higher genetic diversity than the Czech samples. These results are in accordance with the unbalanced distribution of alleles in many land plant species; however, the large genetic diversity in M. rotata differs from levels of genetic diversity found in most land plants.     

Population genetic structure of the round goby in Lake Michigan: implications for dispersal of invasive species

Understanding subsequent dispersal of non-native species following introduction is important for predicting the extent and speed of range expansion and is critical for effective management and risk assessment. Post-introduction dispersal may occur naturally or via human transport, but assessing the relative contribution of each is difficult for many organisms. Here, we use data from seven microsatellite markers to study patterns of dispersal and gene flow among 12 pierhead populations of the round goby (Neogobius melanostomus) in Lake Michigan. We find significant population structure among sampling sites within this single Great Lake: (1) numerous populations exhibited significant pairwise F _ST and (2) a Bayesian assignment analysis revealed three distinct genetic clusters, corresponding to different pierhead locations, and genetic admixture between these clusters in the remaining populations. Genetic differentiation (F _ST) is generally related to geographic distance (i.e., isolation by distance), but is periodically interrupted at the scale of Lake Michigan due to gene flow among geographically distant sites. Moreover, average genetic differentiation among populations exhibit a significant, negative correlation with the amount of shipping cargo at ports. Our results, therefore, provide evidence that genetic structure of the round goby in Lake Michigan results from limited natural dispersal with frequent long-distance dispersal through anthropogenic activities such as commercial shipping. Our study suggests that while round gobies can undoubtedly disperse and found new populations through natural dispersal mechanisms, their spread within and among the Great Lakes is likely aided by transport via ships. We, therefore, recommend that ballast-water treatment and management may limit the spread of non-native species within the Great Lakes after the initial introduction in addition to preventing the introduction of non-native species to the Great Lakes.     

Retracing the history and planning the future of the red squirrel (<Emphasis Type="Italic">Sciurus vulgaris</Emphasis>) in Ireland using non-invasive genetics

The Eurasian red squirrel’s (Sciurus vulgaris) history in Ireland is largely unknown, but the original population is thought to have been driven to extinction by humans in the seventeenth century, and multiple records exist for its subsequent reintroduction in the nineteenth century. However, it is currently unknown how these reintroductions affect the red squirrel population today, or may do so in the future. In this study, we report on the development of a DNA toolkit for the non-invasive genetic study of the red squirrel. Non-invasively collected red squirrel samples were combined with other samples collected throughout Ireland and previously published mitochondrial DNA (mtDNA) data from Ireland, Great Britain and Continental Europe to give an insight into population genetics and historical introductions of the red squirrel in Ireland. Our findings demonstrate that the Irish red squirrel population is on a national scale quite genetically diverse, but at a local level contains relatively low levels of genetic diversity, and there is also evidence of genetic structure. This is likely an artefact of the introduction of a small number of genetically similar animals to specific sites. A lack of continuous woodland cover in Ireland has prevented further mixing with animals of different origins that may have been introduced even to neighbouring sites. Consequently, some of these genetically isolated populations are or may in the future be at risk of extinction. The Irish red squirrel population contains mtDNA haplotypes of both a British and Continental European origin, the former of which are now extinct or simply not recorded in contemporary Great Britain. The Irish population is therefore important in terms of red squirrel conservation not only in Ireland, but also for Great Britain, and should be appropriately managed.     

Planktonic green algae in western Lake Erie: the importance of temporal scale in the interpretation of change

1. Total densities of planktonic Chlorophyceae collected in weekly sampling of the Kingsville (Ontario) municipal water intake in western Lake Erie were evaluated for potential effects of the recent zebra mussel ( Dreissena polymorpha ) invasion and for the longer term effects of the Lake Erie phosphorus loading control programme.
2. At a relatively small temporal scale of about 10 years, an apparent zebra mussel-related impact was clearly revealed in 1988 as an inflection point on the cumulative sum chlorophyte density curve. However, at a temporal scale of nearly three decades, this inflection point was not distinct. There was a steady decline in total Chlorophyceae throughout the 1970s which accelerated during the early 1980s; this corresponds to declining western Lake Erie phosphorus loading rates and phosphorus concentrations reported by others over the same period. In the absence of zebra mussels, average annual chlorophyte density decreased by 94% between the early 1970s and the mid-1980s.
3. The dramatic long-term decline of planktonic chlorophytes in western Lake Erie reveals the success of the phosphorus control programme, places the recent impact of the zebra mussels in its proper perspective and underscores the need for and value of long-term limnological data for management of the Laurentian Great Lakes.     

Evolution and diversity of two cisco forms in an outlet of glacial Lake Algonquin

The diversity of Laurentian Great Lakes ciscoes (Coregonus artedi, sensu lato) arose via repeated local adaptive divergence including deepwater ciscoes that are now extirpated or threatened. The nigripinnis form, or Blackfin Cisco, is extirpated from the Great Lakes and remains only in Lake Nipigon. Putative nigripinnis populations were recently discovered in sympatry with artedi in a historical drainage system of glacial Lake Algonquin, the precursor of lakes Michigan and Huron. Given the apparent convergence on Great Lakes form, we labeled this form blackfin. Here, we test the hypothesis that nigripinnis may have colonized this area from the Great Lakes as a distinct lineage. It would then represent a relict occurrence of the historical diversity of Great Lakes ciscoes. Alternatively, blackfin could have evolved in situ in several lakes. We captured more than 600 individuals in the benthic or pelagic habitat in 14 lakes in or near Algonquin Provincial Park (Ontario, Canada). Fish were compared based on habitat, morphology, and genetic variation at 6,676 SNPs. Contrary to our expectations, both cisco and blackfin belonged to an Atlantic lineage that colonized the area from the east, not from the Great Lakes. Sympatric cisco and blackfin were closely related while fish from different lakes were genetically differentiated, strongly suggesting the repeated in situ origin of each form. Across lakes, there was a continuum of ecological, morphological, and genetic differentiation that could be associated with alternative resources and lake characteristics. This study uncovers a new component of cisco diversity in inland lakes of Canada that evolved independently from ciscoes of the Laurentian Great lakes. The diversity of cisco revealed in this study and across their Canadian range presents a challenge for designating conservation units at the intraspecific level within the framework of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).     

Genetic effects of habitat restoration in the Laurentian Great Lakes: an assessment of lake sturgeon origin and genetic diversity

Lake sturgeon (Acipenser fulvescens) have experienced significant habitat loss, resulting in reduced population sizes. Three artificial reefs were built in the Huron‐Erie corridor in the Great Lakes to replace lost spawning habitat. Genetic data were collected to determine the source and numbers of adult lake sturgeon spawning on the reefs and to determine if the founder effect resulted in reduced genetic diversity. DNA was extracted from larval tail clips and 12 microsatellite loci were amplified. Larval genotypes were then compared to 22 previously studied spawning lake sturgeon populations in the Great Lakes to determine the source of the parental population. The effective number of breeders (N_b) was calculated for each reef cohort. The larval genotypes were then compared to the source population to determine if there were any losses in genetic diversity that are indicative of the founder effect. The St. Clair and Detroit River adult populations were found to be the source parental population for the larvae collected on all three artificial reefs. There were large numbers of contributing adults relative to the number of sampled larvae. There was no significant difference between levels of genetic diversity in the source population and larval samples from the artificial reefs; however, there is some evidence for a genetic bottleneck in the reef populations likely due to the founder effect. Habitat restoration in the Huron‐Erie corridor is likely resulting in increased habitat for the large lake sturgeon population in the system and in maintenance of the population's genetic diversity.     

Genetic variation among endangered Irish red grouse (<Emphasis Type="Italic">Lagopus lagopus hibernicus</Emphasis>) populations: implications for conservation and management

Extant populations of Irish red grouse (Lagopus lagopus hibernicus) are both small and fragmented, and as such may have an increased risk of extinction through the effects of inbreeding depression and compromised adaptive potential. Here we used 19 microsatellite markers to assay genetic diversity across 89 georeferenced samples from putatively semi-isolated areas throughout the Republic of Ireland and we also genotyped 27 red grouse from Scotland using the same markers. The genetic variation within Ireland was low in comparison to previously published data from Britain and the sample of Scottish red grouse, and comparable to threatened European grouse populations of related species. Irish and Scottish grouse were significantly genetically differentiated (F_ST = 0.07, 95% CI = 0.04–0.10). There was evidence for weak population structure within Ireland with indications of four distinct genetic clusters. These correspond approximately to grouse populations inhabiting suitable habitat patches in the North West, Wicklow Mountains, Munster and Cork, respectively, although some admixture was detected. Pair-wise F_ST values among these populations ranged from 0.02 to 0.04 and the overall mean allelic richness was 5.5. Effective population size in the Munster area was estimated to be 62 individuals (95% CI = 33.6–248.8). Wicklow was the most variable population with an AR value of 5.4 alleles/locus. Local (Munster) neighbourhood size was estimated to 31 individuals corresponding to an average dispersal distance of 31 km. In order to manage and preserve Irish grouse we recommend that further fragmentation and destruction of habitats need to be prevented in conjunction with population management, including protection of the integrity of the existing population by refraining from augmenting it with individuals from mainland Britain to maximise population size.     

A Review of the Biology and Ecology of the Quagga Mussel (Dreissena bugensis), a Second Species of Freshwater Dreissenid Introduced to North America

SYNOPSIS. North America's Great Lakes have recently been invadedby two genetically and morphologically distinct species of Dreissena.The zebra mussel (Dreissena polymorpha) became established inLake St. Clair of the Laurentian Great Lakes in 1986 and spreadthroughout eastern North America. The second dreissenid, termedthe quagga mussel, has been identified as Dreissena bugensisAndrusov, 1897. The quagga occurs in the Dnieper River drainageof Ukraine and now in the lower Great Lakes of North America.In the Dnieper River, populations of D. polymorpha have beenlargely replaced by D. bugensis; anecdotal evidence indicatesthat similar trends may be occurring in the lower LaurentianGreat Lakes. Dreissena bugensis occurs as deep as 130 m in theGreat Lakes, but in Ukraine is known from only 0–28 m.Dreissena bugensis is more abundant than D. polymorpha in deeperwaters in Dneiper River reservoirs. The conclusion that NorthAmerican quagga mussels have a lower thermal maximum than zebramussels is not supported by observations made of populationsin Ukraine. In the Dnieper River drainage, quagga mussels areless tolerant of salinity than zebra mussels, yet both dreissenidshave acclimated to salinities higher than North American populations;eventual colonization into estuarine and coastal areas of NorthAmerica cannot be ignored.     

Genetic variability and phylogeographical patterns of a nonindigenous species invasion: a comparison of exotic vs. native zebra and quagga mussel populations

There have been few investigations of the number of founding sources and amount of genetic variability that lead to a successful nonindigenous species invasion, although genetic diversity is believed to play a central role. In the present study, population genetic structure, diversity and divergence patterns were analysed for the zebra mussel Dreissena polymorpha [n=280 samples and 63 putative randomly amplified polymorphic DNA (RAPDs) gene loci] and the quagga mussel D. bugensis (n=136 and 52 loci) from 10 nonindigenous North American and six Eurasian sampling sites, representing their present‐day ranges. Results showed that exotic populations of zebra and quagga mussels had surprisingly high genetic variability, similar to those in the Eurasian populations, suggesting large numbers of founding individuals and consistent with the hypothesis of multiple colonizations. Patterns of genetic relationships indicate that the North American populations of D. polymorpha likely were founded by multiple source populations from north‐western and northcentral Europe, but not from southcentral or eastern Europe. Sampling areas within North America also were significantly divergent, having levels of gene flow and migration about twice those separating long‐established Eurasian populations. Samples of D. bugensis in Lakes Erie and Ontario were significantly different, with the former being more closely related to a native population from the Dnieper River, Ukraine. No evidence for a founder effect was discerned for either species.     

Genetic drift and the population history of the Irish travellers

The Irish Travellers are an itinerant group in Ireland that has been socially isolated. Two hypotheses have been proposed concerning the genetic origin of the Travellers: (1) they are genetically related to Roma populations in Europe that share a nomadic lifestyle or (2) they are of Irish origin, and genetic differences from the rest of Ireland reflect genetic drift. These hypotheses were tested using data on 33 alleles from 12 red blood cell polymorphism loci. Comparison with other European, Roma, and Indian populations shows that the Travellers are genetically distinct from the Roma and Indian populations and most genetically similar to Ireland, in agreement with earlier genetic analyses of the Travellers. However, the Travellers are still genetically distinct from other Irish populations, which could reflect some external gene flow and/or the action of genetic drift in a small group that was descended from a small number of founders. In order to test the drift hypothesis, we analyzed genetic distances comparing the Travellers to four geographic regions in Ireland. These distances were then compared with adjusted distances that account for differential genetic drift using a method developed by Relethford (Hum Biol 68 ( 1996 ) 29–44). The unadjusted distances show the genetic distinctiveness of the Travellers. After adjustment for the expected effects of genetic drift, the Travellers are equidistant from the other Irish samples, showing their Irish origins and population history. The observed genetic differences are thus a reflection of genetic drift, and there is no evidence of any external gene flow. Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.     

Lake morphometry determines Dreissena invasion dynamics

Predicting the ecosystem effects of invasive species and the best control strategies requires understanding population dynamics and population regulation. Invasive bivalves zebra and quagga mussels (Dreissena spp.) are considered the most aggressive invaders in freshwaters and have become major drivers of ecosystem processes in the Laurentian Great Lakes. Combining all lake-wide studies of Dreissena spp. conducted in the Great Lakes, we found that invasion dynamics are largely governed by lake morphometry. Where both species are present, quagga mussels generally become dominant in 8–13 years. Thereafter, zebra mussels remain common in shallow lakes and embayments and lake-wide Dreissena density may remain similar, while in deep lakes quagga led to a near-complete displacement of zebra mussels and an ensuing dramatic increase in overall dreissenid density. In deep lakes, overall Dreissena biomass peaked later and achieved?~?threefold higher levels than in shallow lakes. Comparison with 21 waterbodies in North America and Europe colonized by both dreissenids confirmed that patterns of invasion dynamics found in the Great Lakes are very consistent with other waterbodies, and thus can be generalized to other lakes. Our biophysical model predicted that the long-term reduction in primary producers by mussel grazing may be fourfold less in deep compared to shallow lakes due to thermal stratification and a smaller proportion of the epilimnion in contact with the bottom. While this impact remains greatest in shallow areas, we show that when lakes are vertically well-mixed, dreissenid grazing impact may be greatest offshore, revealing a potentially strong offshore carbon and phosphorus sink.

     

长江中下游不同地理种群鳜遗传结构研究

以长江、通江湖泊(洞庭湖、鄱阳湖)、陆封型湖泊(牛山湖、涨度湖、汤逊湖、肖四海湖)不同水体鳜为研究材料,利用微卫星遗传标记对其种群遗传结构进行分析,结果表明:由期望杂合度(He)和多态信息含量指数(PIC)检测的遗传多样性由大到小的顺序为:长江、通江湖泊群体>无放流陆封型湖泊群体>放流的陆封型湖泊群体,并且发现一些稀有等位基因位点在陆封型湖泊鳜群体中消失;由杂合度检验可以看出,所有群体在绝大多数位点都呈现杂合过剩现象,经过哈代-温伯格平衡检验,显示均显著偏离哈代-温伯格平衡(Pst为0.2727,显示群体间已发生较大遗传分化,其变异主要体现在通江湖泊和陆封型湖泊之间,同时由于陆封型湖泊之间放流管理模式的不同,亦会产生中度分化。研究结果表明,江湖阻隔是造成定居性鱼类鳜种群间遗传分化的重要原因之一。       

Patterns of genetic diversity in Great Lakes bloaters (Coregonus hoyi) with a view to future reintroduction in Lake Ontario

The originally diverse ciscoe fish fauna of the Laurentian Great Lakes has suffered many extinctions and local extirpations. Bloaters (Coregonus hoyi) are presumed extirpated from Lake Ontario and the reintroduction of this deepwater fish is under consideration. Given the demographic fluctuations of this species in the other Great Lakes and its recent intralacustrine origin, we sought to identify a genetically diverse and similar source of C. hoyi via an analysis of genetic diversity and population structure using 10 microsatellite loci. Despite well-documented demographic declines, we found no genetic evidence of bottlenecks in 12 C. hoyi samples from the four potential donor lakes (Huron, Michigan, Superior and Nipigon). By contrast, evidence of bottlenecks in historical samples of C. artedi from Lake Ontario suggested that standard genetic methods frequently used to identify population bottlenecks can only detect very severe and long-lasting demographic declines in naturally large populations. Patterns of genetic differentiation and assignment tests indicated that C. hoyi from Lake Huron and Lake Michigan, which are not differentiated, are genetically most similar to Lake Ontario ciscoes. The small available sample of deepwater ciscoes recently caught in Lake Ontario did not allow determining if these represent a small undetected C. hoyi population or a recent invasion of the deep section by C. artedi. On the basis of genetic criteria, we conclude that C. hoyi from any location within Lake Huron or Lake Michigan would be judicious sources of breeders for reintroducing C. hoyi in Lake Ontario.