Low diversity and high levels of population genetic structuring in introduced eastern mosquitofish (Gambusia holbrooki) in the greater Melbourne area, Australia

Off to new shores: Climate niche expansion in invasive mosquitofish (Gambusia spp.)

AIM

Formerly introduced for their presumed value in controlling mosquito-borne diseases, the two mosquitofish Gambusia affinis and G. holbrooki (Poeciliidae) are now among the world's most widespread invasive alien species, negatively impacting aquatic ecosystems around the world. These inconspicuous freshwater fish are, once their presence is noticed, difficult to eradicate. It is, therefore, of utmost importance to assess their geographic potential and to identify their likely ability to persist under novel climatic conditions.

LOCATION

Global.

METHODS

We build species distribution models using occurrence data from the native and introduced distribution ranges to identify putative niche shifts and further ascertain the areas climatically suitable for the establishment and possible spread of mosquitofish.

RESULTS

We found significant niche expansions into climatic regions outside their natural climatic conditions, emphasizing the importance of integrating climatic niches of both native and invasive ranges into projections. In particular, there was a marked shift toward tropical regions in Asia and a clear niche shift of European G. holbrooki. This ecological flexibility partly explains the massive success of the two species, and substantially increases the risk for further range expansion. We also showed that the potential for additional expansion resulting from climate change is enormous-especially in Europe.

MAIN CONCLUSIONS

Despite the successful invasion history and ongoing range expansions, many countries still lack proper preventive measures. Thus, we urge policy makers to carefully evaluate the risk both mosquitofish pose to a particular area and to initiate appropriate management strategies.

High genetic diversity and strong genetic structure of Strongyllodes variegatus populations in oilseed rape production areas of China

Background

Strongyllodes variegatus (Fairmaire) is a major insect pest of oilseed rape in China. Despite its economic importance, the contribution of its population genetics in the development of any suitable protection control strategy for the management of oilseed rape crops is poorly studied. It is a much urgent need to prevent its spread to the rest of the world.

Results

Using the sequences of mitochondrial DNA cytochrome c oxidase subunit I (COI) and cytochrome b (Cytb) as genetic markers, we analyzed the population genetic diversity and structure of 437 individuals collected from 15 S. variegatus populations located in different oilseed rape production areas in China. In addition, we estimated the demographic history using neutrality test and mismatch distribution analysis. The high level of genetic diversity was detected among the COI and Cytb sequences of S. variegatus. The population structure analyses strongly suggested three distinct genetic and geographical regions in China with limited gene flow. The Mantel test showed that the genetic distance was greatly influenced by the geographical distance. The demographic analyses showed that S. variegatus had experienced population fluctuation during the Pleistocene Epoch, which was likely to be related to the climatic changes.

Conclusion

Overall, these results demonstrate that the strong genetic structure of S. variegatus populations in China, which is attributed by the isolation through the geographical distance among populations, their weak flight capacity and subsequent adaptation to the regional ecological conditions.

Metagenomic sequencing reveals a lack of virus exchange between native and invasive freshwater fish across the Murray-Darling Basin, Australia

Biological invasions are among the biggest threats to freshwater biodiversity. This is increasingly relevant in the Murray-Darling Basin, Australia, particularly since the introduction of the common carp (Cyprinus carpio). This invasive species now occupies up to ninety per cent of fish biomass, with hugely detrimental impacts on native fauna and flora. To address the ongoing impacts of carp, cyprinid herpesvirus 3 (CyHV-3) has been proposed as a potentially effective biological control agent. Crucially, however, it is unknown whether CyHV-3 and other cyprinid herpesviruses already exist in the Murray-Darling. Further, little is known about those viruses that naturally occur in wild freshwater fauna, and the frequency with which these viruses jump species boundaries. To document the evolution and diversity of freshwater fish viromes and better understand the ecological context to the proposed introduction of CyHV-3, we performed a meta-transcriptomic viral survey of invasive and native fish across the Murray-Darling Basin, covering over 2,200 km of the river system. Across a total of thirty-six RNA libraries representing ten species, we failed to detect CyHV-3 nor any closely related viruses. Rather, meta-transcriptomic analysis identified eighteen vertebrate-associated viruses that could be assigned to the Arenaviridae, Astroviridae, Bornaviridae, Caliciviridae, Coronaviridae, Chuviridae, Flaviviridae, Hantaviridae, Hepeviridae, Paramyxoviridae, Picornaviridae, Poxviridae, Reoviridae and Rhabdoviridae families, and a further twenty-seven that were deemed to be associated with non-vertebrate hosts. Notably, we revealed a marked lack of viruses that are shared among invasive and native fish sampled here, suggesting that there is little virus transmission from common carp to native fish species, despite co-existing for over fifty years. Overall, this study provides the first data on the viruses naturally circulating in a major river system and supports the notion that fish harbour a large diversity of viruses with often deep evolutionary histories.

Microplastics biomonitoring in Australian urban wetlands using a common noxious fish (Gambusia holbrooki)

Biomonitoring microplastics in freshwater ecosystems has been insufficient in comparison with its practice in marine environments. It is an important first step to understand microplastic uptake in organisms when assessing risk in natural freshwater habitats. We conducted microplastic biomonitoring within the Greater Melbourne Area; where the microplastic baseline pollution in freshwater organisms was largely unknown. A common noxious fish species, Gambusia holbrooki, was targeted. Individuals (n = 180) from nine wetlands were analyzed. Uptake pathway, size, weight and gender were examined in relation to microplastic uptake in the body (presumed uptake via gut) and head (presumed uptake via gills). On average, 19.4% of fish had microplastics present in their bodies with an abundance of 0.6 items per individual (items/ind) and 7.2% of fish had microplastics in their heads with an abundance of 0.1 items/ind. Polyester was the dominant plastic type and fibers were the most common shape. The amount of microplastics in Gambusia holbrooki in current study is relatively low in a global comparison. The bodies of fish contained more microplastics on average than heads, and the size of microplastics detected in heads were smaller than those found in bodies. Microplastic uptake was directly proportional to size and weight. Furthermore, female individuals showed a tendency to ingest more microplastics than males. Laboratory experiments under controlled conditions are suggested to further explore such relationships. Our findings are important to understanding the potential ecological risks posed by microplastics to organisms in freshwater environments and provide suitable methodologies to conduct biomonitoring in future investigations.

Effects of water pollution and river fragmentation on population genetic structure of invasive mosquitofish

We analyzed variation at the GPI-2 locus and eleven microsatellite loci of eastern mosquitofish Gambusia holbrooki populations introduced to the Ebro River (Spain), sampling above and below a dam (Flix Reservoir) where severe chronic pollution has been well documented. Allele frequency changes at the GPI-2 locus in the sites nearest to the polluted sediments agree with previous results from studies in mercury-exposed populations of this highly invasive fish. Genetic distinction of the mosquitofish collected close to the polluted sediments was detected at the GPI locus but also at the presumptive neutral microsatellite loci. Recent migration rates estimated from microsatellites indicated that around 30% of fish collected in a specific location were immigrants from upstream and downstream sources. Such high migration rates probably contribute to the mosquitofish's invasive success and suggest that the consequences on the mosquitofish regional genetic structured of high levels of water toxicants could be mediated by immigration from other sites, but the effect of pollutants on local diversity might be higher than observed here.

Why does inbreeding reduce male paternity? Effects on sexually selected traits

Mating with relatives has often been shown to negatively affect offspring fitness (inbreeding depression). There is considerable evidence for inbreeding depression due to effects on naturally selected traits, particularly those expressed early in life, but there is less evidence of it for sexually selected traits. This is surprising because sexually selected traits are expected to exhibit strong inbreeding depression. Here, we experimentally created inbred and outbred male mosquitofish (Gambusia holbrooki). Inbred males were the offspring of matings between full siblings. We then investigated how inbreeding influenced a number of sexually selected male traits, specifically: attractiveness, sperm number and velocity, as well as sperm competitiveness based on a male's share of paternity. We found no inbreeding depression for male attractiveness or sperm traits. There was, however, evidence that lower heterozygosity decreased paternity due to reduced sperm competitiveness. Our results add to the growing evidence that competitive interactions exacerbate the negative effects of the increased homozygosity that arises when there is inbreeding.

Mitochondrial DNA revealed the extent of genetic diversity and invasion origin of populations from two separate invaded areas of a newly invasive pest, Cydia pomonella (L.) (Lepidoptera: Tortricidae) in China

Cydia pomonella is a serious invasive insect pest in China, and has caused severe damage to the production of apple and pear in its invaded areas. This species is distributing in the northwest and northeast of China, but no occurrence of it has been recorded in the large areas (about 3000-5000 km away) between the invaded northwestern and northeastern regions despite continuous monitoring. As yet the genetic diversity and invasion origin of the C. pomonella populations in Northwestern and Northeastern China is obscure. In this study, we investigate the genetic diversity of 14 populations of C. pomonella sampled throughout the main distribution regions in Northwestern (Xinjiang and Gansu Provinces) and Northeastern (Heilongjiang Province) China and compared them with nine populations from Europe and other continents using the mitochondrial COI, COII and Cytb genes. Both the populations from Northeastern and Northwestern China shared some haplotypes with populations from other countries. Haplotypes of the three mitochondrial genes had a different distribution in Northeastern and Northwestern China. The northeastern populations had more private haplotypes than the northwestern populations. A large number of the individuals from northwestern populations shared a few haplotypes of each of the three genes. The haplotype numbers and haplotype diversities of the northeastern populations were similar to those of field populations in other countries, but were higher than those of the northwestern populations. Populations from the Northwestern China showed similar haplotype number and haplotype diversity. We conclude that the population genetic background of C. pomonella populations in Northeastern and Northwestern China varies due to different invasion sources and that this should be considered before the application of new pest control tactics.

Mitochondrial genetic variations of an introduced freshwater fish, goldfish Carassius auratus at the frontier between Europe and Asia (western Anatolia, Turkey): proximity to Europe rather than East Asia?

Carassius auratus is one of the most significant ornamental and food fishes of the world that is globally distributed and well known. Although it is known to have existed at least for six decades and expanding its distribution range in Turkish waters, there is a dearth of information on genetic structure and variations of goldfish in Turkey. In this study, four mitochondrial genes (Cytochrome b, cytochrome oxidase II, 12S ribosomal RNA, and 16S ribosomal RNA) were used to infer the genetic variations of goldfish populations sampled from western part of Anatolia, Turkey. Three populations were clustered under three haplotypes for each gene and all haplotypes were special. Cytochrome b was found to have more variable sites and higher genetic diversity than other genes. According to the haplotype networks, goldfish populations in Turkey showed high level of genetic structuring and originated from the common haplotype known in native East Asian populations of the species. Extensive sampling scheme covering whole Anatolia should provide better understanding on the dispersal pattern of the species.

Invasion genetics of vendace (Coregonus albula (L.)) in the Inari-Pasvik watercourse: revealing the origin and expansion pattern of a rapid colonization event

Species invasions can have wide-ranging biological and socio-economic effects and are generally unwanted by legislation. Identification of the source population as well as the ecology and genetics of both the invader population and the receiving community is of crucial importance. The rapid invasion of a small coregonid fish vendace (Coregonus albula) in a major northern European subarctic watercourse has resulted in a labile ecological situation in the receiving community. The ecological impact of the invasion has been thoroughly documented, but the genetics of the invasion remains to be explored. We analyzed the genetic diversity and divergence patterns among the two possible source populations from southern Finnish Lapland and three colonists populations within the Inari-Pasvik watercourse using ten microsatellite loci in order to (i) identify the most likely source of the invasion, (ii) reveal the dispersal pattern and genetic structure of the secondary expansion, and (iii) to investigate whether the initial introduction and the secondary expansion were associated with founder effects. We revealed that repeated translocation of vendace from Lake Sinettäjärvi into a tributary lake of L. Inari in 1964–1966 is the most plausible source for the invasion. Both the initial introduction and the secondary expansion were found not to be associated with significant founder effects. The secondary expansion followed a stepping stone pattern and the source and colonist populations of this expansion have undergone rapid genetic divergence within a period of 15–35 years (ca. 8–17 generations). The rapid divergence may be contributed to lack of gene flow among the source and colonist populations due to the extensive hydroelectric damming in the watercourse. Multiple introductions and substantial genetic variation in combination with the boom-and-bust population development of the species thus likely counteracted the founder effects as well as fueled the rapid establishment and expansion of this species within the Inari-Pasvik watercourse.

Screening for potential effects of endocrine-disrupting chemicals in peri-urban creeks and rivers in Melbourne, Australia using mosquitofish and recombinant receptor-reporter gene assays

Sexually mature male mosquitofish (Gambusia holbrooki) were collected from various sites around Melbourne in 2009 to evaluate the performance of gonopodial indices as a biomarker for endocrine disruption in Melbourne's waterways. The mosquitofish indices assessed were body length (BL), gonopodial length (GL)/BL ratio, ray 4:6 ratio and the absence or presence of hooks and serrae, and these varied between sites. The study was complemented by measurements of estrogenic, retinoid, thyroid and aryl hydrocarbon (AhR) receptor activities of the water. Male mosquitofish were 16.3-21.5 mm in length, and although there was a statistically significant positive relationship showing that bigger fish had longer gonopodia than small fish (r2 = 0.52, p < 0.001), there were few significant differences in GL/BL ratio of fish between sites. Measured estrogenic activity was mostly in the range 0.1-1.7 ng/L EEQ, with one site having much higher levels (~12 ng/L EEQ). Aryl hydrocarbon (AhR) receptor activity was observed in all water samples (7-180 ng/L βNF EQ), although there was no consistent pattern in the level of AhR activity observed, i.e., 'clean' sites were as likely to return a high AhR activity response as urban or wastewater treatment plant (WWTP)-impacted sites. There was no correlation between measurements of receptor actvity and gonopodial length (GL):BL ratio and BL. We conclude that the mosquitofish gonopodia only fulfills part of the criteria for biomarker selection for screening. The mosquitofish indices assessed were cheap and easy-to-perform procedures; however, there is no baseline data from the selected sites to evaluate whether differences in the morpholical indices observed at a site were a result of natural selection in the population or due to estrogenic exposure.

DNA barcoding common non-native freshwater fish species in Turkey: low genetic diversity but high population structuring

Negative impacts of introduced non-native freshwater species on native species have been increasingly recognized in the world as well as in Turkey. However, there has been relatively little attention on genetic characterization of alien freshwater fishes in their non-native distribution range and virtually no study has been conducted in Turkey despite its crucial importance in invasion biology. The purpose of this study was to elucidate genetic diversity of common non-native freshwater fish species (Carassius auratus, Carassius gibelio, Gambusia holbrooki, Lepomis gibbosus, and Pseudorasbora parva) using mitochondrial Cytochrome c oxidase subunit I (COI) sequences; known as DNA barcodes. Through the whole dataset, seventeen haplotypes (haplotype diversity = 0.8908) were found containing 145 COI sequences. Mean Kimura two-parameter genetic distances were calculated as 0.209 for interspecific distance and 0.009 for intraspecific variation. COI barcode diversity among populations of the same species was found to be low, especially for C. gibelio, G. holbrooki, and L. gibbosus populations which were 0.5%, 0.6%, and 0.3%, respectively. Our results clearly demonstrate the effectiveness of the DNA barcoding approach both for identifications at species level and revealing intraspecific variation among populations, which could be used for effective management measures for invasive species and conservation strategies for indigenous and endemic species.

Twenty-five new polymorphic microsatellites for the eastern mosquitofish, Gambusia holbrooki (Actinopterygii : Poeciliidae), an invasive species in Australia

We isolated 25 new polymorphic microsatellite markers from the eastern mosquitofish, Gambusia holbrooki. Initially, 454 shotgun sequencing was used to identify 1187 loci for which primers could be designed. Of these 1187, we trialled 48 in the target species, 40 of which amplified a product of expected size. Subsequently, those 40 loci were screened for variation in 48 individuals from a single population in Canberra, Australia. Twenty loci were in Hardy–Weinberg equilibrium and polymorphic, with observed heterozygosity ranging from 0.04 to 0.72 (mean: 0.45 ± 0.18) and the number of alleles per locus ranged from 2 to 5 (mean: 3.20 ± 1.05). These loci will be useful in understanding genetic variation, paternity analysis and in managing this species across both its native and invasive range.