Mosquitofish Gambusia Affinis Research Articles

Neurotoxic effects of carbamazepine on the mosquitofish Gambusia affinis

In recent years, the presence of pharmaceuticals in the aquatic environment has gained a significant attention. Carbamazepine, a commonly prescribed antiepileptic drug, has been consistently found in aquatic environments at concentrations ranging from nanograms to micrograms, raising concerns about its potential negative impacts on aquatic organisms. The study examined the acute and chronic neurotoxic effects of environmentally relevant and sublethal concentrations of carbamazepine in the mosquitofish Gambusia affinis. After a 96-hour exposure period, the median lethal concentration (LC50) of carbamazepine for G. affinis was determined as 24 mg L − 1. For the current study, sublethal concentrations i.e., one-tenth (2.4 mg L − 1) and one-fifth (4.8 mg L − 1) of the LC50 value were chosen for assessing the neurotoxic effects along with the environmentally relevant concentration (13 ng L − 1). The research findings indicated that carbamazepine had a disruptive impact on the typical growth and behavior of the fish. During the acute exposure phase, physical deformities were observed in the fish, resulting in neonatal and postneonatal fatalities. Furthermore, the neurotoxic effects of carbamazepine were clearly demonstrated through alterations in various neurological parameters, including acetylcholinesterase, dopamine, gamma-aminobutyric acid, serotonin, monoamine oxidase, 5-hydroxyindole acetic acid, adrenaline, and nor-adrenaline. These findings raise concerns about the survival of fish populations in their natural environment.

Increase in the Abundance of Invasive Fish Species in the Ciliwung River, DKI Jakarta and West Java Provinces

The Ciliwung River is one of the important rivers in the Jakarta Special Capital Region (DKI Jakarta) and West Java. The existence of local fish in the Ciliwung River is threatened by the presence of invasive fish. This research aims to identify the types of invasive fish along the Ciliwung River from 2023 to 2024 and compare them with previous research in 2011. The study uses 6 segments according to Minister of Environment and Forestry Decree No. SK.298/Menlhk/Setjen/PKL.1/6/2017. Each segment consists of 3 research plots, totaling 18 research stations. The sampling method involves collecting fish using environmentally friendly fishing gear. The research results show the presence of 10 species from 5 families and 4 non-native fish orders that are invasive. The most abundant invasive fish species in the Ciliwung River are, in order, Plecostomus (Pterygoplichthys pardalis), Mosquito Fish (Gambusia affinis), Guppy (Poecilia reticulata), Platy (Xiphophorus helleri), Nile Tilapia (Oreochromis niloticus), Bristlenose Pleco (Ancistrus temminckii), Glossom (Andinoacara rivulatus), Carp (Cyprinus carpio), Red Devil (Amphilophus labiatus), and African Catfish (Clarias gariepinus). There has been a 100% increase in the number of invasive fish species in the Ciliwung River compared to the 2011 study, which identified only 5 invasive fish species.

Fishes move to transient local refuges, not persistent landscape refuges during river drying experiment

Abstract Anthropogenically driven flow intermittency is increasing in freshwater streams, with important implications for the management and conservation of aquatic ecosystems. Because most freshwater fishes are mobile, they are expected to emigrate from intermittent reaches, but this may not be true in streams transitioning from perennial to intermittent. Here, we attempt to determine if riverine fishes vacate drying reaches before intermittency or remain in local refuges. We implemented a controlled, in situ experimental flow reduction resulting in intermittency, reducing flows from ~1.0 to 0 m3/s over a 3‐week period. We monitored fish and fish‐habitat changes over a 5‐week period before, during and after flow reductions. During flow reductions, total wetted habitat was ultimately reduced by 91%. Habitat loss over time was not equal among habitat types: pool habitat increased slightly as run habit was lost, and backwater and isolated pool habitats were not strongly related to discharge. Likewise, water depth in run habitats decreased faster than other habitats. Only the river carpsucker Carpiodes carpio appeared to move upstream during flow recession; seven other species remained within drying sites. Habitat loss negatively affected fish populations, but at a lower rate than that at which habitat was lost, until sites dried completely. Overall, two species, red shiner Cyprinella lutrensis and western mosquitofish Gambusia affinis, had increased population growth during the study, whereas the remaining species had population declines. Fishes were able to find transient local refuges during flow reductions but did not vacate sites before intermittent conditions. Accounting for lack of emigration from anthropogenic flow‐intermittent reaches will be important for designing conservation actions for fishes threatened by increasing flow intermittency. Creation of refuge habitats may not be effective for widely dispersed species that do not actively seek refuge habitats, unless those habitats support enough individuals to maintain resilience following the intermittent conditions.

Growth and diet of the invasive mosquitofish Gambusia affinis in lotic and lentic habitats in Japan

Growth and diet of the invasive mosquitofish Gambusia affinis in lotic and lentic habitats in Japan

Biotoxicity of Acrostichum aureum L. synthesized zinc oxide nanoparticles against Aedes albopictus, and impact on predation efficiency of mosquito fish Gambusia affinis

Biotoxicity of Acrostichum aureum L. synthesized zinc oxide nanoparticles against Aedes albopictus, and impact on predation efficiency of mosquito fish Gambusia affinis

Transfer of Se from sediments to the western mosquitofish Gambusia affinis: Tissue distribution, accumulation, and effects on the antioxidant physiology

Selenium (Se) has been shown to cause various toxicities in predatory species (i.e., fish and birds) in Se-contaminated aquatic environments. However, trophic transfer of Se from abiotic environments to freshwater fish has been relatively less addressed. In this study, 2-month-old mosquitofish (Gambusia affinis) were fed Se-enriched oligochaete (Lumbriculus variegatus, exposed to different concentrations of Se(IV) at 0.0, 3.0, 10.0, and 30.0 µg/g dry weight for 7 days) for 45 days. Tissue distribution, Se speciation, and effects on the antioxidant physiology in G. affinis were assessed. The results showed Se was rapidly accumulated in the oligochaete, with 6.30 ± 1.20, 16.20 ± 2.10, and 34.50 ± 2.40 µg/g dw of total Se levels in the worms exposed to 3.0, 10.0, and 30.0 µg/g of Se(IV), respectively. Total Se levels were increased in a dose-dependent manner in fish tissues and Se(IV) from sediments was maternally transferred to the fish embryos. Se-Met-and Se-Cys-were the predominant Se species in the worm and fish tissues, accounting for a minimum of 91.01% of the total Se. Furthermore, increased lipid peroxidation and altered the activities of antioxidant enzymes and levels of GSH were noticed in G. affinis fed the Se-enriched L. variegatus. This study has demonstrated that Se(IV) is transferred from an abiotic vector to freshwater organisms, disturbing the antioxidant physiology in G. affinis and potentially their offspring. This study highlights the importance of dietary exposure on the accumulation and toxicity of Se in aquatic organisms.

Impact of the Anti-Tuberculosis Drug Rifampicin on the Feeding, Growth and Embryonic Developmental Profile of the Mosquitofish <i>Gambusia affinis</i>

Although the accumulation of pharmaceutical drugs in aquatic bodies has increased rapidly in recent years, the effect of rifampicin (RIF), a first-line anti-tuberculosis drug, on fish feeding, growth, and embryonic development is unknown. This investigation aimed to determine the impact of RIF on growth and embryonic developmental profile in the mosquitofish Gambusia affinis. Experimental groups included controls, which were kept in normal water for 21 days, whereas those in the second, third, and fourth groups were exposed to 50, 200, and 500 mg RIF/L water, respectively. The food intake rate and Specific Growth Rate (SGR) showed a concentration-dependent significant decrease in RIF-treated fish compared with controls, and a strong positive correlation was found between food consumption and SGR. A significant decrease in the number of embryos at an early stage of development and the total number of embryos in RIF-treated fish was associated with several congenital anomalies such as lack of vitellogenin accumulation, yolk sac regression, decreased pigmentation, aggregations of blood vessels, and curvature of the spinal cord compared with controls. Together, these results reveal for the first time that RIF treatment not only impacts feeding and growth, but also exerts potential teratogenic effect on embryonic developmental stages in the mosquitofish G. affinis.

Toksisitas Letal (LC50) Zat Surfaktan Linear Alkylbenzene Sulfonate terhadap Ikan Cere (Gambusia affinis)

Mosquito fish (Gambusia affinis) is a species often used as a bioindicator because it has high adaptability to water quality changes. Linear alkylbenzene sulfonate (LAS) is a surfactant often found in waters and can cause death for the biota that lives in it. This study aimed to analyze the impact of LAS surfactant on the survival of mosquito fish and to determine the minimum concentration of LAS surfactant that can cause death and tissue damage. Research conducted during April 2022 using 500 mosquito fishes. We did several tests, including a lethal toxicity test to find out the concentration of LAS surfactant that can cause death and tissue damage. The results showed that the LC50 values of LAS surfactants at exposure times of 24, 48, 72, and 96 hours were 7.64, 7.43, 7.29, and 6.83 mg/L, respectively. Mosquito fish blood glucose levels at LAS concentrations of 0, 2.65, 4.30, 6.97, and 11.3 were 56, 75, 79.6, 95, and 95.6 mg/dl. Exposure to LAS surfactant in mosquito fish can cause gill damage in the form of edema, lamella fusion, hyperplasia, lamellae epithelium swelling, and gill filaments necrosis. Another damage occurs to the liver in the form of blockage of blood vessels and sinusoids, hyperplasia, widening of the hepatic sinusoid gap, fat accumulation, and necrosis of hepatocytes.

Massive expansion of sex-specific SNPs, transposon-related elements, and neocentromere formation shape the young W-chromosome from the mosquitofish Gambusia affinis

BackgroundThe Western mosquitofish, Gambusia affinis, is a model for sex chromosome organization and evolution of female heterogamety. We previously identified a G. affinis female-specific marker, orthologous to the aminomethyl transferase (amt) gene of the related platyfish (Xiphophorus maculatus). Here, we have analyzed the structure and differentiation of the G. affinis W-chromosome, using a cytogenomics and bioinformatics approach.ResultsThe long arm of the G. affinis W-chromosome (Wq) is highly enriched in dispersed repetitive sequences, but neither heterochromatic nor epigenetically silenced by hypermethylation. In line with this, Wq sequences are highly transcribed, including an active nucleolus organizing region (NOR). Female-specific SNPs and evolutionary young transposable elements were highly enriched and dispersed along the W-chromosome long arm, suggesting constrained recombination. Wq copy number expanded elements also include female-specific transcribed sequences from the amt locus with homology to TE. Collectively, the G. affinis W-chromosome is actively differentiating by sex-specific copy number expansion of transcribed TE-related elements, but not (yet) by extensive sequence divergence or gene decay.ConclusionsThe G. affinis W-chromosome exhibits characteristic genomic properties of an evolutionary young sex chromosome. Strikingly, the observed sex-specific changes in the genomic landscape are confined to the W long arm, which is separated from the rest of the W-chromosome by a neocentromere acquired during sex chromosome evolution and may thus have become functionally insulated. In contrast, W short arm sequences were apparently shielded from repeat-driven differentiation, retained Z-chromosome like genomic features, and may have preserved pseudo-autosomal properties.

Risk Predictability in Early Life Shapes Personality of Mosquitofish in Adulthood.

Animal personality is of great ecological and evolutionary significance and has been documented in many animal taxa. Despite genetic background, personality might be prominently shaped by external environments, and it is significant to explore the environmental factors that influence the ontogeny of animal personality in early life. Here, we reared newborn mosquitofish Gambusia affinis under different treatments of risk predictability (i.e., no risks, unpredictable risks, risks at 5 min after feeding and risks at 2 h after feeding) and measured their two personality traits at sexual maturity. We measured the behavioral repeatability, correlation between behavioral characteristics, and the impact of risk predictability. We found that the fish showed repeatability in exploration in all risk treatments, as well as repeatability in shyness under predictable risks. When growing up in risk treatments, no matter predictable or unpredictable, shyness and exploration showed a negative correlation, suggesting a behavioral syndrome between the two behavioral traits. The fish reared under predictable risks were less explorative than those under unpredictable risks, while there were no differences in shyness among treatments. Besides, smaller fish were bolder and more explorative than larger ones. Our findings imply that risk predictability in early life may play an important role in shaping animal personality and modifying the average behavioral levels.

Environmental Quality Identification of Wangi the River Polluted by Waste Based on the Environmental Pollution Index

High amount of wastewater release to Wangi riverflow, especially industrial wastewater, can potentially cause pollution. Pollution in river has been occurred since 2015. The aim of this study was to identify the environmental quality of contaminated Wangi River and determine the pollution index. This study was performed through a survey method, and river water sampling was carried out around the Wangi riverflow, Beujeng-Beji, Pasuruan District. Sampling was conducted in three locations, namely industrial, residential, and agricultural areas on different months (June 2020 - July 2021). This study was also conducted to analyze the heavy metal content of Pb, Hg and Cd in Wangi river biota around the watershed, namely mosquito fish (Gambusia affinis). The pollutant identification result was based onthree study areas, namely study area I (factory/industrial waste), study area II (residential waste) and study area III (agricultural waste). Heavy metal contamination occurred in Wangi River hhe as the potential to produce waste containing Pb, Cd and Hg. The average levels of Pb, Cd and Hg in the water were 0.031 ppm, 0.019 and 0.009 ppm, respectively. These values exceeded the acceptable quality standard. The result of data analysis based on the pollution index (PI) and average number of pollution indexes (PIaverage) in the Wangi river (at study areas I, II and III) was 5.503, which means thatthe condition of the Wangi river is classified as a “moderately-polluted” river. The authority is expected to develop a further policy for Wangi riverflow preservation program.

Eco-biological Study of the Mosquitofish Gambusia affinis from Oubeira lake

Gambusia was studied in Oubeira lake in spring 2016. A total of 100 specimens were collected in the lake. The sex ratio was F:M = 5.12: 1. The length-weight relationship was estimated for the population, with Wt = 0.0197Lt2.4451. The condition factor was calculated C=1±0.2 (for population) and a significant difference was observed between males and females. For 100 examined stomachs, the diet mainly consists of algae (N=54.96%, Pi= 166%, O=91%), followed by the mosquito larvae (N=21.52%, Pi= 65%, O=49%), detritus (N=19.2%, Pi= 58%, O=46%) and arthropods (N=4.3%, Pi= 13%, O=13%). For mosquitoes, two genus were recorded: Culiseta and Culex with 4 species: Culex pipiens, Culex theileri, Culex laticinctus and Culex antennatus. The culture experiments confirmed the important predation on mosquito larvae was observed with feeding intensity for females and males of 86 ± 12.28 % and 92 ± 8 % for the Culex larvae and 91 ± 7 and 93.66 ± 5.68 for the Culiseta larvae, respectively. No significant difference was observed between the sexes or for mosquito larvae. Our data support the idea that the introduction of mosquitofish has both negative and positive effects since this fish feeds on the most abundant food and not only on mosquitoes.

Assessment of biochemical biomarkers of mosquitofish (Gambusia affinis (Baird et Girard, 1853)) on exposure to the insecticide cypermethrin

ABSTRACT Cypermethrin (CYP) is a synthetic pyrethroid insecticide, used in agriculture, and one of the most common contaminants in freshwater aquatic systems. This paper reports an evaluation of the toxicity of CYP in the mosquitofish, exposed to two concentrations (0.2 ng/L and 6.25 ng/L). The result revealed a significant modulation in the activity of antioxidants enzymes, superoxide dismutase, catalase and decreased acetylcholinesterase after 7 days. Hydrogen peroxide (H2O2) and malondialdehyde levels remained elevated throughout the exposure duration. CYP causes gills and liver oxidative stress, modifying the antioxidant enzymes. Principal component analysis highlighted relationship between biomarkers in functional response. These findings suggest that exposure to CYP can lead to various antioxidant processes in the fish gills and liver.

Male mate choice in mosquitofish: personality outweighs body size

BackgroundDespite its important implications in behavioural and evolutionary ecology, male mate choice has been poorly studied, and the relative contribution of personality and morphological traits remains largely unknown. We used standard two-choice mating trials to explore whether two personality traits (i.e., shyness and activity) and/or body size of both sexes affect mate choice in male mosquitofish Gambusia affinis. In the first set of trials involving 40 males, we tested whether males would prefer larger females and whether the preference would be affected by males’ body length and personality traits, and females’ activity level. In the second set of trials (using another 40 males), we tested whether males would prefer more active females and whether the preference would be affected by males’ body length and personality traits.ResultsBoth shyness and activity in males were significantly repeatable and constituted a behavioural syndrome. No overall directional preference for large (or small) females with the same activity levels was detected because larger males preferred larger females and smaller males chose smaller females. Males’ strength of preference for larger females was also positively correlated with the activity level of larger females but negatively with the activity level of smaller females. Males spent more time associating with active females regardless of their body lengths, indicating males’ selection was more influenced by female activity level than body size. Males’ preference for inactive females was enhanced when females became active. There was no convincing evidence for the effect of males’ personality traits or body length on their preferences for females’ activity level.ConclusionsOur study supports the importance of body size in male mate choice but highlights that personality traits may outweigh body size preferences when males choose mating partners.

CD4 cell activation with the CD8 marker and metallothionein expression in the gills of cadmium-exposed mosquito fish (Gambusia affinis Baird and Girard 1853) juveniles

This experiment aimed to determine how Cd exposure impacts CD4 cell activation, macrophage cells, pinocytosis activity, metallothionine expression, and Cd levels in juvenile Gambusia affinis gills. Four treatment groups were used, with one control and treatments A, B, C, and D at dosages of 0.03 mg/L, 0.023 mg/L, 0.015 mg/L, and 0.008 mg/L, respectively. The results showed that the number of CD4 with CD8 cell markers differed significantly from each treatment compared to the control (0.33%). The value in A, namely 0.54%, was the highest, followed by B, C, and D of 0.46%, 0.44%, and 0.42%, respectively. The number of macrophages increased as the Cd level of the medium increased, as did the activity of pinocytosis. Furthermore, the immunofluorescence test on the gills with the Anti-MT Mouse and goat IgG fluoresce in Rhodamine on the gills showed that luminescence increased with increasing Cd levels in the gills. Similarly, the MT intensity increased at Cd-exposed gills as compared to the control. As the Cd level in the gills increased, the MT levels ascended significantly.

Behavioral Interactions between a Native and an Invasive Fish Species in a Thermally Heterogeneous Experimental Chamber

Mechanisms of the displacement of native fish by nonnative fish can include agonistic behaviors that push native fish species out of their preferred habitat, including their thermal optima. To examine these interactions, we built an experimental thermal preference chamber to evaluate: (1) the thermal preference of native, glacial relict northern redbelly dace Chrosomus eos; (2) if the thermal preference and movement changed in the presence of the invasive western mosquitofish Gambusia affinis; and (3) the direction of agonistic interactions. We hypothesized that G. affinis would express agonistic behavior toward C. eos, because G. affinis is widely recognized as an aggressive invader. Given the temperature range of the experimental chamber, i.e., 20–30 °C, C. eos selected an average of 24.3 °C as its thermal preference. After G. affinis’ introduction, the thermal preference of C. eos increased by 1.7 °C and the movement, given by distance (cm) travelled, increased by 21%. Contrary to our prediction, more agonistic interactions were observed in C. eos toward G. affinis. These results indicate that agonistic behavior of G. affinis toward native fish species may be species- and condition-specific, and may not always be the primary mechanism of native species’ displacement. Biological invasions are a global issue and altered thermal regimes are expected to continue. This study provided the novel approach using of a thermally heterogeneous thermal chamber to examine thermal preferences and aggressive interactions between a native and an invasive species. Future research should examine other life history traits that may be conveying the competitive advantage to G. affinis.

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

AimFormerly 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.LocationGlobal.MethodsWe 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.ResultsWe 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 conclusionsDespite 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.

Serotonin (5-hydroxytryptamine)-immunoreactive neurons in the brain of the viviparous fish Gambusia affinis

The monoaminergic neurotransmitter serotonin (5-HT) acts as a neuromodulator and is associated with a wide range of functions in fish. In this investigation, 5-HT immunoreactivity was studied in the central nervous system (CNS) of the viviparous mosquitofish Gambusia affinis. 5-HT-immunoreactive (5-HT-ir) cells/fibres were observed throughout the subdivisions of ventral and dorsal telencephalon including the olfactory bulb. Several intensely stained 5-HT-ir cells and/or fibres were detected in different areas of the hypothalamus as well as the proximal pars distalis of the pituitary gland. 5-HT-ir cells were restricted to the dorsal and ventral part of the pretectal diencephalic cluster, but only fibres were detected in the anterior, ventromedial and posterior subdivisions of the thalamic nucleus and in the preglomerular complex. In the mesencephalon, 5-HT-ir perikarya, and fibres were seen in the optic tectum, midbrain tegmentum and torus semicircularis. A cluster of prominently labelled 5-HT-ir neurons was observed in the superior raphe nucleus, whereas numerous 5-HT-ir fibres were distributed throughout the rhombencephalic divisions. In addition, a bundle of rostrocaudally running 5-HT-ir fibres was noticed in the spinal cord. This is the first detailed neuroanatomical study in a viviparous teleost, reporting a widespread distribution of 5-HT-ir somata and fibres in the CNS. The results of this study provide new insights into the evolutionarily well conserved nature of the monoaminergic system in the CNS of vertebrates and suggest a role for 5-HT in regulation of several physiological, behavioural and neuroendocrine functions in viviparous teleosts.

The pivotal protein profile between the conjoined twins and normal mosquitofish Gambusia affinis based on iTRAQ proteomic analysis.

The fish abnormal embryonic development has attracted public attention in the recent few years. In this study, an iTRAQ proteomic analysis of mosquitofish between conjoined twins and normal fishes is applied for the first time by using the genome database of mosquitofish. Three thousand four hundred ninety proteins were identified with 304 differentially expressed proteins (DEPs). One hundred six differentially upregulated proteins (DUPs) and 198 differentially downregulated proteins (DDPs) were identified between the conjoined twins and normal mosquitofish groups. Notably, the proteins related to lipid and proteolysis were the important GO terms for the DUPs while response to light stimulus and response to radiation were the most enriched GO terms for the DDPs. The proteins related to lysosome, apoptosis, autophagy, and phagosome were the functional KEGG pathway for the DUPs while most of the pathways were related to cardiovascular for the DDPs. This study expatiated a pivotal protein profile between the conjoined twins and normal mosquitofish which can provide a conference for fish embryonic development.

Synonymous single nucleotide polymorphism in arsenic (+3) methyltransferase of the Western mosquitofish (Gambusia affinis) and its gene expression among field populations

Naturally occurring arsenic is toxic at extremely low concentrations, yet some species persist even in high arsenic environments. We wanted to test if these species show evidence of evolution associated with arsenic exposure. To do this, we compared allelic variation across 872 coding nucleotides of arsenic (+3) methyltransferase (as3mt) and whole fish as3mt gene expression from three field populations of Gambusia affinis, from water sources containing low (1.9 ppb), medium-low (3.3 ppb), and high (15.7 ppb) levels of arsenic. The high arsenic site exceeds the US EPA’s Maximum Contamination Level for drinking water. Medium-low and high populations exhibited homozygosity, and no sequence variation across all animals sampled. Eleven of 24 fish examined (45.8%) in the low arsenic population harbored synonymous single nucleotide polymorphisms (SNPs) in exons 4 and/or 10. SNP presence in the low arsenic population was not associated with differences in as3mt transcript levels compared to fish from the medium-low site, where SNPs were noted; however, as3mt expression in fish from the high arsenic concentration site was significantly lower than the other two sites. Low sequence variation in fish populations from sites with medium-low and high arsenic concentrations suggests greater selective pressure on this allele, while higher variation in the low population suggests a relaxed selection. Our results suggest gene regulation associated with arsenic detoxification may play a more crucial role in influencing responses to arsenic than polymorphic gene sequence. Understanding microevolutionary processes to various contaminants require the evaluation of multiple populations across a wide range of pollution exposures.