[Show abstract][Hide abstract] ABSTRACT: Many organisms survive fluctuating and extreme environmental conditions by manifesting multiple distinct phenotypes during adulthood by means of developmental processes that enable phenotypic plasticity. We report on the discovery of putative plasticity-enabling genes that are involved in transforming the gill of the euryhaline teleost fish, Fundulus heteroclitus, from its freshwater to its seawater gill-type, a process that alters both morphology and function. Gene expression that normally enables osmotic plasticity is inhibited by arsenic. Gene sets defined by antagonistic interactions between arsenic and salinity show reduced transcriptional variation among individual fish, suggesting unusually accurate and precise regulatory control of these genes, consistent with the hypothesis that they participate in a canalized developmental response. We observe that natural selection acts to preserve canalized gene expression in populations of killifish that are most tolerant to abrupt salinity change and that these populations show the least variability in their transcription of genes enabling plasticity of the gill. We found that genes participating in this highly canalized and conserved plasticity enabling response had significantly fewer and less complex associations with transcriptional regulators than genes that respond only to arsenic or salinity. Collectively these findings, which are drawn from the relationships between environmental challenge, plasticity, and canalization among populations, suggest that the selective processes that facilitate phenotypic plasticity do so by targeting the regulatory networks that gives rise to the response. These findings also provide a generalized, conceptual framework of how genes might interact with the environment and evolve towards the development of plastic traits.
Molecular Biology and Evolution 08/2014; · 14.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Syntheses of research spanning diverse taxa, ecosystems, timescales, and hierarchies are crucial for understanding the cumulative impacts of the Macondo oil spill in the Gulf of Mexico. Four years after the spill, responses of estuarine fishes to oil pollution have been studied at organismal through population levels, and there is an emerging mismatch between consistent negative impacts detected among individual organisms and absence of measurable negative impacts among populations. To reconcile this apparent contradiction, we draw on lessons learned from this and previous spills to consider two classes of mechanisms: factors obscuring negative population impacts despite known organismal responses (e.g., high spatiotemporal variability, offsetting food-web cascades, fishery closures, temporal lags) and factors dampening population-level costs despite known organismal responses (e.g., behavioral avoidance, multiple compensatory pathways). Thus, we highlight critical knowledge gaps that should form the basis of current and future oil-spill research priorities to assess ecosystem responses to basin-scale disturbance. T he 2010 Macondo well blowout challenged the integrity and function of the Gulf of Mexico (GOM) eco-system at an unprecedented scale. GOM fisheries, although stressed even before the spill, remain among the most productive in the world (commercial harvest, 600,000met-ric tons per year, worth $600,000,000 per year dockside; recreational harvest, 25,000 tons per year and 25,000,000 trips per year; Lellis-Dibble etal. 2008), and there has been widespread concern regarding the impact of basin-scale marine oil pollution on fishes and shellfishes that sup-port economies throughout the region (McCrea-Strub etal. 2011). Some project the potential overall economic impact of lost or degraded fisheries in the GOM to be $8.7 billion by 2020 (Sumaila etal. 2012). Given the economic stakes, there is broad-based interest among researchers, government agencies, fishermen, tourism sectors, and the oil industry to consider how science will support natural resource damage assessment and restoration plans for GOM ecosystems. Petroleum hydrocarbons may injure fish through direct or indirect pathways, and via either acute or chronic effects (Peterson etal. 2003). These injuries may occur at organis-mal, population, or community levels, with symptoms that propagate or attenuate across these hierarchies (figure 1). Early life-history stages (e.g., embryo, larvae, juvenile) are often disproportionately susceptible to physiological stress-ors and have, therefore, been a primary focus of attention in previous spills. Indeed, embryos of pelagic species native to the GOM are sensitive to the toxic effects of spilled oil (Incardona et al. 2014). The direct oiling of eggs, embryos, or larvae in locations where surface slicks persisted or came ashore in the northern GOM could have killed animals through smothering of gas-and ion-exchange surfaces, ingestion of toxicants, or the loss of the epithelial mucus that protects fish from infections. As oil weathers, multiringed polycyclic aromatic hydrocarbons (PAHs) that accumulate in seawater can be toxic for fishes at even low concentrations (around 1part per billion). For instance, embryos of Pacific herring (Clupea pallasii) and pink salmon (Oncorhynchus gorbuscha) exposed to Exxon Valdez (EV) oil exhibited elevated genetic damage, greater incidence of morphological deformities, reduced hatch sizes, premature hatching, and increased mortality (Kocan et al. 1996, Carls et al. 1999). For species that deposit benthic eggs or feed demersally, these injuries may last several years, as partially weathered
[Show abstract][Hide abstract] ABSTRACT: Environmental salinity presents a key barrier to dispersal for most aquatic organisms, and adaptation to alternate osmotic environments likely enables species diversification. Little is known of the functional basis for derived tolerance to environmental salinity. We integrate comparative physiology and functional genomics to explore the mechanistic underpinnings of evolved variation in osmotic plasticity within and among two species of killifish; Fundulus majalis harbours the ancestral mainly salt-tolerant phenotype, whereas Fundulus heteroclitus harbours a derived physiology that retains extreme salt tolerance but with expanded osmotic plasticity towards the freshwater end of the osmotic continuum. Common-garden comparative hypo-osmotic challenge experiments show that F. heteroclitus is capable of remodelling gill epithelia more quickly and at more extreme osmotic challenge than F. majalis. We detect an unusual pattern of baseline transcriptome divergence, where neutral evolutionary processes appear to govern expression divergence within species, but patterns of divergence for these genes between species do not follow neutral expectations. During acclimation, genome expression profiling identifies mechanisms of acclimation-associated response that are conserved within the genus including regulation of paracellular permeability. In contrast, several responses vary among species including those putatively associated with cell volume regulation, and these same mechanisms are targets for adaptive physiological divergence along osmotic gradients within F. heteroclitus. As such, the genomic and physiological mechanisms that are associated with adaptive fine-tuning within species also contribute to macro-evolutionary divergence as species diversify across osmotic niches.
[Show abstract][Hide abstract] ABSTRACT: The Deepwater Horizon oil rig disaster resulted in crude oil contamination along the Gulf coast in sensitive estuaries. Toxicity from exposure to crude oil can affect populations of fish that live or breed in oiled habitats as seen following the Exxon Valdez oil spill. In an ongoing study of the effects of Deepwater Horizon crude oil on fish, Gulf killifish ( Fundulus grandis ) were collected from an oiled site (Grande Terre, LA) and two reference locations (coastal MS and AL) and monitored for measures of exposure to crude oil. Killifish collected from Grande Terre had divergent gene expression in the liver and gill tissue coincident with the arrival of contaminating oil and up-regulation of cytochrome P4501A (CYP1A) protein in gill, liver, intestine, and head kidney for over one year following peak landfall of oil (August 2011) compared to fish collected from reference sites. Furthermore, laboratory exposures of Gulf killifish embryos to field-collected sediments from Grande Terre and Barataria Bay, LA, also resulted in increased CYP1A and developmental abnormalities when exposed to sediments collected from oiled sites compared to exposure to sediments collected from a reference site. These data are predictive of population-level impacts in fish exposed to sediments from oiled locations along the Gulf of Mexico coast.
[Show abstract][Hide abstract] ABSTRACT: The killifish Fundulus heteroclitus is abundant in osmotically dynamic estuaries and it can quickly adjust to extremes in environmental salinity. We performed a comparative osmotic challenge experiment to track the transcriptomic and physiological responses to two salinities throughout a time course of acclimation, and to explore the genome regulatory mechanisms that enable extreme osmotic acclimation. One southern and one northern coastal population, known to differ in their tolerance to hypo-osmotic exposure, were used as our comparative model. Both populations could maintain osmotic homeostasis when transferred from 32 to 0.4 p.p.t., but diverged in their compensatory abilities when challenged down to 0.1 p.p.t., in parallel with divergent transformation of gill morphology. Genes involved in cell volume regulation, nucleosome maintenance, ion transport, energetics, mitochondrion function, transcriptional regulation and apoptosis showed population- and salinity-dependent patterns of expression during acclimation. Network analysis confirmed the role of cytokine and kinase signaling pathways in coordinating the genome regulatory response to osmotic challenge, and also posited the importance of signaling coordinated through the transcription factor HNF-4α. These genome responses support hypotheses of which regulatory mechanisms are particularly relevant for enabling extreme physiological flexibility.
[Show abstract][Hide abstract] ABSTRACT: The Gulf killifish (Fundulus grandis) is a euryhaline fish found in coastal marsh along the entire of Gulf of Mexico and southern Atlantic of coast of the United States. The objective of this study was to investigate the effects of salinity on embryogenesis in the Gulf killifish. Four recirculation systems at salinities of 0.4, 7, 15, and 30 g/L were maintained at a static temperature with flow-through trays, containing embryos (n = 39) placed in triplicate into each system. Throughout embryogenesis, the rate of development, ammonia and urea excretion, and heart rate were monitored. Percent hatch was recorded, and morphological parameters were measured for larvae at hatch. As salinity was increased, the rate of embryogenesis decreased. Salinity significantly affected percent hatch with an 80.0% ± 2.6% for 7 g/L and 39.1 ± 4.3, 45.4 ± 4.5, and 36.3% ± 12.0% for 0.4, 15, and 30 g/L, respectively. Salinity and stage of development significantly affected production of ammonia and urea. As salinity increased, the dominate metabolite end product changed from urea to ammonia. However, the 15 g/L salinity treatment had the two highest levels of urea recorded. Heart rate was unaffected by salinity but increased throughout embryogenesis and remained constant once embryos reached stages where hatching has been recorded. While mean total length was not affected by salinity, embryos incubated in 30 g/L produced larvae with significantly thicker body depth at hatch. The 0.4, 7, and 15 g/L salinity treatments all had similar mean hours to hatch. The 30 g/L treatment resulted in a significantly longer mean time to hatch and smaller body cavity area at hatch.
Fish Physiology and Biochemistry 01/2012; 38(4):1071-82. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The biological consequences of the Deepwater Horizon oil spill are unknown, especially for resident organisms. Here, we report results from a field study tracking the effects
of contaminating oil across space and time in resident killifish during the first 4 mo of the spill event. Remote sensing
and analytical chemistry identified exposures, which were linked to effects in fish characterized by genome expression and
associated gill immunohistochemistry, despite very low concentrations of hydrocarbons remaining in water and tissues. Divergence
in genome expression coincides with contaminating oil and is consistent with genome responses that are predictive of exposure
to hydrocarbon-like chemicals and indicative of physiological and reproductive impairment. Oil-contaminated waters are also
associated with aberrant protein expression in gill tissues of larval and adult fish. These data suggest that heavily weathered
crude oil from the spill imparts significant biological impacts in sensitive Louisiana marshes, some of which remain for over
2 mo following initial exposures.
Proceedings of the National Academy of Sciences 09/2011; · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gulf killifish (Fundulus grandis) are the most abundant vertebrate in coastal marsh ecological communities and are economically-important bait fishes. Large populations of killifish inhabit Gulf-exposed marsh habitats that are at high risk of contamination from oil spilled in the Gulf of Mexico; indeed much habitat was oiled following the Deepwater Horizon oil spill. For these reasons, these killifish are strategic models for assessing contaminating oil impacts on Gulf coast marshes. We have launched a project intended to characterize oil spill impacts on the coastal marsh by integrating genomic and physiological indicators of response to oil exposure in situ and under controlled exposure conditions. In field studies genome expression within livers of resident fish was tracked across space (contaminated and reference sites) and time (pre-oil, during oil, and after oil exposure). Genome expression was most distinct at our only field site out of six that was clearly impacted by oil, and at the peak of oil contamination documented by satellite imagery and analytical chemistry, showing a clear genomic footprint of oil exposure. This genomic response is similar to that observed following controlled PCB exposures to developing embryos, which caused developmental abnormalities and death.
American Fisheries Society 140th Annual Meeting; 09/2011
[Show abstract][Hide abstract] ABSTRACT: The gulf killifish, Fundulus grandis, is one of the most abundant and ecologically important fish inhabiting coastal marsh habitats of the Gulf of Mexico; a region severely contaminated with oil from the BP Deepwater Horizon oil spill. Unlike most fish species in these habitats, killifish have high home range fidelity, making them a useful model organism to study the site-specific effects of environmental contamination. We have initiated two separate projects aimed at characterizing the integrated effects of crude oil exposure in situ to gulf killifish. In one study, six populations ranging from Grande Terre, LA to Fort Morgan, AL were sampled pre-oil, and at two times post exposure to oil. This study involves a detailed integrated assessment of effects from the level of the whole animal to genomic-level effects, and includes detailed water chemistry analyses and satellite imagery to document the magnitude of exposure. The second study provides a detailed assessment of in situ effects on fish physiology in 6 reference and 6 heavily-oiled sites within Barataria Bay, Louisiana following the oil spill. Tissues from these fish are being analyzed for various indicators of oil exposure and effect, including the documentation of protein-level effects at the gills, intestines, livers, and kidneys. Results to date demonstrate severe histological damage coincident with dramatic up-regulation of cytochrome P450 1A (CYP 1A) protein expression in the gills and intestines of fish sampled from the most heavily-oiled sites. These results are consistent with previous studies describing the effects of polyaromatic hydrocarbon exposure in teleost fish, including killifish.
American Fisheries Society 140th Annual Meeting; 09/2011
[Show abstract][Hide abstract] ABSTRACT: Landfall of crude oil from The Deepwater Horizon oil spill has been most pronounced in coastal areas of Louisiana. Among the most affected areas is Barataria bay, where heavily oiled marshland is still common place. The Gulf killifish (Fundulus grandis) is one of the most abundant species in coastal Louisiana marshlands and have high home range fidelity making them ideal species for observation of site-specific differences in physiological response to exposure to crude and weathered oil. Seven reference sites and 7 oiled sites were chosen across Barataria Bay, where F. grandis were collected during July, August, November, and December of 2010. Select tissues were processed for immunohistochemical localization and degree of CYP1A1 expression using monoclonal antibody C10-7 as a biomarker of exposure to PAHs. Site specific differences in CYP1A expression were found between oiled and reference locations. The most pronounced differences were found in the intestine, gills, and head kidneys. These studies provide a critical foundation for future endeavors to monitor effects, and to follow remediation of the Barataria Bay and other affected areas in Louisiana. Presently, we are examining physiological differences in fish from these locations to examine effects of exposure to crude oil.
American Fisheries Society 140th Annual Meeting; 09/2011
[Show abstract][Hide abstract] ABSTRACT: The gulf killifish, Fundulus grandis, is one of the most abundant fish species in coastal marsh ecosystems of the northern Gulf of Mexico. Peak oiling of these marsh habitats during the summer of 2010 coincided with the most reproductively active period for this species, putting it at high risk of crude oil exposure during early development. Since F. grandis is non-migratory and has high home range fidelity, impacts during development may be predictive of longer-term population-level effects. To test the effects of oiled waters on killifish development, embryos fertilized in vitro were exposed throughout development to water collected from various sites along the northern Gulf of Mexico before and after oiling. Three different developmental stages were selected for comparison; 3 days post-fertilization (3 DPF), just after hatch (10 DPF), and as larvae (24 DPF). No alterations in development or morphological differences were observed in these fish despite a difference in CYP1A expression in the kidney, gills, liver, intestine, and muscles. These studies have provided a critical foundation for future endeavors to monitor fish health in affected areas. Ongoing efforts are focused on examining tissue and developmental stage-specific expression of proteins indicative of crude oil exposure and effect, including CYP1A, glutathione S-transferase, and other biomarkers of exposure and effect following exposure to hydrocarbons. Presently, we are conducting an ongoing comprehensive health assessment of early-life stage fish exposed to oiled water, both in vitro, and in situ to examine effects of exposure to crude oil.
American Fisheries Society 140th Annual Meeting; 09/2011
[Show abstract][Hide abstract] ABSTRACT: The larvae of unionid freshwater mussels (i.e., glochidia) undergo a parasitic stage requiring their attachment to the external epithelia of fish hosts, where they metamorphose into free-living juveniles. We describe the physiological effects in bluegill sunfish (Lepomis macrochirus) of infection with glochidia from the paper pondshell (Utterbackia imbecillis). Glochidia accumulation on bluegill increased dramatically at concentrations of 2000 glochidia liter(-1) and above, reaching a maximum attachment density of about 30 glochidia g(-1) fish at 4000 glochidia liter(-1). Plasma cortisol was the most sensitive indicator of biological effect to glochidial exposure, increasing significantly in hosts exposed to 2000 glochidia liter(-1) or greater. Glochidia were 31% more likely to undergo successful juvenile metamorphosis when attached to bluegill with elevated plasma cortisol, largely due to the enhanced survivorship of these larvae during the first 48 h after infection. We tested the hypothesis that glochidial attachment and juvenile metamorphosis were stimulated directly by plasma cortisol in fish hosts. Bluegill were given an intraperitoneal injection of cortisol, then infected with 1000 glochidia liter(-1) at 48 h after hormone supplementation. Cortisol-injected fish had a 42% increase in the number of attached glochidia g(-1) fish and a 28% increase in larval metamorphosis compared to sham-injected and control fish. We provide evidence that cortisol enhances glochidial metamorphosis on hosts by improving the retention of attached glochidia. This study gives insights into the influence of host physiology on glochidial attachment and juvenile mussel transformation.
[Show abstract][Hide abstract] ABSTRACT: The rate of acid-stimulated and phenamil-sensitive sodium (Na(+)) uptake was measured in three different cell lineages: pavement cells (PVC), total mitochondrion-rich (MR) cell populations, and peanut lectin agglutinin-negative mitochondrion-rich cells (PNA(-) MR) isolated from the rainbow trout gill epithelium. Despite the presence of basal levels of Na(+) uptake in PVC, this transport was not enhanced by acidification, nor was it inhibited by independent treatment with bafilomycin (i.e., a V-type H(+)-ATPase inhibitor), phenamil (i.e., a specific inhibitor of ENaC), or Ag (a specific inhibitor of active Na(+) transport in fish). In contrast, Na(+) uptake in PNA(-) MR cells was increased by ~220% above basal levels following acidification of near 0.4 pH units in the presence of 1.0 mM external Na(+). Acid-stimulated Na(+) transport was entirely inhibited by both phenamil and bafilomycin. Silver (Ag) and copper (Cu), which are known to interfere with active Na(+) transport in fish, were also responsible for inhibiting acid stimulated Na(+) uptake in PNA(-) MR cells, but by themselves had no effect on basal Na(+) transport. Thus, we demonstrate that Ag specifically prevented acid-stimulated Na(+) uptake in PNA(-) MR cells in a dose-dependent manner. We also demonstrate rapid (<1 min) and significant inhibition of carbonic anhydrase (CA) by Ag in PNA(-) MR cells, but not in PVC. These data lend further support to the idea of a PNA(-) MR cell type as the primary site for Na(+) uptake in the freshwater (FW) gill phenotype of rainbow trout. Moreover, these findings provide support for the importance of intracellular protons in regulating the movement of Na(+) across the apical surface of the fish gill.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 03/2011; 159(3):234-41. · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adaptive variation tends to emerge clinally along environmental gradients or discretely among habitats with limited connectivity. However, in Atlantic killifish (Fundulus heteroclitus), a population genetic discontinuity appears in the absence of obvious barriers to gene flow along parallel salinity clines and coincides with a physiologically stressful salinity. We show that populations resident on either side of this discontinuity differ in their abilities to compensate for osmotic shock and illustrate the physiological and functional genomic basis of population variation in hypoosmotic tolerance. A population native to a freshwater habitat, upstream of the genetic discontinuity, exhibits tolerance to extreme hypoosmotic challenge, whereas populations native to brackish or marine habitats downstream of the discontinuity lose osmotic homeostasis more severely and take longer to recover. Comparative transcriptomics reveals a core transcriptional response associated with acute and acclimatory responses to hypoosmotic shock and posits unique mechanisms that enable extreme osmotic tolerance. Of the genes that vary in expression among populations, those that are putatively involved in physiological acclimation are more likely to exhibit nonneutral patterns of divergence between freshwater and brackish populations. It is not the well-known effectors of osmotic acclimation, but rather the lesser-known immediate-early responses, that appear important in contributing to population differences.
Proceedings of the National Academy of Sciences 03/2011; 108(15):6193-8. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Increased atmospheric CO(2) concentrations are causing greater dissolution of CO(2) into seawater, and are ultimately responsible for today's ongoing ocean acidification. We manipulated seawater acidity by addition of HCl and by increasing CO(2) concentration and observed that two coastal harpacticoid copepods, Amphiascoides atopus and Schizopera knabeni were both more sensitive to increased acidity when generated by CO(2). The present study indicates that copepods living in environments more prone to hypercapnia, such as mudflats where S. knabeni lives, may be less sensitive to future acidification. Ocean acidification is also expected to alter the toxicity of waterborne metals by influencing their speciation in seawater. CO(2) enrichment did not affect the free-ion concentration of Cd but did increase the free-ion concentration of Cu. Antagonistic toxicities were observed between CO(2) with Cd, Cu and Cu free-ion in A. atopus. This interaction could be due to a competition for H(+) and metals for binding sites.
[Show abstract][Hide abstract] ABSTRACT: We have studied intracellular pH (pHi) recovery in isolated trout gill mitochondrion-rich (MR) cells following acidification by the NH4Cl pre-pulse technique. Within a mixed MR cell population, one cell type displayed Na+-independent pHi recovery while the other cell type lacked a Na+-independent pHi recovery. Cells displaying Na+ independent recovery exhibited a significantly higher buffering capacity compared to cells lacking Na+-independent pHi recovery. Cells displaying Na+ independent recovery were identified as PNA+ (peanut lectin agluttinin binding) MR cells while those unable to recover were identified as PNA− (non-peanut lectin agluttinin binding) MR cells. Therefore, recovery from acidification in the absence of Na+ provides a direct functional marker for PNA+ and PNA− MR cells. Re-addition of Na+ to acidified cells resulted in a transient pHi recovery in both cell types. This event was abolished by amiloride (500 µM) but it was insensitive to phenamil (50 µM). The phorbol ester PMA (1 µM) potentiated the Na+ induced pHi recovery suggesting that activation by PKC is required for continuous Na+/H+ exchanger activity in trout gill MR cells. This study is the first functional description of pHi recovery in lectin-identified trout gill MR cells and provides insight into a putative cellular signaling mechanism that may control pHi regulation in the gill epithelium.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology 02/2010; · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Evolutionary solutions to the physiological challenges of life in highly variable habitats can span the continuum from evolution of a cosmopolitan plastic phenotype to the evolution of locally adapted phenotypes. Killifish (Fundulus sp.) have evolved both highly plastic and locally adapted phenotypes within different selective contexts, providing a comparative system in which to explore the genomic underpinnings of physiological plasticity and adaptive variation. Importantly, extensive variation exists among populations and species for tolerance to a variety of stressors, and we exploit this variation in comparative studies to yield insights into the genomic basis of evolved phenotypic variation. Notably, species of Fundulus occupy the continuum of osmotic habitats from freshwater to marine and populations within Fundulus heteroclitus span far greater variation in pollution tolerance than across all species of fish. Here, we explore how transcriptome regulation underpins extreme physiological plasticity on osmotic shock and how genomic and transcriptomic variation is associated with locally evolved pollution tolerance. We show that F. heteroclitus quickly acclimate to extreme osmotic shock by mounting a dramatic rapid transcriptomic response including an early crisis control phase followed by a tissue remodeling phase involving many regulatory pathways. We also show that convergent evolution of locally adapted pollution tolerance involves complex patterns of gene expression and genome sequence variation, which is confounded with body-weight dependence for some genes. Similarly, exploiting the natural phenotypic variation associated with other established and emerging model organisms is likely to greatly accelerate the pace of discovery of the genomic basis of phenotypic variation.
The Journal of heredity 01/2010; 102(5):499-511. · 2.05 Impact Factor