The three endothelin receptors in the killifish, Fundulus heteroclitus : Physiological and phylogenetic relationships
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The purpose of this study was to sequence and characterize the endothelin receptors (ETRs) from the gill of the killifish, Fundulus heteroclitus, where the ET signaling cascade is hypothesized to be involved in control of local blood flow and ion transport. In mammals there are two ETRs termed ETA and ETB. Interestingly, in non-mammalian vertebrates there are three ETRs: ETA, ETB1, and ETB2 (ETC in frogs). Using standard cloning and sequencing, we have sequenced the three ETRs from killifish gill cDNA. Our phylogenetic analysis supports previous findings that the three ETRs are produced by separate genes, and are not simply splice variants. To further characterize these receptors, tissue distribution and quantitative PCR mRNA analyses were performed. Given that animals from fishes to birds have three ETRs while mammals have only two, we hypothesize that mammals have lost the ETB2 gene. Supported by NSF Grants IBN-008942 and IOB-056273 to DHE and Sgima Xi GIAR to KAH.Keywords:
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Abstract High‐level, acute exposures to individual polycyclic aromatic hydrocarbons (PAHs) and complex PAH mixtures result in cardiac abnormalities in developing fish embryos. Whereas acute PAH exposures can be developmentally lethal, little is known about the later life consequences of early life, lower level PAH exposures in survivors. A population of PAH‐adapted Fundulus heteroclitus from the PAH‐contaminated Superfund site, Atlantic Wood Industries, Elizabeth River, Portsmouth, Virginia, United States, is highly resistant to acute PAH cardiac teratogenicity. We sought to determine and characterize long‐term swimming performance and cardiac histological alterations of a subteratogenic PAH mixture exposure in both reference killifish and PAH‐adapted Atlantic Wood killifish embryos. Killifish from a relatively uncontaminated reference site, King's Creek, Virginia, United States, and Atlantic Wood killifish were treated with dilutions of Elizabeth River sediment extract at 24 h post fertilization (hpf). Two proven subteratogenic dilutions, 0.1 and 1.0% Elizabeth River sediment extract (total PAH 5.04 and 50.4 µg/L, respectively), were used for embryo exposures. Then, at 5‐mo post hatching, killifish were subjected to a swim performance test. A separate subset of these individuals was processed for cardiac histological analysis. Unexposed King's Creek killifish significantly outperformed the unexposed Atlantic Wood killifish in swimming performance as measured by Ucrit (i.e., critical swimming speed). However, King's Creek killifish exposed to Elizabeth River sediment extract (both 0.1 and 1.0%) showed significant declines in Ucrit. Histological analysis revealed the presence of blood in the pericardium of King's Creek killifish. Although Atlantic Wood killifish showed baseline performance deficits relative to King's Creek killifish, their pericardial cavities were nearly free of blood and atrial and ventricular alterations. These findings may explain, in part, the diminished swimming performance of King's Creek fish. Environ Toxicol Chem 2017;36:3246–3253. © 2017 SETAC
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Populations of the common killifish Fundulus heteroclitus are found along a latitudinal temperature gradient in habitats with high thermal variability. The objectives of this study were to assess the effects of temperature and population of origin on killifish swimming performance (assessed as critical swimming speed, Ucrit). Acclimated fish from northern and southern killifish populations demonstrated a wide zone (from 7° to 33°C) over which Ucrit showed little change with temperature, with performance declining significantly only at lower temperatures. Although we observed significant differences in swimming performance between a northern and a southern population of killifish in one experiment, with northern fish having an ∼1.5‐fold‐greater Ucrit than southern fish across all acclimation temperatures, we were unable to replicate this finding in other populations or collection years, and performance was consistently high across all populations and at both low (7°C) and high (23°C) acclimation temperatures. The poor swimming performance of southern killifish from a single collection year was correlated with low muscle [glycogen] rather than with other indicators of fuel stores or body condition. Killifish acclimated to 18°C and acutely challenged at temperatures of 5°, 18°, 25°, or 34°C showed modest thermal sensitivity of Ucrit between 18° and 34°C, with performance declining substantially at 5°C. Thus, much of the zone of relative thermal insensitivity of swimming performance is intrinsic in this species rather than acquired as a result of acclimation. These data suggest that killifish are broadly tolerant of changing temperatures, whether acute or chronic, and demonstrate little evidence of local adaptation in endurance swimming performance in populations from different thermal habitats.
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