The functional morphology of the intermandibulo-cervical envelope of the American alligator (Alligator mississippiensis)

Alligators appear to swallow prey items that are large relative to their head size. Therefore, the intermandibulo-cervical envelope (i.e., the skin, Fascia superficialis, and constrictor musculature) was expected to be expandable. The three main layers of the intermandibulo-cervical envelope expand and recoil in tandem, but through different mechanisms. In the skin, which consists of hard-cornified scales and soft-cornified interscale skin segments, only the latter are expandable. Therefore, the width and orientation of the interscale skin segments determine the extent and direction of expansion of the skin. Whereas the intermandibular skin region is very expandable and enables the manipulation and crushing of large prey items in the mouth cavity, the gular and cervical skin regions can expand longitudinally, but have very limited circumferential expansibility. Elastic fibers in the dermis and Fascia superficialis provide the resilience needed to return the skin to its resting condition. The trilaminate Fascia superficialis expands by changing the orientation of its helically arranged collagen fibers. The three main skin regions, which are also characterized by particular scale and interscale skin patterns, are in congruence with the three parts of the underlying constrictor musculature. The expansibility of the constrictor muscles is determined by their proportion of muscle length to tendon length, because muscle fibers can lengthen passively, whereas collagenous tendon fibers resist lengthening. The expansibility of the constrictor muscles diminishes from rostral to caudal. Whereas the longitudinal expansibility of the intermandibulo-cervical envelope allows lateral and dorso-ventral movements of the head and neck, the limited circumferential expansibility of the gular and cervical regions constrains the size of prey items that can pass through the throat and matches the narrow isthmus of the thoracic inlet. Hence, the functional-morphological data of the intermandibulo-cervical envelope require a reinterpretation of feeding mechanics and prey choice of alligators

The effects of natural and anthropogenic stressors on the stress response and tissue-level response in teleost fish

Analysis of integrative physiological responses is a valuable approach to studying the biological impacts of natural and anthropogenic stressors in biota. By measuring fluctuations in multiple physiological characteristics, we are able to predict the impact that exogenous stressors may have on organismal health. Laboratory studies are useful in studying the effects of a single or multiple stressor interactions in a controlled environment, although field-based studies allow for the understanding of how fish are affected in situ, where multiple natural and anthropogenic stressors exist. Using laboratory and field-based experimental design, physiological indices of fish health were measured in fish exposed to natural and anthropogenic stressors in two unique incidences. First, controlled laboratory-based studies were performed where fish were exposed to larval freshwater mussels, a natural stressor found in North American freshwater environments. Unionid freshwater mussel larvae, called glochidia, must attach to a host fish in order to metamorphose into their juvenile state. This obligate stage in the unionid freshwater mussel life-cycle was found to cause a stress response in fish infected at high concentrations, where elevated cortisol in stressed fish was found to be coincident with an increase in glochidia metamorphosis to the juvenile stage. Second, both laboratory and field studies were conducted to understand the effects of the Deepwater Horizon oil spill on populations of Gulf killifish (Fundulus grandis) in oil-impacted areas in Louisiana, compared to reference sites in Louisiana, Mississippi, and Alabama. We show evidence of exposure to crude oil coincident with contamination from the Deepwater horizon oil spill in field-collected fish collected in 2010 and 2011 from oil-impacted sites, which had divergent gene and protein expression patterns compared to fish from unoiled locations. Further, controlled laboratory exposures of Gulf killifish embryos to field-collected sediments from oiled locations revealed that fish exposed to heavily oiled sediments as embryos had reduced cardiovascular defects, delayed hatching, reduced overall hatching success, pericardial edema, and were smaller at hatch. Together, these data suggest that fish were exposed to toxins in crude oil for two successive breading seasons, indicating, that contaminating oil from the Deepwater Horizon oil spill impacts organismal fitness, which may be predictive of long-term effects on Gulf killifish populations, and other biota that inhabit these areas, and also highlights the utility of combining laboratory and field-based techniques to predict the effects of natural and anthropogenic stressors on fish

Influence of cortisol on the attachment and metamorphosis of larval Utterbackia imbecillis on bluegill sunfish (Lepomis macrochirus)

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. © 2011 Marine Biological Laborat006Fry

Biomarkers of Aryl-hydrocarbon Receptor Activity in Gulf Killifish (Fundulus grandis) From Northern Gulf of Mexico Marshes Following the Deepwater Horizon Oil Spill

© 2017, Springer Science+Business Media New York. Following the Deepwater Horizon oil spill, shorelines throughout the Barataria Basin of the northern Gulf of Mexico in Louisiana were heavily oiled for months with Macondo-252 oil, potentially impacting estuarine species. The Gulf killifish (Fundulus grandis) has been identified as a sentinel species for the study of site-specific effects of crude oil contamination on biological function. In November and December 2010, 4–5 months after the Macondo well was plugged and new oil was no longer spilling into the Gulf waters, Gulf killifish were collected across the Barataria Basin from 14 sites with varying degrees of oiling. Fish collected from oiled sites exhibited biological indications of exposure to oil, including increase in cytochrome P4501A (CYP1A) mRNA transcript and protein abundances in liver tissues. Immunohistochemistry revealed increases in gill, head kidney, and intestinal CYP1A protein at heavily oiled sites. Intestinal CYP1A protein was a sensitive indicator of exposure, indicating that intestinal tissue plays a key role in biotransformation of AHR ligands and that ingestion is a probable route of exposure, warranting additional consideration in future studies

Multitissue molecular, genomic, and developmental effects of the deepwater horizon oil spill on resident Gulf killifish (Fundulus grandis)

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. © 2013 American Chemical Society

Deepwater Horizon Oil Spill as a Case Study for Interdisciplinary Cooperation within Developmental Biology, Environmental Sciences and Physiology

This article makes the argument for interdisciplinary teams that bring together scientists with different specialties as an efficient way--and perhaps the only way--to unravel highly complex biological effects of marine oil spills