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Midshipman Fish
Porichthys notatus |
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The Midshipman Fish:
The midshipman fish is found along the west of the US, from Magdalena Bay, CA to Alaska. Consisting of eight different pacific species, the midshipman name is derived from the pattern of photophores on their body. They are primarily found in moderately deep water (50-300 m), except during the breeding months of early May to early August.
During the breeding season, the midshipman migrate from the deep waters to the intertidal zones to mate. The type I males produce a courtship hum that is used to attract females to the nest. The Type I males are the parental caregivers, while the females are only in the hypoxic intertidal zone for one 24 hour mating period. The smallest morph, the type II males, are satellite or sneak spawners, where they attempt to steal fertilizations from Type I males by shooting sperm from a distance.
A suite of neural, physiological, behavioral, and endocrinological differences describe the three morphs. Importantly, The Type I males have enlarged sonic muscles (used for humming) and the Type II’s have larger testes. |
| Reproductive Behavior |
The reproductive behaviors of the midshipman utilize an acoustic pathway, for attenuating and localizing the type I male hum, and a vocal pathway, to produce the hum. The descending and ascending pathways for both vocal and acoustic communication have been studied and mapped. This important tool provides a great deal of functional relevance for studies investigating the expression and action of steroid hormones on physiology and behavior.
The alternative reproductive tactics employed by the midshipman fish (acoustic for females, acoustic/vocal for type I males, and satellite spawning for type II males) represent clear divergence in behavioral and physiological demands. |
| Cornell University - NBB |
University of Denver - Biology, Psychology, Chemistry |
| Link to my design for an Interactive GUI of a Neurodegeneration Disease Tool |
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Midshipman studies:
(My thesis work in the bass lab)
Absolute Quantitative Real-Time PCR (qPCR)
1) Glucocorticoid Receptor (GR):
Breeding Season Expression
-All Morphs
-Type I Male
-Type II Male
-Female
Data shown is normalized value using Beta Actin as a control.
Results: GR expression shows a central focus of GR regulation for the Type II sneaker-males and a peripheral focus for the dominant Type I male. Females show no difference among tissues. |
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Dorsal view of the midshipman CNS. The midhsipman brain contains vocal and acoustic nuclei important for acoustic courtship in the areas noted. The vocal pacemaker is important for final synchronization of the CNS signal to peripheral targets.
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Descending vocal-acoustic pathway: The diagram indicates which nuclei in the CNS are involved in both vocal and auditory behaviors. A common pathway for vertebrate reproductive behavior, in this case vocalization utilizing motor circuits, is from the pre-optic area-anterior hypothalamus, to areas in the midbrain, to areas located near hindbrain/spinal junctions. (As is the case in this diagram)
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In a physiological preparation, where the brain is left in tact but the fish paralyzed, fictive vocalization can be initiated from vocal known vocal nuclei. These areas can be stimulated and the fictive response, indicative of natural vocalization, can be measured, recorded and visualized. This response is subject to modulation by steroid hormones (secreted chemicals synthesized from cholesterol). The diagram above indicates the specific effect that was shown to produced by different steroids. The modulation is rapid, within 5 minutes, and can last up to 120 minutes. Cortisol is one such sterois hormone. |
Tissues assayed were: Liver (L), forebrain (F), midbrain (M), hindbrain (H), gonad (G), sonic (vocal) muscle (SM)..
2) 11 Beta Hydroxysteroid Dehydrogenase (11B HSD):
Breeding Season Expression
-All Morphs
-Type I Male
-Type II Male
-Female
Results: 11B HSD expression coincides with the central and peripheral focus between the males and shows expression in female sonic muscle.
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-->Link to Morph-Specific Behaviors
-->Video of Mating |
Individual demands of behavioral and physiological processes can vary. The ability of an indiivdual to cope with these demands under different situations is in lagre part under the influence of the stress-response (corticosteroid hormones and their receptors). Such behavioral and physiological capability may be determined at the genetic level. In most vertebrate models, stress-response stimulation repies upon novel stressors to investigate individual responses. The midhsipman fish represent a natural model of individual variation (both intra- and inter-sexual) in both behavioral and physiological demands. The role of GR in midhsipman behavior and physiology may provide insights into theraputic treatments for human disease states.
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Stress Response: The stress response is an intricate homeostatic process that serves to regulate many physiological and behavioral parameters. Left is a general diagram of the Hypothamus-Pituitary-Adrenal Axis. Middle is a specific diagram of peripheral (outside CNS) stress Response. Right is a neuroednocrinolgical diagram that shows hoe the peripheral responses of the axis reach central components of the nervous system.
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Evolutionary comparisons of vertebrate glucocorticoid receptors: |
An alignment of teleost and mammal GRs show a remarkable amount of conservation in some areas defined as cononical receptor domains. These domains, typical of steroid hormone receptors, are responsible for the intiation of up/down-regulation of genes responsive to GRs. My project highlights the domain referred to the Ligand Binding Domain, or E/F domain. The LBD is the domain with the most specie to specie conservation and is the first site of action for intitiation of glucocorticoid induced gene regulatioon. Slight variations in domains such as the LBD, can result in GR dysfunction. This dysfunction can cause a myriad changes in a number of cell type (both central and peripheral stress response tissues). Any variation insuch a conserved domain can be targeted as a first line of investiagtion for dysfunction of stress-related regulation (GR-regulation) of both physiology and behavior. These changes in stress-related gene regulation and cellular dysfunction may prove to be fundamental parts of the onset, progression, and pathology of many human disease states.
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CNS mRNA expression of GR:
Preliminary In-situ hybridization labeling of GR in the brain of a Type I male. Blue areas express GR and red areas do not. The areas identified have benn shown to be important nuclei for vocal-acoustic communication. ISH
Conclusions: The stress response is the mechanism of gneomic communication between the envuironment and behavioral/physiological needs. Depending on behavioral state, major components of the stress response (GR, 11B HSD) and androgen-dependent modulation (11B HSD) are regulated individually. These differences in regulation influence the overall hormonal environment of the animal and their ability to interact with the environemnt, specifically during reproductive behavior. Thus, an animals behvaioral state is supported by an ability to react and adapt to stressors from the environemnt. |
