Investigating the nexus of development, physiology and environment

OUR RESEARCH


Read about our research!

 

Research Themes and Experimental Approaches


 

Research in our NSF- and GoMRI-funded program focuses on the nexus of development, environment and physiology, its manifestation as phenotypic plasticity in both vertebrate and invertebrate animals. In particular, we are investigating the ontogeny of regulation of the physiological systems along the life continuum of eggs, embryos, larvae/fetuses and adults.Our experimental approach is broadly comparative by design. By contrasting and comparing regulatory mechanisms in a developmental series of a wide variety of animals, we can distinguish fundamental developmental processes from those processes that have evolved in the early developmental stages of only particular taxa. We are unabashedly opportunistic in using animals that, according to the Krogh principle (or some would say Bernard principle), help us answer our experimental questions. The earlier in development, the more similar are developing animals, and the more we can identify general principles of physiological development and phenotypic plasticity.


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Of special interest is the interplay between environment and development, how the environmental stressors - both natural and anthropogenic - shape emerging phenotype, and how the developing organism can exhibit "self-repair" at the tissue, organ and organismal levels. We typically raise populations of developing animals under challenging environmental conditions to learn if and how the ultimate phenotype is independent of, or linked to, environmental experiences earlier in development.

 

Typically, we chart the development of basic physiological processes such as the onset of heart beat, development of blood pressure and flow gill or lung ventilation, and osmoregulation. In some experiments, we then determine when and how the cardiovascular and respiratory systems come under neural and endocrine regulation, and how these regulatory processes may change with major developmental events such as hatching (birds, reptiles) or metamorphosis (fishes, amphibians).

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We follow up investigation of basic developmental morphology and further investigate developmental phenotypic plasticity by determining what factors can shape and influence the normal developmental trajectories for physiological regulatory mechanisms. Once the developmental timing of these events is known, we will determine the critical windows during development in which these systems are particularly susceptible to both natural and anthropogenic environmental perturbations of temperature, oxygen availability, acidity, toxicants, etc.

developmental trajectory

Our experimental approach is broadly comparative by design. By contrasting and comparing regulatory mechanisms in a developmental series of a wide variety of animals, we can distinguish fundamental developmental processes from those processes that have evolved in the early developmental stages of only particular taxa. In this context, our studies of developmental physiology merge with our lab's additional interests in the evolution of physiological processes.

epigenetics-diagram

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Our Animal Models


 

What is an animal model, when are they used, and what are their limitations? You might find this essay on animal models to be interesting reading on the subject.

The animals listed below are employed in various projects in our laboratory. Why so many different models in our lab, when most labs are "fly labs", "mouse labs", etc? We are interested in the onset of physiological regulation during early development. At these early stages, most of the species below are qualitatively indistinguishable, yet each offers some advantage - transparency, gigantism, life cycle time, etc. At the end of the day, we compare projects, and we can weave a tapestry that is representative of animal development, environment and physiology.

 

Current animal models

Avian Models


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  • Chicken
    (Gallus gallus domesticus)

    Serving as one of the main models for physiological development for decades, if not centuries, we are using the chicken embryo to map the ontogeny of cardiovascular, respiratory, and metabolic in chicken embryos under hypoxic and thermal challenge.

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  • Northern Bobwhite Quail
    (Colinus virginianus)

    Though the eggs of the quail are quite small, this species represents avian development "in the fast lane", hatching after just 21 days of development. In this regard, it makes for a useful comparison with chickens (21 day incubation) and emus (51 day incubation).

 

Fish Models


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  • Zebrafish
    (Danio rerio)

    A relative newcomer yet an incredibly popular model in developmental biology, the zebrafish has also proved very useful in developmental physiology studies. Among other advantages, this teleost fish native to streams in India, is a prolific breeder, producing hundreds of tiny, transparent eggs. Because the heart and circulation can be seen through the translucent body wall for the first 10 days after hatching, we can use optical methods can be used to measure cardiac output, red blood cell velocity, and blood vessel growth and diameter, to name a few. Of course, there is the matter of the embryos weighing only 1/10 mg at hatching, but we have long been on the lunatic fringe in terms of measuring physiological performance in vanishingly small animals...

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  • Blue Gourami
    (Trichogaster trichopterus)

    Very little is known about the developmental physiology of the blue gourami (there have been some papers on the respiratory and metabolic adult physiology), but it has great promise because of its ease of breeding in captivity, its rapid growth, and its obligatory air breathing habitat early in development.

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  • Mahi Mahi
    (Coryphaena hippurus)
    is a keystone pelagic fish species that inhabits the deeper waters in the Gulf of Mexico, often nearby oil drilling operations. They breed in open water during the summer months, producing hundreds of thousands of eggs each summer. As such, it is likely that these early life-stages were exposed to oil following the 2010 Deepwater Horizon oil spill. We are working to characterize the effects of crude oil on the cardiovascular system of early life-stage mahi. By doing so, we are creating a model to not only understand the effects of the Deepwater Horizon oil spill on mahi, but to also predict the potential effects of future spills on these and other pelagic fish populations.

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  • Redfish
    (Sciaenops ocellatus)
    live in two very different environments during their life cycle. During adulthood, they live in fairly deep waters in the Gulf, where oil drilling occurs, often congregating near oil rigs. In the summer, adult redfish travel from the Gulf to the shallow marshland that lines the Gulf coast where they breed. As they grow, redfish remain in the estuary for a number of years before they reach adulthood, when they generally move to deeper waters. Much of the Gulf shoreline was oiled following the spill in 2010 and it is likely that young redfish were exposed as oil made landfall and lingered along the shoreline. We are characterizing the effects of crude oil on the cardiovascular system of developing redfish, to understand the impact on inshore fish populations.

https://biology.unt.edu/sites/biology.unt.edu/files/users/mb0332/Blue%202.jpg
  • Gulf killifish
    (Fundulus grandis)
    is the most populous fish in the Gulf of Mexico estuaries and make up the majority of the vertebrate biomass. This may explain their widespread use as a baitfish along the Gulf coast, making them an economically important species. Gulf killifish spend their entire lives within meters of the grassy coastline. In addition to being an economically important fish species, these fish are a sentinel species in biological research. Interestingly, these fish are also non-migratory, remaining within the same area for their entire lives, which makes them an excellent site-specific indicator of the conditions that exist around their home range (i.e. pollution, low oxygen, etc.) and are being used as indicators of crude oil exposure from the 2010 Gulf oil spill. Using a considerable base of knowledge of killifish physiology, we are further characterizing the effects of crude oil on the cardiovascular system of developing Gulf killifish.

 

Invertebrate Models


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  • Planaria
    (Schmidtea mediterranea)

    Planaria are fresh-water, non-parasitic flatworms best known for their ability to regenerate entire individuals from small body fragments, due to a large population of pluripotent stem cells. Schmidtea mediterranea exits in both asexual and sexual strains. Their regenerative ability allows researchers to create clonal lines of both sexes from individual animals. S. mediterranea are widely used in studies of aging, development, regeneration, learning and memory, germ cell specification, stem cell behavior, and cancer.

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  • Water Flea
    (Daphnia magna)

    The water flea provides several advantages when looking at transgenerational, epigenetic transfer of phenotype.  The life span is short, and clonal populations are readily created and maintained.   Add to that the transparency of the adult, and the fact that each female has ~3 broods of offspring  make it a powerful model for investigating the "washout" of epigenetic physiological, metabolic and morphologic.

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  • Brine Shrimp
    (Artemia franciscana)

    The brine shrimp is an excellent model for studying the interactions of environment and phenotype during development.   Easily reared in small containers, and with a rapid generation time (8-12 days), the brine shrimp model allows high throughput of multiple environmental stressor X development stage experiments.

https://biology.unt.edu/sites/biology.unt.edu/files/users/mb0332/Zebrafish%20school.jpg
  • Brittle star
    (Ophiactis spp.)

    Ophiuroidea is the class of brittle stars belonging to the Echinodermata phylum. Most, if not all, brittle stars are capable of regenerating lost limbs. Several six-armed species (Ophiactis spp.) are capable of asexual reproduction by splitting in half through the central disc and regenerating all of the missing tissue for both halves resulting with two new individuals. (i.e. fissiparity). These same individuals are also capable of reproducing sexually via external fertilization and metamorphosis, which makes this a fascinating model for studying how different modes of reproduction are affected by the same environmental divergence.

 

Other Models We Have Used


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  • Nine-banded Armadillo
    (Dasypsu novemcinctus)

    You gotta love the armadillo! Apart from being the only mammal besides man to carry the bacterium causing leprosy, they also show the phenomenon of polyembryony. Shortly after fertilization, the blastula divides into buds that continue to develop as individuals, and each armadillo litter of four is invariably a clonal group with identical genetic make up. We use armadillos to look at between- and within-litter variation in physiological characteristics.

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  • Emu
    (Dromaius novaehollandiae)

    The emu lays eggs that typically weigh from 650-800 g, about 12-15X greater than a chicken egg. Fortunately, the embryo and all of the extra-embryonic structures are also scaled up by more than an order of magnitude. This makes possible surgical procedures that just can't be done in conventionally studies bird eggs (chicken, quail).

Bullfrog
  • Bullfrog
    (Rana catesbeiana)

    The bullfrog has long been a standard for developmental physiology, in part because of the large, easily available larvae (tadpoles). In fact, our physiological knowledge of development for the bullfrog rivals that of the chicken. Their wonderful transition from pure water breathers (initially skin, then skin + gills), to combined water and air breathers (skin + gills + lungs) make them an ideal subject for evo-devo studies.

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  • Coqui
    (Eleutherodactylus sp.)

    The genus Eleutherodactylus is the single largest vertebrate genus, and each of the >450 species is a direct developer. The pea-sized, transparent, terrestrial eggs hatch to reveal a perfectly formed miniature adult. Because the eggs are transparent, we can monitor cardiac function from first beat through "metamorphosis" within the egg to hatching with the adult morph.

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  • Various Species
    The eggs of many reptiles present wonderful opportunities for exploring how environment (specifically, the hydricenvironment) influences development. For example, by adjusting the water potential of the medium in which the eggs are incubated, the water content of the egg - and the blood volume of the embryo - can be manipulated. We have used these animals in the past to determine how the cardiovascular system's baroreceptors begin to function and reach their set-points.

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  • African Clawed Frog
    (Xenopus laevis)

    Xenopus is the amphibian equivalent of the chicken or the zebrafish with respect to being a prominent developmental model. The normal physiological ontogeny has been well characterized, and our studies now focus on how environmental challenge perturbs normal development, and how the animal in turn copes.

betta
  • Siamese Fighting Fish
    (Betta splendens)

    Selectively bred by fish enthusiasts around the world, the Siamese Fighting Fish is another air-breathing fish species.  The betta is easily bred in captivity and makes a great model for studying the development of air-breathing, particularly in comparison to our other fish model.

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  • Fruit Fly
    (Drosophila melanogaster)

    The fruit fly Drosophila melanogaster provides a complex metazoan that nonetheless has a short generation time. This makes it ideal for our studies of physiological and metabolic maternal effects, the non-genetic transmission of characters from parents to offspring.

 

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Our Methodologies and Expertise


 

Methodologies and techniques we employee in our laboratory include:

 

Collaborators


 

In addition to our lab's close collaboration with the other members of the Developmental Integrative Biology Group at UNT, we also have active, ongoing collaborations at numerous other research institutions: