Hartline Lab Research (overview)

(updated April 2, 2014)

Special areas of interest are:

Also of interest but with less current emphasis is neural integration in simple neural nets.

Research area 1:

Myelin Evolution

Myelin is a multilamellar ensheathment of axons found in vertebrates, oligochaetes, shrimp and copepods (e.g. Hartline and Colman 2007; Hartline 2008). Myelin speeds nerve impulse propagation ten-fold, decreases metabolic costs of neural activity more than 300-fold, and decreases space requirements of the nervous system. These features have clear selective advantage, and their benefits to performance are quantifiable. The increase in conduction speed significantly decreases reaction times to predatory attack, even in organisms as small as a copepod (Lenz et al 2000). Such advantages undoubtedly contribute to the fact that almost all vertebrates possess largely myelinated nervous systems (Zalc and Colman 2000). Why, then, among calanoid copepods, which are distributed widely and most successfully throughout the world's oceans, have non-myelinated forms been equally sucessful as myelinated ones? We are examining the distribution of myelinated vs non-myelinated species across various biomes and are relating this to the predation risk experienced by a taxon. It appears that high, chronic pedation risk from raptorial (pouncing) predators correlates with occurrence of myelinated species, whereas biomes in which predator risk is at least periodically relieved give non-myelinated taxa an opportunity to thrive (Lenz and Hartline, in preparation). This approach to understanding the ecology of copepod myelin is elucidating selective factors that might lead to the evolution of myelin in other organisms.

Myelin provides a promising opportunity for an integrated account of an innovation at many biological levels, linking changes in the genome to changes in proteins expressed to changes in cellular, tissue and organ organization and finally to whole organism behavior and ecology. Although vertebrate myelin has been the focus of much research, most (but not all!) such studies lack an evolutionary perspective and they almost universally ignore the possibilities provided by invertebrate myelin. Viewed in the broad context of innovation, myelin may provide a useful tool for evolutionary biology. The Lenz-Hartline group is working on several aspects of this broad picture, most recently (2014) extending to evolution of myelin in the malacostracan crustaceans, and welcome collaborations with other like-minded labs:

Characterization, distribution, development, evolution and ecological significance of copepod myelin.

Phylogenetic origin and distribution of malacostracan myelin.

Collaborative meetings and working groups initiated by a National Evolutionary Synthesis Center (NESCent) meeting September, 2007.


For selected publications from the lab in the area of invertebrate myelin click here

For general information on this topic, access our Invertebrate Myelin

pages.
Research Area 2:

Feeding Nemo

Copepod interactions with real predators


Photo from Wikipedia

This project is examining predator-prey interactions between larval clown fish and copepods. Much information about the ability of planktonic copepods (our primary research interest) to elude their numerous predators is being gained through studies of the neural responses of copepods to sensory stimuli and of the subsequent behavioral reactions. However, the acid test for our understanding of the copepod's side of this interaction is how well it applies in interactions with real predators. Among the many predators of marine are the various fishes that inhabit the worlds oceans, especially the larval stages of thiose fishes that are small enough to gain significant nutrition from individually-caught prey, yet large enough to capture and subdue them. To implement such a study, we are culturing both copepods and fish in the lab so their interactions can be studied at 3D spatial resolutions in the sub-millimeter range and temporal resolutions in the sub-millisecond range. To do this, we collaborate with Dr. Rudi Strickler of the University of Wisconsin, Milwaukee and Dr. Ed Buskey, of the University of Texas' Marine Sciences Institute in Port Aransas.


Photo from Wikipedia
using state-of-the-art high-speed inline digital holography, supported by the computing power of our research unit's Computer Network Support Facility BEOWULF cluster. We are examining diversity in escape strategies among Hawaiian copepod species, comparing it to diversity in nervous system structure-function, and ultimately expanding into comparisons other copepods and fish that use alternative predatory strategies.

Photo from Wikipedia

Research area 3:

Neuroecology of zooplankton sensory and motor systems

In collaboration with Dr. Petra Lenz, we are examining the relation between physiological and morphological properties of a zooplankter's nervous system (specifically mechano- and photoreceptively-triggered escape reactions and nervous system myelin [see below] in calanoid copepods) and the animal's behavior, ecology and evolution. The systems reflect unusual adaptations to pelagic life when compared to similar systems in benthic and nektonic forms. We have been finding that the antennae in certain copepod groups have mechanoreceptors that are exceptionally sensitive to water-borne disturbances compared to other aquatic invertebrates (Yen et al. 1992; Gassie et al. 1993). They have peak sensitivities to vibrations at frequencies well above those of other aquatic invertebrates. Behavioral studies are showing that sensitivities for triggering rapid escape reactions parallel those for receptor activation. The evidence suggests that one of the keys to the success of copepods as a group may be a very rapid mechanically-triggered activation of a swim motor pattern generator tuned to signals produced by predatory attack. We have discovered a correlation between the most rapid reactions and myelination of the copepod nervous system. While myelin is a rare occurrence in invertebrates, we have shown that nervous systems in more recently-evolved superfamilies of copepods are heavily myelinated, and that these animals react more rapidly to mechanical stimuli than do non-myelinated forms. The former groups seem better able to survive in environments with little protection from predators, emphasizing the links between ecology, evolution and the nervous system. Of particular recent interest have been mechanisms involved in predator-evasion behavior in calanoid copepods including(click red-balls with links for more details):

Behavioral and physiological detection of small hydrodynamic disturbances

Physiological and morphological characterization of mechanoreception in different developmental stages

Species and stage-specific escape reactions of free-swimming copepods to hydrodynamic and photic stimuli (collaboration with Dr. Edward Buskey, of the University of Texas at Austin and Dr. Rudi Strickler of the University of Wisconsin, Milwaukee)

For comparisons of motor performance among various animals species (including copepods), see our Animal Olympians page

Immunohistochemistry of identified neurons in the nervous system (collaboration with Dr. Andy Christie of Mt. Desert Island Biological lab).


For selected publications from the lab in the area of zooplankton sensory systems click here

For general information on this topic, access our web page Zooplankton Sensory Systems


Research area 4

Neuromolecules

This is an area of expanding interest. It includes immunohistochemical investigations in collaboration with Andy Christie into the organization of copepod nervous systems with respect to the distribution and projections of neurons expressing different neurotransmitters and neuromodulators (see Hartline & Christie, 2010, Sousa et al 2008 and Christie et al 2008). Most recently we have been participating in a project headed by Petra Lenz which now has a shotgun assembly of a Calanus finmarchicus transcriptome that includes a multiplicity of sequences for voltage-gated sodium channels, among other important neural molecules.

Research area 5 (inactive):

Integrative mechanisms in simple neural networks

In this largely dormant area of past work, we pursued a broad quantitative approach to the study of integration in neural networks, involving areas of quantitative neurophysiology, biophysics, pharmacology, computer science and mathematical modeling. It utilized simple invertebrate material to provide tractable model systems in which to evolve predictive theories of network operation. The overall goal was to be able to accurately account for the observed output of a network given any input. The approach was to make quantitative measurements of cellular and synaptic properties of individually reidentifiable neurons. The measurements were incorporated into physiologically accurate of the networks. Comparison between model predictions and physiological observations exposed gaps in our understanding, helpedetermine new directions for investigation and provided new insights into the design and functioning of the systems. This project is dormant owing to lack of funding, but we remain interested in low-budget activity in the area involving undergraduates or rotating graudate students, particularly in computational amd modeling investigations. For further details on this project, click here; for information on the computer programs used, click here

The particular system we used for studies on network mechanisms, the stomatogastric ganglion of decapod crustaceans, was also used as a model for how nervous systems generate repetitive coordinated motor patterns, such as those controlling walking, swimming, flying, breathing and heart beat in other animals. Some years ago we found special active cellular properties, that we termed "plateau potentials," which underlie production of rhythmic stomatogastric motor activity. Plateau properties have since been implicated in pattern production in a great variety of other organisms including mammals. We examined the biophysical basis of these plateau potentials and on their modulatory regulation by specific inputs from the central nervous system, as well as by hormones. In addition (in a collaboration with Kathy Graubard at Univ. of Washington) we investigated the role of spatial distribution of cellular mechanisms over branching neuritic trees and the involvement of non-spike synaptic interactions in producing coordinated motor patterns. Specific project areas included (click red-balls with links for more details):

Cellular properties that promote motor pattern generation,

Modulatory regulation of these properties,

"Non-spiking" synaptic interactions involved in motor pattern generation (collaboration with Dr. Katherine Graubard of the University of Washington).

Computational properties of cellular mechanisms distributed over branching dendritic trees (collaboration with Dr. Katherine Graubard of the University of Washington and Dr. Ann Castelfranco of PBRC)

Space-clamp errors in voltage clamp experiments on neurons with attached processes: their nature and correctability (collaboration with Dr. Ann Castelfranco).


For selected publications from the lab in the area of neural nets click here


References:

Hartline, D.k. and D.R. Colman (2007) "Rapid conduction and the evolution of giant axons and myelinated fibers" Curr. Biol. 17: R29-R35 PDF

Lenz, P.H., D.K. Hartline and A.D. Davis (2000) "The need for speed. I. Fast reactions and myelinated axons in copepods" J. Comp. Physiol. 186: 337-345 PDF

Zalc, B. and D.R. Colman (2000) "Origins of vertebrate success" Science 288(5464) 271-272


To view the story I give to the UH Zoology Department, click here.

Return to Hartline Home Page. Return to PBRC Home Page.