Hartline Lab Research
(updated September, 2022)
Special areas of interest are:
Copepod genes and gene expression
In collaboration with Drs. Petra Lenz, Ann Castelfranco and Vittoria Roncalli (Stazione Zoologica Anton Dohrn, Naples), we are examining gene expression in copepods, primarily calanoids from the Gulf of Alaska and environs. We use bioinformatic and statistical approaches (including AI-facilitated tools) to study expression changes at different stages of the copepod's live cycle, different locations (bays, near-shore, off-shore) and different years (hot "blob" years, cooler "normal" years) with an eye to predcting future population shifts under global climate change.
This figure shows the output from a tool borrowed from AI work ("t-distributed stochastic neighbor embedding") to help visualize expression-profile differences in genes associated with stress experienced by copepods (Neocalanus flemingeri) collected from different locations in the Gulf of Alaska (GAK) and a connecting bay (Prince William Sound, PWS). Each point represents the overall expression of 4027 genes of a single individual. The fact that the profiles fall into three clusters (circled) corresponding to three distinct ecological regions of the area suggests that the stress levels and physiological reactions thereto differ significantly (note one exception). This approach is helping us make sense out of the responses of thousands of genes to various environmental and life-history factors (figure from Cieslak et al. 2020).
This is an area of expanding interest. Most recently it has applied bioinformatic approaches to identifying canddates for novel proteins from copepod transcriptomes, with special attention to those molecules that have appeared to arise along side the invention of myelin. This is part of a project headed by Dr. Petra Lenz which now has de novo shotgun assemblies of transcriptomes for 8 species of calanoid copeods (see e.g. Lenz et al 2021), which include a multiplicity of novel sequences for voltage-gated sodium channels, among other important neural molecules. Our research in this area has also included immunohistochemical investigations 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).
Inactive research areas
(Interest continues in these areas, but active research is currently directed to the areas described above)
Inactive research area:
Neuroecology of zooplankton sensory and motor systems
In collaboration with Dr. Petra Lenz, we examined the relation between physiological and morphological properties of a zooplankter's nervous system and the animal's behavior, ecology and evolution. The systems reflect unusual adaptations to both pelagic and strongly seasonal life when compared with similar systems in benthic, nektonic and warm-water forms. We have shown that the antennae in certain copepod groups have mechanoreceptors that are exceptionally sensitive to water-borne disturbances compared with other aquatic invertebrates (Yen et al. 1992; Gassie et al. 1993; Takagi and Hartline 2018). They have peak sensitivities to vibrations at frequencies well above those of other aquatic invertebrates. Behavioral studies have shown 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 among 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 amyelinate 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 (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
For selected publications from the lab in the area of zooplankton sensory systems
For general information on this topic, access our web page Zooplankton Sensory Systems
Inactive research area:
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 examined 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 has worked on several aspects of this broad picture, extending it to evolution of myelin in the malacostracan crustaceans:
Characterization, distribution, development, evolution and ecological significance of copepod myelin.
Phylogenetic origin and distribution of malacostracan myelin.
For selected publications from the lab in the area of invertebrate myelin
For general information on this topic, access our Invertebrate Myelin pages.
Inactive research Area:
Copepod interactions with real predators
Photo from Wikipedia
Photo from Wikipedia
This project examined 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 cultured both copepods and fish in the lab so their interactions could 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
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
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.
Inactive research area:
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,
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
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 material given to the UH Zoology Department,
Return to Hartline Home Page.
Return to PBRC Home Page.