The 36th Annual Meeting of the J.B. Johnston Clubfor Evolutionary Neuroscience and the 28th AnnualKarger Workshop in Evolutionary Neuroscience.
The 2016 meetings of the J.B. Johnston Club for Evolutionary Neuroscience and Karger Workshop in Evolutionary Neuroscience will be held immediately before the annual meeting of the Society for Neuroscience on Thursday, November 10 (the Karger Workshop), and Friday, November 11 (the regular JBJC meeting). Both meetings will take place at the Horton Grand Hotel, San Diego, CA, USA.
Neurotransmitter receptor expression differences between innovative and conservative sister species of Barbados finches
Audet J-N1, Lefebvre L1, Kayello L1, Ducatez S1, O'Connell LA2, Jarvis ED3
1Department of Biology, McGill University, Montréal, Québec, Canada
2Center for Systems Biology, Harvard University, Cambridge, MA, USA
3Department of Neurobiology, Duke University, Durham, NC, USA
Differences in innovativeness and problem-solving in birds are associated with differences in the size of the brain and of pallial areas like the mesopallium and nidopallium. Beyond these volumetric differences, however, little is known about the neuronal processes that lead to divergence in the cognitive abilities of birds. Our approach involves three steps: finding sister species with similar ecologies and social systems, but strong divergence in opportunism and innovativeness in the wild; testing for learning, problem-solving and temperament differences between these species on wild-caught individuals in aviaries; characterizing differences in neurotransmitter receptors between the species using a complement of molecular techniques that includes RNA-Seq and in situ hybridization of candidate genes.
Within the Thraupidae family to which Darwin's finches belong, the innovative bullfinch Loxigilla barbadensis and the conservative grassquit Tiaris bicolor are sister species that show intense differences in opportunism in the field in Barbados. Captive grassquits fail the extractive foraging problems that bullfinches easily solve, but the two species show similar levels of discrimination and reversal learning. RNA-Seq reveals differences in glutamate and dopamine receptors that are confirmed by in situ hybridization. Expression profiles show differences in favor of the bullfinch over the entire associative pallium, and more specifically in the caudolateral nidopallium (NCL), which is thought to be the equivalent of the mammalian prefrontal cortex.
Of Humboldt, Horses, and Leaping Electric Eels – How Eels Turn Up the Volume
Catania KC
Department of Biological Sciences,Vanderbilt University,Nashville, TN, USA
In March of 1800 Alexander von Humboldt observed fisherman collecting electric eels by “Fishing with Horses”. The fisherman herded horses into a pool containing eels, and the result was a legendary spectacle. According to Humboldt, the eels emerged from the mud and attacked the horses while the fisherman prevented their escape from the pool. Although 2 horses died, eventually the eels were exhausted and could be safely collected. Although this story is famous, some have doubted its accuracy (including, until recently, this author). Why would electric eels attack large animals? I will describe a newly discovered defensive behavior by electric eels, during which they leap from the water to directly shock threatening conductors. The behavior allows eels to deliver nearly all of their electrical power to a threat, and provides a formidable defense from potential terrestrial predators.
Questioning the Assumptions of Scaling Brain Size for Body Size
Day L
Department of Biology,University of Mississippi,University, MS, USA
In studies of comparative neuroanatomy, it has become standard to correct brain size, or brain region size, for body size. In order to compare brain capacity between species of vastly different sizes, one must find some way to appropriately account for allometry and put all species on the same scale. In the early 70’s, Harry Jerison and others proposed scaling methods to adjust brain size for body size. Since this time, the method to most accurately scale brain size for body size has been the subject of much debate. Which scaling method is currently most accepted appears to be related to both zeitgeist and scientific progress with arguments being principally statistical rather than theoretical. Such methodological debates have steered us away from the fundamental questions we need to ask, what exactly are we adjusting when we adjust brain size for body size and should such adjustments be general practice. The logic of adjusting brain size for body size relies on several implicit assumptions. The idea behind adjusting brain size for body size is that body size scales with portions of brain related to body control, with larger species having more brain volume devoted to control of their larger bodies than smaller species. Thus, by adjusting brain size for body size we are examining differences in the portion of the brains that underlie cognitive functions and other important functions while eliminating scaled regions related to body control. Whether adjusting brain size for body size actually partials out the appropriate amount of brain to adjust for the portion needed to execute body control appears to be untested. Furthermore, when comparing brain sizes across species, are we really interested in comparing only those parts of the brain that do not relate to body control? When a study is focused on strongly motoric behaviors, do we want to remove parts of the brain that would scale with control of the body? When tool use, courtship display, or feeding behaviors are our focus, are we excluding from our study exactly that part of the brain that is of comparative interest when we adjust brain size for body size? By acknowledging the assumptions implicit in adjusting brain size for body size, we can begin to question whether this adjustment is actually accomplishing the intended function of allowing for accurate comparisons of neural capacities across species.
The hypertrophied pallium in squirrelfish: a model for a “fishy” visuomotor “cortex”
Demski LS
Pritzker Marine Biology Center, New College of Florida, Sarasota, FL, USA
Squirrelfish are corpuscular/nocturnal tropical reef teleosts known for their exceptionally large eyes. At dusk the fish dart and circle over the open reef snapping at small (mostly invisible to me) planktonic organisms. Neural correlates to the behavior include “hypertrophied”: optic nerves; tectum including a massive torus longitudinalis [TL]which is involved in both dimming detection and processing collateral discharges related to saccadic eye movements; dorsal telencephalon which fuses across the midline (pallial expansions of the dorsal part of area dorsalis pars lateralis [Dld] and the adjacent area dorsalis pars centralis [Dcd]; see details below); and a large bean-shaped diencephalic nucleus (n. prethalamicus [nPTh]). Dcd projects to several layers of the ipsilateral tectum that overlap processes of different cells that respectively: receive retinal input; form a neural loop with the TL; project to the lateral region of large cells in nPTh; and project to the lower brainstem. Dcd also projects to the medial small cells of nPTh and a nucleus paracommissuralis [nPC] which sends fibers to the TL and the corpus of the cerebellum [CC]. The lateral TL also projects to the CC. Cells in the lateral nPth project to the Dld via the lateral forebrain bundle [LFB]. The Dld cells innervate the sub-adjacent Dcd cells, thus completing a loop between Dld and the tectum. Additionally, in the nPTh medial cells connect with the lateral cells and a plexiform arrangement between them receives input from the contralateral CC. The situation could mediate Dcd feedback to Dld, CC input to Dld and/or CC modulation of the Dcd feedback. It might also complete Dcd loops with the cerebellum via the tectal-TL loop (see above) and nPC connections to CC (both direct and indirect projections via lateral TL). Dld has both vertical and horizontal cellular stratification and responds to light flashes with evoked unit responses. The cells innervate Dcd with branching-beaded axons that fan out over many interlocking spiny processes of the large Dcd cells. The Dld–tectal loop appears topographically organized. “Unique” bridge [BC] cells extend small dendrites and branched axonal-like processes in Dld. Thick “dendritic” trunks enter Dcd and narrow to branches with brush-like processes. The BCs could provide a short feedback system by sampling Dld input to Dcd and modulating Dld activity through the axon-like processes or perhaps act as comparators sampling input to Dld (via small dendrites) and Dld output to Dcd (via the thick process system). Dld-Dcd appears cortex-like; it processes information from the tectum and most likely the CC/TL as well. The area has a powerful input to the tectum that could modulate processing of: retinal input (demonstrated in catfish); TL functioning; and probably tectobulbar output. The latter could potentially mediate a variety of sensorimotor functions. The Dld-Dcd pallial region likewise has pathways for control of CC function (demonstrated in catfish).
A doubling of eye size and massive increase in visual range enabled complex visually guided behaviors in the first terrestrial vertebrates
MacIverMA1,Schmitz L2
1Northwestern University, Evanston, IL, USA
2Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA, USA
Evolutionary transitions between aquatic and terrestrial habitats pose one of the most physically challenging events in the history of life. Vision in water and in air is fundamentally different, yet the evolutionary and ecological consequences of this for the emergence of tetrapods have seen little exploration. Through measurements of fossilized eye sockets in early tetrapods (N=59 taxa), and computational modeling of their aquatic and terrestrial visual ecology, we show that the visual range of the first land vertebrates is likely to have increased by at least a 100 times over their aquatic ancestors. This dramatic change was initiated by a dorsalization of orbits in aquatic tetrapods and fully unfolded with increased terrestrial activity, primarily due to the higher transparency of air over water. However, an additional increment in range occurred through a doubling of eye size. Modeling of trait evolution with time-calibrated phylogenies and reversible-jump Bayesian methods suggests that the observed pattern is best explained by a double-peak Ornstein-Uhlenbeck process, with a selective regime shift favoring large eyes occurring near the origin of digited tetrapods (fingers and toes present). This is a surprising development given the great increase in range that occurred simply from moving from water to air, and the metabolic costliness of eyes. We therefore suggest that the doubling of eye size is likely due to selection for higher acuity rather than an increase in visual range, but we cannot rule out that the eye size increase is driven by the benefits of higher light sensitivity to support a crepuscular or nocturnal lifestyle. Enhanced visual acuity and range provide several fitness benefits and can afford ethological complexity. We have shown in other work that the proportion of an animal’s reaction time to the time to collision to an ethologically relevant stimulus is an important determinant of the complexity of the resulting behavior. When the proportion is near unity, ie., time to collision is similar to the reaction time (for example, when a predator is sensed only a few body lengths ahead due to turbid water), then only stereotyped rapid responses are possible. When reaction time is a small proportion of the time to collision, such as during gradual approaches from a distance, response variability increases. We propose that the great increase in range and acuity that aerial vision generated in the digited tetrapods afforded the evolution of more complex visually-guided behavior, since the time to collision to behaviorally relevant targets underwent a large increase.
How many degrees of freedom does a cortex need? The implications of a simple universal theory for cortical morphology
Mota B1, Herculano-Houzel S2
1Physics Institute, UFRJ, Centro de Tecnologia, Rio de Janeiro, Brazil
2Comparative Neuroanatomy Lab, UFRJ, CCS, Rio de Janeiro, Brazil
The mammalian cerebral cortex is probably the most complex, and certainly the most adaptable, structure ever described by science. At first glance, any attempt to describe it, or significant features thereof, from first principles, would seem doomed to failure. And yet, its fundamental building blocks are largely conserved across species over a wide range of brain sizes, while its development is controlled by at most a few thousand genes, carrying some paltry kilobits of information. Morphologically, there seems to be a clear distinction between (typically larger) gyrified cortices, on one hand, and (smaller) lissencephalic ones on the other, and the relative scaling of cortical substructures varies considerably and non-systematically across species.
Recently, however, we have shown that a simple model in which folding is the consequence of the dynamics of white matter axonal elongation, constrained by the self-avoiding nature of the cortical surface, is quite successful in predicting the scaling between cortical average thickness, exposed and total areas for a data set of over 60 species. Remarkably, this relation remains valid for both gyrencephalic and lissencephalic cortices of diverse mammalian orders and over four orders of magnitude in size. In short, evolution has only one way of folding (adult and healthy) mammalian cortices. In adaptive terms, this implies that the coarse features of all cortices are a quantifiable consequence of the constrained minimization of axonal wiring of a self-avoiding, growing cortical surface. In addition, in terms of cellular composition, we had shown previously that glial cells are largely invariant across species, in both size and density, even as neurons vary in size by a factor of over a hundred.
Together, these results indicate that evolution has in fact only a few degrees of freedom with which to shape a cortex in response to the various constraints and adaptive pressures that affect the various mammalian species.
Building from these relations, we thus show that a three-parameter model predicts all major coarse-grained morphological features of the cerebral cortex (exposed and total areas, average thickness, numbers and average volumes of neuronal and non-neuronal cells, white and gray matter volumes) from variations in only three parameters: the number of symmetric and asymmetric divisions of progenitor cells in early development, and in the average volume of neurons. It is thus possible that evolutionary diversity in cortical morphology occurs simply through variations in these three parameters. Of course, many other important degrees of freedom must exist at smaller scales to account for the differences between individuals and species. Nonetheless, we find it significant that such regularity can emerge from the huge diversity in form, function and evolutionary histories of the cortices of mammals.
A comparative study of the reptilian and mammalian cortex combining chemoarchitecture, genoarchitecture, and tract-tracing
Naumann RK, Tosches MA, Müller CM, Laurent G
Max Planck Institute for Brain Research, Frankfurt, Germany
One of the most interesting challenges in evolutionary neuroscience is to understand the origin of the cerebral cortex. A clearly laminated cortex first evolved in reptiles, a key group for understanding cortical evolution (Naumann et al., 2015, Curr Biol). However, most studies have compared mammals directly to birds, a highly derived group of reptiles. Hence, the number of theories explaining cortical origins appears to outnumber the available data points on gene expression in non-avian reptiles. Our laboratory focuses on two species, a turtle, Trachemys scripta, and a lizard, Pogona vitticeps. Both lizards and turtles were held to form the most basal branch of the reptiles. Current fossil and genetic evidence favors lizards as the first branch and turtles as nested, but slowly evolving branch, deeper inside the reptile family tree. We study these two distantly related reptiles to identify shared and derived features of reptilian cortical circuits. To build a structural basis for future physiological studies and to overcome the scarcity of principal neuron gene expression data in reptiles, we study the distribution of about 20 proteins and genes with area-specific expression patterns. We combine histochemistry and in-situ hybridization with anterograde and retrograde tract tracing to parcellate reptile cortex into units comparable to mammalian cortical areas. In the reptilian medial cortex, the expression patterns of Prox1, Zbtb20, Dusp5, and Lmo4 show strong similarities to the patterns in the mammalian hippocampal formation. We find specific projections from dorsal cortex to the Prox1-positive and negative parts of medial cortex. In addition, we identify a myelinated fiber tract in the reptile medial cortex, which may be comparable to the longitudinal fiber system of the mammalian hippocampus. In the reptilian dorsal cortex, we describe expression patterns of a large number of markers, including Satb2, Lmo3, Wfs1, Gnb4, Pcp4, and Nurr1. We trace afferent and efferent connections from the subdivisions defined by these markers and evaluate recent proposals about projections from dorsal cortex to subcortical targets and the position of the lateral pallium. Our data bridge the gaps between regulatory gene expression, functional markers, and cortical connections in reptile brains and open new perspectives on function and evolution of the cerebral cortex.