Vocal and Electric Fish: Revisiting a Comparison of Two Teleost Models in the Neuroethology of Social Behavior.

The communication behaviors of vocal fish and electric fish are among the vertebrate social behaviors best understood at the level of neural circuits. Both forms of signaling rely on midbrain inputs to hindbrain pattern generators that activate peripheral effectors (sonic muscles and electrocytes) to produce pulsatile signals that are modulated by frequency/repetition rate, amplitude and call duration. To generate signals that vary by sex, male phenotype, and social context, these circuits are responsive to a wide range of hormones and neuromodulators acting on different timescales at multiple loci.

Social stimuli increase activity of adult-born cells in the telencephalon of zebrafish (Danio rerio).

Fish have particularly high levels of adult neurogenesis, and this high neurogenic capacity may contribute to behavioural plasticity. While it is known that adult-born cells can differentiate into neurons and incorporate into neural circuits, it is unclear whether they are responsive to external stimuli and are thereby capable of contributing to behavioural change. We tested whether cells born in the telencephalon of adult zebrafish are activated by social stimuli.

Reduced brain cell proliferation following somatic injury is buffered by social interaction in electric fish, Apteronotus leptorhynchus.

In many species, the negative effects of aversive stimuli are mitigated by social interactions, a phenomenon termed social buffering. In one form of social buffering, social interactions reduce the inhibition of brain cell proliferation during stress. Indirect predator stimuli (e.

Predation drives the evolution of brain cell proliferation and brain allometry in male Trinidadian killifish, .

The external environment influences brain cell proliferation, and this might contribute to brain plasticity underlying adaptive behavioural changes. Additionally, internal genetic factors influence the brain cell proliferation rate. However, to date, researchers have not examined the importance of environmental versus genetic factors in causing natural variation in brain cell proliferation.

Simulated predator stimuli reduce brain cell proliferation in two electric fish species, and .

The brain structure of many animals is influenced by their predators, but the cellular processes underlying this brain plasticity are not well understood. Previous studies showed that electric fish () naturally exposed to high predator () density and tail injury had reduced brain cell proliferation compared with individuals facing few predators and those with intact tails. However, these field studies described only correlations between predator exposure and cell proliferation.

Fish Neurogenesis in Context: Assessing Environmental Influences on Brain Plasticity within a Highly Labile Physiology and Morphology.

Fish have unusually high rates of brain cell proliferation and neurogenesis during adulthood, and the rates of these processes are greatly influenced by the environment. This high level of cell proliferation and its responsiveness to environmental change indicate that such plasticity might be a particularly important mechanism underlying behavioral plasticity in fish. However, as part of their highly labile physiology and morphology, fish also respond to the environment through processes that affect cell proliferation but that are not specific to behavioral change.

Predators inhibit brain cell proliferation in natural populations of electric fish, Brachyhypopomus occidentalis.

Compared with laboratory environments, complex natural environments promote brain cell proliferation and neurogenesis. Predators are one important feature of many natural environments, but, in the laboratory, predatory stimuli tend to inhibit brain cell proliferation. Often, laboratory predatory stimuli also elevate plasma glucocorticoids, which can then reduce brain cell proliferation.

Influence of long-term social interaction on chirping behavior, steroid levels and neurogenesis in weakly electric fish.

Social interactions dramatically affect the brain and behavior of animals. Studies in birds and mammals indicate that socially induced changes in adult neurogenesis participate in the regulation of social behavior, but little is known about this relationship in fish. Here, we review studies in electric fish (Apteronotus leptorhychus) that link social stimulation, changes in electrocommunication behavior and adult neurogenesis in brain regions associated with electrocommunication.

Social novelty enhances brain cell proliferation, cell survival, and chirp production in an electric fish, Apteronotus leptorhynchus.

For many animals, enriched environments and social interaction promote adult neurogenesis. However, in some cases, the effect is transient, and long-term environmental stimuli have little benefit for neurogenesis. In electric fish, Apteronotus leptorhynchus, fish housed in pairs for 7 days show higher density of newborn brain cells (cell addition) than isolated fish, but fish paired for 14 days have rates of cell addition similar to isolated controls.

Glucocorticoid receptor blockade inhibits brain cell addition and aggressive signaling in electric fish, Apteronotus leptorhynchus.

When animals are under stress, glucocorticoids commonly inhibit adult neurogenesis by acting through glucocorticoid receptors (GRs). However, in some cases, conditions that elevate glucocorticoids promote adult neurogenesis, and the role of glucocorticoid receptors in these circumstances is not well understood. We examined the involvement of GRs in social enhancement of brain cell addition and aggressive signaling in electric fish, Apteronotus leptorhynchus.

Environmental complexity, seasonality and brain cell proliferation in a weakly electric fish, Brachyhypopomus gauderio.

Environmental complexity and season both influence brain cell proliferation in adult vertebrates, but their relative importance and interaction have not been directly assessed. We examined brain cell proliferation during both the breeding and non-breeding seasons in adult male electric fish, Brachyhypopomus gauderio, exposed to three environments that differed in complexity: (1) a complex natural habitat in northern Uruguay, (2) an enriched captive environment where fish were housed socially and (3) a simple laboratory setting where fish were isolated. We injected fish with BrdU 2.

Scanning electron microscopy of the placental interface in the viviparous lizard Sceloporus jarrovi (Squamata: Phrynosomatidae).

Placental membranes mediate maternal-fetal exchange in all viviparous reptilian sauropsids. We used scanning electron microscopy to examine the placental interface in the mountain spiny lizard, Sceloporus jarrovi (Phrynosomatidae). From the late limb bud stage until birth, the conceptus is surrounded by placental membranes formed from the chorioallantois and yolk sac omphalopleure.

Placental specializations of the mountain spiny lizard Sceloporus jarrovi.

The lizard Sceloporus jarrovi (Phrynosomatidae) is one of the most widely studied viviparous reptiles of North America. Past research has assumed that placentation in this species is relatively simple and functions mainly in gas exchange. Our examination of the late stage placenta via transmission electron microscopy reveals that S.

Electrocommunication signals alone are sufficient to increase neurogenesis in the brain of adult electric fish, Apteronotus leptorhynchus.

Social interaction can have profound influences on the structure of the adult brain, but little is known about the precise stimulus feature found within social interaction that induces such brain plasticity. We examined the effects of social stimuli on cell addition and radial glial fiber formation in the brains of adult electric fish. These fish communicate primarily through weak, quasi-sinusoidal electric signals.

Social interaction and cortisol treatment increase cell addition and radial glia fiber density in the diencephalic periventricular zone of adult electric fish, Apteronotus leptorhynchus.

In electric fish, Apteronotus leptorhynchus, both long-term social interaction and cortisol treatment potentiates chirping, an electrocommunication behavior that functions in aggression. Chirping is controlled by the diencephalic prepacemaker nucleus (PPn-C) located just lateral to the ventricle. Cells born in adult proliferative zones such as the periventricular zone (PVZ) can migrate along radial glial fibers to other brain regions, including the PPn-C.

Social interactions and cortisol treatment increase the production of aggressive electrocommunication signals in male electric fish, Apteronotus leptorhynchus.

Brown ghost knife fish, Apteronotus leptorhynchus, continually emit a weakly electric discharge that serves as a communication signal and is sensitive to sex steroids. Males modulate this signal during bouts of aggression by briefly (approximately 15 ms) increasing the discharge frequency in signals termed "chirps." The present study examined the effects of short-term (1-7 days) and long-term (6-35 days) male-male interaction on the continuous electric organ discharge (EOD), chirping behavior, and plasma levels of cortisol and two androgens, 11-ketotestosterone (11KT) and testosterone.

Hormonal and body size correlates of electrocommunication behavior during dyadic interactions in a weakly electric fish, Apteronotus leptorhynchus.

Brown ghost knife fish, Apteronotus leptorhynchus, produce sexually dimorphic, androgen-sensitive electrocommunication signals termed chirps. The androgen regulation of chirping has been studied previously by administering exogenous androgens to females and measuring the chirping response to artificial electrical signals. The present study examined the production of chirps during dyadic interactions of fish and correlated chirp rate with endogenous levels of one particular androgen, 11-ketotestosterone (11KT).