Melissa Gibbs

Lateral Line Receptors: Where Do They Come from Developmentally and Where Is Our Research Going?

The lateral line system is composed of both mechanoreceptors, which exhibit little variation in structure between taxonomic groups, and electroreceptors, which exhibit considerably more variation. Cathodally sensitive ampullary electroreceptors are the primitive condition and are found in agnathans, chondrichthyans, and most osteichthyans. Aquatic amphibians also have ampullary electroreceptors for at least part of their life cycle. The more recently evolved anodally sensitive ampullary electroreceptors and tuberous electroreceptors are only found in four groups of teleost fishes. The basic ontogenetic unit of lateral line development is the dorsolateral placode. Primitively, there are six pairs of placodes, which pass through sequential stages of development into lateral line receptors. There is no question about the origin of primitive mechanoreceptors or electroreceptors, however, we do not have a good understanding of the origin of teleost mechanoreceptors and their ampullary or tuberous electroreceptors; do they come exclusively from dorsolateral placodes or from neural crest or even general ectoderm? A second intriguing lateral line question is how certain teleost fish groups evolved tuberous electroreceptors. Electroreception appears to have re-evolved at least twice in teleosts after being lost during the neopterygian radiation. It has been suggested that the development of tuberous electroreceptors might be due to changes in placodal patterning or a change in the general ectoderm that placodes arise from. Unfortunately, our understanding of lateral line origins in fishes is very sketchy, and, if we are to answer such an evolutionary question, we first need more complete information about lateral line development in a variety of fishes, which can then be combined with gene expression data to better interpret lateral line receptor development.

Development of the Lateral Line System in the Shovelnose Sturgeon

The lateral line systems of aquatic amphibians and all chondrichthyan and osteichthyan fish present a similar array of mechanoreceptors. However, electroreceptors, the second major component of the lateral line system, have clearly undergone more significant evolutionary change. Chondrichthyans and non-neopterygian fish possess primitive ampullary organ electroreceptors, whereas significantly different ‘new’ ampullary organs and tuberous electroreceptors are found in a few groups of teleosts (mormyrids, gymnotids and some catfish). The pairing of mechano- and electroreceptors in the lateral line system, as well as the morphologically and physiologically distinct electroreceptors of teleosts have inspired several recent studies on the origin and evolution of the lateral line receptors. We described the development of the lateral line system in sturgeon (Scaphirhynchus platorynchus) as part of an outgroup analysis of lateral line development in three taxa: vertebrates that have both mechanoreceptive neuromasts and primitive electroreceptors; neopterygian fish that only have mechanoreceptors; and teleosts that have re-evolved new electroreceptors. Development in Scaphirhynchus was consistent with previously studied taxa in that the lateral line system developed from a series of six dorsolateral placodes. Interestingly, we found that the octaval placode was bound rostrally and caudally by large placodal fields, out of which the six lateral line placodes arose. This finding supports recent suggestions for a common placodal primordium for all placodes. Each of the six placodes gave rise to the lateral line nerves before elongating into sensory ridges, which contained neuromast primordia. The ampullary organ fields of Scaphirhynchus arose from the lateral zones of the anterodorsal, anteroventral, otic and supratemporal sensory ridges, which is also consistent with recently studied taxa. Comparisons of the lateral line system of Scaphirhynchus and close relatives, Acipenser and Polyodon, indicate that variation in some aspects of lateral line receptor numbers and distribution are related to changes in head morphology and feeding strategy, whereas other changes, such as a reduction in receptor number without a change in placode field size, indicate changes in placode development.

The Role of Torus longitudinalis in Equilibrium Orientation Measured with the Dorsal Light Reflex

The torus longitudinalis (TL) is a paired elongated structure reciprocally connected with the optic tectum in actinopterygian fishes. Electrophysiological recordings have revealed a sustained neural discharge in TL inversely related to luminance [Northmore, 1984]. This photometric response may play a role in the comparison of light levels between the two eyes, which must occur for the dorsal light reflex (DLR) to orient the body in the environment. Based on the luminance response of TL, it was hypothesized that TL ablation would result in a reduced DLR. Individual goldfish (Carassius auratus) were observed with variable and constant light sources on opposite sides of a test tank. The DLR was measured with respect to angle (degree) and duration (seconds) of body tilt about the longitudinal axis. After baseline readings were obtained, the intertectal commissure was cut and TL was removed bilaterally. Surgical control fish had only the intertectal commissure cut. Following surgery, TL ablatees showed a significantly reduced DLR compared to controls. The results are consistent with the suggestion by Northmore [1984] that TL may be involved in the processing of luminance information.

Spectral sensitivity of the goldfish Torus longitudinalis.

We measured the photopic spectral sensitivity of multiunit activity in the torus longitudinalis and optic tectum of goldfish. Since negative contrast stimuli are most effective for exciting torus longitudinalis, spiking activity was evoked by the shadow of a disc moving through a monochromatic light beam projected upon a screen. The amount of activity evoked in torus longitudinalis generally increased with the monochromatic stimulus radiance at the same rate for all wavelengths, indicating a univariant response. Spiking activity in tectum, however, increased at different rates across the spectrum, indicating color-dependent responses. The action spectra for torus longitudinalis were all similar and relatively flat as expected of a homogeneous, broad-band luminance processing system, and about 1 log unit more sensitive than the tectal action spectra. The latter generally displayed sharp peaks and dips in sensitivity indicative of opponent processing.

Disturbance of the Florida Manatee by an invasive catfish.

Abstract During the winter, Trichechus manatus latirostris (Florida Manatee) depends on long periods of rest in comparatively warm thermal refuges to help conserve energy and maintain stable body temperatures. Pterygoplichthys disjunctivus (Vermiculated Suckermouth Sailfin Catfish) has been observed attached to, and grazing algae from, Florida Manatee in Volusia Blue Spring. We hypothesized that the disturbance caused by grazing armored catfish would significantly alter Florida Manatee behavior. Analyses of 6 hours of underwater video of Florida Manatee behavior, with and without attached armored catfish, revealed that during each observation period, Florida Manatees with attached catfish demonstrated significantly higher activity levels and numbers of active behaviors. Increased Florida Manatee activity caused by the armored catfish may compound the impact of other known threat effects.

Lateral line morphology and cranial osteology of the Rubynose Brotula, Cataetyx rubrirostris

Cranial osteology, canal neuromast distribution, superficial neuromast distribution and innervation, and cephalic pore structure were studied in cleared and stained specimens of the deep sea brotulid Cataetyx rubrirostris. The cranial bone structure of C. rubrirostris is similar to other brotulids (Dicrolene sp.) and zoarcids (Zoarces sp.), except for an unusual amount of overlapping of the bones surrounding the cranial vault. The superficial neuromasts are innervated by the anterodorsal, anteroventral, middle and posterior lateral line nerves and are organized similarly to those of the blind ophidioid cave fish Typhliasina pearsei. The cephalic pores open into a widened lateral line canal system. The canal is compartmentalized into a series of neuromast‐containing chambers that probably amplify signals received by the system. J. Morphol. 241:265–274, 1999.

Fish Assemblage Variability in a Florida Spring

Abstract Florida springs are generally characterized as static ecosystems with unique faunal and floral assemblages that persist under relatively stable physical and chemical conditions. We sampled the fish fauna of Volusia Blue Spring to determine whether this presumption would withstand scrutiny at a higher temporal resolution and over time. We sampled by seining or snorkeling at five stations along the 320-m run weekly or bimonthly from October 2000 to September 2004. This four-year study consisted of 1152 samples that produced approximately 164,000 observations of 30 species of fish on 72 sampling trips. Concurrent water quality samples were collected at 14 sites along the center of the run and at each of the seine sites. Virtually anoxic water discharged from the spring head, but this water accumulated oxygen as it traveled the run. Fish density and species composition also changed dramatically along the length of the run. Species that tolerate low oxygen concentrations, such as poeciliids, dominated the assemblage at the spring head. Species that use patches of algae or small backwater areas, such as fundulids, were prominent in the middle reach of the run. Larger species, such as centrarchids and Lepisosteus spp., were abundant in the lower reach of the run. Within these broad patterns, most species exhibited great variability in density, probably due to the influence of variable emigration of potential predators, and also perhaps smaller species, from the St. Johns River.

Reproduction revisited—a decade of changes in the reproductive strategies of an invasive catfish, Pterygoplichthys disjunctivus (Weber, 1991), in Volusia Blue Spring, Florida

The reproductive patterns of invasive species may undergo changes in response to the pressures of a novel environment. We tracked the reproductive strategies of Pterygoplichthys disjunctivus collected in Volusia Blue Spring, adjoining the St. Johns River, over a 10 year period from 2005 through 2014. After analyzing various measures of fecundity and reproductive seasonality, we found that during that time period, P. disjunctivus reduced investment in individual offspring, while increasing overall fecundity and GSI. In addition, its reproductive season had expanded, and seasonal differences in nearly all measures became significantly smaller. This species does not seem to fit into any one reproductive strategy, nor has it moved in a consistent direction within the Winemiller-Rose reproductive strategy scheme. We suggest that despite the value of such schemes in predicting responses to environmental parameters, they may not be able to adequately describe the strategies of invasive species that have access to ecosystems that are more benign than their native habitats.

The Immune System Game

Abstract We describe a card game that helps introductory biology students understand the basics of the immune response to pathogens. Students simulate the steps of the immune response with cards that represent the pathogens and the cells and molecules mobilized by the immune system. In the process, they learn the similarities and differences between the immune responses to viral and bacterial pathogens and why the primary and secondary responses differ.