The new Conductivity Bridge derives its bridge source. voltage from a self-contained vacuum tube oscilltor adjusted to approximately 1,000 cycles. Voltage for the amplifier and null indicator tubes is provided by a.builtin D.C. power supply which operates directly from the A.C. power source. 9-324 Conductivity Bridge, without Conductivity Cell, for use with 110 volts 5060 cycle A.C. 9-351.Cosi~uCvity Cell, for use with Conductivity Bridge, constant 0.8, $20.00

The Vertebrate Eye and Its Adaptive Radiation.

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Introduction To Electrodynamics

http://academic.oup.com/auk/article-pdf/102/3/661/30080634/auk0661.pdf

Scaling: why is animal size so important?

Revisiting translocation and reintroduction programmes: the importance of considering stress

The stable isotope composition of animal tissues can provide intrinsic tags to study the foraging and migratory ecology of predators in the open ocean. Chapter 13 (this volume) demonstrated that by comparing the isotope values of an animal and its local prey or environment, the animal’s movements can be estimated, given that isotopic variation exists between habitats. The utility of using geographical variations in stable isotopes values, or isoscapes to study the movements of marine predators has been limited because of our lack of knowledge on the spatial variation of the carbon, nitrogen, and oxygen isotope values in the open ocean.

Using Isoscapes to Trace the Movements and Foraging Behavior of Top Predators in Oceanic Ecosystems

The unique head morphology of sphyrnid sharks might have evolved to enhance electrosensory capabilities. The ‘enhanced electroreception’ hypothesis was tested by comparing the behavioral responses of similarly sized carcharhinid and sphyrnid sharks to prey-simulating electric stimuli. Juvenile scalloped hammerhead sharks Sphyrna lewini and sandbar sharks Carcharhinus plumbeus oriented to dipole electric fields from the same maximum distance (approximately 30 cm) and thus demonstrated comparable behavioral-response thresholds (<1 nV cm ‐1 ). Despite the similarity of response threshold, the orientation pathways and behaviors differed for the two species. Scalloped hammerheads typically demonstrated a pivot orientation in which the edge of the cephalofoil closest to the dipole remained stationary while the shark bent its trunk to orient to the center of the dipole. By contrast, sandbars swam in a broader arc towards the center of the dipole. The different orientation patterns are attributed to the hydrodynamic properties of the cephalofoil, which enables the hammerheads to execute sharp turns at high speed. The greater trunk width of the sandbar sharks prevented them from demonstrating the same degree of flexibility. Therefore, although the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields, it does provide (1) a greater lateral search area, which may increase the probability of prey encounter, and (2) enhanced maneuverability, which may aid in prey capture. Movies available on-line

/pdf/electroreception-in-juvenile-scalloped-hammerhead-and-2wui1hf64q.pdf

Electroreception in juvenile scalloped hammerhead and sandbar sharks

Cartilaginous fishes continuously replace their teeth throughout their life (polyphyodonty) and often show a sexually dimorphic dentition that was previously thought to be an invariant sex character. Radial vector analysis of tooth shape in the polyphyodontic stingray Dasyatis sabina across a consecutive 24 month period shows a stable molariform morphology for females but a periodic shift in male dentition from a female-like molariform to a recurved cuspidate form during the reproductive season. The grip tenacity of the male dentition is greater for the cuspidate form that occurs during the mating season than for the molariform dentition that occurs during the non-mating season. Dental sexual dimorphism and its sex-dependent temporal plasticity probably evolved via polyphyodontic preadaptation under selective pressures on both sexes for increased feeding efficiency and sexual selection in males to maximize mating success. These phenomena are important considerations for the identification and classification of cartilaginous fishes and possibly other polyphyodontic vertebrates in the fossil record.

/pdf/seasonal-dynamics-of-dental-sexual-dimorphism-in-the-4ck715ojlu.pdf

Seasonal dynamics of dental sexual dimorphism in the atlantic stingray dasyatis sabina

Synopsis Elasmobranch fishes exhibit a series of complex courtship and mating behaviours in which males inflict significant bite wounds to the body of female mates. However, the variety and frequency of mating wounds are not known across a full reproductive season for any species. We examined the distribution and abundance of dermal wounds in adult Atlantic stingrays, Dasyatis sabina, which have a protracted and defined mating season to determine (1) if dermal wounds can be used as indicators of mating activity, (2) whether different categories of bite wounds can be associated with specific mating behaviours, and (3) whether the skin thickness in females is sexually dimorphic. Adults of both sexes showed fresh wounds during the full duration of the mating season (October‐June) and there was no relationship between ray size and wound density. Females had more total wounds than males in every month with a maximum average of 20.2 wounds per female in April. Mating wounds were categorized into five distinct forms: single track, double track, bite, margin abrasion and excision. Wounds were randomly distributed over the body of males but concentrated on the posterior half of the disc in females. Each wound type occurred in approximately equal proportions among sexes with the exception of the precopulatory and copulatory-induced margin abrasions which accounted for 13.7% of the total wounds in females but only 3.1% in males. We suggest that the pronounced and concurrent appearance of single track, double track and bite wounds among males results from random premating courtship attacks by males because females cannot be visually discriminated. However, the concentration of wounds on the posterior disc of females is consistent with the possible presence of olfactory cues (e.g. pheromones) that are released at the cloaca. The pectoral fin dermis of females was 50% thicker than that of males, which eliminated the excision of margins during male grasping and functions to reduce female injury. The temporal occurrence of wounds from October through June and peak in April is consistent with previous reproductive studies that show fresh sperm in the reproductive tract of females over the protracted mating period and also ovulation in late March or early April. The importance of social reproductive biting is discussed in relation to the reproductive induction hypothesis proposed to possibly explain the protracted mating of this species. Monitoring of dermal wounds provides a useful non-invasive technique to determine reproductive activity and a means for inference of social relationships in elasmobranch populations.

/pdf/dermal-bite-wounds-as-indicators-of-reproductive-seasonality-1qxab8icux.pdf

Dermal bite wounds as indicators of reproductive seasonality and behaviour in the Atlantic stingray, Dasyatis sabina

Selection to maximize electroreceptive search area might have driven evolution of the cephalofoil head morphology of hammerhead sharks (family Sphyrnidae). The enhanced electrosensory hypothesis predicts that the wider head of sphyrnid sharks necessitates a greater number of electrosensory pores to maintain a comparable pore density. Although gross head morphology clearly differs between sphyrnid sharks and their closest relatives the carcharhinids, a quantitative examination is lacking. Head morphology and the distribution of electrosensory pores were compared between a carcharhinid, Carcharhinus plumbeus, and two sphyrnid sharks, Sphyrna lewini and S. tiburo. Both sphyrnids had greater head widths than the carcharhinid, although head surface area and volume did not differ between the three species. The raked head morphology of neonatal S. lewini pups, presumably an adaptation to facilitate parturition, becomes orthogonal to the body axis immediately post-parturition whereas this change is much less dramatic for the other two species. The general pattern of electrosensory pore distribution on the head is conserved across species despite the differences in gross head morphology. Sphyrna lewini has a mean of 3067 ± 158.9 SD pores, S. tiburo has a mean of 2028 ± 96.6 SD pores and C. plumbeus has a mean of 2317 ± 126.3 SD pores and the number of pores remains constant with age. Sphyrnids have a greater number of pores on the ventral surface of the head whereas C. plumbeus has an even distribution on dorsal and ventral surfaces. The greater number of pores distributed on a similar surface area provides S. lewini pups with a higher density of electrosensory pores per unit area compared to C. plumbeus pups. The greater number of ampullae, the higher pore density and the larger sampling area of the head combine to provide hammerhead sharks with a morphologically enhanced electroreceptive capability compared to comparably sized carcharhinids.

/pdf/head-morphology-and-electrosensory-pore-distribution-of-3856uu76qn.pdf

Head morphology and electrosensory pore distribution of carcharhinid and sphyrnid sharks

Elasmobranch fishes are thought to possess greater olfactory sensitivities than teleost fishes due in part to the large amount of epithelial surface area that comprises their olfactory organs; however, direct evidence correlating the size of the olfactory organ to olfactory sensitivity is lacking. This study examined the olfactory morphology and physiology of five distantly related elasmobranch species. Specifically, we quantified the number of lamellae and lamellar surface area (as if it were a flat sheet, not considering secondary lamellae) that comprise their olfactory organs. We also calculated the olfactory thresholds and relative effectiveness of amino acid odorants for each species. The olfactory organs varied in both the number of lamellae and lamellar surface area, which may be related to their general habitat, but neither correlated with olfactory threshold. Thresholds to amino acid odorants, major olfactory stimuli of all fishes, ranged from 10⁻⁹·⁰ to 10⁻⁶·⁹ mol l⁻¹, which indicates that these elasmobranch species demonstrate comparable thresholds with teleosts. In addition, the relative effectiveness of amino acid stimuli to the olfactory organ of elasmobranchs is similar to that previously described in teleosts with neutral amino acids eliciting significantly greater responses than others. Collectively, these results indicate parallels in olfactory physiology between these two groups of fishes.

/pdf/olfactory-morphology-and-physiology-of-elasmobranchs-3btvvmh51l.pdf

Stephen M. Kajiura

Papers

Electroreception in juvenile scalloped hammerhead and sandbar sharks

Seasonal dynamics of dental sexual dimorphism in the atlantic stingray dasyatis sabina

Dermal bite wounds as indicators of reproductive seasonality and behaviour in the Atlantic stingray, Dasyatis sabina

Head morphology and electrosensory pore distribution of carcharhinid and sphyrnid sharks

Olfactory morphology and physiology of elasmobranchs