Andrew E. Dizon

Molecular characterization of a cloned dolphin mitochondrial genome

SummaryDNA clones have been isolated that span the complete mitochondrial (mt) genome of the dolphin,Cephalorhynchus commersonii. Hybridization experiments with purified primate mtDNA probes have established that there is close resemblance in the general organization of the dolphin mt genome and the terrestrial mammalian mt genomes. Sequences covering 2381 bp of the dolphin mt genome from the major noncoding region, three tRNA genes, and parts of the genes encoding cytochrome b, NADH dehydrogenase subunit 3 (ND3), and 16S rRNA have been compared with corresponding regions from other mammalian genomes. There is a general tendency throughout the sequenced regions for greater similarity between dolphin and bovine mt genomes than between dolphin and rodent or human mt genomes.

A Candidate Magnetic Sense Organ in the Yellowfin Tuna, Thunnus albacares

Single-domain magnetite crystals have been isolated and characterized from tissue located in a sinus within the dermethmoid bone of the skull of the yellowfin tuna, Thunnus albacares. Their chemical composition, narrow size distribution, and distinctive crystal morphology indicate that these crystals are biochemical precipitates. Experiments on the interaction between particles reveal the organization of the particles in situ and suggest a possible form for candidate magnetoreceptor organelles. The consistent localization of such particles with similar arrangement within the dermethmoids of this and other pelagic fishes suggests that the ethmoid region is a possible location for a vertebrate magnetic sense organ.

Magnitude and ecological implications of thermal inertia in skipjack tuna,Katsuwonus pelamis (Linnaeus)

SynopsisHeat exchange experiments with sedated and free-swimming skipjack tuna,Katsuwonus pelamis (Linnaeus), yielded the following results: For fish between 0.4 and 3.5 kg in weight (W), 1)inertial resistance to cooling and warming were virtually equal over the same span of temperature (18° to 30° C);2)thermal inertia of red muscle, white muscle, and brain (in intact, living animals) was proportional to W0.45 (i.e., coefficient of temperature change, k, ∞ W−0.45 for each tissue);3)white muscle, brain, and ventricular blood equilibrated with a changed environmental temperature about 1.1, 3.3, and 20 times as rapidly as red muscle;4)the countercurrent heat exchanger was about 95% efficient as a thermal barrier between gills and red muscle; consequently, only about half (30%–80%, depending on W) the total heat transfer between the red muscle and the environment occurred across the gills;5)under conditions of thermal equilibrium, the red muscle and white muscle of sedated fish were warmer than the environment by amounts independent of environmental temperature but proportional to W0.58 and W0.61, respectively; in contrast, the excess temperature of the brain was independent of fish weight but bore a weak, positive relation to environmental temperature; and,6)in two free-swimming fish stimulated to violent activity by chasing, the red muscle warmed at rates up to 0.3° C min−1, ultimately attaining temperatures 1.5° and 3.4° C above pre-chasing equilibrium levels. Comparison of our results with those of other researchers indicated that skipjack tuna exchange core heat with the environment only about 60% as rapidly as do typical teleosts and even somewhat more slowly than do air-breathing aquatic reptiles. Results 1) and 5) were taken to imply no short-term physiological thermoregulation in skipjack tuna; problematic evidence for physiological thermoregulation in other tunas and in aquatic reptiles is discussed. Calculations based on thermal inertia, excess temperature, and rate of warming indicated that minimum and maximum rates of metabolism in the red muscle of skipjack tuna are about 4 and 25 cal g−1 hr−1, respectively. Similar considerations suggested that large thermal inertia and high rates of metabolism may pose an ecological problem for skipjack tuna as they grow in body mass; excess core temperature may become so large that the muscle of the fish overheats, especially during periods of greatest activity in warm waters; speculative upper temperature limits are offered for skipjack tuna as a function of body size and activity level. Two potential benefits of large thermal inertia are discussed and illustrated with simulation models; these are 1) substantial independence from rapid fluctuations of environmental temperatures as the fish move between the upper mixed layer and the thermocline, and 2) inertial ‘memory’ of thermal history to permit or enhance perception of weak temperature gradients.

Chains of single-domain magnetite particles in chinook salmon,Oncorhynchus tshawytscha

SummaryAlthough the presence of magnetite in their tissues is correlated with the ability of different species to detect magnetic fields, proof that the magnetite is involved in magnetoreception has not yet been provided. Using the approach employed to localize and isolate magnetic particles in the yellowfin tuna, we found that single-domain magnetite occurs in chains of particles in tissue contained within the dermethmoid cartilage of adult chinook salmon,Oncorhynchus tshawytscha. The particles are present in sufficient numbers to provide the adult fish with a very sensitive magnetoreceptor system. Magnetite in the chinook can be correlated with responses to magnetic fields in a congeneric species, the sockeye salmon. Based on the presence of the chains of particles, we propose behavioral experiments that exploit the responses of sockeye salmon fry to magnetic fields to test explicit predictions of the ferromagnetic magnetoreception hypothesis.

Thermoregulation in Yellowfin Tuna, Thunnus albacares

To determine their capacity for thermoregulation, yellowfin tuna, Thunnus albacares, were subjected to a series of 12-h periods at Tas of 20, 25, and 30 C. Muscle temperature, measured with an ultrasonic transmitter attached to the fish, and swim speed were simultaneously monitored. No relationship was found between speed and muscle temperature, although metabolic heat production is inexorably linked to the former. Because both direct and inverse muscle temperature/heat production relationships were observed, and because physical (as opposed to physiological) explanations for our data can be discounted, we hypothesize yellowfin tuna are capable of some type of central nervous system (CNS)-mediated physiological thermoregulation.

Applications of Molecular Data in Cetacean Taxonomy and Population Genetics with Special Emphasis on Defining Species Boundaries

Morphological, physiological, and behavioural characters are of great interest in phylogenetic and population genetic analyses. However, the genetic basis is known for very few of these traits, and the influence of environmental factors on the observed character variance is unknown in most cases. On the other hand, molecular methods “open the entire biological world for genetic scrutiny” (Avise, 1994). Indeed, while the identification of the genetic bases and modes of transmission of some phenotypic traits have been possible only for humans and very few species that could rapidly and easily be crossed under controlled conditions (e.g. Pisum sativum, Escherichia coli, Saccharomyces cerevisiae, Mus musculus, Drosophila melanogaster), the mode of transmission of molecular characters can usually be explicitly and readily specified for any species investigated. In addition, molecular genetic techniques give access to an enormous number of characters: a typical mammalian genome contains several billion potentially informative nucleotides. Another great advantage of molecular markers is the objectivity of characters and of their character states (i.e. alternative conditions of a character) relative to morphological, physiological, and behavioural markers. The objectivity of defining discrete molecular character states also makes them easily repeatable by independent researchers. Finally, many molecular characters probably fit character neutrality more closely than non-molecular characters.

Effect of temperature on isotonic twitch of white muscle and predicted maximum swimming speeds of skipjack tuna, Katsuwonus pelamis

SynopsisLatent period, rise time, contraction time, and half relaxation time from isotonic contractions of isolated white muscle samples from skipjack tuna, Katsuwonus pelamis, were determined at 20°, 27°, and 34° C. These parameters were found to be inversely proportional to temperature (Q10 = 1.47, 1.67, 1.62, and 1.72, respectively). The data show that contraction time and the effect of temperature on contraction time of skipjack tuna white muscle are not unique when compared to other equal-sized teleosts. Based on contraction time, maximum swimming speeds at each muscle temperature were calculated and found not significantly to exceed the maximum speeds of other equal-sized teleosts, when comparisons are made at the same white muscle temperatures

Rapid temperature compensation of volitional swimming speeds and lethal temperatures in tropical tunas (Scombridae)

SynopsisObservations on continuously swimming tunas were used to determine effects of temperature upon volitional locomotory activity and to determine upper and lower lethal temperatures. Experimental subjects were 10 skipjack tuna, Katsuwonus pelamis, 9 kawakawa, Euthynnus affinis, and 3 yellowfin tuna, Thunnus albacares.Our results: lower and upper lethal temperatures for the euthynnids (K. pelamis and E. affinis) were 15° and 33° C, respectively. Swimming speed for the euthynnids did not decrease with temperature within most of the zone of thermal tolerance; we observed either temperature independence or increases in speed as the temperature decreased. Yellowfin tuna swam slower as the water temperature decreased, but swimming speed changes lagged behind the water temperature changes. This effect was most certainly due to the large thermal inertia that is a property of tunas. The lag between swim speed and water temperature was eliminated by utilizing an estimate of red muscle temperature, rather than water temperature, as a covariate. Yellowfin tuna swim speed was best correlated with red muscle temperature rather than ambient water or brain temperatures.

Magnetoreception and Biomineralization of Magnetite in Amphibians and Reptiles

Many amphibians and reptiles are seasonally migratory, traveling to and from suitable breeding, feeding, or hibernation grounds. These creatures also carry out small-scale directed movements in local areas. As juveniles, they must locate appropriate areas for growth and maturation, often in environments vastly different from those into which they hatched. Thus, soon after hatching, sea turtles scrabble up through the sand and find their way down the beach to the ocean, while tadpoles, after spending several weeks in an aquatic environment, metamorphose into frogs and climb out of their ponds onto dry land. As adults, the amphibians and reptiles slither, stalk, or swim about in search of food and shelter and to escape predators.

Sensitivity of restrained skipjack tuna (Katsuwonus pelamis) to abrupt increases in temperature.

1. 1. Restrained skipjack tuna (Katsuwonus pelamis) signaled by deceleration of heart rate that they could perceive abrupt temperature increases (1°C/sec) as small as 1°C. 2. 2. A thermal stimulus directed into the oral-branchial cavity was more effective in eliciting responses than stimuli delivered to the nasal cavity or the dorsal, anterior quadrant of the body surface. This finding is discussed in relation to the current belief that thermal sensors in fish are generously scattered over the skin surface.