Integration of multi-tissue PAH and PCB burdens with biomarker activity in three coastal shark species from the northwestern Gulf of Mexico.

Tissue-based burdens of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were integrated with ethoxyresorufin-O-deethylase (EROD) and glutathione S-transferase (GST) enzyme activity in bull (Carcharhinus leucas), blacktip (Carcharhinus limbatus), and bonnethead (Sphyrna tiburo) sharks from Galveston Bay, TX. The potential toxicity of these burdens was evaluated by calculation of toxic equivalents (TEQs). Concentrations of total PAHs (∑PAHs) were significantly greater in blacktip and bonnethead sharks than bull sharks in liver, but did not exhibit differences in muscle among species. Hepatic concentrations of ∑PAHs in these sharks (range of means: 1560-2200 ng/g wet wt.) were greater than concentrations previously reported in oysters from Galveston Bay (range of means: 134-333 ng/g dry wt.), which suggests that trophic dilution of PAHs may not be reflected in sharks. Total PCBs (∑PCBs) were significantly greatest in bull sharks and lowest in bonnetheads, while blacktips were intermediate to these species. EROD activity was greater in bonnetheads than the other species, whereas GST activity was significantly higher in blacktips and bonnetheads than in bull sharks. Integration of hepatic burdens with biomarker activity via constrained multivariate analysis found correlations for only a small number of individual PAH/PCB congeners. Hepatic TEQ measurements suggest potential physiological effects of these burdens compared to established TEQ thresholds for other taxa, although the likelihood of similar effects in sharks requires further study and the inclusion of toxic endpoints. Our findings indicate that sharks may be prone to the accumulation of PAHs and PCBs, which may result in negative health outcomes for these cartilaginous fishes.

Electroreception in the Guiana dolphin (Sotalia guianensis).

Passive electroreception is a widespread sense in fishes and amphibians, but in mammals this sensory ability has previously only been shown in monotremes. While the electroreceptors in fish and amphibians evolved from mechanosensory lateral line organs, those of monotremes are based on cutaneous glands innervated by trigeminal nerves. Electroreceptors evolved from other structures or in other taxa were unknown to date. Here we show that the hairless vibrissal crypts on the rostrum of the Guiana dolphin (Sotalia guianensis), structures originally associated with the mammalian whiskers, serve as electroreceptors. Histological investigations revealed that the vibrissal crypts possess a well-innervated ampullary structure reminiscent of ampullary electroreceptors in other species. Psychophysical experiments with a male Guiana dolphin determined a sensory detection threshold for weak electric fields of 4.6 µV cm(-1), which is comparable to the sensitivity of electroreceptors in platypuses. Our results show that electroreceptors can evolve from a mechanosensory organ that nearly all mammals possess and suggest the discovery of this kind of electroreception in more species, especially those with an aquatic or semi-aquatic lifestyle.

Feeding biomechanics of juvenile red snapper (Lutjanus campechanus) from the northwestern Gulf of Mexico.

Juvenile red snapper settle across several complex habitats, which function as nurseries for young fish. Little is known about their life history or feeding biomechanics during this time. However, recent studies have shown higher growth rates for juveniles located on mud habitats adjacent to low profile reefs, perhaps because of varied prey availability and abundance. To further investigate the habitat needs of juvenile red snapper and test hypotheses of feeding development, individuals were collected from a low profile shell ridge and adjacent mud areas on Freeport Rocks, TX, USA, and divided into three size classes (< or = 3.9, 4.0-5.9, > or = 6.0 cm SL). Output from a dynamic lever model suggested an ontogenetic shift in feeding morphology. Biomechanical modeling also predicted that off-ridge juveniles would have slower, stronger jaws compared with on-ridge juveniles. Kinematic profiles obtained from actual feeding events validated the models' predictive ability. Analysis of prey capture events demonstrated that on-ridge juveniles exhibited larger jaw displacements than off-ridge juveniles. Shape analysis was used to further investigate habitat effects on morphology. Off-ridge juveniles differed from on-ridge juveniles in possessing a deeper head and body. Results from model simulations, kinematic profiles, behavioral observations and shape analysis all compliment the conclusion that on-ridge juveniles exhibited more suction feeding behavior, whereas off-ridge juveniles used more biting behavior. Habitat disparity and possibly available prey composition generated variations in juvenile feeding biomechanics and behavior that may affect recruitment.

Morphological and ecological similarities: wood-boring beetles associated with novel xylose-fermenting yeasts, Spathaspora passalidarum gen. sp. nov. and Candida jeffriesii sp. nov.

Ascomycete yeasts that both ferment and assimilate xylose were reported previously as associates of insects living in woody substrates. Most notable have been reports of Pichia stipitis-like yeasts that are widely associated with the wood-boring beetle, Odontotaenius disjunctus (Coleoptera: Passalidae), in the eastern United States. Our continuing investigation of insect gut yeasts has lead to the discovery of two new xylose-fermenting yeasts that phylogenetic analysis places as sister taxa. The beetle hosts, O. disjunctus and Phrenapates bennetti (Coleoptera: Tenebrionidae), are similar in habitat and appearance, and the presence of similar gut yeasts is an additional common feature between them. Here we describe the new yeast genus Spathaspora, the type species S. passalidarum, and its sister taxon Candida jeffriesii and discuss their natural history, including a comparison with Pichia stipitis, another member of a guild of xylose-fermenting yeasts with similar metabolic traits. In addition a morphologically distinct yeast ascospore type is described for Spathaspora.

Wood ingestion by passalid beetles in the presence of xylose-fermenting gut yeasts.

During a survey of insect gut micro-organisms, we consistently isolated Pichia stipitis-like yeasts (Fungi: Ascomycota, Saccharomycetes) from the wood-ingesting beetles, Odontotaenius disjunctus and Verres sternbergianus (Coleoptera: Passalidae). The yeasts were isolated from passalid beetles over a wide area, including the eastern and midwestern USA and Panama. Phylogenetic analyses of the nuclear encoded small and large subunit rRNA gene (rDNA) sequences distinguished a well-supported clade consisting of the passalid yeasts and Pichia stipitis, P. segobiensis, Candida shehatae and C. ergatensis. Members of this clade have the ability to ferment and assimilate xylose or to hydrolyse xylan, major components of the polysaccharide, hemicellulose. Sexual reproduction was present in the passalid isolates but was rare among the gut yeasts of other beetles to which they were compared. Minor genetic and phenotypic variation among some of the passalid yeasts was detected using markers from the internal transcribed spacer region of the rDNA repeat unit, morphology, and in vitro metabolic tests. The consistent association of xylose-fermenting yeasts of almost identical genotypes with passalid beetles across a broad geographical distribution, suggests a significant symbiotic association.