Interpopulation variation in prey use and feeding biomechanics in Caribbean triggerfishes

The relationships between prey utilization and jaw biomechanics were explored in two Caribbean populations (La Parguera and Mona Island) of four trigger-fishes. The volumetric contribution of major prey types and six biomechanical features of the jaws that characterize biting strength were contrasted between populations. At Mona, Xanthichthys ringens ate 45% benthic organisms, whereas conspecifics at La Parguera fed exclusively on plankton. Balistes vetula at Mona consumed 63% soft and nonelusive invertebrates, in contrast to their La Parguera conspecifics, which consumed 62% hard prey. Differences in diet between populations were associated with differences in jaw biomechanics. Xanthichthys at Mona had jaw muscles, bones, and closing-lever ratios larger than those of fish at La Parguera, indicating a stronger bite. Balistes at Mona had 50% smaller jaw bones, muscles, and closing-lever ratios than their La Parguera conspecifics, indicating a weaker but swifter bite. Melichthys niger and Cantherhines macrocerus ate similar prey at the two locations and showed little difference in trophic anatomy. We hypothesize that the interpopulation differences in morphology are induced by the activities of feeding on different prey and enhance the feeding ability of fishes for locally dominant prey. Plasticity of the feeding mechanism may be a widespread attribute of fish feeding systems that promotes the ability of species to occupy multiple habitat types successfully.     

EVOLUTION OF PUFFERFISH INFLATION BEHAVIOR

The evolution of the extraordinary inflation mechanism of pufferfishes was studied in the light of an independently derived phylogenetic hypothesis of tetraodontiform fishes. Inflation behavior is found in all members of the puffer sister taxa Tetraodontidae and Diodontidae. However, most other tetraodontiform fishes exhibit two functionally similar behaviors. All taxa exhibit a “coughing” behavior and, with the exception of the sister-group to all other tetraodontiforms, represented by the Triacanthidae, all lineages “blow” strong jets of water out of their mouth to excavate prey. Functional specializations associated with the three behaviors were identified from anatomical analyses and electromyographic recordings of muscle activity in representatives of the major lineages of the order. The phylogenetic distribution of the three buccal compression behaviors and their functional bases indicates the following: (1) the evolution of inflation behavior involved major structural modifications of the head that function in a novel mechanism that links depression of the floor of the mouth to posterior expansion of the buccal cavity; (2) the contraction patterns of four key head muscles used in the three behaviors are generally similar both across behaviors and taxa; (3) however, the distribution of the two significant modifications of muscle activity are consistent with the hypothesis that the three behaviors represent a transformation series from coughing to water blowing to inflation. The motor pattern for water blowing is a slightly modified version of that seen in coughing, and the inflation motor pattern retains the blowing specialization and adds a single additional modification. The convergent evolution of a poorly developed inflation behavior in at least one genus of filefish provides evidence that tetraodontiform fishes are predisposed to the evolution of this unusual defensive behavior. The presence of a well developed water-blowing behavior in most tetraodontiform lineages may represent an intermediate functional specialization that increased the probability of the evolution of inflation.     

Morphological and biomechanical changes of the feeding apparatus in developing southern flounder,Paralichthys lethostigma

The feeding biomechanics of premetamorphic, metamorphic, and postmetamorphic southern flounder, Paralichthys lethostigma, were investigated to better understand the origin and design of adult pleuronectiform feeding mechanisms. Larval P. lethostigma were sampled from culture tanks every day from first feeding through metamorphosis. Fish were then fixed, cleared, and double stained for cartilage and bone. Postmetamorphic juvenile and adult fish were obtained from aquaculture facilities, fixed, and the muscles and bones of the head dissected. All fish were digitally photographed from both sides of the head. Measurements from digital images included head depth, head length, and quadratal angle (a measure of articular‐quadrate position). Measurements were also made of closing in‐lever, opening in‐lever, and out‐lever moment arm lengths for the determination of lower jaw opening and closing mechanical advantage. In premetamorphic larvae, quadratal angle increased from 40° to 80°, opening lever ratio increased from 0.10 to 0.37, and closing lever ratio increased from 0.06 to 0.40. From these measurements and observations of cleared and double‐stained specimens, it was determined that lower jaw depression and elevation changed from a hyoid‐based to an opercular‐based mechanism prior to the onset of metamorphosis. With migration of the right eye to the left side of the head, quadratal angle remained relatively unchanged at 72° to 84°, opening lever ratio decreased from a high of 0.32 to a low of 0.14, and closing lever ratio decreased to as low as 0.17. Postmetamorphic fish exhibited little change with a quadratal angle of 83° to 84°, an opening lever ratio of 0.19, and a closing lever ratio of 0.17 to 0.19. Paired measurements made on the left (ocular) and right (blind) sides of the head indicated that quadratal angle was asymmetrical during metamorphosis (P = 0.003, α = 0.017). Mechanical advantage for lower jaw elevation was also bilaterally asymmetrical following metamorphosis (P = 0.002, α = 0.013). Because mechanical advantage for lower jaw depression was not directionally asymmetrical in metamorphic or postmetamorphic P. lethostigma, functional asymmetry (lateral jaw flexion) is not predicted for jaw opening. These results suggest differences in the design and function of feeding mechanisms for premetamorphic, metamorphic, and postmetamorphic P. lethostigma. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Intralocality Variation in Feeding Biomechanics and Prey Use in Archosargus probatocephalus (Teleostei,Sparidae), with Implications for the Ecomorphology of Fishes

Archosargus probatocephalusin a Florida estuary was investigated to explore intraspecific variation in prey utilization and jaw biomechanics. Volumetric contribution of major prey types and seven biomechanical features of the oral jaws that characterize prey-capture and processing performance were contrasted between two locations within the estuary. At Mosquito Lagoon, where A. probatocephalusinhabited mostly oyster beds, mangroves and salt marshes, fish consumed mostly thick-shelled bivalves, gastropods, crabs, and tubiculous polychaetes and amphipods. In contrast, conspecifics at Indian River Lagoon that inhabited mostly seagrass beds and algal turf consumed predominantly algae, seagrass, epiphytic invertebrates and small bivalves and gastropods. Difference in magnitude of durophagy between locations was associated with differences in oral-jaw biomechanics. Analyses of covariance indicated that A. probatocephalusat Mosquito Lagoon had more massive jaw muscles and bones, than conspecifics at Indian River Lagoon. Variations in lever ratios for jaw-opening and jaw-closing between locations were not significant. It is hypothesized that intralocality differences in food habits have induced the development of feeding morphologies that enhance the ability of A. probatocephalusto successfully exploit locally dominant prey resources within the estuary. Plasticity of the feeding mechanism of A. probatocephalusmay buffer the species from the adverse effects of settling on heterogeneous habitats that contain variable prey resources such as those found within estuaries.     

Environmental correlates of the abundance and distribution of <Emphasis Type="Italic">Belonesox belizanus</Emphasis> in a novel environment

Environmental factors, such as temperature, dissolved oxygen, salinity, and pH may influence the population dynamics of an introduced species by imposing limits to its distribution and abundance. In 1957, the non-indigenous pike killifish, Belonesox belizanus Kner, was released into a Miami-Dade County, Florida, canal, from which it has since spread across most of south Florida. The main goal of this study was to characterize patterns of covariation between B. belizanus density and temporal, spatial, and physicochemical variables, and attempt to identify which physicochemical variables may explain variation in densities of this species. Results of AIC_c model selection indicated that patterns of physicochemical variables such as pH, salinity, and temperature correlated with annual change in B. belizanus density, and that these physicochemical-density patterns were mesohabitat specific. For the southern most sites, the interaction between temperature and salinity provide the best model to explain B. belizanus density, whereas variability in pH provides the best model at northern sites. These patterns of covariance between density and specific physicochemical variables suggests that specific mesohabitat characteristics may play a role in mediating the physiological, behavioral, and/or ecological performance of this introduced species in Florida and elsewhere. Future studies will test hypotheses on the direct and indirect effects of these physicochemical variables within the context of specific mesohabitats on the behavior and physiology of B. belizanus in its novel environment in South Florida.     

Trajectories and magnitude of change in coral reef fish populations in Philippine marine reserves: a meta-analysis

Marine reserves are widely implemented worldwide to meet both conservation and fisheries management goals. This study examines the efficacy of Philippine marine reserves using meta-analysis by comparing variations in fish density (1) between reserves and adjacent fished reefs (spatial comparison), (2) within reserves before establishment relative to years following the establishment (temporal comparison), and (3) among reserves classified based on size, age, and enforcement capacity. A grand (total) mean of nineteen 22.3 ha coral reef reserves, protected for a mean duration of 8.2 years, were included in the meta-analyses. The overall density of fishes was higher in the reserves compared with the fished reefs and this difference was largely accounted for by exploited fishes. However, the overall density of fishes within the same reserves remained similar from the period before its establishment to several years following its establishment. Only the density of nonexploited fishes increased significantly during years subsequent to the establishment of the reserves. Neither age nor size of reserves correlated with pattern of change in fish density following the establishment of the reserves; however, fish density was consistently higher in larger and older reserves relative to smaller and younger reserves in the spatial comparison. Furthermore, well-enforced reserves had higher density of exploited fishes relative to less-enforced reserves in both spatial and temporal comparisons. In general, the magnitude and trajectory of change in fish density following the establishment of Philippine marine reserves are influenced by (1) functional groups of fishes under consideration, (2) size and age of the reserve, and (3) level of enforcement of the regulatory mechanisms necessary to sustain a marine reserve.     

Ecomorphological relationships among Caribbean tetraodontiform fishes

The anatomy of the oral jaw apparatus, lever-arm mechanics and the diet of six species of Caribbean fishes in the order Tetraodontiformes were investigated to explore the relationships between trophic morphology and feeding habit in these fishes. Tetraodontiforms use their oral jaw apparatus to capture and reduce a broad range of prey types such as plankton, polychaete worms, holothuroids, sea urchins, crabs, molluscs, gorgonians and algae. The different feeding habits of tetraodontiforms are reflected by differences in the morphological and biomechanical features of their oral jaw apparatus that appear to enhance their abilities to feed on hard prey organisms. Species that bite and crush hard, benthic prey organisms had more massive bones and muscles, longer jaw-opening in-levers, and higher jaw-closing lever ratios than the planktivorous, suction-feeding species. Masses of the jaw and suspensorium bones and lower jaw adductor muscles as well as the jaw-opening in-levers and jaw-closing lever ratios of crushers were greater than those of biters. In contrast, the mass of the adductor muscle of the upper jaw did not vary among species with different diets, indicating that this muscle may not be central to the factors that determine patterns of prey use in these fishes. The diversity of feeding behaviours and the wide range of feeding habits among fishes in the order Tetraodontiformes illustrate the versatility of the oral jaw apparatus as a single functional feeding system in fishes.     

Ontogeny of suction feeding capacity in snook, Centropomus undecimalis

The ontogeny of suction feeding performance, as measured by peak suction generating capacity, was studied in the common snook, Centropomus undecimalis. Suction pressure inside the buccal cavity is a function of the total expansive force exerted on the buccal cavity distributed across the projected area of the buccal cavity. Thus, the scaling exponent of peak suction pressure with fish standard length was predicted to be equal to the scaling exponent of sternohyoideus muscle cross-sectional area, found to be 1.991, minus the scaling exponent for the projected buccal cavity area, found to be 2.009, equal to -0.018. No scaling was found in peak suction pressure generated by 12 snook ranging from 94 to 314 mm SL, supporting the prediction from morphology. C. undecimalis are able to generate similar suction pressures throughout ontogeny.     

Rapid Focused Sequencing: A Multiplexed Assay for Simultaneous Detection and Strain Typing of Bacillus anthracis,Francisella tularensis,and Yersinia pestis

Background

The intentional release of Bacillus anthracis in the United States in 2001 has heightened concern about the use of pathogenic microorganisms in bioterrorism attacks. Many of the deadliest bacteria, including the Class A Select Agents Bacillus anthracis, Francisella tularensis, and Yersinia pestis, are highly infectious via the pulmonary route when released in aerosolized form. Hence, rapid, sensitive, and reliable methods for detection of these biothreats and characterization of their potential impact on the exposed population are of critical importance to initiate and support rapid military, public health, and clinical responses.

Methodology/Principal Findings

We have developed microfluidic multiplexed PCR and sequencing assays based on the simultaneous interrogation of three pathogens per assay and ten loci per pathogen. Microfluidic separation of amplified fluorescently labeled fragments generated characteristic electrophoretic signatures for identification of each agent. The three sets of primers allowed significant strain typing and discrimination from non-pathogenic closely-related species and environmental background strains based on amplicon sizes alone. Furthermore, sequencing of the 10 amplicons per pathogen, termed “Rapid Focused Sequencing,” allowed an even greater degree of strain discrimination and, in some cases, can be used to determine virulence. Both amplification and sequencing assays were performed in microfluidic biochips developed for fast thermal cycling and requiring 7 µL per reaction. The 30-plex sequencing assay resulted in genotypic resolution of 84 representative strains belonging to each of the three biothreat species.

Conclusions/Significance

The microfluidic multiplexed assays allowed identification and strain differentiation of the biothreat agents Bacillus anthracis, Francisella tularensis, and Yersinia pestis and clear discrimination from closely-related species and several environmental background strains. The assays may be extended to detect a large number of pathogens, are applicable to the evaluation of both environmental and clinical samples, and have the potential to be applied in military, public health, and clinical diagnostic settings.     

Relating the ontogeny of functional morphology and prey selection with larval mortality in Amphiprion frenatus

Survival during the pelagic larval phase of marine fish is highly variable and is subject to numerous factors. A sharp decline in the number of surviving larvae usually occurs during the transition from endogenous to exogenous feeding known as the first feeding stage in fish larvae. The present study was designed to evaluate the link between functional morphology and prey selection in an attempt to understand how the relationship influences mortality of a marine fish larva, Amphiprion frenatus, through ontogeny. Larvae were reared from hatch to 14 days post hatch (DPH) with one of four diets [rotifers and newly hatched Artemia sp. nauplii (RA); rotifers and wild plankton (RP); rotifers, wild plankton, and newly hatched Artemia nauplii (RPA); wild plankton and newly hatched Artemia nauplii (PA)]. Survival did not differ among diets. Larvae from all diets experienced mass mortality from 1 to 5 DPH followed by decreased mortality from 6 to 14 DPH; individuals fed RA were the exception, exhibiting continuous mortality from 6 to 14 DPH. Larvae consumed progressively larger prey with growth and age, likely due to age related increase in gape. During the mass mortality event, larvae selected small prey items and exhibited few ossified elements. Cessation of mass mortality coincided with consumption of large prey and ossification of key elements of the feeding apparatus. Mass mortality did not appear to be solely influenced by inability to establish first feeding. We hypothesize the interaction of reduced feeding capacities (i.e., complexity of the feeding apparatus) and larval physiology such as digestion or absorption efficiency contributed to the mortality event during the first feeding period. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.