The impact of paleoclimatic changes on body size evolution in marine fishes.

Body size is an important species trait, correlating with life span, fecundity, and other ecological factors. Over Earth's geological history, climate shifts have occurred, potentially shaping body size evolution in many clades. General rules attempting to summarize body size evolution include Bergmann's rule, which states that species reach larger sizes in cooler environments and smaller sizes in warmer environments, and Cope's rule, which poses that lineages tend to increase in size over evolutionary time. Tetraodontiform fishes (including pufferfishes, boxfishes, and ocean sunfishes) provide an extraordinary clade to test these rules in ectotherms owing to their exemplary fossil record and the great disparity in body size observed among extant and fossil species. We examined Bergmann's and Cope's rules in this group by combining phylogenomic data (1,103 exon loci from 185 extant species) with 210 anatomical characters coded from both fossil and extant species. We aggregated data layers on paleoclimate and body size from the species examined, and inferred a set of time-calibrated phylogenies using tip-dating approaches for downstream comparative analyses of body size evolution by implementing models that incorporate paleoclimatic information. We found strong support for a temperature-driven model in which increasing body size over time is correlated with decreasing oceanic temperatures. On average, extant tetraodontiforms are two to three times larger than their fossil counterparts, which otherwise evolved during periods of warmer ocean temperatures. These results provide strong support for both Bergmann's and Cope's rules, trends that are less studied in marine fishes compared to terrestrial vertebrates and marine invertebrates.

Sound production, hearing sensitivity, and in-depth study of the sound-producing muscles in the cowfish (Lactoria cornuta).

The ability to produce sounds has been reported in various Ostraciidae but not deeply studied. In some Ostracion species, two different sound-producing muscles allow these boxfishes to produce two different kinds of sounds in a sequence. This study investigates sound production in another Indo-Pacific species, the longhorn cowfish Lactoria cornuta that also possesses two pairs of sonic muscles associated with the swim bladder: extrinsic sonic muscles (ESMs) and intrinsic sonic muscles (ISMs). The cowfish produces two kinds of sounds called hums and clicks. Hums are made of trains of low amplitude pulses that last for long periods of time, suggesting that they are produced by fatigue-resistant muscles, whereas clicks correspond to shorter sounds with greater amplitude than the hums, suggesting that they result from more powerful contractions. Ultra-structural differences are found between extrinsic and intrinsic sonic muscles. According to features such as long sarcomeres, long I-bands, a high number of mitochondria, and a proliferation of sarcoplasmic reticulum (SR), ESMs would be able to produce fast, strong, and short contractions corresponding to clicks (the shortest sounds with the greatest amplitude). ISMs have the thinnest cells, the smallest number of myofilaments that have long I-bands, the highest volume of mitochondria, and well-developed SR supporting these muscles; these features should generate fast and prolonged contractions that could correspond to the hums that can be produced over long periods of time. A concluding figure shows clear comparisons of the different fibers that were studied in L. cornuta. This study also compared the call features of each sound with the cowfish's hearing ability and supports L. cornuta was more sensitive to frequencies ranging between at least 100 and 400 Hz with thresholds of 128-143 dB re 1 µPa over this range, meaning that they are sensitive to the frequencies produced by conspecifics.

Two different areas of the nucleus glomerulosus in the South American pufferfish, Colomesus asellus.

The nucleus glomerulosus (NG) in paracanthopterygian and acanthopterygian teleost fishes receives afferents from neurons of the nucleus corticalis (NC), whose dendrites extend to the layers, stratum fibrosum et griseum superficiale (SFGS) and stratum griseum centrale (SGC), of the tectum opticum. A re-examination in this study revealed, by means of tracer experiments using biotinylated dextran amine, a separation among both tectal layers, portions of the NC, and target areas in a laminated type of the NG in the South American pufferfish, Colomesus asellus. Neurons of the lateral part of the NC send their dendrites to the SFGS and project to an area located dorsolaterally and centrally in the NG. In contrast, dendrites from neurons of the medial part of the NC run to the SGC, and projections from these neurons terminate in the NG in an area extending from dorsomedial to ventrolateral in the outer portion. Therefore, these two areas in the NG receive input from different sources. The NG in the visual system of tetraodontids may be involved in higher cognitive functions requiring much energy, becoming apparent by its very high level of cytochrome c oxidase activity.

Spatially restricted dental regeneration drives pufferfish beak development.

Vertebrate dentitions are extraordinarily diverse in both morphology and regenerative capacity. The teleost order Tetraodontiformes exhibits an exceptional array of novel dental morphologies, epitomized by constrained beak-like dentitions in several families, i.e., porcupinefishes, three-toothed pufferfishes, ocean sunfishes, and pufferfishes. Modification of tooth replacement within these groups leads to the progressive accumulation of tooth generations, underlying the structure of their beaks. We focus on the dentition of the pufferfish (Tetraodontidae) because of its distinct dental morphology. This complex dentition develops as a result of (i) a reduction in the number of tooth positions from seven to one per quadrant during the transition from first to second tooth generations and (ii) a dramatic shift in tooth morphogenesis following the development of the first-generation teeth, leading to the elongation of dental units along the jaw. Gene expression and 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) lineage tracing reveal a putative dental epithelial progenitor niche, suggesting a highly conserved mechanism for tooth regeneration despite the development of a unique dentition. MicroCT analysis reveals restricted labial openings in the beak, through which the dental epithelium (lamina) invades the cavity of the highly mineralized beak. Reduction in the number of replacement tooth positions coincides with the development of only four labial openings in the pufferfish beak, restricting connection of the oral epithelium to the dental cavity. Our data suggest the spatial restriction of dental regeneration, coupled with the unique extension of the replacement dental units throughout the jaw, are primary contributors to the evolution and development of this unique beak-like dentition.

Bump-head sunfish Mola alexandrini photographed in the north-west Pacific Ocean mesopelagic zone.

We report a bump-head sunfish Mola alexandrini (120-130 cm estimated total length) photographed from a manned submersible at a depth of 220 m off Kagoshima Prefecture, Japan, in May 2004. Mola alexandrini is often misidentified as the ocean sunfish Mola mola. This individual represented three records for this species: first record by a manned submersible, second record from the mesopelagic zone in the north-west Pacific Ocean and a new distributional record from Kagoshima Prefecture, Japan.

Functional morphology of endurance swimming performance and gait transition strategies in balistoid fishes.

Triggerfishes and filefishes (Balistoidea) use balistiform locomotion to power steady swimming with their dorsal and anal fins, and transition to a gait dominated by body and caudal fin (BCF) kinematics at high speeds. Fin and body shapes are predicted to be strong determinants of swimming performance and gait transitions. The goal of this study was to combine morphometrics and critical swimming tests to explore the relationships between fin and body shapes and swimming performance in a phylogenetic context in order to understand the evolution of balistiform swimming. Among 13 species of balistoid fishes, those with high aspect ratio fins tended to achieve higher critical swimming speeds than fishes with low aspect ratio fins. Species with long, large median fins and wide caudal peduncles used the balistiform gait alone for a larger percentage of their total critical swimming speed than fishes with short, small median fins and narrow caudal peduncles. Although analyses revealed overall positive relationships between median fin aspect ratios and gait transition speeds, fishes on both ends of the aspect ratio spectrum achieved higher swimming speeds using the balistiform gait alone than fishes with median fins of intermediate aspect ratios. Each species is specialized for taking advantage of one gait, with balistiform specialists possessing long, large median fins capable of the large power requirements of high-speed swimming using the median fins alone, while BCF specialists possess short, small median fins, ill-suited for powering high-speed balistiform locomotion, but narrow caudal peduncles capable of efficient caudal fin oscillations to power high-speed locomotion.

Sound production mechanism in triggerfish (Balistidae): a synapomorphy.

The ability to produce sounds for acoustic communication is known in different Balistidae species but the eventual synapomorphic aspect of the mechanism remains to be shown. In Rhinecanthus aculeatus, sounds result from alternate sweeping movements of the right and left pectoral fins, which push a system of three scutes against the swim bladder wall. In this study, we made a comparison between the sounds produced by this species and two additional ones (Balistapus undulatus and Rhinecanthus rectangulus) using hand-held specimens to provide a description of the sound mechanism. The results highlighted that the sound production mechanism is similar in the three species. According to recent phylogenetic data and shared morphological features, this mechanism could be common to the majority of Balistidae family members and all species could be capable of sound production using pectoral fins.

Geographic range expansion of Ephippion guttifer (Tetraodontidae) in the north-eastern Atlantic.

The first record of the prickly puffer Ephippion guttifer (Tetraodontidae) from Galician waters (north-west Spain) is reported based on a male specimen of 570 mm total length (LT ) caught in the Ría de Vigo. Morphometric, meristic and DNA barcode data confirmed the identification. Histological examination of reproductive tissue was carried out in this species for the first time, showing a mature male in an actively spawning phase. A historical revision invalidates a previous record and establishes this as the northernmost confirmed capture ever reported in the north-eastern Atlantic Ocean.

Morphological and histochemical characterization of the digestive tract of the puffer fish Sphoeroides testudineus (Linnaeus 1758) (Tetraodontiformes: Tetraodontidae).

Morphological analysis of the digestive tract of Sphoeroides testudineus showed an esophagus with an anterior and a posterior portion, the abdominal pouch. No stomach was observed between the abdominal pouch and the intestine. The intestine was arranged in three segments and two loops, and the distal portion had the rectum opening into the anus. Histochemical analyses showed that the esophagus secreted acid mucosecretions, and that there was a qualitative increase in goblet cells from the proximal to distal area of the intestine. The rectum showed cells secreting acid and neutral mucus. Given these features, this species presents a morphology which creates a link between its ecology and behavior.

Analysis of an astounding aggregation of Ranzania laevis (Molidae: Actinopterygii) in the tropical south-western Atlantic.

Unusual catches of more than 4200 kg of the slender sunfish Ranzania laevis are described from the south-western Atlantic, corresponding to the largest aggregation records for the species. These unexpected records were associated with unusually warm currents in the area. Males and females were physiologically able to spawn at the moment of capture, suggesting the occurrence of reproductive aggregation in this species.

A new multi-locus timescale reveals the evolutionary basis of diversity patterns in triggerfishes and filefishes (Balistidae, Monacanthidae; Tetraodontiformes).

Balistoid fishes (triggerfishes, filefishes, leatherjackets) represent one of the most successful radiations of tetraodontiform fishes across the world's oceans. Balistids (triggerfishes) are largely circumtropical in coral reef environments while most monacanthids (filefishes, leatherjackets) are distributed across reef and non-reef habitats in the Indo-western Pacific. Although members of these clades share a distinctive mode of locomotion that relies upon coordinated oscillation or undulation of enlarged dorsal and anal fins, species richness as well as morphologial and ecological diversity are generally considered to be higher in monacanthids than in triggerfishes. Explicit evolutionary comparisons of diversity patterns between these sister clades have been hampered by the paucity of systematic studies of filefishes relative to triggerfishes. Furthermore, a well-sampled molecular timescale for balistoids is lacking, hindering our understanding of the evolutionary history of these fishes. Here, we produce the largest balistoid molecular dataset to date, based on two mitochondrial and three nuclear loci, for a total of 86 species, and we time-calibrate it using three tetraodontiform fossils. We show that several of the traditional monacanthid genera are not monophyletic and that the balistid Xenobalistes tumidipectoris is nested within the genus Xanthichthys, and suggest that the generic name Xenobalistes be dissolved. Our timetree reveals a Late Miocene origin of balistids, in accordance with previous studies, but a Late Eocene age for the crown monacanthids, which experienced significant diversification during the Late Oligocene and Early Miocene. Comparative analyses reveal no significant family-level differences in rates of speciation or body size evolution, suggesting that the greater diversity of filefishes can be attributed to their more ancient crown age compared to triggerfishes.

A new phylogeny of tetraodontiform fishes (Tetraodontiformes, Acanthomorpha) based on 22 loci.

Tetraodontiform fishes represent one of the most peculiar radiations of teleost fishes. In spite of this, we do not currently have a consensus on the phylogenetic relationships among the major tetraodontiform lineages, with different morphological and molecular datasets all supporting contrasting relationships. In this paper we present the results of the analysis of tetraodontiform interrelationships based on two mitochondrial and 20 nuclear loci for 40 species of tetraodontiforms (representing all of the 10 currently recognized families), as well as three outgroups. Bayesian and maximum likelihood analyses of the concatenated dataset (18,682 nucleotides) strongly support novel relationships among the major tetraodontiform lineages. Our results recover two large clades already found in mitogenomic analyses (although the position of triacanthids differ), while they strongly conflict with hypotheses of tetraodontiform relationships inferred by previous studies based on morphology, as well as studies of higher-level teleost relationships based on nuclear loci, which included multiple tetraodontiform lineages. A parsimony gene-tree, species-tree analysis recovers relationships that are mostly congruent with the analyses of the concatenated dataset, with the significant exception of the position of the pufferfishes+porcupine fishes clade. Our findings suggest that while the phylogenetic placement of some tetraodontiform lineages (triacanthids, molids) remains problematic even after sequencing 22 loci, an overall molecular consensus is beginning to emerge regarding the existence of several major clades. This new hypothesis will require a re-evaluation of the phylogenetic usefulness of several morphological features, such as the fusion of several jaw bones into a parrot-like beak, or the reduction and loss of some of the fins, which may have occurred independently more times than previously thought.

Tetraodon palustris, a new freshwater pufferfish (Tetraodontiformes: Tetraodontidae) from the Mekong Basin of Thailand.

Tetraodon palustris, new species, is described from the Mekong basin of Thailand. Tetraodon palustris differs from T cochinchinensis and T. fangi in having no ocellus on the flank and spinules dorsally from the interorbital region to the end of the dorsal-fin base. T. etraodon cochinchinensis is distinguished from T. fangi by having a longer snout (43.5-49.2% HL in T. cochinchinensis vs. 37.9-41.1% HL in T. fangi) and is covered with spinules dorsally from the front of the nasal organs to the end of the dorsal-fin base (vs. from the front of the eyes to the end of the dorsal-fin base in T. fangi).

A new species of the genus Heterobothrium (Monogenea: Diclidophoridae) parasitizing the gills of tiger puffer fish Tetraodon lineatus (Tetraodontidae). A light and scanning electron microscopic study.

In the present study, the morphology and morphometric characterization of Heterobothrium lineatus, a monogenean gill parasite infecting the gills and wall of the bronchial cavity of the tiger pufferfish Tetraodon lineatus, were described by means of light and scanning electron microscopy for the first time from the River Nile at Qena Governorate, South Valley, Egypt. In wet mount preparation, the adult worms exhibited an elongated body with anterior pointed and posterior broad ends. The adult worm measured 1.15-1.76 mm (1.53 ± 0.2) in length and 0.30-0.42 mm (0.35 ± 0.02) in width. Light and scanning electron microscopic observations showed the presence of two buccal organs situated anteriorly around the mouth opening. The opisthohaptor was subdivided into four pairs of clamps but had no isthmus separating it from the body proper. The present Heterobothrium species differs from all other described species in the genus, by its lower dimensions of the worm measurements and the presence of a copulatory organ armed with 12-15 genital hooks. Furthermore, it is easily distinguished from Heterobothrium tetrodonis and Heterobothrium okamotoi by the absence of a distinct isthmus, and resembles Heterobothrium lamothei described from the gills of Sphoeroides testodineus in Mexico in its general appearance and the presence of rectangular haptor with the fourth pair of clamps smaller than the previous ones.

Same but different: ontogeny and evolution of the Musculus adductor mandibulae in the Tetraodontiformes.

The morphological diversity of fishes provides a rich source to address questions regarding the evolution of complex and novel forms. The Tetraodontiformes represent an order of highly derived teleosts including fishes, such as the pelagic ocean sunfishes, triggerfishes, and pufferfishes. This makes the order attractive for comparative analyses to understand the role of development in generating new forms during evolution. The adductor mandibulae complex, the main muscle associated with jaw closure, represents an ideal model system within the Tetraodontiformes. The adductor mandibulae differs in terms of partitions and their attachment sites between members of the different tetraodontiform families. In order to understand the evolution of the jaws among the Tetraodontiformes, we investigate the development of the adductor mandibulae in pufferfishes and triggerfishes as representatives of two different suborders (Balistoidei and Tetraodontoidei) that follows two different adaptations to a durophagous feeding mode. We show that the varied patterns of the adductor mandibulae derive from similar developmental sequence of subdivision of the partitions. We propose a conserved developmental program for partitioning of the adductor mandibulae as a foundation for the evolution of different patterns of subdivisions in Tetraodontiformes. Furthermore, we argue that derived conditions in the higher taxa are realized by supplementary subdivisions and altered attachment sites. These findings support a reinterpretation of homology of different muscle partitions among the Tetraodontiformes, as muscle partitions previously thought to be disparate, are now clearly related.

Biomechanics of swimming in the pufferfish Diodon holocanthus: propulsive momentum enhancement is an adaptation for thrust production in an undulatory median and paired-fin swimmer.

A form of large-amplitude elongated-body theory appropriate for the analysis of undulatory fins attached to a rigid body of elliptical section suggests a benefit due to momentum enhancement relative to the fins on their own. This theoretical prediction is experimentally confirmed for the first time. Theoretical momentum enhancement factors for Diodon holocanthus (2.2 and 2.7 for the median and pectoral fins, respectively) compared well to inferred thrust values determined from particle-image velocimetry (PIV) wake measurements (2.2-2.4 and 2.7-2.9). Caudal fin mean theoretical thrust was not significantly different from measured (PIV) values (n = 24, P > 0.05), implying no momentum enhancement. Pectoral-fin thrust was half that of the median and caudal fins due to high fin-jet angles, low circulation and momentum. Average total fin thrust and fish drag were not significantly different (n = 24, P > 0.05). Vortex rings generated by the fins were elliptical, with size dependent on fin chord and stroke amplitude. Hydrodynamic advantages (thrust enhancement at no cost to hydrodynamic efficiency, reduction of side forces minimizing energy wasting yawing motions and body drag) are probably common among rigid-bodied organisms propelled by undulatory fins. A trade-off between momentum enhancement and the rate of momentum generation (thrust force) sets a practical limit to the former. For small fins whilst momentum enhancement is high, absolute thrust is low. In addition, previously suggested limitations on thrust enhancement set by reductions in propulsive force associated with progressive reductions in fin wavelength are found to be biologically unrealistic.

First record of Lagocephalus laevigatus (Tetraodontiformes, Tetraodontidae) from Galician waters (north-west Spain), a northernmost occurrence in the north-east Atlantic Ocean.

The first record of the smooth puffer Lagocephalus laevigatus from Galician waters (north-west Spain) is reported. Three possible mechanisms of introduction of the specimen are considered: natural displacement, the aquarist trade and transport in ballast water.

Distinct startle responses are associated with neuroanatomical differences in pufferfishes.

Despite the key function of the Mauthner cells (M-cells) in initiating escape responses and thereby promoting survival, there are multiple examples of M-cell loss across the teleost phylogeny. Only a few studies have directly considered the behavioral consequences of naturally occurring M-cell variation across species. We chose to examine this issue in pufferfishes, as previous research suggested that there might be variability in M-cell anatomy in this group of fish. We characterized the M-cell anatomy and fast-start responses of two pufferfish species, Tetraodon nigroviridis and Diodon holocanthus. T. nigroviridis showed robust fast-starts to both tactile and acoustic startling stimuli. These fast-starts occurred with a latency typical of M-cell initiation in other fish, and retrograde labeling of spinal-projection neurons revealed that T. nigroviridis does have M-cells. By contrast, D. holocanthus only rarely exhibited fast-start-like behavior, and these responses were at a substantially longer latency and were much less extensive than those of T. nigroviridis. Using three complementary anatomical techniques we were unable to identify obvious M-cell candidates in D. holocanthus. These results provide a clear correlation between M-cell presence or absence and dramatic differences in fast-start behavior. The rich diversity within the pufferfish clade should allow future studies investigating the factors that contribute to this correlated anatomical and behavioral variation.

Double cones are used for colour discrimination in the reef fish, Rhinecanthus aculeatus.

Double cones (DCs) are the most common cone types in fish, reptiles and birds. It has been suggested that DCs are used for achromatic tasks such as luminance, motion and polarization vision. Here we show that a reef fish Rhinecanthus aculeatus can discriminate colours on the basis of the difference between the signals of individual members of DCs. This is the first direct evidence that individual members of DCs are used in colour vision as independent spectral channels.

Aracaniform Swimming: A Proposed New Category of Swimming Mode in Bony Fishes (Teleostei: Tetraodontiformes: Aracanidae).

The deepwater boxfishes of the family Aracanidae are the phylogenetic sister group of the shallow-water, generally more tropical boxfishes of the family Ostraciidae. Both families are among the most derived groups of teleosts. All members of both families have armored bodies, the forward 70% of which are enclosed in rigid bony boxes (carapaces). There is substantial intragroup variation in both groups in body shapes, sizes, and ornamentation of the carapaces. Swimming-related morphology, swimming mode, biomechanics, kinematics, and hydrodynamics have been studied in detail in multiple species of the ostraciids. Ostraciids are all relatively high-performance median and paired fin swimmers. They are highly maneuverable. They swim rectilinearly with substantial dynamic stability and efficiency. Aracanids have not been previously studied in these respects. This article describes swimming-related aspects of morphology, swimming modes, biomechanics, and kinematics in two south Australian species (striped cowfish and ornate cowfish) that are possibly representative of the entire group. These species differ morphologically in many respects, both from each other and from ostraciids. There are differences in numbers, sizes, and placements of keels on carapaces. The most important differences from ostraciids are openings in the posterior edges of the carapaces behind the dorsal and anal fins. The bases of those fins in ostraciids are enclosed in bone. The openings in aracanids free the fins and tail to move. As a result, aracanids are body and caudal fin swimmers. Their overall swimming performances are less stable, efficient, and effective. We propose establishing a new category of swimming mode for bony fishes called "aracaniform swimming."