Dorsal Fin Research Articles

Identifying and Characterizing Signature Whistles Using Photo-Identification of Free-Ranging Bottlenose Dolphins (Tursiops truncatus) in Tampa Bay, Florida

The common bottlenose dolphin (Tursiops truncatus) uses vocal learning and acoustic signals within their highly social, fission-fusion lifestyle. When communicating with other individuals, they often use individually distinctive vocalizations called “signature whistles” that function in conspecific recognition. The objective of this study was to identify signature whistles in a population of bottlenose dolphins in Tampa Bay and use photographic identification to link potential individuals with specific signature whistles. Acoustic recordings from 2009 to 2023 were manually analyzed using the SIGnature IDentification (SIGID) method. Thirty-three unique signature whistles were identified. Whistles were categorized based on their frequency contour, duration, and maximum frequency ranges. A minimally invasive method was used to align dolphin identifications with signature whistles. Using concurrent acoustic and dorsal fin photo-identification data, we potentially attributed signature whistles to two resident dolphins. In addition, group size was tested as a predictor variable for total signature whistle and unique signature whistle presence, which were both found to decrease as group size increased. This study helps us to understand the acoustic communication of this highly resident population of bottlenose dolphins, and it further highlights the importance of acoustic communication for this population in an increasingly urbanized and noisy environment.

Relationship between caudal fin closing motion and acceleration capability of Rudarius ercodes balistiform locomotion

Fish leverage the interaction of multiple fins to improve their swimming ability. Acceleration performance, in particular, is a key aspect of locomotion that directly affects survival through predator evasion and prey capture. Most of these studies have focused on body and caudal fin (BCF) swimmers, which are specialized for high-speed locomotion. In contrast, relatively few studies have examined median and paired fin (MPF) swimmers, and fins’ functional roles under different locomotor modes remain insufficiently understood. Therefore, MPF swimmers may employ acceleration strategies distinct from those of BCF swimmers. Understanding the effects of fin interaction on acceleration performance in MPF swimming can contribute to a unified understanding of how such interactions influence swimming performance across fishes with different locomotor modes. A type of MPF swimmer is the balistiform, which uses its dorsal and anal fins as the main propulsion organs. We observed the closing of the caudal fins in Rudarius ercodes in balistiform locomotion during acceleration. We hypothesized that R. ercodes increased their average acceleration (the time taken to reach the experimentally observed velocity) by closing their caudal fins. We performed water tank observations to capture swimming behavior and three-dimensional computational fluid dynamics (3D-CFD) analysis to clarify the impact of caudal fin opening and closing on acceleration capability in balistiform locomotion. For example, parameters such as swimming speed and caudal fin spreading angle were measured in the swimming observations. In contrast, the fluid dynamic analysis computed the vortex structures, propulsive efficiency (the ratio of input energy contributing to thrust), and the cost of transport (the energy required to travel a unit distance). Our analysis showed that closing the caudal fin increased the average acceleration by 30%, increased the cost of transport, and decreased the dimensionless Froude efficiency. We also clarified the role of the caudal fin in MPF locomotion straight-line swimming. Our findings will help us better understand how fin interactions affect fish’s swimming ability.

A new species of the genus Mystriophis (Anguilliformes: Ophichthidae) from Cabo Verde (Eastern Central Atlantic), with notes on two Mystriophis specimens documented on the R/V Dr. Fridtjof Nansen

A new species of spoon-nose eel, Mystriophis caboverdensis sp. nov., is described from the Cabo Verde Archipelago based on a single adult specimen (723 mm TL). It co-occurs in the tropical eastern Atlantic with two similar looking species, M. rostellatus (Richardson) and M. crosnieri Blache. The new species is distinguished from both congeners by its uniquely advanced position of the dorsal fin origin, the inner and outer maxillary teeth subequal in size, shorter head and predorsal length, fewer pectoral fin rays, more lateral-line pores, along with vertebral formula, and body colouration. The COI sequences of the new species and M. crosnieri (746 mm TL) collected off the Guinean coast are provided for the first time, with a clear genetic divergence (p-distance=3.6%) between the two species. A photographic record of a large Mystriophis (1022 mm TL) from São Tomé, tentatively identified as M. cf. rostellatus, is also presented with a revised key to species of the genus Mystriophis.

First report of anguilliform catfish Olyra praestigiosa Ng & Ferraris 2016 from the state of Arunachal Pradesh, a biodiversity hotspot

Olyra praestigiosa, an anguilliform catfish was first described exclusively from Darjeeling Himalayas of north Bengal. However, during an ichthyological survey along Tissa river system from February 2023 to April 2024, 8 individuals of Olyrids were collected from 7 distinct sampling locations which were later identified as O. praestigiosa. Additionally revealing it’s occurrence very distant from the original type locality of Chel river in West Bengal. Consequently signifying the first report of O.praestigiosa from the state of Arunachal Pradesh. It is defined by having an anguilliform body, first and second dorsal fin rays being non-ossified as well as the upper caudal fin lobe being significantly expanded. A comparison of morphological characteristics of Olyra praestigiosa specimens collected from the Tissa River system with the original description of O. praestigiosa available in the literature revealed slight variation in dorsal fin to adipose fin distance as well as wider range of adipose fin base length in proportion to it’s standard length. Additionally the altitudinal range of its distribution was expanded from 382 m in type locality to 212 – 919 m in Tissa river originating in the Indo-Myanmar borders.

An enigmatic teleost fish from the Eocene of Bolca (Italy) with unusual larval‐like features

Abstract‘Pegasus’ volans is a highly unusual fossil teleost fish from the celebrated Eocene Bolca Lagerstätte. The fossil, known on the basis of two specimens, has been historically assigned to seamoths (Pegasidae), then to oarfishes and relatives (Lampriformes). We describe its enigmatic skeletal anatomy in detail and provide a new genus name: †Dibango. †Dibango volans is an extremely elongate and slender animal, with long anal and dorsal fins and a very well‐developed first dorsal‐fin ray reminiscent of the vexillum of some modern teleost larvae. Most striking is its extreme ventral projection of the pelvic bone (basipterygium), associated with an element of the pectoral girdle (a long process of the coracoid) and developed pelvic‐fin rays. The strongly reduced abdominal region suggests that †D. volans had an external gut, once again reminiscent of those of certain larval teleosts. The unique character state combination of †D. volans makes it impossible to assign it to a specific subclade within perch‐like spiny‐rayed fishes (Percomorpha). Nevertheless, it offers a valuable perspective on the diversity of morphologies and ecological niches occupied by teleost fishes of the early Eocene Bolca fauna.

Using photo identification to assess demographics and fishery interactions of oceanic whitetip sharks Carcharhinus longimanus in the main Hawaiian Islands

Global declines in oceanic whitetip shark Carcharhinus longimanus populations have resulted in international protections and a ‘threatened’ listing under the United States Endangered Species Act in 2018. Despite having international regulations on catch and trade of C. longimanus populations, large gaps remain in our understanding of their basic biology, ecology, and population structure. The main Hawaiian Islands (MHIs), USA, are thought to be a biologically important area for central Pacific C. longimanus, where commercial and recreational fishers have reported seasonal spikes in abundance and interaction rates. Using photo-identification of dorsal fin patterns, this study describes population demographics, reproductive activity, fishery interactions, and associative behaviors of C. longimanus around the MHIs. From 2006 to 2024, 383 individuals were identified, with 42 individuals sighted more than once. The highest number of encounters was recorded during the spring (March-May) and the lowest in winter (December-February). The sex ratio was ~2:1 females:males (females n = 241: males n = 108), and 42 females (17.4%) had visible mating scars while 87 females (36.1%) had distended abdomens, possibly indicating pregnancy. Fishery interactions were observed on 157 individuals (26.3% of all encounters), and 46.8% of sharks observed in this study were found within 0.4 km of a fish aggregation device, while 19.2% were found in association with marine mammals. These results provide baseline information on C. longimanus around the MHIs and are necessary to inform conservation and management efforts for this protected species throughout the central Pacific Ocean.

Natural Occurrence of Hybrid Koi and Mahseer in Artificial Ponds: Evidence of The Dangers of Releasing Non-Native Fish into The Wild

The introduction of non-native species into new environments poses significant ecological risks, including the potential for hybridization with native species, leading to genetic pollution and the creation of hybrid species. This study investigates the natural occurrence of hybridization between koi (Cyprinus carpio var. koi), an ornamental species, and the native mahseer (Tor dourorensis) in an artificial pond in Padang, West Sumatra, Indonesia. The coexistence of these species over five years resulted in the emergence of hybrid offspring, which exhibited a blend of morphological traits from both parent species. Meristic and morphometric analyses revealed that the hybrids closely resembled mahseer in certain characteristics, particularly dorsal and caudal fin rays, while also displaying koi-like traits such as body color and fin shapes. The hybridization of these two species raises concerns about the genetic integrity of native mahseer populations and the potential ecological consequences. Hybrids may possess competitive advantages that could further threaten already vulnerable mahseer populations. The findings emphasize the urgent need for effective management strategies and regulations to prevent the release of non-native species into sensitive ecosystems. Public awareness campaigns and regulatory measures should be strengthened to mitigate the risks of hybridization and protect biodiversity in freshwater environments. This study serves as a critical reminder of the far-reaching consequences of introducing non-native species, particularly in regions with delicate ecological balances.

Assessment Of Morphometric Components Of The Grey Mullet (Mugil Cephalus) In Uta Ewa River Estuary, Southeastern Nigeria

The morphological diversity and growth patterns of fish populations provide crucial insights into their ecology, reproductive strategies, and responses to environmental changes. This study aimed to investigate the variability in morphometric traits of Grey Mullet (Mugil cephalus) from Utaewa Beach, Imo River, Akwa Ibom State. The study involved the monthly measurement of 17 morphometric traits on a total of 290 samples of M. cephalus for six months from May to October 2023. The study applied descriptive statistics, T-test for sex difference, correlation analysis for trait-length relationships, and principal component analysis. The findings revealed a wide range of variability across all measured morphometric traits. Notably, body weight (BW) varied from 7.9g to 273.2g, with a mean of 65.2g. Total length (TL) measurements ranged from 9.9cm to 31.1cm, indicating significant diversity within the population. Also, statistical analysis unveiled significant sexual dimorphism across most traits, with females generally larger than males (e.g., body weight in females: mean = 65.2g, males: significantly lower, p < 0.05). Strong correlations between fish length and morphometric traits such as the distance from the snout to the dorsal fins (DDF1 and DDF2; r > 0.9) were observed, indicating proportional growth patterns. Principal component analysis showed that the first component accounted for 74.13% of the variance, highlighting key morphometric traits contributing to overall variability. These findings underline the necessity for sex-specific management strategies in Grey Mullet fisheries to support sustainable exploitation and conservation, advocating for further research into the environmental and genetic determinants of morphometric diversity.

The tadpole of Chiasmocleis altomontana (Anura: Microhylidae).

Describing the morphology of anuran larvae contributes towards filling gaps in taxonomy and natural history. This is especially relevant for explosive breeders, in which adults remain at the reproduction site for only a short period, while tadpoles may be more conspicuous. Here, we describe the larval external morphology and internal oral anatomy of the microhylid frog Chiasmocleis altomontana from near its type locality in southeastern Brazil. We took 13 linear morphometric measurements of 11 tadpoles between stages 35 and 39 from four ponds. To compare the larval external morphology of the genus, we also built a morphospace based on the log-shape ratio of linear measurements provided by the original descriptions. To impute missing data, we used a trait imputation method that considered the phylogenetic relationships and a Brownian Motion model of multivariate trait evolution. Finally, we provide novel quantitative and qualitative data on the tadpole of Chiasmocleis anatipes based on museum specimens. The tadpole of C. altomontana is the largest among the Atlantic Forest species and the second largest of the genus, after C. anatipes. Like all species of the genus, the tadpole of C. altomontana is exotrophic, suspension feeder, Orton type II, and occurs in lentic temporary environments. Overall, C. altomontana shows subtle differences in dorsal fin height, dorsal fin insertion, tail tip, and snout in lateral view from its congeners. The spiracle of C. anatipes is ventral, single, covering the vent tube, as in all other microhylids. The species has a larger tail and interorbital distance than its congeners. All species of the Atlantic Forest clade are clustered together in the morphospace, suggesting little disparity, while those of the Amazonian clade are more spread, suggesting higher morphological disparity. Chiasmocleis altomontana was close to its sister species, Chiasmocleis mantiqueira, while C. anatipes differs greatly in terms of shape from the remaining species of the genus. Our results can improve our understanding of the morphological diversity of microhylid tadpoles and reduce the diversity shortfall in anuran larval forms.

A New Species of the Eel Genus Gnathophis (Congridae, Anguilliformes) from the Seamounts of the Emperor–Hawaiian Chain, Western and Central North Pacific

Gnathophis johnsoni sp. nov. is described on the basis of 15 specimens (138–380 mm TL) from the Emperor–Hawaiian Seamount Chain in the western and central North Pacific. The new species is most similar in morphology to G. bathytopos (Atlantic), G. cinctus (eastern Pacific), and G. smithi (Nazca and Salas-y-Gomez Seamounts in the southeastern Pacific) by the sensory pore configuration and vertebral count, but differs from these species in the following characters in combination: darkly pigmented pectoral fin, dorsal fin with black margin broadened caudally and extended onto the distal half of the caudal fin, relatively long head, jaws, gill slit and caudal fin, and on average a greater preanal distance. Although most of morphometrics overlap between the new species and its closest relatives, multivariate statistical analyses clearly discriminate this species. Molecular analysis shows sister relationships between the new species and G. cinctus, with 1.81% of genetic divergence, which significantly exceeds the differences between the haplotypes belonging to the same species (0.36 and 1.08% of divergence, usually not exceeding 0.9%) and confirms both species as close but distinct. The close relationship of G. johnsoni sp. nov. and G. cinctus represents a rare case of biogeographical relations between western and eastern Pacific demersal fish faunas. Molecular data suggest that some morphologically similar species may represent independently evolved lineages, though the group of Gnathophis possessing elevated lateral-line pores is likely monophyletic.

Ontogenesis from Embryo to Juvenile in Threadsail Filefish, Stephanolepis cirrhifer

The threadsail filefish, Stephanolepis cirrhifer, is an economically important marine species. However, wild catches have sharply decreased over the past 20 years, causing S. cirrhifer to be added to the IUCN Red List of Threatened Species. Accordingly, this study seeks to promote technological development for artificial breeding and early life-stage farming by defining the morphological characteristics of ontogenesis. The fertilized eggs, with a diameter of 0.62 ± 0.01 mm, were spherical and sticky and contained multiple oil globules of varying sizes. The embryonic development was observed and divided into eight phases, which were cleavage, blastocyst, gastrula, neurula, organogenesis, muscular contraction, heart pulsation, and hatching. At 3 days post-hatching (dph), the yolk sac was completely absorbed. The eye developed rapidly, and the mouth fissure and anus initially formed. Some larvae were fed on S-rotifers (Brachionus plicatilis). At 6–8 dph, the upper and lower jaws of larvae were gradually covered by leathery skin, and the head-to-body proportion increased. At 14–16 dph, the fin differentiation occurred in the dorsal, anal, and pectoral fins, with widespread distribution of yellow and melanin on the body surface. Swim bladder was clear. The swimming ability of larva was enhanced, resulting in an obvious clustering phenomenon. At 22–25 dph, the end of the notochord continued to tilt upwards, forming a tail fin. The trunk was evenly distributed with protruding circular punctate scales. The snout was covered with leathery epidermis, and the mouth began to round. At 40–45 dph, the juvenile completed metamorphosis, with horizontal dark stripes appearing on the trunk. Pigmented spots appeared on the tail fins. The counts of dorsal and anal fin spines were 34–36 and 32–34 dph, respectively. During the development of larvae and juveniles, the growth parameters, such as total length, standard length, body height, and body weight, were made as growth curves. The slopes of growth curves were calculated. We found two inflexion points occurring in the growth curves, which may be associated with metamorphosis and transitions in feeding habits. These results enrich the biological understanding of filefish species while providing guidance for artificial propagation and fry production in S. cirrhifer.

The molecular mechanism of ovary development in Thamnaconus septentrionalis induced by rising temperature via transcriptomics and metabolomics analysis

The greenfin horse-faced filefish, Thamnaconus septentrionalis, which is widely distributed in the Indo-West Pacific Ocean, is an important commercial fish species with characteristic blue-green fins, rough skin, and a spine-like first dorsal fin. Recently, T. septentrionalis has captured the attention of conservation and development due to its sharply declining population, and its great economic value as an important marine aquaculture fish species. To protect the resources of T. septentrionalis and develop its fishery industry, artificial breeding is essential and has been carried out gradually in local farms in China. A previous study has shown that temperature can effectively influence the gonadal development in T. septentrionalis in its overwintering state. However, the molecular mechanisms underlying the effects of temperature on the gonadal development in T. septentrionalis are still unrevealed and worth further study. In the present study, we systematically investigated the effects of temperature on ovary development in T. septentrionalis through transcriptomics and metabolomics analysis. The results showed that temperature rises significantly regulated the metabolic status of T. septentrionalis and promoted ovary development and maturation process through the regulation of the pathways of ECM-receptor interaction, regulation of actin cytoskeleton, oocyte meiosis, steroid hormone biosynthesis, lipid metabolism, ABC transporters, protein digestion and absorption, biosynthesis of amino acids pathways, etc. The histological, scanning electron microscope, and transmission electron microscope analyses showed that the oocytes in the ovaries of T. septentrionalis experiencing the temperature rises developed from phase II to III with increased gonadal somatic index and 17β-estradiol level. The present study for the first time elucidated the potential molecular regulatory mechanism of ovary development in T. septentrionalis induced by temperature and will provide valuable information for the artificial breeding of T. septentrionalis and conservation of T. septentrionalis fishery resources in the future.

A Computational Study of In-Phase and Anti-Phase Interactions of Fish in a Phalanx School

Abstract Biological studies have shown that schooling behavior benefits fish's swimming performance. Particularly, side-by-side, or phalanx, formation, combined with the synchronization of undulation of the neighbors, was shown to allow the group to sustain fast incoming flow. In this work, the hydrodynamic interactions between neighbors in a phalanx school are studied through three-dimensional (3D) flow simulation. Trout-like computational models, composed of trunk (TK), caudal fin (CF), and median dorsal and anal fins (DF and AF), are used with undulatory kinematics prescribed using a traveling-wave equation. An immersed-boundary method direct numerical simulation code is used. Three trout-like models are arranged in a dense phalanx formation so that the middle fish would interact strongly with both its neighbor. The undulation of all the fish are synchronized, with the middle fish undulating either in phase or completely out of phase with its two neighbors, to examine the hydrodynamic interaction in a phalanx school in both in-phase and anti-phase modes. Results show significantly enhanced thrust though at the cost of slightly increased power consumption through anti-phase interaction, which enhanced the 3D pressure fields and momentum of the flow around neighboring CF. The wake of each fish also interacted strongly, producing expanding vortex rings and enhanced wake jets. The addition of median fins to the school additional enhanced the caudal-fin thrust through fin–fin interaction.

Tariqilabeo iranicus, a new species of labeonine fish from the Makran basin in Iran (Teleostei: Cyprinidae)

A new species of labeonine fish, Tariqilabeo iranicus sp. nov. is described from the Makran drainage basin of Iran. It is distinguished from its closest congener, Tariqilabeo diplochilus, by having a silvery spot on the operculum, and a snout shorter than the postorbital length. It is further distinguished from its congeners by a combination of characters: 34–36 lateral-line scales, 11–14 predorsal scales, 22–24 total gill rakers on the first branchial arch, 3+8 ½ dorsal-fin rays, 14–16 pectoral-fin rays, 9 pelvic-fin rays, 3+5½ anal-fin rays, 2–3 scales between anal-fin origin and anus, 7–8 scales between posteriormost pelvic-fin base and anus, 2 pairs of small barbels, presence of fringes on the rostral fold, and absence of horny tubercles on snout and cheek in males. Tariqilabeo iranicus sp. nov. is further distinguished from T. diplochilus by a K2P nearest-neighbor distance of 4% in the COI barcode region. A key to the species of Tariqilabeo is also presented.

Effect of heterozygosity, ploidy and incubation temperature on post-cranial axial skeletal meristics and deformities in Atlantic salmon (Salmo salar).

The teleostean post-cranial axial skeleton is a highly specialized structure for an aquatic mode of life. However, there is limited knowledge regarding parental contributions, early-life environmental impacts on its meristic variation and if reduced heterozygosity challenges its development. To address this, the present study used isogenic homozygous and heterozygous lines of Atlantic salmon (Salmo salar) combined with ploidy manipulation (triploidization) to manipulate parental contributions, and incubation temperature (4 vs. 8°C) as an early-life variable, and reared the fish to ~150 g for a detailed radiological examination. Genetically identical fish incubated at 4°C, but not 8°C, segregated into two size modes (upper/lower), which differed in dorsal and tail fin lepidotrich counts as well as anal-fin pterygiophore counts. Incubation temperature did not impact on vertebrae counts, whereas 8°C incubation produced more supraneurals than 4°C incubation. After 8°C incubation, homozygous diploids (100% maternal chromosomes) and heterozygous triploids (67% maternal chromosomes) developed lower total vertebrae and dorsal- and anal-fin pterygiophore counts than heterozygous diploids (50% maternal chromosomes). For tail fin lepidotrichs, the same groups showed the following pattern: diploid heterozygous > triploid heterozygous > diploid homozygous. Homozygous diploids developed a high level of complete fusions in the vertebral column. The result of the present study indicates that the ability to enter different growth modes is dependent on embryo incubation temperature and may be controlled by epigenetic mechanisms. Further, the results show a strong maternal dosage effect on tail fin lepidotrich counts, whereas for other post-cranial skeletal parts, the presence of extra maternal chromosomes seems to overrule the paternal contribution. The findings may reflect evolutionary adaptations for the shaping of offspring phenotypes. Such mechanisms would impact on important fitness-related traits, such as swimming ability and fecundity, which are relevant for conservation and evolutionary biology and ecological and aquaculture sciences. Vertebral deformities developing in homozygous fish seem to be supported by active repair mechanisms, which may reflect an organism's ability to reduce the cost of inbreeding.

Bio-Inspired Highest Lift-to-Drag-Ratio Fin Shape and Angle for Maximum Surfboard Stability: Flow Around Fish Fins.

Wave surfing is a multi-billion dollar industry involving both maneuverability and speed, yet little research has been performed regarding the highest lift-to-drag-ratio fin shape for these competing qualities. Numerical modeling and laboratory experiments were performed here to identify a bio-inspired fin shape that maximized lateral stability and minimized drag forces, in order to increase surfing maneuverability. Nine fins based on dorsal fins of real fish were tested. Both the CFD and laboratory experiments confirmed that the fin of the same shape as that of the Short-Finned Pilot Whale at an angle of attack of 10° had the greatest lift-to-drag ratios. Flow patterns around fins at a low angle of attack were smooth with negligible flow separation, while at any angle of attack greater than 25°, flow-separation-induced drag forces became excessive.

Stable isotopic differences (δ13C and δ15N) between muscle and fin ray tissues from juvenile Atlantic goliath grouper Epinephelus itajara (Lichtenstein, 1822) using non-lethal sampling.

The Atlantic goliath grouper (Epinephelus itajara) is the largest species of grouper in the Atlantic Ocean and is classified as critically endangered in Brazil. This study compared the isotopic ratios of carbon (δ13C) and nitrogen (δ15N) between the muscle tissue and dorsal-fin rays of 37 juveniles to assess fin rays as a non-lethal alternative to muscle tissue sampling. The δ13C values in rays were significantly higher than those found in muscle, whereas the δ15N values did not differ significantly between tissues. Both stable isotopes showed high Spearman correlation coefficients (>0.80) between tissues. Thus, the study can enhance future research and broaden the application of stable isotope techniques in a non-lethal manner.

Structural basis of the multiple ligand binding mechanisms of the P2X1 receptor.

As important modulators of human purinergic signaling, P2X1 receptors form homotrimers to transport calcium, regulating multiple physiological processes, and are long regarded as promising therapeutic targets for male contraception and inflammation. However, the development of drugs that target the P2X1 receptor, such as the antagonist NF449, is greatly hindered by the unclear molecular mechanism of ligand binding modes and receptor activation. Here, we report the structures of the P2X1 receptor in complex with the endogenous agonist ATP or the competitive antagonist NF449. The P2X1 receptor displays distinct conformational features when bound to different types of compounds. Despite coupling to the agonist ATP, the receptor adopts a desensitized conformation that arrests the ions in the transmembrane (TM) domain, aligning with the nature of the high desensitization rates of the P2X1 receptor within the P2X family. Interestingly, the antagonist NF449 not only occupies the orthosteric pocket of ATP but also interacts with the dorsal fin, left flipper, and head domains, suggesting a unique binding mode to perform both orthosteric and allosteric mechanisms of NF449 inhibition. Intriguingly, a novel lipid binding site adjacent to the TM helices and lower body of P2X1, which is critical for receptor activation, is identified. Further functional assay results and structural alignments reveal the high conservation of this lipid binding site in P2X receptors, indicating important modulatory roles upon lipid binding. Taken together, these findings greatly increase our understanding of the ligand binding modes and multiple modulatory mechanisms of the P2X1 receptor and shed light on the further development of P2X1-selective antagonists.Keywords: Structural biology; Ligand binding mode; Ion channel; Purinergic P2X1 receptor.

Sexual Dimorphism in Fin Size and Shape in North American Killifish.

Sexual dimorphism is intriguing because it suggests that males and females differ in phenotypic optima for traits and that sex-specific trait values can evolve despite a shared genome. Differences in sexual dimorphism across populations or species suggest that the nature of sexual selection and/or genetic constraints differ among species. Here, we measured sexual dimorphism in 20 species of North American killifish (Fundulidae) in size and shape of dorsal, anal, and caudal fins. We observed profound sexual dimorphism in anal and dorsal fin size and shape across all species, suggesting a common direction of selection. Sexual dimorphism was also present in caudal fin size and shape but was much lower in magnitude, with several species not differing from a null expectation of zero. There was little evidence for a phylogenetic signal in the levels of sexual dimorphism in dorsal and anal fin traits. We also found a strong phylogenetic correlation between sexual dimorphism in anal and dorsal fin shape but no phylogenetic correlation between fin area, base length, or ray length across different fins. Our results indicate that there is pronounced sexual dimorphism in anal and dorsal fin size and shape across fundulids. Similar patterns of sexual dimorphism in anal and dorsal fin properties have been documented in other groups, including gars, bichirs, graylings, minnows, and many species in the Atherinomorpha, suggesting that this pattern may be common across Actinopterygii.

Dynamics of foraging interactions between cookiecutter sharks (Isistius spp.) and short-finned pilot whales (Globicephala macrorhynchus) in Hawaiʻi

Cookiecutter sharks (Isistius spp.) are small pelagic squaloid sharks found throughout tropical and sub-tropical waters that are known to feed opportunistically on a range of prey, including animals much larger than themselves. Short-finned pilot whales (Globicephala macrorhynchus) are resident to Hawaiʻi Island and are often observed with fresh and healed cookiecutter shark bites. In this study, cookiecutter bites were used to infer the spatiotemporal patterns of the foraging behaviour of sharks on pilot whales off the Hawaiian Islands (21°N, 158°W to 18.5°N, 154.5°W). A photo-identification catalogue of 399 resident short-finned pilot whales (representing 5,859 identifications of known individuals from 365 encounters from 2003 to 2012), were used to infer the prevalence and seasonal variation in shark presence. The mean proportion of the pilot whale’s body visible for documenting shark bites was 22.2% (SD ± 10.0). A total of 9,281fresh, healed, and scarred bite marks were documented on 396 of 399 whales (99.2%). Bites were most frequently documented on the head (32.9% of all bites), followed by the lateral sides (29.8%) and peduncle (26.1%), while the dorsal fin had the lowest percentage of bites (11.2%). The presence of fresh bites varied with ordinal date, with peaks in April, July and mid-October and were also negatively correlated with sea surface temperature. There was also a peak in fresh bites in the transition between crescent and quarter lunar phases. These results provide further evidence that cookiecutter sharks in Hawaiʻi may perform seasonal migrations or dietary shifts.