ARTICLE | doi:10.20944/preprints202208.0139.v1
Subject: Biology, Animal Sciences & Zoology Keywords: blackfin reef shark; Carcharhinus melanopterus; shark behaviour; shark ethology; shark cognition
Online: 8 August 2022 (09:44:57 CEST)
The chondrichthyan lineage diverged from the osteichthyan line 440 million years ago, resulting in a vast evolutionary gulf between modern elasmobranchs and other vertebrates. Though this has supported the assumption that sharks are ancient, dangerous, and binary-minded, the few ethological studies done have noted intelligent actions including social exchanges. Yet their behaviour remains little known. On seeing that Carcharhinus melanopterus displayed complex actions during incidental meetings, a long-term ethological study of the species was carried out using artificial aggregations, at several sites in the fringe lagoon of Mo’orea Island, French Polynesia. Short and long-term behaviour was recorded in 473 individuals, including an ethogram, roaming patterns, social interactions, and cognition. C. melanopterus is considered sedentary, yet the home range could also be viewed as a place to pause between travels, for most individuals left for long periods. The study community and its visitors travelled in correlation with the lunar phase, in groups of up to six individuals, socializing with conspecifics encountered along the way, and displaying fluid social dynamics. C. melanopterus was highly alert to danger yet prone to investigate novel objects, a combination that generated a variety of tactics to remain hidden while investigating the environment. Basic to this was the use of the visual limit for escape or to screen their presence, indicating an awareness of being present and observable. Using their other senses, they could focus their attention on events beyond visual range and made swift decisions to act as circumstances unfolded. In their non-territorial, non-hierarchical society, any shark could lead, but it was usually the same ones that did so. Therefore, unusual individuals had a significant effect on events through social learning, suggesting the potential for culture. Actions in a variety of situations suggested complex cognition, and individuals displayed both positive and negative subjective states including playfulness.
REVIEW | doi:10.20944/preprints202102.0145.v5
Online: 28 January 2022 (11:13:01 CET)
The market for shark fin soup, a fashionable, high-end Chinese dish, has resulted in intensive shark fishing across all oceans. At the same time, 90% of teleost fish stocks are over-exploited, making sharks the most lucrative target: fisheries that have not previously hunted them are now. As top and middle predators, sharks have high ecological value and poor capacity to withstand fishing mortality, but though their numbers are plummeting, the secretive nature of the fin trade, along with the difficulties of obtaining relevant data, obscure their true status. In consumer countries, shark fin is a luxury item and rich consumers are willing to pay high prices. There is little interest in sustainability or legal trade. Thus market demand will continue to fuel the search for sharks and those accessible to fishing fleets are increasingly endangered. Current legal protections are not working, as is clearly seen in the case of the shortfin mako. Claims that sharks can withstand such targeted, industrial hunting and be sustainably fished under these circumstances are shown to be misguided. In the interests of averting a catastrophic collapse across the planet’s aquatic ecosystems, sharks must be given effective protection. We recommend that all sharks, chimaeras, manta rays, devil rays, and rhino rays be protected from international trade through an immediate CITES Appendix I listing. However, a binding international agreement for protection, not only of sharks, but of the loss of biodiversity in general, is what is most needed to allow marine and fresh water ecosystems to recover.
CASE REPORT | doi:10.20944/preprints202205.0397.v1
Online: 30 May 2022 (11:27:09 CEST)
Tawny nurse shark (Nebrius ferrugineus) is a species of carpet shark distributed across the tropical Indo-Pacific region. Tawny nurse shark is listed as “Vulnerable” on IUCN Redlist and rarely seen, recorded and studied in Indonesia. We recorded this species during SCUBA diving activity in Morotai waters in April 2022. Scientific record of the species is highly important for conservation and habitat management, particularly in Morotai, a region in North Maluku famous for shark-based marine tourism.
ARTICLE | doi:10.20944/preprints202102.0383.v1
Online: 17 February 2021 (11:57:41 CET)
Shark unprovoked attacks consist of fatal and non-fatal cases. Numerous cases have been reported involving shark species from Carcharhinus melanopterus with length of 145.5 cm to half-ton Carcharodon carcharias. Currently there are more (P < 0.05) unprovoked non-fatal cases with the average is 28.46 cases/shark species (95%CI: 3.86-53.1) than unprovoked fatal cases, which the average is 5.12 cases /shark species (95%CI: -0.075-10.3). Hence this paper seeks to select the best shark size model that correlates with the unprovoked fatal and non-fatal cases. The studied sharks consist of 24 shark species with the average length is 268.18 cm (95%CI: 230-306 cm) and the average weight is 225.42 kg (95%CI: 128-323 kg). Based on the model and as described by low values of AIC and the highest values of R2 and adjusted R2 , shark weight followed by combinations of shark weight and length produced unprovoked fatal and non-fatal cases best models. The model for explaining unprovoked fatal cases is the shark weight with high numbers of cases observed in large size shark (weight⁓fatal cases, AIC = 165.359, R2 = 0.72, Adj. R = 0.71). While for non-fatal cases, the best model is also the shark weight (weight⁓non fatal cases, AIC = 246.93, R2 = 0.63, Adj. R = 0.59).
ARTICLE | doi:10.20944/preprints202101.0509.v1
Online: 25 January 2021 (15:05:04 CET)
Otodus megalodon is known as the biggest shark ever alive and recent records show this species was only existed in America, Africa and Europe continents in the last Miocene period 20 million years ago (Ma). Recently, megalodon teeth have been discovered in South coast of West Java. Here this study aims to present and model the presence of O. megalodon. The length of the excavated tooth was ranging from 13 to 19 cm. The lithological analysis shows that the tooth was found in Miocene rock layers. Paleogeographic model shows that during Miocene southern parts of Java island were submerged including the recent locations where the megalodon tooth have been found. Half parts of the modeled West Java were an ocean with depth ranging from 0 to 200 m. High habitat use preferences by juvenile megalodon were estimated in the shelf (depth 0-40 m) with the size of 1365 km2 . Whereas habitat use preference by adult megalodon was low at this depth. Both juvenile and adult habitat use frequencies were low at a depth of between 80 m and 160 m. Habitat use preferences were increasing at a depth of > 200 m. After Miocene, the paleoclimate records show a decline in temperature and lead to the decline of whale population in ocean. The declining of megalodon’s prey explains the declining of this giant shark especially in post Miocene and early Pliocene periods.
BRIEF REPORT | doi:10.20944/preprints201911.0214.v1
Subject: Biology, Animal Sciences & Zoology Keywords: shark; genome; longevity; gigantism; positive selection
Online: 18 November 2019 (07:46:50 CET)
A previous study involving whole genome sequencing of the white shark suggested unique molecular evolution accounting for gigantism and the enhanced longevity of sharks including positive selection of dozens of protein-coding genes potentially involved in genome stability. We performed a reanalysis on some of the genes and identified serious flaws in their results. In this short article, we scrutinize one of the serious problems we identified, report other concerns, and point out a potential bias in analyzing iconic shark species in general.
REVIEW | doi:10.20944/preprints202001.0231.v1
Online: 21 January 2020 (03:19:47 CET)
The progesterone receptor (PR) mediates progesterone regulation of female reproductive physiology, as well as gene transcription in non-reproductive tissues, such as brain, bone, lung and vasculature, in both women and men. An unusual property of progesterone is its high affinity for the mineralocorticoid receptor (MR), which regulates electrolyte transport in the kidney in humans and other terrestrial vertebrates. In humans, rats, alligators and frogs, progesterone antagonizes activation of the MR by aldosterone, the physiological mineralocorticoid in terrestrial vertebrates. In contrast, in elephant shark, ray-finned fishes and chickens, progesterone activates the MR. Interestingly, cartilaginous fishes and ray-finned fishes do not synthesize aldosterone, raising the question of which steroid(s) activate the MR in cartilaginous fishes and ray-finned fishes. The simpler synthesis of progesterone, compared to cortisol and other corticosteroids, makes progesterone a candidate physiological activator of the MR in elephant sharks and ray-finned fishes. Elephant shark and ray-finned fish MRs are expressed in diverse tissues, including heart, brain and lung, as well as, ovary and testis, two reproductive tissues that are targets for progesterone, which together suggests a multi-faceted physiological role for progesterone activation of the MR in elephant shark and ray-finned fish. The functional consequences of progesterone as an antagonist of some terrestrial vertebrate MRs and as an agonist of fish and chicken MRs are not fully understood. Indeed, little is known of physiological activities of progesterone via any vertebrate MR.
Subject: Life Sciences, Biochemistry Keywords: glucocorticoid receptor; allosteric; elephant shark; nuclear receptors; evolution
Online: 19 October 2020 (10:03:00 CEST)
Orthologs of human glucocorticoid receptor (GR) and human mineralocorticoid receptor (MR) first appear in cartilaginous fishes. Subsequently, the MR and GR diverged to respond to different steroids: the MR to aldosterone and the GR to cortisol and corticosterone. We report that cortisol, corticosterone and aldosterone activate full-length elephant shark GR, and progesterone, which activates elephant shark MR, does not activate elephant shark GR. However, progesterone inhibits steroid binding to elephant shark GR, but not to human GR. Together, this indicates partial functional divergence of elephant shark GR from the MR. Deletion of the N-terminal domain (NTD) from elephant shark GR (truncated GR) reduced the response to corticosteroids, while truncated and full-length elephant shark MR had similar responses to corticosteroids. Swapping of NTDs of elephant shark GR and MR yielded an elephant shark MR chimera with full-length GR-like increased activation by corticosteroids and progesterone compared to full-length elephant shark MR. Elephant shark MR NTD fused to GR DBD+LBD had similar activation as full-length MR, indicating that the MR NTD lacked GR-like NTD activity. We propose that NTD activation of human GR evolved early in GR divergence from the MR.
ARTICLE | doi:10.20944/preprints201803.0175.v1
Subject: Earth Sciences, Oceanography Keywords: Hypersaline Bay; circulation; turbulent mixing; exchange flow; Australia; Shark Bay
Online: 20 March 2018 (08:44:49 CET)
In Shark Bay, a large hypersaline bay in Western Australia, longitudinal density gradients force gravitational circulation that is important for Bay-ocean exchange. Observations of vertical stratification and velocity are presented, confirming a steady near-bed dense water outflow from Shark Bay’s northern Geographe Channel that persisted through all stages of the tide. Outflow velocities were 2–3 times stronger than the outflows recorded previously in Naturaliste Channel (in the west) and were more resistant to breakdown by tidal mixing. Estimates of turbulent kinetic energy production derived from ADCP data using the variance method showed a more complex structure in Geographe Channel, due to shear associated with the stratified conditions, with peak levels of turbulence occurring during reversal of tidal flows. For both channels the main source of turbulence was tidal flow along the seabed, with the bottom current speed cubed, |Ub3|, providing a reasonable proxy for tidal mixing and prediction of dense water outflows from Shark Bay the majority of the time. Orientation and deeper water of Geographe Channel along the main axis of the longitudinal density gradient provided an explanation for the predominant outflow from the Bay’s northern entrance. These density-driven currents could potentially influence recruitment of commercially fished scallops and prawns through dispersal and flushing of larvae.
ARTICLE | doi:10.20944/preprints201903.0001.v1
Subject: Biology, Physiology Keywords: shark steroids; steroid receptor evolution; mineralocorticoid receptor evolution; progesterone; aldosterone; cortisol
Online: 1 March 2019 (06:37:37 CET)
We report the analysis of activation by corticosteroids and progesterone of full-length mineralocorticoid receptor (MR) from elephant shark, a cartilaginous fish belonging to the oldest group of jawed vertebrates. Based on their measured activities, aldosterone, cortisol, 11-deoxycorticosterone, corticosterone, 11-deoxcortisol, progesterone and 19-norprogesterone are potential physiological mineralocorticoids. However, aldosterone, the physiological mineralocorticoid in humans and other terrestrial vertebrates, is not found in cartilaginous or ray-finned fishes. Because progesterone is a precursor for corticosteroids that activate elephant shark MR, we propose that progesterone was an ancestral ligand for elephant shark MR. Although progesterone activates ray-finned fish MRs, progesterone does not activate human, amphibian or alligator MRs, suggesting that during the transition to terrestrial vertebrates, progesterone lost the ability to activate the MR. Comparison of RNA-sequence analysis of elephant shark MR with that of human MR suggests that MR expression in the human brain, heart, ovary, testis and other non-epithelial tissues evolved in cartilaginous fishes. Together, these data suggest that progesterone-activated MR may have unappreciated functions in elephant shark ovary and testis.