RESUMO
BACKGROUND: Measuring coastal-pelagic prey fields at scales relevant to the movements of marine predators is challenging due to the dynamic and ephemeral nature of these environments. Whale sharks (Rhincodon typus) are thought to aggregate in nearshore tropical waters due to seasonally enhanced foraging opportunities. This implies that the three-dimensional movements of these animals may be associated with bio-physical properties that enhance prey availability. To date, few studies have tested this hypothesis. METHODS: Here, we conducted ship-based acoustic surveys, net tows and water column profiling (salinity, temperature, chlorophyll fluorescence) to determine the volumetric density, distribution and community composition of mesozooplankton (predominantly euphausiids and copepods) and oceanographic properties of the water column in the vicinity of whale sharks that were tracked simultaneously using satellite-linked tags at Ningaloo Reef, Western Australia. Generalised linear mixed effect models were used to explore relationships between the 3-dimensional movement behaviours of tracked sharks and surrounding prey fields at a spatial scale of ~ 1 km. RESULTS: We identified prey density as a significant driver of horizontal space use, with sharks occupying areas along the reef edge where densities were highest. These areas were characterised by complex bathymetry such as reef gutters and pinnacles. Temperature and salinity profiles revealed a well-mixed water column above the height of the bathymetry (top 40 m of the water column). Regions of stronger stratification were associated with reef gutters and pinnacles that concentrated prey near the seabed, and entrained productivity at local scales (~ 1 km). We found no quantitative relationship between the depth use of sharks and vertical distributions of horizontally averaged prey density. Whale sharks repeatedly dove to depths where spatially averaged prey concentration was highest but did not extend the time spent at these depth layers. CONCLUSIONS: Our work reveals previously unrecognized complexity in interactions between whale sharks and their zooplankton prey.
RESUMO
The pathophysiology of type 2 diabetes mellitus (T2D) is characterized by reduced or absent insulin receptor (INSR) responsiveness to its ligand, elevated hepatic glucose output and impaired glucose uptake in peripheral tissues, particularly skeletal muscle. Treatments to reduce hyperglycemia and reestablish normal insulin signaling are much sought after. Any agent which could be orally administered to restore INSR function, in an insulin-independent manner, would have major implications for the management of this global disease. We have discovered a non-peptidyl small molecule, adenosine, 5'-Se-methyl-5'-seleno-, 2',3'-diacetate [referred to as non-peptidyl compound #43 (NPC43)], which restores INSR signaling in the complete absence of insulin. Initial screening of numerous compounds in human HepG2 liver cells revealed that NPC43 significantly inhibited glucose production. The compound was potently anti-hyperglycemic and anti-hyperinsulinemic in vivo, in insulin-resistant T2D Leprdb/db mice, following either acute or chronic treatment by oral gavage and intraperitoneal injection, respectively. The compound acted at the level of INSR and activated it in both liver and skeletal muscle of Leprdb/db mice. In cell culture, the compound activated INSR in both liver and skeletal muscle cells; furthermore, it cooperated with insulin to depress glucose-6-phosphatase catalytic subunit (G6pc) expression and stimulate glucose uptake, respectively. Our results indicated that the compound directly interacted with INSRα, triggering appropriate phosphorylation and activation of the receptor and its downstream targets. Unlike insulin, NPC43 did not activate insulin-like growth factor 1 receptor in either liver or skeletal muscle. We believe this compound represents a potential oral and/or injectable insulin replacement therapy for diabetes and diseases associated with insulin resistance.
