Top predators induce habitat shifts in prey within marine protected areas.

Emerging conservation efforts for the world's large predators may, if successful, restore natural predator-prey interactions. Marine reserves, where large predators tend to be relatively common, offer an experimental manipulation to investigate interactions between large-bodied marine predators and their prey. We hypothesized that southern stingrays-large, long-lived and highly interactive mesopredators-would invest in anti-predator behavior in marine reserves where predatory large sharks, the primary predator of stingrays, are more abundant. Specifically, we predicted southern stingrays in marine reserves would reduce the use of deep forereef habitats in the favor of shallow flats where the risk of shark encounters is lower. Baited remote underwater video was used to survey stingrays and reef sharks in flats and forereef habitats of two reserves and two fished sites in Belize. The interaction between "protection status" and "habitat" was the most important factor determining stingray presence. As predicted, southern stingrays spent more time interacting with baited remote underwater videos in the safer flats habitats, were more likely to have predator-inflicted damage inside reserves, and were less abundant in marine reserves but only in the forereef habitat. These results are consistent with a predation-sensitive habitat shift rather than southern stingray populations being reduced by direct predation from reef sharks. Our study provides evidence that roving predators can induce pronounced habitat shifts in prey that rely on crypsis and refuging, rather than active escape, in high-visibility, heterogeneous marine habitats. Given documented impacts of stingrays on benthic communities it is possible restoration of reef shark populations with reserves could induce reef ecosystem changes through behavior-mediated trophic cascades.

Occurrence and habitat use of the critically endangered smalltooth sawfish Pristis pectinata in the Bahamas.

This study documents and discusses recent (2002-2015) sightings and captures of smalltooth sawfish Pristis pectinata in the Bahamas. Movement patterns and habitat preferences of five P. pectinata are examined: two tracked with acoustic telemetry in Bimini and three tagged with pop-up archival transmitting tags in Andros. Historically, P. pectinata may have been distributed throughout the Bahamas; however, since 2002 only 61 encounters were recorded including: Andros (30), Bimini (19) and a handful across other Islands (12). In Bimini, all P. pectinata were >225 cm (stretched total length, LST) suggesting that it is not used as a nursery area. Pristis pectinata in Andros ranged from c. 80 to 450 cm (LST) indicating that this island might be an important nursery and breeding habitat. Pristis pectinata tracked in both islands remained at depths <3 m, often adjacent to mangrove habitats, displaying residency from 42 days (Bimini) to 180 days (Andros). These preliminary findings confirm the Bahamas as an important habitat for P. pectinata and emphasize the urgent need for national protection and management of this population.

A common intracellular allosteric binding site for antagonists of the CXCR2 receptor.

BACKGROUND AND PURPOSE: We have previously shown that SB265610 (1-(2-bromo-phenyl)-3-(7-cyano-3H-benzotriazol-4-yl)-urea) behaves as an allosteric, inverse agonist at the C-X-C chemokine (CXCR)2 receptor. The aim of this study was to determine whether SB265610, in addition to two other known antagonists, bind to either of the two putative, topographically distinct, allosteric binding sites previously reported in the Literature. EXPERIMENTAL APPROACH: Ten single point mutations were introduced into the CXCR2 receptor using site-directed mutagenesis. Three CXCR2 antagonists were investigated, SB265610, Pteridone-1 (2-(2,3 difluoro-benzylsulphanyl)-4-((R)-2-hydroxy-1-methyl-ethylamino)-8H-pteridin-7-one) and Sch527123 (2-hydroxy-N,N-dimethyl-3-{2-[[(R)-1-(5-methyl-furan-2-yl)-propyl]amino]-3,4-dioxo-cyclobut-1enylamino}-benzamide), and the effect of these mutations on their binding affinity and ability to inhibit interleukin-8-stimulated binding of [(35)S]GTPgammaS was examined. KEY RESULTS: Seven of the nine mutations introduced into the C-terminal domain and intracellular loops of the receptor produced a significant reduction in affinity at least one of the antagonists tested. Of those seven mutations, three produced a significant reduction in the affinity of all three antagonists, namely K320A, Y314A and D84N. In all but one mutation, the changes observed on antagonist affinity were matched with effects on inhibition of interleukin-8-stimulated [(35)S]GTPgammaS binding. CONCLUSIONS AND IMPLICATIONS: These antagonists bind to a common intracellular, allosteric, binding site of the CXCR2 receptor, which has been further delineated. As many of these mutations are close to the site of G protein coupling or to a region of the receptor that is responsible for the transduction of the activation signal, our results suggest a molecular mechanism for the inhibition of receptor activation.

SB265610 is an allosteric, inverse agonist at the human CXCR2 receptor.

BACKGROUND AND PURPOSE: In several previous studies, the C-X-C chemokine receptor (CXCR)2 antagonist 1-(2-bromo-phenyl)-3-(7-cyano-3H-benzotriazol-4-yl)-urea (SB265610) has been described as binding competitively with the endogenous agonist. This is in contrast to many other chemokine receptor antagonists, where the mechanism of antagonism has been described as allosteric. EXPERIMENTAL APPROACH: To determine whether it displays a unique mechanism among the chemokine receptor antagonists, the mode of action of SB265610 was investigated at the CXCR2 receptor using radioligand and [(35)S]-GTPgammaS binding approaches in addition to chemotaxis of human neutrophils. KEY RESULTS: In equilibrium saturation binding studies, SB265610 depressed the maximal binding of [(125)I]-interleukin-8 ([(125)I]-IL-8) without affecting the K(d). In contrast, IL-8 was unable to prevent binding of [(3)H]-SB265610. Kinetic binding experiments demonstrated that this was not an artefact of irreversible or slowly reversible binding. In functional experiments, SB265610 caused a rightward shift of the concentration-response curves to IL-8 and growth-related oncogene alpha, but also a reduction in maximal response elicited by each agonist. Fitting these data to an operational allosteric ternary complex model suggested that, once bound, SB265610 completely blocks receptor activation. SB265610 also inhibited basal [(35)S]-GTPgammaS binding in this preparation. CONCLUSIONS AND IMPLICATIONS: Taken together, these data suggest that SB265610 behaves as an allosteric inverse agonist at the CXCR2 receptor, binding at a region distinct from the agonist binding site to prevent receptor activation, possibly by interfering with G protein coupling.