Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis)

For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action.     

Removal of the 9-methyl group of retinal inhibits signal transduction in the visual process. A Fourier transform infrared and biochemical investigation

The photoreaction of opsin regenerated with 9-demethylretinal has been investigated by UV-vis spectroscopy, flash photolysis experiments, and Fourier transform infrared difference spectroscopy. In addition, the capability of the illuminated pigment to activate the retinal G-protein has been tested. The photoproduct, which can be stabilized at 77 K, resembles more the lumirhodopsin species, and only minor further changes occur upon warming the sample to 170 K (stabilizing lumirhodopsin). UV-vis spectroscopy reveals no further changes at 240 K (stabilizing metarhodopsin I), but infrared difference spectroscopy shows that the protein as well as the chromophore undergoes further molecular changes which are, however, different from those observed for unmodified metarhodopsin I. UV-vis spectroscopy, flash photolysis experiments, and infrared difference spectroscopy demonstrate that an intermediate different from metarhodopsin II is produced at room temperature, of which the Schiff base is still protonated. The illuminated pigment was able to activate G-protein, as assayed by monitoring the exchange of GDP for GTP gamma S in purified G-protein, only to a very limited extent (approximately 8% as compared to rhodopsin). The results are interpreted in terms of a specific steric interaction of the 9-methyl group of the retinal in rhodopsin with the protein, which is required to initiate the molecular changes necessary for G-protein activation. The residual activation suggests a conformer of the photolyzed pigment which mimics metarhodopsin II to a very limited extent.     

Contrasting rates of nucleotide substitution in the X-Linked and Y-Linked zinc finger genes

We have sequenced the entire exon (1,180 bp) encoding the zinc finger domain of the X-linked and Y-linked zinc finger genes (ZFX and ZFY, respectively) in the orangutan, the baboon, the squirrel monkey, and the rat; a total of 9,442 by were sequenced. The ratio of the rates of synonymous substitution in the ZFY and ZFX genes is estimated to be 2.1 in primates. This is close to the ratio of 2.3 estimated from primate ZFY and ZFX intron sequences and supports the view that the male-to-female ratio of mutation rate in humans is considerably higher than 1 but not extremely large. The ratio of synonymous substitution rates in ZFY and ZFX is estimated to be 1.3 in the rat lineage but 4.2 in the mouse lineage. The former is close to the estimate (1.4) from introns. The much higher ratio in the mouse lineage (not statistically significant) might have arisen from relaxation of selective constraints. The synonymous divergence between mouse and rat ZFX is considerably lower than that between mouse and rat autosomal genes, agreeing with previous observations and providing some evidence for stronger selective constraints on synonymous changes in X-linked genes than in autosomal genes. At the protein level ZFX has been highly conserved in all placental mammals studied while ZFY has been well conserved in primates and foxes but has evolved rapidly in mice and rats, possibly due to relaxation of functional constraints as a result of the development of X-inactivation of ZFX in rodents. The long persistence of the ZFY-ZFX gene pair in mammals provides some insight into the process of degeneration of Y-linked genes.Correspondence to: W.-H. Li     

Estimating the intensity of male-driven evolution in rodents by using X-linked and Y-linked Ube 1 genes and pseudogenes

Using sequence data from the last introns of ZFX and ZFY genes, we previously estimated the male-to-female ratio () of mutation rate to be close to 6 in higher primates and 1.8 in rodents. As the mutation rate may vary among different regions of the mammalian genome, it is interesting to see whether sequence data from other regions will give similar estimates. In this study, we have determined the partial genomic sequences of the ubiquitin-activating enzyme El genes (Ube 1x and Ube 1y for the X-linked and Y-linked homologues, respectively) of mice and rats and two mouse Ube 1y pseudogenes. From the intron sequences of the Ube 1 genes, we calculated the divergence of the Y-linked genes (Y = 0.161) and that of the X-linked genes (X = 0.107) between mouse and rat, and found the Y/X ratio to be 1.50. This ratio led to an estimate of = 2.0 with a 95% confidence interval of (1.0, 3.9). Similar estimates of were obtained if mouse Ube 1y pseudogenes were used instead of the mouse Ube 1y functional gene. These estimates are consistent with our previous estimate for rodents and suggest that the sex ratio of mutation rate in rodents is approximately only one-third of that in higher primates. Our estimate of the divergence time between Ube 1x and Ube 1y supports the view that the two genes separated before the eutherian radiation.Correspondence to: W.-H. Li     

Influence of central command and ergoreceptors on the splanchnic circulation during isometric exercise

The splanchnic circulation can make a major contribution to blood flow changes. However, the role of the splanchnic circulation in the reflex adjustments to the blood pressure increase during isometric exercise is not well documented. The central command and the muscle chemoreflex are the two major mechanisms involved in the blood pressure response to isometric exercise. This study aimed to examine the behaviour of the superior mesenteric artery during isometric handgrip (IHG) at 30% maximal voluntary contraction (MVC). The pulsatility index (PI) of the blood velocity waveform of the superior mesenteric artery was taken as the study parameter. A total of ten healthy subjects [mean age, 21.1 (SEM 0.3) years] performed an IHG at 30% MVC for 90 s. At 5 s prior to the end of the exercise, muscle circulation was arrested for 90 s to study the effect of the muscle chemoreflex (post exercise arterial occlusion, PEAO). The IHG at 30% MVC caused a decrease in superior mesenteric artery PI, from 4.84 (SEM 1.57) at control level to 3.90 (SEM 1.07) (P = 0.015). The PI further decreased to 3.17 (SEM 0.70) (P = 0.01) during PEAO. Our results indicated that ergoreceptors may be involved in the superior mesenteric artery vasodilatation during isometric exercise.     

Enzymes of nitrogen metabolism in legume nodules. Purification and properties of NADH-dependent glutamate synthase from lupin nodules.

An NADH-dependent glutamate synthase has been purified 500-fold from the plant cytoplasm fraction of Lupinus angustifolius nodules. It consists of a single polypeptide chain, Mr 235000. The optimum pH is 8.5, at which Km values for 2-oxoglutarate, glutamine and NADH are 39 micrometer, 400 micrometer and 1.3 micrometer respectively. The catalytic centre activity is of the order of 70 s-1 and is independent of pH between 6.5 and 9.5. Glutamate synthase is inhibited by glutamic acid, oxaloacetic acid, aspartic acid and asparagine, all competitive with 2-oxoglutarate; and by NAD+, which is competitive with NADH. There is evidence of two flavine prosthetic groups per enzyme molecule.