A novel hearing specialization in the New Zealand bigeye,Pempheris adspersa

The New Zealand bigeye, Pempheris adspersa, is a nocturnal planktivore and has recently been found to be an active sound producer. The rostral end of the swim bladder lies adjacent to Baudelot''s ligament which spans between the bulla and the cleithrum bone of the pectoral girdle. The aim of this study was to use the auditory evoked potential technique to physiologically test the possibility that this structure provides an enhanced sensitivity to sound pressure in the bigeye. At 100 Hz, bigeye had hearing sensitivity similar to that of goldfish (species with a mechanical connection between the swim bladder and the inner ear mediated by the Weberian ossicles) and were much more sensitive than other teleosts without ancillary hearing structures. Severing Baudelot''s ligament bilaterally resulted in a marked decrease in hearing sensitivity, as did swim bladder puncture or lateral line blockage. These results show that bigeye have an enhanced sensitivity to sound pressure and provide experimental evidence that the functional basis of this sensitivity represents a novel hearing specialization in fish involving the swim bladder, Baudelot''s ligament and the lateral line.     

Correlations between the content of toxic and essential metals in the organism and characteristics of EEG potentials in youths under conditions of an urban environment

In 18-to 19-year-old students, the content of a number of microelements, as well as of calcium, in biologically stable tissues (hair samples) was measured using X-ray fluorescent analysis. In the tested persons, we observed a certain deficit of main elements (calcium, copper, and zinc), while in some persons the levels of toxic lead and strontium were exceeded. Correlation analysis of the parameters of EEG potentials (current EEG and evoked and event-related potentials, EPs and ERPs, respectively) showed the existence of a few significant (or close to those) correlations of the spectral powers of some rhythms and derivatives of a few indices of the background EEG and more numerous cases of correlations of the parameters of EPs and ERPs (latencies and amplitudes) with the contents of the studied elements. The physiological importance of metals, according to the number of characteristics of EEG potentials that correlate with their contents, can be arranged in descending order as follows: As, Zn > Ca > Cd > Pb > Sr. None of the studied parameters of EEG phenomena correlated with the level of copper. The strength of correlations varied from weak to mild (0.29 < R < 0.50). The densest correlations were observed for the concentrations of toxic lead and cadmium. With respect to the characteristics of ERPs, some of the elements under study demonstrated synergism (e.g., lead and arsenic), while others were in an antagonistic relation (cadmium and calcium). Neirofiziologiya/Neurophysiology, Vol. 38, No. 2, pp. 167–174, March–April, 2006.     

Representation of complex vocalizations in the Lusitanian toadfish auditory system: evidence of fine temporal,frequency and amplitude discrimination

Many fishes rely on their auditory skills to interpret crucial information about predators and prey, and to communicate intraspecifically. Few studies, however, have examined how complex natural sounds are perceived in fishes. We investigated the representation of conspecific mating and agonistic calls in the auditory system of the Lusitanian toadfish Halobatrachus didactylus, and analysed auditory responses to heterospecific signals from ecologically relevant species: a sympatric vocal fish (meagre Argyrosomus regius) and a potential predator (dolphin Tursiops truncatus). Using auditory evoked potential (AEP) recordings, we showed that both sexes can resolve fine features of conspecific calls. The toadfish auditory system was most sensitive to frequencies well represented in the conspecific vocalizations (namely the mating boatwhistle), and revealed a fine representation of duration and pulsed structure of agonistic and mating calls. Stimuli and corresponding AEP amplitudes were highly correlated, indicating an accurate encoding of amplitude modulation. Moreover, Lusitanian toadfish were able to detect T. truncatus foraging sounds and A. regius calls, although at higher amplitudes. We provide strong evidence that the auditory system of a vocal fish, lacking accessory hearing structures, is capable of resolving fine features of complex vocalizations that are probably important for intraspecific communication and other relevant stimuli from the auditory scene.     

Characteristics of reaction field and the reactive distance of a planktivore, Pseudorasbora parva (Cyprinidae), in various environmental conditions

The characteristics of the reaction field and the reactive distance of the Stone moroko (Pseudorasbora parva) were studied under three environmental conditions (structural complexity, light intensity and turbidity) and three prey sizes. In optimal experimental conditions, under no structural complexity, light intensity of 200 lux and turbidity less than 1 NTU (Nephelometric Turbidity Units), the cross-section of the reaction field was found to be elliptic with a bearing angle larger than the elevation angle, but both angles changed slightly depending on environmental conditions. The reactive distance was large, and the fish frequently attacked prey that was located within 15–60 degrees to each side from the frontal direction of a fish (i.e., ± 15 degrees from the axis of the fish body) horizontally. In the light intensity below 50 lux or turbidity above 10 NTU, however, the attack frequency and the reactive distance in the frontal direction of a fish did not differ from other horizontal directions in the reaction field. The average reactive distance increased proportionally with increasing strand distance, but it gradually reached a constant value for strand distances greater than about 3.6 times the fish body length. The average reactive distance increased in the light intensity range of 10–200 lux and decreased negatively with turbidity increasing. The average reactive distance increased with larger prey size, but the rate of increase of the reactive distance gradually decreased.     

Monitoring the acoustic activity of an aquatic insect population in relation to temperature,vegetation and noise

1. Acoustic population monitoring is a noninvasive method that can be deployed continuously over long periods of time and at large spatial scales. One of the newly discovered threats acting on biological diversity is anthropogenic noise. High levels of anthropogenic noise occur in aquatic environments, yet their effects on animals living in freshwater habitats have very rarely been investigated.
2. Here, we used acoustic monitoring and automatic detection to assess the acoustic activity of a population of a soniferous freshwater insect.
3. The sounds emitted by the corixid Micronecta scholtzi were recorded in a Mediterranean pond with an array of 12 hydrophones. An automatic analysis based on a measure of the amplitude found in the frequency band of M. scholtzi was developed to assess the level of acoustic activity. We used functional linear models, accounting for the periodicity of the calling behaviour, to estimate the possible effect of temperature, vegetation and a noise due to an immersed engine.
4. The automatic analysis was validated as an efficient method to measure the acoustic activity. The monitoring revealed a clear 24-hr pattern in the acoustic activity of M. scholtzi and three peaks of activity during the morning. Functional linear models revealed negative effects of both temperature and vegetation and showed that an engine noise, played back for 2 hr during the night, elicited an increase in the level of acoustic activity of the population. Moreover, a cross-correlation procedure showed that noise delayed the acoustic activity of the population.
5. Our results suggest that acoustic survey and automatic detection are efficient methods to monitor the acoustic activity of an insect population especially in response to an anthropogenic disturbance.

     

Nutritional regulation of body condition score at the initiation of the transition period in primiparous and multiparous dairy cows under grazing conditions: milk production, resumption of post-partum ovarian cyclicity and metabolic parameters

The objective of this study was to investigate the effect of different body condition score (BCS) at 30 days before calving (-30 days) induced by a differential nutritional management from -100 days until -30 days on productive parameters, the interval to first ovulation and blood parameters in primiparous and multiparous Holstein cows under grazing conditions until 60 days post partum. The experimental arrangement was a randomized complete block design, where cows were blocked according to BW and expected calving date and then randomly assigned to different nutritional treatments from -100 to -30 days relative to calving to induce different BCS. As the assignment of cows to treatments was random, cows had to lose, maintain or gain BCS; thus, different planes of nutrition were offered with approximately 7, 14 or 20 kg dry matter per day. The BCS score was assessed every 15 days and animals were reassigned in order to achieve the desired BCS at -30 days. Only animals that responded to nutritional treatment were considered and this was defined as follows: primiparous and multiparous high cows (PH and MH) had to gain 0.5 points of BCS, primiparous low (PL) had to lose 0.5 points of BCS and multiparous low (ML) had to maintain BCS at least in two subsequent observations from -100 to -30 days. From -30 days to calving, primiparous and multiparous cows (P and M cows) were managed separately and cows were offered a diet once a day. From calving to 60 days post partum, cows of different groups grazed in separate plots a second year pasture. Cows were also supplemented individually with whole-plant maize silage and commercial concentrate. Cows had similar BCS at -100 days and differed after the nutritional treatment; however, all groups presented similar BCS at 21 days post partum. The daily milk production and milk yield at 60 days post partum was higher in M than P cows. The percentage of milk fat was higher in PH cows compared with PL cows. Concentrations of non-esterified fatty acids (NEFA) were affected by the BCS at -30 days within parity, and in PH cows the concentration of NEFA was higher than in PL cows. The concentrations of total protein were higher in M cows. A lower probability of cycling was found in PL than in PH cows (P < 0.05) and in ML than in MH cows (P < 0.05). Treatment affected various endocrine/metabolic profiles according to parity, suggesting that the metabolic reserves signal the productive/reproductive axis so as to induce a differential nutrient partitioning in adult v. first-calving cows.