Latitudinal gradients of species richness in the deep-sea benthos of the North Atlantic.

Latitudinal species diversity gradients (LSDGs) in the Northern Hemisphere are the most well established biogeographic patterns on Earth. Despite long-standing interest in LSDGs as a central problem in ecology, their explanation remains uncertain. In terrestrial as well as coastal and pelagic marine ecosystems, these poleward declines in diversity typically have been represented and interpreted in terms of species richness, the number of coexisting species. Newly discovered LSDGs in the bathyal (500-4,000 m) benthos of the North Atlantic may help to resolve the underlying causes of these large-scale trends because the deep sea is such a physically distinct environment. However, a major problem in comparing surface and deep-sea LSDGs is that the latter have been measured differently, by using species diversity indices that are affected by both species richness and the evenness of relative abundance. Here, we demonstrate that deep-sea isopods, gastropods, and bivalves in the North Atlantic do exhibit poleward decreases in species richness, just as those found in other environments. A comprehensive systematic revision of the largest deep-sea gastropod family (Turridae) has provided a unique database on geographic distributions that is directly comparable to those used to document LSDGs in surface biotas. This taxon also shows a poleward decline in the number of species. Seasonal organic enrichment from sinking phytodetritus is the most plausible ecological explanation for deep-sea LSDGs and is the environmental factor most consistently associated with depressed diversity in a variety of bathyal habitats.

Universal cytochrome b primers facilitate intraspecific studies in molluscan taxa.

We describe the construction of amplification primers designed to target a portion of the mitochondrial cytochrome b locus in a variety of molluscan taxa. Combinations of two sets of primers successfully amplified cytochrome b from several species of gastropods, bivalves, and cephalopods. Sequence analysis of these amplified products revealed nucleotide diversity in small samples within several of these taxa. We discuss the utility of these primer sets for studies of intraspecific phylogeny in mollusks and potentially other invertebrates.

Electromyography of some respiratory muscles in the horse.

To investigate activity in respiratory muscles, insulated wire electrodes were used to record electromyographic activity in the costal diaphragm and in the intercostal, serratus ventralis, internal abdominal oblique, transversalis and rectus abdominis muscles in conscious horses and in the same animals when anaesthetised. Electromyographic activity was related to respiratory phases as recorded by a stethograph around the chest wall. The costal diaphragm showed tonic and inspiratory activity in both conscious and anaesthetised animals. The principal muscle actively involved in expiration was the transversalis muscle. Intercostal muscle activity, and any increased activity in the second part of either inspiration or expiration recorded in the conscious animal, was absent under anaesthesia. The very marked tonic activity found in the serratus ventralis muscle in standing horses disappeared during anaesthesia. It was concluded that any stabilisation of the chest wall contributed by activity in the serratus ventralis and intercostal muscles in conscious, standing horses is greatly reduced during anaesthesia.

Distribution of indicator bacteria and Vibrio parahaemolyticus in sewage-polluted intertidal sediments.

The impact of a sewage point source on the bacterial densities in an intertidal mud flat in Boston Harbor, Mass., was investigated. The area, Savin Hill Cove, acts as a receiving basin for a combined storm and sewage outlet (CSO). Preliminary examination of sediments and overlying water at high tide demonstrated that fecal coliforms were present in sediments at abundances 2 to 4 orders of magnitude higher than in the overlying water column. The following bacterial counts were determined from sediments along a sampling transect extending 460 m from the CSO: total bacteria by epifluorescent microscopy, heterotrophic bacteria by plate counts on nutrient-rich and nutrient-poor media, fecal coliforms and enterococci by membrane filtration, and Vibrio parahaemolyticus by a most-probable-number technique with a resuscitation step. Median sediment grain size, average tidal exposure, carbon/nitrogen ratio, and total organic carbon were also measured. All bacterial indices, except for V. parahaemolyticus, declined significantly with distance from the outfall. Multiple regression analysis indicated that tidal exposure (low tides) may affect densities of total bacteria. Fecal coliforms and enterococci were still present in appreciable numbers in sediments as far as 460 m away from the CSO. In contrast, V. parahaemolyticus densities did not correlate with the other bacterial counts nor with any of the environmental parameters examined. These results indicate that intertidal sediments which adjoin point sources of pollution are severely contaminated and should be considered as potentially hazardous reservoirs of sewage-borne diseases.

A comparison of different concentrations of lignocaine hydrochloride used for topical anaesthesia of the larynx of the cat.

Electromyographic (EMG) recordings were made from the intrinsic laryngeal muscles (cricothyroid, thyroarytenoid) and the diaphragm of the cat to compare the effect of the same dose of different concentrations of lignocaine hydrocholoride applied topically to the laryngeal mucosa. All concentrations of lignocaine hydrochloride tested, two, five and ten per cent, produced desensitisation of the larynx, as demonstrated by a loss of response of the crocothyroid and thyroarytenoid to mechanical stimulation of the mucosa. Desensitisation was produced in a mean of 1.80 minutes in the thirty experiments performed. Return of baseline response took significantly longer when 5 or 10% lignocaine was used compared with that when 2% was used (p less than 0.05). The usefulness of lignocaine hydrochloride as a topical anaesthetic for the larynx is reviewed.

Electromyographic study of the cat's diaphragm during oesophageal distension.

In 10 cats, under acute experimental conditions, the effects of distension of the oesophagus on diaphragmatic activity were studied. Bipolar recording electrodes were implanted in the diaphragmatic dome muscular fibres and crura muscular fibres. Electrodes similar to those in the diaphragm were inserted in the oesophageal muscular wall above the hiatus and in the rectus abdominis muscle. Changes in the intrathoracic pressure and blood pressure were recorded by catheters placed in the pleural cavity and carotid artery respectively. Distension of the lower part of the thoracic oesophagus (at the level between the heart and the hiatus, 5 to 7 cm from the hiatus) by inflating a balloon with 10 to 15 ml of air produced a partial or total inhibition of the inspiratory electrical activity of the inner hiatal muscular fibres, while the inspiratory electrical activity of the dome muscular fibres was generally unchanged. This inhibition was increasingly pronounced as the distension volume increased and as the balloon was positioned nearer to the hiatus. During the distension period, only electrocardiographic potentials were recorded on the oesophageal muscular wall and rectus abdominis muscle traces and no significant changes were observed from intrathoracic pressure or blood pressure channels. Distension by means of a balloon either inflated with up to 5 ml of air when placed 5 to 7 cm cranial to the hiatus or inflated with 15 ml of air when localised in the cervical oesophagus and intrahiatally produced no effect. All areas of the diaphragm were silent during expiration.

Observations on the use of glyceryl guaiacolate as an adjunct to general anaesthesia in horses.

Twenty-one horses undergoing clinical surgery and diagnostic procedures received 15% glyceryl guaiacolate followed by a rapid intravenous injection of a thiobarbiturate for induction of anaesthesia. Premedication was with atropine and acepromazine. Induction was smooth and free from problems apart from transient apnoea in some horses. Maintenance of anaesthesia was with oxygen and halothane administered by means of a closed circle system with soda-lime absorber and with the vaporiser out of circuit. During the period immediately following induction, the heart rate increased and the respiratory rate fell. Blood gas estimations were carried out on 6 horses during anaesthesia. These horses showed respiratory acidosis. Arterial blood oxygen tension values were above those reported in conscious horses. Use of glyceryl guaiacolate in this way provides a safe induction and enables transition to a stable maintenance period which is followed by a quiet and uneventful recovery.

The effects of lignocaine spray on the laryngeal mucosa of the cat.

The laryngeal mucosa of cats which had been treated with a lignocaine aerosol spray prior to endotracheal intubation was examined histologically. A degree of oedema and cell damage was apparent. When one side of the larynx was sprayed before intubation and the other side protected in the same cat, cellular damage was greater on the side which received the lignocaine spray. In no cat were the changes considered severe enough to constitute a post-anaesthetic hazard.

Deep-sea species diversity: decreased gastropod diversity at abyssal depths.

Gastropod species diversity is low on the continental shelf, high on the continental slope and abyssal rise, and then decreases with increasing distance out onto the abyssal plain. Increased diversity below the continental shelf has been attributed to increased environmental stability. Decreased diversity on the abyss may result from extremely low productivity.