Vascular physiology of the ascidian Pyura praeputialis

Blood pressure was measured at both ends of the heart of Pyura praeputialis (Heller) after removing the tunic.
For posterior anterior heart waves average upstream pressures were 23–25 mm H₂O (positive): corresponding downstream pressures averaged 8 mm H₂O (negative). For anterior posterior waves average upstream pressures were 17–18 mm H₂O (+) and downstream values were 7–8 mm H₂O (-). Maximum pulse amplitudes recorded were about 30 mm H₂O (upstream).
Speed of the peristaltic wave was 25-31 mm/s. In one experiment the speed was demonstrably different over the two halves of the heart (48 mm/s over the rear half and 29 mm/s over the front half).
Number of peristaltic waves per series (i.e. between successive reversals) varied from 20 to 178. Duration of each series varied from 120 s to 690 s. Wave frequency ranged from 8 to 21 per min. Reversal frequency ranged from 5 to 30 reversals per hour.
Most preparations showed periods of reduced heart activity ("rest periods") during the the 2 4 h of the experiment. All showed spasmodic contractions of the mantle muscles which caused pressure "surges" in the vascular system.
It is shown that, in both directions of beat, most or all of the pressure wave is contributed by the front half of the heart (half towards which peristaltic wave is travelling). This can be related to the "reversed spiral" structure of the heart: each "half" of the heart (i.e. each spiral) serves primarily as the pump for one direction.     

Blood volume of the ascidian Pyura praeputialis

Blood dilution curves have been obtained by injecting ¹²⁵I labelled albumin and ¹²⁵I labelled gamma-globulin into the blood of Pyura praeputialis . After mixing is complete the dilution curve shows a two-stepped pattern.
There is some question as to how the two steps of the curve should be interpreted. The first step has been extrapolated to give blood volume s.s. , i.e. volume of the vessels, sinuses and lacunae of the vascular system. Values for this range from 30% to 45 % of body weight, with a mean value of 35%.
The second step has been extrapolated to give total extracellular fluid volume, i.e. blood volume plus interstitial fluid volume. Values for this range from 21 % to 52 % of body weight, the average being 38 %.
The interstitial space ranges from 15 % to 32 % of the weight of the visceral mass, the average being 23 %.
The rationale for the above interpretation of the dilution curve is stated and discussed. Most reliable is extracellular fluid volume which probably corresponds to the blood volume of other invertebrates with open systems.
An attempt was made to assess the relative importance of (a) the visceral circuit and (b) the tunic circuit, by comparing the specific activities of the visceral mass and the tunic. The specific activities indicate little or no blood in the tunic circuit: this result is suspect.     

Laser-evoked potentials: exogenous and endogenous components

The aim of this study was to distinguish the exogenous component (related to the physical properties of the stimulus) and the endogenous component (reflecting event-related cognitive processing) of the laser-evoked potential (LEP). Short painful radiant heat pulses generated by a CO₂-laser were applied to the dorsum of the right and left foot. LEPs were recorded with 5 scalp electrodes in the midline versus linked earlobes in 26 healthy subjects. In order to identify the exogenous component, the LEP was recorded during a standardised distraction task (reading a short story). To identify the endogenous component P3 for the LEP, a 2-stimulus oddball paradigm was used (20% probability of targets). When the task of the oddball paradigm consisted of pressing a button, a movement-related long-latency negativity (N1200) was recorded in frontal leads that was absent in a counting task. The LEP of targets, frequent non-targets and during distraction was dominated by a single large positivity. The amplitude of this positivity was task-dependent and increased the more attention the subject payed to the laser stimuli (distraction < neutral < non-target < target). The laser-evoked positivity during distraction had a peak latency of about 400 msec (P400) and a maximum amplitude at the vertex, which was independent of inter-stimulus interval. The P3 following laser stimulation had a significantly later peak at about 570 msec (P570) and a different scalp topography with a parietal maximum. Its amplitude decreased when the interstimulus interval was reduced from 10 to 6 sec. Under neutral instructions, the LEP positivity consisted of a superposition of both the exogenous P400 and the endogenous P570.     

Foraging behavior of the American oystercatcher Haematopus palliatus pitanay (Murphy 1925) on the intertidal ascidian Pyura praeputialis (Heller 1878) in the Bay of Antofagasta, Chile

Oystercatcher foraging behavior has been described for diverse intertidal prey such as limpets, mussels, and oysters. This paper describes foraging behavior of the American oystercatcher, Haematopous palliatus pitanay, on attached and wave-dislodged ascidians, Pyura praeputialis (prey with a restricted geographic range of 70 km) in the Bay of Antofagasta, Chile. Stabbed holes on the top of the ascidian's tunic, probing excursions, handling time, and five prey-handling sequential stages (striking, hammering, prying, cavity food searching, and swallowing) are described and measured. The need to determine ascidian profit-ability for oystercatcher species in Australia and Chile is highlighted. Received: January 19, 2000 / Accepted: July 23, 2000     

Recent introduction of the dominant tunicate,Pyura praeputialis (Urochordata,Pyuridae) to Antofagasta,Chile

The large sessile tunicate Pyura stolonifera (Pleurogona: Stolibranchiata: Pyuridae), has been regarded as a complex taxon with disjointed distributions, including Australia (Pyura stolonifera praeputialis), South Africa (Pyura stolonifera stolonifera) and South America (Chile, Antofagasta: Pyura sp., the 'piure de Antofagasta'), and has been cited under at least five taxonomic combinations. The 'piure de Antofagasta' is a competitively dominant species in rocky intertidal habitats and shows a limited geographical range (60-70 km) exclusively inside the Bay of Antofagasta. Using cytochrome oxidase I (COI) mitochondrial sequence data from Pyura specimens of the three taxa we tested whether the Chilean taxon represents: (i) a Gondwana relict; (ii) a more recently divergent species; or (iii) a recently introduced species. The results suggest that the Chilean taxon is a recent introduction to Chile from Australian populations and that Pyura stolonifera praeputialis, from Australia, and the 'piure de Antofagasta' are geographical populations of a single species: Pyura praeputialis; whereas the South African taxon represents a second species: Pyura stolonifera.     

Effects of inter-annual temperature variability,including ENSO and post-ENSO events,on reproductive traits in the tunicate Pyura praeputialis

Reproduction in tunicates is considered to be particularly vulnerable to changes in seawater temperature. In the present study we investigated the effects of sea surface temperature and temperature anomalies on reproductive traits of the non-native sessile tunicate Pyura praeputialis. Reproductive traits of this species were investigated over the course of 67 months, based on samples collected at two localities (eastern and western shorelines) of the Bay of Antofagasta. The study period included years with different oceanic and atmospheric conditions: a warm event, El Niño (June 1997 to July 1998); a cold event, La Niña (August 1998 to December 2000); and post-La Niña (January 2000 to December 2002). We compared two common indices (condition and gonadosomatic) and histological sections to evaluate the maximum reproduction index of this introduced species that dominates a large part of the rocky intertidal habitat in the Bay of Antofagasta. We found sexually mature individuals all year-round and a decrease in both reproductive indices matching the reduction in the sea surface temperature during the austral autumn and winter months. The results suggest that gonad development in this species is sensitive to sea surface temperature and thermal anomalies. We conclude that future thermal anomalies or projected global average sea surface warming associated with climate change might have no negative consequences on these reproductive traits of P. praeputialis. This suggests this species is ecologically resilient and that the ecosystem services that this species provides for other invertebrate and algal species will be maintained.     

Self‐sterility of eggs induced by exogenous and endogenous protease in the solitary ascidian,Halocynthia roretzi

The unfertilized eggs (UFE) of the solitary ascidian, Halocynthia roretzi, which are released naturally, are strictly self‐sterile. However, ovarian eggs isolated after spawning, which are expected to develop into UFE on the following day, are self‐fertile. Some exogenous proteases‐trypsin, chymotrypsin, papain and elastase‐induced self‐sterility in the self‐fertile ovarian eggs within an hour in vitro. The establishment of self‐sterility by the exogenous protease did not require the synthesis of new protein, or the participation of follicle cells. Some of the ovarian eggs were able to differentiate into self‐sterile eggs spontaneously in vitro. The protein synthesis inhibitors puromycin and cycloheximide had no effect on the spontaneous establishment of self‐sterility. However, several protease inhibitors such as leupeptin, soybean trypsin inhibitor (SBTI) and antipain, did inhibit the spontaneous establishment of self‐sterility. The possible participation of trypsin‐like protease in the establishment of self‐sterility in the ovary is discussed. Mol. Reprod. Dev. 52:99–106, 1999. © 1999 Wiley‐Liss, Inc.     

Passive flow through an unstalked intertidal ascidian: orientation and morphology enhance suspension feeding in Pyura stolonifera

Passive flow is believed to increase the gains and reduce the costs of active suspension feeding. We used a mixture of field and laboratory experiments to evaluate whether the unstalked intertidal ascidian Pyura stolonifera exploits passive flow. We predicted that its orientation to prevailing currents and the arrangement of its siphons would induce passive flow due to dynamic pressure at the inhalant siphon, as well as by the Bernoulli effect or viscous entrainment associated with different fluid velocities at each siphon, or by both mechanisms. The orientation of P. stolonifera at several locations along the Sydney-Illawarra coast (Australia) covering a wide range of wave exposures was nonrandom and revealed that the ascidians were consistently oriented with their inhalant siphons directed into the waves or backwash. Flume experiments using wax models demonstrated that the arrangement of the siphons could induce passive flow and that passive flow was greatest when the inhalant siphon was oriented into the flow. Field experiments using transplanted animals confirmed that such an orientation resulted in ascidians gaining food at greater rates, as measured by fecal production, than when oriented perpendicular to the wave direction. We conclude that P. stolonifera enhances suspension feeding by inducing passive flow and is, therefore, a facultatively active suspension feeder. Furthermore, we argue that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecologically relevant results.     

Fine‐scale hierarchical genetic structure and kinship analysis of the ascidian Pyura chilensis in the southeastern Pacific

Studying population structure and genetic diversity at fine spatial scales is key for a better understanding of demographic processes that influence population connectivity. This is particularly important in marine benthic organisms that rely on larval dispersal to maintain connectivity among populations. Here, we report the results of a genetic survey of the ascidian Pyura chilensis from three localities along the southeastern Pacific. This study follows up on a previous report that described a genetic break in this region among localities only 20 km apart. By implementing a hierarchical sampling design at four spatial levels and using ten polymorphic microsatellite markers, we test whether differences in fine‐scale population structure explain the previously reported genetic break. We compared genetic spatial autocorrelations, as well as kinship and relatedness distributions within and among localities adjacent to the genetic break. We found no evidence of significant autocorrelation at the scale up to 50 m despite the low dispersal potential of P. chilensis that has been reported in the literature. We also found that the proportion of related individuals in close proximity (<1 km) was higher than the proportion of related individuals further apart. These results were consistent in the three localities. Our results suggest that the spatial distribution of related individuals can be nonrandom at small spatial scales and suggests that dispersal might be occasionally limited in this species or that larval cohorts can disperse in the plankton as clustered groups. Overall, this study sheds light on new aspects of the life of this ascidian as well as confirms the presence of a genetic break at 39°S latitude. Also, our data indicate there is not enough evidence to confirm that this genetic break can be explained by differences in fine‐scale genetic patterns among localities.     

Empirical evidence for large‐scale human impact on intertidal aggregations,larval supply and recruitment of Pyura praeputialis around the Bay of Antofagasta,Chile

In northern Chile, Pyura praeputialis is an invasive species inhabiting rocky intertidal and subtidal habitats restricted exclusively to the Bay of Antofagasta where it forms extensive aggregations. The negative impact of Pyura gathering on mid‐intertidal abundances of this species has recently been reported at the south‐eastern end of this bay. In the present study we have increased sampling sites to cover the entire bay toward the north‐western end and the northern section, where a coastal marine reserve for the scallop fishery partially restricts shellfish gathering. Therefore, the sampling sites were chosen to represent different levels of shellfish gathering access along the northern shore of the bay. Long‐term monitoring (1999–2014) of changes in tunicate cover and the abundances of larvae and recruits at seven sites are reported. The opening of a remodelled artificial and recreational beach in 2012, on the central‐eastern shore of the bay, has increased accessibility to rocky intertidal platforms that started to be massively visited by Pyura gatherers from the summer of 2013. This allowed for the implementation of an intensive short‐term monitoring program of changes in tunicate cover and the abundances of their larvae and recruits. When gathering access was present the reduction in intertidal cover was generalized to the entire bay and followed by reductions in larvae and recruits. However, these reductions were not found in sites with more restricted gathering access. We conclude that continuous extraction by Pyura gatherers followed by reductions of conspecific larvae and recruits are the main drivers behind the reduced abundance of P. praeputialis in the entire bay of Antofagasta. Thus, if gathering is not stopped important ecosystem services provided by this tunicate in the bay may be threatened. Similar consequences may be expected if other massive and irreversible reductions in other species of the Pyura complex, that inhabit other coasts in the southern hemisphere, occur. The controversy concerning the impacts of invasive species and whether they cause negative, positive or neutral impacts to original ecosystems and fisheries is discussed.     

Interactions between exogenous and endogenous retroviruses

Retroviruses are distinguished from other viruses by several features. Notably, some retroviruses are present as normal elements in the genomes of virtually all vertebrates (endogenous proviruses). Others are exogenous, i.e. horizontally transmitted agents, many of which cause fatal diseases. The endogenous retroviruses are genetically transmitted and to a large extent their significance is uncertain. However, there is evidence suggesting that they contribute to the development of diseases in several animal species. Most importantly, some endogenous retroviruses are capable of interacting with exogenous counterparts through a variety of different mechanisms with serious consequences to the host. Conversely, others are advantageous in that they protect against exogenous retroviruses. In this review various types of interactions between endogenous and exogenous retroviruses are discussed, including receptor interference, recombination, phenotypic mixing, immunological interactions and heterologoustrans-activation.     

哺乳动物成体神经元的再生:内、外环境因子的作用

哺乳动物成体神经元的再生现象是最近三十年才被科学家们所认识并逐渐接受的。随着科研方法与实验技术的发展,在成年哺乳动物的一些特定脑区,比如海马齿状回(Dentate gyrus of the hippocampus)、室下区(Subventricular zone)和杏仁核(Amygdala)中发现了新生细胞。研究表明,内外环境因子可影响成体神经元的再生。具体表现在环境多样性、自主活动、有益社会交往、短日光照、化学刺激以及诸如5—羟色胺和脑源性神经营养因子等神经递质水平的增加,都会促进新生细胞的增生或存活。而负面社会交往及应激激素皮质酮对成体神经元的再生有抑制和降低作用。研究还表明,根据种和性别的差异,类脂醇激素对成体神经元的再生起到促进或抑制作用。最新的实验证实新生细胞在成体中具有显著功能[动物学报49(2)：151—162,2003]。