1,720,970 research outputs found
Observations on the life histories of the narcomedusae Aeginura grimaldii , Cunina peregrina and Solmissus incisa from the western North Atlantic
No full textIn this paper, we present evidence of direct development life cycles and brooding behaviour in two narcomedusae species in the family Cuninidae, as well as a histological description of another narcomedusan species from the family Aeginidae. Cunina peregrina were found to be brooding juveniles within the subumbrella. Brood contents varied in size and developmental stage. In addition, pairs of small white spheres enclosed within a membrane, most likely an oocyte and phorocyte (nurse cell) were observed around the stomach wall. It is suggested that two life cycles are occurring simultaneously: (1) asexual budding of actinula larvae from the parent medusa which develop into fully developed medusa; and (2) sexual reproduction producing an egg and phorocyte pair which develops into an actinula and a four-tentacle reduced medusa. In Solmissus incisa opaque spheres of various sizes were attached to the external walls of the gastric pouches. The spheres appeared to start off as a developing oocyte attached firmly to the adult, before developing into a sessile planula larva. The planula had a thick ectoderm and endoderm and was attached to the adult gastric pouches at its oral surface. This attachment appeared to pinch into the adult stomach pouch forcing some stomach tissue into the oral opening of the developing planula, possibly suggesting some nutritional aid from the adult. It is not clear whether this is a parasitism on the adult to gain nutrition or parental brood care. Nine specimens of Aeginura grimaldii were collected. White growths located on the subumbrellar surface in between the gastric pouches were found to be male gonads containing sperm. The gonads had a granular texture consisting of a lightly speckled black pigmentation, which became denser in the red subumbrella tissue. Histology revealed this to be porphyrin bodies. <br/
Thermal adaptations in deep-sea hydrothermal vent and shallow-water shrimp
No full textThe hydrothermal vent shrimp Mirocaris fortunata is commonly exposed to acute thermal gradients and rapid fluctuations in water temperature. The shallow-water shrimp Palaemonetes varians experiences less acute but similar magnitude fluctuations in its thermal regime. Acute respiratory response to temperature shock, and temperature preference was assessed for both species. Oxygen consumption rates were assessed across the natural temperature range reported for M. fortunata. Rates increased with temperature for both species. P. varians had a significantly higher rate of oxygen consumption than M. fortunata at all temperatures except 4°C. The rate of increase in oxygen consumption with increasing temperature was also significantly greater for P. varians. M. fortunata selected a significantly higher temperature than P. varians. Mirocaris fortunata maintains its metabolism at a more stable rate, which is likely an adaptation to acute changes in temperatures occurring at hydrothermal vents
Ocean warming and acidification adjust inter- and intra-specific variability in the functional trait expression of polar invertebrates
Full text linkClimate change is known to affect the distribution and composition of species, but concomitant alterations to functionally important aspects of behaviour and species-environment relations are poorly constrained. Here, we examine the ecosystem ramifications of changes in sediment-dwelling invertebrate bioturbation behaviour—a key process mediating nutrient cycling—associated with near-future environmental conditions (+ 1.5 °C, 550 ppm [pCO2]) for species from polar regions experiencing rapid rates of climate change. We find that responses to warming and acidification vary between species and lead to a reduction in intra-specific variability in behavioural trait expression that adjusts the magnitude and direction of nutrient concentrations. Our analyses also indicate that species behaviour is not predetermined, but can be dependent on local variations in environmental history that set population capacities for phenotypic plasticity. We provide evidence that certain, but subtle, aspects of inter- and intra-specific variation in behavioural trait expression, rather than the presence or proportional representation of species per se, is an important and under-appreciated determinant of benthic biogeochemical responses to climate change. Such changes in species behaviour may act as an early warning for impending ecological transitions associated with progressive climate forcing
Measurements for a 92 day climate manipulation experiment on replicate macrofaunal mesocosms collected on the cruise JR18006 in the Western Barents Sea and at Rothera research station in 2019
No full textMeasurements were collected during the 92 day lab-based experiment carried out on replicate macrofaunal mesocosms of Astarte crenata, Ctenodiscus crispatus, Cistenides hyperborea from the Western Barents Sea and Aequiyoldia eightsi and Laternula elliptica from Rothera Point, Antarctic Peninsula. Macrofauna were collected on cruise JR18006 in the Western Barents Sea and by hand during scuba dives in the cove adjacent to Rothera research station. Experimental measurements include carbonate chemistry indices measured in water samples; carbon dioxide concentration levels; benthic invertebrate response rate, burial rate, sediment particle reworking, bioirrigation, and associated nutrient concentrations; benthic invertebrate body size and individual biomass; sediment organic material content, and sediment particle size.</span
The reproductive ecology of the Antarctic bivalve Aequiyoldia eightsii (Protobranchia: Sareptidae) follows neither Antarctic nor taxonomic patterns
No full textThe accepted paradigm for reproduction in Antarctic marine species is one where oogenesis takes 18 months to 2 years, and a bimodal egg-size distribution where two cohorts of eggs are present in female gonads throughout the year. These slow gametogenic traits are driven by low temperature and/or the restriction of resource availability because of extreme seasonality in the marine environment. Here we present data on the reproductive ecology of the common Antarctic bivalve Aequiyoldia eightsii (Jay, 1839) (Protobranchia: Sarepidae) from monthly samples collected between January 2013 and May 2014 at Hangar Cove, Rothera Point on the West Antarctic Peninsula. These data show that A. eightsii is unusual because it does not follow the typical pattern expected for reproduction in Antarctic marine invertebrates, and differs also from closely related nuculanid protobranch bivalves with respect to gametogenic duration and reproductive periodicity. Continuous oogenesis, evidenced by the year-round occurrence of previtellogenic, vitellogenic, and ripe oocytes in female gonads, is supplemented by a seasonal increase in reproductive intensity and spawning in Austral winter (April–May), evidenced by the loss of maturespermatozoa and ripe oocytes from males and females, respectively. The simultaneous occurrence of these contrasting traits in individuals is attributed to a flexible feeding strategy (suspension and deposit feeding) in response to seasonal changes in food supply characteristic of the Antarctic marine environment. Asynchrony between individual females is also notable. Wehypothesise that the variability may represent a trade-off between somatic and reproductive growth, and previously reported internal interannual cycles in shell growth
Invariant Gametogenic Response of Dominant Infaunal Bivalves From the Arctic Under Ambient and Near-Future Climate Change Conditions
Full text linkArctic marine ecosystems are undergoing a series of major rapid adjustments to the regional amplification of climate change, but there is a paucity of knowledge about how changing environmental conditions might affect reproductive cycles of seafloor organisms. Shifts in species reproductive ecology may influence their entire life-cycle, and, ultimately, determine the persistence and distribution of taxa. Here, we investigate whether the combined effects of warming and ocean acidification based on near-future climate change projections affects the reproductive processes in benthic bivalves (Astarte crenata and Bathyarca glacialis) from the Barents Sea. Both species present large oocytes indicative of lecithotrophic or direct larval development after ∼4 months exposure to ambient [<2°C, ∼400 ppm (CO2)] and near-future [3–5°C, ∼550 ppm (CO2)] conditions, but we find no evidence that the combined effects of acidification and warming affect the size frequency distribution of oocytes. Whilst our observations are indicative of resilience of this reproductive stage to global changes, we also highlight that the successful progression of gametogenesis under standard laboratory conditions does not necessarily mean that successful development and recruitment will occur in the natural environment. This is because the metabolic costs of changing environmental conditions are likely to be offset by, as is common practice in laboratory experiments, feeding ad libitum. We discuss our findings in the context of changing food availability in the Arctic and conclude that, if we are to establish the vulnerability of species and ecosystems, there is a need for holistic approaches that incorporate multiple system responses to change
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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