1,721,136 research outputs found
Long-term acclimation and potential scope for thermal resilience in Southern Ocean bivalves
No full textDifferent physiological thresholds of species across biogeographic boundaries can show a long-term scope for adaptation. Characterised by cold-stenothermal conditions, polar and deep-sea environments are constrained by thermal stability across wide regions, and polar invertebrates are broadly considered to be highly sensitive to only subtle changes in thermal regime. We examine the respiratory response of two distinct biogeographic populations of the widespread bivalve Lissarca notorcadensis from deep waters in the Southern Ocean to acute thermal changes, and present distinct respiratory responses for each population. Populations from the Weddell Sea living in cooler water temperatures (<0 °C) show a lower tolerance to temperature increases, identified by an increase in oxygen consumption at temperatures from ?1 to 4 °C and mortality at 5 °C. In contrast, populations from the Scotia Sea, experiencing a thermally more variable cold-stenothermal environment driven by seasonality, show no significant increase in oxygen consumption up to 6 °C before peaking at 8 °C, and mortality during acclimation to 9 °C. Our results are discussed in relation to the hypothesis that long-term adaptation to thermal envelopes, over multiple generations, likely determines the degree of thermal resilience to warming and at population-specific levels. This contrasts to previous laboratory-based (short-term acclimation or acute) thermal response studies, which have shown high sensitivities and low acclimation capacities to temperature increases. We highlight the need for long-term acclimation studies and pose questions as to how selection for population-specific thermal tolerances may take place in a global warming scenario and within a macroecological context
Ecological plasticity of Southern Ocean bivalves from contrasting environments
No full textThe ability of a species to show plasticity throughout its range is suggested to be significant to the survival, maintenance, and expansion of populations. In the Southern Ocean, plastic traits may have enabled resilience since the onset of cooling, and given species the capacity to exploit empty niches after the retreat of ice in interglacial periods. Phenotypic plasticity has rarely been investigated in Southern Ocean invertebrates however, and the cold stenothermal environment, which prevails, has often been considered homogenous in its selection on fauna. Previous ecological studies have often pooled together material collected within predetermined biogeographic regions to overcome the limitations of sampling difficulties. Subtle differences between environments may however, be forcing ecological divergence in species, with possible implications for speciation processes. This thesis investigates the phenotypic plasticity and reproduction among populations of the small shallow-water brooding bivalve Lissarca miliaris over its Antarctic range, and of deep-sea protobranch bivalves Yoldiella ecaudata, Y. sabrina, and Y. valettei from contrasting benthic regions.The reproductive studies of L. miliaris revealed a previously unknown hermaphrodite trait, maximising the reproductive efficiency in a short-lived species where the female’s capacity to brood its young is limited. Reproduction is also described for the first time in deep-sea Antarctic protobranch bivalves and demonstrates lecithotrophic larval development. Additionally, Y. valettei shows evidence of simultaneous hermaphroditism, which may increase the likelihood of successful reproduction in low population densities. Phenotypic plasticity is observed among populations of bivalves, irrespective of geographical proximity, and with no latitudinal trends, but subtle differences in the environment. Significant differences in morphology and growth rates are identified among populations, and reproductive plasticity identified in L. miliaris and Y. sabrina. Increasing atmospheric temperature is also measured to show an effect on the ecophysiology of intertidal populations of L. miliaris at Signy Island over the past 40 years, with increasing growth rates at the cost of smaller offspring and pressure from endolithic algal decay
An unusual hermaphrodite reproductive trait in the Antarctic brooding bivalve Lissarca miliaris (Philobryidae) from the Scotia Sea, Southern Ocean
No full textThe Antarctic marine environment is extreme in its low temperatures and short periods of primary productivity. Invertebrates must therefore adapt to maximise reproductive output where low temperature and limited food slows larval development. Brooding is a common reproductive trait in Antarctic marine bivalves; larval development occurs within the mantle cavity, and larvae are released as fully developed young. Lissarca miliaris is a small, short lived, shallow-water brooding bivalve of circum-Antarctic distribution and found most abundant in the sub-Antarctic Magellan Region and islands of the Scotia Arc. Here, an unusual hermaphrodite reproductive trait is described for L. miliaris from King George Island (62?14’S, 58?38’W) and Signy Island (60?42’S, 45?36’W), Antarctica, using histological and dissection techniques. Specimens demonstrate simultaneous and sequential hermaphrodite traits; male and female gonads develop simultaneously but the production of oocytes is reduced while testes are ripe. Functional females are more abundant in specimens above 3mm shell length, although male reproductive tissue persists and functional males are found in all size classes. The number of previtellogenic oocytes produced by far exceeds the number of oocytes extruded and brooded, which may indicate an ancestral link to a planktotrophic past. Hermaphroditism in L. miliaris maximises reproductive efficiency in a short-lived species in which the female’s capacity to brood its young is limited, and demonstrates a specialised adaptation to a cold stenothermal and food limited environment prevailing in the Southern Ocean
Gonad morphology and gametogenesis in the deep-sea jellyfish Atolla wyvillei and Periphylla periphylla (Scyphozoa: Coronatae) collected from Cape Hatteras and the Gulf of Mexico
No full textObservations on gonad morphology and the structure of ovaries and testes of the coronate scyphozoans Atolla wyvillei and Periphylla periphylla are described based on samples collected from the Gulf of Mexico and Cape Hatteras (north-western Atlantic). In A. wyvillei, gonads of distinguishable sex were observed in medusae as small as 17 mm bell diameter (BD). Spermatogenesis occurred within follicles (average 366 254 mm) that were evenly distributed throughout the gonad. Oocytes in different stages of development were observed in all the females with gonads. Oocytes arise from the gastrodermis and migrate into the mesoglea to develop from early-mid to late vitellogenic oocytes characterized by a large nucleus and granular (organic-rich) cytoplasm. The largest oocytes measured were 543 mm and 263 mm from the Gulf of Mexico andCape Hatteras respectively. Possible reasons for this difference are discussed. In P. periphylla gonads were also initially observed in medusae 17 mm BD, although not all larger medusae had obvious gonads. Unlike A. wyvillei sperm follicles were arranged in long convoluted rows normally only one follicle thick. The organization of ooytes in female P. periphylla was very similar to A. wyvillei, although the gonads were small and the number of oocytes present in each gonad very low (,22). The largest oocyte measured was 777 mm in a 53 mm BD medusa. Although medusae were collected from one time period only (September) in this study, our findings appear to be in agreement with literature evidence indicating that coronate jellyfish produce few eggs continuously over a long time period. Aspects of gonad development and gametogenesis are discussed with respect to potential differences in site productivity and species identification
Differential adaptations between cold-stenothermal environments in the bivalve Lissarca cf. miliaris (Philobryidae) from the Scotia Sea islands and Antarctic Peninsula
Full text linkThe cold stenothermal nature of the Southern Ocean, and highly adapted fauna living within, raises the question of how much intra-specific variation there is among invertebrate populations, and how variation may have a role in speciation processes through ecological divergence, natural selection, and reproductive isolation. Despite decades of collecting biological material, this question remains largely unanswered, and many studies compare ‘populations’ of pooled material from wide geographic ranges to compensate for sampling constraints. In this study, variations in ecophysiological traits are explored by measuring growth, reproduction, and shell morphology among six populations of the small bivalve Lissarca cf. miliaris (Philippi, 1845) from the Southern Ocean, which experience subtle differences in temperature, disturbance, and food availability. There are significant differences in shell morphology and growth among different populations and slower growth rates at higher latitude populations. Prodissoconch sizes show an inverse ‘U’ shaped relationship with latitude, and are correlated with egg size at South Georgia and King George Island’s Potter Cove. Higher brood sizes at the South Georgia population represent a trade-off with lower egg size, and correlate with shell morphology by offering lower internal capacity to brood young. Lower investment into offspring and morphological variations in Lissarca cf. miliaris highlight the importance of local scale environmental variations on species’ ecology. These variations in physical traits appear to be underestimated in the Southern Ocean, but may be important drivers of ecological divergence and speciation, which should be considered in future genetic investigations on different invertebrate populations
Intracapsular development and dispersal polymorphism in the predatory gastropod Ocenebra erinaceus (Linnaeus 1758)
Full text linkIntraspecific polymorphism during development, such as poecilogony or dispersal polymorphism, has rarely been observed in the marine environment. The ecological advantages of this bet-hedging strategy, whereby the offspring from one species exhibit multiple developmental modes, include the potential for rapid colonization of new habitats whilst simultaneously achieving a degree of gene flow between populations. The muricid gastropod, Ocenebra erinaceus, is an active predator that is common in shallow-water marine environments, across England and France. Historically, O. erinaceus caused significant damage to shellfisheries but more recently it has been impacted by TBT induced imposex. Despite the previous attention given to this species, little is known about its encapsulated development. Studying O. erinaceus egg capsules from the Solent, UK, we describe intracapsular development at 15 °C, the in situ temperature at time of oviposition. Within each capsule all embryos developed; no nurse eggs were present. Development was categorised into eight ontogenetic stages, although not all individuals displayed every stage; embryos hatched as either swimming, late-pediveliger larvae or crawling juveniles after 59–69 days, indicating dispersal polymorphism to occur in this species. Swimming, late-pediveliger larvae completed metamorphosis within 72 h of hatching. As O. erinaceus continues to recover from TBT pollution, dispersal polymorphism may facilitate a rapid expansion in both population size and range. If this occurs, O. erinaceus has the potential to, once again, become a serious problem for shellfisheries around Europe
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/
Reproductive morphology of the deep-sea protobranch bivalves Yoldiella ecaudata, Yoldiella sabrina, and Yoldiella valettei (Yoldiidae) from the Southern Ocean
Full text linkThe protobranch bivalves of the Southern Ocean are poorly understood ecologically, despite their high abundances in soft sediments from the shelf to the deep sea. The subclass has a long evolutionary history predating the formation of the polar front, and knowledge of their reproductive biology is key to understanding better their successful radiation into the Southern Ocean, and within deep-sea basins. In this study, we for the first time investigate the reproductive morphology of three deep-water protobranchs; Yoldiella ecaudata from 500 m in the Amundsen Sea; Y. sabrina from between 200 and 4,730 m in the Amundsen Sea, Scotia Sea, and South Atlantic; and Y. valettei from 1,000 m in the Scotia Sea. All three species demonstrate evidence of lecithotrophic larval development with maximum oocyte size of 130.4, 187.9, and 120.6 µm in Y. ecaudata, Y. sabrina, and Y. valettei, respectively, further supported by prodissoconch I measurements. There is evidence for simultaneous hermaphroditism in Y. valettei. Asynchronous oocyte development within specimens of Y. ecaudata and Y. valettei is described, and also between populations of Y. sabrina separated by depth. The reproductive characteristics, comparable to those of North Atlantic deep-sea protobranch species, are discussed in the context of the cold thermally stable conditions prevailing on the deep-Antarctic continental shelf and deep sea. The requirement for reclassification of this complex subclass is also discussed in relation to observed soft anatomy and shell characteristics
Plasticity in shell morphology and growth among deep-sea protobranch bivalves of the genus Yoldiella (Yoldiidae) from contrasting Southern Ocean regions
Full text linkThe ecology of Antarctic deep-sea fauna is poorly understood and few studies have gone beyond assessing biodiversity when comparing deep regions of the Southern Ocean. Protobranch bivalves are ubiquitous in the deep ocean and are widely distributed in the Southern Ocean. This paper examines the potential respon ses to environmental differences in the common protobranchs Yoldiella valettei, Yoldiella ecaudata, and Yoldiella sabrina from contrasting deep-sea environments of the Weddell Sea, Scotia Sea, Amundsen Sea, and South Atlantic. There are significant differences in morphology between deep-sea regions in all species and a significant difference in shell weight in Y. valettei between the Amundsen Sea and Weddell Seas. Growth rates of Y. valettei and Y. ecaudata in the Amundsen Sea are also higher than elsewhere and Y. valettei have heaviest shells in the Amundsen Sea, suggesting more favourable conditions for calcification and growth. The plasticity observed among deep-sea regions in the Southern Ocean is likely to be driven by different oceanographic influences affecting temperature and food fluxes to the benthos, and demonstrate the species’ ability to differentially adapt between cold-stenothermal environments. This study suggests that subtle changes in the environment may lead to a divergence in the ecology of invertebrate populations and showcases the protobranch bivalves as a future model group for the study of speciation and radiation processes through cold-stenothermal environments
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