Freezing in the Antarctic limpet, Nacella concinna

The process of organismal freezing in the Antarctic limpet, Nacella concinna, is complicated by molluscan biology. Internal ice formation is, in particular, mediated by two factors: (a) the provision of an inoculative target for ice formation in the exposed mucus-secreting foot; and (b) osmoconformity to the marine environment. With regard to the first, direct observations of the independent freezing of pedal mucus support the hypothesis that internal ice formation is delayed by the mucal film. As to the second, ice nucleation parametrics of organismal tissue (head, midgut, gonad, foot) and mucus in both inter- and subtidal populations were characterized by high melting points (range = −4.61 to −6.29 °C), with only c.50% of a given sample osmotically active. At this stage it would be premature to ascribe a cryo-adaptive function to the mucus as the protective effects are more readily attributed to the physical properties of the secretion (i.e. viscosity) and their corresponding effects on the rate of heat transfer. As it is difficult to thermally distinguish between the freezing of mucus and the rest of the animal, the question as to whether it is tolerant of internal as well as external ice formation remains problematic, although it may be well suited to the osmotic stresses of organismal freezing.     

Distribution,growth and reproduction of the limpet Nacella (Patinigera) concinna (Strebel 1908) in relation to potential food availability,in Esperanza Bay (Antarctic Peninsula)

The present work addresses the effect of environmental factors (icing, water temperature, food availability) on the ecology of the patellid limpet Nacella (Patinigera) concinna, in a bay on the Antarctic Peninsula. Sampling was conducted at three depths (intertidal, 5m, 10m) from February 1987 to January 1988. Temperature was recorded and concentrations of Chlorophyll a were measured on the bottom, in the water and in the ice-water layer. The limpets were measured, weighed and a condition coefficient for somatic and gonadal mass was calculated. Their ages were estimated through size frequency distribution analysis and a seasonalized von Bertalanffy growth model was applied. The intertidal subpopulation migrated to deeper levels at the beginning of the icing season and recolonized the intertidal zone after ice retreat. The growth rate was very low (von Bertalanffy K 0.08). Growth rates showed important seasonal variations, with maxima during December and January. Nacella (P.) concinna spawns once a year and spawning coincided with raising water temperature (from -1.33°C to-0.84°C), and probably was also related to increasing spring food availability. Body mass increased during periods of high standing stock of microphytobenthos, revealing that ice-algae and phytoplankton were of minor importance as food sources for limpets in Esperanza Bay.     

Duration tenacity: A method for assessing acclimatory capacity of the Antarctic limpet, Nacella concinna

The limpet, Nacella concinna, collected from the Antarctic Peninsula (67°S), was incubated at − 0.3 °C and 2.9 °C for 9 months to test if the previously reported absence of acclimation capacity in Antarctic marine ectotherms could be due to the extended time it takes for them to adjust their physiology to a new stable state. Acclimation was tested through acute measurements of upper lethal limit and a modified measure of tenacity, that tested muscle capacity by measuring the length of time that N. concinna were able to remain attached to the substratum at different temperatures. Both measures acclimated in response to incubation to the higher temperature. Lethal limits were elevated in N. concinna incubated at 2.9 °C (8.1 ± 0.3 °C) compared to those incubated at − 0.3 °C (6.9 ± 0.4 °C). 2.9 °C incubated N. concinna also had a maximum tenacity at 2.1 °C, a higher temperature than the maximum tenacity of those incubated at − 0.3 °C, which occurred at − 1.0 °C. This study is the first to show that the Antarctic limpet can acclimate its physiology, but that it requires a greater period of time for acclimation to occur than previous studies have allowed for.     

Reproduction and lipids in the sub-Antarctic limpet Nacella (Patinigera) macquariensis Finlay, 1927

The reproductive cycle of the sub-Antarctic limpet, Nacella (Patinigera) macquariensis Finlay, 1927 is described from monthly gonad indices and slide smears of gonadal tissue. Two populations were sampled, from the eulittoral zone and at ≈4 m depth into the sublittoral zone. Gametogenesis started 2 months earlier in the eulittoral zone population; the breeding period, however, was sufficiently long to overlap in the two populations. This phase difference in reproductive cycles is discussed with respect to possible genetic divergence and correlation between timing within the reproductive cycle and environmental factors. Lipid was a prominent component of both the digestive gland and the gonad, but not of the foot. Changes in lipid levels during the reproductive cycle indicated that the digestive gland stored lipids which were transferred to the gonad during gametogenesis.     

Energetic cost of synthesizing proteins in Antarctic limpet, Nacella concinna (Strebel, 1908), is not temperature dependent

The energetic cost of protein synthesis is thought to account for a significant proportion of total metabolism. However, attempts to estimate the energetic cost of synthesizing proteins have resulted in surprisingly variable results, particularly for the small number of polar organisms studied, where cost estimates vary by two orders of magnitude. Much of this variability is probably the result of differing methodologies and experimental designs. Here we have used two different, carefully validated methods to measure the costs of protein synthesis in Antarctic limpets. One method, which utilized a specific protein synthesis inhibitor, was used to measure the cost of protein synthesis at two temperatures to test the hypothesis that the cost of protein synthesis varies with temperature. The cost of protein synthesis measured using the inhibitor cycloheximide was 13.95 +/- 0.77 micromol O2/mg protein, while correlation of absolute protein synthesis with oxygen consumption suggested the cost of protein synthesis was 19.58 micromol O2/mg protein. Water temperature did not alter the cost of protein synthesis in Nacella concinna (Student's t-test, P = 0.849, t = 0.19, df = 12). In a meta-analysis of literature values for the cost of protein synthesis there was no significant effect of temperature, but there was a significant relationship between the concentration of cycloheximide used to inhibit protein synthesis and the measured cost.     

Extinction and recolonization of maritime Antarctica in the limpet Nacella concinna (Strebel, 1908) during the last glacial cycle: toward a model of Quaternary biogeography in shallow Antarctic invertebrates

Quaternary glaciations in Antarctica drastically modified geographical ranges and population sizes of marine benthic invertebrates and thus affected the amount and distribution of intraspecific genetic variation. Here, we present new genetic information in the Antarctic limpet Nacella concinna, a dominant Antarctic benthic species along shallow ice‐free rocky ecosystems. We examined the patterns of genetic diversity and structure in this broadcast spawner along maritime Antarctica and from the peri‐Antarctic island of South Georgia. Genetic analyses showed that N. concinna represents a single panmictic unit in maritime Antarctic. Low levels of genetic diversity characterized this population; its median‐joining haplotype network revealed a typical star‐like topology with a short genealogy and a dominant haplotype broadly distributed. As previously reported with nuclear markers, we detected significant genetic differentiation between South Georgia Island and maritime Antarctica populations. Higher levels of genetic diversity, a more expanded genealogy and the presence of more private haplotypes support the hypothesis of glacial persistence in this peri‐Antarctic island. Bayesian Skyline plot and mismatch distribution analyses recognized an older demographic history in South Georgia. Approximate Bayesian computations did not support the persistence of N. concinna along maritime Antarctica during the last glacial period, but indicated the resilience of the species in peri‐Antarctic refugia (South Georgia Island). We proposed a model of Quaternary Biogeography for Antarctic marine benthic invertebrates with shallow and narrow bathymetric ranges including (i) extinction of maritime Antarctic populations during glacial periods; (ii) persistence of populations in peri‐Antarctic refugia; and (iii) recolonization of maritime Antarctica following the deglaciation process.     

Determinate growth and the scaling of photosynthetic energy intake in the solitary coral Fungia concinna (Verrill)

For many marine invertebrates, the maximum size of an individual is influenced heavily by environmental factors and may be limited by energetic constraints. In this study, an energetic model developed originally for anemones was applied to the free-living scleractinian Fungia concinna (Verrill) from Moorea (French Polynesia) to test the hypothesis that energetic constraints limit the size of this solitary coral. The modified model assumed that photosynthesis was the primary source of metabolic energy, and that metabolic costs were represented by aerobic respiration; these sources and sinks of energy were compared using daily energy budgets that were analyzed using double logarithmic regressions of energy against coral size. With this approach, energy limitation is characterized by a scaling exponent for energetic cost (b_cost) that is larger than the scaling exponent for energy intake (b_intake). For the size range of F. concinna studied, b_intake = 0.73 ± 0.09 and b_cost = 0.46 ± 0.10, thereby demonstrating that large individuals accumulated an energetic surplus, even when the expenditure associated with host tissue and symbiont growth was included in the model. The surplus of energy that this coral acquires as it grows appears to be driven by the scaling of traits associated functionally with the scaling of respiration and photosynthesis. Specifically, tissue biomass displayed a strong positive allometry with respect to surface area (i.e., b > 1), and this constraint on surface area may be the mechanistic basis of the low scaling exponent for metabolic cost. In contrast, the capacity for autotrophy - defined indirectly as Symbiodinium population density and chlorophyll content - increased isometrically with surface area, and likely contributed to the higher scaling exponent for intake relative to cost. Our results suggest that growth in F. concinna is not limited strictly by energy, but instead maximum size must be determined by alternative physiological or ecological constraints.     

Seasonal growth and reproduction of Gelidiopsis variabilis (Greville) Schmitz

Seasonal variations in growth, fruiting, and sporulation of Gelidiopsis variabilis (Greville) Schmitz occurring on the Visakhapatnam coast have been described. Only tetrasporophytes and vegetative plants were found in the populations analysed for 2$\text{1}\text{2}$ yr and seasonal changes were more marked in the abundance of tetrasporophytes, formation of stichidia, and in the spore output, than in the stature of the plants. Maximum development of the plants was observed each year between October and January–February and peak reproductive activity from July to September.     

A case of germinoma in a limpet (Patella coerulea) (Patellogastropoda)

Germinoma is a gonadal neoplasm originating from progenitor cells in germinal epithelium. Frequently described in some populations of bivalve molluscs, to our knowledge, germinoma has never been reported in gastropods so far. In this paper we describe the histopathological findings of some atypical cellular masses, originating in the undifferentiated germ cell layer in the male gonads of a limpet (Patella coerulea), whose morphological appearance resembled that of a germ cell tumor. The abnormal, and independent growth with no evidence of maturation of the undifferentiated and atypical germ cells, the limited number of follicles involved (n < 10%) and the absence of tissue invasion, supported a diagnosis of Stage 1 germinoma.     

Cold,freezing, and desiccation tolerance of the limpet Acmaea digitalis (Eschscholtz)

Cold, freezing, and desiccation tolerance were examined in the limpet, Acmaea digitalis (Eschscholtz). Fifty percent of the experimental population survived freezing at temperatures between ?10 ° and ?12 °C for at least 24 hr. In this temperature range, 60–80 % of the body water was frozen. The LD₅₀ for water loss by desiccation was 76.5% ± 1.3_δ. At 70–80% body water loss, solutes were concentrated between 350 and 500%. Some limpets failed to survive immersion in 450% seawater for 6 hr (100% scawater = salinity of 31‰), suggesting that much of the damage from freezing and desiccation was from an increased solute concentration. No glycerol could be detected in extracts of the foot and the visceral mass of A. digitalis during winter, confirming similar results in studies carried out on other intertidal molluscs.     

Influence of host plants on feeding, growth and reproduction of Papilio polytes (The common mormon)

We studied the feeding, growth and reproductive behaviour of Papilio polytes (common mormon butterfly) on five different host plants, Murraya koenigii, Toddalia asiatica, Glycosmis pentaphylla, Aegle marmelos and Citrus medica. The growth rate of P. polytes was fastest on M. koenigii followed by T. asiatica, C. medica, G. pentaphylla and A. marmelos. We related this to the nutrient contexts of the five plants. The plants T. asiatica and C. medica had higher water contents, which influenced the growth rate of the insect. M. koenigii was found to contain rich quantities of carbohydrate. M. koenigii, T. asiatica and C. medica were also rich in protein when compared to A. marmelos and G. pentaphylla. Total amino acid levels were comparatively higher in M. koenigii, T. asiatica, C. medica rather than A. marmelos and G. pentaphylla.     

Reproductive biology of the antarctic opisthobranch Philine gibba Strebel

Monthly samples (August 1974 to February 1976) and cultured material have been used to describe ovotestis maturation, spawning, and larval development of the Antarctic opisthobranch Philine gibba Strebel. Ovotestis maturation took one year and mature individuals (mean shell length 12 ± 1.4 mm) spawned a single egg mass in April–May containing 975–4760 eggs, 379 μm in diameter.Development was non-pelagic but an active veliger was observed within the egg capsule. Juveniles (mean shell length 375 ± 55 μm), which hatched from August to October, resembled adults except for the presence of eye spots and an exposed shell. The mantle enclosed the shell by February when shell length was 890 ± 30 μm.     

Impact of microphallid trematodes on the survivorship, growth, and reproduction of an isopod (Cyathura carinata)

Crustaceans are second intermediate hosts to several microphallid species (Trematoda). Some of these parasites are potentially pathogenic or manipulative. A laboratory experiment was performed to assess the impact of microphallids on the survival, growth and fecundity of Cyathura carinata, a protogynous hermaphroditic isopod, widespread within European estuaries. For nearly 12 weeks, experimental populations of infected and non-infected isopods were kept at 25 °C. C. carinata carrying microphallid cysts showed higher mortality rates than non-infected specimens and were not able to produce embryos. The reduced fecundity of infected isopods could be caused by parasite-induced castration and/or by mating failure due to behavioural modifications in one of the sexes. It might also be associated with lower growth rates and lower moulting frequencies, since infected C. carinata were significantly smaller than the non-infected after 9 weeks. This may imply a setback for the isopods to achieve sexual maturity (which may also affect the population sex ratio) and for females to lay their eggs in the marsupia. Regardless of the mechanisms involved, microphallids may have severe consequences for their host populations, through negative effects on survival, growth and fecundity. For species with direct development, such as C. carinata, parasite-induced reproduction failure may contribute to temporal fluctuations of abundance. Based on the present results, it is recommended to include parasites as an important factor influencing host populations from shallow-water ecosystems.     

The characterization of N-acetylglucosaminidases from the limpet Patella vulgata (L.)

The α- and β-N-acetylglucosaminidase activity of the limpet Patella vulgata (L.) is due to two enzymes. One of these enzymes hydrolyses both α- and β-N-acetylglucosaminidases and is referred to α,β-N-acetylglucosaminidase. The other is a β-N-acetylglucosaminidase (EC 3.2.1.30). Both enzymes have been isolated and characterized as glycoproteins containing 12% hexose, mainly galactose. The amino acid, neutral sugar and amino sugar content of the two enzymes is very similar, and the main difference lies in the presence of 9% sialic acid in β-N-acetylglucosaminidase. The molecular weight of α,β-N-acetylglucosaminidase is 217 000 and that of β-N-acetylglucosaminidase is 136 000. Evidence has been obtained for the presence of an additional sub-unit in the α,β-enzyme.     

Responses of the limpet, Cellana grata (Gould 1859), to hypo-osmotic stress during simulated tropical, monsoon rains

Although heat stress is often cited as the dominant physical stress on tropical shores, intertidal organisms in regions with monsoonal climates are also regularly exposed to prolonged periods of heavy rainfall. Such events are predicted to have adverse physiological effects on individuals and may result in mortality. In a series of laboratory experiments, the impact of simulated monsoonal rains was investigated on the patellid limpet, Cellana grata. Sub-lethal responses in terms of body water content, body fluid osmolality and heart rate were measured in two different size cohorts maintained on horizontal and vertical substrata. Limpets were unable to achieve any effective behavioural isolation, and exposure to either simulated rainfall or diluted seawater resulted in both large and small C. grata gaining water with subsequent dilution of mantle water and haemolymph osmolalities. With increased duration of rainfall, dilution of body fluids increased with little difference between individuals on horizontal and vertical surfaces. Body fluids generally showed proportional dilution during prolonged rain, but in some individuals there was evidence for regulation of the haemolymph relative to the mantle fluid. Overall, smaller limpets were more susceptible to prolonged rainfall than large animals in terms of swelling of soft tissues and detachment and also had higher heart rates than large limpets. Both cohorts reduced heart rates with prolonged rainfall, suggesting a degree of metabolic depression, especially on horizontal surfaces. In small limpets, no difference in heart rate was found with substratum orientation, whereas large limpets had elevated heart rates on vertical as compared to horizontal substrata, when exposed to either simulated rainfall or washed with dilute seawater. This may reflect the increased energetic costs required to maintain a relatively larger body on a vertical surface under stressful conditions. Monsoonal rainfall during emersion, and subsequent dilution of seawater, therefore, have sub-lethal physiological and possible lethal effects on intertidal limpets. This influence has been largely overlooked, but coupled with the possible synergistic effects of thermal stress, monsoon rains are likely to play an important role in community dynamics on tropical shores.     

Distribution and population dynamics of the limpet Patella aspera (Lamarck) in Bantry Bay

The population ecology of Patella aspera (Lamarck) was studied as part of an oil pollution baseline study. Contrary to earlier reports, P. aspera appears to be a protandrous hermaphrodite. Maturation of the gonads began in May-June and spawning took place in October. Variations in density, standing crop, and mean size were related to exposure to wave action and tidal level. The low shore in extreme exposure may be designated as the centre of P. aspera's range; abundance is high but biomass and mean size are reduced. Higher on the shore, and in reduced exposure to wave action, P. aspera attains a greater mean size and biomass, but is eventually replaced by P. vulgata L. Two main factors are adduced as being critical to competition between the two species. In terms of tidal level, P. aspera is less tolerant of desiccation than P. vulgata, while in terms of the exposure-shelter gradient, P. aspera appears to have a much less variable growth rate. P. aspera may be defined, therefore, as a non-migratory, low shore, specialist species, highly adapted to a specific set of environmental conditions, but lacking the ability to adapt to others.     

Vegetative reproduction in the octocoral Briareumasbestinum (Pallas)

Briareum asbestinum (Pallas), a common octocoral of Caribbean reefs, produces runner-like branches which are capable of attaching to the substratum and establishing new colonies. The subsequent death of the intervening runner leaves groups of genetically identical but physiologically distinct colonies. The origin of these colonies can be deduced by the presence or absence of runners. Analysis of colonies at Marsarkantupo in the San Blas Islands, Panama and at Carrie Bow Cay, Belize indicate that 23–56% and 18–67%, respectively, of the colonies at these sites originate from vegetative runners. In both areas the distribution of colonies of larval origin is not uniform. Colonies originating from larvae are patchily distributed within habitats and are over-represented in shallow habitats. The ability of B. asbestinum to reproduce vegetatively results in the spread and development of large populations of this species in many habitats where it might otherwise be rare.     

Nitrite modulates contractility of teleost (Anguilla anguilla and Chionodraco hamatus, i.e. the Antarctic hemoglobinless icefish) and frog (Rana esculenta) hearts

Being the largest form of intravascular and tissue storage of nitric oxide (NO) and a signalling molecule itself, the nitrite anion (NO₂⁻) has emerged as a key player in many biological processes. Since the heart is under an important NO-mediated autocrine-paracrine control, in mammals the cardiac effects of nitrite are under intensive investigation. In contrast, nothing is known in non-mammalian vertebrates. We evaluated nitrite influence on cardiac performance in the perfused beating heart of three different cold-blooded vertebrates, i.e. two teleost fishes, the temperate red-blooded Anguilla anguilla, the Antarctic stenotherm, hemoglobinless Chionodraco hamatus (icefish), and the frog Rana esculenta. We showed that, under basal conditions, in all animals nitrite influences cardiac mechanical performance, inducing negative inotropism in eel and frog, while being a positive inotrope in C. hamatus. In all species, these responses parallel the inotropic effects of authentic NO. We also demonstrated that the nitrite-dependent inotropic effects are i) dependent from NO synthase (NOS) activity in fish; ii) sensitive to NO scavenging in frog; iii) cGMP/PKG-dependent in both eel and frog. Results suggest that nitrite is an integral physiological source of NO and acts as a signalling molecule in lower vertebrate hearts, exerting relevant inotropic actions through different species-specific mechanisms.     

Field reproductive dynamics of the invasive slipper limpet, Crepidula fornicata

At least part of the invasive success of the slipper limpet, Crepidula fornicata, in European waters must be due to reproductive characteristics, yet the events underlying the easily-observed brooding and non-brooding periods have not yet been studied in this species. The reproductive system dynamics were therefore investigated using topological histology and quantitative histological techniques. Specimens were sampled twice monthly for 18 months from Bourgneuf Bay, France, a mid-latitudinal point in the European distribution of C. fornicata. Both the testicles and ovaries showed active and resting phases, corresponding to the brooding and non-brooding periods, respectively. Maximum spermatozoan production corresponds to the female brooding period (female incubation of oviposited eggs, mid-March to late August), and allows males to possess full spermatozoan stocks at the height of fresh mature oocyte availability. The year-round presence of mature oocytes in the female gonad is misleading, since the histological aspect reveals that they are vestigial oocytes which slowly degenerate during the brooding period, possibly providing metabolites for the developing oocytes that become increasingly abundant during this period. A complete scheme of the C. fornicata reproductive cycle is presented, showing the events in the major reproductive organs.The seminal vesicle shows high inter-month variability in sperm presence, suggesting year-round copulation and sperm storage in the seminal receptacle. The seminal receptacle shows a uniform covering of spermatozoa throughout the year, suggesting rapid renewal after fertilization, again in line with multiple copulation throughout the year. Given the limited available space on the seminal epithelium, against which all spermatozoa abut, as well as polyandrous copulation, it is postulated that sperm competition may take place.