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  • 1
    ISSN: 1573-5117
    Keywords: desiccation ; emergence ; intertidal zonation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Duration of emergence increases with tidal height on rocky shores therefore, emergence adaptations in intertidal species such as littorine and other prosobranch gastropods have been considered correlated with zonation patterns; temperature tolerance, desiccation resistance and aerial respiration rate all commonly assumed to increase progressively with increasing zonation level. Such direct correlations are rarely observed in nature. Maximal aerial gas exchange occurs in mid-shore, not high shore species. Temperature tolerance and desiccation resistance do not increase directly with shore height. Thus, hypotheses regarding physiological correlates of zonation require revaluation. A new hypothesis is presented that the high tide mark presents a single major physiological barrier on rocky shores. Above it, snails experience prolonged emergence and extensive desiccation; below it, predictable submergence and rehydration with each tidal cycle. Thus, desiccation stress is minimal below the high tide mark and maximal above it. Therefore, species restricted below high tide (the eulittoral zone) should display markedly different adaptive strategies to emergence than those above it (the eulittoral fringe). A review of the literature indicated that adaptations in eulittoral species are dominated by those allowing maintenance of activity and foraging in air including: evaporative cooling; low thermal tolerance; elevated aerial O2 uptake rates; and high capacity for radiant heat absorption. Such adaptations exacerbate evaporative water loss. In contrast, species restricted to the eulittoral fringe display adaptive strategies that minimize desiccation and prolong survival of emergence including: foot withdrawal, preventing heat conduction from the substratum; aestivation in air; elevated thermal tolerance reducing necessity for evaporative cooling; position maintenance by cementation to the substratum and increased capacity for heat dissipation. In order to test of this hypothesis the upper thermal limits, tissue and substratum temperatures on emergence in direct sunlight and evaporative water loss and tissue temperatures on emergence in 40 °C were evaluated for specimens of six species of eulittoral and eulittoral fringe gastropods from a granite shore on Princess Royal Harbour near Albany, Western Australia. The results were consistant with adaptation to the proposed desiccation barrier at high tide. The eulittoral species, Austrocochlea constricta, Austrocochlea concamerata, Nerita atramentosa and Lepsiella vinosa, displayed adaptations dominated by maintenance of activity and foraging during emergence while the eulittoral fringe littorine species, Bembicium vittatum and Nodilittorina unifasciata displayed adaptations dominated by minization of activity and evaporative water loss during emergence. The evolution of adaptations allowing tolerance of prolonged desiccation have allowed littorine species to dominate high intertidal rocky shore gastropod faunas throughout the world's oceans.
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  • 2
    ISSN: 1573-5117
    Keywords: acclimation ; Littorina obtusata ; Littorina saxatilis ; Littorinidae ; oxygen consumption ; respiration ; temperature effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two intertidal snails, Littorina saxatilis (Olivi, 1972) (upper eulittoral fringe/maritime zone) and Littorina obtusata (Linnaeus, 1758) (lower eulittoral) were collected from a boulder shore on Nobska Point, Cape Cod, Massachusetts, in July and acclimated for 15–20 days at 4 ° or 21 °C. Oxygen consumption rate (Vo2) was determined for 11–15 subsamples of individuals at 4 °, 11 ° and 21 °C with silver/platinum oxygen electrodes. Multiple factor analysis of variance (MFANOVA) of lo10 transformed values of whole animal Vo2 with log10 dry tissue weight (DTW) as a covariant revealed that increased test temperature induced a significant increase in Vo2 in both species (P〈0.00001). In contrast, MFANOVA revealed that temperature acclimation did not affect Vo2 in either L. saxatilis (P= 0.35) or L. obtusata (P= 0.095). Thus, neither species displayed a capacity for the typical metabolic temperature compensation marked by an increase in Vo2 at any one test temperature in individuals acclimated to a lower temperature that is characteristic of most ectothermic animals. Lack of capacity for metabolic temperature acclimation has also been reported in other littorinid snail species, and may be characteristic of the group as a whole. Lack of capacity for respiratory temperature acclimation in these two species and other littorinids may reflect the extensive semi-diurnal temperature variation that they are exposed to in their eulittoral and eulittoral fringe/maritime zone habitats. In these habitats, any metabolic benefits derived from longer-term temperature compensation of metabolic rates are negated by extreme daily temperature fluctuations. Instead, littorinid species appear to have evolved mechanisms for immediate metabolic regulation which, in L. saxatilis and L. obtusata and other littorinids, appear to centre on a unique ability for near instantaneous suppression of metabolic rate and entrance into short-term metabolic diapause at temperatures above 20–35 °C, making typical seasonal respiratory compensation mechanisms characteristic of most ectotherms of little adaptive value to littorinid species.
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  • 3
    ISSN: 1573-5117
    Keywords: nitrogen excretion ; O:N ratios ; ammonia excretion ; urea excretion ; Littorina saxatilis ; Littorina obtusata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates, the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg−1 h−1) than standard 5 mg L. obtusata (257 ng N mg−1 h−1) for snails acclimated to 21°C. Comparisons of Q10 values of total weight specific N excretion to Q10 values for weight specific oxygen consumption ({xxV}O2) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O2) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O2 in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range: 1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high protein catabolism) at 4°C and highest at 21°C.
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  • 4
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract (1) From May to December 1971 at six sites in upstate New York, samples of freshwater Aufwuchs (the largely algal “scum” flora) were collected on sets of exposed microscope slides. Successive standing crop biomass estimates are presented as analyses of total organic carbon (by wet oxidation) and total nitrogen (by micro-Dumas). Nutritional quality of the Aufwuchs can be assessed in carbon to nitrogen (C:N) ratios, and these are correlated with substantive data from concurrent studies on the growth and fecundity of second trophic level snails (Laevapex and Lymnaea). (2) Peak values of carbon biomass for the six sites range from 1.1 mgC/dm2 to 4.2 mgC/dm2, and mean C:N ratios ranged from 3.7:1 to 10.1:1 (corresponding to 29% protein). Higher snail growth rates (computed as increase in mgC/100 snails/30 days) and greater fecundities correlate, beyond certain minimal levels of carbon biomass, to lower C:N ratios in the corresponding Aufwuchs samples. (3) In discussing these nutritional aspects of Aufwuchs production, it is emphasized that freshwater macrophytes have C:N ratios well above 17:1, and are not much fed upon. In smaller bodies of fresh water, the most important sector of primary production is that of the Aufwuchs, and its nutritional quality in terms of lower C:N ratios is of unique significance to the bioenergetics of the second trophic level invertebrates.
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