Environmentally induced variation in uric acid concentration and xanthine dehydrogenase activity in Littorina saxatilis (Olivi) and L. arcana Hannaford Ellis

Littorina saxatilis and Littorina arcana collected from a boulder field low in the intertidal zone had a uric acid concentration significantly higher than snails collected from nearby cliff crevices that were at the upper limit of their vertical range on the shore. The absolute concentrations varied with different collections, suggesting a possible seasonal fluctuation in uric acid. L. arcana had a greater concentration of uric acid than did L. saxatilis when both were from the boulder field, but the two did not differ significantly when taken from crevices. Samples from the two sites were marked and transplanted; by four weeks the transplanted animals showed a tendency to develop a uric acid concentration similar to that of natives of the site, suggesting a physiological rather than a genetic adaptation. Xanthine dehydrogenase activity differed between animals from the two sites in the same manner as the uric acid concentration.     

The breeding migration of Littorina arcana Hannaford Ellis, 1978 (Prosobranchia: Littorinidae)

Two species of rough winkle, the oviparous Littorina arcana and the ovoviviparous L. saxatilis are very similar in their outward appearance and are commonly syntopic. This has led some researchers to regard these species as conspecific and to suggest that reproductive modality is not a fixed characteristic. However, the syntopy of these species is much more complex than has been supposed and data presented here show how the seasonally reproducing L. arcana migrates downshore during its breeding period, into areas where L. saxatilis is comparatively sparse. This results in a separation of the breeding populations of the two species and consequently a spatial separation of their juveniles, at least in their early stages. Selection pressures on the breeding animals and young juveniles will therefore differ.     

Microgeographic variation in allozyme and shell characters in Littorina saxatilis Olivi (Prosobranchia: Littorinidae)

Twenty-three enzymes and five shell parameters were screened in 11 subpopulations of Littorina saxatilis Olivi (= L. rudis Maton) occupying different habitats over a 1 km stretch of coastline. Shell morphology varied considerably and consistently with respect to degree of exposure, and since there is evidence that such morphology is at least partly under genetic control, it is likely that natural selection selects particular genotypes at particular locations. There was significant allozyme heterogeneity between neighbouring subpopulations, sometimes only metres apart, but little of the allozyme variability could be related directly to environmental pressures. Thus, with the exception of the Odh locus, the considerable morphological differentiation between snails from exposed and sheltered sites was not reflected in differentiation of those genes coding for electrophoretically assayed enzymes. At the Odh locus, virtually all the genetic differentiation between subpopulations was attributable to differentiation between habitat types. Two loci, Sod-1 and Aat-1, showed highly significant genetic disequilibrium, and possible reasons for this are explored. The population structure as assessed electrophoretically accords well with the stepping-stone model which permits greater differentiation of neighbouring populations than the island model, and which seems realistic in the ovoviviparously reproducing L. saxatilis, where the greater part of gene flow is likely to occur through the occasional migration of adults between contiguous populations.     

Rapid colonization of Belgian breakwaters by the direct developer,Littorina saxatilis (Olivi) (Prosobranchia,Mollusca)

The Belgian coast has no natural rocky sites but a number of man-made constructions are colonized by rocky shore organisms. The rough periwinkle, Littorina saxatilis (Olivi), lacks a planktonic larval stage but is found on most breakwaters along the Belgian coast, a few built as recently as 1986. This indicates a good potential of dispersal along this sandy shallow coast, nearly as good as for the planktonic developer Littorina littorea (L.) which is found on generally the same sites in Belgium. The breakwater populations of L. saxatilis, however, tend to be somewhat less variable (level of heterozygosity about 10% less) than non-Belgian L. saxatilis populations of natural sites. This suggests that the breakwater populations have passed through bottlenecks when founded, but probably restored population sizes fairly rapidly afterwards. No relationship is found between geographic and genetic distances between populations of L. saxatilis.     

Inheritance of longitudinal shell bands in the snails Littorina obtusata and Littorina saxatilis (Gastropoda, Prosobranchia)

The hypothesis of a monogenic inheritance of dark longitudinal bands on the shell in the gastropods Littorina obtusata and L. saxatilis was checked. One gene having two alleles proved to be responsible for the shell banding pattern in both of the species. The presence of bands was a dominant character in either case.     

Growth rate differences between upper and lower shore ecotypes of the marine snail Littorina saxatilis (Olivi) (Gastropoda)

Shell polymorphisms are widespread among those intertidal gastropods that lack a pelagic spreading stage. These polymorphisms may indicate diversifying selection in a heterogeneous habitat, but to do this the variation must be at least pardy inherited. Galician populations of Littorina saxatilis (Olivi) living in exposed rocky shores are highly polymorphic in several shell traits, e.g. ornamentation, banding and size. Mature snails of the upper-shore ridged and banded (RB) morph is, for example, often twice as large as mature individuals of the lower-shore smooth and unbanded (SU) morph of the same shore.
We investigated the hypothesis that lower-shore snails grow more slowly and that differences in growth rate were at least partly inherited and could be explained by diversifying selection. We released snails of different origin (upper, mid- and lower shore) and morph (RB, SU and hybrids) at different shore levels and compared their shell increment after one month of growth. We found that despite considerable variation among individuals and among replicate samples (together about 53% of the total variation), average rates of growth differed between morphs. RB snails both from the upper and mid-shores grew at a high rate at all shore levels, SU snails grew considerably less, and hybrids grew at intermediate rates, at all levels. Inherited difference among morphs explained about 34% of the total variation while effects of shore levels and the interaction morph x shore level explained only 5 and 7%, respectively. Thus a large part of the difference in growth rate leading to different adult sizes of the two morphs has probably evolved due to spatially varying selection favouring large sizes in upper-shore and small sizes in lower-shore environments.     

Lack of metabolic temperature compensation in the intertidal gastropods,Littorina saxatilis (Olivi) and L. obtusata (L.)

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.     

Mitigating thermal effect of behaviour and microhabitat on the intertidal snail Littorina saxatilis (Olivi) over summer

High shore intertidal ectotherms must withstand temperatures which are already close, at or beyond their upper physiological thermal tolerance. Their behaviour can provide a relief under heat stress, and increase their survival through thermoregulation. Here, we used infrared imaging to reveal the thermoregulatory behavioural strategies used by the snail Littorina saxatilis (Olivi) on different microhabitats of a high shore boulder field in Finistère (western France) in summer. On our study site, substrate temperature is frequently greater than L. saxatilis upper physiological thermal limits, especially on sun exposed microhabitats. To maintain body temperatures within their thermal tolerance window, withdrawn snails adopted a flat posture, or elevated their shells and kept appended to the rock on the outer lip of their aperture with dried mucous (standing posture). These thermal regulatory behaviours lowered snail body temperatures on average by 1–2 °C. Aggregation behaviour had no thermoregulatory effect on L. saxatilis in the present study. The occupation of biogenic microhabitats (barnacles) was associated with a 1 °C decrease in body temperatures. Barnacles and microhabitats that experienced low sun exposure, low thermal fluctuations and low thermal maxima, could buffer the heat extremes encountered at high shore level especially on sun exposed microhabitats.     

Characterization of polymorphic microsatellites for the rough periwinkle gastropod, Littorina saxatilis (Olivi, 1792) and their cross-amplification in four congeners

Eight new microsatellite loci were characterized for Littorina saxatilis (Olivi, 1792) and tested for their cross-hybridization in congeners. All loci were polymorphic in Irish and Celtic Sea samples, with an average number of alleles per locus of 15 (range, 6–31). Observed and expected locus heterozygosities ranged from 26 to 85% and from 53 to 92%, respectively. Three loci showed excess homozygosity and significant departures from Hardy–Weinberg expectations in one sample, possibly due to null alleles, population structuring or inbreeding. No linkage disequilibrium was detected among loci within samples. A high degree of cross-hybridization was observed in closely related congeners and most loci were polymorphic. These markers will be useful for investigating population genetic diversity and connectivity in coastal populations, especially for marine reserve design.     

Combined effect of environmental temperature and trematodes on fatty acids composition of lipids of Littorina saxatilis (Olivi 1792) (Gastropoda, Prosobranchia)

An effect of environmental temperatures and invasion by helminthes larvae on fatty acids composition of digestive gland lipids of marine littoral gastropod Littorina saxatilis from White Sea and Barents Sea was investigated. We have compared gastropods from boreal and subarctic populations. It was found that gastropods from waters of lower temperature have increased omega3/omega6 fatty acids ratio. However, saturation index of individual membrane phospholipids was not affected. Also, content of eicosenoic acid (20:1) in individual phospholipids was not affected by temperature. Invasion increases the omega3/omega6 ratio of common lipids but not the omega3/omega6 ratio of common and individual phospholipids with the exception of phosphatidilcholine of cold water mollusks from Barents Sea that had this ratio doubled. In contrast to temperature, invasion affects the content of eicosenoic acid that was increased in the investigated organs. Adaptability of these effects is discussed regarding parasite-host system.     

Species relationships and population structure of Littorina saxatilis Olivi and L. tenebrosa Montagu in Ireland using single-strand conformational polymorphisms (SSCPs) of cytochrome b fragments

Littorina saxatilis is a ubiquitous snail of intertidal habitats in the North Atlantic. Shell type in littorinids is extremely polymorphic and defined by habitat. Taxonomy based upon shell type has been revised in the light of anatomic and genetic information, but uncertainties remain. In this study, the population structure of L. saxatilis and L. tenebrosa was studied at 11 sites in Ireland using single-strand conformational polymorphisms of a 375-bp portion of the cytochrome b gene, and the status of L. tenebrosa, the small, fragile-shelled, brackish water type, was considered. The genetic patterns among L. saxatilis and L. tenebrosa populations were examined over varying distances and L. tenebrosa was compared with adjacent L. saxatilis populations at four sites on the west coast of Ireland and one site on the east coast. Haplotype diversity was high with 32 haplotypes present among 995 individuals. Pairwise tests suggest gene flow over small scales among and between habitat types and may reflect the stochastic legacy of postglacial recolonization over larger scales. In AMOVA tests, geography explained nearly twice as much of the variance (30%) as habitat type (18%), indicating that gene flow is more restricted by distance than by habitat type, and supporting the status of L. tenebrosa as an ecotype of L. saxatilis rather than a separate species.     

Horizontal and Vertical Distribution of the Zebra Mussel (Dreissena polymorpha,Pallas) Larvae in the Modrac Reservoir,Bosnia and Herzegovina

In the Modrac Reservoir, loaded with coal separation suspended material, rapid development of the zebra mussel (Dreissena polymorpha) took place from at least 1987. It is probably the first distinguished “infection” for this part of Balkan Peninsula, caused by this organism. Horizontal and vertical distribution of this mussel, at 15 different reservoir profiles, had been investigated.     

Effects of ambient temperature and of temperature acclimation on nitrogen excretion and differential catabolism of protein and nonprotein resources in the intertidal snails,Littorina saxatilis (Olivi) and L. obtusata (L.)

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.     

Distribution of pigments in the shell of the gastropod <Emphasis Type="Italic">Littorina obtusata</Emphasis> (Linnaeus, 1758)

The patterns of pigment distribution in the shell of the gastropod Littorina obtusata were studied. It was determined that the background coloration of the periwinkle shell resulted from the coloration interaction of the external and internal parts of the ostracum. The coloration of the latter can be monochromatic or twolayer. The external and/or internal zones of the ostracum can be colored purple, white, orange, yellow and greenish. Only 11 of 25 possible color combinations were recorded. Four additional versions of shell background coloration resulted from partial depigmentation of external or internal parts of ostracum. The mottling pattern corresponded to white or depigmented lenticular sites in the external part of the ostracum. The bands on the shell may be subdivided into two groups according to their means of formation. The bands that appeared due to redistribution of pigments forming background coloration belonged to the first group, the bands arising as a layer of additional (white, yellow, orange) pigment belonged to the second group. Various band versions could occur simultaneously in the same individual.     

Distribution and abundance of the alkali fly (Ephydra hians) Say at Mono Lake,California (USA) in relation to physical habitat

The distribution and abundance of larval, pupal, and adult stages of the alkali fly Ephydra hians Say were examined in relation to location, benthic substrate type, and shoreline features at Mono Lake. Generation time was calculated as a degree-day model for development time at different temperatures, and compared to the thermal environment of the lake at different depths.Larvae and pupae have a contagious distribution and occur in greatest abundance in benthic habitats containing tufa (a porous limestone deposit), and in least abundance on sand or sand/mud substrates. Numbers increase with increasing area of tufa present in a sample, but not on other rocky substrates (alluvial gravel/cobble or cemented sand). Standing stock densities are greatest at locations around the lake containing a mixture of tufa deposits, detrital mud sediments, and submerged vegetation. Shoreline adult abundance is also greatest in areas adjacent to tufa. The shore fly (ephydrid) community varies in composition among different shoreline habitats and shows a zonation with distance from shore.The duration of pupation (from pupa formation to adult eclosion) becomes shorter as temperature increases. The temperature dependence of pupa development time is not linear and results in prolonged time requirements to complete development at temperatures below 20 °C. About 700 to 1000 degree-days are required to complete a generation. Degree-days of time available in nature declines by 10 to 50% at depths of 5 and 10 metres relative to surface waters (depending on the extent of mixing), resulting in fewer possible generations. Essentially no growth would be expected at 15 m, where temperature seldom exceeds the developmental minimum. It is concluded that reduced substrate availability and low temperatures may limit productivity of the alkali fly at increasing depths in Mono Lake.     

Distribution and abundance of postlarval and juvenile Pleuragramma antarcticum (Pisces, Nototheniidae) off Terra Nova Bay (Ross Sea, Antarctica)

During the Italian Antarctic Expedition of 1987–1988 zooplankton was collected in Terra Nova Bay (Ross Sea) by a multinet BIONESS (250-μm or 500-μm net mesh size). The early life history of Pleuragramma antarcticum was described from 268 samples. More than 98% of a total of 34,436 fish larvae belonged to P. antarcticum. The mean relative abundance in the whole area for positive 0 to 150-m hauls was 434 ind./100 m³ (±720 SD). Postlarvae were most abundant and frequent in the samples (99.8%) while low concentrations of juveniles were found (n=67). Length of age group 0 ranged from 8 to 20 mm and age group 1+ were from 36 to 53 mm. Average growth rate over a period of 1 year was 0.08 mm per day. Based on modal values, the mean daily increment of P. antarcticum postlarvae in the period 5 January to 2 February (29 days) was about 0.21 mm. Highest abundances occurred near Cape Washington (mean: 2,108 ind./100 m³) while lower densities were recorded in the northern basin of the self (31 ind./100 m³). Horizontal and vertical distribution patterns in Terra Nova Bay seem to be strictly correlated to hydrographic features and different water masses with highest densities associated with the westward flowing current of the limb of the Antarctic coastal current and southern limb of the Ross Sea Gyre. These currents become part of the clockwise gyre in Terra Nova Bay. More than 62% of the postlarvae were collected in well-stratified warm surface water (0–50 m) near the summertime thermocline (20–70 m). The northern part of Terra Nova Bay seems to represent nursery ground of early stages of P. antarcticum and the presence of permanent polynya could provide favourable food conditions for development of the first stages of life. Differing distribution patterns probably reflect an interaction of various parameters including bathymetry, floating ice shelf, hydrographic features such as currents, local eddies and frontal systems, with P. antarcticum postlarval biology (spawning) and ecology (feeding, horizontal and vertical distribution patterns). Received: 10 June 1996 / Accepted: 19 July 1997     

Distribution, abundance, and conservation of Vinaceous Amazons (Amazona vinacea) in Argentina and Paraguay

ABSTRACT.   Vinaceous Amazons ( Amazona vinacea ) are endemic to the Atlantic forest of southeastern Brazil, eastern Paraguay, and the province of Misiones in Argentina. We searched for Vinaceous Amazons throughout the western part of its range in Argentina and Paraguay during 1639 days of fieldwork from 1997 to 2006. These parrots have disappeared from most areas where they were historically recorded in these countries, and are now limited to a few sites in northeastern Paraguay and central Misiones (Argentina). We estimate the minimum remaining populations at 220 individuals in Paraguay and 203 individuals in Argentina. Important sites for the species are (1) the farming area from San Pedro to Tobuna (Misiones, Argentina) and (2) the Itaipú reserves complex and Reserva Natural Privada Itabó (Paraguay). In our surveys, Vinaceous Amazons were absent from the largest tracts of forest in Misiones, and were most often observed feeding, roosting, and nesting in small forest remnants and in agricultural areas that included forest fragments and isolated trees. Threats to amazons in these areas include nest poaching, forest clearing, and being shot as a crop pest. We confirmed 40 Vinaceous Amazons kept as pets in 35 homes between San Pedro and Tobuna. Environmental education and law enforcement are urgently needed to reduce threats in populated areas, and subsistence farmers need technical and logistical support to slow or stop the conversion of forest into cropland. Finally, additional study is needed to determine this amazon's habitat preferences, nest site requirements, and demography in different habitats.     

A morphologic and genetic analysis of Littorina saxatilis (Prosobranchia) from Venice, and on the problem of saxatilis—rudis nomenclature

Shell morphology and allozyme patterns of 17 enzymes are analysed within the isolated population of L. saxatilis Olivi (1792) from Venice, the type locality of the species. The shell morphology is compared to three different L. saxatilis phenotypes from Sweden, and showed to be similar to the brackish water 'tenebrosa' type. The Venice population is genetically more distant from British and Swedish populations than are the latter from each other. Less variability (heterozygosity) within the Venice compared to the Atlantic populations is probably a consequence of random genetic drift during a period of small population size.
The nomenclature of L. saxatilis in the Atlantic is discussed and it is suggested that until the exact taxonomic relationship between the Mediterranean and the Atlantic populations has been confirmed by, for example, cross-breeding experiments, the name 'saxatilis' should be kept for the non-Venetian populations (described by Maton (1797) under the name 'rudis').