Determinants of reproductive potential and population size in open populations of Patella vulgata

The importance of external and internal population processes in determining variation in reproductive output and variation in population size were quantified with model simulations for open populations of the sequentially hermaphroditic limpet Patella vulgata using field data from the Isle of Man and South West Ireland. Cross-correlation analyses of model outputs and elasticity analyses show that population dynamics are dominated by the effects of large females, and that recruitment adds little to reproductive output. However, populations experiencing low but highly variable recruitment appear male limited and recruitment pulses carrying young males into the population are correlated to reproductive output with a 2–5-year lag. We conclude that pulses in recruitment can be a major structuring force in these limpet populations, but site-specific post-recruitment processes will determine the relative importance of recruitment to population dynamics and the lag between recruitment and reproductive output.     

Factors affecting variability of foraging excursions in a population of the limpet Patella vulgata (Mollusca,Gastropoda)

Paths moved by the limpet Patella vulgata L. were monitored on a sheltered vertical rocky shore in North Wales using time-lapse photography throughout nocturnal low tides in April and November 1992, roughly corresponding to periods of minimum and maximum gonad ripeness, respectively. Various motion parameters, including total duration, total length, and maximum distance reached from home were computed from 124 complete foraging routes obtained from 18 higher-zoned and 18 lower-zoned limpets. P. vulgata typically performed a single loop per night (average total length, ca. 70 cm), moving from the individual home scar to graze the surrounding algal grounds (average maximum distance, ca. 25 cm), then following its own trail back home. On the average, limpets moved from the home scar during three of four available nocturnal low tides and exploited about half the emersion time. Evidence for size-related variability in behaviour was found, as a positive correlation was assessed between both total duration and legth of the excursions, and shell length. In addition, zonation was proved to affect the limpets' foraging behaviour, since low-shore limpets moved faster and covered greater distances than high-shore ones. Moreover, consistent seasonal variation in foraging behaviour emerged, since in April the excursions were longer and longer-lasting than in November, but limpets exploited a larger fraction of potential activity phases in November than in April. The within-population variability in the temporal and spatial characteristics of the foraging excursions is discussed in relation to the available data on zonal and seasonal variation of food resources and in relation to physiological changes due to reproductive cycle.     

Comparison of allozyme and mitochondrial DNA spatial differentiation in the limpet Patella vulgata

Allozyme and restriction enzyme analysis of mtDNA was used to study variation in samples from British populations of the marine limpet Patella vulgata in two regions. South Wales and Northeast England. Allozyme analysis revealed significant differences in allele frequencies among samples. However F _ST (population differentiation) values were no higher between than within regions, indicating that genetic heterogeneity was localised and not related to geographic separation. For mtDNA, samples from South Wales exhibited higher haplotype diversity values than samples from Northeast England. In addition there were substantial differences in the haplotype distribution between regions. The value of , the haploid analogoue of F _ST , was low within regions (=0.09) but high between regions (=0.44). The estimated difference in migration rate for allozymes and mtDNA exceed the neutral expectation, unless it is assumed that there are influential differences in the magnitude of female and male gametic dispersal.     

Relationships between intertidal zonation and circatidal rhythmicity in littoral gastropods

The presence and phase of circatidal rhythmicity was correlated with vertical zonation and other ecological factors. Ten species were studied in the field and in aktographs under controlled conditions in the laboratory. Retina plicata, Melanerita atramentosa, Bembicium nanum, Austrocochlea obtusa and Morula marginalba occupied mid- or upper-littoral zonations, and were subjected to regular tidal influence. They were active at high water and for a period after the ebb, possibly as these were the times of least desiccation. Each possessed a circatidal activity rhythm under non-tidal conditions. Midlittoral Amphinerita polita and lower-littoral Theliostyla albicilla were active at low water, possibly because their prefered habitats reduced desiccation and other selective forces, for example wave action and predation, determined the phase of the rhythmicity. Supra- and upper-littoral Nodilittorina pyramidalis and Melarapha unifasciata and lower- and infralittoral specimens of Bembicium auratum displayed no overt circatidal rhythmicity, possibly because they were not subjected to regular tidal action.     

Migrational orientation in two species of littoral gastropods (Littorina angulifera and Nerita senegalensis)

Littorina angulifera (Lamark) and Nerita senegalensis Gmelin, both intertidal gastropods, appear to have a preference for specific levels of the shore. In some experiments conducted both in the laboratory and in the field, displaced snails exhibited a general homing behaviour when displaced upshore or downshore. Cues involved in this migrational behaviour have not clearly been identified.     

A comparative study of metabolic energy expenditure in the limpets Patella cochlear,P. oculus and P. granularis

Oxygen consumption of 3 species of Patella was measured in air and water at various temperatures. Measurements at constant temperature over a full tidal cycle showed no tidal or light-dark rhythms. Measurements under conditions simulating natural tidal, temperature and day-night cycles allowed calculation of daily respiratory energy budgets. P. cochlear occurs low on the shore, but experiences a food shortage due to intense intraspecific competition. Its rate of respiration is moderate, but metabolic expenditure is kept low because exposure to air is brief and body temperatures seldom rise above 23°C. P. cochlear has a respiratory rate-temperature (R-T) curve which peaks at 20°C and forms a plateau between 20° and 32.5°C. The midshore P. oculus has abundant food and adopts an exploitative strategy. Growth rate is very high, and this high turnover of energy is linked with a high metabolic rate, high Q10 (temperature coefficient) values, high body temperatures during the day-time low tide, and a respiratory R-T curve peaking at 32.5°C. Small P. oculus occur mainly in intertidal pools and respire faster in water, while larger individuals occur on bare rocks and respire faster in air over the upper temperature range. In contrast, the upper-shore P. granularis has little food, and conservation of energy is essential, particularly as its growth rate is moderate and its reprocurve output high. Respiratory losses are reduced by suppression of the R-T curve and low Q10 values, resulting in relative independence of temperature. Small P. granularis occur low on the shore and respire slower in water. Larger individuals occur at high levels due to migration, and respire slower in air. This further reduces respiratory energy losses. The patterns of respiration in these 3 species are thus related to food availability, resulting in exploitative or conservationist strategies.     

Annual variation in soft-body dry weight,reporductive cycle and sex ratios in populations of Patella vulgata at adjacent sites in the Orkney Islands

The relationships of shell length and internal volume with soft-body dry weight for three populations of Patella vulgata L. at Sandwick Bay in the Orkney Islands were studied between August, 1979 and March, 1982. Seasonal and annual fluctuations in the regression constants were explained by age-related variations both in overall growth rates and in the amount of effort directed toward gonad production. The reproductive cycle at all three sites was well synchronised, rapid development occurring between late June and November, with spawning following sometime between December and February; the whole population then remaining in the neuter/resting stage until July. The sex ratios within the population with respect to size (age) were examined; the majority of small, mature individuals were male, the number of females increased with size, although the largest individuals at each site were males. The sex ratio in the different populations varied from 2:1 to 6:1 in favour of males, but the “functional” ratio was much less in the latter due to the population structure.     

Genetic variation in marine teleosts: High variability in habitat specialists and low variability in habitat generalists

Genetic variation was reviewed in 106 species of marine teleosts. Two heterozygosity estimates were used, one including all protein and enzyme loci and a second excluding the non-enzymatic protein loci. Mean heterozygosities are 0.055±0.036 based on all loci in 106 species and 0.060+0.038 based on enzymatic loci in 89 species. A significant negative correlation was noted between heterozygosity and the proportion of general protein loci included in the estimate. A comparison was made of heterozygosities among taxonomic orders and families, life zones, reproductive mode, geographical range and size. High levels of genetic variation are found in Clupeiformes, Atheriniformes, Pleuronectiformes, temperate pelagic, tropical, intertidal-sublittoral and wide-range species. Low levels of genetic variation are found in Gadiformes, Scorpaeniformes, temperate demersal, polar, and narrowrange species. The most striking differences in heterozygosities are between temperate demersal flatfishes and temperate demersal round fishes. It is suggested that much of the data can be explained by a habitat specialist-generalist model, with high heterozygosities in specialists and low heterozygosities in generalists, but that this is only one of a mosaic of factors which influence genetic variation.     

Genetic variability in Gymnodiniaceae ITS regions: implications for species identification and phylogenetic analysis

The internal transcribed spacer (ITS) regions and 5.8S rRNA genes from several strains of toxic Gymnodiniaceae were sequenced and subjected to phylogenetic analysis with other Gymnodiniaceae species. Sequence comparisons showed that high sequence divergence existed in Gymnodiniaceae, especially in the genus Gymnodinium. The amplicons of the ITS regions from Amphidinium and Gyrodinium species were 438–439 and 604–605 bp, respectively, and those of the Gymnodinium species ranged from 575 to 615 bp. The mean distance value within Gymnodinium, calculated from the ITS sequence, was 0.68827 (range: 0–0.92323), 0.11342 for Amphidinium (range: 0.00467–0.17120) and 0.2005 for Karenia (range: 0.00521–0.29971). Low distance values were found within the species Gyrodinium instriatum (<0.01) and Karlodinium micrum (<0.02). Amphidinium remarkably had a shorter ITS than did other genera in Gymnodiniaceae, this implied that Amphidinium might be distant from the other Gymnodiniaceae and supported Saunders opinion that the taxonomy of Amphidinium needs to be reevaluated. Largely congruent phylogenetic trees were produced by the maximum-parsimony method (PAUP), maximum-likelihood method (PAUP) and Bayesian inference (MrBayes), whereas the three analyses showed that the genera Gymnodinium and Karenia are unresolved groups in phylogeny. Minor sequence divergence was found within the different clones of Amphidinium carterae, suggesting that the ITS regions are suitable as genus- and species-specific oligonucleotide probes to rapidly detect and identify the red tide-forming algal species.Communicated by O. Kinne, Oldendorf/Luhe     

Morphological patterns in high-intertidal gastropods: Adaptive strategies and their limitations

An analysis of shell form in several families of high-intertidal herbivorous gastropods has revealed the existence of morphological gradients. Among tropical littorinids, relative spire height and degree of development of external shell sculpture generally increase interspecifically, and often intraspecifically, from low to high shore levels. This gradient is also evident from temperate to tropical latitudes, and may be modified or overridden by exposure to wave action and other factors. Among acmaeid, patellid, and siphonariid limpets, there is a well-marked interspecific increase in relative shell height with increasing shore level, but latitudinal trends in morphology cannot at present be distinguished. Evidence from both tropical and temperate coasts indicates that limpets found in shaded places tend to have smoother shells than those often exposed to direct sunlight. In the Neritidae, relative shell globosity tends to increase interspecifically from low to high shore levels; most high-shore species have strong shell sculpture, with the base of the shell only slightly excavated. A decrease in the number of neritid species towards higher latitudes is accompanied by selective deletion of globose, strongly sculptured types living at high shore levels. Neritids and some limpets can employ evaporative cooling as a mechanism for temperature regulation. The morphological gradients in these groups reflect a relative increase in the volume of the extravisceral cavity (water reservoir) and a decrease in the area in contact with the substratum, as well as a relative decrease in the rate of water loss, in an upshore direction. Neritids are better adapted than limpets to high temperature and desiccation stresses because of their ability to regulate rate of evaporation and contact between soft parts and substratum. These differences are reflected in the complementary patterns of latitudinal diversity in the two groups. In Littorinidae, which attach to the substratum by a mucus film, the morphological gradients reflect a minimization of water loss and substratum contaet, and a maximization of reflective relative to absorptive surface area.This paper is an expanded version of part of a Ph. D. dissertation presented to Yale University.     

Genetic evidence for the occurrence of a cryptic species with the littoral nemerteans Lineus ruber and L. viridis (Nemertea: Anopla)

Lineus ruber and L. viridis are common intertidal heteronemerteans found on the coasts of northern Europe and the east coast of North America. The two species resemble each other morphologically and were synonymised for many years prior to being separated on the basis of larval development. In this study, specimens of L. ruber and L. viridis were collected from sites along the west and southwest coast of Britain, northern France and the east coast of North America. The external morphology and allele frequencies of isozymes of the two species were compared from all sites. The external morphology of L. ruber and L. viridis was similar but they could generally be separated by colour. Allele frequencies for up to 13 enzyme loci between sympatric populations of L. ruber and L. viridis indicated that these two species are genetically very different (Nei's genetic identity=0.090 to 0.083). Allele-frequency data also indicated the presence of a third genetic type occurring sympatrically with populations of both L. ruber and L. viridis on the coasts of Britain and France but not on the coast of North America. Fixed differences in allele frequencies between populations of the third genetic type and sympatric populations of L. ruber and L. viridis were observed across multiple loci. Genetic identity between the third genetic type and sympatric populations of L. ruber and L. viridis were extremely low (Nei's genetic identity =<0.078). Such large genetic differences between populations indicate a barrier to gene flow and reproductive isolation. The aberrant type, which exhibits sufficient morphological variation to prevent individuals being distinguished from those of both L. ruber and L. viridis, therefore represents a separate species. The low genetic identities found in intrageneric comparisons of species found in this study have been found in other studies on nemerteans. They may indicate systematic problems within these groups or other phenomena such as morphological stasis.     

Selenium deficiency in subtropical littoral pampas: environmental and dietary aspects

Environmental Geochemistry and Health - Se deficiency has a critical effect on human health. The littoral near Patos Lagoon in the south of Brazil is composed of Quaternary sandy deposits and...     

Hatching mode and latitude in marine gastropods: revisiting Thorson's paradigm in the southern hemisphere

For much of the last century the developmental mode of marine invertebrates, particularly of prosobranch gastropods, has been thought to reflect a latitudinal pattern known as Thorson's rule; the proportion of species with pelagic larvae decreases with increase in latitude. Although the predictions of this rule have been criticized recently, its validity along latitudinal transects in the world ocean still remains poorly tested. In the present work, we compare the frequency of occurrence of contrasting prosobranch hatching modes (pelagic versus benthic development) along two latitudinal gradients of the subequatorial coastline of South America: the southeast Pacific and the southwest Atlantic. The results are clearly contrasting. While the pattern observed along the Pacific (Chilean) coast fits the predictions of Thorson's rule very well, benthic development predominates all along the Atlantic coast, even at subtropical latitudes. This difference in observed patterns is attributable to the different compositions of the gastropod assemblages on each side of the South American continent, which are determined, in turn, by differences in the ecological conditions on the two sides of the continent. The scarcity of pelagic development among the Atlantic prosobranch gastropods reflects the near-continuous soft-bottom habitat there, and the consequent prevalence of predaceous, soft-bottom taxa that had acquired in their evolution more evolved, non-pelagic patterns of development. In contrast, the Pacific coast is much more heterogeneous, with a diverse mixture of benthic habitats, including rocky substrates that, in part, support grazing taxa. Our results indicate that two factors are important for Thorson's rule to be valid. First, the habitat needs to include rocky substrates, as soft-bottom habitats appear to favour non-pelagic development. Second, a diverse assemblage of taxa need to be compared to avoid the problem of phyletic constraints, which could limit the evolution of different developmental modes. Received: 23 May 2000 / Accepted: 13 October 2000     

Genetic variability and differentiation in the temperature niche component of the diatom Thalassiosira pseudonana

The acclimated reproduction rates of 14 clones of the diatom Thalassiosira pseudonana were measured at 12°, 16°, 20°, and 24°C. Reproduction rate increased monotonically with an increase in temperature in all 14 clones. Significant genetic variability in reproduction rates and electrophoretic mobility of isozymes were observed among clones within a population from a single water bottle collected in a warm core eddy overlying slope water. The major genetic differentiation was between neritic and oceanic populations, with neritic clones having higher reproduction rates at all 4 temperatures. Surprisingly small genetic differences were observed among clones from neritic waters around the world. The slopes of the temperature-reproduction rate plots of all 14 clones were quite similar.Woods Hole Oceanographic Institution Contribution No. 4679     

Genetic variability in triticale x bread wheat derivatives under normal and phosphorus stress regimes

Twenty six hexaploid triticale (X Triticosecale Wittmack) X bread wheat (Triticum aestivum L. em Thell) derivatives, along with 2 bread wheat and 2 triticale checks, were grown in normal and P-stress environments. Spikes/plant and grain yield/plant, followed by peduncle length, Were the most sensitive to phosphorus deficiency, which also caused a delay in heading and maturity. The heritability and genetic advance for grain yield/plant were high in the stress environment, reflecting the effectiveness of direct selection. The 1000-grain weight, grains/spike and plant height were the important traits for phenotypic selections in both the environments.     

Genetic structure of the flounders Platichthys flesus and P. stellatus at different geographic scales

The genetic structure of the flounders Platichthys flesus L. and P. stellatus Pallas was investigated on different spatial scales through analysis of allozyme variation at 7 to 24 polymorphic loci in samples collected from different regions (Baltic Sea, North Sea, Brittany, Portugal, western Mediterranean, Adriatic Sea, Aegean Sea and Japan) in 1984 to 1987. No geographic variation was evident within a region. Some pattern of differentiation by distance was inferred within the Atlantic, while the Mediterranean comprised three geographically isolated populations and was itself geographically isolated from the Atlantic (fixed allele differences at up to three loci were found among P. flesus populations from the Atlantic, the western Mediterranean, the Adriatic Sea, the Aegean Sea and also P. stellatus from the coast of Japan). Sea temperature during the reproductive period probably acts as a barrier to gene flow between populations. Genetic distances among European flounder populations (P. flesus) were higher than, or of the same magnitude as, the genetic distance between Pacific (P. stellatus) and European flounder populations, suggesting that P. flesus is paraphyletic and/or there is no phylogenetic basis to recognising P. stellatus as a different species. The divergence between P. flesus and P. stellatus was thus inferred to be more recent than the divergence between the present P. flesus populations from the NE Atlantic and eastern Mediterranean. The eastern Mediterranean populations are thought to originate from the colonisation of the Mediterranean by a proto-P. flesus/P. stellatus ancestor, whereas the present western Mediterranean population has undergone a more recent colonisation event by P. flesus. Patterns of mitochondrial DNA variation, established on a smaller array of P. flesus samples, were in accordance with the geographic patterns inferred from the allozyme survey. In addition, they supported the hypothesis of a two-step colonisation of the western Mediterranean. These results contribute to our understanding of the biogeography of the Mediterranean marine fauna, especially the group of boreal remnants to which P. flesus belongs. Received: 7 February 1997 / Accepted: 26 March 1997     

Relationship between larval and juvenile growth rates in two marine gastropods,Crepidula plana and C. fornicata

Previous studies on various marine mollusc species have shown that both larval and juvenile growth rates are substantially heritable, but few workers have examined the extent to which larval and juvenile growth rates covary. We examined the relationship between larval and juvenile growth rates in seven laboratory experiments conducted between 1986 and 1993, using the prosobranch gastropods Crepidula plana Say and C. fornicata (L.). In most experiments larvae were reared individually, measured twice nondestructively to determine larval grwoth rate, allowed or stimulated (daily 5-h exposure to 20 mM excess K⁺ in seawater) to metamophose, and then measured at least twice after metamorphosis to determine juvenile growth rates. Generally, there was no significant (p >0.10) relationship between larval and juvenile growth rates, suggesting that in these two species selection can act independently on the two stages of development. A positive correlation (p=0.007) between larval and juvenile growth rates was observed for C. fornicata in one experiment, but only for offspring from females maturing the most rapidly in laboratory culture. Even for these larvae, however, variation in larval growth rate explained<2% of the variation in juvenile growth rate, so that larval and juvenile growth rates are at most only weakly associated in this species.     

Genetic variability and differentiation of sporophytes and gametophytes in populations of Gelidium arbuscula (Gelidiaceae: Rhodophyta) determined by isozyme electrophoresis

Genetic differentiation and genetic variability of sporophytic and gametophytic populations of Gelidium arbuscula (Bory) from three localities sampled in 1989 and 1990 in the Canary Islands (Spain) were examined by isozyme electrophoresis. Twenty-three to 29 putative alleles corresponding to 22 gene loci, were compared. High deviations in Hardy-Weinberg equilibrium, and significant differences between allelic frequencies of sporophytic and gametophytic subpopulations at the same locality were found, suggesting a predominant asexual reproduction of G. arbuscula. The genetic variability (percentage of polymorphic loci, mean number of alleles per locus and average gene diversity) of haploid subpopulations was lower than that of diploid subpopulations at all three localities, being the lowest described for seaweeds. No correlation between genetic and geographical distance was found. The high genetic differentiation coefficient between all subpopulations suggests a very reduced genetic flow between subpopulations of the same and of different localities. These results suggest that the genetic structure of the populations of G. arbuscula from the Canary Islands is due to a founder-effect combined with a predominance of asexual reproduction. This is the first report comparing allelic frequencies between sporophytic and gametophytic subpopulations of seaweeds.     

Interannual variability of growth and reproduction in Bursera simaruba: the role of allometry and resource variability

Plants are expected to differentially allocate resources to reproduction, growth, and survival in order to maximize overall fitness. Life history theory predicts that the allocation of resources to reproduction should occur at the expense of vegetative growth. Although it is known that both organism size and resource availability can influence life history traits, few studies have addressed how size dependencies of growth and reproduction and variation in resource supply jointly affect the coupling between growth and reproduction. In order to understand the relationship between growth and reproduction in the context of resource variability, we utilize a long-term observational data set consisting of 670 individual trees over a 10-year period within a local population of Bursera simaruba (L.) Sarg. We (1) quantify the functional form and variability in the growth-reproduction relationship at the population and individual-tree level and (2) develop a theoretical framework to understand the allometric dependence of growth and reproduction. Our findings suggest that the differential responses of allometric growth and reproduction to resource availability, both between years and between microsites, underlie the apparent relationship between growth and reproduction. Finally, we offer an alternative approach for quantifying the relationship between growth and reproduction that accounts for variation in allometries.