Maintenance of zonation patterns in two species of flat periwinkle,Littorina obtusata and L. mariae

The zonation patterns of Littorina obtusata (L.) and Littorina mariae Sacchi et Rastelli were shown to be quite distinct on a sheltered rocky shore. L. obtusata was found at all the heights sampled; it reached peak numbers at mid shore on the alga Ascophyllum nodosum L. (Le Jol). There was no difference in the tidal height occupied by adults or juveniles; or in the mean size of L. obtusata along the vertical gradient of the shore. In contrast L. mariae occurred exclusively low on the shore, on Fucus serratus L. Translocation of the two species within their respective levels resulted in random movement after 4 days, although initial movements after 1 and 2 days were sometimes directional. Animals transplanted to the normal level of the other species showed directional movement towards their home zone; this was most pronounced after 4 days. There was no difference in the distance moved by the two species, although the distance moved did vary with tidal height, both species moving further at mid shore than low shore. Distances moved by littorinids at replicate areas in the low shore were similar but those at mid shore did vary. There was an interaction between the species and the different tidal heights which revealed that transplanted species moved further than translocated species at the same tidal level. However, this was only significant in the case of L. mariae. It is suggested that the close relationship between the winkles and their host algae may direct the homing behaviour of displaced individuals.     

Distribution of the species of rough periwinkle (Littorina) in Great Britain

The status of the four currently recognised species in the Littorina saxatilis species-complex, i.e. Littorina nigrolineata Gray, L. arcana Hannaford Ellis, L. saxatilis (Olivi) and L. neglecta Bean is reviewed briefly, with notes on their characteristic features and location on the shore. Since the taxonomy of these rough periwinkles has only become stable relatively recently much of the previously published information on distribution is of little or no use. In this paper their distribution around the coastline of England and Wales (with some notes on Scotland) is described and discussed. L. saxatilis is found in a wide range of habitats from exposed peninsulas to estuaries on all shores where there is a suitable rocky or stony substrate; also in salt marsh pools. L. arcana has a more restricted distribution and is notably absent along much of the south English coast, central Cardigan Bay and possibly northern Scotland; it is not found in estuaries. L. nigrolineata has an even more restricted distribution, although it occurs both on exposed coasts and in estuaries; it has only been found by us in one locality on the east coast. L. neglecta is probably fairly widely distributed but we have few details so far. The implications of the different patterns of distribution are discussed.     

Temporal variation in parasite loading in relation to life history patterns of Littorina obtusata and L. fabalis

Parasitic infection of Littorina obtusata (L.) and Littorina fabalis Turton by larval digeneans was studied in summer (August) and winter (February) on a sheltered shore at St Michael's Island, Isle of Man. Sampling was timed to investigate parasite loading at different stages of the littorinids' life history. Nine species of digeneans were identified and infection rates were similar between the species, with a slightly higher prevalence in females for L. obtusata and males in L. fabalis. Temporal differences in infection were small, although metacercariae and degenerate infections were greater in female L. obtusata in February. Analysis of shell parameters and size of the penis in males and the pallial oviduct in females revealed morphological differences between parasitised and uninfected individuals. Parasitic stunting of the penis was evident in both species and the pallial oviduct was also smaller in parasitised females. There was also a tendency for parasitised individuals to have larger shells; although size also varied with season for L. fabalis.     

Adaptive and non-adaptive variation in two species of rough periwinkle (Littorina) on British shores

Rough periwinkles are notoriously variable in shell characters. There are many reports of substantial local variation on single shores which not only make identification difficult but also may be difficult to understand in terms of likely selective pressures. We show that despite local variation in southern Britain there is evidence of a broader scale of change which is likely to be explicable in adaptive terms. At the same time, along an extreme environmental gradient on a single shore in south Wales we show that there are changes in morphology which are related to avoidance of water loss.     

Shape variation in the rough periwinkle Littorina saxatilis on the west and south coasts of Britain

Variation in the shape of the shell in Littorina saxatilis Olivi has been shown to be due largely to the same variables on both the west and the south coasts of Britain, and it exhibits various clines. Two important aspects are the size of the aperture, which becomes relatively larger from the Isle of Man southwards to Cornwall and eastwards from Devon to the Isle of Wight, and the jugosity of the shell, which increases with distance from Cornwall both northwards as far as the Isle of Man and eastwards as far as Kent. Superimposed on the clines are domains of shape, notably one in Lewis/Harris, where the shells have a relatively large aperture, which is long and narrow, coupled with a rather globose second whorl. The local and geographical aspects of shell shape variation are discussed.     

Induced resistance in intertidal macroalgae modifies feeding behaviour of herbivorous snails

Herbivory in terrestrial and marine systems can induce changes in plant chemistry affecting the foraging behaviour of herbivores. A model based on terrestrial plant-herbivore interactions predicts herbivory-induced changes in leaf chemistry to be manifested in (1) increased herbivore mobility, (2) increased feeding dispersal and (3) reduced tissue consumption by herbivores. This study is the first to demonstrate that herbivory-induced changes in the tissue chemistry of the brown seaweed Ascophyllum nodosum elicit the same response in the feeding behaviour of the gastropod Littorina obtusata as predicted for herbivorous insects, providing good evidence for the models validity across different ecosystems. The potential benefit of increased feeding dispersal to terrestrial plants as suggested by the model is the prevention of concentrated damage to apical tissues thereby preserving the plants ability to compete for light; A. nodosum does not conform to these predictions. Increased dispersal of feeding damage on A. nodosum away from primary frond tissues would reduce the likelihood of frond breakage implying a fitness benefit of induced resistance.     

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.     

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.     

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.     

Method of color measurements of the elements of color in gastropods shell

The method of the accurate determination of the shell color of gastropods has been studied with the example of the gastropod Littorina obtusata. The suggested method is based on using the system of MKO RGB color coordinates and makes it possible to conduct measurements of both color as a whole and the color of the individual elements of the shell picture.     

Notes on the life histories of Boergesenia and Valonia (Siphonocladales,Chlorophyta)

Life history studies were carried out with isolates of Boergesenia forbesii (from Western Australia), Valonia fastigiata (Hawaii) and V. utricularis (Canary Islands, Mediterranean Sea) cultivated under laboratory conditions. Ploidy levels of nuclei were identified by micro spectrophotometric DNA content measurements after Feulgen staining. Fundamentally, the life history in both genera is diplohaplontic. Autodiploidization phenomena have been observed favoring the diploid generation. In contrast to other genera of the Siphonocladales s. str. producing biflagellate diploid zoospores (e.g. Ernodesmis, Boodlea), Valonia develops haploid and diploid zoospores with four flagella. No diploid zoospores were observed in Boergesenia.     

Plant regeneration through direct shoot formation from leaf cultures and from protocorm-like bodies derived from callus of <Emphasis Type="Italic">Encyclia mariae</Emphasis> (Orchidaceae), a threatened Mexican orchid

Two procedures for the in vitro propagation of Encyclia mariae, a threatened Mexican orchid, were developed. In the first procedure, leaves from in vitro germinated seedlings were cultured on Murashige and Skoog medium (MS) supplemented with the range of 2.21–4.4 μM 6-benzylaminopurine (BA) in combination with 2.69–10.74 μM naphthalene acetic (NAA), 2.07–8.29 μM indole-3-butyric (IBA), or 2.85–11.42 μM indole-3-acetic acid (IAA) to determine the best medium for the induction of shooting. Maximum direct shoot formation from leaves was observed on MS containing 22.21 μM BA and 10.74 μM NAA (25 shoots/explant). The second procedure began with the culture of protocorms on media containing NAA, IBA, or IAA, which induced callus formation with high regenerative potential in the form of protocorm-like-bodies (PLBs) that eventually differentiated into shoots. The optimal response was attained when these structures were cultured on medium with 4.14 μM IBA (30 shoots/PLB). To promote the elongation of shoots derived from PLBs, the material was subcultured onto MS medium containing 22.21 μM BA and 5.37 μM NAA. Through the exploration of the effects of auxins and matrix on the rooting of shoots, it was determined that the optimal rooting occurred on media supplemented either with 5.71 μM IAA or 4.14 μM IBA either on agar-gelled medium or in liquid media with coir as the matrix. Rooting was found to be 20% higher in liquid media than in agar-gelled medium.     

Distinct life histories of peracarid crustaceans in a Ria Formosa salt marsh (S. Portugal)

Pitfall traps were exposed between February 1993 andSeptember 1994 every 4th to 6th week near the highwater mark in a Ria Formosa salt marsh (Portugal).With only a few exceptions, peracarid crustaceansaccounted for more than 95% of the individualscaught. Three amphipod species (Orchestiagammarellus(Pallas), Orchestia mediterraneaCosta, Talorchestia deshayesii(Audouin)) and3 isopod species (Tylos ponticus(Arcangeli),Halophiloscia couchi(Kinahan) and Porcellio lamellatus(Uljanin) Budde-Lund) wereidentified. In general, these species were most activefrom spring to autumn.Data collected included information on growth rate,life expectancy and timing of reproduction. Theamphipods displayed more opportunistic life-historypatterns with high growth rates, reproductive activityduring most of the year, early sexual maturity andrelatively short life expectancies. The isopods weremore persistent with slower growth rates, morerestricted reproductive periods and longer lifeexpectancies.There is no indication in the literature that most ofthese species are particularly common in salt marshes.In addition, peracarid crustaceans are not mentionedas dominant taxa in most studies of salt marsh fauna.We suggest that the peracarids play an important rolein the degradation of organic matter in salt marshesand hypothesize that the high numbers of peracaridsfound in Ria Formosa is due to the high contributionof leaf shedding plants.     

The relationship between position on shore and shell ornamentation in two size-dependent morphotypes of Littorina striata,with an estimate of evaporative water loss in these morphotypes and in Melarhaphe neritoides

Shells of small (< 7 mm) Littorina striata are frequently nodulose, but shells of larger individuals are striate. Nodulose L. striata dominated the littoral fringe of a black basalt Azorean shore where daytime rock temperatures rose significantly higher than nearby shores of different rock composition or colour. There was no evidence of intraspecific size-partitioning on the latter shores, where the numbers of striate and nodulose L. striata were approximately equal between high eulittoral (low-shore) and high littoral fringe (high-shore) localities. The prevalence of small L. striata in the littoral fringe is opposite to that usually characteristic of the Littorinidae, where the largest individuals usually occupy the higher positions on the shore. It is hypothesized that small L. striata attain a resting posture better able to minimize heat absorption from the substratum than attained by larger individuals. Smaller individuals also take advantage of both posture and a nodulose shell surface to re-radiate absorbed incident radiant thermal energy more effectively to the atmosphere by convection. Thus, small, nodulose L. striata are especially well adapted to occupy geologically young basaltic rocks commonly found fringing islands of the mid-Atlantic. The rate of evaporative water loss was determined for Melarhaphe neritoides and striate and nodulose L. striata for approximately 11 days emersion. All three groups are exceptionally capable of controlling evaporative water loss. Total percent evaporative water loss by nodulose L. striata (17.9%) was significantly greater than that lost by either striate L. striata (14.1%) or M. neritoides (13.5%) but, among 15 species for which evaporative water loss has been determined by similar methodology, M. neritoides and striate L. striata are the most capable of conserving body water during 11 days of emersion.     

Selection for biennial life histories in plants

The applicability of traditional models of life-history evolution is restricted because models assume constant environments without density-dependence. In these models the geometric growth rate () of a lineage is the natural choice for the fitness criterion. Because in growing populations is very sensitive to changes in generation time, biennials appear at a disadvantage when compared to species with annual reproduction. We propose an alternative fitness criterion for the situation in which recruitment is limited by both the availability of seeds and the (constant) rate at which safe sites for establishment are created by small-scale disturbances. Under the assumptions of the model the evolutionarily stable strategy is to maximize expected seed production, irrespective of the length of the life cycle. For monocarpic plants, this implies that delay of flowering is favourable if the increased seed production compensates for the death of rosettes.Publication of the Meijendel comité, New series No. 89.Nomenclature follows Heukels & van der Meijden (1983), Flora van Nederland, Wolters Noordhoff, Groningen.We would like to thank Prof. K. Bakker, Dr Nora Croin Michielsen, Dr E. van der Meijden and Dr M. Sabelis for their comments on a number of previous drafts. We are indebted to the Netherlands Foundation for Fundamental Research (B.I.O.N.) and to the Netherlands Organization for the Advancement of Pure Research (Z.W.O.) for research grants to T. J. de Jong and P. G. L. Klinkhamer, and to J. A. J. Metz, respectively.     

Migration and life histories of the threespine stickleback: evidence for adaptive variation in growth rate between populations

Synopsis Migratory fishes should exhibit higher growth rates and larger body size than nonmigrants. To test this hypothesis, laboratory reared threespine sticklebacks,Gasterosteus aculeatus, representing three populations from a single drainage in northern California, U.S.A. were compared. These populations differ in their migratory patterns, ranging from highly migratory anadromous forms to nonmigratory freshwater residents. The nonmigratory inland population was significantly smaller in standard length at most ages, with correspondingly reduced growth rates compared to the more migratory upstream and estuary populations. Von Bertalanffy growth functions described the growth trajectories of these fish well, accounting for approximately 99% of the variance in body size exhibited by these populations. Broad sense heritability estimates for body size were significant for all three populations at age 60 days but were significant only for the inland population at later ages. The results of this study provide evidence of genetically-based variation in growth rate and body size among these stickleback populations, and these differences are consistent with the hypothesis that adaptation to different migratory lifestyles has occurred.     

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.     

Comparative life histories and microhabitat use in three sympatric sculpins (Cottidae:Cottus) in northeastern California

Synopsis Life histories of three sculpins endemic to the Pit River system, northeastern California, are detailed.Cottus pitensis is widely distributed throughout the drainage. This species is typically found in rapidly flowing, shallow water on coarse substrate. It grows to a large size, >100 mm, and lives to 5 years. Spawning occurs annually, in early spring. Fecundity is relatively low, <320 oocytes.Cottus asperrimus is restricted to a large population in Fall River and smaller concentrations in Hat Creek and Pit River. It is a relatively small fish, <80 mm, and lives to 5 years. It occurs in deep, slow-moving, often spring-fed streams, typically on fine substrates. Spawning lasts from autumn to early spring. Males establish nests on hard substrates and guard several clutches of eggs. Fecundity ranges from 140–580 oocytes.Cottus klamathensis macrops is relatively rare in the drainage. The largest concentration is in the Hat Creek system, smaller populations exist in Fall River and Pit River. This sculpin is found on coarse substrate, often where aquatic vegetation is abundant. It is typically found in slow, relatively shallow water. It grows to >100mm and lives to 5 years. Males guard eggs during the short spawning season beginning in late winter. Fecundity in this species reaches a maximum of 650 oocytes. Life history strategies vary within the genus, yet the life histories of these sculpins are more similar to each other than they are to many of their congeners. This within-group similarity may have resulted from exposure of all three species to similar environmental pressures. This is predicted by life-history theory.     

Distribution and Seasonal Abundance of Trematode Parasites (Trematoda: Allocreadiidae: <Emphasis Type="Italic">Crepidostomum</Emphasis> spp.) in burrowing-mayfly nymphs (Ephemeroptera: Ephemeridae: <Emphasis Type="Italic">Hexagenia</Emphasis> spp.) from Connecting Rivers of the Laurentian Great Lakes

Burrowing-mayfly nymphs such as Hexagenia spp. have been used extensively in North America and Europe as a biomonitoring tool to indicate mesotrophic water quality, yet infestation by associated parasites has not been well documented. We performed laboratory analysis of archived samples of Hexagenia spp. nymphs collected in 1985 and 1986 to provide base-line data on the distribution (1985) and seasonal infestation (1986) of the trematode parasite Crepidostomum spp. in Hexagenia spp. nymphs in connecting rivers between Lakes Superior and Erie of the Laurentian Great Lakes. In May and June 1985, frequency of occurrence of metacercariae was widely distributed throughout the connecting rivers (63% of 203 stations with nymphs), except in areas where nymph densities were relatively low (i.e.,≤69 nymphs/m²). Distribution was probably underestimated in the present study because of low probability (mean = 31%, range = 0–57%) of detecting infestation in a small number of collected nymphs ( ≤10) at nymph densities ≤69/m². In 1986, seasonal infestation between April and October occurred in 3.3% (627) of 18696 nymphs. Overall prevalence, mean intensity, and mean abundance of parasites at one station in the St. Marys River indicate parasite transmission occurred between June and September. This period of transmission is dependent on the life-cycle of the parasite. In addition, the life-cycle of Hexagenia spp. determines which annual cohort of nymphs is infested and therefore, the duration of infestation. Although, no impacts of infestation on Hexagenia spp. nymphs were observed in the present study, infestation intensities were high enough (≥25 metacercariae per nymph) at one station in the St. Marys River to potentially cause tissue damage in a high proportion (53%) of infested nymphs.     

Ecological life histories of the three aquatic nuisance plants,Myriophyllum spicatum,Potamogeton crispus and Elodea canadensis

The life histories of Myriophyllum spicatum L., Elodea canadensis Michx., and Potamogeton crispus L., serious aquatic nuisances in many regions of the world, are reviewed to provide insights into the life style of successful aquatic nuisance plants. Specifically, their distribution and spread in North America; their life cycle, productive and reproductive potential; and their ecosystem relationships are reviewed. Hopefully this review will improve a manager's ability to deal with aquatic nuisance problems. It also provides suggestions for basic research needed to develop more effective management practices.It was found that all three species possess a number of adaptations, including an ability to rapidly propagate vegetatively, an opportunistic nature for obtaining nutrients, a life cycle that favors cool weather, and a number of mechanisms which enhance photosynthetic efficiency, which allow them to proliferate.These three species do provide benefits to the ecosystem through their roles in materials cycling and energy flow. Therefore, management of these species should take an integrated approach which recognizes these benefits.The life history information available about the three species varies tremendously; however, a better understanding of resource gain and allocation is needed to manage all three species. Specifically, more research is needed to provide a better understanding of: 1) the role bicarbonate plays in photosynthesis, 2) the role roots play in supplying CO₂ to the plabts, 3) resource accumulation and allocation under different temperature and light regimes, 4) resource allocation on a seasonal basis, and 5) nutrient cycling under different management regimes.