The influence of an intermittent food supply on the feeding behaviour of Yoldia hyperborea (Bivalvia: Nuculanidae)

Yoldia hyperborea (Lovén) is a protobranch bivalve of circumboreal distribution and an important bioturbator of muddy sediments of cold-water embayments in Newfoundland, Canada, where it is exposed to a strong seasonal input of sinking phytoplankton during spring, sporadic events of sediment resuspension, and sediment of low nutritional value during winter. To explain field-observed patterns of population dynamics, we quantified the behavioural response of Y. hyperborea to pulses of settling algae and sediment resuspension events, and hypothesised that Y. hyperborea behaviour is modified during settling of nutrient-rich organic matter. Yoldia hyperborea responded rapidly to the arrival of settling microalgae by extending its siphons into the water column. Once the pulse of algal material reached the sediment the animals partially emerged, extended the palp proboscides over the sediment surface and maintained close contact with the area of highest algal concentration. In contrast, the activity of animals not exposed to settling algae or to resuspended sediment was primarily restricted to strata below the sediment surface. Thus the predominant subsurface feeding behaviour of Yoldia hyperborea is switched to surface deposit-feeding as a response to cues contained in microalgae. Results suggest active suspension-feeding during algal sedimentation events, although deposit-feeding resumes once the algae are no longer in suspension, and suspension-feeding is probably of little nutritional significance. The rapid behavioural response of Y. hyperborea to the influx of high quality food, such as fresh microalgae, is probably an adaptive foraging strategy to a food-limited environment and suggests higher bioturbation rates of surface sediments during spring, a key role being played by the protobranch in redistribution of labile phytodetritus within the benthos.     

Physiological energetics of the protobranch bivalve <Emphasis Type="Italic">Yoldia hyperborea</Emphasis> in a cold ocean environment

Yoldia hyperborea is a deposit-feeding circumpolar protobranch that also inhabits muddy sediments of the cold water boreal system of Conception Bay, Newfoundland, Canada. Little is known about this species, despite its wide distribution and frequent high density in the benthos. The present work deals with oxygen consumption and ammonia excretion under cold ambient conditions. Y. hyperborea showed low basal metabolism [0.051 ml O₂ h^у·(g dry weight)^у, T=у°C] and low ammonia excretion rates [4.212 µg·NH₄-N·h^у·(g dry weight)^у, T=у°C]. Low metabolic activity could prove a useful strategy during periods of low food availability. In addition, Y. hyperborea was able to regulate its O₂ consumption rate at very low pO₂ levels, which may be advantageous for a species that may experience periods of hypoxia.     

Influence of an intermittent food supply on energy storage by the subpolar deposit feeder Yoldia hyperborea (Bivalvia: Nuculanidae)

Food supply for deposit feeders varies from highly seasonal phytodetritus to a steady source of older organic matter, resulting in contrasting patterns of nutrient uptake and storage. To identify patterns in energy storage and feeding behaviour driven by different food conditions for the circumpolar deposit-feeding protobranch bivalve Yoldia hyperborea, we measured variations in cytological (digestive cell height) and biochemical (lipid class, fatty acid, glycogen, and protein content) components during controlled experiments. Three treatments with organisms in sediment with high refractory organic matter (12 % OM) were exposed to different feeding regimes resembling (a) the annual spring bloom settlement, (b) low food availability during winter, and (c) sporadic resuspension events. Yoldia exposed to a diatom-supplemented diet showed significantly higher mean values for digestive cell height (28.44 μm), glycogen (30.4 mg g^?1 dry mass, DM), diatom-specific fatty acids, and total lipid (TL) levels (14.4 mg g^?1 DM), but lower protein concentrations, than in non-supplemented treatments (digestive cell height 20.34 μm; glycogen 9.23 mg g^?1 DM; TL 6.7 mg g^?1 DM). All analyses showed no effect of resuspension events; thus, it was unlikely that resuspension improved sediment nutritional value. In the absence of recently deposited diatoms, Y. hyperborea did not increase nutrient storage, suggesting that significant amounts of older refractory OM are not used for growth or reproduction. The rapid storage of nutrients derived from diatoms demonstrates the role of seasonal episodic events of settling algae in the nutrition of subpolar Y. hyperborea and in the transfer of energy from the water column to the benthos.     

Distribution and reproductive biology of the little cuttlefish Sepiola atlantica (Cephalopoda: Sepiolidae) around Anglesey, North Wales

Sepiola atlantica were captured in seine nets at twelve locations around the coast of Anglesey, UK. Animals were most abundant on the very sheltered shore of Y Foryd Bay and the wave-exposed shore of Traeth Penrhos, and these two locations were further sampled seasonally to examine the seasonal occurrence, population structure and reproductive biology of S. atlantica. Sepiola atlantica (5?C28?mm dorsal mantle length (DML)) migrated inshore seasonally and first appeared in July where they attained peak abundances between July and August at seawater temperatures of 17°C. Numbers declined between September and October as temperatures fell below 15?C16°C, and in late October, they migrated offshore. Male S. atlantica was significantly smaller and matured at a smaller DML than females. The number of spermatangia on the bursa copulatrix of female S. atlantica varied seasonally attaining maximum numbers in October with a mean of 22 spermatangia on the bursa copulatrix of Y Foryd Bay females. At Y Foryd Bay and Traeth Penrhos, the number of spermatophores in male and potential fecundity in female S. atlantica ranged between 1 and 147 and 25 and 141, respectively. The spermatophoric complex and gonadosomatic index showed a high degree of variability in individuals of similar wet body weight with the female gonad constituting a far greater percentage of the total wet body weight than the male gonad. It is concluded that S. atlantica of all sizes and maturity stages congregate in the shallow waters around Anglesey between July and October when environmental conditions are favourable for enhanced growth and maturation and where the high numbers of animals enhance opportunities for mating.     

Parasites of three commercially exploited bivalve mollusc species of the estuarine region of the Cachoeira river (Ilhéus, Bahia, Brazil)

This paper reports the parasites found in three commercially exploited bivalve molluscs (Mytella guyanensis, Anomalocardia brasiliana and Iphigenia brasiliana) of an estuarine region of Ilhéus, south of Bahia, Brazil (14°48′23′′S; 39°02′47′′W). Samples of 20 individuals of each species were collected fortnightly from August 2005 to August 2006. A total of 1480 individuals was collected and processed by standard histologic techniques; the histologic sections were stained with Harris haematoxylin and eosin and examined with light microscope. The water temperature in the study area varied from 24 to 30.5 °C and the salinity from 0 to 23 ppt. Remarkable differences were found in the parasitic community between the three mollusc species involved in the study, which occupied different habitats in the estuarine region of the Cachoeira river. The following parasites were found: intracellular rickettsia-like colonies in digestive epithelia; intracellular gregarine Nematopsis sp. in gills, mantle, gonad, digestive gland and foot muscle; sporocysts of a Bucephalidae trematode in gonads, mantle, gills, digestive gland and foot; unidentified digenetic metacercariae in digestive gland and gonad; metacestodes of Tylocephalum sp. in connective tissue in the digestive gland and in gonad; and an unidentified metazoan in mantle and intestinal lumen. No significant temporal variation in the prevalence of any parasite was detected, which could be due to the narrow temperature range of the region and the absence of patterns of salinity and rainfall variation through the year. The infestation by sporocyst was the only pathological threat detected for the studied populations because of its potential for host castration. The low infection intensity and/or prevalence of the other parasites and the lack of obvious lesions suggest that there is no other serious pathological risk for the studied mollusc populations.     

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.     

The Structure and Density of Aggregations of the Hermit Crab <Emphasis Type="Italic">Pagurus proximus</Emphasis> Komai, 2000 in Epibiosis of the Brown Alga <Emphasis Type="Italic">Costaria costata</Emphasis> (C. Agardh) De A. Saunders, 1895 in the Sublittoral Zone of Vostok Bay,Sea of Japan

A study of epibiosis of the brown alga Costaria costata in the sublittoral zone of Vostok Bay, Sea of Japan during the spring and summer of 2016 showed that hermit crabs of the following four species accounted for approximately 85% of the total biomass: Pagurus proximus, P. minutus, P. brachiomastus, and P. middendorffii. Of these, the most abundant one (96.5% of the total number of hermit crabs) was P. proximus, the mean aggregation density of which on C. costata (429 ± 221 ind./m²) was higher by an order of magnitude than that in the adjacent area of the bouldery bottom. The size ranges of males and females of this species in aggregations on boulders and those on C. costata were similar, with a predominance of larger individuals on algae. In the size–frequency distribution, three groups of individuals corresponding to three size–age cohorts were differentiated. The male-to-female ratio was 1 : 1.7. Hermit crab aggregations on C. costata are ephemeral; their existence is determined by the duration of the period of algae development, that is, from late spring to the middle of the summer.     

The reproductive response of the sea urchins Paracentrotus lividus (G.) and Psammechinus miliaris (L.) to a hyperproteinated macrophytic diet

The sea urchins Paracentrotus lividus and Psammechinus miliaris are submitted to the same environmental conditions in the Bay of Brest. The relationship between seasonal changes in food source quality and their gonad production was investigated in reproducing experimentally these conditions. In a first stage two macroalgae (Palmaria palmata and Laminaria digitata) were tested. P. miliaris showed a stronger preference for P. palmata and over a year-long experiment both urchins progressively preferred P. palmata. Seasonal variations in the chemical composition of P. palmaria were observed in the Bay of Brest: total carbohydrates were important and the relative maximum (about 50%) was reached between February and August; the lipid level was low and had a relative maximum of about 1% in June and August. Total protein in P. palmaria was high compared to other seaweeds: the maximum value (25%) was observed in June, which was probably due to the maintenance of nitrogen nutrient in the bay.In the second stage of the study, seasonal changes in biochemical components of ingestion and absorption of the two sea urchins were followed in the laboratory using a monospecific diet of P. palmaria. The patterns of total carbohydrates and lipid absorption were very similar for both sea urchin species. Carbohydrates were absorbed strongly and uniformly, year round. Lipid absorption mimicked the lipid nutrient pattern in the food source. Only changes in protein absorption varied slightly between the two urchin species. Protein absorption was maximal for both species in February and June, but the quantity of absorbed protein was significantly higher in P. miliaris than in P. lividus during February. This increase was concomitant with protein storage in the sea urchin gonads, which peaked in February for P. miliaris and in June for P. lividus. P. lividus had a higher gonad production efficiency, based on gonad yield. The comparison between in situ data and the experimental results suggests that an algal diet more nitrogenous than the in situ algal food source would benefit the herbivorous P. lividus, rather than the more omnivorous species P. miliaris. Although P. milaris has been described as a species with large gonad production potential, P. lividus appears to be a more suitable species for echiniculture conditions.     

Molecular evidence for hybridization in Colias (Lepidoptera: Pieridae): are Colias hybrids really hybrids?

Gene flow and hybridization among species dramatically affect our understanding of the species as a biological unit, species relationships, and species adaptations. In North American Colias eurytheme and Colias eriphyle, there has been historical debate over the extent of hybridization occurring and the identity of phenotypically intermediate individuals as genetic hybrids. This study assesses the population structure of these two species to measure the extent of hybridization and the genetic identity of phenotypic intermediates as hybrids. Amplified fragment length polymorphism (AFLP) marker analysis was performed on 378 specimens collected from northern California and Nevada. Population structure was inferred using a Bayesian/Markov chain Monte Carlo method, which probabilistically assigns individuals to genetic clusters. Three genetic clusters provided the best fit for the data. C. eurytheme individuals were primarily assigned to two closely related clusters, and C. eriphyle individuals were mostly assigned to a third, more distantly related cluster. There appeared to be significant hybridization between the two species. Individuals of intermediate phenotype (putative hybrids) were found to be genetically indistinguishable from C. eriphyle, indicating that previous work based on the assumption that these intermediate forms are hybrids may warrant reconsideration.     

A maturity index for holothurians exhibiting asynchronous development of gonad tubules

The gonad morphology of the sea cucumber Isostichopus badionotus, collected during the months of May to November 1996 in Morrocoy Bay on the northwestern Venezuelan coast, was analyzed. The gonadal cycle was characterized by five stages of development: post-spawning, recovery, growth, advanced growth and maturity. Maturation did not proceed at the same pace in all gonad tubules of any one animal. Due to this asynchronous gonad development an Individual Weighted Maturity Index (IWMI) was devised to determine reproductive state. It was calculated from the proportion of the different tubule stages observed in each specimen. The maximum value attainable is 5 if all tubules are in the mature stage. Towards the months of July and August, most, but not all, of the ovarian and testicular tubules had reached maturity as indicated by IWMI values of 4.32 and 4, respectively. IWMI represents a quantitative estimation of gonad maturation in holothurians exhibiting asynchronous development as it revealed the maturation pattern underlying gonadal chronological development.     

Schistosoma japonicum: Tsunagi/Y14 protein plays a critical role in the development of the reproductive organs and eggs

Tsunagi/Y14 is an evolutionarily conserved RNA-binding protein that is required for the maintenance of oogenesis and the masculinization of the germ-line in many animal models. We speculated that Tsunagi/Y14 might also regulate reproductive organ development in Schistosoma japonicum (S. japonicum, Sj). Sj Tsunagi/Y14 and control double-stranded RNAs were introduced into schistosomula by electroporation respectively. These transfected schistosomula were cultured in vitro for 1, 3 or 5 days. The mRNA and protein levels of the target gene in the cultured schistosomula were significantly suppressed compared with those of the control group. Furthermore, BALB/c mice were infected with the transfected schistosomula for 6 weeks and were sacrificed to harvest the adult worms. We found that the silencing of Sj Tsunagi/Y14 led to defects in reproductive organs development in both male and female worms. Moreover, it also affected the size, quantity and activity of the eggs in the mice liver. Our findings indicated that Tsunagi/Y14 plays a critical role in the development of reproductive organs and eggs in S. japonicum.     

Carbon, nitrogen, and hydrogen isotope ratios in creekside trees in western Kansas

Three species of creekside trees were monitored weekly during the 2007 and 2008 growing seasons. The 2007 growing season was wet early, but became drier as the season progressed. In contrast, the 2008 growing season was dry early, but became wetter as the season progressed. Creekside trees were measured to determine effects of changing water regimes on leaf-level processes. Lonicera tatarica plants were compared to Morus alba and Celtis occidentalis trees. Leaves were monitored for changes in stomatal conductance, transpiration, δ¹³C, δ¹⁵N, δD, leaf temperature, and heat losses via latent, sensible, and radiative pathways. δD of creek water was more similar to ground water than to rain water, but the creek was partially influenced by summer rains. δD of bulk leaf material was significantly higher in individuals of C. occidentalis compared to the other species, consistent with source water coming from shallower soil layers. Despite decreasing water levels, none of these tree species showed signs of water stress. There were no significant differences between species in stomatal conductance or transpiration. Leaf δ¹³C was significantly lower in individuals of L. tatarica compared to the other species. Differences in δ¹³C were attributed to a lower carboxylation capacity, consistent with lower leaf nitrogen content in L. tatarica plants. Leaf δ¹⁵N was significantly lower in individuals of L. tatarica compared to the other species, consistent with uptake of a different N source. Two of the three sites appeared to be affected by inorganic N from fertilizer run-off. Evidence is presented that these species acquired water and nitrogen from different sources, resulting from differences in root uptake patterns.     

Spatio‐temporal variability in reproductive ecology of sand flathead,Platycephalus bassensis,in three Tasmanian inshore habitats: potential implications for management

Temporal and spatial variability in gonad development, duration of spawning period, and size/age at maturity were investigated in sand flathead, Platycephalus bassensis. A 3‐year study (2001–2003) revealed that variation in gonad weight with somatic weight was a function of an interaction between season and study location (Coles Bay, Georges Bay, and Tamar River estuary). Highest gonad weight was recorded in Coles Bay in early summer, which in comparison to Georges Bay, was approximately 50% higher and occurred 3 months later. Tamar River mature individuals were reproductively inactive during the spawning season. The proportion of mature individuals at different stages of maturity differed significantly among the three locations across all times. Coles Bay individuals were reproductively active from October to March, while in Georges Bay females with hydrated oocytes were seen in September but were absent from the population by November. Interannual variation in initiation and duration of spawning activity was evident in each location. Apart from male size at maturity, for both sexes the size and age at maturity (L₅₀) was higher in Georges Bay compared to Coles Bay. The results emphasize the necessity of temporal and spatial management based on population differences in reproductive ecology.     

Age and productivity of the Antarctic scallop, Adamussium colbecki, in Terra Nova Bay (Ross Sea, Antarctica)

Body size, geographical distribution, and biomass make Adamussium colbecki (Smith, 1902) one of the most conspicuous bivalve species in the Antarctic. Based on samples collected in austral summer 1999/2000 in Terra Nova Bay, the annual formation of shell growth bands visible on X-ray photographs was verified by stable isotope analysis. A general von Bertalanffy growth function was fitted to size-at-age data of 25 individuals (H_∞=108.86 mm, K=0.114 year⁻¹, t₀=−0.367, D=1.284). Somatic production calculated from mass-specific growth rates was 234.6 kJ m⁻² year⁻¹. Gonadal productivity amounted to 70.92 kJ m⁻² year⁻¹. Annual somatic and gonad production-to-biomass ratios (P/B) were 0.199 and 0.052, respectively. According to its consumption and production, A. colbecki is likely to play a significant role in the trophic web of Terra Nova Bay.     

Subtidal algal colonization following the removal ofEchinus

Summary 1. On the seaward face of Port Erin breakwater large algae do not occur on the lowest three metres. Here the density ofEchinus esculentus is high.2. Over a three year period allEchinus were removed from a 10 m wide strip at about monthly intervals. The total number of individuals removed approached 3000.3. One year after initial clearance the mean density ofLaminaria hyperborea sporelings on the strip was 22.7/m² and 5.1/m² to one side of it. By the winter these had almost disappeared outside the strip and in the succeeding years second and third year plants were found only on the strip or close to its edge. Other algae were similarly affected.4. It is concluded that the lower limit ofL. hyperborea is determined at least in part by the grazing pressure ofEchinus and that the urchins exercise some control over the numbers of other algae.

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Algenkolonisation im untergetauchten Gezeitenbereich nach Entfernung vonEchinus

Kurzfassung An der Sesseite des Port Erin Wellenbrecherdammes kommen keine größeren Algen im Bereich der unteren 3 m vor. Hier herrscht eine große Besiedlungsdichte des SeeigelsEchinus esculentus (3,6 Individuen pro m²). Über eine Zeitspanne von 3 Jahren wurden nun sämtlicheE. esculentus von einem 10 m breiten und 12 m langen Felsstreifen allmonatlich entfernt; insgesamt wurden dabei etwa 3000 Individuen abgesammelt. Ein Jahr nach Beginn des Absammelns betrug die mittlere Siedlungsdichte der jungenLaminaria hyperborea auf dem von Seeigeln freigehaltenen Felsstreifen 22,7/m². In den folgenden Jahren wurden zwei- und dreijährigeL. hyperborea nur auf diesem Felsstreifen oder in der Nähe seiner Begrenzungen gefunden. Andere Algenarten reagierten in ähnlicher Weise. Aus den Befunden wird gefolgert, daß die untere Verbreitungsgrenze vonL. hyperborea zumindest zum Teil durch Seeigelfraß bestimmt wird, und daßE. esculentus die Siedlungsdichte der anderen Algenarten beeinflußt.

     

Population structure, recruitment, and succession of the brown alga, Padina boryana Thivy (Dictyotales, Heterokontophyta), at an exposed shore of Sirinart National Park and a sheltered area of Tang Khen Bay, Phuket Province, Thailand

The brown algal genus, Padina, has a worldwide distribution in tropical and subtropical climate zones. Padina individuals are common and sometimes dominant in both the intertidal and shallow subtidal regions associated with coral reefs. We investigated the population structure and recruitment of two populations of Padina boryana at an exposed shore in Sirinart National Park (SNP) and a sheltered shore of Tang Khen Bay (TKB), Phuket Province, Thailand. From September 2005 to August 2006, the number of released spores and the height and radius of fronds were measured monthly. New recruits were recorded and monitored on manipulated permanent plots 0.25 m². The experiment was carried out monthly over a year. We found Padina recruits 1 month after the plots were cleared at both sites. There was a significant difference in percentage cover by new individuals between the two locations (P < 0.05) and also at the shore levels within the sites. At SNP, the highest recruitment was found in the uppermost zone, while at TKB high recruitment occurred at all shore levels except at 80-100 m from the shore. The factors influencing recruitment of P. boryana include wave motion, competition with other earlier successional species and sediment. The high availability of reproductive spores throughout the year, the successful recruitment and the Dictyerpa stage promote the successful establishment of Padina populations.     

The effect of food limitation on gonad development and egg production of the planktonic copepod Calanus finmarchicus

Calanus finmarchicus, one of the dominant copepods species of the North Atlantic, often encounters low food concentration or quality during the reproductive period; however, our knowledge on the effect of these conditions on reproduction processes is scarce. The present study combines experiments with histological observations to describe the response of C. finmarchicus to limited food focussing on (1) oocyte maturation processes, (2) gonad morphology, (3) egg production rates as a function of spawning frequency and clutch size, and (4) the fuelling of egg production by measuring carbon and nitrogen content of the females. In the laboratory, C. finmarchicus females were exposed to 0, 10, 50, 150 or >300 μg C l⁻¹ for several days. To account for food quality and season, reproductive activity was compared in April and July 1999 between females feeding on diatoms or dinoflagellates. The effect of feeding history was studied in February with females fed and starving prior to the experiment. Feeding conditions had severe effects on oocyte maturation process. Hence, egg production varied significantly with food concentration and quality, season and feeding history due to variation in both clutch size and spawning frequency. Clutch size differed by a factor of 2-4 between food limited and well fed females, and is thus an important parameter for modelling egg production. Changes in clutch size were related to changes of the number of maturing oocytes in the females gonads indicating that the latter can be used to precise the prediction of egg production from preserved samples. The proportion of females carrying at least some mature oocytes was relatively high at low food availability. Apparently, these females used internal body reserves as the carbon and nitrogen content decreased significantly under these conditions. These results indicate that C. finmarchicus embarks on the strategy to enable reproduction in all or many females of a population at low rates when feeding conditions are unfavourable.     

Space competition between seagrass and Caulerpa prolifera (Forsskaal) Lamouroux following simulated disturbances in Lassing Park, FL

An experimental study was conducted in Tampa Bay, FL to examine the response to disturbance of two co-occurring subtidal plants: the alga Caulerpa prolifera and the seagrass Halodule wrightii (Ascherson). Some recent studies have called into question the assumption that fast-growing rhizoidal Caulerpa species have the potential to outcompete and rapidly replace local seagrasses. In the Fall of 2002 an abrupt appearance of Caulerpa prolifera was noted in a shallow embayment in Tampa Bay previously dominated by seagrasses. Natural disturbance events were simulated by excavating 0.5 × 0.5 m plots in an area with monospecific C. prolifera and mixed C. prolifera and H. wrightii. Above and below-ground biomass were removed, and recovery of above-ground cover into the newly created gaps was monitored over 15 months. In addition to measuring the recovery of both species, the spatial pattern of Caulerpa recovery from the simulated disturbances was also analyzed. Simulated gaps were rapidly (5-8 months, depending on sampling resolution) and exclusively reoccupied by C. prolifera, with the recovery occurring predominantly via lateral expansion from gap edges rather than colonization by fragments. Therefore, while rhizoidal algae may or may not be able to supplant existing seagrasses by overgrowth or other forms of direct competition, disturbance events that remove seagrass and create bare areas may allow C. prolifera to replace seagrasses over time via preemption of space should an algal bloom such as this be persistent.     

Variation in the functioning of autonomous self-pollination, pollinator services and floral traits in three Centaurium species

Background and Aims

Reproductive assurance through autonomous selfing is thought to be one of the main advantages of self-fertilization in plants. Floral mechanisms that ensure autonomous seed set are therefore more likely to occur in species that grow in habitats where pollination is scarce and/or unpredictable.

Methods

Emasculation and pollen supplementation experiments were conducted under laboratory conditions to investigate the capacity for, and timing of autonomous selfing in three closely related Centaurium species (Centaurium erythraea, C. littorale and C. pulchellum). In addition, observations of flower visitors were combined with emasculation and pollen addition experiments in natural populations to investigate the degree of pollinator limitation and pollination failure and to assess the extent to which autonomous selfing conferred reproductive assurance.

Results

All three species were capable of autonomous selfing, although this capacity differed significantly between species (index of autonomous selfing 0·55 ± 0·06, 0·68 ± 0·09 and 0·92 ± 0·03 for C. erythraea, C. littorale and C. pulchellum, respectively). The efficiency and timing of autogamous selfing was primarily associated with differences in the degree of herkogamy and dichogamy. The number of floral visitors showed significant interspecific differences, with 1·6 ± 0·6, 5·4 ± 0·6 and 14·5 ± 2·1 floral visitors within a 2 × 2 m² plot per 20-min observation period, for C. pulchellum, C. littorale and C. erythraea, respectively. Concomitantly, pollinator failure was highest in C. pulchellum and lowest in C. erythraea. Nonetheless, all three study species showed very low levels of pollen limitation (index of pollen limitation 0·14 ± 0·03, 0·11 ± 0·03 and 0·09 ± 0·02 for C. erythraea, C. littorale and C. pulchellum, respectively), indicating that autonomous selfing may guarantee reproductive assurance.

Conclusions

These findings show that limited availability of pollinators may select for floral traits and plant mating strategies that lead to a system of reproductive assurance via autonomous selfing.