Temporal and spatial components of variability in benthic recruitment,a 5-year temperate example

Deployment of artificial substrata is a common method of investigating early community development and recruitment, but rarely are such experiments of long enough duration to include even year time scales. We placed replicate, machined-slate panels (15×15 cm) in the intertidal and at depths of 6 and 12 m at two sites of differing flow rate at Lough Hyne, SW Ireland. These were serially replaced every 30–60 days for a period of 5 years (1997–2002), except in the intertidal (2000–2002). The number and identity of all recruits were recorded. Recruitment varied over several orders of magnitude both on temporal and spatial scales. The greatest source of variability was between the intertidal (with few species or recruit numbers) and the subtidal zones (many species, some with thousands of recruits per panel per 30 days). Highest levels of recruitment occurred at the low-flow site (Labhra Cliff). Here, recruitment was dominated by the serpulid polychaete, Pomatoceros sp., reaching ~4000 individuals per panel per 30 days. Highest species richness occurred, however, at the high flow site (Whirlpool Cliff). At this site more colonial forms (e.g. bryozoans) settled. Season was found to be the dominant pattern explaining subtidal recruit and species number variability. Year, however, was the dominant temporal pattern explaining change in diversity (Shannon–Wiener H). In space, depth explained most variability of recruit numbers, whereas site explained more variation in species richness. Both these spatial factors contributed similarly to variability of diversity (H). Recruitment has long been known to vary considerably over large spatial scales, such as with latitude and isolation, but we that show changes of a similar magnitude in recruitment can occur across small spatial scales. Individual taxa showed varied temporal patterns of recruitment including continuous, regular seasonal fluctuations and irregular pulses in particular years.     

Ingestion of bivalve larvae by<Emphasis Type="Italic"> Mytilus edulis</Emphasis>: experimental and field demonstrations of larviphagy in farmed blue mussels

Ingestion of bivalve larvae by Mytilus edulis was investigated. Laboratory experiments revealed that ~ 90% of bivalve larvae offered to mussels was ingested and apparently fully digested. The shell of the bivalve larvae offered no protection against digestive processes, resulting in high larval mortality once inside the stomach. Stomach content analysis (September 2001–January 2003) showed that bivalve larvae were ingested by farmed mussels year-round, with the exception of March 2002. Numbers of ingested larvae were highest in October 2001 and May 2002, which coincides with known spawning times of farmed mussels in Ireland. Mussels ingested a large size-range of bivalve larvae, suggesting that all stages of the bivalve life cycle are vulnerable to predation. It is suggested that adult bivalves routinely filter larvae from the surrounding water and that, given the high biomass of mussels present in mussel farms, filtration by adult bivalves significantly reduces numbers of bivalve larvae in nearby waters.Communicated by J.P. Thorpe, Port Erin     

Reproductive effort in relation to maternal social rank in reindeer (<Emphasis Type="Italic">Rangifer tarandus</Emphasis>)

In polygynous mammals, high-quality females may increase their fitness by providing superior care to their offspring. Based on the agonistic interactions of female reindeer in an experimental herd during two consecutive years (1997 and 1998), we tested whether maternal social rank influenced: (1) winter body-mass change of females, (2) preparturition reproductive effort (measured as fecundity, the birth mass and the birth date of their calves), (3) preweaning maternal effort (measured as calves preweaning mortality, early preweaning and late preweaning growth rate and September body mass of calves), and (4) postweaning maternal effort (measured as calves body-mass change during their first winter). In the models, we included September females body mass as a covariate to separate the effects of maternal rank and body mass. We also tested whether the effect of social rank on maternal efforts was dependent on offspring sex. High-ranked females gained body mass whereas low-ranked females lost weight during the winter. Fecundity was higher and date of birth was earlier in high-ranked females than in subordinates, whereas no effect of females rank on birth mass of calves was found. Early preweaning growth rate and September body mass of calves increased with increasing females social rank, whereas late preweaning daily growth rate of calves was not influenced by females rank. Calves preweaning mortality was only influenced by year, which also explained most of the variance in the winter body-mass change of calves. The effects of females rank on the reproductive-efforts parameters studied were not specific to offspring sex. These findings suggest that females rank influences reproductive effort during the preparturition, as well as the preweaning, period, the effect being sex independent.Communicated by R. Gibson     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>–ATPase activity and gill ultrastructure in the hyper-hypo-regulating crab<Emphasis Type="Italic"> Chasmagnathus granulatus</Emphasis> acclimated to dilute,normal, and concentrated seawater

We studied Na⁺/K⁺ –ATPase activity and ultrastructure in gills of the hyper-hypo-regulating crab Chasmagnathus granulatus Dana, 1851 acclimated to different salinities: 10, 30 and 45, known to be hypo-, iso-, and hyper-osmotic to the hemolymph, respectively. After centrifugation of homogenates at 11,000 g, Na⁺/K⁺–ATPase activity was almost entirely found in the pellets from the posterior (6–8) and anterior (3–5) gills, whereas very little was detected in the supernatant liquid. Specific activity of gill 6 was 41.3, 30.2, and 28.2 µmol Pi h^–1 mg prot^–1 for crabs acclimated to 10, 30, and 45, respectively, the result for 10 being significantly higher than those at 30 and 45. Although the concentration of sodium at which the reaction rate is half-maximal (K _M) was similar in the three acclimation salinities, only the enzyme from crabs acclimated to 10 was inhibited by high sodium concentration. Specific activity of gill 5 increased with the increment in external salinity (10.1, 15, and 18.1 µmol Pi h^–1 mg prot^–1 for 10, 30, and 45, respectively), the only significant difference being that between the extreme salinities. The epithelium thickness of the dorsal portion of gill 6 showed a variation among salinities: 21.7, 15.8 and 17.2 µm for 10, 30 and 45, respectively. There were significant differences in epithelium thickness between the 10 and the other salinities. In all three salinities, the ultrastructure of gill 6 epithelium showed a high density of mitochondria, estimated by their volume fraction (Vv _m=0.307–0.355). These mitochondria were packed between extensive basolateral membrane interdigitations in ionocytes and pillar cells. Gill 5 showed three cell types: pillars which possess mitochondria packed between membrane folds only in their interdigitations with neighbouring cells; type-I cells 8.0 µm thick with low density of mitochondria (Vv _m=0.088), and type-II cells, 9.9 µm thick and rich in mitochondria (Vv _m=0.423), but lacking basolateral interdigitations. Vv _m of type-I cells of gill 5 was significantly lower than those of type-II cells of the same gill and the ionocytes of gill 6. No significant difference in Vv _m was detected between the latter cell types.Communicated by P.W. Sammarco, Chauvin     

Fractionation of heavy metals in surface sediments of Taihu Lake, East China

The BCR (European Communities Bureau of Reference) three-step sequential extraction procedure was applied to fractionate heavy metals in the sediment of Taihu Lake. For the determination of total metal concentration of the sediments, sample digestion was achieved by using HF/H2O2/HNO3 (2/1/1) acid mixture in a microwave-irradiated closed vessel system. The concentrations of Cd, Ni, Cr, Zn, Cu and Pb in various extracts solutions were analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The results obtained from the BCR three-step sequential extraction indicated relatively high mobility of Zn, Cu, Pb and Ni in the sediments while Cd and Cr were poorly mobile. Enrichment of heavy metals was found in the sediments collected in the northern parts of Taihu Lake. In the sediments collected in the southern and western sides of the Lake, heavy metal concentrations were relatively low. The relationship between total organic carbon (TOC) and heavy metals concentrations in the sediments is discussed.     

An experimental examination of female preference patterns for components of the male advertisement call in the quacking frog,<Emphasis Type="Italic"> Crinia georgiana</Emphasis>

Even though females prefer particular components of a male display, their preferences may not be expressed during mate choice. Here, we quantified female preference patterns in the frog Crinia georgiana for call rate, pulse number and dominant frequency using two-speaker trials. Females typically chose signals emitted at a higher rate, with more pulses (when variation was extreme) and with an average dominant frequency. The results for pulse number and call rate agree with a previous field study which found that these two call components explained significant variation in male mating success. In contrast, the strong preferences for average dominant frequencies detected here disagree with the previous field study which failed to find any relationship between dominant frequency and male mating success. To explain the discrepancy we investigated whether the patterns of female preference for dominant frequency changed when another property, call rate, was varied simultaneously. Most females chose the call with an average dominant frequency when offered a choice between a call with an average dominant frequency and call rate or a non-average dominant frequency (±2 SD) and high call rate. When the differences in dominant frequency were reduced (±1 SD), females showed no clear preference for either signal. Accordingly, female preference patterns for one call component can vary with the expression of another. These results do not explain why dominant frequency did not account for any variation in male mating success under field conditions.Communicated by T. Beschlitz     

Escape responses of copepod nauplii in the flow field of the blue mussel,<Emphasis Type="Italic"> Mytilus edulis</Emphasis>

Bivalves are important grazers on phytoplankton in shallow waters. However, very little is known about their ability to capture actively moving zooplankton. We investigated the escape response and success of early and late nauplii of three copepod species (Acartia tonsa, Temora longicornis and Eurytemora affinis) in the flow field of a blue mussel, Mytilus edulis, using both video observations and incubation experiments. An empirical model was created to describe the spatial distribution of the fluid deformation rate. Nauplii responded with escape jumps at mean fluid deformation rates of 0.6-1.9 s^у. Escape success differed between taxa. T. longicornis was the poorest escaper, while A. tonsa and E. affinis were more efficient and similar to one another. Deformation rates differed in different parts of the flow field, which resulted in differences in escape success between the sectors. Nauplii were caught most often in the sector furthest away from the exhalent siphon, where the deformation rate was the weakest. There the nauplii were unable to detect an escape signal in time to react and flee.     

Chemical aspects of mass spawning in corals. I. Sperm-attractant molecules in the eggs of the scleractinian coral Montipora digitata

This paper provides the first evidence for sperm chemotaxis in the Scleractinia. Montipora digitata Dana, 1845 (Scleractinia: Coelenterata) is a hermaphroditic coral which reproduces bi-annually, releasing egg-sperm bundles during the mass spawning at Magnetic Island (19°10S; 146°52E) in late spring-early summer, and autumn each year. The buoyant egg-sperm bundles float to the surface where they break apart, releasing eggs and sperm into the ocean. Fertilisation occurs after 30 min. Unfertilized eggs were collected, washed free of sperm, and freeze-dried. The eggs were extracted with dichloromethane, fractionated by chromatography on silica gel, and the fractions assayed for their ability to attract M. digitata sperm. The active fraction was further fractionated by high-performance liquid chromatography, resulting in the isolation of three highly unsaturated fatty alcohols: (1) dodeca-2,4-diynol; (2) tetradec-13-ene-2,4-diynol; (3) (14Z)-heptadeca-14,16-diene-2,4-diynol. Of these three compounds, only Compound 1 attracted sperm of M. digitata. Synthetic Compound 1, produced from simple precursors by known reactions, possessed sperm-attracting activity comparable to the naturally derived attractant. Preliminary experiments suggest that the natural mixture of Compounds 1, 2 and 3 in the ratio 1:4:9 is more effective in attracting sperm from M. digitata than sperm from other Montipora species. Sperm attractants may act to reduce the incidence of hybridisation between different species of Montipora.     

Genetic analysis of parentage within experimental populations of a male dimorphic beetle,<Emphasis Type="Italic"> Onthophagus taurus</Emphasis>, using amplified fragment length polymorphism

We used the multilocus DNA fingerprinting technique, amplified fragment length polymorphism, to examine parentage of 902 offspring from eight experimental populations of the dung beetle, Onthophagus taurus. The males of this species exhibit a suit of morphological and behavioural traits that characterise alternative mating tactics. Hornless minor males sneak copulations with females that are guarded by horned major males. Our aims were to provide a prospective assessment of the potential role of frequency dependence in the maintenance of alternative mating tactics, to assess the levels of polyandry, and to determine the patterns of sperm usage by multiply mated females. The average proportion of offspring sired by major and minor males did not co-vary with the relative frequency of each morph present in experimental populations. However, there was some indication that the effective mating frequency (number of females producing offspring sired by a given male) of major and minor males may exhibit frequency dependence. Mating success of both male types declined with increasing numbers of major males. Paternity was positively associated with effective mating frequency. Females produced offspring sired from between one and eight males and, on average, paternity was distributed equally amongst a females mates, regardless of the number of males mated. Differences in fertilisation success among males were not associated with alternative male phenotypes. Neither did a males fertilisation success depend on his genetic dissimilarity with the female. These results are discussed in the context of the evolution of alternative mating strategies, and mechanisms of postcopulatory sexual selection.Communicated by N. Wedell     

How Kentish plovers,<Emphasis Type="Italic"> Charadrius alexandrinus</Emphasis>, cope with heat stress during incubation

Biparental incubation is frequent among shorebirds and is expected when the survival prospects of offspring increase relative to uniparental incubation. To understand why this occurs, it is important to identify the factors that constrain uniparental incubation. It is assumed that birds choose nesting sites that provide an appropriate microclimate for incubation. Many shorebirds nest in sites with no or little cover, where ambient temperatures at ground level might be >50°C during very hot days. Shorebirds nest in exposed sites because predation risk on incubating adults is higher in covered sites. In hot environments, incubating shorebirds might experience heat stress in exposed sites, and this may compromise nesting success if adults are unable to attend their nests continuously, limiting the possibilities of uniparental incubation and thus the expression of a sexual conflict over incubation. The operative temperatures of Kentish plovers (Charadrius alexandrinus) were recorded in exposed and covered sites, and the thermal behaviour and incubating tactics of pair members were studied in a hot environment. During the hottest part of the day, there was a difference of 10–15°C in the operative temperatures of plovers between covered and exposed sites. Plovers in covered sites did not exhibit any thermoregulatory behaviour indicative of thermal stress, probably because the thermal range encountered by them in such places during most of the daytime was close to the thermo-neutral zone. The frequency with which plovers in exposed sites exhibited thermoregulatory behaviour was related to ambient temperature. Under very hot conditions, incubating birds were probably unable to maintain homeostasis for long periods and pair members resorted to shortening incubation bouts. Female Kentish plovers mainly incubate in the daytime and males during the night. However, the probability of diurnal incubation by males increased with ambient temperature in exposed nests, but not in covered ones. In fact, the frequency of participation in diurnal incubation by males was greater in exposed than in covered sites, suggesting that the participation of males in diurnal incubation may be related to the inability of females to stay at the nest during long periods when the ambient temperature is high. Even after resorting to shortened incubation bouts, the plovers may be unable to attend their nests continuously during heat waves, and the nests may be deserted. The propensity of plovers to desert their nests was affected by proximity to water, with nests located close to water being deserted less frequently. It seems likely that susceptibility to thermal stress changed in relation to proximity to water because in sites close to water it was possible to belly-soak, which would allow a more continuous nest attendance. Therefore, despite the adoption of behavioural solutions to face heavy heat loads, nesting success was vulnerable to these solutions because heat stress during extended periods may constrain parental nest attendance, and this may limit the opportunities for sexual conflicts over incubation.Communicated by J. Graves