<Emphasis Type="Italic">Pinna nobilis</Emphasis> L., 1758 age determination by internal shell register

The age of the Mediterranean endemic Bivalve mollusc Pinna nobilis is estimated using the total size and the number and position of posterior adductor muscle scars (PAMS): a series of straight lines and rings observed in the dorsal nacre-lobe. Nevertheless, the position of PAMS of adult individuals inhabiting the same population and depth is highly variable. To assess the source of this variability, the shells of nine individuals were cut into radial sections along PAMS and the inner register was studied. The cuts showed clear marks of the inner register formed around the PAMS composed by a short nacre tongue introduced within the calcitic layer and two calcitic strips of differing colour (bright and dark). The three components are directed towards the posterior of the shell. The marks of the inner register coincide only with the straight lines of PAMS, but are observed in an anterior position further than the straight lines and rings, and in a posterior position further than the rings. Also, some of the most posterior marks can be observed one under the other in the oldest individuals. The existence of the inner register’s marks in a position further anterior than the straight lines and rings implies that a variable number of PAMS are obscured beneath nacreous deposits. Eventually, we advise against the utilization of PAMS to study P. nobilis age. We instead recommend the use of the inner register as it records more accurately the life history of the individuals, and data indicates that each mark is formed annually.     

Cardiac output during exposure to <Emphasis Type="Italic">Chattonella</Emphasis><Emphasis Type="Italic">marina</Emphasis> and environmental hypoxia in yellowtail (<Emphasis Type="Italic">Seriola</Emphasis><Emphasis Type="Italic">quinqueradiata</Emphasis>)

The experiments were undertaken to measure, for the first time, cardiac output in yellowtail (Seriola quinqueradiata) during exposure to a harmful red tide flagellate (Chattonella marina). The responses were compared with those during exposure to environmental hypoxia to evaluate the significance of the drop of arterial oxygen partial pressure (PaO₂) in the fish-kill mechanisms by C. marina. PaO₂ immediately decreased, whereas heart rate (HR) was maintained until shortly before death during exposure to C. marina. Suffocation developing during the exposure resulted from a decrease in blood oxygen content, but not from lowered blood flow to the tissue. Although exposure to both C. marina and hypoxia immediately decreased PaO₂, arterial oxygen content (CaO₂) and pH (pHa) were significantly lower, whereas HR and cardiac output (&Qdot;) remained significantly higher, for the C. marina-exposed fish than for hypoxia-exposed fish. Although the drop in PaO₂ appears to play a pivotal role in the mechanisms of fish death by C. marina, other physiological response(s) should also be considered.     

Viable algae released by the seastar <Emphasis Type="Italic">Dermasterias</Emphasis><Emphasis Type="Italic">imbricata</Emphasis> feeding on the symbiotic sea anemone <Emphasis Type="Italic">Anthopleura elegantissima</Emphasis>

Echinoderms are major predators of anemones in temperate ecosystems. The fate of two algae, zooxanthellae and zoochlorellae, after their host anemone (Anthopleura elegantissima Brandt) was consumed by the leather star Dermasterias imbricata Grube was determined in experiments conducted in July and August 2004. Productivity, photosynthetic pigments, and mitotic index (percent of cells dividing) were used as indicators of algal health; algae released after leather stars consumed their host were compared with algae freshly isolated from anemones. Two types of waste products contained algae: pellets resulting from extraoral digestion, and feces. Zooxanthellae and zoochlorellae isolated from these waste products were photosynthetic, although to different extents. For algae from feces and pellets, light-saturated photosynthetic rates (P _max) were 85 and 13%, respectively, of P _max of freshly isolated zooxanthellae; and were 20 and 46%, respectively, for zoochlorellae. The photosynthetic pigments and mitotic index (percent of dividing cells) were not altered by the feeding activities of the leather star. These results show that algae released by seastar predation on their hosts remain viable, and are hence available for establishing symbioses in A. elegantissima and other potential hosts.     

Effects of substrate type on growth and mortality of blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">edulis</Emphasis>) exposed to the predator <Emphasis Type="Italic">Carcinus</Emphasis><Emphasis Type="Italic">maenas</Emphasis>

Structure and complexity of the substrate are important habitat characteristics for benthic epifauna. The specific growth and mortality rates and inducible defence characters on medium-sized blue mussels (Mytilus edulis L.) exposed to shore crabs (Carcinus maenas L.) were examined on three different substrate types in combined field and laboratory experiments. The experiments showed that complexity of the substrate increased blue mussel survival significantly, through a decrease in predation pressure. However, increased intraspecific competition for food on the complex substrate resulted in significantly lower growth rates of the mussels. Inducible defence characters were also influenced by substrate type. Blue mussels were more affected by predators on the structurally simple substrate, where they developed thicker shells and a larger posterior adductor muscle.     

Mate preferences in <Emphasis Type="Italic">Drosophila</Emphasis> infected with <Emphasis Type="Italic">Wolbachia</Emphasis>?

The maternally inherited bacterium Wolbachia pipientis generates strong reproductive incompatibilities between uninfected females and infected males (cytoplasmic incompatibility), significantly reducing both female and male reproductive success. Such fitness costs are thought to place selective pressure on hosts to evolve pre-copulatory preferences for mating with compatible mates, thereby enabling them to avoid the reproductive incompatibilities associated with Wolbachia. Therefore, uninfected females are predicted to prefer mating with uninfected males, whereas infected males are predicted to prefer mating with infected females. Despite these predictions, previous investigations of pre-copulatory mate preferences in Wolbachia-manipulated Drosophila have not found evidence of female preference for uninfected or compatible males. However, none of these studies utilised a design where focal individuals are provided with a simple choice in a relatively non-competitive situation. We examined both female and male pre-copulatory mate preference based on mate infection status in Drosophila simulans and D. melanogaster using simple choice assays involving between 30–50 replicates per treatment. Although we found no evidence of female pre-copulatory mate preferences in either species, male D. simulans exhibited some preference for mating with females of the same infection status. However, this preference was not evident when we repeated the experiment to confirm this finding. Consequently, we conclude that neither male nor female D. melanogaster and D. simulans exhibit significant Wolbachia-associated pre-copulatory mate preferences.     

Settlement of the wreckfish (<Emphasis Type="Italic">Polyprion</Emphasis><Emphasis Type="Italic">americanus</Emphasis>)

The wreckfish (Polyprion americanus) is a panoceanic, long-lived, deep-water demersal species, characterized by an extended pelagic juvenile phase associated with floating objects. In the present study morphometric data from 435 specimens collected from Greece (Crete), Italy (Ionian Sea) and the Atlantic coast of France from September 1999 to March 2001 were analyzed to estimate the settlement size of the species and associated changes in morphology. The fishery sample included specimens from both the pelagic and the demersal stage. Length-at-settlement (TL₅₀) and 95% confidence intervals were estimated by fitting a logistic function. Eleven morphometric characters were analyzed, and the existing inflection points, reflecting alterations in body shape, were defined: (1) iteratively, as the transition point, splitting the data set into two groups, for which the reduced major axis functions, between a character and total length, of the successive groups best fit (minimum sum of squares of residuals) the combined data set and (2) where the second derivative of the fitted third-order polynomial functions to morphometric ratios equaled zero. The main size range within which wreckfish settled was 56-65 cm, and the means of the inflection points defined by the two methods were 61 and 64 cm. These results indicate changes in functional morphology associated with settlement. The monitoring of wreckfish juveniles caught in the wild and kept individually in captivity showed changes in growth and food intake at approximately the estimated settlement length and suggested that temperature was the most likely factor triggering settlement.     

Individual specialization in the hunting wasp <Emphasis Type="Italic">Trypoxylon</Emphasis> (<Emphasis Type="Italic">Trypargilum</Emphasis>) <Emphasis Type="Italic">albonigrum</Emphasis> (Hymenoptera,Crabronidae)

Individual-level variation in resource use occurs in a broad array of vertebrate and invertebrate taxa and may have important ecological and evolutionary implications. In this study, we measured the degree of individual-level variation in prey preference of the hunting wasp Trypoxylon albonigrum, which inhabits the Atlantic Forest in southeastern Brazil. This wasp captures several orb-weaving spider genera to provision nests. Individuals consistently specialized on a narrow subset of the prey taxa consumed by the population, indicating the existence of significant individual-level variation in prey preferences. The population niche was broader in the wet season in terms of both prey size and taxa. In the case of prey size, the population niche expansion was achieved via increased individual niche breadths, whereas in the case of prey taxa, individual niches remained relatively constrained, and the population niche expanded via increased interindividual variation. The observed pattern suggests the possibility of functional trade-offs associated with the taxon of the consumed prey. The nature of the trade-offs remains unknown, but they are likely related to learning in searching and/or handling prey. We hypothesize that by specializing on specific prey taxa, individuals increase foraging efficiency, reducing foraging time and ultimately increasing reproductive success.     

Molecular population structure of the kuruma shrimp <Emphasis Type="Italic">Penaeus</Emphasis><Emphasis Type="Italic"> japonicus</Emphasis> species complex in western Pacific

In a previous study on the kuruma shrimp Penaeus japonicus from the South China Sea, we detected high genetic divergence between two morphologically similar varieties (I and II) with distinct color banding patterns on the carapace, indicating the occurrence of cryptic species. In the present study, we clarify the geographical distribution of the two varieties in the western Pacific by investigating the genetic differentiation of the shrimp from ten localities. Two Mediterranean populations are also included for comparison. Based on the mitochondrial DNA sequence data, the shrimps are separated into two distinct clades representing the two varieties. Variety I comprises populations from Japan and China (including Taiwan), while variety II consists of populations from Southeast Asia (Vietnam, Singapore and the Philippines), Australia and the Mediterranean. Population differentiation is evident in variety II, as supported by restriction profiles of two mitochondrial markers and analysis of two microsatellite loci. The Australian population is genetically diverged from the others, whereas the Southeast Asian and Mediterranean populations show a close genetic relationship. Variety I does not occur in these three localities, while a small proportion of variety II is found along the northern coast of the South China Sea and Taiwan, which constitute the sympatric zone of the two varieties. The present study reveals high genetic diversity of P. japonicus. Further studies on the genetic structure of this species complex, particularly the populations in the Indian Ocean and Mediterranean, are needed not only to understand the evolutionary history of the shrimp, but also to improve the knowledge-based fishery management and aquaculture development programs of this important biological resource.     

Growth and mortality rates of the fan mussel <Emphasis Type="Italic">Pinna nobilis</Emphasis> in Lake Vouliagmeni (Korinthiakos Gulf,Greece): a generalized additive modelling approach

The temporal patterns and the effect of shell size and depth on growth and mortality rates of the endangered fan mussel Pinna nobilis were investigated in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). A total of 160 individuals were tagged and monitored monthly for a period of 17 months. At each visit, the size of the tagged individuals (shell width, w) was measured in situ and recorded. Any mortality event was also recorded and attributed to natural causes or (illegal) fishing. Growth and mortality rates were modeled with generalized additive models, which are non-parametric flexible models that free the researcher from the limiting concept of a strict parametric shape. The use of GAMs allowed the exploration of shapes of growth and mortality response curves in relation to predictor variables and allowed the fitting of statistical models that better agree with ecological theory. Growth rates had a seasonal pattern, with an extended period of very slow growth between late autumn and early spring, i.e., during the cold season, another short period of slow growth during August (when water temperatures reached their maximum values exceeding 29°C), and a peak in growth rates during late spring–early summer, probably related to an optimum combination of temperature and food availability. Growth rates varied with shell size, with a peak at w ∼4.5 cm, followed by a sharp decline to an approximately constant level, with sizes ranging from 9 to 15 cm, and a further decline with larger sizes down to almost zero for w > 20 cm. Growth rates did not vary substantially with depth. Although P. nobilis is a protected species in the EU and its fishing is strictly prohibited, fishing mortality was very high in Lake Vouliagmeni (much greater than natural mortality), especially during the hot season when the lake was crowded by summer visitors. The fan mussels were poached exclusively by free-diving and due to the high turbidity of the lake’s water, fishing mortality was higher in shallow areas (and mostly for large individuals) and was practically zero at depths >9 m. Due to fishing mortality, a size segregation of P. nobilis was observed in the lake: large individuals were restricted to deeper areas, while young and small individuals were more abundant in shallow areas where there was preferential recruitment. Natural mortality was strikingly size dependent and P. nobilis suffered high natural mortality during the first year of life; the probability of death by natural causes quickly diminished as the fan mussels grew in size. No depth-related differences in natural mortality were found.     

Evidence of a spawning area of <Emphasis Type="Italic">Anguilla</Emphasis><Emphasis Type="Italic">marmorata</Emphasis> in the western North Pacific

Leptocephali of the tropical eel Anguilla marmorata have been consistently collected in the same area of the North Equatorial Current (NEC) in the western North Pacific during three consecutive cruises in June and July of 1991 (N=28) and 1994 (N=20), and July and September of 1995 (N=27), indicating that this is a spawning area of this species. These leptocephali were collected from 130°E to 142°E and 12°N to 20°N, to the west of the Mariana Islands, in 20 tows in 1991, in 13 tows in 1994 and in 17 tows in 1995, indicating a widespread presence, but a relatively low abundance. Six of these specimens (16.3-36.0 mm total length) from the 1995 cruise, which were of the typical size range of these leptocephali, were genetically confirmed to be A. marmorata in a previous study. The consistent presence of recently spawned A. marmorata leptocephali (9-20 mm) in all 3 years, suggests that the western region of the NEC is the spawning area of the northern population of A. marmorata that was identified in a recent population genetics study. These leptocephali would thus be transported westward by the NEC and then transported north into the Kuroshio Current and toward Taiwan and Japan, or south toward the southern Philippines and into the Celebes Sea by the Mindanao Current. Available evidence indicates that A. marmorata may have potentially year-round spawning, and the presence of a spawning area of this species in the same region as that of Anguilla japonica suggests that the northern population of A. marmorata has evolved a spawning migration from East Asia, the Philippines and the Celebes Sea region to the NEC area, but differs from A. japonica by having some individuals that recruit to more southern areas.     

Small effective number of parents (<Emphasis Type="Italic">N</Emphasis><Subscript><Emphasis Type="Italic">b</Emphasis></Subscript>) inferred for a naturally spawned cohort of juvenile European flat oysters <Emphasis Type="Italic">Ostrea edulis</Emphasis>

The great fecundity and very high larval mortality of most marine invertebrates and fish make possible substantial variance in the number of offspring contributed by adults to subsequent generations. The reproductive success of such organisms may thus resemble a sweepstakes lottery, in which a minority of progenitors succeeds in replacing an entire population, while the majority fails to procreate. One specific prediction of this hypothesis, that genetic diversity of newly settled cohorts should be less than that of the adult population, is tested in the present study. Microsatellite DNA markers were examined in naturally spawned juvenile European flat oysters Ostrea edulis (L.), collected over a 12-day period in 1993 from the western Mediterranean Sea, near Sète, France (43°32′N, 3°56′E) and grown out for a period of up to 10 months. Variation in these juveniles was compared to that in a pooled sample of adults collected in 1994 from two locations (Thau Lagoon and Port St. Louis) that had statistically homogeneous allelic frequencies. Though nearly twice as large as the pooled adult sample, the juvenile sample had only 60% of the adult allelic diversity. Analyses of linkage disequilibrium and kinship, as well as estimation of the effective number of parents, suggested that 10–20 adults produced this juvenile cohort. This observation supports the hypothesis of sweepstakes reproductive success and suggests that partial inbreeding may occur even in species with large populations and dispersing planktonic larvae. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Altered c-Fos expression demonstrates neuronal stress in mummichog, <Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>, exposed to <Emphasis Type="Italic">Pfiesteria shumwayae</Emphasis> and <Emphasis Type="Italic">Chaetoceros concavicornis</Emphasis>

To better understand sublethal effects of harmful algal blooms (HABs) on fish, mummichog, Fundulus heteroclitus (L.), were exposed in the laboratory to varying, environmentally relevant densities of Pfiesteria shumwayae (Glasgow et Burkholder, CCMP 2089, dinoflagellate) and Chaetoceros concavicornis (Mangin, CCMP 169, diatom). Two experiments were conducted during the spring of 2003 and 2004 to quantitatively examine the effects of acute (2 h) P. shumwayae and C. concavicornis algal exposure on mummichog brain activity using c-Fos expression as a marker of altered neuronal activity. Brains from HAB-exposed fish were removed, sectioned, and stained using immunocytochemistry prior to quantifying neuronal c-Fos expression. Fish exposed to P. shumwayae and C. concavicornis showed increased c-Fos expression compared to unexposed control fish. A significant dose-response relationship was observed, with increased labeling in brains of fish exposed to higher cell densities for both HAB species tested (P ≤ 0.01). Increased labeling was found in the telencephalon, optic lobes, midbrain, and portions of the medulla. The greatest increases in expression were observed in the telencephalon of P. shumwayae-exposed fish, and in the telencephalon and optic lobes of C. concavicornis-exposed fish (P ≤ 0.01). These increases in c-Fos expression are consistent with other physical and chemical stress exposures observed in fish. Neuronal stress, evidenced by c-Fos expression, demonstrates a sublethal effect of exposure and changes in brain activity in fish exposed to HAB species.     

Antennal responses to floral scents in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae)

Summary. To better understand the biological role of floral scents for butterflies, electrophysiological responses to floral scents were investigated using combined gas chromatography and electroantennographic detection (GC-EAD). The antennal responses of three butterfly species, Aglais urticae L. (Nymphalidae), Inachis io L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae) to floral scent compounds from both natural and synthetic mixtures were examined. Floral scents were collected from the butterfly nectar plants Cirsium arvense (L.) (Asteraceae), and Buddleja davidii Franchet cv. (Loganicaeae) with dynamic head-space methods on Tenax-GR and eluted with pentane. These eluates, composed of natural floral scent blends, represent an array of compounds in their natural state. In the GC-EAD analyses eleven compounds were identified from C. arvense with the benzenoid compound phenylacetaldehyde in highest abundance. Seventeen compounds were identified from B. davidii with the irregular terpene oxoisophorone in highest abundance. Thirty-nine synthetic floral scent compounds were mixed in pentane, in equal amounts; about 35 ng were allowed to reach the antennae. The butterflies showed antennal responses to most of the floral scent compounds from both natural and synthetic blends except to the highly volatile monoterpene alkenes. Certain benzenoid compounds such as phenylacetaldehyde, monoterpenes such as linalool, and irregular terpenes such as oxoisophorone, were emitted in relatively large amounts from C. arvense and B. davidii, and elicited the strongest antennal responses. These compounds also elicited strong antennal responses when present in the synthetic scent blends. Thus, the butterflies seem to have many and /or sensitive antennal receptors for these compounds, which points to their biological importance. Moreover, these compounds are exclusively of floral scent origin. For B. davidii, which depends highly on butterflies for pollination, the exclusive floral scent compounds emitted in high abundance could be the result of an adaptive pressure to attract butterflies. Received 2 Septemter 2001; accepted 9 September 2002.     

Foraging responses in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae) to floral scents

Summary. For butterflies to be efficient foragers, they need to be able to recognize rewarding flowers. Flower signals such as colours and scents assist this recognition process. For plant species to attract and keep butterflies as pollinators, species-specific floral signals are crucial. The aim of this study is to investigate foraging responses to floral scents in three temperate butterfly species, Inachis io L. (Nymphalidae), Aglais urticae L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae), in behavioural choice bioassays. The butterflies were allowed to choose bet-ween flower models varying in scent and colour (mauve or green). Flowers or vegetative parts from the plants Centaurea scabiosa L. (Asteraceae), Cirsium arvense (L.) (Asteraceae), Knautia arvensis (L.) (Dipsacaceae), Buddleja davidii Franchet (Loganicaeae), Origanum vulgareL. (Lamiaceae), Achillea millefolium L. (Asteraceae), and Philadelphus coronarius L. (Hydrangiaceae) were used as scent sources. All visits to the models — those that included probing and those that did not — were counted, as was the duration of these behaviours. Both flower-naive and flower-experienced (conditioned to sugar-water rewards, the colour mauve, and specific floral scents) butterflies were tested for their preference for floral versus vegetative scents, and to floral scent versus colour. The butterflies were also tested for their ability to switch floral scent preferences in response to rewards. Flower-naive butterflies demonstrated a preference for the floral scent of the butterfly-favourable plants C. arvense and K. arvensis over the floral scent of the non-favourable plants Achillea millefolium (Asteraceae), and Philadelphus coronarius cv. (Hydrangiaceae). Most of the butterflies that were conditioned to floral scents of either C. arvense, K. arvensis, or B. davidii readily switched theirfloral scent preferences to the one most recently associated with reward, thus demonstrating that floral scent constancy is a result from learning. These findings suggest that these butterflies use floral scent as an important cue signal to initially identify and subsequently recognize and distinguish among rewarding plants. Received 2 September 2001; accepted 9 September 2002.     

Intraguild predatory interactions between the jellyfish <Emphasis Type="Italic">Cyanea capillata</Emphasis> and <Emphasis Type="Italic">Aurelia aurita</Emphasis>

While qualitative observations of jellyfish intraguild predation abound in the literature, there are only few rate measurements of these interactions. We quantified predation rates among two common jellyfish in northern boreal waters, Cyanea capillata and its prey Aurelia aurita, both of which also feed on crustacean zooplankton and fish larvae. A series of incubation experiments using a wide range of prey concentrations (0.38–3.8 m⁻³) in large containers (2.6 m³) was carried out. By replenishing the prey continuously as they were captured we maintained a nearly constant prey concentrations. Ingestion rates increased linearly up to prey concentrations of 1.92 m⁻³, yielding maximum clearance rates of ∼2.37 ± 0.39 m³ predator⁻¹ h⁻¹ for C. capillata predators 16 ± 2.3 cm in diameter. Mean ingestion rate at saturated prey concentrations (1.92–3.85 m⁻³) was 4.01 ± 0.78 prey predator⁻¹ h⁻¹. Behavioral observations suggested that predators did not alter their swimming behavior during meals, and thus that feeding rates were generally handling limited rather than encounter limited. Predators captured more prey than needed, and semi-digested prey was often discarded when fresh prey was encountered.     

Genetic evidence for the cryptic species pair, <Emphasis Type="Italic">Lottia digitalis </Emphasis>and <Emphasis Type="Italic">Lottia austrodigitalis</Emphasis> and microhabitat partitioning in sympatry

It has been proposed that the common West Coast limpet, Lottia digitalis, is actually the northern counterpart of a cryptic species duo including, Lottia austrodigitalis. Allele frequency differences between southern and northern populations at two polymorphic enzyme loci provided the basis for this claim. Due to lack of further evidence, L. austrodigitalis is still largely unrecognized in the literature. Seven additional enzyme loci were examined from populations in proposed zones of allopatry and sympatry to determine the existence of L. austrodigitalis as a sibling species to L. digitalis. Significant allele frequency differences were found at five enzyme loci between populations in Laguna Beach, southern California, and Bodega Bay, northern California; strongly supporting the existence of separate species. Both species exhibit two microhabitat morphotypes, a gooseneck barnacle morph in the mid-intertidal zone and a rock morph in the high-intertidal zone. In sympatry, L. austrodigitalis was more abundant higher in the intertidal on rocks, whereas L. digitalis was more abundant lower in the intertidal on barnacles. This finding supports earlier claims of microhabitat partitioning in this sibling species pair. In addition to this finding, the transition zone between the species was found to have shifted substantially northward in only two decades, from Monterey Peninsula, CA to near Pigeon Point, CA, where L. digitalis previously dominated.