Covering behaviour in <Emphasis Type="Italic">Paracentrotus</Emphasis><Emphasis Type="Italic">lividus</Emphasis>: is light important?

"Covering" or "heaping" behaviour is common to a number of regular echinoids living in a variety of different habitats. Many theories have been proposed to explain this behaviour, among which are several that link covering to light, including ultraviolet (UV) light. However, previous investigations of this light theory have been largely qualitative. In the present study, we used a systematic laboratory protocol to examine quantitatively the covering behaviour of the shallow water echinoid, Paracentrotus lividus, under four different light regimes: white light (400-700 nm), UV-A+B (315-400 nm), UV-A (320-400 nm), and darkness. These experiments demonstrated that light, in particular UV light, influences the covering behaviour of P. lividus. Under the UV regimes, significantly more individuals were found to display covering behaviour, and individuals spent more time at the base of aquaria, farthest from the light source. Moreover, covering items were retained for the longest period of time under the UV-A+B regime. We propose that protection against the harmful effects of UV radiation may be one of the functions of covering behaviour in P. lividus.     

Life cycle of <Emphasis Type="Italic">Oithona</Emphasis> <Emphasis Type="Italic">similis</Emphasis> (Copepoda: Cyclopoida) in Kola Bay (Barents Sea)

The annual population dynamics (nauplii, old copepodites CIV–CV and adults) and seasonal variations in reproductive parameters of the cyclopoid copepod Oithona similis were investigated on the basis of the data 1999–2006 in Kola Bay, a large subarctic fjord in the Barents Sea. Population density of O. similis ranged from 110 to 9,630 ind m⁻³ and averaged 1,020 ± 336 ind m⁻³. The relative abundance of adults was high during winter (~60%). At the end of winter (mid-March), the population included a large percentage of later-stage copepodites (stage CIV 23% and stage CV 57%). There were two periods of mass spawning, in late June and September. Autumn and summer generations strongly differed in abundance, average prosome length (PL), clutch size (CS), egg diameter (D), egg production rates (EPR and SEPR) and female secondary production. Average PL decreased with increasing water temperature, while D and CS were strongly correlated with PL but unaffected by temperature. Annual average EPR and SEPR were 0.55 ± 0.18 eggs female⁻¹ day⁻¹ and 0.0011 ± 0.003 day⁻¹, respectively. Female secondary production averaged 0.8 ± 0.3 μg C m⁻³ day⁻¹ (range 0.001–3.58). There were positive relationships between abundance, EPR, SEPR, production and water temperatures. Reproductive parameters appeared to be controlled by hydrological factors and food conditions.     

(<Emphasis Type="Italic">Z</Emphasis>)-9-Pentacosene − contact sex pheromone of the locust borer, <Emphasis Type="Italic">Megacyllene robiniae</Emphasis>

Summary. Male locust borers, Megacyllene robiniae (Förster), responded to females only after contacting them with their antennae, indicating that mate recognition was mediated by a contact sex pheromone. GC-MS analyses of whole-body extracts of males and females determined that the profiles of compounds in the extracts were qualitatively similar, but differed considerably in the ratios of compounds between sexes. Biological activities of reconstructed blends of the most abundant straight-chain (nC₂₃, nC₂₄, nC₂₅, nC₂₆), methyl-branched (3me-C₂₃, 3me-C₂₅), and unsaturated (Z9:C₂₃, Z9:C₂₅, Z9:C₂₇ compounds in extracts from females were assessed in arena bioassays, assessing four distinct steps in the mating behavior sequence of males (orientation, arrestment, body alignment, mounting and attempting to couple the genitalia). Males were unresponsive to freeze-killed, solventwashed females treated with blends of straight-chain and methyl-branched alkanes, but responded strongly to females treated with the blend of alkenes. Further trials determined that the complete sequence of mating behaviors, up to and including coupling the genitalia, was elicited by Z9:C₂₅ alone. Z9:C₂₅ comprised 16.4 ± 1.3% of the total hydrocarbons in whole-body hexane extracts of females and was co-dominant with two other hydrocarbons that were not active. In contrast, in solid phase microextraction (SPME) wipe samples from several areas of the cuticle, Z9:C₂₅ appeared as the single dominant peak, comprising 34.6 – 37.8% of the sampled hydrocarbons. Our data indicate that Z9:C₂₅ is a contact sex pheromone of M. robiniae, being the most abundant hydrocarbon on the surface of the cuticular wax layer of females where it is readily accessible to the antennae of males.     

Variation in colony geometry modulates internal light levels in branching corals, <Emphasis Type="Italic">Acropora humilis</Emphasis> and <Emphasis Type="Italic">Stylophora pistillata</Emphasis>

Colonial photosynthetic marine organisms often exhibit morphological phenotypic plasticity. Where such plasticity leads to an improved balance between rates of photosynthesis and maintenance costs, it is likely to have adaptive significance. To explore whether such phenotypic plasticity leads to more favourable within-colony irradiance for reef-building branching corals, this relationship was investigated for two coral species Acropora humilis and Stylophora pistillata, along a depth gradient representing light habitats ranging from 500 to 25 μmol photons m⁻² s⁻¹, during 2006 at Heron Island, Great Barrier Reef (23.44°S, 151.91°E). In the present study changes in flow-modulated mass transfer co-varied with light as a function of depth. In low-light (deep) habitats, branch spacing (colony openness) in A. humilis and S. pistillata was 40–50% greater than for conspecifics in high-light environments. Also, branches of A. humilis in deep water were 40–60% shorter than in shallow water. Phenotypic changes in these two variables lead to steeper within-colony light attenuation resulting in 38% higher mean internal irradiance (at the tissue surface) in deep colonies compared to shallow colonies. The pattern of branch spacing was similar for S. pistillata, but this species displayed an alternate strategy with respect to branch length: shade adapted deep and cave colonies developed longer and thinner branches, allowing access to higher mass transfer and irradiance. Corals in cave habitats allowed 20% more irradiance compared to colonies found in the deep, and had a 47% greater proportion of irradiance compared to colonies in the shallow high-light environment. Such phenotypic regulation of internal light levels on branch surfaces partly explains the broad light niches of many branching coral species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic variation among life-history stages of mussels in a<Emphasis Type="Italic"> Mytilus edulis–M</Emphasis>.<Emphasis Type="Italic"> trossulus</Emphasis> hybrid zone

The mussel species Mytilus edulis L. and M. trossulus Gould coexist and hybridize throughout a large area that includes the north coast of Maine and Atlantic Canada. Previous studies provided genetic evidence for limited hybridization between the two species for mussels >15 mm. The present study used two genetic markers (ITS, Glu-5) to examine the genetic composition of early life-history stages by sampling veliger and pediveliger larvae, juveniles (<2.0 to 15.0 mm shell length) and adults (>15 mm shell length) in Trinity Bay, Newfoundland, during three consecutive years (1995–1997) to determine if differential mortality limits the relative abundance of hybrids. The relative frequency of the two species and the different hybrid genotypes was similar among the larvae, juveniles and small adult mussels. The double hybrid genotype (F₁-like) was the rarest genotype observed. There was no evidence for differential mortality during the early life-history stages, and factors limiting production of hybrids appear to operate before the late larval stage. The observed frequency of hybrids is probably due to a combination of pre- and postzygotic reproductive isolating mechanisms operating early in the mussels life history. M. trossulus dominated the early life-history stages, possibly due to a higher population density and a greater reproductive output than M. edulis. Differential mortality may explain the observed decrease in frequency of M. trossulus and increase in frequency of M. edulis with increasing shell length. A similar frequency of hybrid mussels from larvae to the size class of 55 mm shell length may indicate a rate of mortality intermediate between the two parental species. The M. edulis–M. trossulus hybrid zone appears to be maintained by reproductive isolating mechanisms limiting the production of hybrids and life-history differences that allow the two species to coexist.Communicated by J.P. Grassle, New Brunswick     

Sex pheromone of <Emphasis Type="Italic">Ectinus aterrimus</Emphasis> (L<Emphasis Type="SmallCaps">inné</Emphasis>, 1761) (Coleoptera: Elateridae)

Summary.   Ectinus aterrimus (L.) is a fairly common European click beetle species which develops mainly in forests. In pheromone gland extracts of female E. aterrimus, examined using gas chromatography – mass spectrometry (GC-MS), one single compound was present. This was identified as 7-methyloctyl 9-methyldecanoate by comparison with a synthetic sample. Field trapping trials revealed a highly significant attraction of male E. aterrimus towards this ester. The structure of the compound differs remarkably from the pheromones of the closely related Agriotes spp., which exclusively use terpene esters.     

Does the antidiabetic drug metformin affect embryo development and the health of brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> f. <Emphasis Type="Italic">fario</Emphasis>)?

Background

Due to the rising number of type 2 diabetes patients, the antidiabetic drug, metformin is currently among those pharmaceuticals with the highest consumption rates worldwide. Via sewage-treatment plants, metformin enters surface waters where it is frequently detected in low concentrations (µg/L). Since possible adverse effects of this substance in aquatic organisms have been insufficiently explored to date, the aim of this study was to investigate the impact of metformin on health and development in brown trout (Salmo trutta f. fario) and its microbiome.

Results

Brown trout embryos were exposed to 0, 1, 10, 100 and 1000 µg/L metformin over a period from 48 days post fertilisation (dpf) until 8 weeks post-yolk sac consumption at 7 °C (156 dpf) and 11 °C (143 dpf). Chemical analyses in tissues of exposed fish showed the concentration-dependent presence of metformin in the larvae. Mortality, embryonic development, body length, liver tissue integrity, stress protein levels and swimming behaviour were not influenced. However, compared to the controls, the amount of hepatic glycogen was higher in larvae exposed to metformin, especially in fish exposed to the lowest metformin concentration of 1 µg/L, which is environmentally relevant. At higher metformin concentrations, the glycogen content in the liver showed a high variability, especially for larvae exposed to 1000 µg/L metformin. Furthermore, the body weight of fish exposed to 10 and 100 µg/L metformin at 7 °C and to 1 µg/L metformin at 11 °C was decreased compared with the respective controls. The results of the microbiome analyses indicated a shift in the bacteria distribution in fish exposed to 1 and 10 µg/L metformin at 7 °C and to 100 µg/L metformin at 11 °C, leading to an increase of Proteobacteria and a reduction of Firmicutes and Actinobacteria.

Conclusions

Overall, weight reduction and the increased glycogen content belong to the described pharmaceutical effects of the drug in humans, but this study showed that they also occur in brown trout larvae. The impact of a shift in the intestinal microbiome caused by metformin on the immune system and vitality of the host organism should be the subject of further research before assessing the environmental relevance of the pharmaceutical.

     

Sibling competition in guinea pigs (<Emphasis Type="Italic">Cavia aperea</Emphasis> f. <Emphasis Type="Italic">porcellus</Emphasis>): scrambling for mother’s teats is stressful

Lactation is the most energy-intense period in the life of a female mammal. This can cause severe conflict between mother and offspring over the duration of lactation but also between siblings over the amount of milk each pup gets from its mother. Thus, competitive interactions between siblings are expected, and competition is likely to increase with litter size, particularly in species where the number of offspring exceeds the number of teats. We studied sibling competition in the domestic guinea pig (Cavia aperea f. porcellus), which has two teats, but frequently bears litters of up to five pups. By cross-fostering we created non-competition (control) litters with two pups and competition litters with four pups and observed nursing behaviour on days 5, 10, 15 and 20 postpartum. Pups of larger litters had lower growth rates, indicating increased competition among siblings in these litters. Pups of larger litters had to wait longer for access to a teat and spent less time suckling than pups of smaller litters but ate more solid food instead. Additionally, we manipulated the individual short-term need of pups by separating half of the pups of each litter for 2 h from their mothers before observation. Within a litter, hungry pups achieved access to milk faster and spent more time suckling than non-hungry pups. Pups competed mostly by scramble competition. Aggressive interactions occurred only in large litters. Pups of large litters had higher cortisol levels than pups in small litters. These effects decreased with age as pups became increasingly independent of maternal milk. Pup behaviour appears to fit better with models of scramble competition than with those of honest signalling. This contribution is part of the special issue “Sibling competition and cooperation in mammals” (guest editors: Robyn Hudson and Fritz Trillmich).     

Strategies of a parasite of the ant–<Emphasis Type="Italic">Acacia</Emphasis> mutualism

Mutualisms can be exploited by parasites—species that obtain resources from a partner but provide no services. Though the stability of mutualisms in the presence of such parasites is under intensive investigation, we have little information on life history traits that allow a species to be a successful mutualist or rather a parasite, particularly in cases where both are closely related. We studied the exploitation of Acacia myrmecophytes by the ant, Pseudomyrmex gracilis, contrasting with the mutualistic ant Pseudomyrmex ferrugineus. P. gracilis showed no host-defending behavior and had a negative effect on plant growth. By preventing the mutualist from colonization, P. gracilis imposes opportunity costs on the host plant. P. gracilis produced smaller colonies with a higher proportion of alates than did the mutualist and thus showed an “r-like” strategy. This appears to be possible because P. gracilis relies less on host-derived food resources than does the mutualist, as shown by behavioral and stable isotope studies. We discuss how this system allows the identification of strategies that characterize parasites of mutualisms.     

δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N values in reef corals <Emphasis Type="Italic">Porites lutea</Emphasis> and <Emphasis Type="Italic">P. cylindrica</Emphasis> and in their epilithic and endolithic algae

In summer 1998, shallow water corals at Sesoko Island, Japan (26°38′N, 127°52′E) were damaged by bleaching. In August 2003, partially damaged colonies of the massive Porites lutea and the branching P. cylindrica were collected at depths of 1.0–2.5 m. The species composition of epilithic algal communities on dead skeletal surfaces of the colonies (‘red turfs’, ‘green turfs’, ‘red crusts’) and the endolithic algae (living in coral skeletons) growing close to and away from living coral polyps was determined. Carbon and nitrogen stable isotope values of organic matter (δ¹³C and δ¹⁵N) from all six of these biological entities were determined. There were no significant differences in the isotope composition of coral tissues of the two corals, with P. lutea having δ¹³C of −15.3 to −9.6‰ and δ¹⁵N of 4.7–6.1‰ and P. cylindrica having similar values. Polyps in both species living close to an interface with epilithic algae had similar isotope values to polyps distant from such an interface. Despite differences in the relative abundance of the algal species in red turfs and crusts, their δ¹³C and δ¹⁵N values were not significantly different from each other (−18.2 to −13.9, −20.6 to −16.2, 1.1–4.3, and 3.3 to 4.9‰, respectively). The green algal turf had significantly higher δ¹³C values (−14.9 to −9.3‰) than that of red turfs and crusts but similar δ¹⁵N (1.2–4.1‰) to the red algae. The data do not suggest that adjoining associations of epilithic algae and coral polyps exchange carbon- and nitrogen-containing metabolites to a significant extent. The endolithic algae in the coral skeletons had δ¹³C values of −14.8 to −12.3‰ and δ¹⁵N of 4.0–5.4‰. Thus they did not differ significantly from the coral polyps in their carbon and nitrogen isotope values. The similarity in carbon isotope values between the coral polyps and endolithic algae may be attributed to a common source of CO₂ for zooxanthellae and endolithic algae, namely, from respiration by the coral host. While it is difficult to fully interpret similarity in the nitrogen isotope composition of coral tissue and of green endolithic algae and the difference in δ¹⁵N between green epilithic and endolithic algae, the data are consistent with nitrogen-containing metabolites from the scleractinian coral serving as a significant source of nitrogen for the endolithic algae.     

How does burrowing by the isopod <Emphasis Type="Italic">Limnoria agrostisa</Emphasis> (Crustacea: Limnoriidae) affect the leaf canopy of the southern Australian seagrass <Emphasis Type="Italic">Amphibolis griffithii</Emphasis>?

In south-western Australia, the isopod Limnoria agrostisa commonly burrows into leaf clusters and immature shoots of Amphibolis griffithii. The isopod also burrows into the sheath and rhizomes of Posidonia species. In A. griffithii, the isopod consumes new tissue within the sheath, damaging or destroying the meristem. This results in malformation of new leaves or destruction of whole leaf clusters with the potential to reduce the photosynthetic area of a shoot. The isopod has been found in all but one meadow of A. griffithii examined over 1,000 km of the Western Australian coastline. It was present throughout the year and showed little variation in abundance. Young were produced year round, but were more abundant in the summer months. Females, 3.5 mm in length or larger, produced 2–5 young that were brooded within the leaf cluster or base of an immature shoot. Within a meadow, 40–70% of shoots and 10–20% of leaf clusters were damaged by isopods. Seasonal trends were not consistent, but damage appeared to be higher in summer when isopod abundance was higher. Approximately 40% of clusters were destroyed by isopod damage. Isopods attack shoots of all ages, but damage was often located on apical clusters. There was no evidence that isopod damage initiated branching or leaf cluster formation. Estimations of clusters damaged or destroyed may be conservative, as only those clusters remaining on a shoot could be counted, and cluster loss could not be quantified. Examination of defoliated stems on upright shoots and horizontal rhizomes indicated that many were destroyed by isopods. The effect of L. agrostisa although substantial appears to be a feature of healthy seagrasses throughout southern Australia.     

Variation along the shy–bold continuum in extremophile fishes (<Emphasis Type="BoldItalic">Poecilia mexicana</Emphasis>, <Emphasis Type="BoldItalic">Poecilia sulphuraria</Emphasis>)

One potential trade-off that bold individuals face is between increased predation risks and gains in resources. Individuals experiencing high predation and hungry individuals (or individuals with low body condition) are predicted to show increased boldness. We examined one behavioral trait previously reported to be associated with boldness (the time individual fish needed to emerge from shelter) in various populations of mollies (Poecilia spp.). Our study system included several southern Mexican surface streams with high piscine predation and high food availability, sulfidic surface streams with high avian predation, in which the inhabiting fish show reduced body condition, and a sulfidic cave, where predation and body condition are low. Our comparison revealed very short times to emerge from the start box in populations from non-sulfidic streams. In sulfidic habitats (whether surface or cave), it took individual Poecilia mexicana considerably longer to emerge from the start box, and the same difference was also found in an independent comparison between P. mexicana and the closely related, highly sulfide-adapted Poecilia sulphuraria. Fish reared under common garden conditions (in the absence of predators and hydrogen sulfide) showed intermediate boldness scores to the extremes observed in the field. Our data thus indicate that (a) boldness is shaped by environmental conditions/experiential effects, but is not heritable, (b) predation affects boldness in the predicted direction, but (c) low body condition leads to reduced boldness. Extremophile Poecilia spp. spend most of their time surfacing to survive under sulfidic and hypoxic conditions, which exposes them to increased levels of predations, but the fish forage on the bottom. Hence, in this system, increased boldness does not increase foraging success. We argue that energy limitation favors reducing energetically costly behaviors, and exploring novel environments may be just one of them.     

The life cycles of two coexisting copepods, <Emphasis Type="Italic">Calanus chilensis</Emphasis> and <Emphasis Type="Italic">Centropages brachiatu</Emphasis>s,in the upwelling zone off northern Chile (23°S)

A time series study of the copepods Calanus chilensis and Centropages brachiatus was carried out at the coastal upwelling zone of Mejillones (23°S, northern Chile), to analyze their annual life cycles in association with upwelling variation. These species co-exist in the upwelling zone. Weekly sampling of zooplankton and oceanographic variables including Chlorophyll-a and phytoplankton composition were obtained during January–December 2002 at a fixed station (ca. 90 m depth). Stages of abundances, their proportions, changes in body length of adult females, sex ratio and egg production rate (EPR), were used as proxies to examine copepods’ demography. Upwelling, assessed by weekly Ekman transport and oceanographic conditions, was intermittent throughout the year with lack of periodicity components. Populations of both copepod species did not correlate with these non-predictable upwelling events. C. chilensis reproduced year-round and the population showed ca. 15 peaks of adults with an average time interval between peaks of 20 days. C. brachiatus showed a similar life cycle, also having 15 peaks of adults at about 22 days of time intervals. Cross-correlation functions and spectral analysis showed that both populations correlated positively through time, but not in phase, evidencing a time lag for their reproductive cycles. The lag was also evident in their population abundances. Both species differ in their development rates and this may result in non-in phase life cycles. Our findings suggest that species-dependent attributes, such as development rates, modulated by adaptations to temperature, might impose constraints in the species life cycles determining the population cycles. Such attributes must be considered when modeling and understanding population dynamics and secondary production of copepods.     

Influence of male harassment and female competition on female feeding behaviour in a sexual–asexual mating complex of mollies (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, <Emphasis Type="Italic">P. formosa</Emphasis>)

Differential interests between the sexes regarding the number of copulations can result in sexual harassment. Hence, females may have less time available for foraging. Male sexual harassment often leads to fitness reduction in females. We used the mating complex of the bisexual fish Poecilia mexicana and the co-occurring all-female Poecilia formosa to study sexual harassment and its incurred cost on female feeding efficiency. P. formosa is a sperm-dependent parthenogen that requires mating with host males to induce embryogenesis, but the male genes are not used. We therefore predicted P. mexicana males to prefer conspecific females. Hence, costs of male sexual harassment should not occur in unisexuals. While P. formosa are at a disadvantage compared to P. mexicana females due to male mate choice (leading to sperm limitation), this could be traded-off by suffering less from sexual harassment. In our experiment, we found males to direct significantly more pre-copulatory mating behaviour towards conspecific females, whereas actual mating attempts did not differ between species. Contrary to our prediction, both types of females started feeding later and spent less time feeding in the presence of a male partner compared to the time spent feeding with another female, suggesting that females of both species suffer from male harassment. The focal females' feeding time declined with increasing body size of the female competitor, and the same pattern was found when a male was present. We discuss that—besides sexual harassment—other factors such as food competition and female mate choice may affect female feeding efficiency.     

<Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> on a coastal dune system: a thorny issue?

The study mapped the spread of the invasive non-native shrub, Hippophae rhamnoides, on a coastal dune system in South Wales. H. rhamnoides colonies spread across the system, covering around 60.9 ha in 1996 compared to 2.4 ha in 1957. Clearance activities have since decreased the total to around 23 ha. The effects of this expansion on ground flora were assessed through comparison of species assemblages in colonised, never colonised and cleared areas. Dichotomisation presented a number of markedly different communities which correlated to their status of H. rhamnoides invasion. Colonised quadrats were overwhelmingly composed of H. rhamnoides and a few shade-tolerant species such as Galium aperine and Urtica dioica. Cleared quadrats did not support desirable dune grassland species present in never colonised sites, although those which had been cleared for the longest period may be regaining some characteristic species. Clearance work in future needs to concentrate on the complete removal of smaller H. rhamnoides patches whilst also preventing the establishment of Chamerion angustifolium and other ruderal species which in turn inhibit the development of typical dune grassland communities.     

A Fine-Scale <Emphasis Type="Italic">k</Emphasis>−ε Model for Atmospheric Flow over Heterogeneous Landscapes

A multi-purpose model for small-scale atmospheric flows over heterogeneous landscapes is being developed. The aim of this research is to build a tool able to predict the dynamical (wind, turbulence) and diffusive (gases, particles) fields over landscapes characterised by heterogeneous plant cover. In its present stage of development the model is based on the numerical integration of neutral atmospheric flow equations, using an energy-dissipation closure scheme and over a domain that may include vegetation layers. Three validation cases of the model are presented: (i) response of the airflow to a change in surface roughness; (ii) airflow within and above a horizontally homogeneous plant canopy; (iii) airflow over two complex forest-to-clearing and clearing-to-forest transitions. All simulations provide results in good agreement with the experimental data, except for turbulent kinetic energy just after a clearing-to-forest transition. This result is not surprising for a statistical k– model in a flow region characterised by strong distorsion and intermittent turbulence. However the overall good performance of the model is promising for environmental research at fine scales over heterogeneous landscapes.     

Marine aquaculture and bottlenose dolphins’ (<Emphasis Type="Italic">Tursiops truncatus</Emphasis>) social structure

In this study, we investigate association patterns of 249 bottlenose dolphin feeding groups off Sardinia Island (Italy) from January 2000–May 2007 and describe how their association behaviour is related to their response to food patches created by a marine fin fish farm. We also tested the hypothesis that dolphins have different social structures with different feeding activities: Associations should decrease during opportunistic feeding behaviours as it is easier to capture prey, and cooperation is not as necessary. Sixteen individually identified bottlenose dolphins were observed participating in both opportunistic and not opportunistic feeding activities, with a mean of 30 ± 8 times and 9.6 ± 1 times, respectively. Bottlenose dolphins show non-random social behaviour during feeding and this behaviour differs depending on their specific foraging activity. Dolphin associations during feeding can be divided into three categories: acquaintances, affiliates, and feeding associates. Association behaviour during fish farm feeding is consistent with our hypothesis that during opportunistic behaviours, benefits from cooperation decrease, as it is easier to capture prey. Group size homogeneity in both feeding activities demonstrates that the number of dolphins engaging in foraging is not necessarily related with cooperation levels. Moreover, an adult dolphin may prefer to associate with a specific individual, independent of the sex, who shares the same foraging priorities. This study is the first to show how aquaculture is not only directly affecting marine predators but could also indirectly affect their social structure and behaviour.     

Does begging affect growth in nestling tree swallows,<Emphasis Type="Italic"> Tachycineta bicolor</Emphasis>?

Much of the theoretical work on the evolution of begging assumes this elaborate display is costly. The evidence for an energetic cost to begging has, however, been equivocal. Metabolic studies on nestling birds suggest that begging requires minimal energy, but some growth studies have shown that excess begging reduces growth rates. One difficulty in interpreting these results is that metabolic and growth studies have each been performed on different species. Here, we test whether high begging frequencies depress growth in nestling tree swallows, Tachycineta bicolor, a species in which the metabolic cost of begging has been measured. When we compared the growth of nestlings stimulated to beg at either high or low frequencies, we found no significant differences in their mass gained, wing growth or portion of ingested energy devoted to begging either during the experimental period or in the 24 h following the end of the experiment. We also found no significant relationship between begging intensity and growth measurements. The results of our study are consistent with previous metabolic studies on this species suggesting that the energetic cost of begging is relatively low. More generally, evidence for a fitness cost of begging via decreased growth is equivocal.Communicated by J. Dickinson     

Short-term effects of data-loggers on Cory’s shearwater (<Emphasis Type="Italic">Calonectris diomedea</Emphasis>)

We investigated the possible effects of a 12-g data-logger attached to a darvic ring on the performance of Corys shearwater (Calonectris diomedea, 600–850 g) from two different colonies in the western Mediterranean Sea. We compared return rates, current breeding success and body condition between equipped and unequipped birds. Effects on feeding ecology during winter and breeding period was also evaluated through the measurement of stable isotopes of carbon (¹³C) and nitrogen (¹⁵N) in one of the colonies. We found no evidence of negative effects of loggers on demographic parameters analysed or in feeding ecology. Power analyses suggested a high power to detect medium effect size, but a low power to detect small changes. Despite the non-significant results we could only exclude medium to strong effects of the devices on one of these parameters. We detected some short-term negative effects on body condition for the equipped birds, but these were unlikely to have had important consequences. Results suggest that the use of loggers is an adequate methodology to obtain information from seabirds at sea, but data should be carefully interpreted with regard to potential biases during severe environmental conditions.Communicated by S.A. Poulet, Roscoff     

Optimal maternal investment in the dung beetle<Emphasis Type="Italic"> Onthophagus taurus</Emphasis>?

Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parents investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.Communicated by D. Gwynne