Support for maternal manipulation of developmental nutrition in a facultatively eusocial bee, <Emphasis Type="Italic">Megalopta genalis</Emphasis> (Halictidae)

Developmental maternal effects are a potentially important source of phenotypic variation, but they can be difficult to distinguish from other environmental factors. This is an important distinction within the context of social evolution, because if variation in offspring helping behavior is due to maternal manipulation, social selection may act on maternal phenotypes, as well as those of offspring. Factors correlated with social castes have been linked to variation in developmental nutrition, which might provide opportunity for females to manipulate the social behavior of their offspring. Megalopta genalis is a mass-provisioning facultatively eusocial sweat bee for which production of males and females in social and solitary nests is concurrent and asynchronous. Female offspring may become either gynes (reproductive dispersers) or workers (non-reproductive helpers). We predicted that if maternal manipulation plays a role in M. genalis caste determination, investment in daughters should vary more than for sons. The mass and protein content of pollen stores provided to female offspring varied significantly more than those of males, but volume and sugar content did not. Sugar content varied more among female eggs in social nests than in solitary nests. Provisions were larger, with higher nutrient content, for female eggs and in social nests. Adult females and males show different patterns of allometry, and their investment ratio ranged from 1.23 to 1.69. Adult body weight varied more for females than males, possibly reflecting increased variation in maternal investment in female offspring. These differences are consistent with a role for maternal manipulation in the social plasticity observed in M. genalis.     

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.     

Monitoring acoustically tagged king prawns <Emphasis Type="Italic">Penaeus</Emphasis> (<Emphasis Type="Italic">Melicertus</Emphasis>) <Emphasis Type="Italic">plebejus</Emphasis> in an estuarine lagoon

Fine-scale movement patterns in penaeid prawns are rarely observed in situ, but are essential in understanding habitat use, foraging, and anti-predator behaviour. Acoustic telemetry was applied to examine the activity, space utilization, and habitat use of the eastern king prawn Penaeus (Melicertus) plebejus, at small temporal and spatial scales. Tracking of sub-adult P. plebejus (n = 9) in Wallagoot Lake (36.789°S, 149.959°E; 23 April–12 May 2009) and calculation of a minimum activity index (MAI) revealed high variation in activity rates across diel periods and in different habitats. Elevated activity rates and movement indicated foraging in unvegetated habitats during the night. Areas within the 95 and 50% space utilization contours averaged 2,654.1 ± 502.0 and 379.9 ± 103.9 m², respectively, and there was a significant negative relationship between these areas and prawn activity rates in unvegetated habitats. This study provides the first estimates of prawn activity rates and space utilization in the field. Application of acoustic telemetry can increase knowledge of prawn movements and their interactions with other marine species in different habitats.     

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.     

Lack of sequestration of host plant glucosinolates in <Emphasis Type="Italic">Pieris rapae</Emphasis> and <Emphasis Type="Italic">P. grarricae</Emphasis>

Summary. Sequestration of plant toxins in herbivores is often correlated with aposematic coloration and gregarious behaviour. Larvae of Pieris brassicae show these conspicuous morphological and behavioural characteristics and were thus suggested to sequester glucosinolates that are characteristic secondary metabolites of their host plants. P. rapaeare camouflaged and solitary, and are thus not expected to sequester. To test this hypothesis and to check the repeatabi-lity of a study that did report the presence of the glucosinolate sinigrin in P. brassicae, larvae were reared on three species of Brassicaceae (Sinapis alba, Brassica nigra and Barbarea stricta), and different leaf and insect samples were taken for glucosinolate analysis. The major host plant glucosinolates could only be found in traces or not at all in larval haemolymph, bled or starved larvae, faeces or pupae of both species or P. brassicae regurgitant. Haemolymph of both Pieris spp. was not rejected by the ant Myrmica rubra in dual-choice assays; the regurgitant of P. brassicae was rejected. This suggests the presence of compounds other than glucosinolates that might be sequestered in or produced by P. brassicae only. In faeces of both Pieris spp. a compound which yielded 4-hydroxybenzylcyanide (HBC) upon incubation with sulfatase was detected in high concentrations when larvae had been reared on S. alba. This compound may be derived from hydrolysis of sinalbin, the main glucosinolate of that plant. The unidentified HBC progenitor was apparently not sequestered in the two Pieris spp., and was not detected in faeces of larvae reared on B. nigra or B. stricta. Received 18 July 2002; accepted 11 September 2002.     

The dynamics of social learning in an insect model,the bumblebee (<Emphasis Type="Italic">Bombus terrestris</Emphasis>)

Bumblebees (Bombus terrestris) are attracted to those particular inflorescences where other bees are already foraging, a process known as local enhancement. Here, we use a quantitative analysis of learning in a foraging task to illustrate that this attraction can lead bees to learn more quickly which flower species are rewarding if they forage in the company of experienced conspecifics. This effect can also be elicited by model bees, rather than live demonstrators. We also show that local enhancement in bumblebees most likely reflects a general attraction to conspecifics that is not limited to a foraging context. Based on the widespread occurrence of both local enhancement and associative learning in the invertebrates, we suggest that social influences on learning in this group may be more common than the current literature would suggest and that invertebrates may provide a useful model for understanding how learning processes based on social information evolve.     

Environmental controls on shell growth rates and δ<Superscript>18</Superscript>O of the shallow-marine bivalve mollusk <Emphasis Type="Italic">Phacosoma</Emphasis><Emphasis Type="Italic">japonicum</Emphasis> in Japan

Microgrowth patterns and the oxygen isotope composition of juvenile, shallow-marine bivalve mollusk shells of Phacosoma japonicum (Reeve) in Japan were analyzed and cross-calibrated with environmental parameters. Mark-and-recovery experiments indicate that a pair of two microgrowth lines and two microgrowth increments is produced every lunar day. This finding makes it possible to assign exact calendar dates to each portion of the shell. Average daily growth rates decrease by 61% from age two to three and 55% from age three to four. The length of the growing season and the growth rate are mainly controlled by temperature: shell growth ceases below 14.2°C (age two) and 16.8°C (age four) and is most rapid between 24.6°C and 27.2°C. Based on local temperature cycles, the growing season is longest in Seto Inland Sea, central Honshu (from May to November) and shortest at Hakodate Bay, North Japan (from June to October). The annual oxygen isotope profiles of the shells reflect the temperature cycle and the varying amounts of freshwater added to the seawater by precipitation. The most negative '¹⁸O values of -3.15‰ occur during the rainy season, i.e. during the monsoon and typhoon seasons. Growth rates are only slightly affected by salinity changes. Strongly reduced growth rates during the second half of the year at Seto Inland Sea and to a lesser extent at Tokyo Bay are explained by nutrient deprivation. Our study provides the basis for the use of P. japonicum in high-resolution ecological studies and environmental reconstructions.     

Worker policing and nest mate recognition in the ant <Emphasis Type="Italic">Formica fusca</Emphasis>

A conflict over male production arises in social insects where workers are able to lay unfertilized male eggs. This happens because each female (queen or worker) is most closely related to her own sons and is thus predicted to reproduce. The conflict is modulated by worker policing where workers prevent each other from reproducing by aggression or egg cannibalism. In this study, we show that in the ant Formica fusca, worker policing occurs by egg cannibalism rather than by overt aggression among workers. Furthermore, we show that, contrary to bees, wasps and other ant species, egg discrimination in F. fusca is not based only on a universal queen signature chemical and that nest mate recognition of eggs occurs.     

Weaning in the guinea pig (<Emphasis Type="Italic">Cavia aperea</Emphasis> f. <Emphasis Type="Italic">porcellus</Emphasis>): Who decides and by what measure?

Offspring should be selected to influence maternal effort to maximize their own fitness, whereas mothers are selected to limit investment in present progeny. In mammals, this leads to a conflict over the amount of milk provided and the timing of weaning. The intensity and time course of such conflict has so far mostly been investigated experimentally in altricial rodents. However, it is expected that offspring options for conflict will depend on developmental state. We therefore investigated in the highly precocial domestic guinea pig (Cavia aperea f. porcellus) who decides over nursing performance and weaning and how pup state influences these decisions. Specifically, we tested whether a threshold mass of pups predicts weaning time. By exchanging older litters against neonates and vice versa, we produced a situation in which females differed in lactational stage from the cross-fostered pups. Our results indicate that females decide about the timing of weaning, as cross-fostered younger pups were weaned at a much younger age than controls and older pups benefited from continuing lactation of foster mothers. Growth rates did not differ in the treatment groups, and different weaning ages resulted in differing weaning mass refuting the hypothesis that weaning is based on a threshold mass of offspring. This constitutes clear evidence that in a precocial rodent, the guinea pig, decisions about maternal care are primarily determined by maternal state and little influenced by pup state despite the extreme precociality of offspring. We suggest that precocial pups show little resistance to early weaning when food is abundant, as they reach sufficient nutritional independence by the middle of lactation to enable independent survival.     

Comparison of the flower scent of the sexually deceptive orchid <Emphasis Type="Italic">Ophrys iricolor</Emphasis> and the female sex pheromone of its pollinator <Emphasis Type="Italic">Andrena morio</Emphasis>

Summary. Ophrys flowers mimic the female produced sex pheromone of their pollinator species to attract males for pollination. The males try to copulate with the putative female and thereby pollinate the flower. Using electrophysiological and chemical analyses, floral volatiles released by O. iricolor as well as the female sex pheromone of its pollinator species, Andrena morio are investigated. Overall, 38 peaks comprising 41 chemical compounds, were found to release reactions in the antennae of male A. morio bees. Analyses using coupled gas chromatography-mass spectrometry revealed the presence of alkanes and alkenes with 20 to 29 carbon atoms, aldehydes (C9 to C24) and two esters. Almost all of those compounds were found in similar proportions in both, the floral extracts of O. iricolor and cuticle surface extracts of A. morio females. The pattern of biologically active volatiles described here is very similar to that used by other Ophrys species pollinated by Andrena males.     

Experimental analysis of worker division of labor in bumblebee nest thermoregulation (<Emphasis Type="Italic">Bombus huntii</Emphasis>, Hymenoptera: Apidae)

Bumblebee colonies experience daily and seasonal fluctuations in ambient temperature, but proper brood development requires a stable nest temperature. This study examined how adaptive colony responses to changing ambient temperature are achieved through the in-nest workers’ behavioral plasticity. We studied three Bombus huntii colonies in the laboratory. In the first experiment, we manipulated ambient temperature and recorded brood cell incubation and wing fanning by individually marked, known-age bees. The colonies maintained their nests closer to appropriate brood development temperatures (28 to 32°C) when exposed to a range of ambient temperatures from 10.3 to 38.6°C. Incubation activity was greater in cooler treatment conditions, whereas in the highest temperature treatment, some bees fanned and others moved off the brood. As the ambient temperature dropped, workers increased the duration of their incubating bouts, but, except at the highest temperature, the number of workers that incubated did not differ significantly among treatments. A subset of the bees incubated significantly more than their nest mates, some of which never incubated. Worker body size, but not age, was a good predictor of incubation rates, and smaller bees incubated at higher rates. In the second experiment, we removed the most actively incubating workers. Immediately after removals, the total colony incubation effort was lower than pre-removal levels, but incubation effort rebounded toward pre-removal levels after 24 h. The increased thermoregulatory demand after removals was met primarily by bees increasing their rates of incubation rather than by bees switching from a different task to incubation. We conclude that some B. huntii workers specialize on nest thermoregulation, and that changes in work rates are more important than task switching in meeting thermal challenges.     

<Emphasis Type="Italic">Semibalanus</Emphasis><Emphasis Type="Italic">balanoides</Emphasis> in winter and spring: larval concentration,settlement, and substrate occupancy

This study measured the progression from pelagic larvae to juvenile barnacles, and examined whether recruitment of barnacles, Semibalanus balanoides Linnaeus, at two intertidal sites in contrasting hydrodynamic regimes was determined by pre-settlement or post-settlement processes. The two sites were 1.5 km apart in the vicinity of Woods Hole, Mass., USA. Quantitative plankton samples were taken twice weekly from December 1997 to May 1998 at a nearby site as an estimate of nearshore larval abundance. The presence of S. balanoides nauplii was noted, and cyprids were enumerated and measured. Larval settlement at the two sites [Gansett Point, Buzzards Bay (GP) and Little Harbor, Vineyard Sound (LH)] was estimated from examination of replicate settlement plates exposed for 2 or 3 days throughout the settlement season, and from replicate plots on marked rock quadrats at each site. On both plates and rocks settled cyprids and metamorphs were enumerated. Space occupancy on unmanipulated rock quadrats by all stages from cyprids to adult barnacles was also examined. Settlement occurred from 2 January to 20 May, and major settlement peaks coincided with peaks in pelagic cyprid concentration at LH, but not at GP. Space occupied by juvenile barnacles was close to zero up until late February despite substantial settlement prior to that. At LH, juvenile barnacle cover was zero at the end of the observations; all settlement failed. Almost 100% of settled cyprids failed to metamorphose within 2 days from late January to late March. Then the proportion metamorphosing increased sharply coinciding with a sudden increase of 3°C in water temperature. Observed site differences in space occupancy by juvenile barnacles suggest that while cyprid supply is a necessary condition for barnacle settlement, other factors affecting metamorphosis of settled cyprids and early juvenile mortality determine recruitment.     

Embryo development and maternal–embryo nutritional relationships of piked spurdog (<Emphasis Type="Italic">Squalus</Emphasis><Emphasis Type="Italic"> megalops</Emphasis>)

The maternal–embryo relationship was determined for the piked spurdog (Squalus megalops). In addition, the increase in offspring size with maternal size was studied and the embryonic development was described. Wet weight of in utero eggs and offspring size was correlated with maternal size; larger females produced larger embryos which would have higher survival rate and reproductive value. All embryos present in a female were at a similar stage of development. The external yolk sac is reabsorbed late in gestation, suggesting that embryos are mostly nourished by yolk sac reserves. Embryo size-at-birth varied considerably (180–244 mm total length) as a result of the significant variability in ova size at ovulation. The amounts of water, organic and inorganic matter of embryos at different stages of development were measured to determine possible maternal contributions during embryonic development. Total wet weight from smallest and largest in utero eggs to smallest and largest term embryos changed by +46 and +58%, respectively. This pattern was due to a change in water content by +137 and +154%, and inorganic matter by +100 and +156%. Organic matter of smallest and largest in utero eggs changed by −23 and −17%, respectively. The uterus of pregnant females became specialised for water and mineral transport, not nutrient provision. These results indicate that S. megalops is a strict yolk-sac viviparous species with no maternal contribution of organic matter during development.     

Mixed sex allocation strategies in a polytocous mammal,the house mouse (<Emphasis Type="Italic">Mus musculus</Emphasis>)

The issue of adaptive adjustment of offspring sex ratio (proportion of male births) in polytocous mammals, producing several offspring per litter, is controversial because females of these species can maximize their fitness mainly by adjusting offspring number. To address this issue, we examined the effect of maternal condition at mating, experimentally decreased by pre-mating food restriction, on the sex ratio variation in 137 female mice. We tested two basic sex allocation hypotheses plausible for polytocous mammals: (1) the Myers hypothesis, predicting that cheaper sex should be favored in poor environmental conditions to maximize offspring number; and (2) the Williams hypothesis, predicting maximum fitness returns by adjusting size- and sex-specific composition of the litter according to the maternal condition. The food-restricted mothers produced larger litters with a higher proportion of cheaper daughters than the control mothers. By contrast, the control mothers optimized size and sex composition of the litter according to their weight at mating. In addition, the offspring of the food-restricted mothers suffered less from pre-weaning mortality than those of the control mothers. Therefore, when comparing the groups, the Myers hypothesis had a general significance while the Williams hypothesis was plausible only for the control mothers. Furthermore, some of the food-restricted mothers partly coped with the pre-mating food restriction and increased the proportion of sons in the litter with the increasing maternal weight loss (during the period of food restriction). The sex ratio variation was thus a result of three sex allocation strategies depending on the maternal condition at mating.     

Cofoundress relatedness and group productivity in colonies of social <Emphasis Type="Italic">Dunatothrips</Emphasis> (Insecta: Thysanoptera) on Australian <Emphasis Type="Italic">Acacia</Emphasis>

Facultative joint colony founding by social insects provides opportunities to analyze the roles of genetic and ecological factors in the evolution of cooperation. Although cooperative nesting is observed in range of social insect taxa, the most detailed studies of this behavior have been conducted with Hymenoptera (ants, bees, and wasps). Here, we show that foundress associations in the haplodiploid social thrips Dunatothrips aneurae (Insecta: Thysanoptera) are most often comprised of close relatives (sisters), though groups with unrelated foundresses are also found. Associations among relatives appear to be facilitated by limited female dispersal, which results in viscous population structure. In addition, we found that per capita productivity declined with increasing group size, sex ratios were female-biased, and some female offspring apparently remained in their natal domicile for some time following eclosion. D. aneurae thus exhibits a suite of similarities with eusocial Hymenoptera, providing evidence for the convergent evolution of associated social and life-history traits in Hymenoptera and Thysanoptera.     

Dynamics of pigment degradation by the copepodite stage of <Emphasis Type="Italic">Pseudodiaptomus</Emphasis><Emphasis Type="Italic">euryhalinus</Emphasis> feeding on <Emphasis Type="Italic">Tetraselmis</Emphasis><Emphasis Type="Italic">suecica</Emphasis>

Short-term (3 h) changes in concentration of chlorophylls and their derivatives in stage V Pseudodiaptomus euryhalinus and their fecal material were followed by HPLC during a 24 h experiment. Copepodites were fed with the prasinophyte Tetraselmis suecica. Intact chlorophyll a and b were found in animals and fecal material and had similar dynamics of accumulation over time. The extent of transformation of chlorophyll a and b to colorless compounds was different with chlorophyll a being more extensively degraded. Additionally, several chlorophyll derivatives (pheophytin and pyropheophytin-like pigments) were found. Pyropheophytin a was the most abundant followed by pheophytin b, pheophytin a, and pheophorbide a. Relative amounts of pheopigments were different in copepodites and fecal material, and pheophytin a, pheophorbide a, and pheophytin b concentrations were low and variable. The amount of ingested chlorophyll recovered as chlorophyll a and its derivatives in fecal and copepodite pools was generally low (<5%), with one exception occurring after 9 h, when it accounted for >70%. These data suggest individual pheopigments are produced at different rates and that chemical or enzymatic mechanisms in the gut of copepodites act on the two chlorophylls in different ways.     

Survival and productivity benefits to social nesting in the sweat bee <Emphasis Type="Italic">Megalopta genalis</Emphasis> (Hymenoptera: Halictidae)

Facultatively solitary and eusocial species allow for direct tests of the benefits of group living. We used the facultatively social sweat bee Megalopta genalis to test several benefits of group living. We surveyed natural nests modified for observation in the field weekly for 5 weeks in 2003. First, we demonstrate that social and solitary nesting are alternative behaviors, rather than different points on one developmental trajectory. Next, we show that solitary nests suffered significantly higher rates of nest failure than did social nests. Nest failure apparently resulted from solitary foundress mortality and subsequent brood orphanage. Social nests had significantly higher productivity, measured as new brood cells provisioned during the study, than did solitary nests. After accounting for nest failures, per capita productivity did not change with group size. Our results support key predictions of Assured Fitness Return models, suggesting such indirect fitness benefits favor eusocial nesting in M. genalis. We compared field collections of natural nests to our observation nest data to show that without accounting for nest failures, M. genalis appear to suffer a per capita productivity decrease with increasing group size. Calculating per capita productivity from collected nests without accounting for the differential probabilities of survival across group sizes leads to an overestimate of solitary nest productivity.     

Seasonal lipid dynamics of the copepods <Emphasis Type="Italic">Pseudocalanus minutus</Emphasis> (Calanoida) and <Emphasis Type="Italic">Oithona similis</Emphasis> (Cyclopoida) in the Arctic Kongsfjorden (Svalbard)

Seasonal lipid dynamics of various developmental stages were investigated in Pseudocalanus minutus and Oithona similis. For P. minutus, the dominance of 16:1(n−7), 16:4(n−3) and 20:5(n−3) fatty acids indicated a diatom-based nutrition in spring, whereas 22:6(n−3), 16:0, 18:2(n−6) and 18:1(n−9) pointed to a flagellate-based diet during the rest of the year as well as omnivorous/carnivorous low-level feeding during winter. The shorter-chain fatty alcohols 14:0 and 16:0 prevailed, also reflecting biosynthetic processes typical of omnivores or carnivores. Altogether, the lipid signatures characterized P. minutus as an opportunistic feeder. In contrast, O. similis had consistently high amounts of the 18:1(n−9) fatty acid in all stages and during all seasons pointing to a generally omnivorous/carnivorous/detritivorous diet. Furthermore, the fatty alcohol 20:1(n−9) reached high percentages especially in adult females and males, and feeding on Calanus faecal pellets is suggested. Fatty alcohols, as wax ester moieties, revealed significant seasonal variations in O. similis and a seasonal trend towards wax ester accumulation in autumn in P. minutus. P. minutus utilized its lipid deposits for development in the copepodite stages III and IV and for gonad maturation in CV and females during the dark season. However, CVs and females depended on the spring phytoplankton bloom for final maturation processes and reproduction. O. similis fueled gonad maturation and egg production for reproduction in June by wax esters, whereas reproduction in August/September co-occurred with the accumulation of new depot lipids. Both species revealed significantly higher wax ester levels in deeper (>50 m) as compared to surface (0–50 m) dwelling individuals related to a descent prior to overwintering.     

Interactions between an invasive and a native bryozoan (<Emphasis Type="Italic">Membranipora membranacea</Emphasis> and <Emphasis Type="Italic">Electra pilosa</Emphasis>) species on kelp and <Emphasis Type="Italic">Fucus</Emphasis> substrates in Nova Scotia,Canada

Most research on biological invasions to date has focused on the population dynamics of very successful and disruptive introduced species; however, additional knowledge of the biology of the native species is essential for understanding interactions between the two and may reveal factors that limit invasion success. The invasive bryozoan Membranipora membranacea interacts with native Electra pilosa on two substrates in northwest Atlantic subtidal habitats: highly dynamic and fast-growing kelps; and smaller, more stable, and slow-growing fucoid algae. We quantified the relative abundance and evaluated encounter outcomes in different seasons of these two bryozoans on kelp and Fucus at four sites in Nova Scotia. We also examined the effects of substrate (kelp, Fucus), temperature (7, 10, 13°C), and food (limited, unlimited) on growth rates of E. pilosa in laboratory experiments and using field manipulations. We compared our findings on factors affecting the growth of E. pilosa to those on M. membranacea obtained in similar and thus directly comparable experiments from a previous study. The proportional abundance of M. membranacea was greater than that of E. pilosa on kelps, but the opposite was observed on Fucus. Competitive standoffs between the two bryozoans were more frequent than expected, with no differences recorded between substrates; most encounters were won by M. membranacea. Growth of E. pilosa was faster on Fucus than kelp, decreased with increasing temperature only on Fucus, and was not affected by food. Growth rate of E. pilosa in all treatments was slower than that previously measured for M. membranacea. Faster growth and strong overgrowth abilities likely interact on kelps to ensure success of the invasive bryozoan. Success can be limited by low space availability, which in turn restricts growth rate, and consequently, colony size, such as on fucoid substrates. The incorporation of alternative contexts into invasion research can reveal factors involved in the resilience of native communities.     

Spatial variability in reproductive cycle of the gorgonians <Emphasis Type="Italic">Paramuricea clavata</Emphasis> and <Emphasis Type="Italic">Eunicella singularis</Emphasis> (Anthozoa,Octocorallia) in the Western Mediterranean Sea

Paramuricea clavata (Risso, 1826) and Eunicella singularis (Esper, 1794) are the most representative gorgonian species in hard bottoms sublittoral communities in the Western Mediterranean Sea. Reproductive cycles of two populations of both species were studied in two distinct locations approximately 600 km apart (Medes Islands and Cape of Palos), in order to assess interpopulation variability on a relevant geographic scale. Seasonal variation of lipid concentration levels in the gorgonian tissue was used as a tool to quantify energy storage by each studied population in order to explain possible interpopulation differences in gonadal output. Sex ratio in Medes Islands populations of both species was 1:1, while in Cape of Palos sex ratio was significantly male biased (1:7) in P. clavata, and female biased (1.7:1) in E. singularis populations. Spawning timing occurred in all cases coinciding with a marked increase in sea-water temperature in spring, and after the most successful feeding season, but comparing localities there was a clear temporal shift in the time of gametes release, appearing well linked to the shift in sea-water temperature rising in spring in both sites at the depth where populations are placed. Therefore, in this study the temperature appears as the main synchronizing factor of gonadal development within these populations. Significant differences in gonadal volume per polyp were found in both species owing mainly to differences in the number of gonads per polyp between populations, with Cape of Palos populations displaying higher values in both studied species, suggesting that the exposition to different local conditions may be reverted in a different gonadal output. But the observed patterns in lipid concentrations levels in gorgonians disable us to conclude that lipid concentration levels explain the observed differences in gonadal output found in this study.