Effects Of Food Supply Research Articles

Effects of food supply on northern bay scallops Argopecten irradians reared under two pCO2 conditions

For calcifying organisms such as bivalves, short-term exposure to increased ocean acidification (OA; elevated pCO2) may reduce growth rate, increase mortality, and disrupt shell formation. A growing body of research suggests that clearance rates and what particles bivalves select may change under high pCO2 exposure; however, these experiments are acute, ranging from days to weeks. The effects of food supply on bivalves under long-term OA exposure remain incompletely understood. In this study, juvenile northern bay scallops Argopecten irradians (Lamarck) that had been reared since 4 h post-fertilization under one of 2 OA conditions (∼500-600 or ∼750-850 µatm pCO2; ∼1.37-1.5 or ∼1.0-1.2 Ωaragonite), were subjected to 2 food levels for 42 d (low food: ∼400, high food: ∼1400 chlorophyll cells ml-1). Standard metabolic rate (SMR) and clearance rate (CR) were measured on Day 0, and SMR, CR, growth, and survivorship were measured at 14 and 42 days of exposure to 2 food levels for each of the OA treatments. Juveniles under food scarcity had reduced survivorship and growth independent of OA treatment. We found no effect of OA treatment or an OA × food interaction for these metrics. There was only a food-level effect for SMR and no OA treatment effect; however, there was an interaction between food and OA for CR. Under elevated pCO2 concentrations, scallops cleared Chaetoceros neogracile (strain Chaet-B) over Tetraselmis chui (strain PLY429) and natural seston. Altogether, these data suggest that tolerance to OA mediated by food may depend on food quality or other characteristics that influence particle selection under short-term experimental challenges.

Scope for Developmental Plasticity of Feeding Larvae of a Holothuroid, Contrasted with Other Echinoderm Larvae.

AbstractFeeding larvae of echinoderms appear to differ in scope for adaptive developmental plasticity in response to food. Extension of the ciliary band on narrow arms supported by skeletal rods, as in echinoid and ophiuroid larvae, may enable a greater increase in maximum clearance rate per cell added, conferring greater advantages from developing longer ciliary bands when food is scarce. Formation of the juvenile mouth and water vascular system at a new site, as in echinoid and asteroid larvae, permits extensive growth of the juvenile rudiment during larval feeding, with advantages from earlier or more growth of the rudiment when food is abundant. In contrast, plasticity in storage of nutrients is unrelated to the form of the ciliary band or the site of formation of the juvenile's mouth. Feeding larvae (auriculariae) of holothuroids lack arms supported by skeletal rods and formation of the mouth at a new site but as a unique feature store nutrients in hyaline spheres. In this study, more food for auriculariae of Apostichopus californicus resulted in juveniles (pentactulae) with longer and wider bodies and larger hyaline spheres, but effects of food supply on the size of most body parts of auriculariae were small. Auriculariae with more food developed relatively larger stomachs and larger posterior hyaline spheres, indications of greater nutrient storage. Auriculariae with less food developed relatively wider mouths and differed in some exterior dimensions, which might enhance the capture of food. Plasticity is limited in rudiment development and perhaps in structures for feeding, but plasticity in nutrient storage can provide advantageous compromises between duration of growth as a feeding larva and the condition of juveniles formed at metamorphosis.

Short-term extra food supply effects on detectability of two rodent species in Pampean agroecosystems, Argentina

Short-term extra food supply effects on detectability of two rodent species in Pampean agroecosystems, Argentina

Microplastic burden in Daphnia is aggravated by elevated temperatures

Contamination of freshwater habitats with microplastic is threatening particularly filter-feeders within the aquatic community. Using Daphnia magna and Daphnia pulex as models, the effects of food supply and temperature on the ingestion of polystyrene spheres (diameter 1 μm, concentration of 200 ng*ml-1) was analysed. The ingestion rates of microplastic beads were increased in conditions of low food and high temperatures, reflecting the complex regulation patterns of the water current generated by the animals’ thoracic limbs. Maximal enrichment of 1160 times the concentration in the ambient medium was observed within one hour. Analyses of the impact of microplastic ingestion on physiological parameters used the carbohydrate concentration as an indicator for the animals’ metabolic state. Exposure to the microplastic beads for three days in the presence or absence of Desmodesmus subspicatus did not affect the animals’ glycogen reserves beyond the response to the prevailing food and temperature conditions. Projecting the insights from laboratory experiments to the habitat situation, increased burdens of microplastic particles can be expected in filtering zooplankton organisms in warm water and scarce supply of food, like the clear-water phase of lakes in the summer.

The effects of food supply on reproductive hormones and timing of reproduction in an income-breeding seabird

Current food supply is a major driver of timing of breeding in income-breeding animals, likely because increased net energy balance directly increases reproductive hormones and advances breeding. In capital breeders, increased net energy balance increases energy reserves, which eventually leads to improved reproductive readiness and earlier breeding. To test the hypothesis that phenology of income-breeding birds is independent of energy reserves, we conducted an experiment on food-supplemented (“fed”) and control female black-legged kittiwakes (Rissa tridactyla). We temporarily increased energy costs (via weight handicap) in a 2 × 2 design (fed/unfed; handicapped/unhandicapped) during the pre-laying period and observed movement via GPS-accelerometry. We measured body mass, baseline hormones (corticosterone; luteinising hormone) before and after handicap manipulation, and conducted a gonadotropin-releasing hormone challenge. Females from all treatment groups foraged in similar areas, implying that individuals could adjust time spent foraging, but had low flexibility to adjust foraging distance. Consistent with the idea that income breeders do not accumulate reserves in response to increased food supply, fed birds remained within an energy ceiling by reducing time foraging instead of increasing energy reserves. Moreover, body mass remained constant until the onset of follicle development 20 days prior to laying regardless of feeding or handicap, implying that females were using a ‘lean and fit’ approach to body mass rather than accumulating lipid reserves for breeding. Increased food supply advanced endocrine and laying phenology and altered interactions between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, but higher energy costs (handicap) had little effect. Consistent with our hypothesis, increased food supply (but not net energy balance) advanced endocrine and laying phenology in income-breeding birds without any impact on energy reserves.

Food supply effects on the asexual reproduction and respiratory metabolism of Aurelia aurita polyps

Because Aurelia spp. blooms have important regional effects, it is urgent to determine factors that may affect their proliferation and their effects on food webs. The life cycle of most scyphozoans includes an attached stage (polyp or scyphistoma) that reproduces asexually. To test the effects of food availability (unfed, fed 1-, 2-, or 3-times weekly), we measured production rates, mass, and metabolism of Aurelia aurita polyps. Metabolic measurements were physiological respiratory O2 consumption (R), potential O2 consumption (Φ), and potential CO2 production (ψNADP). Φ and ψNADP were calculated from enzymatic activities of the respiratory electron transport system (ETS) and from the CO2-producing enzyme, NADP+-dependent isocitrate dehydrogenase (NADP-IDH), respectively. The production of polyps dramatically increased from ~ 0.1 polyp day−1 (unfed) to ~ 0.65 polyp day−1 (fed 3-times week−1) over 33 days. Mass and metabolism (R, Φ, ψNADP) per polyp were significantly lower in unfed polyps, but indistinguishable among fed polyps. Our results suggested that the polyps maintained low-metabolic rates, putting available energy into asexual reproduction. The polyps were adapted to survive and reproduce when unfed, confirming their contribution to population persistence and potential jellyfish blooms.

Effects of food supply and stream physical characteristics on habitat use of a stream‐dwelling fish

AbstractIdentifying the environmental factors that affect freshwater fish can be crucial for their conservation and management. Despite the widespread investigation of relationships between fish habitat use and environmental variables, there is a paucity of knowledge on how abiotic and biotic factors jointly influence stream fish habitat use. Three New Zealand South Island streams were selected to investigate the habitat preference of a stream‐dwelling galaxiid, banded kokopu (Galaxias fasciatus). Fish abundance in several permanent pools was determined by spotlighting at night once a month from June 2008 to May 2009. Drifting invertebrates and key physical features of each pool were measured at the time of fish sampling. An information‐theoretic approach (AIC) indicated that the most parsimonious candidate model to predict banded kokopu biomass was the one that included pool area, undercut banks, water velocity, overhanging vegetation, invertebrate drift density and an interaction term between invertebrate drift density and water velocity. Banded kokopu biomass was positively related to pool area, undercut banks, overhanging vegetation and invertebrate drift density. Our study suggests that fish resource use patterns need to be understood in the context of multiple interacting ecological factors, including prey abundance.

温度和食物水平对海月水母螅状体无性繁殖的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 温度和食物水平对海月水母螅状体无性繁殖的影响 DOI: 10.5846/stxb201404170751 作者: 作者单位: 中国海洋大学,中国海洋大学,中国海洋大学,中国海洋大学,中国海洋大学,中国海洋大学,中国海洋大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家基础研究重大项目(2011CB403602) The effect of temperature and food supply on the asexual reproduction of moon jelly (Aurelia sp.1) polyps Author: Affiliation: Ocean Univisity of China,Ocean Univisity of China,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:水母暴发给近岸人类的生活、渔业资源以及海洋生态系统带来影响。这些近岸海域暴发的水母可以通过有性繁殖和无性繁殖来维持或扩大水母种群数量。在水母生活史中,螅状体的无性繁殖是决定水母体数量的关键阶段,因此对此阶段进行研究。设置了4个温度水平(9、12、15、18 ℃)、3个食物水平(5 个卤虫/螅状体、20 个卤虫/螅状体、40 个卤虫/螅状体),在12个组合条件下研究温度和食物水平对海月水母螅状体无性繁殖能力和方式的影响。研究结果表明,在海月水母螅状体繁殖子体的各种方式中,匍匐茎生殖是主要的繁殖方式,出芽生殖次之,纵向分裂以及足囊出现几率极低。食物对海月水母螅状体产生总子体数影响显著,温度的影响不显著,食物水平越高,海月水母螅状体繁殖子体的能力越强。食物和温度对螅状体发生横裂均有影响,但温度对螅状体横裂的影响更大。温度对螅状体的横裂率影响显著,食物影响不显著。碟状体的释放发生在12、15、18 ℃的条件下,温度是影响海月水母螅状体通过横裂生殖释放碟状体数量的最重要因素。可见在螅状体无性繁殖阶段,温度和食物对繁殖方式的影响各不相同。 Abstract:Jellyfish outbreaks negatively affect humans who live near the coast, and cause harm to fishery resources and marine ecosystems. Jellyfish appearing around the East China Sea maintain or expand their populations by both sexual and asexual reproduction. In the jellyfish's life cycle, asexual reproduction of polyps is a key stage in determining the number of medusa in the following year; therefore, we focused on this life stage in this study. Previous studies have examined the total number of polyps produced by asexual reproduction under varying environmental conditions, but few studies have examined in detail on the number of new polyps formed via each method of asexual reproduction. Our research aimed to describe the methods of asexual polyp reproduction under different temperatures and food availability levels. In our experiment, following other similar studies we used four temperatures (9, 12, 15, and 18℃) and three food amounts (5, 20, and 40 newly-hatched Artemia nauplius per polyp) in a full-factorial experimental design to observe their effects on the asexual reproduction ability and method of moon jellyfish polyp formation. We systematically recorded the number of new polyps, the method of asexual reproduction, strobilation time, rate of strobilation, and the number of ephyrae released. Stolon formation was the most frequent method of asexual polyp reproduction, followed by direct budding. Longitudinal fission and podocyst methods were rarely observed. Food availability had a significant impact on all of the new moon jellyfish polyps, but the influence of temperature was not significant. Reproduction ability was positively correlated with food availability. Both food and temperature treatments influenced strobilation, and temperature had a greater impact on strobilation than food availability. Temperature significantly increased the incidence of strobilation compared with that of other methods of reproduction, but the effect of food supply was not significant. The rate of strobilation was highest in the moderate temperature group (12℃), the 15℃ and 18℃ groups had lower strobilation rates, and the 9℃ group had the lowest strobilation rate. Ephyrae were released at the three higher temperatures (12℃, 15℃, and 18℃). Temperature was the most important factor influencing the progress of the ephyrae released by strobilation, but food supply also had an important influence. The number of ephyrae released per moon jellyfish polyp in the 12℃ group was the greatest at all three food supply levels (5, 20, and 40 newly-hatched Artemia nauplius per polyp), while the 9℃ group did not release ephyrae at any food supply level. The greater the availability of food, the more ephyrae were released by the 12℃, 15℃, and 18℃ groups. At the three highest temperatures, the number of ephyrae released was greatest when 40 newly hatched Artemia nauplius were fed per polyp. Using two-way ANOVA to analyze the influences of temperature and food availability on strobilation and ephyrae release, we conclude that temperature controlled the timing of strobilation, while food amount controlled the number of ephyrae released per polyp. Temperature and food availability have different effects on the asexual methods of jellyfish polyp reproduction. 参考文献 相似文献 引证文献

Sequential polyandry in female Tengmalm's owl (Aegolius funereus) during a poor rodent year

In birds of prey, food availability affects the entire breeding process, including reproductive success. Sequential polyandry, sometimes documented in raptors and owls, has been observed occasionally in Tengmalm's owl in years of high food availability. In this study, the effect of food supply on the reproductive strategy of the central European Tengmalm's owl population has been investigated. The availability of the main prey of owls was significantly below average in the study year 2014. This resulted in low breeding density of owls, delayed egg laying, small clutch sizes, and low reproductive success. Nevertheless, successful sequential polyandry of one Tengmalm's owl female was recorded during the breeding season. The polyandrous female laid four eggs in each nests, and 50 % and 75 % of four hatched nestlings left the nest during the first and second breeding, respectively. In both nesting attempts, the two-year old female was of a substandard body mass and she abandoned the fledglings before they left the nests. Prey delivered by males to both nests was comprised mainly of alternative prey (birds and shrews). The results of this study suggest that there are probably some other factors, in addition to food availability, that may play a role in Tengmalm's owl's decisions in matters of parental care.

Supplementary feeding increases Common Buzzard Buteo buteo productivity but only in poor‐quality habitat

Temporal heterogeneity in the effects of food supply during the breeding season on the productivity of the Common Buzzard Buteo buteo was investigated in a supplementary feeding experiment. Pairs were fed artificially (1) before egg‐laying, (2) after chicks hatched and (3) continuously throughout the season, and compared with (4) unfed controls. Pairs fed before egg‐laying had marginally larger clutches than those not fed, but lay date, egg volume and weight, brood size and hatching success were unaffected. Territorial quality had far greater effects, with pairs nesting in low‐quality habitats (bog, scrub and semi‐natural grassland) laying later and having lower hatching success, smaller broods and fewer fledglings than those in more productive agricultural landscapes. Supplementary feeding after egg hatching neutralized the negative effect of poor habitat, resulting in fed birds having significantly more fledglings. This study emphasizes the importance of food availability when provisioning chicks in suboptimal habitats and has implications for the success of diversionary feeding in reducing game losses to Buzzards.

Effects of changes in food supply at the time of sex differentiation on the gonadal transcriptome of juvenile fish. Implications for natural and farmed populations.

BackgroundFood supply is a major factor influencing growth rates in animals. This has important implications for both natural and farmed fish populations, since food restriction may difficult reproduction. However, a study on the effects of food supply on the development of juvenile gonads has never been transcriptionally described in fish.Methods and FindingsThis study investigated the consequences of growth on gonadal transcriptome of European sea bass in: 1) 4-month-old sexually undifferentiated fish, comparing the gonads of fish with the highest vs. the lowest growth, to explore a possible link between transcriptome and future sex, and 2) testis from 11-month-old juveniles where growth had been manipulated through changes in food supply. The four groups used were: i) sustained fast growth, ii) sustained slow growth, iii) accelerated growth, iv) decelerated growth. The transcriptome of undifferentiated gonads was not drastically affected by initial natural differences in growth. Further, changes in the expression of genes associated with protein turnover were seen, favoring catabolism in slow-growing fish and anabolism in fast-growing fish. Moreover, while fast-growing fish took energy from glucose, as deduced from the pathways affected and the analysis of protein-protein interactions examined, in slow-growing fish lipid metabolism and gluconeogenesis was favored. Interestingly, the highest transcriptomic differences were found when forcing initially fast-growing fish to decelerate their growth, while accelerating growth of initially slow-growing fish resulted in full transcriptomic convergence with sustained fast-growing fish.ConclusionsFood availability during sex differentiation shapes the juvenile testis transcriptome, as evidenced by adaptations to different energy balances. Remarkably, this occurs in absence of major histological changes in the testis. Thus, fish are able to recover transcriptionally their testes if they are provided with enough food supply during sex differentiation; however, an initial fast growth does not represent any advantage in terms of transcriptional fitness if later food becomes scarce.

Latitudinal variation in clutch size–lay date regressions in Tachycineta swallows: effects of food supply or demography?

In a study of almost 16 000 nest records from seven swallow species across the entire Western Hemisphere, clutch sizes decline with relative laying date in each population, but the slope of this decline grows steeper with increasing distance from the equator. Late‐laying birds at all latitudes lay clutches of similar sizes, suggesting that latitudinal differences may be driven primarily by earlier‐laying birds. Focused comparisons of site‐years in North America with qualitatively different food availability indicate that food supply significantly affects mean clutch size but not the clutch size–lay date regression. Other studies on the seasonality of swallow food also indicate that steeper clutch size–lay date declines in the North are not caused by steeper earlier food peaks there. The distribution of lay dates grows increasingly right‐skewed with increasing latitude. This variation in lay‐date distributions could be due to the predominance of higher quality, early‐laying (and large‐clutched) individuals among populations at higher latitudes, resulting from latitudinal variation in mortality rates and the intensity of sexual selection. Our results underscore the importance of studying clutch size and lay date in tandem and suggest new research into the causes of their joint geographic variation.

Effect of Food Supply on Foraging Patterns and Body Weights of Long-Toed Stints(Calidris Subminuta)

Multiple species of shorebirds are now globally threatened, particularly across tropical Asia, yet we know relatively little of the detailed habitat usage and resource characteristics of sites in the region. The objective of this study was to determine how seasonal variation in food density affected foraging patterns and body weights of Long-toed Stint (Calidris subminuta), a relatively common winter visitor. Research was conducted during the passage and overwintering seasons in wastewater treatment ponds and salt-pans on the Inner Gulf of Thailand. Predictions were that during periods of higher food density, shorebirds should be relatively more abundant and heavier, and have increased foraging attempts, reduced step rates and reduced chase rates. Furthermore, adults were expected to have higher weights than juveniles. Overall, shorebird abundance was significantly positively correlated with invertebrate abundance during the 2-year study period. Long-toed Stints had greater body mass following their arrival in July-September, compared with later periods during the winter. Although food density and Long-toed Stint step rate were not significantly correlated, the data were consistent with previous studies suggesting a negative relationship. Step rates in salt-pans were significantly higher than in the wastewater treatment ponds, probably reflecting lower food densities in the salt-pans. There was no clear relationship between food density and Long-toed Stint peck rate, perhaps reflecting the weak correlation between number of pecks and the number of successful foraging bouts as well as limited sample sizes for prey estimates. There was no significant relationship between food density and chase rates. There was no significant difference in median body mass between adults and juveniles/first-year birds, implying young birds learn to forage as efficiently as adults relatively rapidly. This study suggests that further work on invertebrate dynamics and shorebird diets in the region is needed in order to build more predictive models of shorebird site usage and population dynamics.

Factors Influencing Aggression Levels in Root Vole Populations under the Effect of Food Supply and Predation

Which factor determines animal aggressivity? Wynn-Edwards proposed the hypothesis that aggressive level increases with population density; Adams and Mesterton-Gibbons proposed the hypothesis that body weight is an indicator of animal aggressivity; however, Smith and Price hypothesized that aggression level varied with external conditions; that is, the population lived in the most unfavorable environment demonstrated the highest average aggression level, and the population that lived under the most favorable external conditions demonstrated the lowest average aggression level. In this paper, we tested these three hypotheses by manipulating enclosed root vole (Microtus oeconomus) populations under different food and predation treatments and observed their aggressive behavior. Aggressive behavior was measured by matching mice in a neutral arena. The experimental results supported Smith and Price’s hypothesis and Adams and Mesterton-Gibbons’s hypothesis; however, they did not support Wynn-Edwards’ hypothesis. Moreover, we found that reproductively active individuals were more aggressive. We concluded that the growth of population density did not cause or otherwise bring about increased aggressive behavior of root voles, but the external factors (predation and food supply) and physical factors (body weight and reproductive condition) were significantly correlated with aggression levels in a root vole population.

Beverton and Holt Reloaded – Incorporating Variable Growth into a Yield Per Recruit Model

Animals to be fattened must be fed with nearly the maximum feeding rate to achieve maximum yields – food supply and food consumption must coincide. This we know for centuries from agriculture. Yields decline immediately when the food supply is limited. Are there parallels between agriculture and fisheries? The only way to control the food consumption of fish stocks is by influencing the population size by fishing. In standard yield per recruit analyses fixed growth parameters are assumed. The effect of food supply on growth is not considered and thus, the implications of changes in growth for yield- and spawner-per-recruit curves due to variations in the availability of food are neglected. Under stock recovery density dependent changes in growth may severely bias biological reference points derived from such curves. Here, we present a revised Beverton and Holt yield per recruit model including a revised von Bertalanffy Growth model that is triggered by available food for assimilation and demonstrate the implications for fisheries reference points such as Fmax. The traditional Beverton and Holt yield-model should be replaced by our model; for overfished stocks it delivers identical output values but, if dietary deficiency is detected in overstocked populations then the results correspond to the measured response of the ecosystem.

Effects of temperature and resource abundance on small- and large-bodied cladocerans: Community stability and species replacement

Understanding when small- or large-bodied cladocerans dominate zooplankton communities has received considerable debate over the past 50 years. While a large body of research has proposed that large-bodied species are superior competitors over small-bodied species, other studies have shown that small-bodied species can dominate at least under some environmental conditions. We tested the hypothesis that dominance by small- and large-bodied cladocerans varied in response to the coupled effects of food supply and temperature. Laboratory experiments with poly- and monocultures of small- and large-bodied cladocerans were performed at three temperatures (16°C, 22°C and 27°C) and with varying amounts of food supply. The results of the experiments showed that the small-bodied species (Ceriodaphnia quadrangula) dominated at low food supply and higher temperature, while the large-bodied species (Daphnia magna and Daphnia pulex) in contrast dominated at lower temperature and higher food supply. Furthermore, although there were variations in the relative biomass of the small- and large-bodied cladocerans in the polycultures, C. quandrangula replaced the two larger Daphnia species when they declined in biomass at low food supply. Species replacement in response to temperature and food supply helped to maintain the relatively constant level of total cladoceran biomass in the polycultures which was the most pronounced at the intermediate temperature. We suggest that the observed changes in dominance were similar to facilitative replacement rather than competitive exclusion. Physiological processes such as clearance rates can help to promote the succession of large- and small- bodied populations within a community along gradients of temperature and food availability.

菌床シイタケ害虫ナガマドキノコバエ成虫の生存日数, 産卵数, および孵化率に対する餌および温度の影響

菌床シイタケ害虫ナガマドキノコバエ成虫の生存日数, 産卵数, および孵化率に対する餌および温度の影響

Material input rates and dietary breadth during the Upper Paleolithic through Mesolithic at Franchthi and Klissoura 1 Caves (Peloponnese, Greece)

Two deeply stratified cave sites in southern Greece show how the relations between material input rates and human prey choice may reflect local site function and regional food supply effects simultaneously. The Upper Paleolithic through Mesolithic faunas at Klissoura Cave 1 and Franchthi Cave on the Argolid Peninsula (Peloponnese) provide clear evidence of diet expansion with time, based on increasing use of costly small animals. These cases also reflect, albeit to very different degrees, variation in occupation intensity as determined from sediment and artifact accumulation rates. Centrality is a critical issue for residential sites, and consistency (or the lack of it) in use provides a relative indication of site “importance” in the overall territory of foragers. Changes in site importance explain much of the variation in material inputs in Klissoura Cave 1, with the heaviest use of the site during the Upper Paleolithic and lighter use in the later periods. Small game data from Klissoura 1 nonetheless present a single general trend toward greater resource intensification with time. At Franchthi Cave, the intensity of occupations of the cave increased in tandem with intensified use of animal and plant resources. The parallel trends are explained by greater temporal consistency in the central importance of the latter site on the Pleistocene and early Holocene landscape.

The Influence of Food and Con-specifics on the Flight Potential of the Parasitoid Ibalia leucospoides

For insect parasitoids, knowledge of their flight capability is essential for a general understanding of the relationship with their hosts. For instance, flight capacity might partly determine their efficacy as biological control agents. Ibalia leucospoides Hochenwarch (Hymenoptera: Ibaliidae) is a solitary, pro-ovigenic parasitoid of the woodwasp, Sirex noctilio Boidin (Hymenoptera, Siricidae), an economically important pest of softwood forestation. This study explores the flight capacities of I. leucospoides females and assesses the effects of a sugar-rich food supply and crowding on female flight performance, by using computer-linked flight mills. The present study shows: (1) a high variability in flight potential of I. leucospoides females, (2) no effects of food supply and grouping on wasp flight (flight distance and speed), (3) a significant effect of body size and wing loading on flight performance and, (4) a significant body mass loss during the flight dependent on the total distance flown. The lack of effect of food on a highly energy-demanding activity as flight may be related to the life-history traits and nutritional strategies of this parasitoid. The relevance of these observations for the use of I. leucospoides as a biological control agent is discussed.

Settling where the food is: prey abundance promotes colony formation and increases group size in a web-building spider

The parasocial-route hypothesis postulates that coloniality in spiders is driven by the occurrence of high prey densities. This hypothesis is partially supported by comparative studies of colonial species. However, experimental evidence is lacking to confirm that prey availability directly promotes colony formation. We used the web-building spider Cyrtophora citricola (Araneidae) as a model species to investigate the effect of prey availability on coloniality. We conducted field surveys on colonies located on acacia trees in the Arava valley, Israel, to compare colony group size between sites differing markedly in insect abundance. We then performed experiments in net houses to test (1) the effect of prey remains in the females’ webs on juvenile establishment decisions and (2) the effect of food supply on web site fidelity of juveniles. Colony group size and reproductive investment were greater in prey-rich sites than in poor sites. In the experiments, juveniles released on adult females’ webs that contained remains of prey consumed by the adults were more likely to settle than those released on empty webs. Once established, food deprivation slightly increased the number of juveniles leaving the female’s web, suggesting that they are reluctant to disperse after settlement. Relocation in C. citricola is costly, as their webs demand high energy investment. Hence, cues of prey availability are crucial, enabling spiders to acquire information about habitat quality before investing in web construction. Together, our findings provide evidence that prey availability facilitates coloniality and thus supports the parasocial route in the evolution of spider group living.