Does variation in host plant association and symbiont infection of pea aphid populations induce genetic and behaviour differentiation of its main parasitoid, Aphidius ervi?

The host-associated differentiation (HAD) hypothesis states that higher trophic levels in parasitic associations should exhibit similar divergence in case of host sympatric speciation. We tested HAD on populations of Aphidius ervi the main parasitoid of the pea aphid Acyrthosiphon pisum, emerging from host populations specialized on either alfalfa or red clover. Host and parasitoid populations were assessed for genetic variation and structure, while considering geography, host plant and host aphid protective symbionts Regiella insecticola and Hamiltonella defensa as potential covariables. Cluster and hierarchical analyses were used to assess the contribution of these variables to population structure, based on genotyping pea aphids and associated A. ervi with microsatellites, and host aphid facultative symbionts with 16S rDNA markers. Pea aphid genotypes were clearly distributed in two groups closely corresponding with their plant origins, confirming strong plant associated differentiation of this aphid in North America. Overall parasitism by A. ervi averaged 21.5 % across samples, and many parasitized aphids producing a wasp hosted defensive bacteria, indicating partial or ineffective protective efficacy of these symbionts in the field. The A. ervi population genetic data failed to support differentiation according to the host plant association of their pea aphid host. Potential for parasitoid specialization was also explored in experiments where wasps from alfalfa and clover aphids were reciprocally transplanted on alternate hosts, the hypothesis being that wasp behaviour and parasitic stages should be most adapted to their host of origin. Results revealed higher probability of oviposition on the alfalfa aphids, but higher adult emergence success on red clover aphids, with no interaction as expected under HAD. We conclude that our study provides no support for the HAD in this system. We discuss factors that might impair A. ervi specialization on its divergent aphid hosts on alfalfa and clover.     

Does insecticide resistance alone account for the low genetic variability of asexually reproducing populations of the peach-potato aphid Myzus persicae?

The typical life cycle of aphids includes several parthenogenetic generations and a single sexual generation (cyclical parthenogenesis), but some species or populations are totally asexual (obligate parthenogenesis). Genetic variability is generally low in these asexually reproducing populations, that is, few genotypes are spread over large geographic areas. Both genetic drift and natural selection are often invoked to account for this low genetic variability. The peach-potato aphid, Myzus persicae, which encompasses both cyclical and obligate parthenogens, has developed several insecticide resistance mechanisms as a consequence of intense insecticide use since the 1950s. We collected asexually reproducing M. persicae from oilseed rape and examined genetic variability at eight microsatellite loci and three insecticide resistance genes to determine whether their genetic structure was driven by drift and/or selection. We identified only 16 multilocus microsatellite genotypes among 255 individuals. One clone, which combined two insecticide resistance mechanisms, was frequently detected in all populations whatever their location over a large geographical area (the northern half of France). These unexpected findings suggest that drift is not the unique cause of this low variability. Instead, the intensification of both insecticide treatments and oilseed rape cultivation may have favored a few genotypes. Thus, we propose that selective pressures resulting from human activities have considerably modified the genetic structure of M. persicae populations in northern France in a relatively short period of time.     

The functional significance of E-β-Farnesene: Does it influence the populations of aphid natural enemies in the fields?

Aphids cause much damage to Chinese cabbage in northern China. Over reliance on pesticides have large environmental and human health costs that compel researchers to seek alternative management tactics for aphid control. The component of aphid alarm pheromone, E-β-Farnesene (EβF), extracted from Matricaria chamomilla L., which attracts natural enemies in the laboratory, may have significant implications for the design of cabbage aphid control strategies. The purpose of this paper is to understand the effects of EβF on natural enemies to cabbage aphid control in Chinese cabbage fields. Ladybeetles on Chinese cabbage leaves in EβF released plots and Aphidiidae in EβF released yellow traps were significantly higher than those of in controls. No significant differences were detected in the interactions of different treatments and the two years for all natural enemies. More important, lower aphid densities were found in EβF released plots. Our results suggested that the EβF extracted from M. chamomilla L. could attract natural enemies to reduce cabbage aphids in the Chinese cabbage fields.     

Does reduced heterozygosity influence dispersal? A test using spatially structured populations in an alpine ungulate

Despite having a profound effect on population dynamics, the reasons that animals disperse are poorly understood. Evolutionary explanations have focused on inbreeding and competition, where the potential cost of philopatry is negated through dispersal. Such scenarios lead to the prediction that less successful individuals preferentially disperse, termed 'fitness-associated dispersal'. Since heterozygosity is associated with fitness, we assessed whether dispersed animals had less observed heterozygosity (H(O)) than residents. We tested this prediction using both genetic and population-monitoring data of mountain goats (Oreamnos americanus). Individuals classified as dispersers through cross-assignment had the lowest mean H(O), followed by residents, and then admixed individuals. Dispersed individuals had 6.3 per cent less H(O) than their subpopulation of origin. In the long-term study of the mountain goat herd at Caw Ridge, Alberta, immigrants had the lowest H(O); however, the opposite pattern was seen in emigrants, which may be related to density dependence. This study is the first to provide empirical evidence that heterozygosity is associated with dispersal.     

Fine-scale genetic pattern and evidence for sex-biased dispersal in the túngara frog, Physalaemus pustulosus

Túngara frogs (Physalaemus pustulosus) are a model system for sexual selection and communication. Population dynamics and gene flow are of major interest in this species because they influence speciation processes and microevolution, and could consequently provide a deeper understanding of the evolutionary processes involved in mate recognition. Although earlier studies have documented genetic variation across the species' range, attempts to investigate dispersal on a local level have been limited to mark-recapture studies. These behavioural studies indicated high mobility at a scale of several hundred metres. In this study we used seven highly polymorphic microsatellite loci to investigate fine-scaled genetic variation in the túngara frog. We analysed the influence of geographical distance on observed genetic patterns, examined the influence of a river on gene flow, and tested for sex-biased dispersal. Data for 668 individuals from 17 populations ranging in distance from 0.26 to 11.8 km revealed significant levels of genetic differentiation among populations. Genetic differentiation was significantly correlated with geographic distance. A river acted as an efficient barrier to gene flow. Several tests of sex-biased dispersal were conducted. Most of them showed no difference between the sexes, but variance of Assignment Indices exhibited a statistically significant male bias in dispersal.     

Testing the efficacy of an estuarine eutrophic condition index: Does it account for shifts in flow conditions?

Eutrophication of estuaries via anthropogenic nutrient enrichment is an issue being addressed extensively on a global scale, however it remains a topic that garners further attention due to its complexity. The aim of this study was to test the efficacy of a recently proposed eutrophic condition index in five permanently open estuaries, subsequent to flow variations. Further, in order to elucidate their potential role in augmenting eutrophic conditions, the influence of vegetated habitats on associated microalgal communities was investigated. The study took place in the summer of 2014 and 2015. On each sampling occasion, all of the proposed ‘state’ indicators (nutrients, oxygen and microalgal communities) were assessed and supplemented with a heuristic ‘pressure’ component (flow conditions). Overall, the proposed index was shown to be sensitive to environmental perturbations providing shifts in classification ratings illustrating the dilution (Swartkops Estuary) or augmenting (Kromme, Gamtoos, and Kariega estuaries) effect of freshwater pulse events. Additionally, the sensitivity of selected epiphyte and microphytobenthos (MPB) parameters to water quality variations was verified, thus supporting their inclusion as indicators in the proposed index. Regarding the role of microhabitats in promoting microalgal growth, it was found that MPB biomass was higher (5–290%) and benthic diatom diversity generally lower (5–50%) in vegetated compared to unvegetated habitats – an important consideration when applying the index. The habitat complexity and stabilisation provided by estuarine macrophytes (Phragmites australis and Zostera capensis) supported notable autotroph colonisation. This highlights their importance in structuring trophic pathways, whilst also potentially providing a corridor for the intensification of eutrophic symptoms in estuaries. Overall, this study provides an important step towards the verification of a proposed assessment methodology which may serve to provide a baseline from which the eutrophic status of estuaries can be monitored – particularly in countries where such assessment frameworks are lacking.     

Does rearing an aphid parasitoid on one host affect its ability to parasitize another species?

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Expressing an (E)-β-farnesene synthase in the chloroplast of tobacco affects the preference of green peach aphid and its parasitoid

(E)-β-Famesene(EβF) synthase catalyses the production of EβF,which for many aphids is the main or only component of the alarm pheromone causing the repellence of aphids and also functions as a kairomone for aphids' natural enemies.Many plants possess EβF synthase genes and can release EβF to repel aphids.In order to effectively recruit the plant-derived EβF synthase genes for aphid control,by using chloroplast transit peptide(CTP) of the small subunit of Rubisco(rbcS) from wheat(Triticum aestivum L.),we targeted AαβFS1,an EβF synthase gene from sweet wormwood(Artemisia annua L),to the chloroplast of tobacco to generate CTP + AαβFS1 transgenic lines.The CTP +AαβFS1 transgenic tobacco plants could emit EβF at a level up to 19.25 ng/day per g fresh tissues,4-12 fold higher than the AαβFS1 transgenic lines without chloroplast targeting.Furthermore,aphid/parasitoid behavioral bioassays demonstrated that the CTP + AαβFS1 transgenic tobacco showed enhanced repellence to green peach aphid(Myzus persicae) and attracted response of its parasitoid Diaeretiella rapae,thus affecting aphid infestation at two trophic levels.These data suggest that the chloroplast is an ideal subcellular compartment for metabolic engineering of plant-derived EβF synthase genes to generate a novel type of transgenic plant emitting an alarm pheromone for aphid control.     

Naiveté and an aquatic-terrestrial dichotomy in the effects of introduced predators

There is much evidence that suggests that freshwater systems are more sensitive to introduced predators than are terrestrial or marine systems. We argue here that this dichotomy reflects widespread naiveté toward introduced predators among freshwater prey. Continental terrestrial animals are seldom naive toward novel predators owing to the homogenizing effects of historical biotic interchanges. Comparable biotic interchanges might have also precluded prey naiveté in most marine systems. By contrast, freshwater systems exhibit persistent large- and small-scale heterogeneity in predation regimes. This heterogeneity promotes naiveté at multiple spatial scales in freshwater prey, thereby producing a systemic vulnerability to introduced predators that is not seen in continental terrestrial or marine systems.     

Does the surrounding matrix influence corridor effectiveness for pollen dispersal in farmland?

Recent decades have seen a shift in agricultural land use from pasture to arable combined with increased use of fertilisers and pesticides. In this quite hostile landscape matrix, pollinator movements between native vegetation remnants may be impeded. Linear landscape elements (LLEs) in farmland can function as biological corridors by facilitating pollinator movements and pollen flow between fragmented plant populations. The type of landscape matrix surrounding LLEs and plant populations, and LLE habitat quality may influence the effectiveness of LLEs as corridors for pollen dispersal through the availability of floral resources and nesting opportunities for pollinators. Using fluorescent dyes as pollen analogues, we investigated dye dispersal patterns between fragmented populations of the rare insect-pollinated Primula vulgaris connected by existing LLEs. We examined how dye deposition on P. vulgaris and within LLEs (on other co-flowering insect-pollinated species) could be influenced by the surrounding matrix type (pasture, arable field), the recipient population traits of P. vulgaris (flowering population size, flower display, flowering plant density and co-flowering floral resources) and by LLE traits (LLE length and co-flowering floral resources). Dye dispersal through corridors was significantly higher when the landscape matrix surrounding P. vulgaris recipient populations and LLEs consisted of pastures rather than arable fields (or a mix of both), even after accounting for differences in floral resources. A higher cover and diversity of insect-pollinated plants increased dye deposition when co-flowering within small P. vulgaris populations, but led to dye loss within LLEs. Large P. vulgaris populations appeared more attractive thereby increasing heterospecific dye deposition in the LLEs. Our study shows that farming practices shifting from pastures to maize arable fields have a negative impact on dye dispersal patterns, and so possibly affect pollen dispersal of P. vulgaris, likely through a reduced pollinator service. Corridor effectiveness depends on the type of surrounding matrix, and the abundance of floral resources directly influences dye dispersal patterns. Preserving the remaining pastureland is essential, but restoring rich flowering vegetation at field boundaries and along LLEs may also promote corridor effectiveness for pollen dispersal.     

Localised control of an introduced predator: creating problems for the future?

Introduced mammalian predators have had significant impacts on many native prey species. Although control of such predators for conservation management is becoming increasingly commonplace, it is often undertaken at a relatively small scale in relation to the overall predator population. Processes such as immigration mean that it remains difficult to determine the effectiveness of control measures. We investigated the impacts of feral ferret Mustela furo removal on the entire feral ferret population on Rathlin Island, UK. Removal of ferrets prior to breeding led to a substantial increase in the post-dispersal population through the enhanced survival of juveniles. Despite increased numbers, overwinter survival remained high, potentially aided by the reduced territoriality shown by this feral species compared to wild carnivores. The response of this ferret population to control is a further illustration of the complex ecological processes and outcomes arising from the anthropogenic disruption of wildlife populations. It highlights how partial or localised management may prove ineffective, and at worst might exacerbate the problems that management was designed to avert.     

Does social complexity lead to sex-biased dispersal in polygynous mammals? A test on ground-dwelling sciurids

Mating systems are well known to influence the dispersing sex,but the magnitude of the sex-biased dispersal has not actuallybeen measured, whereas many theoretical predictions have beenmade. In this study, we tested a new prediction about the coevolutionbetween natal dispersal and sociality from a recent evolutionarilystable strategy (ESS) approach. From a comparative approach,we showed that, in agreement with the model, the male-biaseddispersal increases with increasing level of sociality in polygynousground-dwelling sciurids. In addition, the increase in male-biaseddispersal with increasing sociality results from an increasein male dispersal rates, whereas female dispersal rates remainconstant, contrary to what is expected from the ESS model. Althoughthe mating system through the level of polygyny could act asa confounding factor, our results strengthen previous work thatstates that inbreeding avoidance plays a major role in the evolutionof dispersal for the most social mammalian species.     

Regulation of aphid populations by aphidiid wasps: does parasitoid foraging behaviour or hyperparasitism limit impact?

Aphidiid parasitoids (Hymenoptera: Aphidiidae) of aphids generally exploit only a small percentage of the available host resources in the field. This limited impact on aphid populations has often been explained as a consequence of hyperparasitism. We propose that a wasp's reproductive strategy, as opposed to hyperparasitism, is the dominant factor in aphidiid population dynamics. A wasp's foraging efficiency and oviposition decisions are influenced by several variables, including searching behaviour between and within patches, host choice (as modified by the aphids' defensive behaviours), and plant structural complexity. Two broadly different patterns of host exploitation have evolved in aphidiid wasps in relation to ant-aphid mutualism. Firstly, in species that are exposed to predation and hyperparasitism, a female may leave a patch before all suitable hosts are parasitized. Because predators and hyperparasitoids tend to aggregate at high aphid or aphidiid densities, or in response to aphid honeydew, this strategy enables females to reduce offspring mortality by spreading the risk over several host patches. Secondly, in species that have evolved mechanisms to avoid aggression by mutualistic ants, females are able to exploit a hyperparasitoid-free resource space. Such species may concentrate their eggs in only a few aphid colonies, which are thus heavily exploited. Although hyperparasitism of species in the first group tends to reach high levels, its overall impact on aphid-aphidiid population dynamics is probably limited by the low average fecundity of most hyperparasitoids. We discuss the foraging patterns of aphidiid wasps in relation to aphid population regulation in general, and to classical biological control in particular. We argue that a parasitoid's potential to regulate the host population is largely determined by its foraging strategy. In an exotic parasitoid, a behavioural syndrome that has evolved and presumably is adaptive in a more diverse (native) environment may, in a more uniform (managed) environment, result in suboptimal patch-leaving and oviposition decisions, and possibly increased resource usage.     

Do natural enemies really make a difference? Field scale impacts of parasitoid wasps and hoverfly larvae on cereal aphid populations

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Does predation drive morphological differentiation among Adriatic populations of the three‐spined stickleback?

Morphometric differentiation among freshwater fish populations is a commonplace occurrence, although the underlying causes for this divergence often remain elusive. We analysed the degree and patterns of morphological differentiation among nine freshwater three‐spined stickleback (Gasterosteus aculeatus) populations inhabiting isolated karst rivers of the Adriatic Sea basin, to characterise the phenotypic diversity and differentiation in these populations. The analyses revealed marked and significant morphometric differentiation – especially in traits related to predator defence amongst most populations – even among those located within close geographic proximity in the same catchment system. Accordingly, the degree of morphometric and neutral genetic differentiation, as assessed from variability in 15 microsatellite loci from a parallel study, were uncorrelated across the populations. However, P_ST/F_ST comparisons revealed that the degree of phenotypic differentiation (P_ST) among populations exceeded that to be expected from genetic drift alone, suggesting a possible adaptive basis for the observed differentiation. In fact, avian predation pressure and several physiochemical environmental variables were identified as the main putative drivers of the observed differentiation, particularly in the dorsal spines, ascending process and lateral plates. Hence, the high degree of morphometric differentiation among Adriatic three‐spined stickleback populations appears to reflect adaptation to local ecological conditions. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 219–240.     

Can increased niche opportunities and release from enemies explain the success of introduced Yellowhammer populations in New Zealand?

Some introduced species succeed spectacularly, becoming far more abundant in their introduced than in their native range. 'Increased niche opportunities' and 'release from enemy regulation' are two hypotheses that have been advanced to explain the enhanced performance of introduced species in their new environments. Using an introduced bird species, the Yellowhammer Emberiza citrinella , which was first released in New Zealand in 1862, as a model, we tested some predictions based on these hypotheses. By quantifying habitat availability and quality, and measuring nest predation rates, we investigated whether increased niche opportunities or release from nest predation could explain the higher density of the Yellowhammer in New Zealand farmland, compared to farmland in their native Britain. Yellowhammer territory densities were over three times higher in New Zealand (0.40 territories per ha) than in comparable British farmland (0.12 territories per ha), and Yellowhammer densities remained significantly higher in New Zealand, after accounting for differences in habitat availability. The density and diversity of invertebrates, a key food resource for nestling Yellowhammers, was significantly lower in New Zealand than in Britain. Hence, these aspects of niche availability and quality cannot explain the higher density of Yellowhammers in New Zealand. Nest predation rates in New Zealand were similar to those in Britain, suggesting that release from nest predation also could not account for the higher density of Yellowhammers in New Zealand. Differences in winter survival, due to differences in winter food supply or the severity of the winter climate, along with release from other types of 'enemy' regulation are possible alternative explanations.     

Does the introduced polychaete Alitta succinea establish in the Caspian Sea?

Members of the polychaete family Nereididae do not occur naturally in the Caspian Sea but are documented intentional human introductions that commenced in 1939. However, the identity of the species involved has been uncertain; material has been identified as both Alitta succinea and Hediste diversicolor. In this study, we confirm the presence of both species in the Caspian Sea. We discuss the distribution of both species, based on tolerance to physical factors, especially salinity. Although establishment of this partially predatory Nereidid, as a food reservoir could facilitate the recreation of commercially exploited fish stock, the consequences for native benthic communities are unclear and may be subject to unforeseen negative impacts.