Vestigial prototroch in a basal nemertean, Carinoma tremaphoros (Nemertea; Palaeonemertea)

Nemerteans have been alleged to belong to a protostome clade called the Trochozoa that includes mollusks, annelids, sipunculids, echiurids, and kamptozoans and is characterized by, among other things, the trochophore larva. The trochophore possesses a prototroch, a preoral belt of specialized ciliary cells, derived from the trochoblast cells. Nemertea is the only trochozoan phylum for which presence of the trochophore larva possessing a prototroch had never been shown. However, so little is known about nemertean larval development that comparing it with development of other trochozoans is difficult. Development in the nemertean clade Pilidiophora is via a highly specialized planktonic larva, the pilidium, and most of the larval body is lost during a drastic metamorphosis. Other nemerteans (hoplonemerteans and palaeonemerteans) lack a pilidium, and their development is direct, forming either an encapsulated or planktonic "planuliform" larva, producing a juvenile without a dramatic change in body plan. We show that early in the development of a member of a basal nemertean assemblage, the palaeonemertean Carinoma tremaphoros, large squamous cells cover the entire larval surface except for the apical and posterior regions. Although apical and posterior cells continue to divide, the large surface cells cleavage arrest and form a contorted preoral belt. Based on its position, cell lineage, and fate, we suggest that this belt corresponds to the prototroch of other trochozoans. Lack of differential ciliation obscures the presence of the prototroch in Carinoma, but differentiation of the trochoblasts is clearly manifested in their permanent cleavage arrest and ultimate degenerative fate. Our results allow a meaningful comparison between the development of nemerteans and other trochozoans. We review previous hypotheses of the evolution of nemertean development and suggest that a trochophore-like larva is plesiomorphic for nemerteans while a pilidium type of development with drastic metamorphosis is derived.     

Why don't predators have positive effects on prey populations?

Summary Three mechanisms by which increasing predation can increase prey population density are discussed: (1) Additional predation on species which have negative effects on the prey; (2) Predation on consumer species whose relationship with their own prey is characterized by a unimodal prey isocline; (3) Predation on species which adaptively balance predation risk and food intake while foraging. Possible reasons are discussed for the rarity of positive effects in previous predator-manipulation studies; these include the short-term nature of experiments, the large magnitudes of predator density manipulation, and various sources of bias in choice of system and interpretation of results.     

Spatial and temporal patterns of predation by ants on eggs of Cactoblastis cactorum

ABSTRACT.

• 1 Predation of Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) eggs by ants was studied for a summer and a winter generation on prickly pear Opuntia ficus-indica (L.) Miller plants in the field.
• 2 Egg Predation between plants was spatially density-dependent in the winter but not in the summer generation.
• 3 To test for the presence of delayed density-dependent mortality within generations, percentage egg Predation during 5-day periods was plotted against the number of eggs available in each period. Data points joined in a time sequence moved in an anticlockwise direction in the summer generation, suggesting a delayed density-dependent response by the ants, whereas in the winter generation the points moved in a clockwise direction.
• 4 The degree of coincidence of the C. cactorum eggs with the peak larval production periods of the ants is suggested as the main reason for the temporal changes in egg Predation.

     

The rate of predation by fishes on hatchlings of the green turtle (Chelonia mydas)

This study addresses the need for empirical data on the survival of sea turtle hatchlings after entry into the sea by (1) developing a method for measuring marine predation; (2) estimating predation rates while crossing the reef; and (3) investigating the effect of environmental variables on predation rates. Predation rates were quantified by following individual hatchlings, tethered by a 10m monofilament nylon line, as they swam from the water's edge towards the reef crest. Predation rates under particular combinations of environmental variables (tide, time of day, and moon phase) were measured in separate trials. Predation rates varied among trials from 0 to 85% with a mean of 31% (SE=2.5%). The simplest logistic regression model that explained variation in predation contained tide and moon phase as predictor variables. The results suggest that noctural emergence from the nest is a behavioral adaptation to minimize exposure to the heat of the day rather than a predator-escape mechanism. For the green turtle populations breeding in eastern Australia, most first year mortality is caused by predation while crossing the reef within the first hour of entering the sea.     

Impact of predation by spiders on a territorial damselfly (Odonata: Calopterygidae)

Summary Predation by orb-weaving spiders and crab spiders on the damselfly Calopteryx haemorrhoidalis was studied at a small stream in Southern France. One species of orb-weaving spider, Larinioides folium, caught 76% of the damselflies which fell prey to spiders. Displacement experiments on spiders on sections of bank and the positioning of webs in male territories show that the density and distribution of damselflies is not influenced by orbweb density or by the position of webs. Predation rates corresponded to orb-web density, but neither for sex nor for stage was there a relationship with damselfly density. Mean daily predation rates ranged between 0.9% for females and 4.1% for adult males. Predation risk to adult damselflies by orb-weaving spiders was male biased, whereas among tenerals there was no bias. Males were captured more frequently at territories near the water. Captures show a maximum at noon when territorial disputes of adult males were most frequent. After orbwebs were placed within territories predation rate of males was strongly increased. Predation risk to adult females in the direct vicinity of the stream was less than in the bank vegetation where they perch close to orbwebs. The risk of predation by crab spiders, which catch damselflies at their perching sites, was not sex-biased.     

Can polyphagous predators control the bird cherry-oat aphid (Rhopalosiphum padi) in spring cereals?: A simulation study

Predation by two carabid species,Bembidion lampros (Herbst.) andPterostichus cupreus L., on the cereal aphid,Rhopalsiphum padi L., was described using a discrete event simulation model. The results were incorporated into an aphid population growth model. The aphid model was run using actual temperatures,R. padi emigration rates, field densities and distributions from three years with distinctly different aphid population levels. Predation was incorporated at different time periods. Predation during the arrival of emigrants and establishment of aphid populations had approximately the same effect as predation over the entire aphid period, whereas predation during the 20 days prior to peak had very little effect on resulting peak populations. We conclude that a) yearly levels ofR. padi infestation are mainly determined by the volume and intensity of emigrants; b) peak levels are sensitive to changes in predator density; and c) in some cases an outbreak ofR. padi may be prevented by the action of spring active polyphagous predators alone.     

Whole-genome comparison clarifies close phylogenetic relationships between the phyla Dictyoglomi and Thermotogae

The anaerobic thermophilic bacterial genus Dictyoglomus is characterized by the ability to produce useful enzymes such as amylase, mannanase, and xylanase. Despite the significance, the phylogenetic position of Dictyoglomus has not yet been clarified, since it exhibits ambiguous phylogenetic positions in a single gene sequence comparison-based analysis. The number of substitutions at the diverging point of Dictyoglomus is insufficient to show the relationships in a single gene comparison-based analysis. Hence, we studied its evolutionary trait based on whole-genome comparison. Both gene content and orthologous protein sequence comparisons indicated that Dictyoglomus is most closely related to the phylum Thermotogae and it forms a monophyletic group with Coprothermobacter proteolyticus (a constituent of the phylum Firmicutes) and Thermotogae. Our findings indicate that C. proteolyticus does not belong to the phylum Firmicutes and that the phylum Dictyoglomi is not closely related to either the phylum Firmicutes or Synergistetes but to the phylum Thermotogae.     

Predator–prey interactions between the South Polar skua Catharacta maccormicki and Antarctic tern Sterna vittata

Antarctic terns have to co‐exist in a limited space with their major nest predator, the skuas. We conducted artificial nest experiments to evaluate the roles of parental activity, nest location and nest and egg crypsis in this simple predator–prey system. Predation on artificial (inactive) nests was higher in traditional nesting sites than in sites previously not occupied by terns, which suggests that skuas memorized past tern breeding sites. Predation on artificial nests in inactive colonies was higher than in active (defended) colonies. Parental defense reduced predation in colonies to the level observed in artificial nests placed away from colonies. This suggests that communal defense can balance the costs of attracting predators to active colonies. Within colonies, predation was marginally higher on experimental eggs put in real nests than on bare ground. Although it seems that the presence of a nest is costly in terms of increased predation, reductions in nest size might be constrained by the need for protective nest structures and/or balanced by opposing selection on nest size. Predation did not differ markedly between artificial (quail) and real tern eggs. A simultaneous prey choice experiment showed that the observed predation rates reflected egg/nest detectability, rather than discrimination of egg types. In summary, nesting terns probably cannot avoid being detected, and they cannot defend their nest by attending them. Yet, by temporarily leaving the nest, they can defend it through communal predator mobbing, and at the same time, they can benefit from crypsis of unattended nest and eggs.     

Artificial nest predation and habitat fragmentation: different trends in bird and mammal predators

Predation on artificial nests was studied in Belgian deciduous forest fragments between 1 and 200 ha Predation rates were compared to fragment size, distance from the forest edge, time period (three replicates), and nest type (ground and tree) Logistic regression analysis showed that overall nest predation did not vary with distance from the edge, forest size, and time period Birds represented over 70% of all predator attacks but their importance decreased in larger areas and away from the forest edge where mammals were responsible for much of the nest predation It is concluded that the effect of habitat fragmentation depends on the composition of the local predator community     

Predation risk for herbivorous insects on tropical vegetation: A search for enemy-free space and time

Spatial and temporal variability in predation risk for herbivores on 13 rainforest species of Ficus (Moraceae) in Papua New Guinea was studied in order to assess whether predator-free refuges exist on their foliage and if so, whether herbivorous insects concentrate their activity in such refugia. Predation risk from invertebrate predators was measured as the disappearance rate of live termites set up as baits on the foliage. By far the most important predators were ants, accounting for 77% of attacks. No consistent differences in predation rate between Ficus species were found so that tree identity could not be used as an indicator of enemy-free space. Predation risk was highly variable among conspecific trees and also changed rapidly in time, over periods as short as 10 days. Such short-term and unpredictable predator-free refuges may be difficult for herbivores to find and exploit. Predation risk during the day was three times higher than during the night, but abundance of herbivores on the foliage was also higher during the day. Thus, night was confirmed as a relatively enemy-free time which, however, was not exploited by herbivores.     

Predation on artificial,solitary and aggregated wader nests on farmland

Predation rates on artificial wader nests, solitary curlew (Numenius arquata) and lapwing (Vanellus vanellus) nests and lapwing nests in colonies were studied on a farmland site in central Sweden. Predation rates were highest on artificial wader nests, intermediate on solitary curlew and lapwing nests and lowest on lapwing nests in colonies, probably because of active defence of adults at real nests and/or because of selection of nest sites with lower predation risk by breeding birds. A comparison of nests close to (50 m) and far away from (200 m) forest edges revealed no increased predation risk close to edges for any of the studied nest types. Predation risk changed during the season for artificial nests (highest in the middle of May), while predation rates on lapwing and curlew nests were more stable. Artificial nests seem to be inappropriate for measuring actual predation rates and temporal differences in predation rates on real nests, but they might be suitable for use as an index of spatial differences.     

Can predators regulate wild Rabbit Oryctolagus cuniculus population density in England and Wales?

Predation has usually been interpreted as being a compensatory mortality factor, removing only the doomed surplus. The literature on the wild Rabbit Oryctolagus cuniculus L. is reviewed to collate counter-evidence for a regulating influence of predation. This evidence is almost entirely circumstantial, not experimental. Predation has been reported to extend the length of time Rabbit populations remain low following a significant reduction of Rabbits by some other agent. Rabbit populations have been shown to increase very rapidly when predator density has suddenly been reduced. It has been suggested that predators affect the spread and dispersion of Rabbits both at the geographical and local levels. Predation has not, however, been shown to have an important influence at high Rabbit densities. Thus, its role can be that of a limiting factor rather than a density-dependent regulatory mortality factor. The concept of predator pressure is presented and discussed, pointing out that there is currently no standard technique used for its measurement. Further evidence on the importance of predation is presented from four recent studies in England and Wales that relate, by association, the distribution and abundance of local Rabbit populations to the local attitude towards predators. Rabbits were found to be significantly more widespread and abundant where predators were removed (not restricted to keepered game estates) or at low density, than when predators were undisturbed or at a high density. The significance of these results is discussed. The circumstantial and corroborative evidence leads strongly to the conclusion that predator pressure can act as an additive rather than compensatory mortality factor in some circumstances, and can thus be a potential regulating factor. Predation is more likely to be a limiting factor at low Rabbit density however, since a density-dependent relationship has not been demonstrated throughout the range of Rabbit densities that occur. This requires experimental demonstration to determine the threshold pressure below which predation becomes limiting. If so, reductions in Rabbit populations by short-term control operations could allow natural predation to help maintain low Rabbit densities for several years in some habitats. Conversely, the implications for Rabbit populations and thus crop damage resulting from predator control (e.g. in game management regimes) should be appreciated.     

The phylogenetic position of Rhopalura ophiocomae (Orthonectida) based on 18S ribosomal DNA sequence analysis

The Orthonectida is a small, poorly known phylum of parasites of marine invertebrates. Their phylogenetic placement is obscure; they have been considered to be multicellular protozoans, primitive animals at a "mesozoan" grade of organization, or secondarily simplified flatworm- like organisms. The best known species in the phylum, Rhopalura ophiocomae, was collected on San Juan Island, Wash. and a complete 18S rDNA sequence was obtained. Using the models of minimum evolution and parsimony, phylogenetic analyses were undertaken and the results lend support to the following hypotheses about orthonectids: (1) orthonectids are more closely aligned with triploblastic metazoan taxa than with the protist or diploblastic metazoan taxa considered in this analysis; (2) orthonectids are not derived members of the phylum Platyhelminthes; and (3) orthonectids and rhombozoans are not each other's closest relatives, thus casting further doubt on the validity of the phylum Mesozoa previously used to encompass both groups.      

Predation on hatchery-reared and wild smolts of Atlantic salmon, Salmo salar L., in the estuary of River Orkla, Norway

Predation on wild and hatchery-reared Atlantic salmon smolts was studied in the estuary of River Orkla. Cod and saithe congregating in the estuary were the most serious predators on smolts. There was no difference between the mortality rates of wild and hatchery-reared smolts. Predation by cod was estimated at 20%. No evidence was found to indicate selective predation on the smallest wild and hatchery-reared smolts.     

Laboratory cultivation of widespread and previously uncultured soil bacteria

Most soil bacteria belong to family-level phylogenetic groups with few or no known cultivated representatives. We cultured a collection of 350 isolates from soil by using simple solid media in petri dishes. These isolates were assigned to 60 family-level groupings in nine bacterial phyla on the basis of a comparative analysis of their 16S rRNA genes. Ninety-three (27%) of the isolates belonged to 20 as-yet-unnamed family-level groupings, many from poorly studied bacterial classes and phyla. They included members of subdivisions 1, 2, 3, and 4 of the phylum Acidobacteria, subdivision 3 of the phylum Verrucomicrobia, subdivision 1 of the phylum Gemmatimonadetes, and subclasses Acidimicrobidae and Rubrobacteridae of the phylum ACTINOBACTERIA: In addition, members of 10 new family-level groupings of subclass Actinobacteridae of the phylum Actinobacteria and classes Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria of the phylum Proteobacteria were obtained. The high degree of phylogenetic novelty and the number of isolates affiliated with so-called unculturable groups show that simple cultivation methods can still be developed further to obtain laboratory cultures of many phylogenetically novel soil bacteria.     

Exploring wildlife predation in the Limpopo Province of South Africa: A double‐hurdle approach

Predation is a well‐known problem in South Africa with large losses in the small and large livestock sectors. Predation in the wildlife ranching industry has also become more of a concern, as the financial losses due to predation on valuable antelope species are large. Predation data for small, large, and scarce/colour‐variant antelope species were collected using a structured questionnaire from wildlife ranchers in the Limpopo province, South Africa. We explore the factors that influence predation on these species by determining whether the perceptions of predation and consequent managerial decisions affect predation. The use of nonlethal control methods can be successfully employed to reduce the probability of predation occurrences, however, a combination of lethal and nonlethal control methods were used to reduce the level of predation. The type of antelope species will determine the type of predation control method to be employed. Therefore, the antelope species should be taken into account when making predation management decisions.     

Bioreactor microbial ecosystems for thiocyanate and cyanide degradation unravelled with genome‐resolved metagenomics

Gold ore processing uses cyanide (CN^?), which often results in large volumes of thiocyanate‐ (SCN^?) contaminated wastewater requiring treatment. Microbial communities can degrade SCN^? and CN^?, but little is known about their membership and metabolic potential. Microbial‐based remediation strategies will benefit from an ecological understanding of organisms involved in the breakdown of SCN^? and CN^? into sulfur, carbon and nitrogen compounds. We performed metagenomic analysis of samples from two laboratory‐scale bioreactors used to study SCN^? and CN^? degradation. Community analysis revealed the dominance of Thiobacillus spp., whose genomes harbour a previously unreported operon for SCN^? degradation. Genome‐based metabolic predictions suggest that a large portion of each bioreactor community is autotrophic, relying not on molasses in reactor feed but using energy gained from oxidation of sulfur compounds produced during SCN^? degradation. Heterotrophs, including a bacterium from a previously uncharacterized phylum, compose a smaller portion of the reactor community. Predation by phage and eukaryotes is predicted to affect community dynamics. Genes for ammonium oxidation and denitrification were detected, indicating the potential for nitrogen removal, as required for complete remediation of wastewater. These findings suggest optimization strategies for reactor design, such as improved aerobic/anaerobic partitioning and elimination of organic carbon from reactor feed.     

Lophotrochozoan relationships and parasites. A snap-shot

Lophotrochozoa has been consistently recovered in molecular phylogenetic analyses using different markers. Current knowledge of lophotrochozoan relationships is reviewed and the place that parasites occupy in this phylogeny is discussed. Two major taxa are identified within Lophotrochozoa: Platyzoa and Trochozoa. Monophyly of both taxa is still under debate. Relationships within Trochozoa remain largely unclear, however, there is strong evidence that the so called "minor phyla" Sipuncula, Echiura, and Myzostomida are all nested within annelids. Monophyly of the former "Lophophorata" is rejected, and a close relationship between phoronids and brachiopods, as well as between bryozoans and kamptozoans is suggested instead. The movement of the field of systematics into the genomic era will greatly improve our knowledge in the near future.     

The influence of temperature, photoperiod and plant type on the predation rate of Macrolophus pygmaeus on Myzus persicae

The effect of temperature and photoperiod on the rate of predation of nymphs and adults of the predator Macrolophus pygmaeus was studied using Myzus persicae prey feeding on egg-plant and pepper plants. The experiments were conducted at three photoperiods (16L:8D, 12L:12D and 8L:16D), three temperatures (20, 25 and 30 °C), and at 65% r.h. The rate of predation increased with temperature. Predation rate was affected by photoperiod on pepper but not on egg-plant. Females and fifth instar nymphs were the most voracious stages followed by third and fourth instar nymphs and males. First and second instar nymphs consumed far fewer aphids. Predation rate was higher on leaves of pepper than egg-plant, especially at 30 °C. Variation in the efficacy of this predator is discussed.