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PubMed1997

Role of detritus in a general prey-predator model of Sunderban Estuary, India.

In this paper we consider a general deterministic model consisting of a micro-organism pool living on detritus of mangrove litter and its invertebrate predators. Here the growth rate of micro-organism is assumed in the general form and Holling type-II functional response of the invertebrate predators is incorporated. We find a globally attracting steady state for some parameter values, and a stable limit cycle for some other parameter values. It is also shown that there exists Hopf-Andronov bifurcation with respect to the control parameters. It is found that the specific growth rate and the food conversion efficiency rate of invertebrate predator governs the dynamics of such a model.

Animals↗
PubMed1999

The parasites, predators, places and people I have known: a great adventure.

I am extremely proud to receive the WAAVP/Pfizer Animal Health award, and particularly so in Africa, the continent where I have spent a large part of my professional life. In the nearly 40 years in research I have had the privilege and excitement of being involved with many great parasites, predators, places and people. In my early days in Kenya I saw all the great wild animal predators, but soon came to appreciate that the greatest predator of all was disease, particularly parasitic disease, with the devastating effects of tsetse and ticks and the infections they transmitted, and of the all-prevailing roundworms. I learned several key lessons while working with research teams to develop better diagnostics, to improve epidemiological understanding as a basis for rational treatment and control, and to extend the understanding of disease processes with the view to developing novel methods of treatment or prevention. The Power of Pathology in diagnosing diseases, identifying new diseases and as a major tool for pathogenic diseases. The Power of Pathogenesis in identifying key mechanisms that led to new diagnostic techniques, improved methods of treatment, and possibly to future vaccines. The Power of Application of what we already know; while recognising that molecular biology will make a massive contribution to improving animal and human health, it is important to appreciate that we already have a very powerful armamentaria to diagnose, treat, control or prevent disease, and when used properly they have been successful and cost-effective. The Power of Genetic Resistance: the recognition that certain species, certain breeds, and certain individuals within breeds possess remarkable resistance to certain parasitic diseases such as trypanosomosis and helminthosis, and that this trait is genetically correlated with production, opens up a very powerful additional approach to improving animal health. The Importance of Measurement: I completely endorse the sentiments of Lord Kelvin, Professor of Natural Philosophy at Glasgow University who stated in 1846: "When you can measure what you are speaking about, and express it in numbers, you know something about it: but when you cannot measure it, your knowledge is of a meagre and unsatisfactory kind." This applies very much to Parasitology. The future is bright. The combination and integration of the new technologies of Biotechnology, Mathematical Methods and Bioinformatics coupled with advances in Computer Power will produce new standards in animal and human health in the 21st century. New methods of predicting, diagnosis, treating, controlling, prognosing and preventing disease will become available. WAAVP has a major role to play by ensuring that veterinary parasitologists are provided with the proper training, infrastructure and forum to advance new technologies and that the veterinary profession plays a leading role in the future direction they take.

Africa↗
PubMed1998

Occurrence of digestive cysteine proteases in Perillus bioculatus, a natural predator of the Colorado potato beetle.

Oryzacystatins (OCs) are protease inhibitors (PIs) that inhibit Colorado potato beetle (CPB) digestive proteases, and transgenic potato plants containing these PIs are currently under test. However, OCs could interfere with the digestive system of beneficial insects. Protease activity and susceptibility to class-specific protease inhibitors were studied in protein extracts of Perillus bioculatus, a stinkbug predator that has shown potential for biological control of the CPB. At physiological pH, the analysis of protease activity showed that up to 90% of P. bioculatus protease activity is of the cysteine type. All active life stages of the predator were tested, and electrophoretic characterization detected no major qualitative variation in protease pattern between stages. Protease activity in extracts of P. bioculatus nymphs was significantly reduced, up to 70%, by the two recombinant cystatins from rice (OCI and OCII), and by stefin A, a PI encoded by a human gene. These results clearly indicate that cysteine PIs are active not only against the CPB digestive protease complex, but also against proteases of one of its most important natural predators.

Animals↗
PubMed2000

Neither acute nor chronic exposure to a naturalistic (predator) stressor influences the interleukin-1beta system, tumor necrosis factor-alpha, transforming growth factor-beta1, and neuropeptide mRNAs in specific brain regions.

Physical (neurogenic) stressors may influence immune functioning and interleukin-1beta (IL-1beta) mRNA levels within several brain regions. The present study assessed the effects of an acute or repeated naturalistic, psychogenic stressor (predator exposure) on brain cytokine and neuropeptide mRNAs. Acute predator (ferret) exposure induced stress-like behavioral effects, including elicitation of a startle response and reduced exploratory behaviors; these responses diminished after 30 sessions. Moreover, acute and repeated predator exposure, like acute restraint stress, increased plasma corticosterone levels measured 5 min later, but not 2 h after stressor exposure. In contrast, none of the stressors used influenced IL-1beta, IL-1 receptor antagonist, IL-1 receptor type I, IL-1 receptor accessory proteins I and II, or tumor necrosis factor-alpha mRNA levels in the prefrontal cortex, amygdala, hippocampus, or hypothalamus. Likewise, there were no stressor effects on transforming growth factor-beta1, neuropeptide Y, glycoprotein 130, or leptin receptor mRNAs in brain regions. Thus, the naturalistic/psychogenic stressor used does not affect any of the brain cytokine component mRNAs studied. It is suggested that this type of stressor activates homeostatic mechanisms (e.g., glucocorticoid release), which act to preclude brain cytokine alterations that would otherwise favor neuroinflammatory/neuroimmunological responses and the consequent increase of brain sensitivity to neurotoxic and neurodegenerative processes.

Analysis of Variance↗
PubMed1999

Amplified detection, using a monoclonal antibody, of an aphid-specific epitope exposed during digestion in the gut of a predator.

Monoclonal antibodies are invaluable tools for identifying and quantifying prey remains in the fore-guts of predators. However, they must be target-specific, detect an epitope that is well replicated within the prey (to enhance assay sensitivity) and, critically, recognise a site that can resist digestion. A monoclonal antibody is reported that proved to be aphid-specific and capable of detecting, and accurately identifying, as little as 16.5 ng of aphid protein within a heterologous mixture of invertebrate material. The antibody was selected by screening hybridoma lines for antibodies that bound with semi-digested aphid proteins. The antibody detected an epitope that was found, against expectation, to significantly increase in concentration with time (by approx. 50% over 6 h) in the gut of the carabid predator Pterostichus melanarius. The resultant extended antigen detection period and half-life, and the high specificity of this antibody, showed it to be an enhanced tool for studying interactions between aphids and their predators in the field. It was concluded that the antibody was initially generated to a surface epitope on a high molecular weight native protein (> 200 kD). This epitope, however, was then either replicated on internal sites progressively revealed by digestion, or new epitopes became available as the conformation of the protein changed during digestion.

Animals↗
PubMed2000

Predation of beetles (Tenebrio molitor) infected with tapeworms (Hymenolepis diminuta): a note of caution for the manipulation hypothesis.

Previous laboratory studies have indicated that tenebrionid beetles infected with Hymenolepis diminuta display behavioural alterations. These are assumed to increase the likelihood of this intermediate host being predated by the Rattus sp. definitive host, and hence provide support for the Manipulation Hypothesis. We tested this hypothesis by both assessing beetle behaviour and predation rates in semi-naturalistic environments. Behavioural assays showed that infected beetles were more often exposed (not concealed under boxes) than uninfected beetles. However, there were no differences in predation rates between infected and uninfected beetles. We discuss this in terms of the historical and evolutionary contexts under which such altered behaviours could evolve and their implications for the Manipulation Hypothesis.

Analysis of Variance↗
PubMed2001

Response of some scolytids and their predators to ethanol and 4-allylanisole in pine forests of central Oregon.

Lindgren multiple funnel traps were set up in pine forests of central Oregon to determine the response of scolytid bark beetles to ethanol and 4-allylanisole (4AA). Traps were baited with two release rates of ethanol (4.5 or 41.4 mg/hr) and three release rates of 4AA (0, 0.6, or 4.3 mg/hr) in a 2 x 3 factorial design. All traps also released a 1:1 mixture of alpha- and beta-pinene at 11.4 mg/hr. Of 13,396 scolytids caught, Dendroctonus valens made up 60%, Hylurgops spp. 18.5%, Ips spp. 16%, Hylastes spp. 1.8%, Ganthotrichus retusus 0.9%, and bark beetle predators another 2.8%. Increasing the release rate of ethanol in the absence of 4AA increased the number of most scolytid species caught by 1.5-3.7 times, confirming its role as an attractant. Ips latidens, Temnochila chlorodia, and clerid predators were exceptions and did not show a response to higher ethanol release rates. Release of 4AA at the lowest rate inhibited attraction of most scolytids, with a significant reduction in G. retusus, Hylastes macer, and Hylurgops porosus when compared to traps without 4AA. A high release rate of 4AA further inhibited responses for most beetles compared to low 4AA. Seven species were significantly deterred by high 4AA, including the latter three, and Hylastes longicollis, Hylastes nigrinus, Hylurgops reticulatus, and Ips latidens. Exceptions include Hylurgops subcostulatus, which was significantly attracted to both low and high 4AA, and I. pini, which was attracted to low and high 4AA in combination with low ethanol, but unaffected by either release of 4AA with high ethanol. Dendroctonus valens was significantly attracted to low 4AA and unaffected by high 4AA. Predators appeared to be less inhibited by 4AA than most bark beetles. Although 4AA can deter the attraction of some secondary bark beetles to ethanol in combination with alpha- and beta-pinene, this inhibition could be weakened for certain species by increasing ethanol release rates. 4-Allylanisole may have some utility for managing the behavior of secondary bark beetles sensitive to this compound.

Animals↗
PubMed2001

Brook charr alevins alter timing of nest emergence in response to chemical cues from fish predators.

Brook charr (Salvelinus fontinalis) lay their eggs in gravel nests called redds. The nests are not defended for extended periods and the eggs and young may be subject to predation from predators that travel through the substrate into the redd. In this study we tested whether long-term exposure of brook charr eggs to chemical cues from predatory sculpins (Cottus cognatus) resulted in an adaptive shift in the timing of emergence of charr alevins from artificial redds. We reared brook charr eggs in the presence of chemical cues from sculpins fed brook charr eggs, sculpins fed brine shrimp, and a well water control. Significantly more alevins emerged during the first week of the emergence period when exposed to chemical cues from sculpins fed eggs than from cues from sculpins fed brine shrimp or from well water. Alevins that emerged sooner were smaller and possessed larger yolk sacs than alevins that emerged later in the emergence period. Our results suggest that alevins that emerge sooner may escape predation in the redd, but may pay a cost in being under-developed upon emergence into the open water of the stream or lake.

Adaptation, Physiological↗
PubMed2000

Cannibalism and intraguild predation among phytoseiid mites: are aggressiveness and prey preference related to diet specialization?

We tested whether specialist and generalist phytoseiid mites differ in aggressiveness and prey choice in cannibalism and intraguild predation. Specialists tested were Galendromus occidentalis, Neoseiulus longispinosus, Phytoseiulus persimilis, and P. macropilis; generalists tested were Amblyseius andersoni, Euseius finlandicus, E. hibisci, Kampimodromus aberrans, Neoseiulus barkeri, N. californicus, N. cucumeris, NM fallacis, and Typhlodromus pyri. Aggressiveness of cannibalistic females against larvae was not related to diet specialization except that highly aggressive species were exclusively generalists. Seldom to moderately cannibalizing species occurred in both generalist and specialist phytoseiids. In contrast to aggressiveness in cannibalism, generalists and specialists differed in aggressiveness in intraguild predation. Adult females of specialists were only slightly aggressive against heterospecific larvae, whereas adult females of all generalists except T. pyri were highly aggressive. Adult females of generalists were able to discriminate between con- and heterospecific larvae and preferentially consumed the latter when given a choice. Adult females of specialists except G. occidentalis showed no preference when given a choice between con- and heterospecific larvae. We conclude that aggressiveness in intraguild predation, species recognition and subsequent preferential consumption of heterospecifics when given a choice is common in generalist but not specialist phytoseiids. We discuss the evolutionary pathways that might have led to the difference between specialists and generalists in species discrimination.

Aggression↗
PubMed2002

Phytoseiid predators suppress populations of Bemisia tabaci on cucumber plants with alternative food.

Phytoseiids are known to attack whiteflies, but it is an open question whether they can be used for biological control of these pest insects. Preselection experiments in the laboratory showed that two out of five phytoseiid species tested, Euseius scutalis and Typhlodromips swirskii, stood out in terms of their ability to develop and reproduce on a diet of Bemisia tabaci immatures. In this paper, we show that both predators are able to suppress whitefly populations on isolated cucumber plants in a greenhouse. Predatory mites were released 2 weeks in advance of the release of B. tabaci. To enable their survival and promote their population growth, they were provided weekly with alternative food, that is, Typha sp. pollen. A few weeks after whitefly introduction, the numbers of adult whiteflies on plants with predators were consistently lower than on plants without predators, where B. tabaci populations grew exponentially. After 9 weeks, this amounted to a 16- to 21-fold difference in adult whitefly population size. This shows that the two phytoseiid species are promising biocontrol agents of B. tabaci on greenhouse cucumber.

Animals↗
PubMed2003

Quinolizidine alkaloids in Ormosia arborea seeds inhibit predation but not hoarding by agoutis (Dasyprocta leporina).

Quinolizidine alkaloids (QAs) are secondary compounds found in seeds of many species of plants, possibly protecting them against pathogens and seed predators. QAs were isolated from Ormosia arborea seeds and bioassayed against red-rumped agoutis (Dasyprocta leporina, Rodentia: Caviomorpha) to verify if they inhibit seed predation and food hoarding (seed dispersal). Three treatments were used: (1) seeds of O. arborea, (2) palatable seeds of Mimusops coriacea (Sapotaceae) treated with MeOH, and (3) seeds of M. coriacea treated with QAs dissolved in MeOH in similar concentration to that present in O. arborea. Palatable seeds were significantly more preyed upon than seeds treated with QAs and Ormosia seeds, but QAs did not influence hoarding behavior. QAs in O. arborea may have a strong effect in avoiding seed predation by rodents, without reducing dispersal.

Adaptation, Physiological↗
PubMed2003

Phytoseiid predators of whiteflies feed and reproduce on non-prey food sources.

Two phytoseiid species, Euseius scutalis (Athias-Henriot) and Typhlodromips swirskii (Athias-Henriot), are able to suppress whitefly populations on single plants and are candidate biological control agents for whiteflies such as Bemisia tabaci (Gennadius). These species can feed on pollen and insect-produced honeydew and these food sources are likely to be available in crops. If the utilization of these food types results in increased reproduction or survival, populations of predators can persist when whitefly prey is scarce or absent. We studied the impact of pollen and whitefly-produced honeydew on the life history of the two phytoseiids. Cattail pollen allowed for survival, development and reproduction of both predators. Whitefly-produced honeydew greatly increased survival of E. scutalis, allowed for development into adulthood and for a sustained low rate of oviposition. The survival of adult T. swirskii was high on cucumber leaf tissue, either with or without pollen or honeydew. Oviposition by adults and juvenile survival of T. swirskii was very low in presence of honeydew. Biological control of whiteflies may benefit from both pollen and honeydew because these non-prey food sources have a positive effect on the life history of the two predator species, especially E. scutalis.

Acari↗
PubMed2004

Iberian rock lizards (Lacerta monticola) assess short-term changes in predation risk level when deciding refuge use.

Prey might assess that risk level estimated in the first encounter with a predator was fixed in subsequent responses, whereas prey using flexible behavior would track short-term changes in risk. The authors examined, in the field, refuge use of Iberian rock lizards (Lacerta monticola) after simulated predator attacks and tested (a) how risk was assessed when multiple sources of risk were present simultaneously, (b) how short-term changes in risk level of successive attacks affected refuge use, and (c) whether the interval between attacks was important, insofar as attacks were considered to be coming from the same or different predators. Results suggest that lizards have a flexible estimate of risk that is based on multiple sources and flexibly dependent on previous estimates.

Animals↗
PubMed1993

Population oscillations of boreal rodents: regulation by mustelid predators leads to chaos.

The four-year cycle of microtine rodents in boreal and arctic regions was first described in 1924 (ref. 1). Competing hypotheses on the mechanisms underlying the small mammal cycle have been extensively tested, but so far the sustained rodent oscillations are unexplained. Here we use two mutually supportive approaches to investigate this question. First, building on studies of the interaction between rodents and their mustelid predators, we construct a predator-prey model with seasonality. Second, we use a new technique of nonlinear analysis to examine empirical time-series data, and compare them with the model dynamics. The model parameterized with field data predicts dynamics that closely resemble the observed dynamics of boreal rodent populations. Both the predicted and observed dynamics are chaotic, albeit with a statistically significant periodic component. Our results suggest that the multiannual oscillations of rodent populations in Fennoscandia are due to delayed density dependence imposed by mustelid predators, and are chaotic.

Animals↗
PubMed2006

Predator learning favours mimicry of a less-toxic model in poison frogs.

Batesian mimicry--resemblance of a toxic model by an edible mimic--depends on deceiving predators. Mimetic advantage is considered to be dependent on frequency because an increase in mimic abundance leads to breakdown of the warning signal. Where multiple toxic species are available, batesian polymorphism is predicted--that is, mimics diversify to match sympatric models. Despite the prevalence of batesian mimicry in nature, batesian polymorphism is relatively rare. Here we explore a poison-frog mimicry complex comprising two parapatric models and a geographically dimorphic mimic that shows monomorphism where models co-occur. Contrary to classical predictions, our toxicity assays, field observations and spectral reflectances show that mimics resemble the less-toxic and less-abundant model. We examine "stimulus generalization" as a mechanism for this non-intuitive result with learning experiments using naive avian predators and live poison frogs. We find that predators differ in avoidance generalization depending on toxicity of the model, conferring greater protection to mimics resembling the less-toxic model owing to overlap of generalized avoidance curves. Our work supports a mechanism of toxicity-dependent stimulus generalization, revealing an additional solution for batesian mimicry where multiple models coexist.

Animals↗
PubMed2005

Predation on prokaryotes in the water column and its ecological implications.

The oxic realms of freshwater and marine environments are zones of high prokaryotic mortality. Lysis by viruses and predation by ciliated and flagellated protists result in the consumption of microbial biomass at approximately the same rate as it is produced. Protist predation can favour or suppress particular bacterial species, and the successful microbial groups in the water column are those that survive this selective grazing pressure. In turn, aquatic bacteria have developed various antipredator strategies that range from simply 'outrunning' protists to the production of highly effective cytotoxins. This ancient predator-prey system can be regarded as an evolutionary precursor of many other interactions between prokaryotic and eukaryotic organisms.

Animals↗
PubMed2000

Developing SCAR markers to study predation on Trialeurodes vaporariorum.

DNA markers of Trialeurodes vaporariorum were developed to detect remains of these whitefly in the gut of the predator Dicyphus tamaninii. A 2400-bp DNA fragment of T. vaporariorum, absent in other closely related prey species and in the predator banding pattern, was identified by random amplified polymorphic DNA (RAPD) analysis. After cloning and sequencing this fragment, two pairs of sequence-characterized amplified region (SCAR) primers were developed, amplifying single bands of 2100 bp and 310 bp, respectively. Detection of T. vaporariorum DNA in the predator gut was only possible using the primers that amplified the shortest fragment. Specificity tests performed with this pair of primers showed the presence of the 310-bp band for T. vaporariorum in all stages.

Animals↗
PubMed2003

Genetic marker investigation of the source and impact of predation on a highly endangered species.

In September and October 2000, the remains of a number of apparently predated northern hairy-nosed wombats (Lasiorhinus krefftii) were discovered in Epping Forest National Park, the site of the only known population of this highly endangered species. Analysis of DNA recovered from six carcasses and a section of intestine found nearby was carried out using microsatellite and Y-specific primers. This identified seven individual wombats, the identity of three of which was inferred from a genotype database prepared from animals sampled during trapping programmes. Six victims were male and one female, suggesting that female-biased predation rates are unlikely to be the cause of the current male-biased population sex ratio. DNA isolated from four canid faeces found in the vicinity revealed three distinct canid microsatellite genotypes with very high probabilities of belonging to dingoes (Canis familiaris dingo). A wombat genotype matching that of one of the dead individuals was identified from scats of two of the dingoes. In addition, two macropod microsatellites were amplified from two dingo scats. These observations provided vital information regarding predation on northern hairy-nosed wombats, and prompted the permanent exclusion of dingoes from the park by the erection of a dingo-proof fence.

Animals↗