3,516 research outputs found

    Analysing co-evolution among artificial 3D creatures

    Get PDF
    This paper is concerned with the analysis of coevolutionary dynamics among 3D artificial creatures, similar to those introduced by Sims (1). Coevolution is subject to complex dynamics which are notoriously difficult to analyse. We introduce an improved analysis method based on Master Tournament matrices [2], which we argue is both less costly to compute and more informative than the original method. Based on visible features of the resulting graphs, we can identify particular trends and incidents in the dynamics of coevolution and look for their causes. Finally, considering that coevolutionary progress is not necessarily identical to global overall progress, we extend this analysis by cross-validating individuals from different evolutionary runs, which we argue is more appropriate than single-record analysis method for evaluating the global performance of individuals

    Is there a 'Neutral theory of Anthropology'?

    Get PDF
    Lansing and Cox open a welcome discussion of the potential for neutral models in anthropology—it has been almost 50 years since the original neutral models were applied to DNA sequences (e.g., Kimura 1968) and then later to biological phenotypes (e.g., Lande 1976) and cultural data (Cavalli-Sforza and Feldman 1981; Neiman 1995). This long history of research is a gold mine for studies of culture evolution

    Nest Predation by brown-headed cowbirds (Molothrus ater)

    Get PDF
    The reproductive success of parasites is entirely dependent on their ability to encounter suitable hosts. Obligate brood parasitic birds may increase host encounter rate, and consequently their reproductive output, if they cause unsuitable late-stage host nests to fail thereby stimulating the host to create another nest that they can parasitize. I tested key predictions of this ‘farming’ hypothesis for the brown-headed cowbird (Molothrus ater). I found evidence that cowbird attacks are not uncommon, a basic requirement of the hypothesis. Furthermore, I found multiple lines of evidence that cowbird attacks are not indiscriminate, but directed at non-parasitized nests and at those at a developmental stage too late to be suitable for parasitism. I experimentally demonstrate that cowbirds determine the age of a nest by directly puncturing a portion of the clutch or indirectly by attending to the absolute number of eggs. Cowbirds also parasitized a high proportion of the re-nesting attempts following their attacks suggesting that they take advantage of the reproductive opportunities they create. A Monte Carlo model comparing simulated farming and non-farming cowbirds also shows that a farming strategy may lead to higher reproductive output likely by enhancing individual nest discovery as opposed to increasing the number of nests. How cowbirds occupy space may also provide insight into how they encounter potential hosts. Utilization distributions (UDs) are among the most applicable methods of quantifying space use. In one of the first practical applications of a multidimentional UD that includes time as a dimension, I show that cowbirds were significantly more likely to be found around nesting sites when a nest was active suggesting that cowbirds optimize their nest searching. I did not, however, find a difference in probability of occurrence depending on the developmental stage of a nest. I also found evidence that cowbirds become less territorial later in the day. Comparisons to strictly spatial UDs suggest that including a time dimension may provide a more realistic model of how cowbirds find host nests and interact with one another. Thus, cowbirds can discriminate appropriate vs inappropriate nests and adjust their predatory and spatial behaviour accordingly to improve their encounters with hosts

    Busted by the bite

    Get PDF
    Large herbivores are charismatic species known to engineer ecosystems through a variety of effects. Conflicts can sometimes arise when these effects are undesirable. However, without detailed knowledge on herbivore selectivity for landscapes, patches and plants, these positive and negative effects remain difficult to predict. Such species and sex-specific selectivity have inherent evolutionary and ecological mechanisms. In order to study such mechanisms it is important to study the partitioning of resources at multiple scales. Most studies have looked at large-scale resource partitioning (such as movement patterns) but fewer study the fine-scale levels of selectivity such as the individual bites taken by herbivores. This level of detail is, however, important because it is essentially the direct mechanism through which ecosystem effects are manifested. Specifically for the browsing herbivore guild, such fine-scale studies have largely been impractical due to forested habitats which limit direct observation of behaviors. DNA-based diagnostics are becoming more and more popular within ecology as they provide vital data to answer certain questions. In this thesis I developed two versions of a method to differentiate between five species of large herbivore browsers using trace amounts of environmental DNA left at browsed twigs. The first version uses a traditional amplification method for identifying the species of browsers and the second uses an advanced and more sensitive method for identifying the species and sex of browsers. Using environmental DNA, I determined species-specific browsing patterns across three studies. I found overall that traditional methods for attributing browsing at the species level tend to be misleading. In one study I show that although one species may be blamed for forest plantation damages, DNA evidence showed a partitioning between three herbivore species. I also document the partitioning of plant parts among different sized ungulates and show that overlap in browsing heights and bite diameters is much larger than previously assumed. In another study I experimentally verified the selectivities of free-ranging herbivores for three species of trees. This thesis thus not only develops new molecular ecological tools but also provides new insights into resource partitioning and hence the ecosystem effects of herbivores

    Evolutionary concepts in predicting and evaluating the impact of mass chemotherapy schistosomiasis control programmes on parasites and their hosts

    Get PDF
    Schistosomiasis is a parasitic disease of significant medical and veterinary importance in many regions of the world. Recent shifts in global health policy have led towards the implementation of mass chemotherapeutic control programmes at the national scale in previously ‘neglected’ countries such as those within sub-Saharan Africa. Evolutionary theory has an important role to play in the design, application and interpretation of such programmes. Whilst celebrating the rapid success achieved to date by such programmes, in terms of reduced infection prevalence, intensity and associated human morbidity, evolutionary change in response to drug selection pressure may be predicted under certain circumstances, particularly in terms of the development of potential drug resistance, evolutionary changes in parasite virulence, transmission and host use, and/or competitive interactions with co-infecting pathogens. Theoretical and empirical data gained to date serve to highlight the importance of careful monitoring and evaluation of parasites and their hosts whenever and wherever chemotherapy is applied and where parasite transmission remains

    The Economics of Agricultural Development: What Have We Learned? Processes

    Get PDF
    Agricultural development thinking has gone through several stages of fad and fancy, often without an understanding of previous fallacies. Its current doldrums are unfortunate given the unrivaled importance of agricultural development for poverty reduction in most development countries. After reviewing several policy and program areas, lessons are synthesized, and a forwardlooking research framework suggested, especially regarding role of specialization in the evolution of economic organization. The corresponding role of government is seen to be the facilitation of economic cooperation, rather than social engineering.

    Host-parasite adaptations and interactions between honey bees, Varroa mites and viruses

    Get PDF
    The ectoparasitic mite, Varroa destructor, has become the largest threat to apiculture and honey bee health world-wide. Since it was introduced to the new host species, the European honey bee (Apis mellifera), it has been responsible for the near complete eradication of wild and feral honey bee populations in Europe and North America. Currently, the apicultural industry depends heavily on chemical Varroa control treatments to keep managed colonies alive. Without such control the mite populations in the colony will grow exponentially and the honey bee colony will succumb to the development of overt virus infections that are vectored by the mite typically within three years. Two unique sub-populations of European honey bees (on Gotland, Sweden and in Avignon, France) have adapted to survive for extended periods (over ten years) without the use of mite control treatments. This has been achieved through a natural selection process with unmanaged mite infestation levels enforcing a strong selection pressure. This thesis reveals that the adaptation acquired by these honey bee populations mainly involve reducing the reproductive success of the parasite, that the different populations may have evolved different strategies to do so, and that this mite-resistant trait is genetically inherited. In addition, results of this thesis demonstrate that chemical mite control treatments used by beekeepers to inhibit the mite population growth within a colony can actually worsen bee health by temporarily increasing the bee's susceptibility to virus infection. The results of this thesis highlight the impact that apicultural practices otherwise have on host-parasite interactions and the development of disease in this system. Possible solutions to the threat of Varroa are discussed such as the potential to breed for mite-resistant honey bees, which may offer a sustainable long-term solution, and the need for better general beekeeping techniques that reduce the use of chemical treatments and inhibit the spread of disease

    Tracking costs of virulence in natural populations of the wheat pathogen, Puccinia striiformis f.sp.tritici

    Get PDF
    <p>Abstract</p> <p>Background</p> <p>Costs of adaptation play an important role in host-parasite coevolution. For parasites, evolving the ability to circumvent host resistance may trade off with subsequent growth or transmission. Such costs of virulence (<it>sensu </it>plant pathology) limit the spread of all-infectious genotypes and thus facilitate the maintenance of genetic polymorphism in both host and parasite. We investigated costs of three virulence factors in <it>Puccinia striiformis </it>f.sp.<it>tritici</it>, a fungal pathogen of wheat (<it>Triticum aestivum</it>).</p> <p>Results</p> <p>In pairwise competition experiments, we compared the fitness of near-isogenic genotypes that differed by a single virulence factor. Two virulence factors (<it>vir4</it>, <it>vir6</it>) imposed substantial fitness costs in the absence of the corresponding resistance genes. In contrast, the <it>vir9 </it>virulence factor conferred a strong competitive advantage to several isolates, and this for different host cultivars and growing seasons. In part, the experimentally derived fitness costs and benefits are consistent with frequency changes of these virulence factors in the French pathogen population.</p> <p>Conclusion</p> <p>Our results illustrate the variation in the evolutionary trajectories of virulence mutations and the potential role of compensatory mutations. Anticipation of such variable evolutionary outcomes represents a major challenge for plant breeding strategies. More generally, we believe that agro-patho-systems can provide valuable insight in (co)evolutionary processes in host-parasite systems.</p

    Why one-size-fits-all vaso-modulatory interventions fail to control glioma invasion: in silico insights

    Full text link
    There is an ongoing debate on the therapeutic potential of vaso-modulatory interventions against glioma invasion. Prominent vasculature-targeting therapies involve functional tumour-associated blood vessel deterioration and normalisation. The former aims at tumour infarction and nutrient deprivation medi- ated by vascular targeting agents that induce occlusion/collapse of tumour blood vessels. In contrast, the therapeutic intention of normalising the abnormal structure and function of tumour vascular net- works, e.g. via alleviating stress-induced vaso-occlusion, is to improve chemo-, immuno- and radiation therapy efficacy. Although both strategies have shown therapeutic potential, it remains unclear why they often fail to control glioma invasion into the surrounding healthy brain tissue. To shed light on this issue, we propose a mathematical model of glioma invasion focusing on the interplay between the mi- gration/proliferation dichotomy (Go-or-Grow) of glioma cells and modulations of the functional tumour vasculature. Vaso-modulatory interventions are modelled by varying the degree of vaso-occlusion. We discovered the existence of a critical cell proliferation/diffusion ratio that separates glioma invasion re- sponses to vaso-modulatory interventions into two distinct regimes. While for tumours, belonging to one regime, vascular modulations reduce the tumour front speed and increase the infiltration width, for those in the other regime the invasion speed increases and infiltration width decreases. We show how these in silico findings can be used to guide individualised approaches of vaso-modulatory treatment strategies and thereby improve success rates

    Coevolution in Action: Disruptive Selection on Egg Colour in an Avian Brood Parasite and Its Host

    Get PDF
    Trait polymorphism can evolve as a consequence of frequency-dependent selection. Coevolutionary interactions between hosts and parasites may lead to selection on both to evolve extreme phenotypes deviating from the norm, through disruptive selection.Here, we show through detailed field studies and experimental procedures that the ashy-throated parrotbill (Paradoxornis alphonsianus) and its avian brood parasite, the common cuckoo (Cuculus canorus), have both evolved egg polymorphism manifested in discrete immaculate white, pale blue, and blue egg phenotypes within a single population. In this host-parasite system the most common egg colours were white and blue, with no significant difference in parasitism rates between hosts laying eggs of either colour. Furthermore, selection on parasites for countering the evolution of host egg types appears to be strong, since ashy-throated parrotbills have evolved rejection abilities for even partially mimetic eggs.The parrotbill-cuckoo system constitutes a clear outcome of disruptive selection on both host and parasite egg phenotypes driven by coevolution, due to the cost of parasitism in the host and by host defences in the parasite. The present study is to our knowledge the first to report the influence of disruptive selection on evolution of discrete phenotypes in both parasite and host traits in an avian brood parasitism system
    corecore