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360 results for “Defence”
Defence procurement in India
<p>Selected observations from CAG defence audit reports (2005, 2010-2016) making a note of delays in defence procurement in India in recent years.</p>
Phenotypic plasticity in chemical defence allows butterflies to diversify host use strategies
<p>Hostplant specialization is a major force driving ecological niche partitioning and diversification in insect herbivores. The cyanogenic defences of Passiflora plants keeps most herbivores at bay, but not larvae of Heliconius butterflies, which can both sequester and biosynthesize cyanogenic compounds. Here, we demonstrate that both Heliconius cydno chioneus, a host plant generalist, and H. melpomene rosina, a specialist, have remarkable plasticity in their chemical defence. When feeding on Passiflora species with cyanogenic compounds they can readily sequester, both species downregulate the biosynthesis of these compounds. In contrast, when fed on Passiflora plants that do not contain cyanogenic glucosides that can be sequestered, both species increase biosynthesis. This biochemical plasticity comes at a significant fitness cost for specialist like H. m. rosina, as growth rates for this species negatively correlate with biosynthesis levels, but not for a generalist like H. c. chioneus. In exchange, H. m rosina has increased performance when sequestration is possible as on its specialised hostplant. In summary, phenotypic plasticity in biochemical responses to different host plants offers these butterflies the ability to widen their range of potential host within the Passiflora genus, while maintaining their chemical defences.</p>
Convergent evolution of elaborate nests as structural defences in birds
The pendent nests of some weaverbird and icterid species are among the most complex structures built by any animal, but why they have evolved remains to be explained. The precarious attachments and extended entrance tunnels characteristic of these nests are widely speculated to act as structural defences against invasion by nest predators, particularly tree-climbing snakes, but this hypothesis has yet to be systematically tested. We use phylogenetic comparative methods to investigate the relationship between nest structure and developmental period length, a proxy for offspring mortality, in weaverbirds (Ploceidae) and icterids (Icteridae), two bird families in which highly elaborate pendent nests have independently evolved. We find that more elaborate nests, particularly those with entrance tunnels, are associated with longer developmental periods in both families. This finding is robust to potentially confounding effects of body mass, phylogenetic relationships, nest location and latitude. Our results are consistent with the hypothesis that elaborate nest structures in birds can function as structural defences, resulting in lower offspring mortality and slower development. More generally, our findings suggest that constructing complex, protective structures may buffer against environmental hazards, reducing extrinsic mortality and contributing to the evolution of slower life histories in diverse animal lineages, even humans.
Data from: Season and herbivore defence trait mediate tri-trophic interactions in tropical rainforest
<p>Bottom-up effects from host plants and top-down effects from predators on herbivore abundance and distribution vary with physical environment, plant chemistry, predator and herbivore trait and diversity. Tri-trophic interactions in tropical ecosystems may follow different patterns from temperate ecosystems due to differences in above abiotic and biotic conditions. We sampled leaf-chewing larvae of Lepidoptera (caterpillars) from a dominant host tree species in a seasonal rainforest in Southwest China. We reared out parasitoids and grouped herbivores based on their diet preferences, feeding habits, and defence mechanisms. We compared caterpillar abundance with leaf numbers ('bottom-up' effects) and parasitoid abundance ('top-down' effects) between different seasons and herbivore traits. We found bottom-up effects were stronger than top-down effects. Both bottom-up and top-down effects were stronger in the dry season than in the wet season, which were driven by polyphagous rare species and host plant phenology. Contrary to our predictions, herbivore traits did not influence differences in the bottom-up or top-down effects except for stronger top-down effects for shelter-builders. Our study shows season is the main predictor of the bottom-up and top-down effects in the tropics and highlights the complexity of these interactions. </p>
Data for: Fitness costs of female competition linked to resource defence and relatedness of competitors
<p>Female reproductive success is often limited by access to resources and this can lead to social competition both within and between kin groups. Theory predicts that both resource availability and relatedness should influence the fitness consequences of social competition. However, testing key predictions requires differentiating the effects of these two factors. <span>Here we achieve this experimentally by manipulating the social environment of house mice, a facultative communal breeding species with known kin discrimination ability. </span>Our results support the hypothesis that resource defence can be costly for females, potentially trading off against maternal investment. When competition for nest sites was more intense, subjects: 1) were more active during resting phases, 2) responded more strongly to simulated territory intrusions via competitive signalling, and 3) produced smaller weaned offspring. However, we found no evidence that the propensity for kin to cooperate was influenced by relatedness of rivals. Communal breeding between sisters occurred independently of the relatedness of competitors, and costs of competition with non-kin were not mitigated by greater inclusive fitness benefits. Rather, communally breeding sisters weaned fewer offspring when competing with unrelated females, indicating that competition with non-kin is more costly overall. Our findings thus demonstrate that social competition has fitness costs and that associating with kin is beneficial to avoid negative fitness consequences of competing with non-kin, in addition to more widely recognised kin-selected benefits.</p>
Herbivory selects for tolerance and constitutive defence across stages of community succession
<p>Plants defend themselves from herbivory by either reducing damage (resistance) or minimizing its negative fitness effects with compensatory growth (tolerance). Factors mediating the selection for defenses such as herbivory and competition are in constant flux in an early secondary successional community, which can create temporal variation in selection for these traits. We manipulated successional age of the community and insect herbivory in a genotypic selection experiment with the perennial herb Solidago altissima. We found selection for investment in aboveground biomass in early succession but not in mid-succession, suggesting that the importance of competition is highest in the very first years of succession. Herbivory selected for smaller and better defended plants in both successional ages but decreased plant survival and probability of flowering only in mid-succession. Despite dramatic differences in herbivory between early and mid-succession, selection on defense traits did not change. These results demonstrate that changes in the community that affect key life-history traits in an individual species can occur over very short timescales in a dynamic secondary successional environment. Such temporal variation may be an important, yet overlooked, contributor to adaptive mosaics across populations.</p>
EXPERIMENTAL GROWTH CONDITIONS AFFECT DIRECT AND INDIRECT DEFENCES IN TWO COTTON SPECIES
<p>The file "R code CHappuis et al. 2023.txt" contains the R code for all the analyses shown in the research article "EXPERIMENTAL GROWTH CONDITIONS AFFECT DIRECT AND INDIRECT DEFENCES IN TWO COTTON SPECIES". The other files contain the raw data used for the analyses.</p> <p> </p> <p> </p>
Disentangling the relative contributions of factors determining seed physical defence: a global-scale data synthesis
<p>Physical defence investment in seeds varies greatly among plant species and is affected by many potential factors. However, the relative importance of influential factors has not yet been systematically evaluated. Here, we compiled a global database of the seed coat ratio (SCR), a proxy of seed physical defence, for 1,357 species. Using partial R<sup>2</sup> calculation that can estimate the reduction in explained variance of a given factor after removing it from a full model containing all the other factors, we disentangled the relative contributions of seven factors commonly used to explain variation in the SCR. Seed desiccation response and phylogeny explained a large amount of SCR variation among species, with a partial R<sup>2</sup><sub>lik</sub> value of 13.31% and 10.62%, respectively. Seed dormancy, plant growth form, seed mass, climate region, and fruit type showed little power to explain SCR variation, although they are often cited in the literature as potential factors. Our results highlight the important roles of seed desiccation response and phylogeny in shaping interspecific variation in the SCR. These findings provide a detailed interpretation of both evolutionary and ecological patterns underlying the physical defence mechanisms and allocation strategies of plant seeds.</p>
Data from: Silicon supplementation and jasmonate activation synergistically increase phenolic defences against a legume herbivore
<p>The accumulation of silicon (Si) is widely reported to have anti-herbivore defensive properties in grasses. There is emerging, but fragmentary, evidence that Si could play a similar role in legumes. Here, we sought to understand the effects of Si supplementation on anti-herbivore defensive properties in lucerne (<em>Medicago sativa</em>), especially in relation to other potential defences (i.e. phenolics) and the phytohormone that regulates anti-herbivore defences, jasmonic acid or jasmonate (JA), which is also linked to Si accumulation. We determined how growth, root nodulation and chemistry (carbon, nitrogen and phenolic concentrations) of four genotypes of lucerne responded to Si supplementation, with and without the application of JA, and we used feeding assays to determine the subsequent effects on the feeding success of adult Sitona discoideus weevils. Si supplementation increased plant mass and root nodulation of <em>M. sativa</em> by 61% and 227%, respectively, and reduced relative consumption (RC) and frass production by S. discoideus by 38% and 30%, respectively. Si supplementation had no effect on foliar nitrogen concentrations, most likely due to the dilution effects of increased plant growth and foliar carbon. Phenolic concentrations were negatively correlated with leaf RC; RC also decreased by 34% when JA was applied to plants. When Si was combined with JA application, phenolics were significantly enhanced, demonstrating the potential to stimulate multiple anti-herbivore properties in M. sativa. The novel findings suggest that Si accumulation may play a more important role in legume resistance to herbivorous animals than previously thought. The ubiquity of soil Si and its emerging functional role in plant biology, including plant–animal interactions, suggest that these patterns could be common amongst legumes.</p>
Data from: When perfection isn't enough: host egg signatures are an effective defence against high-fidelity African cuckoo mimicry
<p class="MsoNormal"><span>Most mimicry systems involve imperfect mimicry, whereas perfect and high-fidelity mimicry are rare. When the fidelity of mimicry is high, mimics might be expected to have the upper hand against their antagonists. However, in coevolving systems, diversification of model phenotypes may provide an evolutionary escape, because mimics cannot simultaneously match all model individuals in the population. Here we investigate high-fidelity mimicry in a highly specialised, Afrotropical brood parasite-host system: the African cuckoo and fork-tailed drongo. Specifically, we test whether host egg polymorphisms are an effective defence against such mimicry. We show, using a combination of image analysis, field experiments, and simulations, that 1) egg colour and pattern mimicry of fork-tailed drongo eggs by African cuckoos is near-perfect on average; 2) drongos show fine-tuned rejection of foreign eggs, exploiting unpredictable pattern differences between parasitic eggs and their own; and 3) the high degree of interclutch variation (polymorphic egg 'signatures') exhibited by drongos gives them the upper hand in the arms race, with 93.7% of cuckoo eggs predicted to be rejected, despite cuckoos mimicking the full range of drongo egg phenotypes. These results demonstrate the effectiveness of model diversification as a defence against mimics, even when mimicry is highly accurate. </span></p>
Data from: Efficacy of multiple defences of mimics from the golden mimicry complex against two predators
<p>Many prey species employ multiple defences during interactions with predators. Multiple defences can provide a selective advantage against a single predator at different stages of the interaction or attack, as well as against multiple predator types. However, the efficacy of multiple defences both during different sequences of an attack and against multiple predator types, remains poorly understood. We measured and classified defensive traits used by five mimics (Müllerian and Batesian) of the myrmecomorphic golden mimicry complex and one non-mimetic species. We then performed predatory trials using two different predators that differed markedly in their body size, trophic specialisation, and how they handle prey – one being an ant specialist (spider) and the other a generalist which avoided ants (skink). We identified 12 defensive traits and classified them into four groups (primary, chemical, mechanical, behavioural), which were strongly correlated. Skinks were much less likely to attack and capture mimics than the ant-eating spider predators. Our results show that multiple defences (five or six) were used against each predator. The defensive behaviours and features that were most effective against skinks included appendage waving and large body size, whereas the golden 'shine' warning signal, large body size, cuticle thickness, and defensive gland size were most effective against spiders. Most defences appeared to be predator-specific. We conclude that potential prey in the golden mimicry complex have been selected for multiple defences because of their vulnerability to different predator types and consequently, the efficacy of some of these defences likely represents a trade-off.</p>
Data from: predator-induced defences under tropicalisation: a biogeographic approach
<p>Aim: The biogeography of predator-induced defences is an understudied area of predator-prey dynamics. Range overlap with predators that induce the response and local demographics (e.g., prey abundances) are likely to be important factors for determining the biogeographic distribution of induced defences within species. However, with climate warming, range expanding warm-water predators are increasingly preying upon temperate species. This is a consequence of a wider phenomenon known as tropicalisation. We aim to determine: (i) if individuals of a temperate barnacle with induced defences ("bent morphs") are primarily present where they co-occur with range-expanding warm-water predators (muricid snails) and, (ii) if bent morphs are size-structured within populations.</p> <p>Location: North-eastern Pacific rocky intertidal zone (~26-40ºN)</p> <p>Taxon: <em>Tetraclita rubescens</em> (Nilsson-Cantell, 1931), Balanomorpha</p> <p>Methods: We use photo quadrats from sites across the range of <em>T. rubescens</em> to determine the biogeographic distribution of populations with bent morphs and to assess size-structure. We use a combination of field surveys, literature, and museum occurrences to assess range overlap between cool and warm-water predators of <em>T. rubescens</em> and their association with populations with bent morphs and abundance patterns of <em>T. rubescens</em>.</p> <p>Results: Bent morphs are commonly found within the equatorward portion of the species' range (where abundances are highest), in populations overlapping with range expanding warm-water predators. Bent morphs primarily occur within the smaller size classes.</p> <p>Main conclusions: To be partly resilient to the effects of tropicalisation, temperate prey must acclimatize/adapt to altered predator-prey dynamics. Predator-induced defences are one way to do this. We show that bent morphs within a temperate prey species (<em>T. rubescens</em>) are largely restricted to populations that overlap with large-bodied and range-expanding warm-water predators. This is evidence for the partial resilience of <em>T. rubescens</em> to tropicalisation and provides the rationale for further exploration of the eco-evolutionary consequences of tropicalisation in this study system and others.</p>
Silicon and Epichloë-endophyte defences in a model temperate grass diminish feeding efficiency and immunity of an insect folivore
<p>Plants deploy diverse anti-herbivore defences which reduce feeding and performance of herbivores. Temperate grasses use silicon (Si) accumulation and<em> Epichloë</em>-endophytes for physical and chemical (i.e. endophytic-alkaloids) defence against insect herbivores. Recent studies suggest that <em>Epichloë</em>-endophytes increase Si accumulation in their host grass. It is unknown, however, how this affects Si-deposition on the leaf surface, their impacts on insect herbivore feeding efficiency and their immunity to potential infection/parasitism.</p> <p>To address this knowledge gap, we grew tall fescue (<em>Festuca arundinacea</em>) hydroponically with and without Si, in the absence or presence of the novel AR584 <em>Epichloë</em>-strain. We exposed plants to <em>Helicoverpa armigera</em> (Lepidoptera: Noctuidae) in both in-situ (intact leaves) and ex-situ (excised leaves) feeding trials and determined the effects of Si and endophyte defences on herbivore feeding efficiency, growth rates and immunity against potential infection/parasitism.</p> <p>Endophytic plants supplied with Si showed 110% and 143% increases in leaf silica density and leaf Si concentrations, respectively, when exposed to herbivory, compared to non-endophytic plants that were herbivore-free. Despite the endophyte-mediated increases in Si concentrations, <em>H. armigera</em> was only affected by Si supply; growth rates decreased by 87% and most feeding efficiency indices decreased by at least 30%. Si supply also increased mandibular wear by 16%, which was negatively correlated with <em>H. armigera</em> growth rates. Cellular and humoral immunity of <em>H. armigera</em> were negatively affected by both Si and endophytes. Endophytic-loline alkaloid concentrations were unaffected by Si supply or herbivory, whereas herbivory increased peramine concentrations by 290%. </p> <p>To our knowledge, this is the first report of Si defences and <em>Epichloë</em>-endophyte-derived alkaloids compromising insect immunity <em>via</em> reduced melanisation response. Using tall fescue and <em>H. armigera</em>, our study suggests that deploying both physical (i.e. Si accumulation) and chemical (i.e. endophytic-alkaloids) defences acting against multiple insect herbivore traits, including feeding efficiency, growth and immunity, may be a successful defence strategy in temperate grasses. This multi-faceted defence may be particularly difficult for insect herbivores to overcome.</p>
Data and code for Caves, Dixit, Colebrook-Robjent, Hamusikili, Stevens, Thorogood, and Spottiswoode: Hosts elevate either within-clutch consistency or between-clutch distinctiveness of egg phenotypes in defence against brood parasites
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Plant carbohydrate-active enzymes in bamboo (Neosinocalamus affinis): identification, classification and function in lignocellulose biosynthesis in herbivore defence
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Silicon and Epichloë-endophyte defences in a model temperate grass diminish feeding efficiency and immunity of an insect folivore
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Effects of soil salinity on the expression of direct and indirect defences in wild cotton (Gossypium hirsutum)
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Data from: Disentangling the relative contributions of factors determining seed physical defence: a global-scale data synthesis
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Data from: The effect of root-associated microbes on plant growth and chemical defence traits across two contrasted elevations,
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Elevated atmospheric CO2 changes defence allocation in wheat but herbivore resistance persists
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