Silicon fertilisation affects morphological and immune defences of an insect pest and enhances plant compensatory growth

Herbivorous insects have evolved various anti-predator defences, including morphological, behavioural, and immune defences, which can make biocontrol of herbivorous pests challenging. Silicon (Si) accumulation in plants is a potent physical defence against mandibulate insects. However, it remains uncertain how Si affects the anti-predator defences of insect herbivores and plant defences following herbivory. We grew the model grass, Brachypodium distachyon, hydroponically with (+Si) or without (–Si) Si and investigated the plant-mediated effects of Si on the anti-predator defences of the cotton bollworm, Helicoverpa armigera, integrating morphological (i.e. integument resistance and thickness), behavioural, and immune defences. We also examined the effects of Si on plant compensatory growth and leaf trichome production. Larval growth, leaf consumption, and integument resistance were lower when feeding on +Si plants compared to when feeding on –Si plants. Larval integument thickness, defensive behaviours, haemocyte density, and lysozyme-like activity in the haemolymph were unaffected by Si. Larvae fed on +Si plants had higher haemolymph phenoloxidase (PO) and total-PO activities than larvae fed on –Si plants, although this did not enhance the melanisation response of larvae. Furthermore, Si supplies increased plant compensation for herbivory and constitutive trichome production, whereas herbivory induced trichome production only on –Si plants. We provide the first evidence for plant-mediated effects of Si on anti-predator defences of an insect herbivore. We suggest that the lower integument resistance of larvae when feeding on Si-supplemented plants could contribute to their vulnerability to natural enemies and that high PO activity may impose fitness costs (e.g. delayed development).

Silicon Fertilisation Affects Morphological and Immune Defences of an Insect Pest and Enhances Plant Compensatory Growth

Insect herbivores employ various defences, including morphological, behavioural, and immune responses against their natural enemies (e.g., predators, parasitoids) which can make biocontrol of herbivorous pests challenging. Silicon (Si) accumulation in plants is a potent physical defence against herbivores. However, it remains uncertain how Si affects pest defences to their enemies and plant defences following herbivore attack. We grew the model grass, Brachypodium distachyon, hydroponically with (+Si) or without (–Si) Si and investigated the impacts of Si on morphological (integument resistance and thickness), behavioural (flee, headrear, thrash, and regurgitation), and immune defences of the cotton bollworm, Helicoverpa armigera. We further examined the effects of Si on plant compensatory growth and leaf trichome production. Larval growth, leaf consumption, and integument resistance were lower when feeding on +Si plants compared to when feeding on –Si plants. Larval integument thickness, defensive behaviours, hemocyte density and lysozyme-like activity in the hemolymph were unaffected by Si. Larvae fed on +Si plants had higher hemolymph phenoloxidase (PO) and total-PO activities than larvae fed on –Si plants, although this did not enhance larval melanisation response. Furthermore, Si supply increased plant compensatory growth and constitutive trichome production whereas herbivory induced trichome production only on –Si plants. We provide the first evidence that Si fertilisation affects insect defences in addition to reducing their growth and feeding. Lower integument resistance might enhance larval vulnerability to parasitoids and pathogens and higher PO activities could impose fitness costs (e.g., delayed development), potentially increasing overall insect susceptibility to enemies.

Hippocampal-hypothalamic circuit controls context-dependent innate defensive responses

Preys use their memory - where they sensed a predatory threat and whether a safe shelter is nearby - to dynamically control their survival instinct to avoid harm and reach safety. However, it remains unknown which brain regions are involved, and how such top-down control of innate behaviour is implemented at the circuit level. Here, we show that the anterior hypothalamic nucleus (AHN) is best positioned to perform this task as an exclusive target of the hippocampus (HPC) within the medial hypothalamic defense system. Selective optogenetic stimulation and inhibition of hippocampal inputs to the AHN revealed that the HPC→AHN pathway not only mediates the contextual memory of predator threats but also controls the goal-directed escape by transmitting information about the surrounding environment. These results reveal a new mechanism for experience-dependent, top-down control of innate defensive behaviours.

Threat-anticipatory psychophysiological response is enhanced in youth with anxiety disorders and correlates with prefrontal cortex neuroanatomy

Background: Threat anticipation engages neural circuitry that has evolved to promote defensive behaviours; perturbations in this circuitry could generate excessive threat-anticipation response, a key characteristic of pathological anxiety. Research into such mechanisms in youth faces ethical and practical limitations. Here, we use thermal stimulation to elicit pain-anticipatory psychophysiological response and map its correlates to brain structure among youth with anxiety and healthy youth. Methods: Youth with anxiety (n = 25) and healthy youth (n = 25) completed an instructed threat-anticipation task in which cues predicted nonpainful or painful thermal stimulation; we indexed psychophysiological response during the anticipation and experience of pain using skin conductance response. High-resolution brain-structure imaging data collected in another visit were available for 41 participants. Analyses tested whether the 2 groups differed in their psychophysiological cue-based pain-anticipatory and pain-experience responses. Analyses then mapped psychophysiological response magnitude to brain structure. Results: Youth with anxiety showed enhanced psychophysiological response specifically during anticipation of painful stimulation (b = 0.52, p = 0.003). Across the sample, the magnitude of psychophysiological anticipatory response correlated negatively with the thickness of the dorsolateral prefrontal cortex (pFWE < 0.05); psychophysiological response to the thermal stimulation correlated positively with the thickness of the posterior insula (pFWE < 0.05). Limitations: Limitations included the modest sample size and the cross-sectional design. Conclusion: These findings show that threat-anticipatory psychophysiological response differentiates youth with anxiety from healthy youth, and they link brain structure to psychophysiological response during pain anticipation and experience. A focus on threat anticipation in research on anxiety could delineate relevant neural circuitry.

Defensive over Climate Change? Climate Shame as a Method of Moral Cultivation

The climate crisis is an enormous challenge for contemporary societies. Yet, public discussions on it often lead to anger, mocking, denial and other defensive behaviours, one prominent example of which is the reception met by the climate advocate Greta Thunberg. The paper approaches this curious phenomenon via shame. It argues that the very idea of anthropogenic climate change invites feelings of human failure and thereby may also entice shame. The notion of “climate shame” is introduced and distinguished from “climate guilt”. Whereas climate guilt prioritises the flourishing of the environment and is focused on actions and morality, climate shame is concerned with human identity and selfhood. The paper then explores whether shame is a morally destructive or constructive emotion. Making use of both psychological and philosophical literature on shame, it argues that although shame faces many challenges that question its usefulness in moral pedagogy, these challenges can be met with “moral maturity”—moreover, following a utilitarian approach, the overall benefits of climate shame can justify its costs to individuals. My argument is that climate shame holds the potential of being a highly effective moral psychological method of persuasion, capable of inviting wholesale critical reflection on current, environmentally damaging practices and cultivation of more virtuous ways of co-existing with the rest of the natural world and other species.

Evolution of macroglands and defensive mechanisms in Leiuperinae (Anura: Leptodactylidae)

Anurans show a wide variety of anti-predator mechanisms, and the species of the Neotropical clade Leiuperinae display several of them. Most species of Edalorhina, Physalaemus and Pleurodema show eyespots, hidden bright colours, macroglands in a inguinal/lumbar position, defensive behaviours and/or chemical defence. We conducted a histological analysis of dorsal and lumbar skin and revised the colour patterns, defensive behaviours and glandular secretions to study the diversity and evolution of anti-predator mechanisms associated with macroglands. We describe 17 characters and optimize these in a phylogenetic hypothesis of Leiuperinae. In the most recent common ancestor of Edalorhina + Engystomops + Physalaemus + Pleurodema, a particular type of serous gland (the main component of macroglands) evolved in the lumbar skin, along with the absence of the Eberth–Katschenko layer. A defensive behaviour observed in leiuperines with macroglands includes four displays (‘crouching down’ behaviour, rear elevation, body inflation and eye protection), all present in the same ancestor. The two elements associated with aposematism (hidden bright colours and eyespots) evolved independently in several species. Our results provide phylogenetic evidence for the startle-first hypothesis, which suggests that behavioural displays arise as sudden movements in camouflaged individuals to avoid predatory attacks, before the origin of bright coloration.