“…Workers, on the contrary, perform a wide range of cognitively demanding tasks, such as foraging, building of nest structures, feeding of dependent castes, egg and brood care, corpse management, and grooming 41 , 42 . In addition, they also ensure passive defence by building and repairing the nest structure, and active defence by biting, grasping and, in some cases, performing suicidal behaviours against enemies 36 , 43 – 45 . Figure 1 Body and brain morphology of sterile castes (workers and soldiers) of the higher neotropical termite Procornitermes araujoi .…”
Comparing the size of functionally distinct brain regions across individuals with remarkable differences in sensory processing and cognitive demands provides important insights into the selective forces shaping animal nervous systems. We took advantage of the complex system of worker-to-soldier differentiation in the termitid Procornitermes araujoi, to investigate how a profound modification of body morphology followed by an irreversible shift in task performance are translated in terms of brain structure and size. This behavioural shift is characterised by a reduction of the once wide and complex behavioural repertoire of workers to one exclusively dedicated to nest defence (soldiers). In accordance with soldier’s reduced cognitive and sensory demands, we show here that differentiation of workers into soldiers is associated with a size reduction of the mushroom body (MB) compartments, higher-order brain regions responsible for multimodal processing and integration of sensory information, as well as learning, memory, and decision-making. Moreover, in soldiers, we found an apparent fusion of the medial and lateral MB calyces likely associated with its volume reduction. These results illustrate a functional neuroplasticity of the MB associated with division of labour, supporting the link between MB size and behavioural flexibility in social insect workers.
“…Workers, on the contrary, perform a wide range of cognitively demanding tasks, such as foraging, building of nest structures, feeding of dependent castes, egg and brood care, corpse management, and grooming 41 , 42 . In addition, they also ensure passive defence by building and repairing the nest structure, and active defence by biting, grasping and, in some cases, performing suicidal behaviours against enemies 36 , 43 – 45 . Figure 1 Body and brain morphology of sterile castes (workers and soldiers) of the higher neotropical termite Procornitermes araujoi .…”
Comparing the size of functionally distinct brain regions across individuals with remarkable differences in sensory processing and cognitive demands provides important insights into the selective forces shaping animal nervous systems. We took advantage of the complex system of worker-to-soldier differentiation in the termitid Procornitermes araujoi, to investigate how a profound modification of body morphology followed by an irreversible shift in task performance are translated in terms of brain structure and size. This behavioural shift is characterised by a reduction of the once wide and complex behavioural repertoire of workers to one exclusively dedicated to nest defence (soldiers). In accordance with soldier’s reduced cognitive and sensory demands, we show here that differentiation of workers into soldiers is associated with a size reduction of the mushroom body (MB) compartments, higher-order brain regions responsible for multimodal processing and integration of sensory information, as well as learning, memory, and decision-making. Moreover, in soldiers, we found an apparent fusion of the medial and lateral MB calyces likely associated with its volume reduction. These results illustrate a functional neuroplasticity of the MB associated with division of labour, supporting the link between MB size and behavioural flexibility in social insect workers.
“…Although soldiers compose the defensive frontline in termite colonies (Noirot & Darlington, 2000), workers also play an important role in defensive tasks, especially in soldierless species or in those that present a low proportion of soldiers (Krishna & Araujo, 1969;Costa-Leonardo, 2004;Šobotník et al, 2010a). The defensive strategies that workers have developed are sometimes extreme, involving body wall rupture and the consequent release of a harmful secretion, which leads to death for both defender and predator (Prestwich, 1984;Šobotník et al, 2012;Poiani & Costa-Leonardo, 2016;Costa-Leonardo et al, 2019a, 2019b. When the body rupture is triggered by a gland, this process is referred to as autothysis (Sands, 1982).…”
Suicidal behavior in termite workers is an extreme defensive strategy, probably a consequence of having a low number of soldiers available in the colony and there being high predation from enemies. We investigated the suicidal mechanism in workers of the Neotropical termite Neocapritermes opacus, which involves salivary gland autothysis followed by body cuticle rupture and the release of a defensive secretion. Autothysis was triggered by a physical stimulus such as a soldier bite that causes the protrusion of the salivary acini, burst reservoirs, and foregut. Histochemical and ultrastructural analyses showed salivary acini composed of peripheral parietal cells and two types of central cells, types I and II. Type I cells are filled with large electron-lucent secretory vesicles, which reacted positively to bromophenol blue and xylidine-Ponceau tests, indicating the occurrence of proteins. Type II cells are elongated and display smaller apical secretory vesicles. Parietal cells present an intracellular canaliculus with dense microvilli and cytoplasm rich in mitochondria and large electron-dense vesicles, which may participate in the self-destructive mechanism. Worker suicidal behavior was previously reported for N. taracua and N. braziliensis. N. opacus is a new species in which a salivary weapon has been developed and factors contributing to this altruistic response are discussed.
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