Revealing hidden density-dependent phenotypic plasticity in sedentary grasshoppers in the genus Schistocerca Stål (Orthoptera: Acrididae: Cyrtacanthacridinae)

Comparative analysis of phenotypic plasticity sheds light on the evolution and molecular underpinnings of locust phase polyphenism

“…Using a nonparametric multivariate analysis of behavioural traits, we found a significant interaction effect between species and rearing density (Supplementary Table S1 ), indicating that the four species differed in the magnitude of behavioural reaction norms. We subsequently compared each variable separately across species and rearing densities with a two-step hurdle model, involving logistic regression of zero and nonzero values and modeling of nonzero data 31 (Supplementary Fig. S2 , Tables S2 , S3 ).…”

“…Locust phase polyphenism is one of nature’s most striking examples of coordinated alternative phenotypes involving a myriad of density-dependent plastic reaction norms 3 , 19 . Recent studies have shown that some of these individual reaction norms are not only present in locust species, but also in closely-related non-swarming species 26 , 30 , 31 , 33 . This suggests that they likely evolved independently along the phylogeny 26 , and became coordinated in locust species.…”

“…At low density, nymphs are green, but at high density, they show a combination of yellow and black patterns, which advertises their toxicity 32 , 73 . It has been hypothesised that the ancestral plasticity, or at least the ancestral genetic variation for expressing density-dependent colour plasticity, could have been retained in sedentary Schistocerca species 31 , 73 , which can become a starting point for the evolution of novel traits. Indeed, many contemporary Schistocerca species retain hidden density-dependent phenotypic plasticity, which is difficult to observe in nature, but can be induced in the lab 30 , 31 .…”

“…These first three species belong to the same clade 26 , are morphologically very similar to each other 41 , 42 , and can even hybridise in the lab and produce viable offspring 43 (Foquet and Song, unpublished data). The fourth species is S. nitens (Thunberg), a sedentary grasshopper which is broadly representative of most non-swarming species in the genus 25 , 26 , 31 , 35 , 44 and serves as an outgroup, as it belongs to a different clade than the other three species 26 and differs morphologically 45 , 46 . We first measure variation in the extent of density-dependent phenotypic plasticity in each of the four species by quantifying behavioural reaction norms (activity level, attraction to conspecifics) and morphological reaction norms (nymphal colouration, size, and a morphometric ratio) after experimentally isolating and crowding the insects during nymphal development.…”

Desert locust and its management in Nepal: a review

“…Body colour of solitarius nymphs serves as camouflage in its natural environment (Tanaka et al, 2012) whereas gregarious locusts produce colour pattern which serves as warning coloration (aposematism) to vertebrate predators, signalling that the locust is toxic prey by virtue of feeding on noxious plant (Sword et al, 2000). F/C ratio (length of hind femur/width of head or caput) of gregarious is smaller than solitarious whereas E/F ratio (Elytron/femur) is larger in gregarious (Stower et al, 1960;Urarov, 1966;Symmons, 1969;Kilpatrick et al, 2019).…”