Phylogeny of locusts and grasshoppers reveals complex evolution of density-dependent phenotypic plasticity

Abstract

Locusts are grasshoppers that can form dense migrating swarms through an extreme form of density-dependent phenotypic plasticity, known as locust phase polyphenism. We present a comprehensive phylogeny of the genus Schistocerca, which contains both non-swarming grasshoppers and swarming locusts. We find that the desert locust, S. gregaria, which is the only Old World representative of the genus, is the earliest diverging lineage. This suggests that the common ancestor of Schistocerca must have been a swarming locust that crossed the Atlantic Ocean from Africa to America approximately 6 million years ago, giving rise to the current diversity in the New World. This also implies that density-dependent phenotypic plasticity is an ancestral trait for the genus. Through ancestral character reconstruction of reaction norms, we show that colour plasticity has been largely retained in most species in the genus, but behavioural plasticity was lost and regained at least twice. Furthermore, we show that swarming species do not form a monophyletic group and non-swarming species that are closely related to locusts often express locust-like plastic reaction norms. Thus, we conclude that individual reaction norms have followed different evolutionary trajectories, which have led to the evolutionary transition between grasshoppers and locusts - and vice versa.

Too much too many: comparative analysis of morabine grasshopper genomes reveals highly abundant transposable elements and rapidly proliferating satellite DNA repeats

“…For grasshoppers and crickets (Orthoptera), high-throughput sequencing analyses detected 316 satDNA families in ~20 species [12,21,[27][28][29][30][31][32]. Because of the large divergence time between these Orthopteran species (73-224 millions years, Myr) [33], none of these 316 satDNA families showed interspecific homology, except for partial sequence homology within satDNAs of Gryllus cricket species [27] (unknown divergence time) and within Schistocerca grasshopper species [21] with divergence time < 8 Myr [34]. Because homology between satDNAs often cannot be detected between distantly related species due to rapid sequence divergence, an explicit examination of the library hypothesis requires well-annotated genomes of closely related species.…”

Machine learning approach to locate desert locust breeding areas based on ESA CCI soil moisture

“…6 Alike to other species in the animal kingdom, desert locusts have a phase polyphenism that implies drastic changes when population density increases, either in adult or nymph stage. 2,7,8 Even though behavioral gregarization may occur within hours, 9 it takes several generations to fully display gregarious characters. 10 The phase transition induces physiological changes in lifespan, metabolism, immune responses, and reproductive physiology.…”

Identifying Desert locust breeding areas by means of Earth Observation in Mauritania

“…Desert locust is the earliest diverging species among the genus Schistocerca and the unique one settled in Africa, what indicates its high adaptability to the local conditions. Unlike other species of the same genus, it has kept some of its original traits such as the ability to change their behavior (Song et al, 2017).…”

“…Egg mortality can be caused by several factors that vary from habitat to habitat. Source: Symmons & Cressman, 2001 Alike other species in the animal kingdom, desert locust has a phase polyphenism that implies drastic changes when population density increases, either in adult or nymph stage (Pener & Simpson, 2009;Simpson et al, 2011;Song et al, 2017). Even though behavioural gregarization may occur within hours (Ellis, 1962), it takes several generations to fully display gregarious characters (Ernst et al, 2015).…”

“…Outbreaks might not end up being a plague and it may take at least one year to be established as so (Cressman, 2008). According to (Song et al, 2017), desert locust is the earliest diverging species among the genus Schistocerca and the unique settled in Africa. This study suggests that the ancestral Schistocerca species was rather similar with respect to the current desert locust, indicating high adaptability to local conditions.…”