Subspecific taxonomy of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae), based on molecular and morphological characters

Abstract

We evaluated the validity of the subspecific designation for Schistocerca gregaria gregaria (Forskål) and Schistocerca gregaria flaviventris (Burmeister), isolated in distinct regions along the north-south axis of Africa. Towards this goal, we assessed the variation of multiple morphological and molecular traits within species. We first used elliptic Fourier and landmark-based relative warps analyses to compare the size and shape of two internal and two external structures of male genitalia. We provide a discriminant function which classified the specimens with 100% accuracy and selected shape elements of the external structures only (cercus and epiproct). We also tested eight molecular markers, and because of either absence of variation or contamination by mitochondrial DNA (mtDNA)-like sequences, we used a clone-and-sequence analysis of the standard cytochrome c oxidase subunit I mitochondrial DNA barcode only. We differentiated 185 true mitochondrial sequences from 66 mitochondrial DNA-like sequences, most of which were from S. g. gregaria specimens. On the dataset of mitochondrial origin, we identified three characteristic point mutations that diagnosed the two allopatric subspecies with 94% accuracy. Minimum spanning network and parsimony tree analyses identified S. g. flaviventris as a monophyletic lineage distinct from the nominate subspecies. Accordingly, microsatellite data indicate rarely occurring admixture events only, showing that independent evolutionary history is the norm.

Climate‐driven geographic distribution of the desert locust during recession periods: Subspecies’ niche differentiation and relative risks under scenarios of climate change

“…Indeed, a histogram of the four climatic gradients used in these analyses shows that the climatic conditions in the southern study area are a narrow subset of the climatic conditions present in the northern portion of the study area (Appendix S4). As there is molecular evidence for a southern colonization of Africa from the northern region (Chapuis et al, 2016) this result suggests that, in spite of contrasted selective pressures in the more recent southern distribution, the climatic niche has been conserved throughout evolutionary time. This is in agreement with a review study by Peterson (2011), who found that the evidence for niche conservatism was strong when separating studies that dealt with small temporal scales, including scales of speciation events.…”

“…The desert locust is a polytypic species distributed in two distinct geographic regions in each side of the tropical forests and savannahs of Central Africa (Chapuis et al., ; Dirsh, ; Uvarov, ). The nominal subspecies, S. g. gregaria , is the most well‐known, spanning from West Africa to Southwest Asia (latitudes 5°N–33°N; 32 million km²).…”

“…The desert locust is a polytypic species distributed in two distinct geographic regions in each side of the tropical forests and savannahs of Central Africa (Chapuis et al, 2016;Dirsh, 1953;Uvarov, 1977).…”

A young age of subspecific divergence in the desert locustSchistocerca gregaria, inferred by ABC Random Forest

“…All 472 scenarios assumed a northern origin for the common ancestor of the two subspecies and a 473 subsequent southern colonization of Africa. This assumption is supported by recent mitochondrial 474 DNA data showing that S. g. gregaria have higher levels of genetic diversity and diagnostic bases 475 shared with outgroup and congeneric species, whereas S. g. flaviventris clade was placed at the 476 apical tip within the species tree (Chapuis et al 2016). In agreement with this assumption, 477 preliminary analyses based on observed data showed a low support for a southern origin for the 478 common ancestor of the two subspecies and a subsequent northern colonization of Africa (results 479 not shown).…”

“…The southern populations of the desert locust are termed S. g. flaviventris 103and are geographically separated by nearly 2,500 km from populations of the nominal subspecies 104 from northern Africa, S. g. gregaria (Uvarov 1977). The isolation of S. g. flaviventris and S. g. 105 gregaria lineages was recently supported by highlighting distinctive mitochondrial DNA 106 haplotypes and male genitalia morphologies (Chapuis et al 2016). Yet, the precise history of 107 divergence remains elusive.…”