Ecological drivers of body size evolution and sexual size dimorphism in short-horned grasshoppers (Orthoptera: Acrididae)

Abstract

Sexual size dimorphism (SSD) is widespread and variable in nature. Although female-biased SSD predominates among insects, the proximate ecological and evolutionary factors promoting this phenomenon remain largely unstudied. Here, we employ modern phylogenetic comparative methods on 8 subfamilies of Iberian grasshoppers (85 species) to examine the validity of different models of evolution of body size and SSD and explore how they are shaped by a suite of ecological variables (habitat specialization, substrate use, altitude) and/or constrained by different evolutionary pressures (female fecundity, strength of sexual selection, length of the breeding season). Body size disparity primarily accumulated late in the history of the group and did not follow a Brownian motion pattern, indicating the existence of directional evolution for this trait. We found support for the converse of Rensch’s rule across all taxa but not within the two most speciose subfamilies (Gomphocerinae and Oedipodinae), which showed an isometric pattern. Our results do not provide support for the fecundity or sexual selection hypotheses and we did not find evidence for significant effects of habitat use. Contrary to that expected, we found that species with narrower reproductive window are less dimorphic in size than those that exhibit a longer breeding cycle, suggesting that male protandry cannot solely account for the evolution of female-biased SSD in Orthoptera. Our study highlights the need to consider alternatives to the classical evolutionary hypotheses when trying to explain why in certain insect groups males remain small.

Characterization and analysis of full-length transcriptomes from two grasshoppers, Gomphocerus licenti and Mongolotettix japonicus

“…At the same time, Acrididae are extremely diverse in terms of size, body shape, feeding biology, ecology, geographical distribution and life-history traits 12,40,41 , and thus, this family has high potential to provide model candidates for functional genomics research. Although Acrididae are favored by many researchers for these reasons [42][43][44][45] , the lack of genome and transcriptome information has seriously hindered functional genomics studies of Acrididae. With the development of NGS technology, short-read RNA-seq has been widely applied in Acrididae functional genetic studies, although the transcripts must be assembled from short reads with assemblers such as Trinity 26 , SOAPdenovo-Trans 46 or Trans-ABySS 47 .…”

Steep converse Bergmann's cline in a carrion beetle: between‐ and within‐population variation in body size along an elevational gradient

“…In insects, body size frequently differs between males and females (sexual size dimorphism, SSD), with females being the larger sex in most species (Teder & Tammaru, ; Blanckenhorn et al ., ; Chown & Gaston, ; García‐Navas et al ., ). The difference in body size between sexes is likely caused by different net selection pressures acting on males and females (Blanckenhorn, ).…”

Genomic data reveal deep genetic structure but no support for current taxonomic designation in a grasshopper species complex

“…The grasshopper subgenus Dreuxius Defaut, 1988 (genus Omocestus , Bolívar, 1878) is a complex of nine recently diversified species distributed in the Iberian Peninsula (six species) and northwestern Africa (three species; Cigliano, Braun, Eades, & Otte, ; García‐Navas, Noguerales, Cordero, & Ortego, ). Most taxa have allopatric distributions and are often isolated at high elevations in different mountain systems (Cigliano et al, ).…”