Morphometric Differentiation in Cornops aquaticum (Orthoptera: Acrididae): Associations With Sex, Chromosome, and Geographic Conditions

Abstract

The water-hyacinth grasshopper Cornops aquaticum (Bruner) (Orthoptera: Acrididae) is native to South America and inhabits lowlands from southern Mexico to central Argentina and Uruguay. This grasshopper feeds and lays eggs on species from the genera Eichhornia and Pontederia. Particularly, Eichhornia crassipes is considered “the world’s worst water weed,” and the release of C. aquaticum was proposed as a form of biological control. Morphometric variation on the chromosomally differentiated populations from the middle and lower Paraná River and its possible association with geographic, sex, and chromosomal conditions was analyzed. Significant phenotype variation in C. aquaticum population was detected. C. aquaticum presents body-size sexual dimorphism, females being bigger than males. Female-biased sexual size dimorphism for all five analyzed traits was detected. The assessment of variation in sexual size dimorphism for tegmen length showed that this trait scaled allometrically, indicating that males and females did not vary in a similar fashion. The detected allometry was consistent with Rensch’s rule demonstrating greater evolutionary divergence in male size than in female size and suggests that males are more sensitive to environmental condition. The analysis of morphometric variation in the context of chromosome constitution showed that the presence of fusion 1/6 was related to body-size variation. Fusion carriers displayed bigger body size than standard homozygotes. Besides, a positive relationship between tegmen length and the number of fused chromosomes was detected, showing a chromosome dose effect. Because the highest frequency of fusions has been found in the lower Paraná River, a marginal environment for this species, the results found would support the hypothesis that some supergenes located in the fusions may be favored in the southern populations, thus contributing to the establishment and maintenance of the polymorphism.

Geographic variation in wing size and shape of the grasshopper Trilophidia annulata (Orthoptera: Oedipodidae): morphological trait variations follow an ecogeographical rule

“…These patterns of ecological variation are typical examples of Bergmann or converse-Bergmann clines. The debate on whether the size of grasshoppers along altitudinal or latitudinal gradients follows Bergman’s rule is ongoing 35 36 37 38 39 . However, researchers are more interested in the relationship between morphological variation and environmental factors over a large geographic area.…”

Phenotypic pattern over centric fusion clinal variation in the water-hyacinth grasshopper, Cornops aquaticum (Orthoptera: Acrididae)

“…Moreover, a preliminary morphometric study of two polymorphic populations indicates an association between fusion 1/6 and body size (Romero et al, 2014). As one of the centric fusions is correlated with body size-related variables (Romero et al, 2014), we suggest that the increasing cline for fusion frequency in the southern populations could be the indirect result of selection for increased body size (Colombo & Remis, 2015).…”

“…Moreover, a preliminary morphometric study of two polymorphic populations indicates an association between fusion 1/6 and body size (Romero et al, 2014). As one of the centric fusions is correlated with body size-related variables (Romero et al, 2014), we suggest that the increasing cline for fusion frequency in the southern populations could be the indirect result of selection for increased body size (Colombo & Remis, 2015). However, we did not reject the operation of other factors, such as a correlation with as yet undisclosed environmental variables or, given the geographic marginal situation of the polymorphic populations, stochastic factors.…”

“…In fact, in Orthoptera most of the species so far studied follow the converse Bergmann's rule, whereby body size decreases with latitude or altitude, but some report they follow Bergmann's rule, with larger individuals at high latitudes and altitudes (for review see Blackburn et al, 1999;Blanckenhorn & Demont, 2004;Whitman, 2008). Colombo & Remis (2015), using a continent-wide morphometric dataset published by Adis et al (2008) and Romero et al (2014), which includes several South-American populations of C. aquaticum distributed between lat. 10°N and 35°S, suggest that this species' body size-related variables are correlated positively with latitude.…”

Geometric Morphology and Population Genomics Provide Insights into the Adaptive Evolution of Apis Cerana in Changbai Mountain

“…The morphology and size of insect wings can be used as indicators of environmental stress or environmental conditions [56,57]. We found that the differences between the wing morphology of Changbai Mountain population and the average wing morphology of A. cerana were stably concentrated in several sites.…”