Morphometric differentiation in Cornops aquaticum (Orthoptera: Acrididae): associations with sex, chromosome, and geographic conditions.
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.
Laboratorio de Genética de la Estructura Poblacional, Departamento de Ecología, Genética y Evolución, Instituto IEGEBA (CONICET-UBA), Facultad de Ciencias, Exactas y Naturales, Universidad de Buenos Aires, Argentina Present address: Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA, Buenos Aires, Argentina mlucianar@hotmail.com.
María Luciana
ML
Romero
Laboratorio de Genética de la Estructura Poblacional, Departamento de Ecología, Genética y Evolución, Instituto IEGEBA (CONICET-UBA), Facultad de Ciencias, Exactas y Naturales, Universidad de Buenos Aires, Argentina Present address: Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA, Buenos Aires, Argentina.
Pablo César
PC
Colombo
Laboratorio de Genética de la Estructura Poblacional, Departamento de Ecología, Genética y Evolución, Instituto IEGEBA (CONICET-UBA), Facultad de Ciencias, Exactas y Naturales, Universidad de Buenos Aires, Argentina Present address: Intendente Güiraldes 2160, Ciudad Universitaria, C1428EGA, Buenos Aires, Argentina.
María Isabel
MI
Remis
D000818:Animals; D001118:Argentina; D001699:Biometry; D049628:Body Size; D059006:Chromosomes, Insect; D005260:Female; D006110:Grasshoppers / Q000502:physiology*; D059785:Karyotype; D008297:Male; D058974:Phylogeography; D045483:Rivers; D012727:Sex Characteristics
chromosome rearrangement; morphometric variation; semiaquatic grasshopper; sex dimorphism