Mitochondrial DNA and phylogeography of the grasshopper Trimerotropis pallidipennis in relation to clinal distribution of chromosome polymorphisms

Abstract

Trimerotropis pallidipennis is an American grasshopper whose South American populations are polymorphic for pericentric inversions. Colonization of southern latitudes was by North American grasshoppers with basic chromosome arrangements, presumably along the Andean dry lands of South America. In Argentina, the frequencies of some of the rearrangements are correlated with geographical and climatic variables, following similar patterns among different ecological gradients, and are probably maintained by geographically variable coefficients of selection. Restriction site variation of mitochondrial DNA is used as a tool for determining the species history in relation to the formation of clines. Populations located along an altitudinal gradient, and others outside the cline, are analysed through phylogeographical studies. There is no strong geographical orientation in the unrooted tree connecting all 17 mitochondrial DNA haplotypes found. Many of them are present in most of the populations analysed, indicating high gene flow. The fact that there is no obvious differentiation in haplotype distribution between both extremes of the cline nor between chromosomally differentiated populations shows that the cline is not the result of a hybrid zone and reinforces the selection hypothesis. The estimation of the overall nucleotide divergence between the hypothetical ancestral haplotype and the other molecules shows that T. pallidipennis haplotypes started diverging from each other about 3 Myr ago. This result is in agreement with the time when the Isthmus of Panamá rose (2-3 Myr ago), probably favouring the migration of many species between both hemispheres.

B Chromosome Polymorphism in Maize Landraces: Adaptivevs. Demographic Hypothesis of Clinal Variation

“…Altitudinal and longitudinal clines of morphological traits, or allelic frequencies, have long been interpreted as evidence of selection. However, clines can also be produced by the interplay between drift and spatially restricted gene flow (isolation by distance) or by admixture between previously isolated populations that have come into secondary contact (Confalonieri et al 1998;Storz and Dubach 2004). One means of distinguishing between adaptive vs. nonadaptive causes of clinal variation is to compare the relative levels of between-population divergence in the trait under study and in neutral DNA markers (Storz 2002).…”

Cytogeography and the evolutionary significance of B chromosomes in relation to inverted rearrangements in a grasshopper species

“…In this case, multiple regression analyses with latitude and longitude were performed, and other environmental variables such as minimum temperature, humidity and precipitation were also evaluated (Table 1). It was demonstrated that three inversions (4AI, 7SM2, 8SM4) correlate simultaneously with altitude, latitude and minimum temperature, and two other inversions (6M and 8SM3) correlate with longitude and humidity, in such a way that the frequency distribution of these chromosome rearrangements could be predicted for unstudied regions (Colombo and Confalonieri, 1996; individual frequencies for each chromosome pair can be found in Confalonieri and Colombo, 1989;Confalonieri, 1994;Colombo and Confalonieri, 1996;Matrajt et al, 1996;Confalonieri et al, 1998). In other words, they follow similar patterns among independent geographic areas with similar ecological gradients.…”

“…According to White (1973), the colonization presumably descended along the Andean dry lands of South America and was probably made by North American T. pallidipennis, carrier of a basic chromosome arrangement. This migration could have taken place 2-3 Myr ago, when the Isthmus of Panamá rose, favoring the movement of many insects between both hemispheres (Confalonieri et al, 1998). In southern latitudes, this species became adapted to a wider ecological range, extending its distribution to lower altitudes and more humid habitats, where pericentric inversion sequences appear in polymorphic or even fixed state, B chromosomes being present or absent.…”

“…In T. pallidipennis, the cytogeographic analysis suggests that selection of some sort is more likely to act because of the repetition patterns of variation observed over a wide geographic area and their stability over time (Confalonieri et al, 1998). If current clines were hybrid zones, selection could be acting against recombinant genotypes based on inversion types.…”

Biochemical characterisation of α-amylase in two aphid species, Aphis fabae Scopoli (Hemiptera: Aphididae) and A. gossypii Glover (Hemiptera: Aphididae)

“…If digestion of food in the aphid gut happens, then the aphids, like the other species of chewing insects, are prone to enzyme inhibitors. Using enzyme inhibitors to control insect pest has already been demonstrated to be an important system for the insect pest control since these inhibitors have detrimental effects on the insect growth and development by interfering in food digestion (Confalonieri et al 1998). α-Amylase activity has been described from different species of several insect orders including Orthoptera, Coleoptera, Hymenoptera, Diptera, Lepidoptera, and Hemiptera (Baker & Woo 1985;Terra et al 1988;Mendiola-Olaya et al 2000;Zeng & Cohen 2000;Oliveira-Neto et al 2003;Kazzazi et al 2005;Safaei-Khorram et al 2010;.…”