Parallel adaptive patterns of allozyme and inversion polymorphisms on an ecological gradient

Abstract

Trimerotropis pallidipennis is an American grasshopper whose South American populations are polymorphic for pericentric inversions. The frequencies of some of these rearrangements are correlated with geographical and climatic variables, following similar patterns among different ecological gradients. Hence, this species constitutes a promising model in which the evolutionary significance of inversion systems can be analysed as possible sources of coadapted groups of linked genes. Six samples collected along an altitudinal gradient were assayed jointly for genetic and chromosomal variation. Interestingly, the phenograms constructed with Nei's genetic distances obtained from allozyme and chromosome data were almost identical. This result is produced mainly by esterase loci variation, probably as a consequence of linkage disequilibrium. The evolutionary significance of this association is briefly discussed.

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

“…Because testes were not available from the population of Quilmes, data from Ampimpa are given instead, a locality which is only 25 km from Quilmes and almost at the same altitude and latitude. All four populations along the altitudinal cline (Puente del Inca, Uspallata, Tunuyán and Observatorio) showed chromosome frequencies that correlate very significantly with altitude (Matrajt et al, 1996). Previous macrogeographical studies have revealed that the altitude at which monomorphism for standard sequences is reached, decreases with increasing latitude as a consequence of minimum temperature dependence (Colombo & Confalonieri, 1996).…”

“…In this latter case, deterministic forces may not be involved in the formation of clines, but are necessary for a long continuation of this pattern of variation. In T. pallidipennis, selection of some sort is very likely to be acting, because of the repetition of patterns of variation of inversion polymorphisms over a wide geographical area and their stability over time (Confalonieri & Colombo, 1989;Confalonieri, 1994;Colombo & Confalonieri, 1996;Matrajt et al, 1996). If the current clines were primary hybrid zones, selection could be acting against recombinant genotypes based on inversion types.…”

“…From here, it would have extended its distribution to lower altitudes (Vaio et al, 1979), where inversion sequences appear in polymorphic or fixed states. Chromosome clines observed in T. pallidipennis do not obviously fit any hybrid-zone model and are most probably maintained by geographically variable coefficients of selection (Matrajt et al, 1996).…”

“…The number of individuals analysed is indicated in parentheses. PI, U, Tu: data from Matrajt et al (1996). Q: data are from Ampimpa (Confalonieri, 1994) near to the Quilmes sample location.…”

“…South American populations of Trimerotropis pallidipennis (2n = 23, X0 in males), polymorphic for three to seven pericentric inversions in four medium-sized chromosome pairs, exhibit a clinal distribution of inversion polymorphisms (Confalonieri & Colombo, 1989;Confalonieri, 1994;Matrajt et al, 1996). In fact, three inversions (4 AI, 7 SM2, 8 SM4) correlate simultaneously with altitude, latitude and minimum temperature, and two other inversions (6 M and 8 SM4) correlate with longitude and humidity in such a way that the frequency distribution of these chromosome rearrangements could be predicted for previously unstudied regions (Colombo & Confalonieri, 1996).…”