An adaptive pattern of inversion polymorphisms in Trimerotropis pallidipennis. Correlation with environmental variables: an overall view

COLOMBO, P.C. ; CONFALONIERI, V.A

HEREDITAS

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 1996 vol. 125 p. 284 - 290

0018-0661

Correlation of a trait with environmental factors is a common means of measuring natural selection in natural populations. If the same correlation is seen in independent groups of populations over a wide area, selection is then a likely explanation. Natural populations of T. pallidipennis (2n = 23, X0) — polymorphic for 3-7 pericentric inversions in 4 medium-sized pairs — show altitudinal clines for 9 chromosome sequences over a wide area in Argentina. Joint analysis has shown correlations with latitude and longitude. In order to identify the climatic variables responsible for this clinal variation, 7 populations sited on an altitudinal gradient were scored for inversion frequency. Multiple regression analyses among chromosome frequencies and environmental variables do not only confirm the consistency of altitudinal gradients for all sequences but also identify minimum temperature (Tmin) as the main climatical variable responsible for this pattern, to such extent that populations with extreme Tmin values are monomorphic. In addition, some sequences are correlated with humidity. These results do not only reinforce the hypothesis of a selective origin for cline maintenance but are also a new example of monomorphism associated to marginal environments. Three inversions (4A1, 7SM2, 8SM4) correlate simultaneously with altitude, latitude, and minimum temperature; two other inversions (6M and 8SM4) correlated with longitude and humidity, because this variable decreases westward in Argentina. The identification of the causes of clinal variation leads to a predictive pattern of inversion distribution for still unexplored regions.