Chromosomal Influences on Life-History Variation Along an Altitudinal Transect in Drosophila robusta

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Abstract
Life-history variation was associated with the inversion polymorphisms on three of five of the chromosomal arms in experimental populations of Drosphila robusta. Karyotypic differences were associated with variation in egg-to-adult developmental time (DEVT), age at first reproduction, and early fecundity, but not adult longevity. Variations in DEVT among gene arrangements on the left arm of the second chromosome were changed by temperature, but consistently across populations. Some low-elevation karyotypes were associated with shorter DEVT in warmer-temperature conditions. Third-chromosome karyotypes were also associated with differences in DEVT, but in a population-specific way, indicating variation in genic contents of third-chromosome gene arrangements among populations along this elevational transect. Third-chromosome gene arrangements were also associated with correlated sets of fitness characters. Not all life-history differences suggested adaptation to changes in elevation, but differences in DEVT were correlated with clinal variation in second-chromosome gene arrangements. Since life-history differnences were associated with karyotypic variation, changes in inversion frequencies through time may influence the course of life-history evolution for inversions with genic contents that are relatively uniform from population to population. Genetic variation in life histories can be preserved by inversion polymorphisms if alternative gene arrangements contain contrasting sets of alleles. Conversely, these data also suggest through which components of fitness long-term changes in gene-arrangement frequencies, previously documented in D. robusta, may be mediated.