The Yank of Dobzhansky’s Bequest

Abstract

Dobzhansky studied mechanisms of balancing selection using systems of inversions in Drosophila and he soon found that changes in inversion frequencies along generations in experimental populations conformed to the expectation for a simple model of heterosis. However, other more complex modes of selection, like rare male advantage, were later found to affect the maintenance of inversion polymorphisms. Here we show that a more realistic (and complex) model than heterosis-integrating all known fitness component estimates obtained in independent experiments for the ST/CH system of inversions in Drosophila pseudoobscura-not only conforms to but actually also predicts the inversion frequencies. This concludes this line of work and points to other selection mechanisms than heterosis that were also considered by Dobzhansky-frequency-and sex-dependent selection-as potential mechanisms of balancing selection responsible for the maintenance of the inversion polymorphisms in Drosophila.Keywords Dobzhansky Á Mechanisms of balancing selection Á Fitness components Á Drosophila Á Heterosis Theodosius Dobzhansky made good use of his diverse scientific background to become the focal point of the Synthetic Theory of Evolution. He successfully condensed

Selection and inertia in the evolution of holocentric chromosomes in sedges (Carex, Cyperaceae)

“…Chromosome rearrangements have previously been argued to be adaptatively significant in Carex (Faulkner, 1972; Luceño & Castroviejo, 1991; Bell, 1982), as they have been for numerous other organisms (e.g. Alvarez‐Castro & Alvarez, 2005; Butlin, 2005; Alvarez‐Castro & Carlborg, 2008; Hoffmann & Rieseberg, 2008). The current study is the first to demonstrate that chromosome number itself – which may be a result of many independent and different rearrangements – may be in part a product of correlation with life‐history traits or (more weakly supported) adaptation to the environment.…”

Within-Niche Constant Selection ofDrosophilaInversions?

“…As pointed out above, numerous studies found complex modes of selection to occur in the maintenance of Drosophila inversion polymorphisms reviewed in [19–21]. Furthermore, the stage-, sex-, and frequency-dependent fitness estimates obtained in competition experiments of Drosophila pseudoobscura have been successfully used to replicate the trajectories of frequencies of experimental populations along generations [25], which supports those multifaceted fitness estimates—instead of the minimal MCV with heterosis—as the selection mechanisms underlying the maintenance of inversion polymorphisms in experimental populations. Similarly, it cannot be argued that selection in heterogeneous environments is the only force maintaining the polymorphisms, since other balancing forces (different from heterosis) are known to act within niches.…”

“…This strategy has recently shown a more than reasonably good fit of predicted-to-observed trajectories, using from the last ones only their starting points [25, 26]. However, this positive result is not sufficient for completely understanding the balanced inversion polymorphisms of Drosophila's natural populations, with individuals migrating among niches with different selection pressures [27–30].…”

“…The integrative approach proposed by Prout [ 15 , 17 , 18 , 24 ] consists in modelling the trajectories of frequency of Drosophila inversions along generations using the fitness-component estimates obtained in competition experiments. This strategy has recently shown a more than reasonably good fit of predicted-to-observed trajectories, using from the last ones only their starting points [ 25 , 26 ]. However, this positive result is not sufficient for completely understanding the balanced inversion polymorphisms of Drosophila's natural populations, with individuals migrating among niches with different selection pressures [ 27 – 30 ].…”