Adaptive Organization of the Gene Pools of Drosophila Populations

Population Differentiation in an Annual Legume: Genetic Architecture

“…Our results corroborate earlier work documenting inbreeding and genetic coadaptation in Drosophila (Wallace 1953;Brnic 1954;Wallace and Vetukhiv 1955;Anderson 1968) and conform to more recent studies using marker assisted techniques (Clegg et al 1978;Cavener and Clegg 1981;Burton 1987Burton , 1990Hard et al 1992Hard et al , 1993Palapoli and Wu 1994;Doebley et al 1995;Lark et al 1995;Rieseberg et al 1995;Armbruster et al 1997;Hatfield 1997;Li et al 1997;Routman and Cheverud 1997) and others (reviewed in Whitlock et al 1995;Fenster et al 1997). Our observation of epistasis contributing to divergence at a very local scale has also been observed in a number of other studies (Templeton et al 1976;Price and Waser 1979;Burton 1987Burton , 1990Waser andPrice 1989, 1994;Parker 1992;Deng and Lynch 1996).…”

“…Where the F 1 outperformed the MP, it frequently outperformed both parents (Fenster and Galloway 2000a), indicating that the loss of fitness due to the fixation of deleterious alleles may be substantial. Similar findings of enhanced performance of F 1 progeny of interpopulation crosses relative to their parents has been observed in previous work in C. fasciculata (Fenster 1991b) and in a number of other studies, for example, Drosophila (Wright et al 1942;Wallace 1955), Phlox (Levin 1977(Levin , 1984, Sabatia (Dudash 1990), Scabiosa (van Turen et al 1994, and other examples cited in Waser (1993), suggesting that fixation of deleterious alleles within populations due to drift may be a general phenomenon. Large environmental effects on the expression of inbreeding depression found here and in other studies (Dudash 1990;Pray et al 1994;Lynch and Walsh 1997) imply that deleterious mutations may experience extreme variation in purifying selection, which may also account for their high frequency.…”

“…The findings of the earlier Drosophila experiments that quantified a large effect of linkage on the expression of hybrid breakdown are especially relevant (Brnic 1954;Wallace 1955;Wallace and Vetukhiv 1955;Ohta 1980). In our study, negative epistasis is mostly observed in the F 3 and less consistently in the F 2 generation.…”

“…There is abundant evidence for the role of natural selection in population divergence (Endler 1986;Futuyma 1997), and empirical work over the last 40 years has demonstrated that species exhibit significant population genetic structure, and thus the opportunity for drift to influence evolution (Hastings and Harrison 1994). This latter conclusion is based on studies documenting small population sizes (e.g., Levin 1981;Fenster 1991a,b), heterosis in progeny of interpopulation crosses (e.g., Wallace 1955;Fenster 1991b;reviewed in Waser 1993), and population differentiation for neutral molecular markers (Slatkin 1987;Hamrick and Godt 1989). Although the conditions for drift to influence evolution have been demonstrated, there are only several well-documented cases where drift has been shown to contribute to the evolution of adaptations (reviewed in Coyne et al 1997).…”

An Evaluation of Narrow Hybrid Zones in Vertebrates

“…The hybrid-superiority hypothesis has largely been ignored because the occurrence of adapted hybrids would be inconsistent with the central dogma of animal speciation theory, namely, that the integrity of a species, at least in its infancy, is maintained by coadaptation of the species gene pool. That coadaptation exists is unequivocal (e.g., Wallace and Vetukhiv, 1955), but its universal importance as a cause of speciation is a presumption and not a demonstrated fact.…”