Ecological Genetics

The Evolutionary History of Drosophila buzzatii. VIII. Evidence for Endocyclic Selection Acting on the Inversion Polymorphism in a Natural Population

“…If assumptions are confirmed, the most stable arrangement is 2 standard while the most dynamic is Zjq', Inversion Zjq? undergoes significant and opposite changes in frequency in two different parts of the life cycle, thus exemplifying the concept of endocyclic selection (Ford, 1979). This kind of selection is to be distinguished from the well-known cyclic selection generating seasonal changes in inversion frequencies (Dobzhansky, 1970), which apparently is not present in D. buzzatii.…”

“…Juvenile zygotic selection was the only significant component of fitness revealed by the thorough studies of Christiansen and collaborators (see Christiansen [1977] for a review) on the Est-III polymorphism in natural populations of Zoarces viviparus. Strong viability selection has also been found using allozyme markers in populations of the slender wild oat Avena barbata (Clegg and Allard, 1973), ryegrass Lolium multiflorum (Allard et al, 1977), barley Hordeum vulgare (Clegg et al, 1978b) and in an additional number of instances including both experimental (Hedrick and Murray, 1983) and natural (Ford, 1979) systems. Larval viability estimates, however, are obtained in a Drosophila natural population for the first time here.…”

“…This kind of selection is to be distinguished from the well-known cyclic selection generating seasonal changes in inversion frequencies (Dobzhansky, 1970), which apparently is not present in D. buzzatii. Endocyclic selection has been found acting on the spotting pattern of the Meadow Brown butterfly Maniola jurtina (Ford, 1979 and references therein), but evidence of its occurrence in Drosophila is scarce (Crumpacker et al, 1977). Nonetheless, it may be a regular feature of many inversion polymorphisms, contributing substantially to their maintenance in nature.…”

“…In order to account for the observed changes in third-chromosome arrangement frequencies, Crumpacker et al (1977) proposed a discrete model with selection acting against one inversion (Arrowhead) during the zygote-to-adult stage and against the other common arrangement (Pike's Peak) during the adult-to-zygote stage. This pattern of adaptive values with opposite signs in different life-cycle phases, has been termed "endocyclic selection" (Ford, 1979). Although the available evidence is scanty, endocyclic selection may playa significant role in the maintenance of chromosomal variation in nature.…”

Analysis of regional patterns of phenotypic diversity in the Ethiopian tetraploid and hexaploid wheats

“…Besides. Ford's numerical increase under reduced selection seems hypotetical since, for example, under density dependent natural selection numerical increase of prey or predator will result in catastrophic events reducing much of the variability, which is particularly true in the examples mostly cited by FORD (1979).…”