Mark H. Gromko

UNPREDICTABILITY OF CORRELATED RESPONSE TO SELECTION : PLEIOTROPY AND SAMPLING INTERACT

Given a set of loci that contribute additive genetic variation for a trait being selected, the pleiotropic effects of these loci on a second trait may vary. I simulated selection on genetic systems having different combinations of pleiotropic effects to investigate the variability of correlated responses to selection. The simulation shows that there are many possible combinations of pleiotropic effects that are characterized by the same value of the genetic correlation; the genetic correlation does not uniquely determine a set of pleiotropic effects. Furthermore, for a given value of the genetic correlation, differences in pleiotropic effects have a substantial impact on the variation in correlated responses. Some combinations of pleiotropic effects constrain correlated response to a narrow range of possible values; others allow a wide range, including some correlated responses in a direction opposite the sign of the genetic correlation. The genetic correlation is not a reliable predictor of pleiotropic constraint. Whereas it has been previously established that genetic correlations are not necessarily constraints, the alternative is also true: correlated response can be strictly constrained despite a genetic correlation of zero. Given the frequency of correlated responses in a direction opposite to the one predicted by the genetic correlation, it follows that correlated response is not a reliable predictor of genetic correlation in the base population.

Genetic basis for remating inDrosophila melanogaster. II. Response to selection based on the behavior of one sex

Selection for fast and slow remating was carried out, with selection being based on the behavior of one sex. None of the male selection lines produced a significant response to selection, in lines selected either on the basis of the first male to mate with a female or on the basis of the second male to mate with a female. In contrast, three of four female selection lines showed significant responses to selection. Males in the female selection lines were tested for changes in their mating speed when paired with unselected females. These tests suggest that genes affecting remating speed in females are largely sex limited in their action. The gender difference in response to selection is discussed in terms of sexual selection theory.

Selection on copulation duration in Drosophila melanogaster : predictability of direct response versus unpredictability of correlated response

Estimates of heritabilities and genetic correlations for seven reproductive attributes had previously been obtained from parent‐offspring regression (Gromko, 1987, 1989). Copulation duration was shown to have a heritability of 0.23 and to be genetically correlated with courtship vigor (rA = −0.41) and with fertility (rA = 0.27). These observations form the basis for the prediction of direct and correlated responses to selection for increased and decreased copulation duration, which are reported here. The direct response corresponded closely to prediction, but the correlated responses did not provide consistent qualitative fit. A hypothesis is proposed to explain this difference in predictability of direct and correlated response to selection. The major postulate is that the different polygenes involved in the direct response to selection for copulation duration have different pleiotropic effects.

Increased density does not increase remating frequency in laboratory populations of Drosophila melanogaster

ofsong dialect populations. Evolution 36: 10201029. CUNNINGHAM, M. A., AND M. C. BAKER. 1983. Vocal learning in White-crowned Sparrows: sensitive phase and song dialects. Behav. Ecol. Sociobiol. 13:259-269. DIXON, W. J. (ED.). 1981. BMDP Statistical Software. Univ. Calif. Press, Berkeley. ENDLER, J. A. 1977. Geographic Variation, Speciation, and Clines. Princeton Univ. Press, Princeton. HANDFORD, P., AND F. NOTTEBOHM. 1976. Allozymic and morphological variation in population samples of Rufous-collared Sparrow Zonotrichia capensis, in relation to vocal dialects. Evolution 30:802-817. HEINEMANN, D. 1981. Song dialects, migration, and population structure ofPuget Sound Whitecrowned Sparrows. Auk 98:512-521. NEI, M. 1978. Estimation of average heterozy-

Genetic constraint on the evolution of courtship behaviour in Drosophila melanogaster.

A quantitative genetic analysis of male courtship behavior in Drosphila melanogaster was carried out. Heritabilities and genetic correlations were calculated from data collected from 330 father–son combinations. Only copulation duration had a heritability significantly different from zero. Copulation duration and fertility were related by a significant positive genetic correlation. A highly significant negative genetic correlation of copulation duration with courtship vigor (towards a virgin female) is possibly responsible for constraining further evolution of copulation duration in this population. It is noteworthy that genetic correlations between traits with low heritabilities were not detectable; practical and theoretical considerations concerning genetic correlations between traits with low heritabilities are discussed.

Female receptivity to remating and early fecundity in Drosophila melanogaster.

Fecundity and receptivity to remating in 3 populations of D. melanogaster derived recently from the field. We also compared four stock-maintenance procedures for their effects on remating and related attributes

Quantitative genetic analysis of courtship and reproduction in female Drosophila melanogaster.

Three hundred mother–daughter pairs were analyzed for seven attributes related to courtship and reproduction. Only the lag time from first courtship to copulation was significantly heritable; genetic correlations involving this attribute were not significant. The genetic correlation between fertility and lag time to first courtship was negative and significant. However, this genetic correlation is expected to have little impact on the retention of additive genetic variance or on response to selection because it involves two attributes with low heritabilities. The pattern of phenotypic covariation among traits is largely explained by environmental causes and is consistent with that found in a previous analysis of father–son pairs (Gromko, 1987).

Genetic basis for remating inDrosophila melanogaster. III. Correlated responses to selection for female remating speed

Two natural populations ofDrosophila melanogaster selected for fast and slow female remating (Gromko and Newport,Behav. Genet.18: 621–632, 1988) were analyzed for correlated responses to selection. Several of the correlated responses differed between the lines derived from the two different source populations. In particular, the degree to which female receptivity to remating was dependent on the number of sperm in storage ceptivity to remating was dependent on the number of sperm in storage remained high in one pair of fast and slow selected lines but not in the other. In the line which retained sperm dependence (JEFFERS), fast and slow remating was achieved by changes in the threshold at which remating occurred. In the other line (COMP) changes in the temporal pattern of sperm use were seen. Thus both the level of the receptivity threshold and the existence of a sperm effect appeared to be selectable features of this species. Mated female attractiveness and receptivity were shown to be genetically distinct from virgin female attractiveness and receptivity. Effects of the genotype of the female on copulation duration were found.

Response to selection for early and late development of sexual maturity in Drosophila melanogaster

Abstract Selection for early and late development of sexual maturity (switch-on) in Drosophila melanogaster was successful. There was greater response for late than for early maturity. Furthermore, only females showed a response for early development of sexual maturity, whereas both sexes responded to selection for late development of sexual maturity. Four correlated responses appeared consistently across replicates: flies selected for late development of sexual maturity were slower to mate as mature flies, slower to mate a second time, had lower fecundity, and had shorter egg-to-adult development time. The selection response is consistent with the interpretation of past natural selection for rapid development of sexual maturity, particularly in males. The coordinated response of sexual maturity, mating speed and fecundity suggests the involvement of juvenile hormone in the selection response.

Genetic basis for remating in Drosophila melanogaster. IV. A chromosome substitution analysis.

Drosophila melanogaster lines previously selected for fast and slow return of female receptivity were subjected to a chromosome substitution analysis. Chromosomal effects on direct response to selection were distinctively different between selection lines derived from two different base populations. All three chromosomes tested affect the trait in the JEFFERS selection lines. In contrast, only chromosome II was found to have a main effect in the COMP selection lines. Significant interactions between chromosome II and the other chromosomes were also found in both of the selection lines. All of the components of virgin fly mating behavior measured were affected by chromosome II.