Causes and consequences of esterase 6 enzyme activity variation in pre-adult Drosophila melanogaster

Abstract

We report heritable threefold differences in both larval and pupal esterase 6 activity among 17 isoallelic lines of D. melanogasrer extracted from a natural population. The activity differences in the two stages are only weakly correlated with each other or with previously determined values for esterase 6 activity in adults of these lines. The pre-adult activity variation is also unrelated to polymorphisms among the lines for six esterase 6 allozymes and six restriction sites in a region encompassing the esterase 6 coding DNA and the first kbp of 5' flanking DNA. However, two insertions, of 8.0 and 6.8 kbp, located about 1.4 kbp 5' of the esterase 6 coding region are associated with low activity in larvae and, to a lesser extent, in pupae, albeit not in adults. Restriction mapping reveals similarity between the 8.0 kbp insert and the 7.4 kbp retrotransposon 17.6. The differences in larval activity among lines are positively correlated with fitness as assessed from assays of pre-adult viability and development time but no significant associations between pupal esterase 6 activity and these measures are detected. Some effects of esterase 6 allozyme differences are also found for viability and development time but these effects could be explained by linkage disequilibrium between the 8.0 kbp insert and the EST6-9 allozyme.

Genetic polymorphism at two linked loci, Sod and Est-6 , in Drosophila melanogaster

“…The role of Est-6 in D. melanogaster mating propensity (Richmond et al, 1980(Richmond et al, , 1990Ludwig et al, 1993); its association with increased reproductive fitness, pre-adult viability, tissue expression pattern, and levels of enzyme activity strongly indicate that natural selection is involved in shaping the S/F and Rsa I 2 / Rsa I þ polymorphisms (Gromko et al, 1984;Game and Oakeshott, 1990;Richmond et al, 1990;Ludwig et al, 1993;Oakeshott et al, 1994Oakeshott et al, , 1995Odgers et al, 1995;Tamarina et al, 1997). Our window analysis also supports that these are balanced polymorphisms (Fig.…”

“…Game and Oakeshott (1990) found that a polymorphism at an Rsa I site in the 5 0 -flanking region of Est-6 shows significant association with the amount and activity of EST-6 in males. Given the evidence from other studies that differences in male EST-6 activity affect the reproductive success of their mates (Richmond et al, 1990), Game and Oakeshott (1990) have proposed that Est-6 cisacting regulatory polymorphisms may be important contributors to adaptive variation (see also Oakeshott et al, 1994;. Odgers et al (1995) identified a nucleotide substitution responsible for the Rsa I polymorphism (T !…”

Associations of esterase 6 allozyme and activity variation with reproductive fitness inDrosophila melanogaster

“…As in the current study, our parallel studies of juvenile fitness (juvenile survival and development time) in the same lines found no clear fitness associations for EST6 allozyme status but some strong associations for EST6 activity levels (Oakeshott et al, 1994). The physiological basis for the selection underlying the EST6-F/EST6-S allozyme clines therefore remains a mystery, while the evidence that EST6 activity levels are subject to selection is strengthened.…”

“…In all except one case, the various fitness components were tested on the same panel of lines; line 3 was lost before the tests of remating frequency were carried out, so line 11, of similar allozyme and activity status (Table 1), was measured for this variable instead. Media and other culture conditions were as in Oakeshott et al (1994).…”

“…The fitness components tested are the mating time and copula duration of males from the different lines with females from a standard reference line, and then the remating frequency, egg production and fertility of these females. This work complements a separate comparison of these lines for aspects of juvenile development time and viability related to the role of EST6 in feeding and digestion (Oakeshott et al, 1994).…”