Mating propensities and variations in enzyme activities in long-term cage populations of Drosophila melanogas ter

: Environmentdependent reproductive isolation was established between cage population? (Bs) of Drosophila melanogaster originated from a Greek natural population (summer 1973) and maintained ?. r about five years under different diets (poor-rich). The detected deviation from random mating involved no homogametic or heterogametic pref-erence but rather, a significantly increased activity of males from populations maintained on the rich food medium. This observation indicates that the male parental investment is not negligible and under certain conditions sexual isolation can be a function not only of female behavior but also of male behavior. Differences also were found in various enzyme activities an the inter- and intra-vpulation levels. Given those observations as well as the observed different behavioral patterns of Be and Cs-Dc population^^^, a preliminary attempt was made to associate adaptive evolution with differences in enzyme activities. The differences in enzyme activities between populations reared on different media are not due to allozymic differences. It also was shown that in some populations environmental effects do not always ellicit differences in enzyme activity. It was concluded, therefore, that the observed variations were the result of environmental effects interacting with modifier genes.

W Hanover. New Hampshire for helpful ':%ions 'Â¥' . h e r i~d n Genetic Association ABSTRACT: Environmentdependent reproductive isolation was established between cage population? (Bs) of Drosophila melanogaster originated from a Greek natural population (summer 1973) and maintained ?. r about five years under different diets (poor-rich). The detected deviation from random mating involved no homogametic or heterogametic preference but rather, a significantly increased activity of males from populations maintained on the rich food medium. This observation indicates that the male parental investment is not negligible and under certain conditions sexual isolation can be a function not only of female behavior but also of male behavior. Differences also were found in various enzyme activities an the inter-and intra-vpulation levels. Given those observations as well a s the observed different behavioral patterns of Be and Cs-Dc population^^^, a preliminary attempt was made to associate adaptive evolution with differences in enzyme activities. The differences in enzyme activities between populations reared on different media are not due to allozymic differences. It also was shown that in some populations environmental effects do not always ellicit differences in enzyme activity. It was concluded, therefore, that the observed variations were the result of environmental effects interacting with modifier genes.

ONE OF ' I H E important questions in evo-
lutionary theory. relates to how species are formed and what kind and magnitude of genetic differentiation characterizes species formation Heretofore, several mechanisms l^,-mrn h.i-.ixrn amrih ~i c -i v r -' " l a <T th'at cnor'iatinn invnlvpc a a p n~t i r r~n r w i n i m t i o r denendent on a founder event, followed by one or more cycles of exponential population growth and a sudden contraction or crash9-'2. Moreover, according to P r a k a~h~~ founder e ents, inbreeding, and geographic isolation are considered as major factors in the development of reproductive isolation.
In contrast, speciation also is considered a by-product of the process of adaptation, characterized by changes in behavioral and structural gene [allozymic) v a r i a t i~n~-~~-~~. Experimental evidence exists for all the above view~6,30-3~, a fact indicating that the development of reproductive isolation is not unimodal.
We recently demonstrated1" tha, stable environment-dependent sexual isolation had been established between cage pop+ lations of Drosophila melanoguster maintained under different environmental r n i r l i t i n n c ftrtmnoraturi^ ~n r l hiimiirlih~! f n~ ahoilt five w a r s w h~r~a s the isolation o f populations alone did not lead to ethological isolation. Since the isolation of populations is considered to be an important factor in the development of reproductive isolat i~n~~, we investigated a set of four additional cage populations (possessing a common gene pool at their origin) maintained [in duplicate] under different food media (poor-rich)l, for about six years, in order to assess: 1) whether or not reproductive isolation was established and, if so, whether it was correlated to environmental manipulation or to the isolation of populations.

2)
Since the environmental factor used in the present study (food medium) differs from those utilized beforeI9 (temperature-relative humidity), a comparison also was made regarding the patterns of ethological isolation.
The ecological factor food medium (poor-rich] was found to induce dramatic genetic differentiation in Adh and a-Gpdh allozymic and inversion frequencies3 as well as in the frequencies of lethal bearing chromosomes1 during the initial 30 generations. Tak'ng into account the situation already revealed in the populations, we thought it of interest also to measure the quantitative genetic variation of enzyme activities in our preliminary effort to see whether or not correlcition exists between changes in enzyme activities and in reproductive isolation. Since it was suggested21 that in natural populations there may be several polymorphic loci affecting the expression of a given structural gene and therefore contribute to variation in the enzyme activity, this study may ultimately prove useful to test the adaptive significance of enzyme qua~..itative variability. At the same time, it also \\ill have a bearing on the suggestion that regulatory variation of enzyme activity is a more important source of adaptive variation than structural vari-ati0n8 1-1.21.34.

Materials and Methods
Four cage populations designated lBi, 1B2, 1B3, lBj were studied. Enzyme activi-ties were measured in flies from two addi-9A X dB and 9 B X <5A. respectively, and \ tional cage populations [lC, ID). The last = XAA + Xt3t3 + X.\H + XB.X two populations have been studied and SE of I = \'(I -J V N . described p r e v i o u~l y~~. The B5 populations originated from a common parental popu-A value of zero for this index indicates lation (1B) by replication, 10 generations random mating; <0, negative assortative after the latter originated. Consequently, we and >0, positive assortative mating, ~h~ may regard the four derived populations as flies of each sex that were mated werp possessing practically the same gene pool tested by chi-square if females and males at their origin. Population 1B was estabof one population mated more frequent]\ lished in the autumn of 1973 from flies than those from other populations, and if captured during the summer of 1973 from assortative mating occurred. Experiments, the Greek island of -a (for more were carried out 210 weeks after the origin details see Alahiotisl]. All Bs populations of populations.