Maria Monclus

THE COLONIZATION OF DROSOPHILA SUBOBSCURA IN CHILE. II. CLINES IN THE CHROMOSOMAL ARRANGEMENTS

Drosophila subobscura is a Palearctic species that was first detected in the New World in Puerto Montt (Chile) in February 1978. Since that time, it has spread over a broad area and increased in population density. The South American populations exhibit a high level of chromosomal polymorphism: 20 different arrangements exist, distributed among five chromosomes. Chromosomal arrangement heterozygosity varies from 0.55 to 0.61 in the nine populations examined. Incipient clines in the frequencies of the arrangements are appearing; these clines follow the same latitudinal direction as in the Old World. Wing length significantly decreases with latitude, as it does in Europe. The colonization of South America by D. subobscura appears to be a major natural experiment with outcomes that duplicate the distributional patterns—in chromosomal polymorphism and in wing length—observed in the Old World, thereby strongly supporting the adaptive significance of these patterns. The data show a very rapid effect of natural selection promoting genetic differentiation among natural populations.

Colonization of Drosophila subobscura in Chile I. First population and cytogenetic studies

In February 1978, in Puerto Montt (Chile) the palearctic species Drosophila subobscura was detected. The expansion of the species in this country has been very rapid, and now it is found over a distance of at least 2000 km North-South. The newly established populations are very flourishing and show a high degree of inversion chromosomal polymorphism. On the basis of the chromosomal arrangements present, an hypothesis can be formulated about the origin and characteristics of the founder group. Possibly, the founders came from Eastern or South Eastern Spain and formed a group of 10 or more individuals. The colonization of D. subobscura in Chile seems to follow the model of expansion of a cosmopolitan species, passively transported by man rather than the more active expansion of colonizers less tied to human activity, envisaged in Carsons models of colonization processes. The high level of chromosomal polymorphism observed in the populations of D. subobscura in Chile, coincides with this interpretation.

CLINES OF CHROMOSOMAL ARRANGEMENTS OF DROSOPHILA SUBOBSCURA IN SOUTH AMERICA EVOLVE CLOSER TO OLD WORLD PATTERNS

HAWKINS, A. J. B., B. L. BAYNE, AND A. J. DAY. 1986. Protein turnover, physiological energetics and heterozygosity in the blue mussel, Mytilus edu/is: The basis of variable age-specific growth. Proc. Roy. Soc. Lond. B 229:161-176. HAWKINS, A. J. B., B. L. BAYNE, A. J. DAY, J. RUSIN, AND C. M. MORALL. 1989. Genotype-dependent interrelations between energy metabolism, protein metabolism and fitness, pp. 283-292. In J. S. Ryland and P. A. Tyler (eds.), Reproduction, Genetics and Distributions of Marine Organisms. Proceedings of the XXIII European Marine Biology Symposium. Olsen and Olsen, Fredensborg, Denmark. KOEHN, R. K. 1990. Heterozygosity and growth in marine bivalves: Comments on the paper by Zouros, Romero-Dorey and Mallet (1988). Evolution 44:213-216. KOEHN, R. K., W. J. DIEHL, AND T. M. SCOTT. 1988. The differential contribution by individual enzymes of glycolysis and protein catabolism to the relationship between heterozygosity and growth rate in the coot clam, Mu/inia latera/is. Genetics 118: 121-130. KOEHN, R. K., AND P. M. GAFFNEY. 1984. Genetic heterozygosity and growth rate in Mytilus edu/is. Mar. Biol, 82: 1-7. KOEHN, R. K., AND S. E. SHUMWAY. 1982. A genetic physiological explanation for differential growth rate among individuals ofthe oyster Crassostrea virginica (Gmelin). Mar. Biol, Lett. 3:35-42. VOLCKAERT, F., AND E. ZoUROS. 1989. Allozyme and

High ethanol tolerance in two distantly related Drosophila species: A probable case of recent convergent adaptation

Abstract 1. D. lebanonensis was found to be more abundant in wine cellars of Spain than outdoors. 2. This suggested that the species could have developed a high alcohol tolerance in a similar way to D. melanogaster . 3. Laboratory analysis confirmed this hypothesis and, surprisingly, showed that D. lebanonensis was much more tolerant to alcohol and more able to use it as as food than is D. melanogaster . 4. Environmental alcohol seems to be the selective factor which determined this convergent adaptation. 5. However the difference between the two species could also be explained by assuming that the main target of natural selection was not the same in the two species: ethanol detoxification in D. melanogaster and metabolic utilization in D. lebanonensis .

Colonization and Establishment of the Paleartic Species Drosophila Subobscura in North and South America

Until 1978 Drosophila subobscura was a Palearctic species distributed all over Europe (except in Central and Northern Scandinavia), the Macaronesian Islands, North Africa and some parts of Western Asia. In most of this area it is a common species with rather dense populations. This species was detected for the first time in Chile in February 1978, in Puerto Montt in the South of the country (Brncic et al. 1981). Subsequently it has spread very quickly in Chile and in 1981 was present from La Serena (29°55′ LS) to Punta Arenas (53°10′ LS) (Budnik and Brncic 1982). In November 1981 we did find the species in large numbers in San Carlos de Bariloche (Argentina), east of the Andes (Prevosti et al. 1983). Later on, in November 1986, it was collected east of the Andes in Argentina from San Juan (31°33′ LS) to Esquel (42°55′ LS) (Table 1). A small and isolated collection by Lopez (1985) in Mar del Plata on the Atlantic Coast, about 400 km south of Buenos Aires, is the only finding of the species in other parts of Argentina. The same author (personal communication) did not find the species in other parts of the Buenos Aires province.

Genetic differentiation between natural populations of Drosophila subobscura in the Western Mediterranean Area with respect to chromosomal variation.

Summary The chromosomal arrangement frequencies of 27 populations of Drosophila subobscura from the western Mediterranean region have been compared. To evaluate the relationships between these populations, factorial analysis of correspondences (B1973) and a distance proposed by P (1974 a) have been used. The general clines present throughout the distribution of the species were also detected in the western Mediterranean area. Distinct chromosomal polymorphism was found in three areas : Tunisia, continental Europe and the whole of Sicily and Sardinia. Smaller islands were subject to stronger foreign influences. Iviza, Ponza and Ventotene showed small differences with the nearest continental populations. Ustica was rather similar to Sicily, its nearest major area ; however, Lipari, in spite of its vicinity to Sicily, showed greater similarity to the more distant continental Italian populations. The Corsican population seemed to be influenced by all its surrounding populations. The observed differences appear to be correctly interpreted as the consequence of adaptive selection (expressed in latitudinal clines) interacting with historical factors related to physiographical conditions which determine the degree of isolation between populations. Also, the size of the concerned regions seemed to be important : two of the three well differentiated areas were continental and the third included the two larger islands, Sicily and Sardinia. Corsica, next in size, showed a high frequency of a generally rare arrangement, 0 if genetic drift were a main factor in the differentiation of these populations, the reverse situation would be true.

THE RELATIONSHIP BETWEEN MATING SPEED AND WING LENGTH IN DROSOPHILA SUBOBSCURA

Mating speed is an important component of fitness as shown by Prakash (1967) who found a positive correlation between fast mating, repeat mating, and fertility in Drosophila robusta. Maynard Smith (1956) has shown that the Drosophila subobscura female performs only one effective mating during its life, so mating speed in this species should be of special significance in the males. In this paper the relationship between mating speed and wing length is studied. This study is part of a wider analysis of the correlations between wing length and the main components of fitness, aiming to get information about the selection mechanisms controlling size. Preliminary results of these experiments have been published elsewhereby Monclus and Prevosti (1967).