Crossing over does occur in males of Drosophila ananassae from natural populations

Spontaneous crossing over in males of Drosophila ananassae has been well demonstrated using [F.sub.1] individuals from crosses between marker stocks and wild type strains. However, the question of its occurrence in males from natural populations remained open. Here we present the cytological evidence that crossing over does occur in males of D. ananassae from two Brazilian populations, sampled nearly 21 years apart, and in two recently sampled populations, one from Indonesia and one from Okinawa, Japan. Cytological analysis of meiosis in males collected from nature and in sons of females from the same population inseminated in nature revealed the presence of chiasmata, inversion chiasmata, and isosite chromosome breakages in the diplotene cells in all sampled populations. These data demonstrate that reciprocal and nonreciprocal exchanges and chromosome breakages, previously reported as related events of male crossing over, do occur at variable frequencies among males from natural populations. Key words: meiotic chromosomes, chiasmata, chromosome breakages, Brazil, Indonesia, Japan. L'occurrence d'enjambements spontanes chez les males du Drosophila ananassae a ete bien documentee au moyen d'individus [F.sub.1] issus de croisements entre des souches marquees et des souches sauvages. Cependant, la question de son occurrence chez des males issus de populations naturelles demeure sans reponse. Dans ce travail, les auteurs presentent des evidences cytologiques d'enjambements au sein de males du D. ananassae chez deux populations bresiliennes, echantillonnees a 21 ans d'ecart, ainsi que deux populations echantillonnees recemment, l'une de l'Indonesie et l'autre d'Okinawa au Japon. L' analyse cytologique de la meiose chez des males provenant des populations naturelles ou les fils de femelles provenant de ces memes populations inseminees en nature a revele la presence de chiasmas, de chiasmas typiques d'inversions et de cassures chromosomiques a des sites identiques chez les cellules en diplotene chez toutes les populations echantillonnees. Ces donnees demontrent que des echanges reciproques et non-reciproques ainsi que des cassures chromosomiques, rapportes anterieurement comme etant des evenements apparentes survenant lors de la meiose chez les males, surviennent a des frequences variables chez les males provenant de populations naturelles. Mots-cles : chromosomes meiotiques, chiasmas, cassures chromosomiques, Bresil, Indonesie, Japon. [Traduit par la Redaction]
Introduction Spontaneous crossing over in males of Drosophila ananassae was discovered by Kikkawa (1937) and Moriwaki (1938). Both Kikkawa (1938) and Moriwaki (1940) reported that recombination in males of D. [...]