Section 8 — Cytatoxonomy and Experimental Taxonomy 



localities, belonging to D. Willistoni and sibling 

 species, disclosed several levels in the speciation 

 process. A total of 90 different intercrosses, with 

 five repetitions, each with 10 pairs of flies, gave 

 450 replications, which were periodically trans- 

 ferred to new vials until the death of the females 

 (about 60 days). 



Amongst the most significant results is the 

 production of Fi, fertile inter se from paulistorum 

 males x willistoni females strains from Southern 

 Brazil, edge of D. paulistorum distribution. The 

 reciprocal cross yielded few sterile individuals. 



The offspring of paulistorum males x equi- 

 noxialis females showed a large excess of fertile 

 females and rare, sterile and always mutant 

 males (eyes, wings or bristles). The reciprocal 

 crosses yielded few descendants, the sex-ratio 

 being normal, but all males sterile and mutants 

 (eyes, wings and bristles). 



The degrees of affinities in regard to the 

 cytoplasm allowing the development of inter- 

 specific hybrids, at least until larvae, can be 

 stated very briefly as follows: insularis (all 

 other tested) > willistoni {tropicalis, paulistorum, 

 equinoxialis and rarely with insularis) > paulis- 

 torum (equinoxialis, tropicalis, some strains of 

 willistoni and rarely with insularis) > equino- 

 xialis (paulistorum, tropicalis and rarely with 

 willistoni) > tropicalis tropicalis from Palma 

 (other tropicalis and paulistorum) > tropicalis 

 cubana and tropicalis from Tefe and Trinidad 

 (inter se only). 



D. tropicalis cubana (Townsend, 1954) can be 

 ranked to D. cubana with sub-species distributed 

 over the Antilles, Trinidad and the Amazon 

 basin (Tefe to Belem). Males of D. cubana from 

 Cuba, Trinidad or Tefe crossed with D. tropicalis 

 tropicalis from the type locality, Palma, yielded 

 few descendants, the males being sterile and 

 females fertile with paternal strains only. The 

 reciprocal crosses produced no descendants. 



The D. cubana "complex" of sub-species 

 from Cuba, Tefe and Trinidad produced, inter 

 se abundant Fi with fertile females and sterile 

 males in both ways. 



8.25. Cytological Studies in the Cardini Superspecies 

 of Drosophila. William B. Heed and Jean 

 S. Russell (Tucson, U.S.A.). 



In order to determine the phylogenetic re- 

 lationships among the 15 species in the cardini 

 superspecies of Drosophila, a salivary gland 

 chromosome map has been constructed from a 

 homozygous population of D. acutilabella from 

 Cuba. Nine species have been analysed thus far 



and their inversions have been compared with 

 the standard sequence from Cuba. Eight of the 

 nine species form a natural subgroup in that 

 their population structures are dependent upon 

 the position and size of the islands in the Carib- 

 bean Sea. A total of 26 inversions were found 

 among 34 separate laboratory populations and 

 strains. Fifteen inversions are homozygous and 

 11 inversions are heterozygous. D. acutilabella 

 is homozygous for the standard gene sequence 

 in Florida (4 localities), Jamaica (6 localities) 

 and Cuba (1 locality). It is highly polymorphic, 

 however, in Haiti (3 localities) with 8 hetero- 

 zygous inversions. Five separate populations 

 of D. dunni from 3 localities in Puerto Rico are 

 homozygous, and they are all fixed for 3 in- 

 version differences from standard in the X chro- 

 mosome. Analysis of the polymorphism in the 

 Haitian acutilabella is in progress. 



8.26. Cytotaxonomy in the Drosophila melanica 

 Species Group. Harrison D. Stalker (St. 

 Louis, U.S.A.). 



On the basis of morphology and reproductive 

 isolation the six New World species of this 

 predominantly Nearctic group may be arranged 

 in a sub-group of four sibling species: D. mela- 

 nica, D. paramelanica, D. euronotus and D. mela- 

 nura; and two more distinct species: D. micro- 

 melanica and D. nigromelanica. D. micromelanica, 

 considered to be the most nearly ancestral, has 

 a rod-shaped, single-element X in most strains; 

 the other five species have V-shaped, two- 

 element X chromosomes. Salivary chromosome 

 differences in banding sequence were studied by 

 hybridization and by the comparison of photo- 

 graphs and composite photomaps. In all six 

 species chromosome II is the most variable, show- 

 ing 57 inversion differences within species. Chro- 

 mosomes XR, XL, III and IV show 10, 6, 1 and 2 

 intraspecific inversion differences respectively. 

 Chromosomes showing the largest number of 

 heterozygous inversions within species also show 

 the most homozygous inversion differences 

 between species. Chromosome comparisons 

 indicate the following phylogenetic sequence 

 for the group: D. micromelanica — D. euronotus 

 and D. melanura — D. paramelania — D. mela- 

 nica. (D. nigromelanica is apparently derived 

 from D. micromelanica independently of the 

 D. euronotus, D. melanura pair.) Within the group 

 of four sibling species, the ratio of heterozygous 

 inversions within species to homozygous inversion 

 differences between species is approximately 

 3.5: 1, suggesting a rapid isolation of the four 

 sibling species, followed by an extensive period 



139 



