Sexual isolation of genetically differentiated sympatric populations of Drosophila melanogaster in Brazzaville, Congo: the first step towards speciation?

Two sympatric populations of Drosophila melanogaster were collected in the Brazzaville area in Congo, one from the suburban countryside and the other from a brewery located in the city. They were compared for several genetically determined traits including morphology, allozymes, microsatellites, cuticular hydrocarbons, and sexual behaviour. The two populations were similar to other African populations for morphological traits, but differed significantly from each other for all other characters. The countryside population resembled other African populations, whereas the urban population was consistently similar to European populations. Mating choice experiments showed incipient reproductive separation between the populations. In agreement with the hypothesis that D. melanogaster originated in Africa and spread to the rest of the world by invading human-modified habitats, we suggest that man-adapted fruit fly populations have returned 'back to Africa', and remained partially isolated from older native stocks.

Differentiation of dialects and courtship strategies in allopatric populations of Drosophila teissieri.

Intra-specific differentiation has been investigated between two geographically isolated populations of D. teissieri, one from Brazzaville (Congo) and the other from Silinda (Zimbabwe). Courtship songs were analyzed on 23 parameters. In addition, certain parameters related to sexual activity (five) and wing morphology (five) were also examined. As in other Drosophilidae, there are two types of courtship songs resulting from wing vibration: the love song, and the sine song. Love songs from Brazzaville are longer than those from Silinda (334ms vs. 216) with a tendency to smaller and more regular inter-pulse intervals (24.56ms vs. 25.5). The sine songs (SS) are about six times longer than the love songs in each population, with an adaptation of their duration according to the receptivity of the female in Brazzaville. All the LS temporal parameters, except the interpulse interval mean, are significantly different between the two populations. The Brazzaville flies show a greater acoustic activity and have higher mating success than the Silinda ones (53.3% vs. 27.7%). Their wings are slightly shorter and wider than those from Silinda. The role of acoustic parameters, sexual activity and wing physical constraints are discussed in the perspective of incipient speciation.

Differences in patterns of pup care in mice. V--Pup ultrasonic emissions and pup care behavior.

Newborn mice, like all newborn rodents, are able to emit high frequency signals, in particular when they are put out of the nest. Moreover, it is known that in this situation retrieving behaviors are induced in the foster mother, which are likely to reveal stable differences across inbred strains of mice. The question that arises is whether these differences are causally linked to differences in the pup rate of signalling and/or to the capacity of the females of these strains to perceive them. To provide insights into this question, the behavior of 8 inbred strains of mice was observed: A/J, BALB/c, CBA/H, C57BL/6, C57Br, DBA, NZB and XLII. Pup ultrasonic calls of each of these strains, emitted in the same conditions as a retrieving test, were recorded and tabulated. Auditory sensitivities of females belonging to these strains were determined by auditory evoked potentials recorded in the inferior colliculus. These two variables were analysed in relation to scores of females of these strains on three variables of a retrieving test. Results show that the presence of other factors than auditory cues must be taken into account to describe differences across strains in retrieving performances. This conclusion has been confirmed by results obtained using cross-fostering procedure. Female mice unable to utilize ultrasonic information may use other sensory channels. Furthermore, female mice capable of perceiving ultrasounds may also be able to use different sensory modalities in different situations.