Lee Ehrman

Developmental Isolation and Subsequent Adult Behavior of Drosophila paulistorum.IV. Courtship

Early social experiences play important roles in adult Drosophila paulistorummate selection. Differences in courtship between control males and wholly socially isolated males were observed in chambers. Socially isolated males displayed more courtship toward virgin females than did controls. Socially isolated males were more successful in competing for mates. Yet socially isolated males from all six semispecies also displayed notable frequencies of homosexual behavior.

HUMAN HANDEDNESS: THE INFLUENCE OF LEARNING

55 subjects were divided by writing-hand preference and further divided into control and experimental conditions. All subjects were administered a manipulative skill at pretest, counterbalanced for starting hand. Experimental subjects were given 5 practice sessions, and then all subjects were administered a posttest. Posttest scores of both hands of experimental subjects indicated significant improvement as a result of practice, with the nonpreferred hand showing no significant difference from the preferred hand. These findings were related to the etiology of handedness which is hypothesized to involve two factors, one verbal and dichotomous, the other nonverbal and continuous.

Male-Specific Cuticular Compounds of the Six Drosophila paulistorum Semispecies: Structural Identification and Mating Effect

We have identified cuticular pheromones that sustain the integrity of the six Drosophila paulistorum semispecies. Hexane extracts of male and female cuticles were separated on a silica gel column and analyzed using gas chromatography/mass spectrometry. Both sexes of each of the six semispecies have the same fifteen major cuticular components, all hydrocarbons ranging from C31 to C37. However, all males have four additional ester compounds. Bioassay observations showed that this four-component ester complex imparts a strong anti-aphrodisiac effect on intra-semispecific mating behavior, thus confirming its pheromonal role. The three major ester components are methyl (Z)-9-tetradecenoate (C15H28O2), 11-docosenyl acetate (C24H46O2), and 19-triacontenyl acetate (C32H62O2). The fourth ester is a di-unsaturated acetate with molecular formula C32H60O2, but the positions of unsaturation have not been determined. Bioassays indicate that the male-specific complex of the transitional semispecies, the relict ancestor, imparts anti-aphrodisiac effects on the other semispecies as well, but effectiveness decreases with phylogenetic distances. Across the six semispecies, the male-specific compounds are the same, but vary quantitatively. Apparently, the quantitative differences among these incipient species act efficiently to preclude hybridization in nature. Because Drosophila paulistorum is a cluster of incipient species, this opportunity to observe pheromonal influences on speciation is unique.

The Drosophila paulistorum endosymbiont in an alternative species

Drosophila paulistorum consists of six semispecies that are the intracellular, cytoplasmic hosts for cell-wall-deficient microorganisms (streptococcal L-forms). Drosophila pavlovskiana is its uninfected sibling species, which can be crossed with D. paulistorum with difficulty. Parental types and hybrids resulting from crosses of these drosophilids were subjected to ultrastructural analyses via transmission-electron microscopy for the presence of endosymbionts. Drosophila paulistorum has naturally infected, but functional, gonads. In contrast, D. pavlovskiana has normal, symbiont-free gonads. The absence of endosymbionts in D. pavlovskiana correlates well with the lack of infectivity shown by the genetic crosses. The F1 generation consisted of fertile daughters, but sterile, hybrid sons, burdened by excessive microbial growth in their testes and retarded spermatogenesis. These results were coupled with a wholly negative survey of D. pavlovskiana for infectivity under microbial protocols producing positive results for D. paulistorum.

Reproductive Isolation in a Neotropical Insect: Behavior and Microbiology

The Drosophila paulistorum Dobzhansky & Pavan complex offers an excellent opportunity for the study of the relationship between an insect host and its microbial symbiont. Electron microscopy reveals that all members of this insect group harbor endosymbionts which, by all appearances, are cell-wall deficient organisms (CWD). While it is not known if the CWDs of D. paulistorum are essential to their hosts, it is clear that a stable, benign relationship exists between the host and its own CWD. However, our evidence indicates that transfer of an endosymbiont from one semispecies of D. paulistorum to another semispecies results in male sterility. The specificity exhibited by the endosymbionts increases reproductive isolation between semispecies and may have contributed to the evolutionary and taxonomic complexity of D. paulistorum as a widespread superspecies.