Genetic analysis of Drosophila virilis sex pheromone: genetic mapping of the locus producing Z-(11)-pentacosene

Characterisation of the chemical profiles of Brazilian and Andean morphotypes belonging to the Anastrepha fraterculus complex (Diptera, Tephritidae)

Fruit fly sexual behaviour is directly influenced by chemical and non-chemical cues that play important roles in reproductive isolation. The chemical profiles of pheromones and cuticular hydrocarbons (CHs) of eight fruit fly populations of the Andean, Brazilian-1 and Brazilian-3 morphotypes of the Anastrephafraterculus cryptic species complex originating from Colombia (four populations) and Brazil (four populations) were analysed using two-dimensional gas chromatography with mass spectrometric detection. The resulting chemical diversity data were studied using principal component analyses. Andean morphotypes could be discriminated from the Brazilian-1 and Brazilian-3 morphotypes by means of male-borne pheromones and/or male and female CH profiles. The Brazilian-1 and Brazilian-3 morphotypes were found to be monophyletic. The use of chemical profiles as species- and sex-specific signatures for cryptic species separations is discussed.

Role of sexual selection in speciation in Drosophila

The power of sexual selection to drive changes in the mate recognition system through divergence in sexually selected traits gives it the potential to be a potent force in speciation. To know how sexual selection can bring such type of divergence in the genus Drosophila, comparative studies based on intra- and inter-sexual selection are documented in this review. The studies provide evidence that both mate choice and male-male competition can cause selection of trait and preference which thereby leads to divergence among species. In the case of intrasexual selection, various kinds of signals play significant role in affecting the species mate recognition system and hence causing divergence between the species. However, intrasexual selection can bring the intraspecific divergence at the level of pre- and post-copulatory stage. This has been better explained through Hawaiian Drosophila which has been suggested a wonderful model system in explaining the events of speciation via sexual selection. This is due to their elaborate mating displays and some kind of ethological isolation persisting among them. Similarly, the genetic basis of sexually selected variations can provide yet another path in understanding the speciation genetics via sexual selection more closely.

On the scent of speciation: the chemosensory system and its role in premating isolation

Chemosensory speciation is characterized by the evolution of barriers to genetic exchange that involve chemosensory systems and chemical signals. Here, we review some representative studies documenting chemosensory speciation in an attempt to evaluate the importance and the different aspects of the process in nature and to gain insights into the genetic basis and the evolutionary mechanisms of chemosensory trait divergence. Although most studies of chemosensory speciation concern sexual isolation mediated by pheromone divergence, especially in Drosophila and moth species, other chemically based behaviours (habitat choice, pollinator attraction) can also play an important role in speciation and are likely to do so in a wide range of invertebrate and vertebrate species. Adaptive divergence of chemosensory traits in response to factors such as pollinators, hosts and conspecifics commonly drives the evolution of chemical prezygotic barriers. Although the genetic basis of chemosensory speciation remains largely unknown, genomic approaches to chemosensory gene families and to enzymes involved in biosynthetic pathways of signal compounds now provide new opportunities to dissect the genetic basis of these complex traits and of their divergence among taxa.

Evolution of sexual mimicry in the orchid subtribe orchidinae: the role of preadaptations in the attraction of male bees as pollinators

BACKGROUND

Within the astonishing diversity of orchid pollination systems, sexual deception is one of the most stunning. An example is the genus Ophrys, where plants attract male bees as pollinators by mimicking female mating signals. Unsaturated hydrocarbons (alkenes) are often the key signal for this chemical mimicry. Here we investigate the evolution of these key compounds within Orchidinae by mapping their production in flowers of selected species onto their estimated phylogeny.

RESULTS

We found that alkenes, at least in trace amounts, were present in 18 of 20 investigated species together representing 10 genera. Thus, the reconstruction of ancestral state for alkene-production showed that this is a primitive character state in Ophrys, and can be interpreted as a preadaptation for the evolution of sexual deception. Four of the investigated species, namely Ophrys sphegodes, Serapias lingua, S. cordigera, and Anacamptis papilionacea, that are pollinated primarily by male bees, produced significantly larger amounts and a greater number of different alkenes than the species pollinated either primarily by female bees or other insects.

CONCLUSION

We suggest that high amounts of alkenes evolved for the attraction of primarily male bees as pollinators by sensory exploitation, and discuss possible driving forces for the evolution of pollination by male bees.

Genetic analysis of cuticular hydrocarbons and their effect on courtship in Drosophila virilis and D. lummei

Genetical factors controlling the cuticular hydrocarbons (CHC) of Drosophila virilis and D. lummei, and the effect of CHC on female attractivity were studied. A strong sexual dimorphism was found in D. virilis where (Z)-10-heneicosene and (Z)-11-pentacosene were major CHC for males and females, respectively. In D. lummei, (Z)-9-pentacosene was the major CHC for both sexes. These CHC are under a complex genetical control: the level of male (Z)-10-heneicosene was mainly sex-linked; chromosome 2 exerted a marked hypermorphic effect on it as well as on female (Z)-11-pentacosene; other autosomes had additional smaller effects on the CHC. Further, these two species showed differences in the double bond position pattern: Monoenes, with double bonds in (Z)-11 or (Z)-13, were more abundant in D. virilis (monoenes-vi), while monoenes, with double bonds in (Z)-7 or (Z)-9, were more abundant in D. lummei (monoenes-lu). In agreement with previous studies of perfumed dummies, experiments with live females showed that a higher proportion of (Z)-11-pentacosene or of monoenes-vi induced D. virilis males to court sooner. On the other hand, monoenes-lu showed antagonistic effects.

Evolutionary genetics of reproductive behavior in Drosophila: connecting the dots

Species of the genus Drosophila exhibit enormous variation in all of their reproductive behaviors: resource use and specialization, courtship signaling, sperm utilization, and female remating. The genetic bases of this variability and its evolution are poorly understood. At the same time, Drosophila comparative genomics now has developed to a point at which approaches previously only possible with D. melanogaster can be exploited to address these questions. We have taken advantage of the known phylogenetic relationships of this group of flies not only to place these behaviors in an evolutionary framework, but to provide a roadmap for future genetic studies.

Cuticular hydrocarbons: their evolution and roles in Drosophila pheromonal communication

I review the recent literature on cuticular hydrocarbons (CHs) in Drosophila. First, the major structural features of CHs are examined in a variety of species with regard to phylogeny. The genetic bases of the CH variation between and within species have been investigated with some of the genes involved characterized and manipulated. The effect of non-genetic factors as temperature, food and development is also examined with regard to CH production. Using a model involving the stimulating or the inhibiting role of CHs, it is possible to speculate on the mechanisms of CH perception and on the role(s) that these substances could play on sexual isolation and on the evolution of pheromonal communication.

Sequential learning of pheromonal cues modulates memory consolidation in trainer-specific associative courtship conditioning

BACKGROUND

Associative memory formation requires that animals choose predictors for experiences they need to remember. When an artificial odor is paired with an aversive experience, that odor becomes the predictor. In more natural settings, however, animals can have multiple salient experiences that need to be remembered and prioritized. The mechanisms by which animals deal with multiple experiences are incompletely understood.

RESULTS

Here we show that Drosophila males can be trained to discriminate between different types of female pheromones; they suppress courtship specifically to the type of female that was associated with unsuccessful courtship. Such "trainer-specific" learning is mediated by hydrocarbon olfactory cues and modifies the male's processing of those cues. Animals that are unable to use olfactory cues can still learn by using other sensory modalities, but memory in this case is not specific to the trainer female's maturation state. Concurrent and serial presentation of different pheromones demonstrates that the ability to consolidate memory of pheromonal cues can be modified by the temporal order in which they appear.

CONCLUSION

Suppression of memory by new learning demonstrates that the dynamics of memory consolidation are subject to plasticity in Drosophila. This type of metaplasticity is essential for navigation of experience-rich natural environments.

Courtship learning: scent of a woman

Learning to predict an outcome based on previous experience is of considerable selective advantage. Getting it wrong can be costly. In a complex environment, however, using the appropriate predictor is not necessarily a trivial task.

Courtship in Drosophila

Courtship is a complex behavior in Drosophila that recruits a wide range of genes for its realization, including those concerning sex determination, ion channels, and circadian rhythms. Results from different experimental approaches-behavioral and genetic comparisons between species, analysis of mutants and mosaics, and identification of specific sensory stimuli-sketch the outlines of a set of pleiotropic genes acting on a distributed system in the brain to produce the species-specific sequence of responses and actions.