GENETICS OF SEXUAL ISOLATION AND COURTSHIP DYSFUNCTION IN MALE HYBRIDS OF DROSOPHILA PSEUDOOBSCURA AND DROSOPHILA PERSIMILIS

Despite the importance of sexual isolation to speciation, few studies have analyzed the genetic basis of interspecific mating discrimination, particularly using hybrid males. In this study, I investigated the genetic basis of sexual isolation using male hybrids of Drosophila pseudoobscura and D. persimilis. Hybrid male mating success was caused by interactions between the X-chromosome and autosomes (or Y-chromosome), and different arms of the X-chromosome contributed to mating success with females of each species. Further, although there was an X-chromosome component to mating success, its magnitude was not disproportionately large when compared with the proportion of the genome contained on this chromosome. Some hybrid males courted with an anomalously low intensity, so I simultaneously mapped the genetic basis of this “courtship dysfunction.” The courtship dysfunction was caused by an interaction between the left arm of the X-chromosome in D. persimilis with the autosomes or Y-chromosome from D. pseudoobscura. Anomalous courtship behavior in interspecific hybrids can obscure the conclusions of studies of the genetics of sexual isolation, so courtship intensity should be evaluated in all such investigations.     

INTERSPECIFIC HYBRIDS OF DROSOPHILA HETERONEURA AND D. SILVESTRIS I. COURTSHIP SUCCESS

Drosophila heteroneura and D. silvestris are well-defined, sympatric species of the planitibia subgroup of Hawaiian Drosophila. D. silvestris can be subdivided into two allopatric morphotypes that differ in the number of bristle rows on the front tibia (two rows versus three rows). We measured courtship success of intraspecific and interspecific hybrids as the proportion of females inseminated during a two-week period with a single sib male. Proportions were arcsin-transformed so that the values were asymptotically normal in distribution, and tests of homogeneity and of mean differences were performed. Of key importance is the discovery of genetic variation for the proportion of inseminated females within both D. heteroneura and D. silvestris. The interspecific crosses and the D. silvestris intraspecific crosses also provide evidence for a coadapted gene complex with some dominance or heterosis. This coadapted gene complex correlates with the morphotypes of these flies, rather than with the D. heteroneura/D. silvestris contrasts per se. This observation stresses the importance of recognizing both behavioral and morphological components of the mate-recognition system. The incompatible coadaptation that separates the two-row from the three-row forms also supports recent molecular studies which indicate that the three-row form split from the two-row form prior to the split between D. heteroneura and two-row D. silvestris. The observations of intraspecific variability and coadaptation support the predictions of a genetic-transilience model which explains the origin of a new mate-recognition system in terms of sexual selection in the context of a founder-flush event.     

用新的计量方法研究黑腹果蝇的求爱歌

对雄果蝇求爱脉冲歌的研究已有多年的历史,但对脉冲间隔的计量方法并不方便。本文介绍我们采用微机终端计时新技术,自动对脉冲进行计数,可在范围更为广泛的数据信息内,对果蝇脉冲歌进行测量统计,对ipi分布中纵数与平均值的关系提出我们的看法,并首次对ipf及npb的分布进行了研究。     

THE GENETIC BASIS OF EVOLUTION OF THE MALE COURTSHIP SOUNDS IN THE DROSOPHILA VIRILIS GROUP

When courting, males of the Drosophila virilis group vibrate their wings and emit species-specific courtship sounds consisting of trains of polycyclic sound pulses. To analyze the genetic basis of evolutionary changes in the sounds we made an F₁ diallel set of reciprocal crosses between the members of the virilis phylad of the group (two stocks of D. virilis and one of D. americana americana, D. a. texana, D. novamexicana, and D. lummei). We also crossed the D. virilis stocks with the members of the montana phylad of the same group (D. kanekoi, D. littoralis, D. borealis, D. flavomontana, D. lacicola, and D. montana) and made a backcross (D. virilis x D. littoralis) x D. virilis using a D. virilis marker stock (b; sv t tb gp; cd; pe). The sounds of the hybrids were analyzed using the following parameters: the length of a pulse train (PTL), the number of pulses in a train (PN), the interpulse interval (IPI), the length of a pulse (PL), the number of cycles in a pulse (CN), and the length of a cycle (CL). In the virilis phylad, the differences between species appeared to be determined mainly by autosomal genes in each sound trait. The heritabilities (narrow-/broad-sense) obtained from the diallel tables were the following: PTL 0.662/0.817, PN 0.651/0.841, IPI 0.193/0.546, PL 0.408/0.552, CN 0.425/0.719, and CL 0.361/0.764. The direction of dominance is for longer PTL, higher PN and CN, and shorter IPI and CL. PL shows ambidirectional dominance. In the sounds of the virilis phylad species, PTL and PL seem to be phenotypically the most important parameters, since their components (PN and IPI for PTL, CN and CL for PL) are negatively correlated. In crosses between D. virilis and D. littoralis or D. flavomontana reciprocal hybrids differed from each other in PTL, IPI, PL, and CN indicating X-chromosomal or cytoplasmic inheritance. In the backcrosses between D. virilis and D. littoralis the role of the X chromosome was ascertained to be decisive. We conclude that an X-chromosomal major change allowing variation in IPI has occurred during the separation of the two D. virilis group phylads, the long IPI allowing variation also in PL (and CN). The evolution of the sounds in the virilis phylad has probably gone towards longer and denser pulse trains, while in the montana phylad the sounds have evolved in different directions.     

MORPHOLOGICAL AND FUNCTIONAL ASPECTS OF AN INSECT EPIDERMAL GLAND

The sternal gland of primitive termites of the genus Zootermopsis (Z. nevadensis or Z. angusticollus) (Hagen) seems more organized than that of higher termites, in being comprised of three cell layers. It is also studded with about 200 campaniform sensilla. Below the meshwork cuticle of the gland lies a layer of columnar epithelial cells whose apical surfaces form a brush border, and whose basal surfaces are sculptured into a basketwork into which the second layer fits. Below the brush border are small microtubule-associated pits and coated vesicles. No channels can be seen either within or, except for the sensilla, between the cells. The second cell layer probably secretes the trail-following pheromone. Numerous electron-lucent droplets and large channels containing lipid micelles are found in the cytoplasm here, but the channels cannot be traced out of the secretory layer. The third layer consists of large pyriform cells. The campaniform sensilla are composed of three cells: the sensory cell proper whose dendrite carries a modified 9 + 0 sensory process, an accessory supporting cell that secretes an electron-opaque sheath, and an enveloping cell. At the cell borders of the sensillum, regions of septate and tight junction appear. There are also septate junctions between columnar cells and possibly tight junctions between columnar and secretory cells that would open an intracellular and molecular pathway to the endocuticle. The campaniform sensilla may be part of a feedback control system that determines the amount of pheromone deposited during trail laying.     

INHERITANCE OF MALE COURTSHIP BEHAVIOR,AGGRESSIVE SUCCESS,AND BODY SIZE IN DROSOPHILA SILVESTRIS

We describe a combined phenotypic and quantitative genetic investigation of the traits that may contribute to reproductive success in the picture-winged fly, Drosophila silvestris. These were courtship behavior, aggressive success, and body size and shape. Behavioral tests were conducted on wild-caught sires and their laboratory-reared sons. Neither size, shape, nor aggressive success predicted mating success. In both generations, males that spent more time courting and in wing-vibration were more likely to mate. However, components of courtship, overall aggressive success, and overall mating success had very low and nonsignificant heritabilities. The genetic estimates did not depend on whether they were based on males reared in both environments or reared only in the laboratory.     

PHORESY AS MIGRATION - SOME FUNCTIONAL ASPECTS OF PHORESY IN MITES

I. The dispersive role of mite phoresy, which has merely been presumed, is presented in the light of modern theories of migration with the aim of its characterization behaviourally, ecologically and physiologically. II. Data on phoresy accords well with modern, behavioural definitions of migration, as a phase of the depression of growth-promoting functions, during which the phoretic mite is transported while it shows a special readiness for being moved. III. Thus, modern definitions of migration encompass ‘passive’ movements which, none the less, involve active phases of seeking out of the host. IV. An examination of mite loads suggests that phoresy is most effective where the host gathers within the range of the mite; hence the association of phoresy with micro-habitats between which the mite requires to be carried. Monocultural plant-stands and ecological climaxes are not characterized by phoretic associations. V. The role of phoretic mites in colonization is clarified, in that phoretic migration is associated with sub-climactic communities. Thus, phoresy is invited where habitats are discrete and temporary, in which case it is manifest, as typical of migration, as a means of colonizing and exploiting irregularly changing habitats by r-selected, pre-reproductive individuals. VI. Waiting-stages, marked by the depression of growth-promoting functions, occur within the life-cycle of the phoretic mite. The ‘hypopus facies' characterize the typical phoretic stage, whose association with the host is an adaptation for survival in extreme environments. VII. Attachment pattern is a function of specificity towards the host. Structural and behavioural adaptations for attachment are developed and some sensory mechanisms have been shown, as have some physiological relationships with changes in the substrate; these changes also affect detachment. VIII. That phoresy is not caused by unfavourable conditions but is related to those that allow optimum dispersal is supported by sound evidence. IX. Physiologically, waiting stages have analogies with diapause which, together with migration, have been characterized by a temporary failure of the migrant to respond, by further growth and development, to the conditions that will eventually promote these processes. X. With phoresy are contrasted relations, between mite and insect, where the association is assured and more or less permanent. XI. The study of phoresy is very fragmented. However, a case has now been made for putting the dispersive role of phoresy beyond presumption, so that phoretic associations can clearly be fitted into modern treatments of migration.