Mating Barriers Research Articles

Response : Mating Types in Screwworm Populations?

Response is given to questions raised by L.E. LaChance, et al., regarding the types of screwworm that occur in Mexico and anatomical differences in male genitalia among types. Errors in chromosome length and arm ratios are discussed. Results of testing the V-81 strain (sterile males) indicate that mating barriers exist even at high release rates. Mating discrimination must be high for a population to withstand an excess of sterile flies. The relevance of this to eradication programs is discussed. (RJC)

Mating Types in Screwworm Populations?

Response is given to questions raised by L.E. LaChance, et al., regarding the types of screwworm that occur in Mexico and anatomical differences in male genitalia among types. Errors in chromosome length and arm ratios are discussed. Results of testing the V-81 strain (sterile males) indicate that mating barriers exist even at high release rates. Mating discrimination must be high for a population to withstand an excess of sterile flies. The relevance of this to eradication programs is discussed. (RJC)

MORPHOMETRIC EVIDENCE FOR INCIPIENT SPECIATION IN DROSOPHILA SILVESTRIS FROM THE ISLAND OF HAWAII.

Carson and Bryant (1979) reported a case of variability in a secondary sexual character of males of Drosophila silvestris, a giant fly endemic to the high-altitude rainforests of the geologically very new island of Hawaii. In populations from the north and east (NE it is wholly lacking in females and shows high heritability in crosses (Bryant and Carson, 1979). Both chromosomal and electrophoretic distances among populations of silvestris are negligible and silvestris has therefore been considered a clear example of a single biological (Carson and Bryant, 1979; Craddock and Johnson, 1979). The evidence for differentiation in the NE three of these are allopatric to silvestris and are endemic to separate, geologically older islands. The data support the notion that the radical new burst of evolutionary change has occurred relatively recently and solely within the N&E populations of D. silvestris, and that we are observing a case of incipient speciation. The discovery of a in statu nascendi is not in itself unusual. Many examples of incipient are known. The exciting implication of the D. silvestris situation is that here we have an example of the beginning of the development of a morphological character which is intimately concerned with sexual behavior. Male tibial cilia have a clearly-defined biological importance: the only function of this leg surface appears to be a ritualized stimulation of the female's abdomen during the final and crucial stage of courtship (Spieth, 1978). Although such a character might first arise simply in response to altered sexual selection in the population, the same character might later serve as an ethological barrier to hybridization. With newly-formed full which are sympatric, it is impossible to know whether ethological barriers to interbreeding arose in allopatry or upon secondary contact (Futuyma, 1979). We are left to speculate. In present-day communities, where rich species swarms appear to be maintained through prezygotic mating barriers, we can only surmise that these barriers arose in the absence of gene flow. In D. silvestris, we see a mechanism by which behaviorally-related reproductive isolation may arise in allopatry.

Hybridisation studies on sibling species of the Anopheles gambiae Giles complex (Diptera: Culicidae) in the laboratory

AbstractAssortative mating amongst species of the complex of Anopheles gambiae Giles that occur sympatrically in West Africa was investigated in laboratory mating-choice experiments using dieldrin resistance and hybrid sterility as genetic markers. In competition experiments involving A. gambiae and A. arabiensis Patt., mating was found to be assortative. No effect of cage volume was observed on the operation of the specific mate-recognition system. On the other hand, experiments in which A. gambiae and A. arabiensis were caged separately with A. melas Theo. failed to show the presence of mating barriers known to operate in nature. Similar cage experiments conducted with two different strains of A. gambiae showed that there was no marked mating barrier between the strains. Other experiments showed that hybrid females from the cross between A. gambiae females and A. arabiensis males and the reciprocal cross would mate with both parental types as well as their own males in cages.

REPRODUCTIVE ISOLATION IN SYMPATRIC SPECIES OF DAYFLYING MOTHS (HEMILEUCA: SATURNIIDAE).

Studies of mating barriers among closely related species are often considered profitable methods to investigate the process of speciation (Bush, 1975). For this reason the pheromone mating system in moths is of particular interest to the evolutionary biologist as an example of a mechanism through which reproductive isolation may develop. Species specificity of pheromone systems has been evaluated by observation of behavioral responses to chemically defined pheromone molecules and from electroantennograms of male response to pheromone sources. In general, direct observation of male response to calling females under field conditions has lagged behind laboratory work, perhaps because many economically important species are nocturnal (Carde et al., 1977; Bartell, 1977; Grant and Brady, 1977). During 1972 we observed interspecific attraction between two of three sympatric species of Hemileuca moths inhabiting the east slope of the Sierra Nevada mountains in California. Since no apparent breakdown of species phenotypes occurs in these populations, we decided to investigate the mechanism of reproductive isolation. The Hemileuca are large, diurnal, nonfeeding moths. Adult behavior is almostentirely reproductive. In this paper we present both qualitative and quantitative data on pheromone response and reproductive isolation in natural populations. The three species investigated were Hemileuca nuttalli (Cockerell), H. eglanterina (Boisduvall), and H. hera (Harris) (Fig.

A Re-Evaluation of Introgression Between Dacus Tryoni and Dacus Neohumeralis (Diptera: Tephritidae).

The humeral calli in D. tryoni range from completely yellow to almost entirely brown. This variation is largely genetic and the character responds readily to selection in the laboratory. In field populations, selection favours flies with little or no brown pigment on the calli (around 3% brown) and there is a strong natural selection against the darker forms. However, field populations of D. tryoni show only a limited response to this selection, since flies with dark calli are regularly present in field samples. One possible explanation is that the loss of genes through selection is balanced by recurrent gene exchange with D. neohumeralis, a species in which selection favours flies with dark calli. Gene exchange between the two species is restricted, because their periods of sexual activity do not coincide. This mating barrier is incomplete however, since limited gene exchange can be induced in the laboratory. D. tryoni is sympatric with D. neohumevalis for only part of its range in eastern Australia. It is shown that callus variability in D. tryoni is uniform over its entire range and is therefore independent of possible gene exchange with D. neohumeralis. An alternative mechanism is proposed to explain the maintenance of callus variability in D. tryoni, namely, a stabilizing selection that operates against flies at both extremes of its callus range.

THE INFLUENCE OF CYTOPLASMIC POLLEN STERILITY ON GENE EXCHANGE BETWEEN POPULATIONS

Abstract : The behavior of cytoplasm and plasmon-sensitive genes producing, in combination, pollen sterility has been reinvestigated taking into account gene flow between populations. It has been repeatedly suggested that cytoplasmic pollen sterility may give rise to a mating barrier which would tend to inhibit gene exchange between populations and in this way initiate speciation. This investigation confirms the findings of an earlier paper (Watson and Caspari, 1960) that there is no basis for this belief. (Author)