Homogamic Matings Research Articles

Does adaptation to different diets result in assortative mating? Ambiguous results from experiments on Drosophila.

The emergence of behavioural isolation between populations under divergent selection can be crucial for ecological speciation, but the mechanisms underlying such isolation are poorly understood. Several experimental evolution studies have shown that positive assortative mating (preference for similar mates) can arise rapidly in Drosophila laboratory populations reared in different stressful conditions, while other studies failed to confirm this effect. Here, we present the results of an evolution experiment in which outbred lines of Drosophila melanogaster were reared for 1-2years on one of the three different diets (standard, starch based or high salt). We show that nonrandom mating arose in some, but not all lines, and that the manifestations and possible interpretations of this nonrandomness depend strongly on the type of tests used to assess mating preferences. More specifically, multiple-choice four-fly tests revealed positive assortative mating (prevalence of homogamic matings) in some starch-adapted and salt-adapted lines when paired with a control line reared on the standard diet, but competitive three-fly tests rather revealed competitive advantage of control males and females over the flies reared on stressful diets. The results imply that divergent adaptation can result in differences in mating propensity or competitive ability, which, in turn, may either facilitate or hamper speciation depending on the relative frequency of high- vs. low-competition settings in natural habitats of the diverging populations. The results also emphasize the importance of using diverse tests for assessing mating structure in natural and laboratory populations.

Effect of chromosome arrangements on mate recognition system leading to behavioral isolation in Drosophila ananassae

The mechanisms of speciation that appear in the early stages of reproductive isolation has been of recent interest to evolutionary biologists. Experiments were conducted to study behavioral isolation between karyotypically different homozygous strains derived from natural populations of Drosophila ananassae. Three mass cultures stocks established from flies collected from natural populations were employed and homozygous stocks (ST/ST and AL/AL) were made through selection for homozygosity. By employing male-choice technique, mating success was scored by direct observation in the Elens-Wattiaux mating chamber. There is preference for homogamic matings in all the three populations and the differences between homogamic and heterogamic matings are statistically significant in two populations (Lucknow and Varanasi). These findings provide evidence that there is incipient sexual isolation between karyotypically different strains of D. ananassae derived from natural populations which shows that chromosome arrangements may affect the mate recognition system in D. ananassae.

Conservation of the red-winged grasshopper, Oedipoda germanica (Latr.): the influence of reproductive behaviour

Reproductive isolation can function as a mechanism to maintain locally adapted gene complexes while decreasing the heterozygosity in distinct populations. As a result, reproductive behaviour should be considered a fundamental factor influencing reproductive isolation. This is of interest to conservation biology when one desires to regulate gene flow between two populations either by creating opportunities for increased dispersal, by relocation of individuals, or by re-introduction of a species to its natural habitat. Reproductive behaviour can also influence the effective population size and the actual population size through the Allee effect. We investigated the reproductive behaviour of individuals from two isolated populations of the red winged grasshopper, Oedipoda germanica, an endangered species in Central Europe. We detail several methods to show how several aspects of the reproductive behaviour of this species interact with the conservation of this species. Foreign males were not disfavoured in mate choice and male body size was also unimportant in mating success. Heterogamic matings were as productive as homogamic matings in terms of total number of eggs per female, egg hatching rate, or nymph survival. Therefore, we suggest that cross-matings of individuals from different populations do not positively influence population size by heterosis effects nor act they negatively in the form of outbreeding depression. We found that female O. germanica were able to store viable sperm for extended periods but egg pods showed a decrease in hatching rate when these females were deprived of additional mating opportunities. Multiple mated females laid more eggs than once-mated females. Hence, females are capable of founding new populations even after only one mating but their reproductive output may be reduced. Present-day gene flow between populations of O. germanica probably does not occur. Consequently, there is an urgent need to pursue habitat management and release programmes that maintain current population sizes of this species. With regard to the reproductive behaviour of the red-winged grasshopper, we suggest that relocation programmes release males and female together and at an early adult stage. Also, because female reproductive output increases with mating activity, the initial release should involve excess females. Because males have a shorter lifespan than females a subsequent release of males at a later time may enhance the overall success of local conservation efforts by resulting in more offspring per female.

Incipient sexual isolation in the nasuta-albomicans complex of Drosophila: mating preference in male-, female- and multiple-choice mating experiments.

Interracial divergence is an important facet of speciation. The nasuta-albomicans complex of Drosophila with sixteen morphologically identical, karyotypically different but cross-fertile races is an excellent system to study a few dimensions of raciation. Drosophila nasuta nasuta, Drosophila nasuta albomicans, Cytorace 1, Cytorace 2, Cytorace 3 and Cytorace 4 of this subgroup have been subjected to male-, female- and multiple-choice mating experiments. Out of 8456 crosses conducted, 7185 had successful matings. The overall impression is that mating is far from random amongst these six closely related races of the nasuta-albomicans complex. The males of D. n. albomicans, Cytorace 1 and Cytorace 4 in male-choice, the females of Cytorace 1 and Cytorace 2 in female-choice, and the males and females of D. n. nasuta, D. n. albomicans, Cytorace 1 and Cytorace 4 against the males and females of Cytorace 2 in multiple-choice experiments, had significantly more homogamic matings than expected. Thus in this study of evolutionary experimentation on raciation under laboratory conditions, we have documented the initiation of preference for conspecific matings among closely related and independently evolving members of the nasuta-albomicans complex of Drosophila.

Frequency dependent selection: I. Rare male phenomenon in D. subobscura dependent on the proportion of Amy genotypes and substrate composition

AbstractAnalysis of the rare male mating advantage in D. subobscura, as a type of frequency dependent selection on maltose and starch media, was done by applying different statistical approaches (χ2, cross‐product ratio, variance and regression analysis). They reveal that mating occurs at random when proportions of prospective mates are equal, and that mating success of the males homozygous for Amy‐locus genotypes (S/S and F/F) depends on their proportion. Regression analysis showed that the F/F males are sexually more active (have higher vigour) than S/S males. Rare male effect is one‐sided and appears in F/F males that partake in more heterogamic matings. Comparison of the number of observed and expected homo‐ and heterogamic matings shows that homogamic matings are more frequent. Multifactorial analysis of variance shows that the number of matings are different for nine pairs of lines and four possible mating types (SfSm, SfFm, FfSm, FfFm). The rare male phenomenon is not dependent on different food composition, but is associated with variations in individual genotypes.

Direct observation of sexual competition inDrosophila melanogaster: The mutantWhite in competition with other genotypes

When two types of Drosophila are in competition, the frequency dependence of mating success routinely is measured in our laboratory by direct observation of mating pairs in "Elens-Wattiaux" observation chambers. The present experiments concern white mutants (used here as a reference standard) in competition with three other genotypes: wild-type Canton S, "giant" gt wa, and "giant" gt13z/w+ Y/C(1)Dx, y f. From the present observations, the frequency dependence of mating success seems a very common phenomenon: a rare-type sexual advantage exists for females and for males. Sexual activity of male and female white mutants is significantly higher when food is present in the mating chamber. Males of the other strains also are more active in the presence of food. Homogamic matings are more frequent among gt13z/w+ Y/C(1)Dx, y f flies.

Sexual selection in Drosophila silvestris of Hawaii

Previous discovery that Drosophila melanogaster females tend to discriminate in mating against phenotypes of earliest courting males prompted a study of the Hawaiian species D. silvestris. Tibial bristle variation in males from opposite coasts of the island of Hawaii functions in courtship, and the possibility that females can distinguish males differing in the tibial trait is explored. Mating tests, designed to give each female and male an alternative choice between two individuals of opposite sex every 30 min, consisted of intrapopulation tests with a strain derived from an eastern (Kilauea) population and interpopulation tests between that strain and one derived from a western (Kahuku) population. Males were given initial combat tests, with "winners" then used in mating (except one test with "loser" males). Matings (52-55%) were classified into categories according to the readiness of the female to mate and sequence of courtship. Low-threshold females (accepting the first male after less than four courtship bouts) occurred at 30-35%. Among intrapopulational tests, females (with higher threshold) accepted first- and second-courting males about equally (25:36, respectively), but for male success in mating, the winning of initial intermale combats and the uniformity of courtship effort tended to be important criteria. Among interpopulation tests, homogamic matings were nearly equal (25% each), but heterogamic matings contrasted in that Kilauea females were reluctant to mate with Kahuku males (14%), while reciprocal matings occurred most frequently (34%). Females favored males second to court, particularly when a Kilauea male (with extra tibial bristles) was the second male. Thus a morphological feature likely to be influential in mating is demonstrated to be so; and sexual selection is operating via male-male combat plus discrimination in favor of particular opposite-sex individuals in this species.

Mating Preferences and Sexual Isolation Within and Between the Incipient Species of Drosophila Paulistorum

The male choice experimental method was used to test mating preferences of six races of Drosophila paulistorum. The races (number of strains in parentheses) are: Centro-American (3); Amazonian (4); Orinocan (5); Andean-South Brazilian (6); Transitional (4); and Guianan (1). Strains of the same race often showed significant preferences for homogamic matings, but strains of different races showed such preferences to a much greater extent. On the average, sexual isolation was lower in matings between the Transitional race strains and strains of other races than it was in matings between strains of the other five races. The degree of sexual isolation showed only a weak positive correlation with fertility or sterility of the hybrids between the strains crossed. An addendum contains additions and corrections to the data reported (1959) on D. paulistorum by Dobzhansky and Spassky with regard to the production of sterile and fertile F, hybrids in various crosses between strains. Drosophila paulistorum Dobzhansky and Pavan is a taxon which contains an extraordinary complex of geographic races or incipient species. Five of them have almost reached the status of reproductively isolated but morphologically indistinguishable species. These are the Centro-American, Orinocan, Amazonian, Andean-South Brazilian, and Guianan races. They are mostly allopatric, but in some places their geographic ranges overlap, and two incipient species may coexist sympatrically without interbreeding. When placed together in laboratory experiments, females of one and males of another race exhibit a pronounced and in some instances nearly complete, sexual isolation. If hybrids are produced, the females are fertile but the males are sterile. The sixth, or Transitional, race occurs in Colombia; all strains of this race can be crossed and will produce fertile hybrids of both sexes with at least one of the other five races (Dobzhansky and Spassky, 1959). The two isolating mechanisms, sexual isolation and hybrid sterility, are quite different in their genetic bases. The former is determined by polygenic differences between the races; the latter involves a remarkable predetermination of the egg cytoplasm by the genotype present in the egg before meiosis an,d fertilization (Ehrman 1960, 1961). It is mainly because of the existence of the Transitional race that Drosophila paulistorum is regarded as a single species. It still has a single, though deeply cleft, gene pool. The races (incipient species) of 67 This content downloaded from 157.55.39.123 on Mon, 18 Jul 2016 05:57:34 UTC All use subject to http://about.jstor.org/terms 68 THE AMERICAN MIDLAND NATURALIST 68(1) D. paulistorum are among the best known examples of borderline situations bridging the gap between race and species (Dobzhansky, 1961). Analysis of such borderline situations presents a challenging problem to evolutionists. It is highly improbable that the reproductive isolation which is observed between the incipient species could have arisen simultaneously as an absolute barrier to gene exchange. More likely, it arose gradually, and is probably in the process of construction now. \;: :,IONNDURAs SALVADO OSTA RICA ~ NAM 5NT MARTA 9 T~~ A6 BUCARAMANGA. BUENAVENTURA* *TRINIDAD P0NR LLANSANT )MINGGO