Misregulation of spermatogenesis genes in Drosophila hybrids is lineage-specific and driven by the combined effects of sterility and fast male regulatory divergence.

Hybrid male sterility is a common outcome of crosses between different species. Gene expression studies have found that a number of spermatogenesis genes are differentially expressed in sterile hybrid males, compared with parental species. Late-stage sperm development genes are particularly likely to be misexpressed, with fewer early-stage genes affected. Thus, a link has been posited between misexpression and sterility. A more recent alternative explanation for hybrid gene misexpression has been that it is independent of sterility and driven by divergent evolution of male-specific regulatory elements between species (faster male hypothesis). The faster male hypothesis predicts that misregulation of spermatogenesis genes should be independent of sterility and approximately the same in both hybrids, whereas sterility should only affect gene expression in sterile hybrids. To test the faster male hypothesis vs. the effect of sterility on gene misexpression, we analyse spermatogenesis gene expression in different species pairs of the Drosophila phylogeny, where hybrid male sterility occurs in only one direction of the interspecies cross (i.e. unidirectional sterility). We find significant differences among genes in misexpression with effects that are lineage-specific and caused by sterility or fast male regulatory divergence.

Quantitative trait loci and interaction effects responsible for variation in female postmating mortality in Drosophila simulans and D. sechellia introgression lines.

Mating appears to inflict a cost to Drosophila females, resulting in a reduction of their lifespan shortly after mating. Males from different chromosome extracted lines differ significantly in their detrimental effects on postmating female survival, and seminal fluid proteins produced in the male accessory glands are at least partially responsible for the effect. This suggests that there is a genetic basis underlying the male inflicted effect on female's postmating mortality. However, the genes responsible for this effect remain elusive. Using males from introgression lines between D. simulans and D. sechellia genomes and a quantitative trait locus (QTL) mapping approach, we identified chromosomal regions that affect postmating mortality of females. We found a second chromosome QTL with an effect on average female lifespan after mating and a third chromosome QTL with an effect on postmating female mortality rate. Under the general observation of a faster divergence of sex-related genes among closely related species, it is predicted that genes for reproductive traits other than hybrid sterility will show evidence of epistatic effects when brought into a heterospecific background. We detected a significant epistatic genetic effect on postmating female mortality rate that supports this prediction.

Genome size and longevity in fish.

The wide variety of genome sizes (measured as C-value) observed across taxa is not related to organismal complexity or number of coding genes. Partial answers to this C-value enigma have been found by establishing associations between C-value and particular phenotypic characteristics. One such controversial association has been recently suggested between genome size and longevity in birds. In order to determine whether genome size is a general predictor of longevity, we have extended the analysis to the Actinoptergyian fish, a widely divergent group in terms of both longevity and genome size. We collected data on genome size, longevity and body mass for species covering fourteen orders of bony fish. Analysis of covariance using order as a cofactor shows a significant effect of genome size on longevity (corrected for body mass), with lifespan increasing as a function of genome size. Analysis of phylogenetically independent contrasts for orders with a large number of species with a well resolved phylogenetic relationship (Acipenseriformes, Cypriniformes, and Salmoniformes) found the same trend of longer lifespan with increases in genome size but the relationship was not significant. Our results consistently show an increase in lifespan for fish with larger genomes.

Correlated effects of sperm competition and postmating female mortality.

Adaptations in one sex may impair fitness in the opposite sex. Experiments with Drosophila melanogaster have shown that seminal fluid from the male accessory gland triggers a series of postmating responses in the female, including increased egg laying rate and lower remating propensity, but that accessory gland proteins also increase female death rate. Here, we tested the relationships among the longevity of females mated to males from 51 chromosome-extracted D. melanogaster lines, male-mating ability, and sperm-competitive ability. We found significant differences in longevity of females mated to males of different genotypes, and all mated females showed a higher death rate than control virgin females shortly after mating. Both the age-independent mortality parameter (the intercept of the female's survival function) and the slope of the mortality rate curve were significantly correlated with the proportion of progeny sired by the first male to mate relative to tester males (sperm-defense ability, P1). No significant correlation was found between the proportion of progeny sired by the second-mating male relative to tester males (sperm-offense ability, P2) and any mortality parameter. Our results support the hypothesis of a tradeoff between defensive sperm-competitive ability of males and life-history parameters of mated females.

Nontransitivity of sperm precedence in Drosophila.

Sperm competition is an important component of fitness in Drosophila, but we still do not have a clear understanding of the unit of selection that is relevant to sperm competition. Here we demonstrate that sperm competitive ability is not a property of the sperm haplotype, but rather of the diploid male's genotype. Then we test whether the relative sperm competitive ability of males can be ranked on a linear array or whether competitive ability instead depends on particular pairwise contests among males. Sperm precedence of six chromosome-extracted lines was tested against three different visible marker lines (cn bw, bwD, and Cy), and the rank order of the six lines differed markedly among the mutant lines. Population genetic theory has shown that departures from transitivity of sperm precedence may be important to the maintenance of polymorphism for genes that influence sperm competitive ability. The nontransitivity seen in sperm precedence should theoretically increase the opportunity for polymorphism in genes that influence this phenotype.

Chromosomal effects on male and female components of sperm precedence in Drosophila.

Recent experiments with Drosophila have demonstrated that the success of sperm in multiply mated females depends on the genotype of both the male and the female. To further characterize the distinction between male and female roles in sperm success, we scored variation in both sexes in sperm competitive ability among a set of chromosome replacement lines that allow identification of effects to each chromosome. We detected significant male and female effects on sperm precedence, defined as the ability of a male's ejaculate to displace resident sperm (P2) or avoid being displaced by subsequent matings (P1). Tests of effects of first, second and third chromosome substitutions revealed significant differences among third chromosomes in male sperm precedence (both P1 and P2) and a first x second chromosome interaction in female's effect on sperm precedence (only P1). We found no significant correlation between male and female effects on sperm precedence, suggesting that the variation found in both P1 and P2 has a different genetic cause in the two sexes.

Direct visualization of sperm competition and sperm storage in Drosophila.

Drosophila females engage in multiple matings [1] [2] [3] [4] even though they can store sperm in specialized organs for most of their life [5]. The existence of sperm competition in Drosophila has been inferred from the proportion of progeny sired by the second male in double-mating experiments [6] [7] [8]. Investigators have used this approach to quantify genetic variation underlying sperm competition [8] [9] [10], to elucidate its genetic basis [11], to identify the dependence of different male competitive ability on the genotype of the females with which they mate [12] and to discern the potential role of sperm competition in species isolation [13] [14]. This approach assumes that the sperm from two males stored in a female compete to fertilize the eggs. The mechanism by which sperm competition is accomplished is still unknown, however. Here, fluorescence microscopy, cytometry, and differently labeled sperm were used to analyze the fate of sperm inside the female's sperm storage organs, to quantify sperm competition, and to assess how closely paternity success corresponds to the appearance and location of the sperm. The results show that the first male's sperm is retained for a shortened period if the female remates, and that the second males that sire more progeny either induce females to store and use more of their sperm or strongly displace resident sperm.

Broad-sense sexual selection, sex gene pool evolution, and speciation.

Studies of sexual selection have traditionally focused on explaining the extreme sexual dimorphism in male secondary sexual traits and elaborate mating behaviors displayed by males during courtship. In recent years, two aspects of sexual selection have received considerable attention in the literature: an extension of the sexual selection concept to other traits (i.e., postcopulatory behaviors, external and internal genital morphology, gametes, molecules), and alternative mechanistic explanations of the sexual selection process (i.e., coevolutionary runaway, good-genes, sexual conflicts). This article focuses on the need for an extension of sexual selection as a mechanism of change for courtship and (or) mating male characters (i.e., narrow-sense sexual selection) to all components of sexuality not necessarily related to courtship or mating (i.e., broad-sense sexual selection). We bring together evidence from a wide variety of organisms to show that sex-related genes evolve at a fast rate, and discuss the potential role of broad-sense sexual selection as an alternative to models that limit speciation to strict demographic conditions or treat it simply as an epiphenomenon of adaptive evolution.

Sex-related genes, directional sexual selection, and speciation.

Reproductive isolation and speciation can result from the establishment of either premating or postmating barriers that restrict gene flow between populations. Recent studies of speciation have been dominated by a molecular approach to dissect the genetic basis of hybrid male sterility, a specific form of postmating reproductive isolation. However, relatively little attention has been paid to the evolution of genes involved in premating isolation and genes generally involved in other sex-related functions (e.g., mating behavior, fertilization, spermatogenesis, sex determination). We have assembled DNA sequences from 51 nuclear genes and classified them based on their functional characteristics. The proportion of nonsynonymous to synonymous nucleotide substitutions were compared between Drosophila melanogaster, Drosophila simulans, and Drosophila pseudoobscura, as well as between Caenorhabditis elegans and Caenorhabditis briggsae. We found a high ratio of nonsynonymous to synonymous substitutions for sex-related genes (i.e., genes involved in mating behavior, fertilization, spermatogenesis, or sex determination). The results suggest that directional sexual selection has shaped the evolution of sex-related genes and that these changes have more likely occurred during the early stages of speciation. It is possible that directional selection becomes relaxed after reproductive isolation has been completed between more distantly related species (e.g., D. melanogaster and D. pseudoobscura). However, a saturation in the number of nucleotide substitutions since the time of species separation may mask any sign of directional selection between more distantly related species.

High divergence of reproductive tract proteins and their association with postzygotic reproductive isolation in Drosophila melanogaster and Drosophila virilis group species.

The possible association between gonadal protein divergence and postzygotic reproductive isolation was investigated among species of the Drosophila melanogaster and D. virilis groups. Protein divergence was scored by high-resolution two-dimensional electrophoresis (2DE). Close to 500 protein spots from gonadal tissues (testis and ovary) and nongonadal tissues (malpighian tubules and brain) were analyzed and protein divergence was calculated based on presence vs absence. Both testis and ovary proteins showed higher divergence than nongonadal proteins, and also a highly significant positive correlation with postzygotic reproductive isolation but a weaker correlation with postzygotic reproductive isolation. Particularly, a positive and significant correlation was found between proteins expressed in the testis and postzygotic reproductive isolation among closely related species such as the within-phylad species in the D. virilis group. The high levels of male-reproductive-tract protein divergence between species might be associated with F1 hybrid male sterility among closely related species. If so, a lower level of ovary protein divergence should be expected on the basis that F1 female hybrids are fully fertile. However, this is not necessarily true if relatively few genes are responsible for the reproductive isolation observed between closely related species, as recent studies seem to suggest. We suggest that the faster rate of evolution of gonadal proteins in comparison to nongonadal proteins and the association of that rate with postzygotic reproductive isolation may be the result of episodic and/or sexual selection on male and female molecular traits.

Uterine motility and cervical ripening in second trimester elective abortion by two different PGE analogues.

The clinical effects were studied of two different PGE analogues on the uterine motility and cervical ripening of eighty pregnant women asking for a second trimester elective abortion for fetal abnormalities. Forty women received vaginal suppositories each containing 1 milligram of 16, 16-dimethyl-trans-s2-PGE1 (Gemeprost) every 3 hours (5 mg max). Intramuscular injections of 500 micrograms of 16-phenoxy-w 17, 18, 19, 20 tetranor PGE2 methyl-sulphonylamide (Sulprostone) were administered every four hours (2000 mcg max.) to the remaining forty patients. Thirty-three Gemeprost treated patients (82.5%) and 34 Sulprostone treated patients (85%) experienced a complete abortion in the mean of 12.92 +/- 6.95 hours and 11.88 +/- 6.8 hours respectively. The histological and ultrastructural findings of cervical ripening were similar in both groups, while the tocographic patterns showed different characteristics. Side effects occurred in 16 Sulprostone (40%), but only in 9 (22.5%) Gemeprost treated patients, demonstrating that Gemeprost, although equally effective, is better tolerated.

PIP: Researchers analyzed data on 80 pregnant women seeking a 2nd trimester abortion due to fetal abnormalities at the Federico II Medical School at the University of Naples in Italy to determine the effectiveness and side effects of 2 different prostaglandin analogues and their ability to bring about cervical ripening and uterine contractions. 40 women received 1 mg Gemeprost every 3 hours up to 5 mg in vaginal suppository form while the other 40 women who tended to be primigravidae received an intramuscular injection of 500 mcg Sulprostone every 4 hours up to 2000 mcg. Sulprostone achieved an 85% success rate and Gemeprost achieved an 82.5% success rate. Complete abortion occurred more quickly for multigravidae patients than it did for primigravidae patients (in hours, 10.6 vs. 16.5 for Gemeprost, p.1; 9.83 vs. 15.65 for Sulprostone, p.01). There was no statistically significant difference between the 2 treatment groups, however. Side effects were more common among Sulprostone patients than among Gemeprost patients (40% vs. 22.5%). The most common side effects among Sulprostone patients were, in descending order, abdominal pain (75%), diarrhea (50%), and nausea (50%). For Gemeprost patients, they were abdominal pain (55.5%) and headache (44.4%). In terms of uterine contractility, Sulprostone brought about hypertone more quickly than did Gemeprost (in minutes, 18.32 vs. 36.75; range 10-30 vs. 25-50). Gemeprost treatment was more like physiological labor than was Sulprostone treatment. Both prostaglandin analogues produced similar histological and ultrastructural findings of cervical ripening. These results indicated that the women were better able to tolerate Gemeprost.