Evolution of the Amylase Isozymes in the Drosophila melanogaster Species Subgroup

The relationship between the net charge of molecules and their mobility on electrophoresis was analyzed for Drosophila alpha-amylases. Most of the differences in electrophoretic mobility, 98.2%, can be explained by the charge state. Therefore five reference amino acid sites, which are informative residues for charge differences among amylase isozymes, were considered for the evolution of the isozymes in Drosophila melanogaster. The amylase isozymes in D. melanogaster can be classified into three groups, I (AMY1, AMY2, and AMY3-A), II (AMY3-B and AMY4), and III (AMY5, AMY6-A, and AMY6-B), based on the differences in the reference sites. The most primitive amylase in D. melanogaster was found to belong to Group I, most likely the AMY2 isozyme. Groups II and III could have been derived from Group I. These results were confirmed by the analysis of 38 amino acid sites with charge differences in Drosophila.     

Morphometric Analysis of Male Genitalia in Sibling Species of Drosophila virilis Sturt.

The structure of male genital organs in sibling species of the virilis group of Drosophila was examined using methods of multivariate statistics. The differences among these species were estimated using 33 indices and 2 angle parameters. The intraspecific and interspecific correlation structure of the examined characters and the order of their divergence were established. The key characters with respect to forming interspecific differences in the virilis species group were identified. Based on these results, the relative systematic positions of the sibling species are discussed as well as similarities and differences of the pattern of relationships among the species from that generally accepted for the virilis group.     

Effect of Drosophila melanogaster Female Size on Male Mating Success

In this study, we examined the influence of female size on mating success in Drosophila melanogaster. The results that were obtained from experiments performed in mating chambers allowed us to confirm the results of previous studies, demonstrating higher mating success of larger D. melanogaster males, and to conclude that female size also affects mating success, either when considering a single male or two competing males. We observed that the advantage for larger males depends on their size relative to that of the female, demonstrating a previously unknown role for female size in mating behavior studies. This effect of female size on mating success depends on various factors: males take longer to initiate courtship toward larger females, large females receive more wing vibrations from males prior to mating, and large females tend to keep moving for longer periods during male courtship. The importance of this finding is discussed in the context of recent reports on sexual conflict in D. melanogaster, in which males were observed to depress fitness in females as a result of intercourse.     

Female Genitalia Concealment Promotes Intimate Male Courtship in a Water Strider

Violent coercive mating initiation is typical for animals with sexual conflict over mating. In these species, the coevolutionary arms-race between female defenses against coercive mating and male counter-adaptations for increased mating success leads to coevolutionary chases of male and female traits that influence the mating. It has been controversial whether one of the sexes can evolve traits that allow them to “win” this arms race. Here, we use morphological analysis (traditional and scanning electron micrographs), laboratory experiments and comparative methods to show how females of a species characterized by typical coercive mating initiation appear to “win” a particular stage of the sexual conflict by evolving morphology to hide their genitalia from direct, forceful access by males. In an apparent response to the female morphological adaptation, males of this species added to their typically violent coercive mounting of the female new post-mounting, pre-copulatory courtship signals produced by tapping the water''s surface with the mid-legs. These courtship signals are intimate in the sense that they are aimed at the female, on whom the male is already mounted. Females respond to the signals by exposing their hidden genitalia for copulatory intromission. Our results indicate that the apparent victory of coevolutionary arms race by one sex in terms of morphology may trigger evolution of a behavioral phenotype in the opposite sex.     

Molecular Spectrum of Spontaneous de Novo Mutations in Male and Female Germline Cells of Drosophila melanogaster

We carried out mutation screen experiments to understand the rate and molecular nature of spontaneous de novo mutations in Drosophila melanogaster, which are crucial for many evolutionary issues, but still poorly understood. We screened for eye-color and body-color mutations that occurred in the germline cells of the first generation offspring of wild-caught females. The offspring were from matings that had occurred in the field and therefore had a genetic composition close to that of flies in natural populations. We employed 1554 F₁ individuals from 374 wild-caught females for the experiments to avoid biased contributions of any particular genotype. From ~8.6 million alleles screened, we obtained 10 independent mutants: two point mutations (one for each sex), a single deletion of ~6 kb in a male, a single transposable element insertion in a female, five large deletions ranging in size from 40 to 500 kb in females, and a single mutation of unknown nature in a male. The five large deletions were presumably generated by nonallelic homologous recombination (NAHR) between transposable elements at different locations, illustrating the mutagenic nature of recombination. The high occurrence of NAHR that we observed has important consequences for genome evolution through the production of segmental duplications.     

X-Y Exchange and the Coevolution of the X and Y Rdna Arrays in Drosophila melanogaster

The nucleolus organizers on the X and Y chromosomes of Drosophila melanogaster are the sites of 200-250 tandemly repeated genes for ribosomal RNA. As there is no meiotic crossing over in male Drosophila, the X and Y chromosomal rDNA arrays should be evolutionarily independent, and therefore divergent. The rRNAs produced by X and Y are, however, very similar, if not identical. Molecular, genetic and cytological analyses of a series of X chromosome rDNA deletions (bb alleles) showed that they arose by unequal exchange through the nucleolus organizers of the X and Y chromosomes. Three separate exchange events generated compound X·Y ^L chromosomes carrying mainly Y-specific rDNA. This led to the hypothesis that X-Y exchange is responsible for the coevolution of X and Y chromosomal rDNA. We have tested and confirmed several of the predictions of this hypothesis: First, X· Y^L chromosomes must be found in wild populations. We have found such a chromosome. Second, the X·Y^L chromosome must lose the Y^L arm, and/or be at a selective disadvantage to normal X⁺ chromosomes, to retain the normal morphology of the X chromosome. Six of seventeen sublines founded from homozygous X·Y^Lbb stocks have become fixed for chromosomes with spontaneous loss of part or all of the appended Y^L. Third, rDNA variants on the X chromosome are expected to be clustered within the X⁺ nucleolus organizer, recently donated (" Y") forms being proximal, and X-specific forms distal. We present evidence for clustering of rRNA genes containing Type 1 insertions. Consequently, X-Y exchange is probably responsible for the coevolution of X and Y rDNA arrays.     

Rapid Divergent Evolution of Male Genitalia Among Populations of Drosophila buzzatii

Increasing evidence from multiple animal systems suggests that genital evolution and diversification are driven by rapid and strong evolutionary forces. Particularly, the morphology of male genital structures is considered to be among the fastest evolving traits in animal groups with internal fertilization. In this study, we investigated patterns of male genital variation within and between natural populations of the cactophilic fly Drosophila buzzatii in its original geographic distribution range in the Neotropics. We detected significant morphological differences among populations and distinguished five differentiated groups. Moreover, among population differentiation in genital morphology was associated with the degree of geographic isolation among populations and clearly contrasted with the general homogeneity detected for the putatively neutral mitochondrial gene COI. Integrating our present data with previous molecular population genetic surveys, our results suggest that male genital morphology has rapidly diverged after the recent demographic expansion that D. buzzatii has undergone in the arid zones of South America. Because the “lock and key” hypothesis failed to explain the present pattern, we explored alternative explanations for the observed pattern of genital diversification including drift-facilitated sexual selection.     

Comparative Genomics of Mitochondrial DNA in Members of the Drosophila melanogaster Subgroup

In this study, a comparative genomics approach is employed to investigate the forces that shape evolutionary change in the mitochondrial DNA (mtDNA) of members of the Drosophila melanogaster subgroup. This approach facilitates differentiation of the patterns of variation resulting from processes acting at a higher level from those acting on a single gene. The mitochondrial genomes of three isofemale lines of D. simulans (siI, -II, and -III), two of D. melanogaster (Oregon R and a line from Zimbabwe), and D. mauritiana (maI and -II), and one of D. sechellia were sequenced and compared with that derived from D. yakuba. Data presented here indicate that at least three broad mechanisms shape the evolutionary dynamics of mtDNA in these taxa. The first set of mechanisms is intrinsic to the molecule. Dominant processes may be interpreted as selection for an increased rate of replication of the mtDNA molecule, biases in DNA repair, and differences in the pattern of nucleotide substitution among strands. In the genes encoded on the major strand (62% of the coding DNA) changes to or from C predominate, whereas on the minor changes to or from G predominate. The second set of mechanisms affects distinct lineages. There are evolutionary rate differences among lineages, possibly owing to population demographic changes or changes in mutational biases. This is supported by the heterogeneity found in synonymous, nonsynonymous, and silent substitutions. The third set of mechanisms differentially affects distinct genes. A maximum-likelihood sliding-window analysis detected four disjunct regions that have a significantly different nucleotide substitution process from that derived from the complete sequence. These data show the potential for comparative genomics to tease apart subtle forces that shape the evolution of DNA. Received: 30 July 1999 / Accepted: 16 March 2000     

Infanticide as Sexual Conflict: Coevolution of Male Strategies and Female Counterstrategies

One of the earliest recognized forms of sexual conflict was infanticide by males, which imposes serious costs on female reproductive success. Here I review two bodies of evidence addressing coevolved strategies of males and females. The original sexual selection hypothesis arguing that infanticide improves male mating success by accelerating the return of females to fertilizable condition has been generally supported in some taxa—notably, some primates, carnivores, rodents, and cetaceans—but not in other taxa. One result of recent research has been to implicate other selective benefits of infanticide by males in various taxa from insects to birds to mammals, such as acquisition of breeding status or improvement of the female breeding condition. In some cases, however, the adaptive significance of male infanticide remains obscure. The second body of data I review is arguably the most important result of recent research: clarifying the possible female counterstrategies to infanticide. These potential counterstrategies span diverse biological systems, ranging from sexual behavior (e.g., polyandrous mating), to physiology (e.g., the Bruce effect), to individual behavior (e.g., maternal aggression), to social strategies (e.g., association with coalitionary defenders of either sex). Although much remains to be studied, these current data provide compelling evidence of sexually antagonistic coevolution surrounding the phenomenon of infanticide.At its most elemental level, infanticide is the killing of a newborn individual by a conspecific. With the growing appreciation of its biological significance, however, infanticide came to be defined more broadly as any “behavior that makes a direct and significant contribution to the immediate death of an embryo or newly hatched or born member of the performer’s own species” (Mock 1984, p. 4) or “any form of lethal curtailment of parental investment in offspring brought about by conspecifics” (Hrdy and Hausfater 1984, p. xv). These definitions highlight the heterogeneous and variable nature of the phenomenon, which can be perpetrated by either sex, by parents or other kin, by individuals unrelated to the victim, in a wide variety of social and mating systems, under a range of seasonal or aseasonal breeding regimes, and across diverse taxa straddling vertebrates and invertebrates.One adaptive form of infanticide—the killing of infants by unrelated males—is arguably the archetype of sexual conflict. In 450 BCE, Herodotus not only documented the behavior among Egyptian cats, but explained it as a male “trick” to obtain sexual access to females otherwise preoccupied with maternal duties (Delibes et al. 2012). Among the myriad ideas inaugurating sociobiology in the 1970s, the hypothesis that infanticide is a male strategy that improves reproductive success at the expense of female fitness (Hrdy 1974) constituted one of the first demonstrations of the “battle of the sexes” theory developed by Williams (1966) and Trivers (1972). Partly because of the controversy surrounding the appearance of this hypothesis (Rees 2009), however, subsequent research focused more on male strategy than on the other party in this sexual dialectic, the female. Thus, field and laboratory research has helped to establish its many forms and conditional occurrence, describe its distribution across taxa, and clarify its adaptive significance, but it is only relatively recently that female counterstrategies have become the subjects of rigorous study, even though their potential importance was grasped early on (Hrdy 1979).In this article, I review selected aspects of this body of data and analysis. My focus is on nonparental male infanticide targeting dependent young—in mammals, nursing individuals—as opposed to older, weaned offspring, the killing of which is variably rendered “juvenilicide,” “pedicide,” or “filicide” (e.g., Agoramoorthy and Mohnot 1988; Palombit 2014, in press).     

中国特有果蝇 Drosophila curviceps 种亚组在Drosophila immigrans种组中的种系发生地位

果蝇immigrans种组中的curviceps种亚组是1992年新建立的中国特有果蝇类群。该种亚组中的物种主要分布在中国大陆和台湾。目前除了形态学水平的研究外,还没有其他证据支持建立该种亚组的合理性及其起源和种系发生地位。为了在DNA分子水平上探讨果蝇curviceps种亚组在果蝇immigrans种组中的种系发生地位,从而为今后更深入地研究中国特有果蝇,甚至为果蝇亚属的进化遗传学提供理论依据,测定了immigrans种组5个种亚组（nasuta、immigrans、hypocausta、quadrilineata、curviceps)中12个代表物种的rDNA的ITS1和部分Adh基因的序列。其中ITS1序列的长度为513－587bp,共有191个信息位点;Adh基因片段的长度在714－747bp之间,共99个信息位点。考虑到单个分子提供的信息较少,将两个分子的序列综合起来,组成一个较长的复合序列。分别根据ITS1,Adh和两个分子的复合序列排比（Alignment)结果,和最大简约法和邻接法构建分子系统树,其中根据复合序列构建的系统树与形态学研究结果最为一致。分子树显示curviceps种亚组的特种确定单独形成一个分枝,为种亚组级的分类阶元,支持了形态学将其建立为一个新种亚组。根据Kimura距离,估算了复合分子的替换速率约为每百万年1．48％,进而计算出5个种亚组的分 歧年代。结合各物种的地理分布,推测了immigrans种组的进化历史：curviceps种亚组与quadrilineata种亚组的亲缘关系最近,主要分布在中国南部的温带地区。它们之间的分歧时间大约为3．4百万年,是最年轻的两个种亚组。主要分布在苏门答腊及附近的热带地区的hypocausta种亚组的物种是最早分化出来的,与其他种亚组的分歧时间约为9．2百万年。该结果与形态学和生物地理学研究相吻合。值得一提是的,目前归属仍存在争议的物种D.neohypocausta,在分子系统树中与hypocausta种亚组的物种相距较远,而与immiagrasn种亚组的关系较近,但分枝置信度较低（＜50％）。由于还缺乏其他方面的证据,因此D.neohypocausta的归属有待今后的研究来作定论。     

The Female Post-Mating Response Requires Genes Expressed in the Secondary Cells of the Male Accessory Gland in Drosophila melanogaster

Seminal proteins from the Drosophila male accessory gland induce post-mating responses (PMR) in females. The PMR comprise behavioral and physiological changes that include increased egg laying, decreased receptivity to courting males, and changes in the storage and use of sperm. Many of these changes are induced by a “sex peptide” (SP) and are maintained by SP’s binding to, and slow release from, sperm. The accessory gland contains two secretory cell types with distinct morphological and developmental characteristics. Products of these “main” and “secondary” cells work interdependently to induce and maintain the PMR. To identify individual genes needed for the morphology and function of secondary cells, we studied iab-6^cocu males, whose secondary cells have abnormal morphology and fail to provide products to maintain the PMR. By RNA-seq, we identified 77 genes that are downregulated by a factor of >5× in iab-6^cocu males. By functional assays and microscopy, we tested 20 candidate genes and found that at least 9 are required for normal storage and release of SP in mated females. Knockdown of each of these 9 genes consequently leads to a reduction in egg laying and an increase in receptivity over time, confirming a role for the secondary cells in maintaining the long-term PMR. Interestingly, only 1 of the 9 genes, CG3349, encodes a previously reported seminal fluid protein (Sfp), suggesting that secondary cells may perform essential functions beyond the production and modification of known Sfps. At least 3 of the 9 genes also regulate the size and/or abundance of secondary cell vacuoles, suggesting that the vacuoles’ contents may be important for the machinery used to maintain the PMR.     

A Comparison of Female Postcopulatory Behavior in Drosophila melanogaster and Drosophila biarmipes

The postcopulatory behavior of Drosophila biarmipes and Drosophila melanogaster females was analyzed and compared. Females from both species were shown to undergo a series of behavioral changes following mating, including significant reductions in both sexual attractiveness and receptivity. However, while both attractiveness and receptivity returned to “virgin-like” levels within a few days in D. melanogaster, D. biarmipes females, which regained their sexual attractiveness within a few days, remained unreceptive to copulation for at least 2 weeks. With respect to fecundity, D. melanogaster females produced more offspring when given opportunities to remate, while D. biarmipes females did not benefit from remating opportunities. These observations suggest that D. biarmipes females may have the ability to store sperm and produce offspring from a single mating over longer periods of time than other drosophilids.     

果蝇nasuta亚群求爱歌的种间识别与进化遗传学研究

果蝇ｎａｓｕｔａ亚群由１４个种、亚种和分类群组成,广泛分布于印度－太平洋区域。本文首次记录了ｎａｓｕｔａ亚群种的求爱歌,测量了脉冲歌时域模式的参数：脉冲串间隔（ＩＢＩ）、脉冲间隔（ＩＰＩ）、脉冲串时间长度（ＰＴＬ）、每个脉冲串的脉冲数（ＰＮ）、脉冲时间长度（ＰＬ）、波动周期时间长度（ＣＬ）。采用计算机声谱分析技术,作出求爱歌信号的三维数字功率谱图,进行频率分析。发现Ｄ．ｐｕｌａｕｎａ和Ｔａｘｏｎ－Ｆ不发出求爱歌声信号,视觉在交配中可能起重要作用。对其余种、亚种和分类群的求爱歌分析表明,ｎａｓｕｔａ亚群种的求爱歌分为脉冲歌和正弦歌。对部分种的正反交Ｆ１求爱歌分析表明,脉冲歌时域参数,如ＩＰＩ平均值为Ｘ染色体连锁或常染色体多基因控制,正弦歌频率偏向母方。根据不同种、亚种和分类群脉冲歌的时域模式构建ｎａｓｕｔａ亚群的系统树,对亚群中不同种、亚种和分类群的亲缘关系进行讨论。     

Female sterile mutations and egg chamber development in Drosophila melanogaster

Drosophila oogenesis provides an excellent opportunity to study fundamental aspects of developmental biology and to learn the importance of multiple signalling pathways in the regulation of cellular morphogenesis. Taking advantage of the genetic and molecular approaches extremely powerful in this organism, over the years an enormous collection of data has accumulated on the genes involved in important steps of egg chamber development, such as germline and somatic stem cell maintenance, division and differentiation; oocyte determination and positioning; establishment of follicle cell fate and axes formation. These different processes are mediated by a reciprocal cross-talk between germline and somatic follicle cells. Here, in a schematic and simplified form, we point out what we believe are the main recent results on the molecular and cellular mechanisms underlying ovarian development and outline our recent contribution to this field.     

Male genotype influences female reproductive investment in Drosophila melanogaster

In many species, males can influence the amount of resources their mates invest in reproduction. Two favoured hypotheses for this observation are that females assess male quality during courtship or copulation and alter their investment in offspring accordingly, or that males manipulate females to invest heavily in offspring produced soon after mating. Here, we examined whether there is genetic variation for males to influence female short-term reproductive investment in Drosophila melanogaster, a species with strong sexual selection and substantial sexual conflict. We measured the fecundity and egg size of females mated to males from multiple isofemale lines collected from populations around the globe. Although these traits were not strongly influenced by the male's population of origin, we found that 22 per cent of the variation in female short-term reproductive investment was attributable to the genotype of her mate. This is the first direct evidence that male D. melanogaster vary genetically in their proximate influence on female fecundity, egg size and overall reproductive investment.     

Genetic Architecture and Functional Characterization of Genes Underlying the Rapid Diversification of Male External Genitalia Between Drosophila simulans and Drosophila mauritiana

Male sexual characters are often among the first traits to diverge between closely related species and identifying the genetic basis of such changes can contribute to our understanding of their evolutionary history. However, little is known about the genetic architecture or the specific genes underlying the evolution of male genitalia. The morphology of the claspers, posterior lobes, and anal plates exhibit striking differences between Drosophila mauritiana and D. simulans. Using QTL and introgression-based high-resolution mapping, we identified several small regions on chromosome arms 3L and 3R that contribute to differences in these traits. However, we found that the loci underlying the evolution of clasper differences between these two species are independent from those that contribute to posterior lobe and anal plate divergence. Furthermore, while most of the loci affect each trait in the same direction and act additively, we also found evidence for epistasis between loci for clasper bristle number. In addition, we conducted an RNAi screen in D. melanogaster to investigate if positional and expression candidate genes located on chromosome 3L, are also involved in genital development. We found that six of these genes, including components of Wnt signaling and male-specific lethal 3 (msl3), regulate the development of genital traits consistent with the effects of the introgressed regions where they are located and that thus represent promising candidate genes for the evolution these traits.     

Clonal analysis in hybrids between Drosophila melanogaster and Drosophila simulans

We have analysed the viability of cellular clones induced by mitotic recombination in Drosophila melanogaster/D. simulans hybrid females during larval growth. These clones contain a portion of either melanogaster or simulans genomes in homozygosity. Analysis has been carried out for the X and the second chromosomes, as well as for the 3L chromosome arm. Clones were not found in certain structures, and in others they appeared in a very low frequency. Only in abdominal tergites was a significant number of clones observed, although their frequency was lower than in melanogaster abdomens. The bigger the portion of the genome that is homozygous, the less viable is the recombinant melano-gaster/simulans hybrid clone. The few clones that appeared may represent cases in which mitotic recombination took place in distal chromosome intervals, so that the clones contained a small portion of either melanogaster or simulans chromosomes in homozygosity. Moreover, Lhr, a gene of D. simulans that suppresses the lethality of male and female melanogaster/simulans hybrids, does not suppress the lethality of the recombinant melanogaster/simulans clones. Thus, it appears that there is not just a single gene, but at least one per tested chromosome arm (and maybe more) that cause hybrid lethality. Therefore, the two species, D. melanogaster and D. simulans, have diverged to such a degree that the absence of part of the genome of one species cannot be substituted by the corresponding part of the genome of the other, probably due to the formation of co-adapted gene complexes in both species following their divergent evolution after speciation. The disruption of those coadapted gene complexes would cause the lethality of the recombinant hybrid clones.     

Male recombination with single and homologous P elements in Drosophila melanogaster

It has previously been shown that, in the presence of a source of P element transposase, male recombination in Drosophila melanogaster is induced at a rate of about 1% in the region of a single P[CaSpeR] element. This paper shows that recombinant chromosomes retain unaltered P[CaSpeR] elements at the original site in a high proportion of cases. This result is incompatible with a simple model in which recombination occurs by resolution of a Holliday junction following P element excision and repair. It has also previously been shown that homozygous regions containing a P element produce male recombination levels of 10–20%, an order of magnitude higher than that given by a single element. This paper shows that reciprocal recombinant chromosomes retaining P[CaSpeR] elements can be combined to produce similarly high levels of recombination. This result potentially allows for recombinant chromosomes from homologous recombination to be analysed at the molecular level in the region of the inserted element.