POLLEN PERFORMANCE AND SEX-RATIO EVOLUTION IN A DIOECIOUS PLANT

There has been a proliferation of studies, in a variety of taxa, that have detected sex-linked or cytoplasmic genes that enhance their own transmission via sex-ratio distortion. One of the most important parameters influencing the dynamics of these elements is the magnitude of their transmission advantage. In many systems, the mechanism of sex-ratio distortion is to abort X- or Y-bearing gametes. With this mechanism, the transmission advantage associated with sex-ratio distortion is diminished when the production of male gametes limits offspring production or when competition among the gametes of different males is intense. In this study, we analyzed the outcome of pollen competition between males that produced different sex ratios in the dioecious plant, Silene alba, and estimated how the sex-ratio bias influenced the transmission properties of the sex chromosomes. We varied the intensity of pollen competition by controlling the quantity of pollen used in crosses and used a combination of single-male pollinations and pollen mixtures to evaluate the effects of multiple paternity. Paternity in pollen mixtures was estimated using allozymes. Sex-ratio bias was directly influenced by the quantity of pollen, but the magnitude of this effect was small. The relative performance of pollen from different males varied substantially, especially when there was multiple paternity. Specifically, males with biased sex ratios sired far fewer offspring of either sex in pollen mixtures. In crosses involving single males, however, these “sex-ratio” males produced the same number of offspring as other males, so the female bias caused a significant transmission advantage for X-linked genes. X-linked genes could enhance their transmission via sex-ratio distortion in Silene populations, but the magnitude of this transmission advantage will depend on the ecological circumstances that influence the opportunity for multiple paternity.     

SEX RATIO SELECTION AND THE EVOLUTION OF ENVIRONMENTAL SEX DETERMINATION IN LABORATORY POPULATIONS OF MENIDIA MENIDIA

What happens when a population with environmental sex determination (ESD) experiences a change to an extreme environment that causes a highly unbalanced sex ratio? Theory predicts that frequency-dependent selection would increase the proportion of the minority sex and decrease the level of ESD in subsequent generations. We empirically modeled this process by maintaining five laboratory populations of a fish with temperature-dependent sex determination (the Atlantic silverside, Menidia menidia) in extreme constant temperature environments that caused highly skewed sex ratios to occur initially. Increases in the minority sex consistently occurred from one generation to the next across all five populations, first establishing and then maintaining a balanced sex ratio until termination of the experiment at 8 to 10 generations. The extent to which the level of ESD changed as balanced sex ratios evolved, however, was not consistent. Two populations that experienced high temperatures each generation displayed a loss of ESD, and in one of these ESD was virtually eliminated. This suggests that temperature-insensitive, sex-determining genes were being selected. In populations maintained in low temperature environments, however, the level of ESD did not decline. Instead, the response of sex ratio to temperature was adjusted upward or downward, perhaps by selection of sex-determining genes sensitive to higher (or lower) temperatures. The two different outcomes at low versus high temperatures occurred independent of the geographic origin of the founding population. Our results demonstrate that ESD is capable of evolving in response to selection.     

REPLICATED ORIGIN OF FEMALE‐BIASED ADULT SEX RATIO IN INTRODUCED POPULATIONS OF THE TRINIDADIAN GUPPY (POECILIA RETICULATA)

There are many theoretical and empirical studies explaining variation in offspring sex ratio but relatively few that explain variation in adult sex ratio. Adult sex ratios are important because biased sex ratios can be a driver of sexual selection and will reduce effective population size, affecting population persistence and shapes how populations respond to natural selection. Previous work on guppies (Poecilia reticulata) gives mixed results, usually showing a female‐biased adult sex ratio. However, a detailed analysis showed that this bias varied dramatically throughout a year and with no consistent sex bias. We used a mark‐recapture approach to examine the origin and consistency of female‐biased sex ratio in four replicated introductions. We show that female‐biased sex ratio arises predictably and is a consequence of higher male mortality and longer female life spans with little effect of offspring sex ratio. Inconsistencies with previous studies are likely due to sampling methods and sampling design, which should be less of an issue with mark‐recapture techniques. Together with other long‐term mark‐recapture studies, our study suggests that bias in offspring sex ratio rarely contributes to adult sex ratio in vertebrates. Rather, sex differences in adult survival rates and longevity determine vertebrate adult sex ratio.     

SEX RATIO VARIATION IN A PARASITIC WASP I. REACTION NORMS

To understand genetic and phenotypic constraints on the sex ratio in a parasitic wasp that attacks fly pupae, I carried out a laboratory study of sex ratio variability in five strains of Muscidifurax raptor (Hymenoptera: Pteromalidae). I manipulated the environment through combinations of temperature and day length, and the numbers of females that attack a group of hosts. The change of phenotype in each strain over the range of environmental conditions describes the norm of each reaction for that strain, and measures how a strain responds to environmental variation to create phenotypic variability. Sex ratio in parasitic wasps is a complex trait that has several components—the numbers of eggs laid by an ovipositing wasp and the fraction of eggs that are fertilized (female). Further, sex ratio may be influenced by a female's reaction to other females exploiting the same hosts (superparasitism). I found no strain-environment interactions in either sex ratio or fecundity when I varied environmental conditions. Although strains differed in sex ratio and fecundity, all strains produced a more female-biased sex ratio and had higher fecundity when temperature and day length increased. Sex ratio and fecundity were phenotypically correlated, and strains with greater fecundity also produced a more female-biased sex ratio. All strains facultatively shifted sex ratio toward a higher fraction of males with increasing female density, despite apparent differences in superparasitism among strains. Males and females survived equally during development, so that mortality differences among strains and across environments could not account for sex ratio variability. This study indicates that sex ratio variability among strains is constrained by the correlation between sex ratio and fecundity, and that strains display similar facultative shifts in sex ratio as female density increases because sex ratio shifts are insensitive to differing levels of superparasitism.     

THE QUANTITATIVE GENETICS OF SEXUAL DIMORPHISM IN SILENE LATIFOLIA (CARYOPHYLLACEAE). I. GENETIC VARIATION

It is widely recognized that there are basic conflicts between the resource needs of a plant for paternal versus maternal functions. In dioecious species, these divergent demands, and the selection pressures they impose, can lead to the evolution of sexual dimorphism. The present study was conducted to assess the potential for the evolution of sexual dimorphism in Silene latifolia by evaluating the genetic variation and genetic correlation between characters and between the sexes for a range of growth and reproductive characters. Sexual dimorphism is largely restricted to reproductive characters, particularly flower number and flower size. A canonical correlation analysis revealed considerable intercorrelation between growth characters, such as germination date, height, and leaf size, and reproductive characters; plants that grow fast early on also flower earlier, and plants that produce big leaves also produce big flowers. There was genetic variation for several sexually dimorphic characters; much of the focus in this analysis was on flower size, particularly calyx diameter. Finally, genetic correlations within and between the sexes were found that limit the rate of evolutionary divergence between the sexes. The genetic results suggest that S. latifolia has been subject to divergent selection on the two sexes for a long period of time, bringing about a gradual fixation of sex-limited gene effects, so that the remaining genetic effects are expressed in both sexes. Genetic correlations between the sexes that arise from this residual variation impose limits on further evolutionary change.     

COMPARATIVE ANALYSES OF SEX‐RATIO VARIATION IN DIOECIOUS FLOWERING PLANTS

Dioecious plant species commonly exhibit deviations from the equilibrium expectation of 1:1 sex ratio, but the mechanisms governing this variation are poorly understood. Here, we use comparative analyses of 243 species, representing 123 genera and 61 families to investigate ecological and genetic correlates of variation in the operational (flowering) sex ratio. After controlling for phylogenetic nonindependence, we examined the influence of growth form, clonality, fleshy fruits, pollen and seed dispersal vector, and the possession of sex chromosomes on sex‐ratio variation. Male‐biased flowering sex ratios were twice as common as female‐biased ratios. Male bias was associated with long‐lived growth forms (e.g., trees) and biotic seed dispersal and fleshy fruits, whereas female bias was associated with clonality, especially for herbaceous species, and abiotic pollen dispersal. Female bias occurred in species with sex chromosomes and there was some evidence for a greater degree of bias in those with heteromorphic sex chromosomes. Although the role of interactions among these correlates require further study, our results indicate that sex‐based differences in costs of reproduction, pollen and seed dispersal mechanisms and sex chromosomes can each play important roles in affecting flowering sex ratios in dioecious plants.     

MITOCHONDRIAL DNA SEQUENCE VARIATION AMONG NATURAL POPULATIONS OF THE TRINIDAD GUPPY,POECILIA RETICULATA

Guppies were sampled from eight populations representing four river drainage basins in northern Trinidad, and from one population on the nearby island of Tobago. For each individual, a 465 base pair (bp) segment of the control region of the mitochondrial genome was sequenced. The resulting DNA sequences were subjected to sequence divergence calculations and the populations were linked by maximum parsimony analysis to determine their phylogenetic relationships. Mitochondrial DNA (mtDNA) sequence variation was found both within and between river drainages, correlated with the geographic features of northern Trinidad. The variation observed exists primarily between drainages, particularly between the Oropuche drainage and all other Trinidad drainages examined. Estimates of time of divergence between guppy populations of different drainages, based on mtDNA sequence variation, ranged from 100,000 to 200,000 for the most recently separated populations and from 600,000 to 1.2 million years between the Oropuche populations and all others examined. Examination of fish from northeastern South America will be required to determine whether these populations differentiated in their present locations or were the result of separate invasions of Trinidad from different Venezuelan sources. However, genetic isolation of these populations appears to predate the current physical separation of the island of Trinidad from the Venezuelan mainland.     

UNUSUAL POPULATION GENETICS OF A PARASITIC NEMATODE: mtDNA VARIATION WITHIN AND AMONG POPULATIONS

Very little is known about the distribution of genetic variance within and among populations of parasitic helminths. In this study we used mitochondrial DNA (mtDNA) restriction fragment analysis to describe the population genetic structure of Ostertagia ostertagi, a nematode parasite of cattle, in the United States. Estimates of within-population mtDNA diversity are 5 to 10 times greater than typical estimates reported for species in other taxa. Although populations are genetically differentiated for a key life–history trait, greater than 98% of the total genetic diversity is partitioned within populations, and the geographic distribution of individual mtDNA haplotypes suggests high gene flow among populations.     

SEX RATIO VARIATION IN A PARASITIC WASP II. DIALLEL CROSS

Sex ratio has been studied from many theoretical and empirical perspectives, but a general assumption in sex ratio research is that changes in sex ratio occur because of selection on sex ratio itself. I carried out a quantitative genetic experiment—a diallel cross among three strains—on a parasitic wasp, Muscidifurax raptor (Hymenoptera: Pteromalidae), to measure genetic variation for sex ratio. I also tested whether sex ratio may change as a consequence of selection on other life-history traits by estimating genetic covariances between sex ratio, fecundity, longevity, and development time. Most of the variation among strains could be accounted for by a maternal effect, likely caused by a microsporidian parasite that was transmitted through the West Germany (WG) strain. Genetic variation was small by comparison, but almost all traits were affected by dominance. The only significant additive genetic effect was for fecundity early in life. Upon crossing, all traits displayed heterosis: more female-biased sex ratio, greater fecundity, longer life, and faster development time. All life-history traits were correlated phenotypically, but the correlations were mainly the result of decreased performance in crosses with the WG strain that carried the microsporidian parasite. Dominance genetic correlations were also found between sex ratio, fecundity, and longevity. How the correlation between sex ratio and other life-history traits would affect sex ratio evolution depends upon the frequencies of sex-ratio genotypes within a population as well as the signs of the correlations, because sex ratio is under frequency-dependent selection whereas other traits are generally under directional selection. Although the results from crosses among laboratory populations should be approached with caution, the inbreeding depression (the difference between inbred and outcrossed progeny) found in M. raptor implies that the evolution of a female-biased sex ratio could be affected by selection for inbreeding avoidance.     

SEX ALLOCATION IN THE ANT COLOBOPSIS NIPPONICUS (WHEELER). I. POPULATION SEX RATIO

The relative power of queens and workers at controlling sex allocation in the ant Colobopsis nipponicus is investigated in this study. Results show that C. nipponicus completely satisfies Hamilton's assumptions concerning colony social structure: monogyny, monoandry, and no worker reproduction. A genetic survey of the population structure rejects possibilities of local mate competition, local resource enhancement, and local resource competition, which all can bias population-allocation ratios from 0.5. Although these factors are absent, the observed sex-allocation ratio (male investment/total sexual investment; 0.250 ± 0.027) is significantly biased toward females and is not different from the estimated optimal ratio for workers (0.252). Thus, it appears that workers are likely to win in conflicts over sex allocation with queens.     

云杉天然群体遗传多样性的等位酶变异

采用等位酶淀粉凝胶电泳和聚丙烯酰胺凝胶电泳技术对中国西部亚高山特有树种云杉(Picea asperata)10个天然群体的300个个体的遗传多样性和遗传分化进行研究。对8个酶系统17个酶位点(27个等位基因)的检测分析结果表明,10个位点为单态位点,云杉具有中等偏低的遗传变异水平。群体水平上的遗传多样性指标分别为:多态位点的百分率P_P=29.41%~41.18%,等位基因平均数A_P=1.4~1.6,平均期望杂合度H_ep=0.06~0.131;种级水平的遗传多样性指标分别为:P_s=41.18%,A_s=1.2,H_es=0.138。10个群体的群体水平的观测杂合度为0.094 3,期望杂合度为0.096 4;10个群体中,7个多态位点的单位点的观测杂合度(H_o)的均值为0.229(变幅为0.142 9~0.342 9),期望杂合度(H_e)的均值为0.234 1(变幅为0.160 8~0.317 3), 云杉天然群体间遗传分化度(F_ST)为0.311,云杉群体间变异占总变异的31.1%,基因流低(N_m=0.553 9),说明群体间的基因交流有限。异交率高(t=0.957),近交率低(F_is=0.005),这些研究结果表明:云杉群体间等位基因的频率分化显著,其它云杉属树种基因的渐渗、群体微生境差异和不同强度的选择压力可能是造成群体间分化显著的主要原因;Fdh-2-B基因与综合生态梯度值呈显著的负相关(r=-0.661 1^*),H_e与经度呈显著负相关(r=-0.683^*),云杉群体间的地理和遗传距离相关不显著。10个群体均含有绝大部分等位基因,且群体间分化很大,应加以重点保护和管理,作为云杉种质资源原地保存的基地和该树种进一步遗传改良的重要育种群体。     

TEMPORAL VARIATION IN ISOMORPHIC PHASE AND SEX RATIOS OF A NATURAL POPULATION OF ULVA PERTUSA (CHLOROPHYTA)1

The green macroalga Ulva L. is well known as having an alternation of isomorphic biphases: gametophyte and sporophyte. However, an examination of the temporal alternation in phase dominance has not been carried out. By inducing reproduction of thallus samples in the laboratory, this study reports the temporal changes in the two phases and sex ratios in a natural population of Ulva pertusa Kjellm. in the Seto Inland Sea, Japan, over a period of >3 years. The results showed that a temporal alternation in phase dominance occurred after 11–20 months; seasonal changes in phase dominance were not observed in the Ulva population. The sex ratio of male and female gametophytes remained ～1:1 throughout the investigated period, although skewed sex ratios were observed in several collections.     

中华鳖非特异性免疫功能的群体差异研究

从补体总量、红细胞C3 b受体花环率、红细胞天然免疫肿瘤细胞花环率、T淋巴细胞活性E花环率及白细胞吞噬活性五方面 ,探讨了黄河鳖、淮河鳖、洞庭湖鳖、鄱阳湖鳖及太湖鳖在非特异性免疫功能上的差异。主要结果 :(1)在补体总量及红细胞天然免疫肿瘤细胞花环率上 ,五群体之间差异不显著 (F <0 .0 5 ) ;(2 )在红细胞C3 b受体花环率上 ,黄河鳖显著地高于鄱阳湖鳖与太湖鳖 (P <0 .0 5 ) ,而其余群体间则差异不显著 (F <0 .0 5 ) ,花环率大小顺序为 :黄河鳖 >淮河鳖 >洞庭湖鳖 >鄱阳湖鳖 >太湖鳖 ;(3)在T淋巴细胞活性E花环率上 ,黄河鳖显著高于鄱阳湖鳖 (P <0 .0 5 ) ,太湖鳖极显著地低于其他四个群体 (F >0 .0 1) ,其余群体间则差异不显著 (P >0 .0 5 ) ,花环率大小顺序为 :黄河鳖 >淮河鳖 >洞庭湖鳖 >鄱阳湖鳖 >太湖鳖 ;(4 )在白细胞吞噬活性上 ,除淮河鳖与鄱阳湖鳖差异不显著外 (P >0 .0 5 ) ,其余群体间则差异极显著 (F >0 .0 1) ,活性大小顺序为 :黄河鳖 >洞庭湖鳖 >淮河鳖 >鄱阳湖鳖 >太湖鳖。综上所述 ,在非特异性免疫功能上 ,黄河鳖最强 ,太湖鳖较弱。     

ANTHER-SMUT DISEASE IN SILENE DIOICA: VARIATION IN SUSCEPTIBILITY AMONG GENOTYPES AND POPULATIONS,AND PATTERNS OF DISEASE WITHIN POPULATIONS

In an archipelago in northern Sweden, populations of the perennial, dioecious, and insect-pollinated herb Silene dioica are commonly infected by the sterilising anther-smut fungus Microbotryum violaceum. The results from transplantation and inoculation experiments in this study show that variation between populations in the incidence of disease may partly be due to variation in resistance among populations. In the transplantation experiment in which plants were naturally exposed to the fungus, disease levels varied greatly among transplants from three healthy populations when transplanted to three diseased populations in the archipelago. Clear genotypic differences in susceptibility among 25 replicated genotypes of the host plants were found when inoculated manually with two different isolates. Susceptibility varied between 0-90%, but the two isolates used did not differ in inoculation success. The results also suggest a geographical structuring in resistance of the host and virulence of the fungus. First, disease levels among experimental plants from two of the disease-free populations of S. dioica (originating from inner and outer archipelago, respectively), were high when transplanted to a diseased population nearby, but low when transplanted far away. Second, regardless of origin, plants from all healthy populations became diseased in the diseased experimental populations located in the middle part of the archipelago. Due to isostatic land upheaval in the studied archipelago, there is a vertical age-axis within islands such that the highest point on an island is the oldest. Since this may affect the demography of the host, disease spread, and the dynamics of disease, spatial patterns in adult and seedling densities, and disease and spore deposition along the age-axis were studied within three diseased populations. A low incidence of disease was found in the young, low and old, high parts of the populations and a high incidence in the vertical, middle parts of the populations. The higher disease incidence in the middle part compared with the lower part of the population may reflect less disturbance and an increased probability of disease with age.     

中国云南西部小哺乳动物革螨的性比及年龄结构(英文)

1990～ 1 996年对中国云南西部 1 3个县进行了调查 ,从所捕获的 38种、30 2 3只小哺乳动物体表采集到革螨 70种、7485只。绝大多数革螨的雌性个体比例 ( 80 %～ 1 0 0 % )高于其雄性个体比例 (P <0 .0 1 ) ,唯贡山血革螨Haemogamasusgongshanensis和格氏血厉螨Haemolaelapsglasgowi例外。贡山血革螨的雄性个体比例高于其雌性个体比例 (P <0 .0 1 ) ,格氏血厉螨的雌雄比例接近 (P >0 .0 5)。在现场采集中 ,绝大多数革螨种类未见幼虫阶段。除柏氏禽刺螨Ornithonyssusbacoti及格氏血厉螨Haemolaelapsglasgowi的若虫比例 (分别为 62 .84%和 49.48% )较高外 ,绝大多数革螨的未成熟期 (主要是前若虫和后若虫 )比例( 0～ 1 2 .84% )明显低于成虫期比例 (P <0 .0 1 )。采自小哺乳动物体表革螨雌雄性比的不同可能与雌雄螨的吸血习性及孤雌生殖有关。绝大多数革螨在其宿主体表缺乏幼虫阶段以及若虫比例很低提示 :这些革螨的幼虫或若虫阶段可能不取食或不吸血 ,主要生活在宿主的窝巢内。另一种可能原因是某些革螨的雌螨可能直接产前若虫或后若虫 ,因此难以从宿主体表发现幼虫。     

THE GENOMIC ARCHITECTURE OF SEXUAL DIMORPHISM IN THE DIOECIOUS PLANT SILENE LATIFOLIA

Evaluating the genetic architecture of sexual dimorphism can aid our understanding of the extent to which shared genetic control of trait variation versus sex‐specific control impacts the evolutionary dynamics of phenotypic change within each sex. We performed a QTL analysis on Silene latifolia to evaluate the contribution of sex‐specific QTL to phenotypic variation in 46 traits, whether traits involved in trade‐offs had colocalized QTL, and whether the distribution of sex‐specific loci can explain differences between the sexes in their variance/covariance matrices. We used a backcross generation derived from two artificial‐selection lines. We found that sex‐specific QTL explained a significantly greater percent of the variation in sexually dimorphic traits than loci expressed in both sexes. Genetically correlated traits often had colocalized QTL, whose signs were in the expected direction. Lastly, traits with different genetic correlations within the sexes displayed a disproportionately high number of sex‐specific QTL, and more QTL co‐occurred in males than females, suggesting greater trait integration. These results show that sex differences in QTL patterns are congruent with theory on the resolution of sexual conflict and differences based on G ‐matrix results. They also suggest that trade‐offs and trait integration are likely to affect males more than females.     

SEX RATIO AND AGE STRUCTURE OF GAMASID MITES FROM SMALL MAMMALS IN WESTERN YUNNAN,CHINA*

Abstract A total of 70 species of gamasid mites (7485 individuals) were collected from the body surface of 38 species of small mammals (3023 individuals) during an investigation of 13 counties of western Yunnan, China, from 1990 to 1996. Most species of gamasid mites have more females (80% 100%) than males (P <0.01). Exceptions are Haemogamasus gongshanensis where males outnumber females (P < 0.01) and Haemolaelaps glasgowi where there are similar numbers of males and females (P > 0.05). No larva was found in most of the mite species. The proportion of individuals at the immature stages (mainly protonymphs and deutonymphs) in most mite species is small (0–12.84%) compared to the adults (P < 0.01). Exceptions are Ornithonyssus bacoti and Haemolaelaps glasgowi where 62.84% and 49.48% respectively are nymphs. The biased sex ratios may reflect the probable different bloodsucking preferences and parthenogenesis of the gamasid mites. The absence of larvae and a low proportion of nymph stages in most mite species probably reflect that the larvae or nymphs of most mite species are non‐feeding or non‐blood sucking and are in their hosts' nests. Another possibility is that some species directly produce protonymphs or even deutonymphs without eggs and larvae which makes it difficult to find the larval stage.     

多辐溲疏群体同工酶变异的数量分析

研究了四川南川金佛山特产的多辐溲疏不同海拔和生境的５个群体的４１个个体叶片过氧化物酶,过氧化氢酶,酯酶,淀粉酶,柠檬酸脱氢酶及谷氨酸脱氢酶同工酶谱带位置上的变异式样,来自同一群体的不同个体在谱带上表现出极大的相似性,而来源于不同群体的个体却表现出明显的趋异性,显示出酶谱带位置与群体生长的生境有显著的相关性,一定的群体具有某些特有的酶谱带,空间隔离限制了群体间个体的相互基因交流,在进化中那些适应新的