REPRODUCTIVE PATTERNS SHAPE INTROGRESSION DYNAMICS AND SPECIES SUCCESSION WITHIN THE EUROPEAN WHITE OAK SPECIES COMPLEX

The reproductive system of hybrids is an important factor shaping introgression dynamics within species complexes. We combined paternity and parentage analyses with previous species characterization by genetic assignment, to directly identify reproductive events that occurred within a stand comprising four European white oak species. Comparing species status of parent pairs provided a precise quantification of hybridization rate, backcrosses, and intraspecific matings in two life stages. The detailed mating system analysis revealed new findings on the dynamics of interspecific gene flow. First, hybrids acted successfully as both male and female during reproduction. They produced acorns and seedlings that were as viable as those sired by purebreds. Second, species maintenance could be due to a relatively low level of interspecific mating contrasting with a large proportion of intraspecific crosses and backcrosses. Despite a high proportion of hybrids and extensive interspecific gene flow, partial species integrity is maintained by genetically controlled pollen discrimination, ensuring preferential matings within purebreds and high parental species fidelity in hybrid reproduction, which impedes complete collapse into a continuous hybrid swarm. Finally, we showed that pollen from the different species had unequal contributions to reproduction suggesting that introgression processes could ultimately lead to extirpation or expansion of some species.     

ISOLATING MECHANISMS IN SEABIRDS

In most species of birds, differences in plumage coloration or song structure act as isolating mechanisms. In seabirds, plumages are generally drab, and vocal repertoires are limited so that other phenotypic attributes must act as isolating mechanisms. One classic study of gulls suggests that the contrast between eye color and head color acts as a reproductive isolating mechanism, but this idea has been largely refuted by widespread evidence of hybridization in gulls in the last 20 years. An examination of more than 100 species of seabirds that breed sympatrically with congeners reveals that species with bills and feet similar in color hybridize in all areas where they breed sympatrically. Species that have bills or feet of different colors either do not hybridize or they produce rare hybrids that are unable to obtain mates as adults. This suggests that bill and foot coloration act as the primary isolating mechanisms in all surface-nesting seabirds and some burrow nesters. It may be a general pattern in birds that foot color acts to supplement bill color in reproductive isolation and mate choice.     

REPRODUCTIVE ASSURANCE MECHANISMS IN THREE TAXA OF THE MIMULUS GUTTATUS COMPLEX (SCROPHULARIACEAE)

The evolution of inbreeding in plants has often been attributed to selection for the ability to set seed in the absence of mates or pollinators. Mechanisms of reproductive assurance in five populations of mixed mating Mimulus guttatus, three populations of inbreeding M. platycalyx, and two populations of inbreeding M. nasutus were examined in a pollinator-free greenhouse. Reproductive assurance was manifested in all populations by autofertility, vegetative reproduction, or both. The inbreeding taxa had significantly greater levels of autofertility and less vegetative reproduction. Three modes of autofertility were identified: 1) due to corolla abscission only, occurring in three M. guttatus populations; 2) due to both corolla abscission and direct anther-stigma contact by curling of the lower stigmatic lobe into the anthers, occurring in two M. guttatus populations; and 3) direct stigma-anther contact by stigma curling alone prior to corolla abscission, found in each M. platycalyx and M. nasutus population. Stigma-anther distance and its interaction with stigma curling contributed to differences in autofertility among populations. Significant levels of intrapopulation quantitative genetic variation were found for seven of ten traits examined; average levels were similar between inbreeding and mixed mating populations. Genetic variation within populations for autofertility per se was not detected, but significant levels controlling stigma-anther distance were found in two M. guttatus populations. These results show that evolution of inbreeding by natural selection for reproductive assurance is possible in Mimulus, and illustrate the complex changes in floral dynamics and morphology it may involve.     

REPRODUCTIVE BEHAVIOR OF FEMALE BUNTINGS: ISOLATING MECHANISMS IN A HYBRIDIZING PAIR OF SPECIES

The plumage characteristics of male Indigo and Lazuli Buntings are distinct, but the two species can learn each other's songs. Populations comprising Indigo, Lazuli and hybrid individuals occur in the Great Plains of North America, and assortative mating has been inferred from morphometric data. We devised a laboratory assay for determining female preferences for visual and vocal characteristics of conspecific and heterospecific males and for mixtures of these characteristics, such as might be encountered in an overlap population. Females of both species gave more copulation-solicitation displays when exposed to conspecific plumage and vocalizations than when exposed to heterospecific plumage and vocalizations. Females gave intermediate and similar responses to the combinations of conspecific plumage with heterospecific vocalizations and heterospecific plumage with conspecific vocalizations. Thus, in the absence of other potentially important variables, female reproductive behavior is consistent with the hypothesis of assortative mating, based upon both vocal and visual traits of the males and caused by female choice in this semispecies pair.     

HYBRIDIZATION AND INTROGRESSION IN THE GRASS GENUS ELYMUS

Brown , W. V., and G. A. Pratt . (U. Texas, Austin.) Hybridization and introgression in the grass genus Elymus. Amer. Jour. Bot. 47 (8) : 669–676. Illus. 1960.—The production of artificial F₁ hybrids that produce some seed between E. virginicus and E. canadensis, E. virginicus and E. interruptus, and E. canadensis and E. interruptus proves that similar plants found in nature are true hybrids. The artificial hybrids constituted the basis of comparison in an analysis of natural local populations in the Austin region. Analysis by scatter diagrams indicates that there is introgression of genes of some species into the genomes of others through the development of hybrid swarms. In the area studied the great variability of virginicus is due to the introgression of canadensis and, possibly, interruptus genes. Such hybridization and subsequent introgression have occurred many times and in many places and are still taking place. It is likely that the named varieties of canadensis and virginicus may be introgressant types that are the results of hybridizations between those species and others that occur sympatrically in Eastern United States.     

AMPHIPLOIDY AND INTROGRESSION IN STIPA

Johnson , B. Lennart . (U. California, Los Angeles.) Amphiploidy and introgression in Stipa. Amer. Jour. Bot. 49(3): 253–262. Illus. 1962.—Frequent specimens heretofore referred to Stipa californica (2n = 36) were found to be similar to an undescribed polyploid (2n = 68) species of Stipa on the ratio of lemma to palea length. On other individual diagnostic characters, S. californica and the polyploid were not separable. However, on the discriminant function (Z) comprising 5 such attributes, their mean difference was highly significant. The polyploid is given the new species name, Stipa nevadensis . Appropriate tests using the function Z excluded S. californica as a possible parent of the polyploid and pointed to S. lettermani (2n = 32) and the combined species S. occidentalis (2n = 36) and S. elmeri (2n = 36) as the putative parents. The last 2 species were barely separable on multigenic differences measured by the discriminant function, and the mean Z for S. californica fell near the mid point between them and S. columbiana (2n = 36). This fact together with evidence from the frequency distribution of Z suggested a hybrid origin for S. californica and introgression with its putative parents.     

THE DISTRIBUTION OF POSTMATING REPRODUCTIVE ISOLATING GENES IN POPULATIONS OF THE YELLOW MONKEY FLOWER,MIMULUS GUTTATUS

Postmating reproductive isolating barriers are generally believed to arise as the chance by-product of genetic differentiation. The classical view is that these barriers normally involve differentiation at many loci, and therefore require long periods of allopatric isolation. The formal genetics of, and the distribution of genes responsible for, such barriers are known in very few cases. This paper examines the distribution of the genes responsible for two different postmating barriers in 18 populations of the yellow monkey flower, Mimulus guttatus. The genetic relatedness of the populations was measured by a morphometrical analysis. Widespread polymorphism was found for three of the four components of the two genetic systems responsible for the two barriers, with at least 13 populations possessing genes for one or both of the barriers. In one system (the C7/U8 system; Christie and Macnair, 1984), the distribution of the two component genes was correlated with the morphometrical similarity and geographical location of the populations. This pattern could be produced by a historical association or by an adaptive response. In the other system (the Cerig/C10 system; Macnair and Christie, 1983), the genes were more widely dispersed, and there was no obvious morphometrical or geographical association. Populations possessing the complementary factors causing partial reproductive isolation are not always widely separated geographically. These results indicate that the spread of postmating reproductive isolating genes through drift, selection, or hitchhiking could readily cause reproductive isolation to evolve in this species.>     

REPRODUCTIVE COMPATIBILITY AND RDNA SEQUENCE ANALYSES IN THE SELLAPHORA PUPULA SPECIES COMPLEX (BACILLARIOPHYTA)1

We tested whether internal transcribed spacer (ITS) rDNA sequence differences are correlated with sexual compatibility in the Sellaphora pupula complex, a model system for investigations of the species concept and speciation in diatoms. The phylogenetic relationships among the demes and the systematic position of the genus within the raphid diatoms were also investigated. The division of clones of S. pupula and S. laevissima into groups, based on sequence similarities and phylogenetic analyses, resembled groupings based on sexual compatibility: A high ITS sequence divergence, making full alignment difficult or impossible, was found among clones whose gametangia do not interact, whereas there was little sequence divergence among interfertile clones. This is clearly consistent with the idea that “Z clades” exhibit less intraclade than interclade variation in ITS and, as comparisons of secondary structure models for the RECT and PSEUDOCAP clones showed, that there is an equivalence of “CBC” and Z clades in the rectangular and pseudocapitate demes of S. pupula, as earlier hypothesized for chlorophytes. Intraclonal, presumably intraindividual, variation in ITS was found in S. pupula, though with a degree of variation less than that found within a single Z clade; it was too minor to affect the interclonal relationships in the ITS phylogeny. Sellaphora, which appears monophyletic in 18S phylogenies, with Pinnularia and “Navicula”pelliculosa as its closest allies, may also include some species currently classified in Eolimna. The S. pupula–S. laevissima group began to diversify in or before the Miocene.     

SOME OBSERVATIONS ON THE OLIVACEOUS WARBLER HIPPOLAIS PALLIDA IN EGYPT.

Preliminary obsenations on Olivaceous Warblers Hippolais pallida were made at Fayid, Egypt, in the summers of 1949–50. General notes are given on habitat, possible competitors, song and field-characters. Males arrive before females and establish territories, where the females later locate them. One male built an incomplete nest while still unmated. It is probable that the male initially treats a female as an intruder in the territory. Some notes are given on pair-relationship; male song declines on pair-formation. The male builds while the female incubates, leaving the nest to feed. The incubation period is 11 days± 1 day (once), the nestling period 15 days± 1 day (once). Average clutch-size is apparently smaller in Egypt than in the Balkans, Spain and Tunisia, but exact figures are lacking. Both sexes care for the young. After the breeding season birds remain in a limited area, moult and show no aggression to intruders, leaving for the south in August and September.     

THE EVIDENCE OF REPRODUCTIVE MECHANISMS IN FOSSIL DASYCLADS (ALGAE: CHLOROPHYTA)

Dasyclads (members of Order Dasycladales: Algae, Chlorophyta) are reviewed for evidence of reproductive structures in the fossil state, and then compared with what is known of the reproductive processes in living examples. The effects of poor preservation in most of the fossils are shown to result in many uncertainties, and the resulting degree of interpretation required is emphasized. Selected genera of fossil dasyclads considered relevant to this problem are briefly analysed and discussed: Archaeobatophora (Ordovician), Kulikia (Carboniferous), Imperiella (Permian), Stichoporella (Jurassic) and Cympolia (Cretaceous to Recent). The pioneer views of J. Pia on dasyclad reproduction through geological time are seen to need much modification in the light of later work. The fundamental dasyclad nucleus-fragmentation-reproduction mechanism is believed to have operated within the great morphological variety of known dasyclads, giving rise to modification in genera where basic evolution was structural. In this way the variety of dasyclads can be seen to be the result of varied morphological evolution, often modified by the consistently simple basic reproductive mechanism.     

短翅树莺的繁殖习性

短翅树莺是森林益鸟。本文着重记述了其种群的分布和数量及迁徙动态,并对其歌唱声和惊叫声作了录音分析及文字描述。文内较全面地记述了繁殖习性和食性。并对其繁殖力和雏鸟(257只)生长曲线方程作了较深入的探讨。     

竹红菌甲素与半胱氨酸作用的ESR研究

本文用ESR方法研究了竹红菌甲素和半胱氨酸在光和暗条件下产生活性氧的过程.我们发现甲素具有氧化还原反应中间载体的作用,即巯基化合物将电子转移给甲素,而甲素在有氧的条件下再将电子转移给氧生成超氧阴离子自由基.光照可以加快这一步骤,使用化学方法定量研究证明激发态甲素与半胱氨酸的反应速率大于基态甲素.除半胱氨酸外,巯基乙醇和还原谷胱甘肽均可以将电子经甲素传给氧,而甲硫氨酸和胱氨酸不具这一能力,这说明巯基在反应中很重要而硫原子不是必需的.