Ecology and evolution of plant mating

Plants exhibit complex mating patterns because of their immobility, hermaphroditism and reliance on vectors for pollen transfer. Research on plant mating attempts to determine who mates with whom in plant populations and how and why mating patterns become evolutionarily modified. Most theoretical models of mating-system evolution have focused on the fitness consequences of selling and outcrossing, stimulating considerable empirical work on the ecology and genetics of inbreeding depression. Less attention has been given to how the mechanics of pollen dispersal influence the transmission of self and outcross gametes. Recent work on the relation between pollen dispersal and mating suggests that many features of floral design traditionally interpreted as anti-selling mechanisms may function to reduce the mating costs associated with large floral displays.     

POLLEN DISCOUNTING AND THE SPREAD OF A SELFING VARIANT IN TRISTYLOUS EICHHORNIA PANICULATA: EVIDENCE FROM EXPERIMENTAL POPULATIONS

Floral traits that increase self-fertilization are expected to spread unless countered by the effects of inbreeding depression, pollen discounting (reduced outcross pollen success by individuals with increased rates of self-fertilization), or both. Few studies have attempted to measure pollen discounting because to do so requires estimating the male outcrossing success of plants that differ in selfing rate. In natural populations of tristylous Eichhornia paniculata, selfing variants of the mid-styled morph are usually absent from populations containing all three style morphs but often predominate in nontrimorphic populations. We used experimental garden populations of genetically marked plants to investigate whether the effects of population morph structure on relative gamete transmission by unmodified (M) and selfing variants (M‘) of the mid-styled morph could explain their observed distribution. Transmission through ovules and self and outcross pollen by plants of the M and M’ morphs were compared under trimorphic, dimorphic (S morph absent), and monomorphic (L and S morphs absent) population structures. Neither population structure nor floral morphology affected female reproductive success, but both had strong effects on the relative transmission of male gametes. The frequency of self-fertilization in the M' morph was consistently higher than that of the M morph under all morph structures, and the frequency of self-fertilization by both morphs increased as morph diversity of experimental populations declined. In trimorphic populations, total transmission by the M and M' morphs did not differ. The small, nonsignificant increase in selfing by the M' relative to the M morph was balanced by decreased outcross siring success, particularly on the S morph. In populations lacking the S morph, male gamete transmission by the M' morph was approximately 1.5 times greater than that by the M morph because of both increased selfing and increased success through outcross pollen donation. Therefore, gamete transmission strongly favored the M' morph only in the absence of the S morph, a result consistent with the distribution of the M' morph in nature. This study indicates that floral traits that alter the selfing rate can have large and context-dependent influences on outcross pollen donation.     

柱萤叶甲属研究（Ⅰ）鞘翅具黑色刻点的种类记述（鞘翅目：叶甲科）

本文就萤叶甲亚科中柱萤叶甲属鞘翅具黑色刻点的种类进行研究,共记述４种,我国已记录３种,其中１种为新种。     

Partial sequence analysis of 130 randomly selected maize cDNA clones.

As part of a project to identify novel maize (Zea mays L. cv B73) genes functionally, we have partially sequenced 130 randomly selected clones from a maize leaf cDNA library. Data base comparisons revealed seven previously sequenced maize cDNAs and 18 cDNAs with sequence similarity to related maize genes or to genes from other organisms. One hundred five cDNAs show little or no similarity to previously sequenced genes. Our results also establish the suitability of this library for large-scale sequencing in terms of its large insert size, proper insert orientation, and low duplication rate.     

The importance of phytoflagellate, heterotrophic flagellate and ciliate grazing on bacteria and picophytoplankton sized prey in a coastal marine environment

The uptake of bacteria and picoplankton sized fluorescentlylabelled beads was measured off the west coast of the SouthIsland of New Zealand in winter. Phytoflagellates and heterotrophicflagellates showed similar grazing rates on 0.49 µm beads,with mean clearance rates of 1.1 and 1.8 nl ind.^–1 h^–1,respectively. Clearance rates for 1.09 µm beads were 0.9nl ind.^–1 h^–1 for heterotrophic flagellates and0.5 nl ind.^–1 h^–1 for phytoflagellates. Non-loricateciliates had clearance rates of 1.5 µl ind.^–1 h^–1for the picoplankton sized particles. The heterotrophic flagellatesshowed no significant difference between clearance rates of0.49 and 1.09 µm particles. Phytoflagellates, however,showed an apparent preference for the smaller particles. Themeasurement of significant grazing by phytoflagellate populationsin the marine environment is important and indicates that weneed to reassess our concepts of food web structure.     

An isoelectric focusing study of the effect of methyl-esterified pectic substances on the production of extracellular pectin isoenzymes by soft rot Erwinia spp.

The production of extracellular pectic isoenzymes by seven strains of soft rot bacteria, Erwinia carotovora subsp. carotovora, E.c. atroseptica and E. chrysanthemi , when grown in media containing four different pectic substances with different degrees of methylation or with potato tuber cell-wall extract was examined by isoelectric focusing activity staining. In addition to the isoenzymes of pectate lyase, polygalacturonase and pectin methyl esterase produced constitutively or following induction by polygalacturonic acid (PGA) and coded by known genes, between two and seven novel isoenzymes of the three enzymes with a wider pI range were apparently induced by the pectins and cell-wall extract. Pectin lyase, which is induced in vitro by DNA-damaging agents, was not produced in the absence of mitomycin C in a medium containing PGA but up to two isoenzymes were found with pectin or cell-wall extract. In contrast, cellulase isoenzyme production was not affected by pectin or cell-wall extract. A greater number of novel isoenzymes of all pectic enzymes except pectin lyase tended to be produced in media containing Link pectin, which is PGA methylated to 98%, than the other pectic substances and cell-wall extract. Pectate lyase and polygalacturonase were induced by pectin lyase-degraded products of highly methylated pectin but not by PGA in an E. chrysanthemi strain with all its known pei and peh genes mutated. The results suggest that the production of novel pectic isoenzymes could be related to the presence of CH⁺₃ groups and that their induction differs from that for isomers induced by PGA-degraded products and DNA-damaging agents or produced constitutively.     

Multiple origins of self-fertilization in tristylous Eichhornia paniculata (Pontederiaceae): Inferences from style morph and isozyme variation

Populations of Eichhornia paniculata (Pontederiaceae) exhibit a wide range of mating systems, from predominant outcrossing to high levels of self-fertilization. The origin of self-fertilization in this tristylous species is associated with the loss of style-length morphs from populations and the spread of self-pollinating, floral variants. We examined geographic variation in style morph and allozyme frequencies to determine whether the loss of style morphs and transition to selfing could have multiple origins in E. paniculata. Surveys of floral variation in 167 populations from six states in northeastern Brazil revealed that at least one style morph was absent from 29.3%. Non-trimorphic populations occurred in all states and ranged in frequency from 9% in Ceará to 68% in Alagoas. Selfing variants occurred in 8.5% and 55% of trimorphic and non-trimorphic populations, respectively, and were distributed among five of six states with primary concentrations in Alagoas and Pernambuco. A comparison of electrophoretic variation at 24 isozyme loci in 28 trimorphic, 13 dimorphic and 3 monomorphic populations indicated that non-trimorphic populations contained 84% of the allelic variation present in trimorphic populations and were markedly differentiated from one another. Analyses of genetic distance and the distribution of rare alleles indicated that non-trimorphic populations were often more similar to neighbouring trimorphic populations than to one another. Populations with selfing variants occurred at low frequency in three genetically distinct parts of the range. These results, in combination with genetic and morphological evidence suggest that style morphs are lost repeatedly from populations of E. paniculata and that selfing variants may have originated on at least three separate occasions in northeastern Brazil.