You-Hao Guo

Evolution of apocarpy in Alismatidae using phylogenetic evidence from chloroplast rbcL gene sequence data

The apocarpous groups in the monocotyledons are mainly concentrated in the subclass Alismatidae. The molecular phylogeny of Alismatidae based on analysis of chloroplast rbcL gene sequence data serves as a framework with which to evaluate character evolution with respect to the derivation of apocarpy in the group. 20 of the 27 genera in the subclass that display apocarpy have been included in our study. Our analysis indicates that apocarpy is polyphyletic within the subclass Alismatidae. Two independent origins of apocarpy in Alismatidae are explored in this study. Three separate origins of a single carpel and two separate origins of syncarpy in the subclass are also proposed. Basally connate carpel condition was the ancestral character in Alismatidae and evolved in two directions. It is possible for the unicarpellate condition to have been directly derived by reduction from syncarpy, and it could also be that the unicarpellate state has been derived from apocarpy by reduction in carpel number. The present results indicate that a progression has occurred in the evolution of carpels in Alismatidae from basally connate carpels through syncarpy or apocarpy to a single carpel.

The presence of co-flowering species facilitates reproductive success of Pedicularis monbeigiana (Orobanchaceae) through variation in bumble-bee foraging behaviour

Background and Aims The presence of co-flowering species can alter pollinator foraging behaviour and, in turn, positively or negatively affect the reproductive success of the focal species. Such interactions were investigated between a focal species, Pedicularis monbeigiana, and a co-flowering species, Vicia dichroantha, which was mediated by behaviour alteration of the shared bumble-bee pollinator. Methods Floral display size and floral colour change of P. monbeigiana were compared between pure (P. monbeigiana only) and mixed (P. monbeigiana and V. dichroantha) plots in two populations. Pollinator visitation rates, interspecific floral switching and successive within-plant pollinator visits were recorded. In addition, supplemental pollination at plant level was performed, and the fruit set and seed set were analysed in pure and mixed plots with different densities of P. monbeigiana. Key Results Pollinator visitation rates were dramatically higher in mixed plots than in pure plots. The higher pollinator visitation rates were recorded in both low- and high-density plots. In particular, successive flower visits within an individual plant were significantly lower in mixed plots. Supplemental pollination significantly increased fruit set and seed set of individuals in pure plots, while it only marginally increased seed set per fruit of plants in mixed plots. Conclusions The presence of V. dichroantha can facilitate pollination and increase female reproductive success of P. monbeigiana via both quantity (mitigating pollinator limitation) and quality (reducing geitonogamy) effects. This study suggests that successive pollinator movements among flowers within a plant, as well as pollinator visitation rates and interspecific flower switching, may be important determinants of the direction and mechanisms of interaction between species.

Selective nectar robbing in a gynodioecious plant (Glechoma longituba) enhances female advantage

Nectar robbing not only affects the reproductive fitness of the plant but it may also potentially affect the pollination dynamics of the associated coflowering individuals. In this study, we established that the nectar robber Xylocopa sinensis robs nectar only from the hermaphrodite ramets of the gynodioecious plant Glechoma longituba but not from the female ramets. In populations with high rates of nectar robbing, this results in hermaphrodite ramets having reduced seed set whereas the female ramets have a slightly increased seed set. We hypothesize that selective nectar robbing confers an advantage to female individuals and thus ensures their maintenance in gynodioecious populations. Results of controlled experiments indicated that the reduction in the amounts of nectar available occasioned by nectar robbing resulted in some legitimate pollinators switching to visiting flowers on female rather than hermaphrodite ramets. This resulted in lower pollination rates and seed set for hermaphrodites and higher pollination rates and seed set for females. This study presents a previously unreported mechanism causing female advantage in gynodioecious plants.

Within-season adjustment of sex expression in females and hermaphrodites of the clonal gynodioecious herb Glechoma longituba (Lamiaceae)

The within-season modification or adjustment of sex expression was studied in the gynodioecious herb Glechoma longituba. The results from seven natural populations indicated that the seed sets of hermaphrodite ramets were relatively stable compared to those of female ramets. However, a negative correlation was detected between the seed set of female ramets and their frequency of occurrence in a population. Moreover, a negative correlation was also detected between the degree of gender modification in the late flowering period and the seed set in female ramets. Controlled experiments on both wild and cultivated plants indicated that the resource adjustment, presumably caused by flower removal or the hand pollination of flowers, in the early-middle flowering season could induce a greater degree of gender modification in later flowers from female to hermaphrodite and vice versa. However, the ranges of degree of gender modification were different between the two sex morphs, and the variation in females was greater than in hermaphrodites. This phenomenon could not be adequately explained based on the sequential adjustment of investment hypothesis which has been invoked in previous studies. We propose that the results of this study may provide a variation to the model of sequential adjustment of investment in serial flowering annual gynodioecious plants, including Glechoma longituba. We postulate that the variation of sex expression might be beneficial for the female in order to avoid pollen limitation and, further, to obtain a selective advantage.

Pollination in a patchily distributed lousewort is facilitated by presence of a co-flowering plant due to enhancement of quantity and quality of pollinator visits.

BACKGROUND AND AIMS Plants surrounded by individuals of other co-flowering species may suffer a reproductive cost from interspecific pollen transfer (IPT). However, differences in floral architecture may reduce or eliminate IPT. METHODS A study was made of Pedicularis densispica (lousewort) and its common co-flowering species, Astragalus pastorius, to compare reproductive and pollination success of lousewort plants from pure and mixed patches. Floral architecture and pollinator behaviour on flowers of the two plants were compared along with the composition of stigmatic pollen load of the louseworts. The extent of pollen limitation of plants from pure and mixed patches was also explored through supplemental pollination with self- and outcross pollen (PLs and PLx). KEY RESULTS Mixed patches attracted many more nectar-searching individuals of Bombus richardsi. These bumble-bees moved frequently between flowers of the two species. However, they pollinated P. densispica with their dorsum and A. pastorius with their abdomen. This difference in handling almost completely eliminated IPT. Lousewort plants from mixed patches yielded more seeds, and seeds of higher mass and germinability, than those from pure patches. Moreover, louseworts from mixed patches had lower PLs and PLx compared with those from pure patches. CONCLUSIONS Differences in floral architecture induced differences in pollinator behaviour that minimized IPT, such that co-flowering plants significantly enhanced quantity and quality of pollinator visits for the lousewort plants in patchy habitat. These findings add to our understanding of the mechanisms of pollination facilitation.

Change of floral orientation affects pollinator diversity and their relative importance in an alpine plant with generalized pollination system, Geranium refractum (Geraniaceae)

Floral orientation may affect pollinator attraction and pollination effectiveness, and its influences may differ among pollinator species. We, therefore, hypothesized that, for plant species with a generalized pollination system, changes in floral orientation would affect the composition of pollinators and their relative contribution to pollination. Geranium refractum, an alpine plant with downward floral orientation was used in this study. We created upward-facing flowers by altering the flower angle. We compared the pollinator diversity, pollination effectiveness, and pollinator importance, as well as female reproductive success between flowers with downward- and upward-facing orientation. Results indicated that the upward-facing flowers were visited by a wider spectrum of pollinators (classified into functional groups), with higher pollinator diversity than natural flowers. Moreover, due to influences on visitation number and pollen removal, the pollinator importance exhibited by the main pollinator groups differed between flower types. Compared with natural flowers, the pollination contribution of principal pollinators (i.e., bumblebees) decreased in upward-facing flowers and other infrequent pollinators, such as solitary bees and muscoid flies, removed more pollen. Consequently, stigmatic pollen loads were lower in upward- than in downward-facing flowers. These findings reveal that floral orientation may affect the level of generalization of a pollination system and the relative importance of diverse pollinators. In this species, the natural downward-facing floral orientation may increase pollen transfer by effective pollinators and reduce interference by inferior pollinators.

Genotypic diversity and genetic structure of populations of the distylous aquatic plant Nymphoides peltata (Menyanthaceae) in China

Nymphoides peltata is a distylous aquatic plant. In order to explore the relative importance of clonal growth and sexual reproduction within populations and also to reveal the origin of the commonly occurring one style morph populations in China, we studied the clonal diversity and population genetic structure of this species. By using seven single sequence repeat primer pairs, a total of 192 multilocus genotypes (MLGs) were identified among the 472 samples from the 21 populations analyzed; each population had two or more MLGs. The number of MLGs was lower for the one style morph populations than distylous populations. Analysis of molecular variance showed that a smaller proportion of genetic variation resided among populations (36.8%). A neighbor‐joining tree indicated that there was no significant geographical structure of the genetic variation among populations of N. peltata. The Bottleneck tests indicated that there had been significant bottlenecks in most of the studied populations. The successful sexual recruitment from seeds may have contributed to the high clonal diversity in distylous populations of N. peltata in China. Demographic stochasticity or bottleneck should account for the one style morph population with several MLGs. And also the bottleneck effects or demographic changes caused by human activities occurring randomly in populations should account for the finding of no significant geographical structure of the genetic variation among the investigated populations of N. peltata.

The differential contributions of herkogamy and dichogamy as mechanisms of avoiding self‐interference in four self‐incompatible Epimedium species

Self‐interference is one of the most important selective forces in shaping floral evolution. Herkogamy and dichogamy both can achieve reductions in the extent of self‐interference, but they may have different roles in minimizing self‐interference in a single species. We used four self‐incompatible Epimedium species to explore the roles of herkogamy and dichogamy in avoiding self‐interference and to test the hypothesis that herkogamy and dichogamy may be separated and become selected preferentially in the taxa. Two species (E. franchetii and E. mikinorii) expressed strong herkogamy and weak protogyny (adichogamy), whereas another two species (E. sutchuenense and E. leptorrhizum) expressed slight herkogamy and partial protandry. Field investigations indicated that there was no physical self‐interference between male function and female function regarding pollen removal and pollen deposition in all species. Self‐pollination (autonomous or facilitated) was greater in species with slight herkogamy than in those with strong herkogamy. Artificial pollination treatments revealed that self‐pollination could reduce outcrossed female fertility in all species, and we found evidence that self‐interference reduced seed set in E. sutchuenense and E. leptorrhizum in the field, but not in E. franchetii and E. mikinorii. These results indicate that well‐developed herkogamy is more effective compared with dichogamy in avoiding self‐interference in the four species. In genus Epimedium, herkogamy instead of dichogamy should be selected preferentially and evolved as an effective mechanism for avoiding self‐interference and might not need to evolve linked with dichogamy.

Isolation and characterization of polymorphic microsatellite loci from the invasive plant Solidago canadensis (Asteraceae).

Solidago canadensis, a clonal herb originally from North America (common name: Canada goldenrod), is an invasive species in many countries. We developed microsatellite primers for this species. Eleven polymorphic loci were generated and primers were designed. Polymorphism of these 11 loci was assessed in 35 plants from two populations (Wuhan and Shanghai) in China. The number of alleles per locus ranged from 3 to 14. The observed and expected heterozygosities varied from 0.0732 to 0.7391 and from 0.1177 to 0.8687, respectively. These microsatellite markers will be useful tools for studies of population genetics in the native and invasive range of this species.

Phylogeography of the widespread plant Ailanthus altissima (Simaroubaceae) in China indicated by three chloroplast DNA regions

Ailanthus altissima (Mill.) Swingle, a temperate tree species, has a wide distribution in China. To infer its refugia and patterns of migration during past climatic changes in China, genetic variations among different populations were studied. Gene sequences of three chloroplast DNA spacer regions, psbA‐trnH, trnL‐trnF, and trnD‐trnT, were obtained from 440 individuals of 44 populations. The distribution of haplotype and the relationships among them were investigated by haplotype network. In addition, the genetic diversity of the sampled regions was inferred, and the biogeographic history was also reconstructed. Twelve haplotypes were identified, among which, five were unique. The phylogenetic analysis and geographical distribution of haplotypes indicate that multiple glacial refugia existed in mainland China during the Quaternary oscillations. Due to the combined effects of contiguous range expansion and allopatric fragmentation, significant genetic structure was not found in this study. Based on biogeographic and demographic analysis, three main dispersal routes were identified for the major haplotypes, whereas others were more likely localized demographic expansion.