Sachiko Nishida

Alien dandelion reduces the seed-set of a native congener through frequency-dependent and one-sided effects

In conservation biology, increasing numbers of studies have focused on reproductive interference (RI) between a native species and related aliens. However, few studies have examined the frequency dependence of RI, despite of its key importance to invasiveness. Here, we report for the first time frequency-dependent RI in a pair of native and alien dandelions: Taraxacum japonicum and T. officinale, respectively. Taraxacum japonicum has been displaced rapidly by the alien congener T. officinale in Japan and its causal mechanism are still poorly understood. Field observations revealed that the seed-set of natives decreased substantially as the proportion of alien neighbors increased. Subsequently, in a field experiment, the removal of alien flowers only greatly increased the seed-set of natives. We synthesized these results with existing theoretical models of RI and concluded that RI, which is mediated by strong frequency dependence, is presumably responsible for the displacement of T. japonicum by T. officinale.

Effective range of reproductive interference exerted by an alien dandelion, Taraxacum officinale, on a native congener

Reproductive interference (RI), defined as the fitness cost of interspecific sexual interactions, such as interspecific pollen transfer (IPT) in plants, is ecologically important. Theoretically, RI could result in competitive exclusion, as it operates in a frequency-dependent manner. Additionally, IPT may have a greater range than resource competition, although information about the range of IPT is lacking. In the present study, we measured the range of IPT exerted by Taraxacum officinale (an alien species) on a native dandelion, T. japonicum. We used two approaches. In one, we analyzed the RI effect on a native seed set at three spatial scales. In the second, we tracked IPT from alien to native flower heads using fluorescent pigments as markers. We estimated that pollination distances were in the order of several meters. These distances exceeded the mean distance from each native plant to the nearest alien. As hypothesized, the effect of RI reached farther than neighboring individuals. These data indicate the spatial range from which alien dandelions should be removed to allow the conservation of natives.

Are Cuticular Characters Useful in Solving Generic Relationships of Problematic Species of Lauraceae

We report on the cuticular features of a number ofLauraceae species belonging to the genera Aspidostemon, Beilschmiedia, Cryptocarya and Potameia, all from Madagascar. The goal of this project was to ascertain if cuticular features could be used to determine the generic placement of a poorly known species previously placed in Cryptocarya and Aspidostemon and of several specimens which combine characters of Potameia and Beilschmiedia. We conclude that cuticular features define groups of species or genera of Lauraceae and that these characters are a promising tool in solving the generic placement of poorly known species or specimens which possess characters typical of more than one genus.

Differential effects of reproductive interference by an alien congener on native Taraxacum species

Reproductive interference (RI) has been suggested to play a critical role in native plant displacement by alien congeners. However, although co-existence of native and alien congeners may provide an opportunity to refute the RI hypothesis, few studies have examined such a case. Using a native Japanese dandelion, Taraxacum longeappendiculatum, and a co-existing alien congener, Taraxacum officinale, we tested the hypothesis that differences in RI by the alien between native recipient congeners explain whether a native will co-exist with or be displaced by an alien. We conducted a field survey to investigate the effects of alien relative abundance on T. longeappendiculatum seed set, and a hand-pollination experiment to identify the extent of pollen interference by the alien on T. longeappendiculatum. We compared these results with those obtained previously for another Japanese native species, Taraxacum japonicum, which was displaced by the alien. In our field survey, alien relative abundance had little effect on seed set in nearby T. longeappendiculatum, and hand-pollination with mixed pollen grains produced no substantial decrease in seed set of the native species. Model selection supported these tendencies; the effect of RI by the alien differed between the two native species. Other potential factors, such as resource competition or habitat changes, could not explain the co-existence of T. longeappendiculatum with and exclusion of T. japonicum by the alien in the same explanatory framework. Considering the consistent explanatory power, the findings suggest that RI is a critical mechanism that can determine both co-existence with and displacement of native dandelions by an alien congener.

Taxonomic revision of Beilschmiedia (Lauraceae) in Borneo

A revision of Beilschmiedia Nees (Lauraceae) in Borneo is given. Descriptions, distribution maps, illustrations of leaves, terminal buds, and flowers, and a key to the species are provided. Twenty-six species were recognized, including one newly described species. The new species is distinguished from the other Beilschmiedia species of Borneo in having pubescent anther apices. Beilschmiedia reticulata was excluded from the revision as an imperfectly known species because of a lack of flowering specimens. Beilschmiedia eusideroxylocarpa was also excluded because it had only six stamens representing the second and third whorls, which is characteristic for the genus Endiandra.

An Evaluation of Classification By Cuticular Characters of the Lauraceae: A Comparison To Molecular Phylogeny1

Abstract Cuticular characters are epidermal or stomatal characters and are often used in the taxonomy and classification of fossil or extant Lauraceae. However, there is no consensus on their usefulness, especially as to which characters take priority and at which taxonomic level. This study compared the cuticular characters of species within the Neotropical genera of the Ocotea Aubl. complex to the reported molecular phylogeny. Species of the following genera are included in this study: Aiouea Aubl., Aniba Aubl., Dicypellium Nees & Mart., Endlicheria Nees, Kubitzkia van der Werff, Licaria Aubl., Nectandra Rol. ex Rottb., Ocotea, Paraia Rohwer, H. G. Richt. & van der Werff, Pleurothyrium Nees, Rhodostemonodaphne Rohwer & Kubitzki, Umbellularia (Nees) Nutt., and Urbanodendron Mez. Species groups based on cuticular characters, especially characters of the stomata, agreed well with the various clades in the molecular phylogeny, but did not agree with species grouped according to the traditional generic concepts. Stomata characters showed little or no variation within the clades found in the molecular phylogeny. Because the number of character states is limited, cuticular features by themselves cannot be used to define genera or clades or will not allow the identification of specimens.

Pollen–pistil interactions in reproductive interference: comparisons of heterospecific pollen tube growth from alien species between two native Taraxacum species

Summary nReproductive interference (RI), any negative interspecific interaction during the reproductive process, has been gaining increasing attention due to its potential explanatory power for the mutually exclusive distribution of closely related species. RI in plants may occur during any of three stages: pollen transfer, pollen–pistil interactions or hybridization. Pollen–pistil interactions may be especially important as most studies of RI have suggested the involvement at this stage. Details of these interactions are required to fully explore RI and are especially relevant in considering the impact of RI in the field. nWe present a plausible explanation of how RI functions in the pollen–pistil interaction stage using two Japanese native dandelions, Taraxacum japonicum and Taraxacum longeappendiculatum, of which only the former is vulnerable to RI from an alien congener, Taraxacum officinale. We conducted a series of hand pollinations in these native dandelions and compared pollen tube behaviour to examine differences associated with vulnerability and imperviousness to RI from the alien. nThe two native dandelions differed in terms of the absence/presence of pollen tube elongation after heterospecific pollination (pollination with only T.xa0officinale): pollen tubes grew through the ovaries of the vulnerable T.xa0japonicum, but not through those of the impervious T.xa0longeappendiculatum. In vitro hand pollination verified that the alien pollen tubes could extend into the ovaries of T.xa0japonicum. nOur results show that RI from the alien dandelion consumed ovules by heterospecific pollen deposition. The pistils of the impervious native species could prevent growth of the alien pollen tubes, thereby sparing the ovules for fertilization by conspecific pollen. The pistils of the vulnerable species lacked interspecific incompatibility against the alien, and thus, the alien pollen tube entered the ovary, eliminating an opportunity for conspecific pollen fertilization. This consumption of ovules by heterospecific pollen tubes would cause a seed set failure, leading to reduced abundance and a further exertion of RI in the next generation, which explains displacement of the vulnerable species by the alien in the field.

Yasunia (Lauraceae), a New Genus with Two Species from Ecuador and Peru

Abstract A new genus of the Lauraceae, Yasunia van der Werff, is described. It consists of two undescribed species, Y. quadrata van der Werff and Y. sessiliflora van der Werff, known from lowland rainforest in Ecuador and Peru. The new genus is closely related to Beilschmiedia Nees, but differs in its conspicuous, pubescent staminodia, exserted stamens, and reduced number of stamens. The relationships of the new genus and its placement in the Cryptocaryeae are discussed.

Dominant Occurrence of Cleistogamous Flowers of Lamium amplexicaule in relation to the Nearby Presence of an Alien Congener L. purpureum (Lamiaceae)

Here we document a novel phenomenon that, based on field observations in central Japan, cleistogamous flowers (or closed flowers) of an annual herb Lamium amplexicaule were dominantly expressed near an alien congener L. purpureum. The proportion of cleistogamous flowers in an individual L. amplexicaule increased with the frequency of L. purpureum occurring in the same patches but did not increase with the total density of Lamium plants and their own size. To confirm the consistency of the effect of the coexisting alien species, we assessed the cleistogamous frequency at the patch level for three other populations. In these populations as well, the proportion of L. amplexicaule producing cleistogamous flowers increased with the frequency of L. purpureum. Our transplant experiment at one site found no effect of the nearby presence of L. purpureum on the seed set of L. amplexicaule and therefore did not support the hypothesis that the adverse effect on the reproduction via interspecific pollination favored cleistogamous flowers that accepted no external pollen. Further studies must be conducted to examine the negative interactions between the related species before and after seed development.

Variation in the strength of reproductive interference from an alien congener to a native species in Taraxacum

Reproductive interference (RI) may be a contributing factor to the displacement of native species by an alien congener, and RI strength has been shown theoretically to affect distributional relationships between species. Thus, variations in RI strength from alien to native species result in different consequences of invasions and efforts to conserve native species, but the variations have seldom been examined empirically. We therefore investigated RI strength variations from the alien species Taraxacum officinale and its hybrids to eight populations of native dandelions, four T. japonicum populations and two populations each of two subspecies of T. platycarpum. We examined the association between alien relative abundance and native seed set in field surveys, and we also performed hand-pollination experiments to investigate directly the sensitivity of native flowers to alien pollen. We found that the effect of alien relative abundance on native seed set of even the same native species could differ greatly in different regions, and that the sensitivity of native flowers to alien pollen was also dependent on region. Our results, together with those of previous studies, show that RI from the alien to the native species is strong in regions where the alien species outnumbers the native species and marginal where it does not; this result suggests that alien RI can critically affect distributional relationships between native and alien species. Our study highlights the importance of performing additional empirical investigations of RI strength variation and of giving due attention to alien RI in efforts to conserve regional native biodiversity.