Female frequency and relative fitness of females and hermaphrodites in gynodioecious Geranium sylvaticum (Geraniaceae)

We determined female frequency of 23 populations of the gynodioecious Geranium sylvaticum (Geraniaceae) in Finland. We compared our results to previous results on this species from the 1960s in order to reveal putative changes in female frequencies. Because females may be maintained in gynodioecious populations if their seed production or offspring quality is higher than that of hermaphrodites, we explored reproductive success of females and hermaphrodites in detail in 11 populations for two consecutive years. Female frequencies varied from 0.4 to 27.2%; this variation is similar to that observed in the 1960s. Contrary to previous results that indicated lower seed production in females, females produced 1.2 and 1.7 times more seeds per flower than hermaphrodites in 2000 and 2001, respectively. Females also had higher fruit set than hermaphrodites. Thus, higher seed production of females partly explains the maintenance of gynodioecy in this species. Furthermore, female frequency correlated negatively with relative seed fitness of hermaphrodites suggesting that relative seed fitness is related to population sex ratio. Female frequency and the distance of the population from the most southern population also tended to correlate positively, suggesting that harsher environmental conditions in the north may benefit female plants. Given the observed yearly variation, our results also highlight the importance of temporal variation for the relative seed fitness of females and hermaphrodites.     

Mating system contributes only slightly to female maintenance in gynodioecious Geranium maculatum (Geraniaceae)

Gynodioecy, the co-occurrence of female and hermaphroditic individuals within a population, is an important intermediate in the evolution of separate sexes. The first step, female maintenance, requires females to have higher seed fitness compared with hermaphrodites. A common mechanism thought to increase relative female fitness is inbreeding depression avoidance, the magnitude of which depends on hermaphroditic selfing rates and the strength of inbreeding depression. Less well studied is the effect of biparental inbreeding on female fitness. Biparental inbreeding can affect relative female fitness only if its consequence or frequency differs between sexes, which could occur if sex structure and genetic structure both occur within populations. To determine whether inbreeding avoidance and/or biparental inbreeding can account for female persistence in Geranium maculatum, we measured selfing and biparental inbreeding rates in four populations and the spatial genetic structure in six populations. Selfing rates of hermaphrodites were low and did not differ significantly from zero in any population, leading to females gaining at most a 1–14% increase in seed fitness from inbreeding avoidance. Additionally, although significant spatial genetic structure was found in all populations, biparental inbreeding rates were low and only differed between sexes in one population, thereby having little influence on female fitness. A review of the literature revealed few sexual differences in biparental inbreeding among other gynodioecious species. Our results show that mating system differences may not fully account for female maintenance in this species, suggesting other mechanisms may be involved.     

Frequency-dependent pollinator discrimination acts against female plants in the gynodioecious Geranium maculatum

MethodsTo test the severity and consequences of this type of pollinator discrimination in Geranium maculatum, experimental populations with the range of sex ratios observed in nature were created, ranging from 13 % to 42 % females. Pollinators were observed in order to measure the strength of discrimination, and pollen deposition and seed production of both sexes were measured to determine the fitness consequences of this discrimination. Additionally a comparison was made across the sex ratios to determine whether discrimination was frequency-dependent.ConclusionsThe results suggest that pollinator discrimination negatively affects females'' relative fitness when they are rare. Thus, the initial spread of females in a population, the first step in the evolution of gynodioecy, may be made more difficult due to pollinator discrimination.     

Taxonomic revision of Geranium sect. Gracilia (Geraniaceae)

Geranium sect.Gracilia (Geraniaceae) comprises nine species in the Andes of Venezuela and Colombia.Geranium lindenianum andG. gracilipes are synonymized withG. holosericeum. The identity ofG. multiceps is clarified. Its differences from the two Colombian species,G. santanderiense andG. lainzii, are discussed.Geranium lignosum, G. sebosum, G. stoloniferum, G. subnudicaule, andG., velutinum are now considered to be members of sect.Gracilia. The identity ofG. pilgerianum could not be clarified because the type was destroyed and other collections have not been found. Micromorphological leaf and seed characters are discussed. Six lectotypes and one neotype are designated.

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Resumen  Se revisaGeranium sect.Gracilia (Geraniaceae), un grupo formado por nueve especies distribuidas por los Andes de Venezuela y Colombia. Se sinonimizanG. lindenianum y G. gracilipes aG. holosericeum. Se aclara la identidad deG. multiceps y se establecen sus diferencias conG. santanderiense y conG. lainzii, ambas esencialmente colombianas. Se aceptan en esta secciónG. lignosum, G. stoloniferum yG. sebosum, propuestos tras la descripción de la sect.Gracilia, yG. subnudicaule yG. velutinum, ya tratados por otros autores en como pertenecientes a este grupo. Por el contrario, la identidad deG. pilgerianum no ha podido ser aclarada tras la destrucción del tipo y ante la falta de otros materiales de la especie. Se estudian diversos caractere micromorfológicos, especialmente algunos referibles a la anatomía foliar y la de la semilla. Se designan seis lectótipos y un neótipo.

     

Geranium hanaense (Geraniaceae), a new species from Maui,Hawaiian Islands

Geranium hanaense, a new species endemic to two small montane bogs (20 ha total) on northeast Haleakala, Maui, Hawaiian Islands, is described. This new species is postulated to have evolved from the high elevation xeromorphic species,G. cuneatum, in a fashion similar to that of the two other bogGeranium species. The ecology and evolution of HawaiianGeranium species, includingG. hanaense, are discussed.     

Morphology, ontogeny and histochemistry of secretory trichomes of Geranium robertianum (Geraniaceae)

Geranium robertianum bears three types of glandular uniseriate trichomes which originate from a single protodermal cell and develop through periclinal divisions. Type I trichomes are procumbent and have an oval apical cell, two stalk cells and a basal cell. Type II trichomes are erect and have a pear shaped apical cell, two stalk cells and a basal cell. Type III trichomes are much longer than the other two types and have an elongated apical cell, five long stalk cells and a basal cell. Type I and type II trichomes are common on leaves while III trichomes are more abundant on flower structures.
Type I and type II trichomes secrete terpenoids and phenols. Type III trichomes are characterized by the accumulation of anthocyanins in the apical cell and secrete flavonoids.     

A cladistic analysis of Geranium subgen. Erodioidea (Picard) Yeo (Geraniaceae)

Subgenus Erodioidea , comprising 19 species, is diagnosed exclusively by the type of fruit discharge and associated morphological characters, all of which are of widespread occurrence within the Geraniaceae. We have no evidence to suggest that the three included sections ( Erodioidea, Aculeolata and Subacaulia) form a monophyletic group. Cladistic analysis of a data set containing 30 morphological characters has confirmed our doubts of monophyly of the subgenus by placing part of the outgroup within the ingroup. Subsequent analyses of the two included non-monotypic sections, Erodioidea and Subacaulia , give different results. For both sections, the monophyly assumption is reasonably well-supported by characters. However, while analysis of sect. Erodioidea results in an explicit hypothesis of relationships and a fully resolved cladogram, resolution within sect. Subacaulia is low. For analysis of the latter, seven different outgroups were used and, in each one, the successive approximations weighting procedure (available in the program Hennig 86) was followed to improve resolution. Despite this, lower nodes in the cladogram remained unresolved, and strict consensus trees of all the analyses resulted in only a few replicated subterminal clades. These results are discussed in connection with biogeographical data and with the hypothesis that representatives of sect. Subacaulia are schizoendemics.     

Development of nuclear microsatellite markers for the threatened wetland plant Geranium soboliferum var. kiusianum (Geraniaceae)

Nuclear microsatellite markers were developed for the threatened plant Geranium soboliferum var. kiusianum, which has decreased its population size as a result of loss of its wetland habitat in Kyushu, Japan. Utilizing RNA‐seq data obtained by next‐generation sequencing techniques, 10 polymorphic microsatellite markers with 3–16 alleles in a nuclear genome were developed and characterized. Two to 15 alleles were observed in G. soboliferum. These markers will be used to investigate the genetic circumstance of remnant populations of G. soboliferum var. kiusianum and their phylogenetic relationship with G. soboliferum.     

Determinants of seed production in Geranium maculatum

Summary We experimentally examined factors limiting seed production in two populations of the perennial woodland herb Geranium maculatum in central Illinois, USA. To test the pollinator-limitation hypothesis, we compared the seed production of plants whose flowers were supplementarily pollinated with outcross pollen to that of control plants receiving natural pollination only. To test if fruit production by early flowers suppresses fruit and seed formation by late flowers, a third group of plants was prevented from producing seed from the first 50% of the flowers to open (stigmas were excised at flower opening). Finally, to test if seed maturation and flower initiation are correlated with photosynthetic capacity, we performed a defoliation experiment in which either the stem leaves within the inflorescence, the stem leaves below the inflorescence, or the rosette leaves were removed during late flowering. Plants that reccived supplemental pollination produced 1.5–1.6 times more seeds than control plants. We found no difference between hand-pollinated plants and controls in mortality, flowering frequency or number of flowers produced in the year following the experiment. In both control and hand-pollinated plants, the fruit set and total seed production of early flowers were more than twice as high as those of late flowers. In one of the two populations, plants whose early flowers were prevented from setting seed produced significantly more seeds from their late flowers than did control plants. Seed predation was low and did not differ between early and late flowers. Leaf removal did not affect seed number or size in the year of defoliation, nor did it reduce survival or flower production in the subsequent year. This suggests that the plants were able to compensate for a partial defoliation by using stored resources or by increasing photosynthetic rates in the remaining leaves. Taken together, the results demonstrate that both pollinator activity and resource levels influence patterns of seed production in G. maculatum. While seed production was pollinatorlimited in both populations, a seasonal decline in resource availability was apparently responsible for the low seed production by late flowers.     

Geranium kikianum sp. nov. (Geraniaceae) from the southern Peloponnese,Greece

Geranium kikianum Kit Tan & G. Vold sp. nov. (Geraniaceae) is illustrated and described as a new species endemic to Greece. It occurs beside streams and other wet places in open Pinus nigra forest at the foothills of Mt Taigetos in the southern Peloponnese. It is closely related to G. macrorrhizum, a species more widely distributed in southern and central Europe, ranging from the southern Alps to the Balkan Peninsula. It differs from the latter by its smaller and narrower deflexed petal limb, slender claw and occurrence in wet habitats. The genome sizes of G. kikianum and of Greek populations of G. macrorrhizum are presented here for the first time. The nuclear DNA content (2C values) of 2.84 pg for G. kikianum and 2.83 and 2.87 pg for two G. macrorrhizum populations from Greece probably corresponds to a 2n=92 cytotype while the smaller genome size of 1.45 pg in a population of G. macrorrhizum from Mt Smolikas, Greece may correspond to a 2n=46 cytotype.     

Variation in the intensity of inbreeding depression among successive life-cycle stages and generations in gynodioecious Silene vulgaris (Caryophyllaceae)

Inbreeding depression is one of the hypotheses explaining the maintenance of females within gynodioecious plant populations. However, the measurement of fitness components in selfed and outcrossed progeny depends on life-cycle stage and the history of inbreeding. Comparative data indicate that strong inbreeding depression is more likely to occur at later life-cycle stages. We used hermaphrodite individuals of Silene vulgaris originating from three populations located in different valleys in the Swiss Alps to investigate the effect of two generations of self- and cross-fertilization on fitness components among successive stages of the life cycle in a glasshouse experiment. We detected significant inbreeding depression for most life-cycle stages including: the number of viable and aborted seeds per fruit, probability of germination, above ground biomass, probability of flowering, number of flowers per plant, flower size and pollen viability. Overall, the intensity of inbreeding depression increased among successive stages of the life cycle and cumulative inbreeding depression was significantly stronger in the first generation (delta approximately 0.5) compared with the second generation (delta approximately 0.35). We found no evidence for synergistic epistasis in our experiment. Our finding of more intense inbreeding depression during later stages of the life cycle may help to explain the maintenance of females in gynodioecious populations of S. vulgaris because purging of genetic load is less likely to occur.     

Germination of up to 129-year old, dry-stored seeds of Geranium bohemicum (Geraniaceae)

Old dry-stored seeds of the annual pyrophyte Geranium bohemicum from seed collections and herbaria were tested to determine their germinability. Ten samples of seed, ranging in age from 3 to 200 years, were used. The oldest seeds to germinate (three out of ten) were from a 129-year old collection. All three seedlings developed into healthy plants. This finding supports the assumption that G bohemicum can emerge from a bank of long-lived seeds after forest fires.     

Herbivore pressure by weevils associated with flower color polymorphism in Geranium thunbergii (Geraniaceae)

Although floral herbivory has recently received increased attention as an important factor influencing plant reproduction, relatively little is known about how its frequency and intensity vary depending on traits of host plants. Here we report that herbivore pressure by a weevil, Zacladus geranii, is associated with a flower color polymorphism of Geranium thunbergii (Geraniaceae). Pink and white flower color morphs have been reported in G. thunbergii, and we found in a three-year field survey in multiple populations that, generally, adult weevils more preferentially visited white flowers than pink flowers. Consistently, we found more severe damage by weevil larvae in white flowers. Overall herbivore pressure for G. thunbergii varied strongly between populations, and the difference seems to be partly explained by the co-occurrence of a related plant species, Geranium yezoense, in a population, as weevils preferred it to both color morphs of G. thunbergii, thereby relaxing overall herbivore pressure for G. thunbergii. Nonetheless, despite such high variability, the preference of weevils for white morphs over pink morphs of G. thunbergii was found across multiple populations. We discuss possible mechanisms causing the association between flower color and herbivore preference as well as its evolutionary consequences.     

Fruit-discharge-type in Geranium (Geraniaceae): its use in classification and its evolutionary implications

Three main types of seed-discharge in Geranium are made the basis of its division into subgenera: Geranium subgenus Geranium , with a ballistic expulsion of the seed from the mericarp, termed 'seed-ejection'; Geranium subgenus Robertium , with forcible discharge of the mericarp with the seed in it, separately from the awn, termed 'carpel-projection', and Geranium subgenus Erodioideae , with the seed-containing mericarp being thrown off with the attached awn, which becomes helically coiled, called the 'Erodium-type'. Variants of the seed-ejecting type permit the division of Geranium subgenus Geranium into three sections. Other criteria are used to divide Geranium subgenus Robertium into eight sections and Geranium subgenus Erodioideae into two. Species are fully enumerated except for Geranium section Geranium , which comprises the bulk of the genus, and for which some tentative subgroups are given in an Appendix. Diversity of fruit-type in Geranium is greatest in the Mediterranean Region. Characters of the fruit in other genera of Geraniaceae are surveyed. Geographical distributions, chromosome numbers, pollen morphology and phytochemistry are reviewed. It is suggested that Erodium-type fruit discharge, shared with the four remaining genera of the family, is primitive, and that carpel-projection and seed-ejection arose from it separately, the latter probably more than once. The very large, mainly perennial, Geranium subgenus Geranium is contrasted with Geranium subgenus Robertium , half of which is hapaxanthic, and which occupies marginal habitats and shows greater morphological and chromosomal variation despite its being only one tenth the size. Geranium subgenus Erodioideae is smaller still and probably relictual.     

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.     

Preferences of pollinators and herbivores in gynodioecious Geranium sylvaticum

BACKGROUND AND AIMS: For the maintenance of gynodioecy (i.e. the coexistence of female and hermaphroditic plants), females need to compensate for the lack of pollen production through higher seed production or better progeny quality compared to hermaphrodites. In Geranium sylvaticum, females produce more seeds per flower than hermaphrodites. This difference in seed production might be modified by biological interactions with pollinators and herbivores that may favour one sex and thus affect the maintenance of gynodioecy. METHODS: Sexual dimorphism in flower size and flowering phenology, and in attractiveness to pollinators, pre-dispersal seed predators and floral herbivores were examined in natural populations of G. sylvaticum. KEY RESULTS: Pollinators preferred hermaphrodites 25 % more often than females in two of the three study populations, and floral herbivores attacked hermaphrodites 15 % more often than females in two of the six study populations. These preferences might be explained by the larger flower size of hermaphrodites. In contrast, seed predators did not prefer either sex. CONCLUSIONS: The data suggest that pollinator preference does not benefit females, whereas the higher floral herbivory of hermaphrodites might enhance the maintenance of females in G. sylvaticum. Thus, although the data support the view that ecological factors may contribute to the maintenance of gynodioecy, they also suggest that these contributions may vary across populations and that they may function in opposite directions.     

Pre-dispersal seed predation in gynodioecious Geranium sylvaticum is not affected by plant gender or flowering phenology

Sex-specific interactions with antagonists may explain female maintenance in gynodioecious populations if seeds produced by hermaphroditic plants are preferred over seeds produced by female plants. Among antagonistic interactions, pre-dispersal seed predators have received relatively little attention even though they may exert sex-specific selective pressures on the evolution of floral and flowering traits. In this work, I investigate temporal variation in seed predation in gynodioecious Geranium sylvaticum, where in addition to female and hermaphrodite individuals, plants with an intermediate sexual expression are also present in most populations. Specifically, I examined whether seed predation is linked to flowering phenology, plant gender, and sexual dimorphism in floral and seed traits over the flowering season using an experimental field population. Within the population, I selected female, intermediate, and hermaphrodite plants with different timing of flowering onset (early, mid, or late), and collected seeds across the fruiting period. Seeds were weighed and examined for seed predator damage. The results show that the three genders experienced similar levels of seed predation attack regardless of their flowering phenology, and that overall seed predation was not related to changes in seed production or seed mass. These results suggest that sexual dimorphism in seed predation cannot be responsible for female maintenance in this species.