Mixed Breeding System Research Articles

Pollination biology of the crypto-viviparous Avicennia species (Avicenniaceae)

Floral biology, sexual system, breeding system, pollinators, fruiting and propagule dispersal ecology of crypto-viviparous Avicennia alba Bl., A. marina (Forsk.) Vierh. and A. officinalis L. (Avicenniaceae) were studied in Godavari mangrove forests of Andhra Pradesh State, India. All the three plant species initiate flowering following the first monsoon showers in June and cease flowering in late August. The flowers are hermaphroditic, nectariferous, protandrous, self-compatible and exhibit mixed breeding system. Self-pollination occurs even without pollen vector but fruit set in this mode is negligible. In all, the flowers are strictly entomophilous and the seedlings disperse through self-planting and stranding strategies.

Apis mellifera pollination improves agronomic productivity of anemophilous castor bean (Ricinus communis)

Castor bean (Ricinus communis L.) is cultivated mainly for biodiesel production because of its oil-rich seeds; it is assumed to be an anemophylous species. But pollination deficit can lead to low productivity often attributed to other reasons. In this paper, we investigated pollination requirements, pollination mechanism, occurrence of pollination deficit, and the role of biotic pollinators in a large commercial plantation of castor bean. Our results show that R. communis bears a mixed breeding system favoring selfing by geitonogamy, although the wind promotes mostly outcrossing. We also found that the honey bee (Apis mellifera L.) foraging on castor bean can both transfer pollen from male to female flowers within the same raceme and boost the release of airborne pollen by male flowers. Both situations increase geitonogamy rates, raising significantly fruit set and seed yield. This is the first report of an animal foraging activity increasing seed yield in an anemophilous and geitonogamous crop and elucidates the role of biotic pollinators in castor bean reproduction.

Declining Genetic Diversity and Increasing Genetic Isolation toward the Range Periphery ofStipa pennata, a Eurasian Feather Grass

A common assumption in ecology and evolutionary biology is that genetic diversity declines and differentiation increases toward the edge of a species’ geographic range, where populations tend to be smaller and more isolated. We tested these predictions in a characteristic Eurasian steppe plant, Stipa pennata, by inspecting 230 AFLP bands in 26 populations (345 individuals) along a 3300-km longitudinal gradient from the range core, in Russia, to the range periphery, in central Europe. Overall, our study species showed low genetic diversity within populations (mean proportion of polymorphic ) and moderately high genetic differentiation among them (mean ). As predicted, genetic diversity declined significantly from the range core to the periphery but was not correlated with population size. Pairwise genetic differentiation was significantly higher among peripheral populations than central populations but did not show a pronounced relationship with geographic distance. Our results indicate that peripheral populations may experience higher genetic drift and lower gene flow than their central counterparts, possibly because of smaller population sizes, spatial isolation, and a more complex landscape structure. In addition, historic range fluctuations and the mixed breeding system could have enhanced the observed patterns in our study species.

Radiation of European Eubosmina (Cladocera) from Bosmina(E.) longispina—concordance of multipopulation molecular data with paleolimnology

We investigated the evolutionary radiation of a freshwater zooplankter that possesses a mixed breeding system and a detailed, dated, subfossil record. We estimated the phylogenetic relationships among the proposed species with complete nicotinamide adenine dinucleotide dehydrogenase subunit 2 mitochondrial gene sequence variation. We sequenced 374 Eubosmina specimens representing 10 out of 11 distinct morphospecies from 86 water bodies in three separate Holarctic regions. As expected for a Holocene radiation, there was a lack of monophyly for the proposed species and rare sharing of derived haplotypes among some species. Nevertheless, the proposed species exhibited little or no sharing of mitochondrial deoxyribonucleic acid haplotypes. Moreover, the phylogenetic and haplotype network results revealed a radiation pattern that is concordant with the subfossil record—with an older Bosmina (E.) longispina radiating into several new forms. Our results bolster the subfossil, morphometric, experimental, and within‐population genetic evidence that B. (E.) longispina has radiated into several incipient species during the Holocene.

Coexisting Cyclic Parthenogens Comprise a Holocene Species Flock in Eubosmina

BackgroundMixed breeding systems with extended clonal phases and weak sexual recruitment are widespread in nature but often thought to impede the formation of discrete evolutionary clusters. Thus, cyclic parthenogens, such as cladocerans and rotifers, could be predisposed to “species problems” and a lack of discrete species. However, species flocks have been proposed for one cladoceran group, Eubosmina, where putative species are sympatric, and there is a detailed paleolimnological record indicating a Holocene age. These factors make the Eubosmina system suitable for testing the hypotheses that extended clonal phases and weak sexual recruitment inhibit speciation. Although common garden experiments have revealed a genetic component to the morphotypic variation, the evolutionary significance of the morphotypes remains controversial.Methodology/Principal FindingsIn the present study, we tested the hypothesis of a single polymorphic species (i.e., mixing occurs but selection maintains genes for morphology) in four northern European lakes where the morphotypes coexist. Our evidence is based on nuclear DNA sequence, mitochondrial DNA sequence, and morphometric analysis of coexisting morphotypes. We found significant genetic differentiation, genealogical exclusivity, and morphometric differentiation for coexisting morphotypes.ConclusionsWe conclude that the studied morphotypes represent a group of young species undergoing speciation with apparent reproductive barriers despite coexistence in the freshwater pelagic zone.

Pollination and seed set in tropical wetland grasses

This study concerns 39 different grass species occurring in the wetland regions of Godavari delta in the west Godavari district (16°15′–17°30′N and 80°50′–81°55′E) of Andhra Pradesh, southern India. In each species, the sexual status of lemmas, the period of stigma receptivity, pollen/ovule ratio, pollen longevity and daily pollen release were examined. The functional sexual systems were determined after performing controlled pollinations and testing seed quality by weight and germination potential. The florets of 35 species are morphologically hermaphroditic. Among the other four species, Chionachne koenigii and Iseilema laxum are monoecious; Chrysopogon aciculatus and Pennisetum pedicellatum are andromonoecious. Examination of the sequential opening of florets and controlled pollinations revealed that C. koenigii and I. laxum are obligate outcrossers with incompatibility to geitonogamous pollen; C. aciculatus and P.pedicellatum have a high level of compatibility to xenopollen. These and another nine species were treated as predominantly outcrossing species. Yet another five species were predominantly self-fertilized, while the remaining 21 species displayed a mixed breeding system. In a majority of the species the P/O ratios are not high and thus do not conform to the expected large P/O ratios in wind-pollinated plants and postulated breeding systems except in a few species. The majority of these grasses shed pollen over a short period spreading from 2 am to 8 am, when usually low turbulent conditions exist, thus allowing short distance transport and restricted pollen shadows with higher concentration of pollen near the source. This appears to be the appropriate strategy for maximization of pollination in view of the short lifespan of pollen that extends mostly over 1–3 h period, and the patchy distribution of the grasses under study. The restricted pollen shadows facilitate the low levels of pollen production in the grass species under study to fertilize most or all the available ovules.

Rapid ecological isolation and intermediate genetic divergence in lacustrine cyclic parthenogens

BackgroundEcological shifts can promote rapid divergence and speciation. However, the role of ecological speciation in animals that reproduce predominantly asexually with periodic sex and strong dispersal, such as lacustrine cladocerans, is poorly understood. These life history traits may slow or prevent ecological lineage formation among populations. Proponents of the postglacial ecological isolation hypothesis for Daphnia suggest that some species have formed postglacially in adjacent, but ecologically different habitats. We tested this hypothesis with ecological, morphological, and multilocus coalescence analyses in the putative lacustrine sister species, Daphnia parvula and Daphnia retrocurva.ResultsDaphnia parvula and D. retrocurva showed strong habitat separation with rare co-occurrence. Lakes inhabited by D. parvula were smaller in size and contained lower densities of invertebrate predators compared to lakes containing D. retrocurva. In the laboratory, D. retrocurva was less vulnerable to invertebrate predation, whereas D. parvula was less vulnerable to vertebrate predation and was smaller and more transparent than D. retrocurva. The species are significantly differentiated at mitochondrial and nuclear loci and form an intermediate genetic divergence pattern between panmixia and reciprocal monophyly. Coalescence and population genetic modelling indicate a Late or Post Glacial time of divergence with a demographic expansion.ConclusionsDespite their young age and mixed breeding system, D. parvula and D. retrocurva exhibit significant ecological and genetic divergence that is coincident with the formation of deep temperate glacial lakes. We propose that predation may have facilitated the rapid divergence between D. parvula and D. retrocurva and that intermediate divergence of aquatic cyclic parthenogens is likely more common than previously thought.

Life-history variation and breeding system in the hermaphroditic land snail Succinea putris (Pulmonata: Succineidae)

Life-history variation and breeding system in the hermaphroditic land snail Succinea putris (Pulmonata: Succineidae)

Effects of population size on genetic diversity, fitness and pollinator community composition in fragmented populations of Anthericum liliago L.

The genetic and fitness consequences of habitat fragmentation on the dry grassland species Anthericum liliago L. (Anthericaceae) were examined. We used random amplified polymorphic DNA (RAPD) markers to determine the distribution of genetic diversity within and among 10 German A. liliago populations, ranging in size from 116 to over 2 million ramets. The genetic diversity of an A. liliago population was highly positively correlated with its population size. The overall differentiation among populations (Phi-ST = 0.41, P < 0.0001, AMOVA) was considerably higher than expected for a species with a mixed breeding system. No strong correlation (P < 0.01) was detected between fitness parameters and population size and genetic diversity. The reproductive output (seeds per ramet) was only highly correlated (P < 0.001) with the proportion of flowering ramets in a population which could be caused by a more effective pollination in large populations which are more attractive to specialized pollinators. The specialized A. liliago pollinator Merodon rufus (Syrphidae) and high abundances of solitary bees could only be found in A. liliago populations with more than 10,000 individuals. Genetic differentiation among the investigated A. liliago populations may have been caused by limited seed and pollen dispersal and a mixed mating system permitting a high selfing rate. The differentiation among the small and isolated populations lacking main pollinators seems to be caused by genetic drift.

Cross‐species transfer of nuclear microsatellite markers: potential and limitations

Molecular ecologists increasingly require 'universal' genetic markers that can easily be transferred between species. The distribution of cross-species transferability of nuclear microsatellite loci is highly uneven across taxa, being greater in animals and highly variable in flowering plants. The potential for successful cross-species transfer appears highest in species with long generation times, mixed or outcrossing breeding systems, and where genome size in the target species is small compared to the source. We discuss the implications of these findings and close with an outlook on potential alternative sources of cross-species transferable markers.

Allozyme Diversity and Population Genetic Structure of Three Medicinal Epimedium Species from Hubei

Three Epimedium species, E. pubescens Maxim., E. sagittatum (Sieb. & Zucc.) Maxim., and E. wushanense T. S. Ying, which are sympatrically distributed in the western Hubei Province, have been used in traditional Chinese medicine (TCM) for about 2,000 years. Genetic variability and population genetic structure of 11 natural populations of these Epimedium species were investigated using isoelectric focusing in thin-layer polyacrylamide slab gels. Of the 22 enzyme systems prescreened, six coding for 13 loci and 45 alleles were resolved, which were used for analyzing genetic diversity and population structure at both intraspecific and interspecific levels. The results showed that: 1) high levels of genetic diversity were observed in all three species ( A = 2.6-3.2, P = 69.2%-84.6%, H O = 0.274-0.377, H E = 0.282-0.369), which were higher than that of other herbaceous and animal-pollinated species with similar life-history characteristics; 2) there was significant deviation from Hardy-Weinberg Equilibrium, with one half of the loci showing heterozygote excess and the other homozygote excess, in all populations, suggesting the complicated breeding system of Epimedium species; 3) the low level of intraspecific and interspecific genetic differentiation ( G ST = 0.0246-0.0409 and 0.0495-0.1213, respectively) indicated a high level of gene flow among populations and close genetic relationship among the three species; and 4) UPGMA cluster analysis further showed that E. pubescens was more closely related to E. sagittatum than to E. wushanense, which was in good agreement with the morphological characters and the recent phylogenetic analysis of these species. On the basis of these results, it was concluded that the mixed breeding system, long-lived perennial life form, ancient evolutionary history, and seed dispersal by ants in Epimedium are responsible for the genetic variation and population structure of these species.

Molecular systematics of the Carinarion complex (Mollusca: Gastropoda: Pulmonata): a taxonomic riddle caused by a mixed breeding system

The original description of the slugs Arion (Carinarion) fasciatus, Arion (Carinarion) silvaticus and Arion (Carinarion) circumscriptus was based on subtle differences in body pigmentation and genital anatomy. However, body pigmentation in these slugs may be influenced by their diet, whereas the genital differences between the species could not be confirmed by subsequent multivariate morphometric analyses. Hence, the status of the three nominal morphospecies remains controversial, with electrophoretic studies based on albumen gland proteins and allozymes also providing conflicting results. These studies suggested that Carinarion species are difficult to reconcile with the biological species concept because there is evidence of interspecific hybridization in places where these predominantly self-fertilizing slugs apparently outcross. Therefore, in the present study, the three Carinarion species are evaluated under a phylogenetic species concept, using nucleotide sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS-1) and the mitochondrial 16S rDNA. ITS-1 showed no species specific variation. However, 16S rDNA yielded five haplotype groups. Three of these grouped haplotypes by species, whereas the two others joined haplotypes of different species and included all haplotypes that were shared by species (22% of all haplotypes). Hence, the three nominal Carinarion species appear to be inconsistent with a phylogenetic species concept. The present data also confirmed that North American Carinarion populations are genetically impoverished and may be not sufficiently representative with respect to the taxonomy of Carinarion. In conclusion, we currently regard Carinarion as a single species-level taxon, whose taxonomically deceiving, correlated phenotypic and genetic intraspecific variation is caused by sustained self-fertilization.

Breeding system of a plesiomorphic floral type: an investigation of small flowered Streptocarpus (Gesneriaceae) species

Six different floral morphologies can be found among the ca. 146 species of Streptocarpus occurring in Africa and Madagascar. One of these, a simple, small pouch type, was found to be plesiomorphic for the genus after mapping these floral types onto a molecular phylogeny. The breeding systems and population structure of three species possessing the plesiomorphic small floral morphology, S. micranthus, S. ibityensis and S. lanatus, have been investigated using nuclear microsatellite markers. Significant deviations from panmixia were found both at the between and within population level (S. micranthus θ = 0.708, f = 0.786; S. ibityensis, θ = 0.173, f = 0.138; S. lanatus, θ=0.539, f = 0.646). As a florally diverse genus, Streptocarpus is unusual in having a predominantly selfing, mixed mating breeding system as a plesiomorphic condition.

Genetic diversity within and between remnant populations of the endangered calcareous grassland plant Globularia bisnagarica L.

Changes in agricultural production methods over the last century have caused a massive reduction and fragmentation of the area of European semi- natural grasslands. It remains unclear whether small and isolated grassland fragments can support viable plant populations in a sustainable way. In our study area in southern Belgium, the extent of calcareous grasslands was reduced from c. 650 ha in 1775 to less than 30 ha in 2004. We used AFLP markers to quantify the effects of present and historical grassland frag- mentation on the genetic structure of 27 populations of the rare perennial plant species Globularia bisnagarica. Given the mixed breeding system of the species and the relatively small area of the studied system, the populations were characterized by high genetic differ- entiation (Fst range: 0.42-0.48; Fst=0.53). A Mantel test revealed significant isolation by distance of the popu- lations. Average within population genetic diversity, measured as expected heterozygosity or gene diversity, was low (Hj=0.081) and was negatively related to population isolation. This suggests more gene flow into less isolated populations. Population size and local habitat characteristics did not significantly influence population genetic diversity. Both, high selfing rates in G. bisnagarica and a population genetic response to habitat fragmentation may explain our findings. Finally, a clear geographical clustering was observed, with cluster membership partially explainable by his- torical grassland connectivity. If populations indeed started to differentiate after fragmentation, this pro- cess was not (yet) strong enough to erase the genetic similarity between fragments that historically belonged to the same large grassland fragment.

Population Genetic Structure in Temperate and Tropical Species ofViola(Violaceae) with a Mixed Breeding System

Inter–simple sequence repeat (ISSR) molecular markers were used to characterize inter‐ and intrapopulation genetic diversity in populations of two contrasting species of Viola, Viola striata of the eastern United States and Canada and Viola grahamii of central Mexico. Both species show a mixed breeding system with the production of both chasmogamous and cleistogamous flowers, although the temporal pattern of flowering varies between the two species. In both species the majority of the seeds produced in a given season are the result of cleistogamous flowers; additionally, V. grahamii reproduces asexually by means of runners. Our results indicate similar high levels of genetic diversity, low levels of population subdivision, and weak interpopulation differentiation in both species. In particular V. grahamii showed a slightly higher level of genetic diversity than V. striata, which does not reproduce vegetatively. Modest chasmogamous reproduction is proposed to maintain levels of outcrossing sufficient to am...

Inter-simple sequence repeat (ISSR) variation in populations of the cutgrass Leersia hexandra

Genetic variability of a perennial clonal aquatic weed Leersia hexandra was estimated by the ISSR assay. A total of 225 L. hexandra individuals collected from 10 populations in China were analyzed. The 12 used ISSR primers generated 175 bands, with an average of 14.6 per primer. The average values of percentage of polymorphic bands (PPB), effective number of alleles ( A e), and gene diversity ( H e) in these populations were 49.7%, 1.258, and 0.154, respectively, indicating a considerable genetic diversity in this species. Significant genetic differentiation was found among populations with the major genetic variability within populations based on Nei's genetic diversity analysis ( G st = 0.417) and AMOVA (40.1%). Genetic variation is independent of geographical distance. This pattern of genetic variation may be associated with reproductive mode of its mixed breeding systems although mainly through vegetative propagation.

Hormonal induction of undescribed males resolves cryptic species of cladocerans

Cyclic parthenogens have a mixed breeding system with both meiotic and ameiotic eggs. Although investment in sexual stages is often synchronized with seasonal cycles, the degree of investment is a quantitative trait associated with habitat instability. Populations of cyclic parthenogens from stable environments, such as large lakes and oceans, generally show reduced or undetectable investment in males. Indeed, males of many species of lacustrine cyclic parthenogens are unknown to science. Methyl farnesoate (MF), a crustacean juvenile hormone, has been implicated as an inducer of male formation in Daphnia magna (Crustacea: Cladocera), a denizen of unstable habitats with marked sexual recruitment. Here, we show experimentally that MF induces male production in four distantly related lacustrine species of cladocerans under growth conditions unfavourable for male production. The males of three species are new to science. Unlike females, the anatomy of the previously unknown males of Bosmina (Lunobosmina) oriens permitted ready morphological diagnosis of sibling species and subfossils. The results suggest that the role for MF in the sex determination of cladocerans is general.

Microsatellite variation and structure of 28 populations of the common wetland plant, Lychnis flos‐cuculi L., in a fragmented landscape

Habitat fragmentation is known to cause genetic differentiation between small populations of rare species and decrease genetic variation within such populations. However, common species with recently fragmented populations have rarely been studied in this context. We investigated genetic variation and its relationship to population size and geographical isolation of populations of the common plant species, Lychnis flos-cuculi L., in fragmented fen grasslands. We analysed 467 plants from 28 L. flos-cuculi populations of different sizes (60 000-54 000 flowering individuals) in northeastern Switzerland using seven polymorphic microsatellite loci. Genetic differentiation between populations is small (F(ST) = 0.022; amova; P < 0.001), suggesting that gene flow among populations is still high or that habitat fragmentation is too recent to result in pronounced differentiation. Observed heterozygosity (H(O) = 0.44) significantly deviates from Hardy-Weinberg equilibrium, and within-population inbreeding coefficient F(IS) is high (0.30-0.59), indicating a mixed mating breeding system with substantial inbreeding in L. flos-cuculi. Gene diversity is the only measure of genetic variation which decreased with decreasing population size (R = 0.42; P < 0.05). While our results do not indicate pronounced effects of habitat fragmentation on genetic variation in the still common L. flos-cuculi, the lower gene diversity of smaller populations suggests that the species is not entirely unaffected.

Diversity and spatial structure of clones inVaccinium uliginosumpopulations

In Belgium, a total of three Vaccinium species with a shrub or dwarf shrub growth form can be found: Vaccinium myrtillus L., Vaccinium vitis-idaea L., and Vaccinium uliginosum L. Vaccinium uliginosum is the only one of these for which the extent of clonality is unknown. Therefore, the clonal structure of two V. uliginosum populations was inferred from random amplified polymorphic DNA (RAPD) markers. Among the 47 sampled patches, 61 clones were identified. The mean values of the number of clones divided by the number of samples (G/N), the Simpson's index (D), and the genotypic evenness (E) were 0.28, 0.95, and 0.96, respectively. Vaccinium uliginosum exhibited a typical phalanx growth strategy that resulted in structured populations at the ramet level, that is, ramets belonging to the same clone were closely associated and formed distinct clumps. However, at the clone level, populations were not structured, that is, genetic distances between pairs of clones were not correlated with the spatial distances between the clones within a population. Genetic diversity was as high as that in nonclonal species (mean value of Shannon's diversity index (Ho) = 0.647). In accord with the life history traits of V. uliginosum (long-lived species with a mixed breeding system and potentially high seed dispersal), most of the genetic variation was found within populations.Key words: genetic diversity, genetic structure, seedling recruitment, vegetative propagation, Ericaceae.

Polymorphism Maintenance in Populations with Mixed Random Mating and Apomixis Subjected to Stabilizing and Cyclical Selection

We analysed a diploid population model with a mixed breeding system that includes panmixia and apomixis. Each individual produces a part (ss) of its progeny by random mating, the remainder (1- ss) being a result of precise copying (vegetative reproduction or apomixis) of the parental genotype. Both constant and periodically varying selection regimes were considered. In the main model, the selected trait was controlled by two diallelic additive or semidominant loci,A /a and B/b, whereas the parameter of breeding system (ss) was genotype-independent. A numerical iteration of the evolutionary equations were used to evaluate the proportion (V) of population trajectories converging to internal (polymorphic) fixed points. The results were the following. (a) A complex pattern of dependence of polymorphism stability on interaction among the breeding system, recombination rate, and the genetic architecture of the selected trait emerged. (b) The recombination provided some advantage to sex at intermediate period lengths and strong-to-moderate selection intensities. (c) The complex limiting behavior (CLB) was quite compatible with sexual reproduction, at least within the framework of pure genetic (not including variations in population density) models of multilocus varying selection.