Hopping or Jumping on the Cliffs: The Unusual Phylogeographical and Demographic Structure of an Extremely Narrow Endemic Mediterranean Plant

Several past and recent climatic and geological events have greatly influenced the current distribution of coastal species around the Mediterranean Basin. As a consequence, the reconstruction of the distributional history of these species is challenging. In this study, we used both chloroplast and nuclear SNPs to assess the levels of genetic differentiation, contemporary/historical levels of gene flow, and demographic history for the three only known (one mainland and two insular) populations of Eokochia saxicola, a rare Mediterranean coastal rocky halophyte. Plastid genome analysis revealed very low intraspecific haplotype variation and partial admixture among Capri and Palinuro populations with at least two independent colonization events for the Strombolicchio islet. Nuclear SNPs variation consistently identified three distinct genetic clusters corresponding to our sampling localities. Furthermore, strong genetic isolation was confirmed by both historical and contemporary levels of migration among the three populations. The DIYABC analysis identified two introductions temporally separated from Palinuro to Capri (ca.25 Mya) and subsequently to Strombolicchio (ca.09 Mya) as the most likely hypothesis for the current distribution of E. saxicola. Regardless of their small population sizes, all study sites supported high-genetic diversity maintained by outcrossing and random mating between individuals owing largely to wind pollination, an exclusive trait among Mediterranean narrow endemics. In conclusion, the patterns observed confirm that some Mediterranean endemics are not necessarily “evolutionary dead-ends” but rather represent species that have extensive demographic stability and a strong evolutionary legacy.

Distance Dependent Contribution of Ants to Pollination but Not Defense in a Dioecious, Ambophilous Gymnosperm

Dioecious plants are obligate outcrossers with separate male and female individuals, which can result in decreased seed set with increasing distance between the sexes. Wind pollination is a common correlate of dioecy, yet combined wind and insect pollination (ambophily) could be advantageous in compensating for decreased pollen flow to isolated females. Dioecious, ambophilous gymnosperms Ephedra (Gnetales) secrete pollination drops (PDs) in female cones that capture airborne pollen and attract ants that feed on them. Plant sugary secretions commonly reward ants in exchange for indirect plant defense against herbivores, and more rarely for pollination. We conducted field experiments to investigate whether ants are pollinators and/or plant defenders of South American Ephedra triandra, and whether their contribution to seed set and seed cone protection varies with distance between female and male plants. We quantified pollen flow in the wind and assessed the effectiveness of ants as pollinators by investigating their relative contribution to seed set, and their visitation rate in female plants at increasing distance from the nearest male. Ants accounted for most insect visits to female cones of E. triandra, where they consumed PDs, and pollen load was larger on bigger ants without reduction in pollen viability. While wind pollination was the main contributor to seed set overall, the relative contribution of ants was distance dependent. Ant contribution to seed set was not significant at shorter distances, yet at the farthest distance from the nearest male (23 m), where 20 times less pollen reached females, ants enhanced seed set by 30% compared to plants depending solely on wind pollination. We found no evidence that ants contribute to plant defense by preventing seed cone damage. Our results suggest that, despite their short-range movements, ants can offset pollen limitation in isolated females of wind-pollinated plants with separate sexes. We propose that ants enhance plant reproductive success via targeted delivery of airborne pollen, through frequent contact with ovule tips while consuming PDs. Our study constitutes the first experimental quantification of distance-dependent contribution of ants to pollination and provides a working hypothesis for ambophily in other dioecious plants lacking pollinator reward in male plants.

Notes on the natural history of Stillingia aquatica (Euphorbiaceae): with special attention to reproductive biology

Stillingia aquatica, a wetland shrub in the Southeastern U.S., was profiled in Southeast Florida from a natural history standpoint. The stem has exceptionally lightweight wood in common with other periodically root-inundated woody plants. Pseudowhorled tufts of conspicuous yellow leaves subtend the similarly colored spikelike thyrsoid inflorescences. The plants are monoecious, self-compatible, protogynous with respect to inflorescences, and with a mixed mating system. After a pistillate-only phase, pistillate and staminate phases overlap in time, and are positioned in close physical proximity within inflorescences. Then follows a prolonged phase of only staminate flowers plus maturing fruits. The inflorescences attract ants, bees, and especially abundant wasps, switching from mixed bees and wasps in the dry season to essentially just wasps in the wet season. Wind-pollination is minimal to none. Ants are often abundant in the inflorescences and believed to contribute to geitonogamy but are not necessary for fruitset. Agamospermy is none to negligible. The seeds often fail, with the failure rates varying between populations and between individual plants.

Three options are better than two: compensatory nature of different pollination modes in Salix caprea L.

Mixed pollination systems have been reported for many angiosperms. Here, we report on a dioecious willow, Salix caprea L., which employs three pollination modes, namely pollination by wind, nocturnal moths, and diurnal bees. In four field populations of S. caprea in Germany, we addressed the following questions: (a) How are the pollination modes affected by local mate availability? (b) What is the contribution of each pollination mode to seed set? (c) How does flower opening time affect pollination? We compared seed set among seven pollination treatments (wind pollination, diurnal pollination, nocturnal pollination, natural pollination, apomictic reproduction, daytime/night-time artificial pollination). Pollen limitation was observed across populations. On the other hand, limitations in mate availability affected the pollination modes differently. Insect pollination outperformed wind pollination in situations where nearby males were few or all positioned in the same direction from the females. The contribution of nocturnal moths was lower than that of the other pollen vectors. However, moth pollination worked complementarily with bee pollination in compensating for the lack of wind pollination. Furthermore, we found that the onset of flower anthesis peaked at sunset, and that cold night temperatures had no negative effect on seed set or pollen viability. Thus, nocturnal anthesis and prior pollination by moths may minimize male fitness loss due to pollen collection and grooming by bees. We suggest that S. caprea maximizes its fitness by combining multiple pollination modes that work in different environmental conditions, while optimizing the anthesis so that more pollen would be delivered to stigmas.

Global wind patterns shape genetic differentiation, asymmetric gene flow, and genetic diversity in trees

Wind disperses the pollen and seeds of many plants, but little is known about whether and how it shapes large-scale landscape genetic patterns. We address this question by a synthesis and reanalysis of genetic data from more than 1,900 populations of 97 tree and shrub species around the world, using a newly developed framework for modeling long-term landscape connectivity by wind currents. We show that wind shapes three independent aspects of landscape genetics in plants with wind pollination or seed dispersal: populations linked by stronger winds are more genetically similar, populations linked by directionally imbalanced winds exhibit asymmetric gene flow ratios, and downwind populations have higher genetic diversity. For each of these distinct hypotheses, partial correlations between the respective wind and genetic metrics (controlling for distance and climate) are positive for a significant majority of wind-dispersed or wind-pollinated genetic data sets and increase significantly across functional groups expected to be increasingly influenced by wind. Together, these results indicate that the geography of both wind strength and wind direction play important roles in shaping large-scale genetic patterns across the world’s forests. These findings have implications for various aspects of basic plant ecology and evolution, as well as the response of biodiversity to future global change.

Diversity Patterns of Bermuda Grass along Latitudinal Gradients at Different Temperatures in Southeastern China

Cynodon dactylon (L.) Pers. (common Bermuda grass) has a limited capacity to grow at low temperatures, which limits its geographical range. Exploring its evolutionary relationship across different environmental gradients is necessary to understand the effects of temperature change on the genetics of common Bermuda grass. In this study, high-throughput transcriptome sequencing was performed on 137 samples of C. dactylon from 16 latitudinal gradients to explore the differential molecular markers and analyze genetic diversity and structure along latitudinal gradients at different temperatures. We primarily sampled more high-quality single nucleotide polymorphisms (SNPs) from populations at lower and middle latitudes. Greater intraspecific genetic variation at each level of temperature treatment could be due to factors such as wind pollination and asexual breeding. Populations of C. dactylon at high latitudes differed from populations at middle and low latitudes, which was supported by a principal component analysis (PCA) and genetic structure analysis, performed at different temperatures. We observed more genetic variation for low-latitude populations at 5 °C, according to an analysis of three phylogenetic trees at different temperature levels, suggesting that low temperatures affected samples with low cold resistance. Based on the results of phylogenetic analysis, we found that samples from high latitudes evolved earlier than most samples at low latitudes. The results provide a comprehensive understanding of the evolutionary phenomenon of landscape genetics, laying the groundwork for future structural and comparative genomic studies of C. dactylon.

Joint evolution of mycorrhizal type, pollination, and seed dispersal mode in trees

Mycorrhizal type, pollination, and seed dispersal mode are key drivers of tree diversity, but because they are usually studied in isolation, their evolutionary relationships are poorly understood. We investigated the evolutionary relationships among mycorrhizal type (arbuscular mycorrhizal [AM], ectomycorrhizal [EM], and AM + EM), seed dispersal mode (anemochorous, endozoochorous, and unspecialized), and pollination mode (biotic and wind) in 821 tree species. We found evidence of joint evolution of all three features. Most AM-associated trees had endozoochorous seed dispersal and biotic pollination, whereas most EM-associated trees had anemochorous seed dispersal and wind pollination. Overall, mycorrhizal type, seed dispersal mode, and pollination mode were linked, emphasizing the importance joint study of these traits for understand of tree diversity.

Facilitating candidate gene discovery in an emerging model plant lineage: Transcriptomic and genomic resources for Thalictrum (Ranunculaceae)

ABSTRACTThe plant genus Thalictrum is a representative of the order Ranunculales (a sister lineage to all other Eudicots) with diverse floral morphologies, encompassing four sexual systems and two pollination modes. Previous studies suggest multiple transitions from insect to wind pollination within this genus, in association with polyploidy and unisexual flowers, but the underlying genes remain unknown. We generated a draft reference genome for Thalictrum thalictroides, a representative of a clade with ancestral floral traits (diploidy, hermaphroditism, and insect pollination) and a model for functional studies. To facilitate candidate gene discovery in flowers with different sexual and pollination systems we also generated floral transcriptomes of T. thalictroides and of wind-pollinated, andromonoecious (staminate and hermaphroditic flowers on the same plant) T. hernandezii.The T. thalictroides draft genome assembly consisted of 44,860 contigs (N50=12,761 bp. and 243 Mbp. total length) and contained 84.5% conserved embryophyte single-copy genes. Floral transcriptomes from Illumina sequencing and de novo assembly contained representatives of most eukaryotic core genes (approximately 80%), with most of their genes falling into common orthologous groups (orthogroups). Simple Sequence Repeat (SSR) motifs were also identified, which together with the single-copy genes constitute a resource for population-level or phylogenetic studies. Finally, to validate the utility of these resources, putative candidate genes were identified for the different floral morphologies using stepwise dataset comparisons. In conclusion, we present genomic and transcriptomic resources for Thalictrum, including the first genome of T. thalictroides and potential candidate genes for flowers with distinct sexual and pollination systems.

Profitability of Artificial Pollination in ‘Manzanillo’ Olive Orchards

The fruit set in monovarietal ‘Manzanillo’ olive orchards is significantly increased under cross-pollination. This response lead to pollination designs including pollinizer selection, the number of pollinizer trees per hectare and their distribution in the orchard. However, the assignment of a substantial area to pollinizers of lesser commercial value might decrease profits. The strong influence of variable climates on the overlap of the blooming phenology of ‘Manzanillo’ and its pollinizer, and on pollen production and dispersal, are also notable risks. Artificial pollination is a feasible alternative to pollination designs, especially for wind-pollination crops such as olives. Here, we present the effects of treatments with different number (zero, one, two or four) of mechanical applications of ‘Barouni’ pollen on fruit set, size, yield, and cost–benefit ratios in heavy- and light-flowering trees of ‘Manzanillo’ trees situated in monovarietal orchards in Sonora, Mexico. Our results showed that, in “on” years (seasons where most trees display abundant flowering), a larger number of cross-pollen artificial applications increased more the final fruit set, yield and, hence, the profits. Fruit size was scarcely affected by the number of applications, although treatments with lower fruit sets had a higher proportion of large-sized fruit and less fruit of petite size. Despite its higher costs, the higher increase in yield made it more profitable to apply cross-pollination four times throughout the blooming period. On the other hand, no significant differences were observed among treatments, regardless of the number of pollinations, in the “off” season (the season in which most trees had a light flowering level).