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.

Morpho-anatomical affinities and evolutionary relationships of three paleoendemic podocarp genera based on seed cone traits

Background and Aims The three relict genera Pherosphaera, Microcachrys and Saxegothaea in Podocarpaceae produce quite distinct seed cone types in comparison to other genera and does not form a clade along with Acmopyle. The detailed seed cone morpho-anatomy of these three relict genera and affinities with other podocarps are poorly known. This study aims to understand the seed cone morpho-anatomy and affinities among these three disjunct relict genera and with other podocarps. Methods We comparatively analysed the seed cone morpho-anatomical traits of the three podocarps genera and used ancestral state reconstruction to understand the evolution of these traits. Key Results We described the seed cone morpho-anatomical structures of the three relict genera in detail. The three genera produce aggregated multiovulate cones. Both Microcachrys and Saxegothaea has an asymmetrical free cup-like epimatium. Both species of Pherosphaera lack epimatium. The ancestral state reconstruction implies that the presence of epimatium is an ancestral trait in podocarps and independently lost in Pherosphaera and Phyllocladus. The seed cones are fleshy in Microcachrys and non-fleshy in Saxegothaea and Pherosphaera. The seed cone macrofossils of both extinct and living podocarps also show the presence of epimatium and fleshiness in podocarps. Conclusions Altogether, the morpho-anatomy suggests Pherosphaera, Microcachrys and Saxegothaea present affinities with each other and other podocarps but the reconstruction of ancestral seed cone in Podcarpaceae is quite complex due to multiple convergent evolutions of several structures. These structures (e.g. epimatium, aril, receptaculum) are of low taxonomic value but of great evolutionary and ecologically significance and are responsive adaptations to ever-changing environmental conditions.

Ancient diversity and turnover of cunninghamioid conifers (Cupressaceae): two new genera from the Upper Cretaceous of Hokkaido, Japan

Conifers of the taxodiaceous grade of Cupressaceae were more diverse and widespread during the Mesozoic than they are today. The earliest diverging subfamily, Cunninghamioideae, only includes a single extant genus, but has at least 10 fossil genera. Here, two additional cunninghamioid genera are characterized on the basis of permineralized seed cones from the Upper Cretaceous of Hokkaido, Japan. These conifers display seed cone characters typical of cunninghamioids; however, they have a mosaic of characters that are not seen in any reported conifer of Cupressaceae. They are, therefore, designated as two new extinct species: Ohanastrobus hokkaidoensis gen. et sp. nov. and Nishidastrobus japonicum gen. et sp. nov. These newly reported conifers expand the taxonomic and morphological diversity of cunninghamioids. The stratigraphic and paleobiogeographic records of cunninghamioids and other fossil Cupressaceae with foliate seed cones indicate they peak in diversity during the Cretaceous. The living genera Taiwania and Cunninghamia appear during the Albian and Campanian, respectively, and maintain a nearly continuous fossil record through to today, while nearly all other extinct genera of Cupressaceae with foliate cones disappear by the close of the Campanian. As more ancient cunninghamioids are recovered, our understanding of macroevolutionary patterns of this once diverse lineage will be further elucidated.

Colourful cones: how did flower colour first evolve?

Angiosperms that are biotically pollinated typically produce flowers with bright and contrasting colours that help to attract pollinators and hence contribute to the reproductive success of the species. This colourful array contrasts with the much less multicoloured reproductive structures of the four living gymnosperm lineages, which are mostly wind pollinated, though cycads and Gnetales are predominantly pollinated by insects that feed on surface fluids from the pollination drops. This review examines the possible evolutionary pathways and cryptic clues for flower colour in both living and fossil seed plants. It investigates how the ancestral flowering plants could have overcome the inevitable trade-off that exists between attracting pollinators and minimizing herbivory, and explores the possible evolutionary and biological inferences from the colours that occur in some living gymnosperms. The red colours present in the seed-cone bracts of some living conifers result from accumulation of anthocyanin pigments; their likely primary function is to help protect the growing plant tissues under particular environmental conditions. Thus, the visual cue provided by colour in flower petals could have first evolved as a secondary effect, probably post-dating the evolution of bee colour vision but occurring before the subsequent functional accumulation of a range of different flower pigments.

Fossil evidence reveals how plants responded to cooling during the Cretaceous-Paleogene transition

Background Around the Cretaceous-Paleogene (K-Pg) boundary, an obvious global cooling occurred, which resulted in dramatic changes in terrestrial ecosystems and the evolutionary trends of numerous organisms. However, how plant lineages responded to the cooling has remained unknown until now. Between ca. 70–60 Ma Mesocyparis McIver & Basinger (Cupressaceae), an extinct conifer genus, was distributed from eastern Asia to western North America and provides an excellent opportunity to solve this riddle. Results Here we report a new species, Mesocyparis sinica from the early Paleocene of Jiayin, Heilongjiang, northeastern China. By integrating lines of evidence from phylogeny and comparative morphology of Mesocyparis, we found that during ca.70–60 Ma, the size of seed cone of Mesocyparis more than doubled, probably driven by the cooling during the K-Pg transition, which might be an effective adaptation for seed dispersal by animals. More importantly, we discovered that the northern limit of this genus, as well as those of two other arboreal taxa Metasequoia Miki ex Hu et Cheng (gymnosperm) and Nordenskioldia Heer (angiosperm), migrated ca.4–5° southward in paleolatitude during this time interval. Conclusions Our results suggest that the cooling during the K-Pg transition may have been responsible for the increase in size of the seed cone of Mesocyparis and have driven the migration of plants southwards.

A morphometric analysis of Tobleria bicuspis, a Voltziales seed cone from the early Permian Jambi palaeoflora, Sumatra (Indonesia)

Tobleriabicuspis, a coniferophyte seed cone, is described from the Jambi Palaeoflora, Sumatra of Asselian (early Permian) age. A morphometric analysis based on cones, paired fertile units, and fertile and sterile scales, demonstrates their close relationship. Small paired fertile units occur mainly in cones. Medium-sized paired fertile units occur mainly on scales. And large paired fertile units are mainly dispersed. The cones are considered female and the paired fertile units are considered to represent the seeds. The cones are composed of helicoidal, bilaterally symmetrical and deeply incised scales with paired seeds. A comparison can be made with the Voltziales female taxon Schizolepis from the Triassic and Jurassic. Tobleria is regarded as having a voltzian Voltziales affinity and dates from approximately 16 to 26 million years before any other such cones.