American Journal of Botany最新文献

Premise: Flowers that present their anthers and stigma in close proximity can achieve precise animal-mediated pollen transfer, but risk self-pollination. One evolutionary solution is reciprocal herkogamy. Reciprocity of anther and style positions among different plants (i.e., a genetic dimorphism) is common in distylous plants, but very rare in enantiostylous plants. We investigated the pollination and reproductive system of the enantiostylous Caribbean plant Cubanicula xanthorrhizos (Haemodoraceae).

Methods: We assessed stylar orientation of flowers and conducted controlled pollination experiments. We used videography of flower visitors and pollen load analysis to determine the pollination mechanism. We also measured floral morphology, pollen production, spectral reflectance, and volatile emissions.

Results: Cubanicula xanthorrhizos exhibits dimorphic enantiostyly with c. 50:50 left- to right-styled morphs. Plants are self-compatible, but pollinator dependent for seed production. Intra- and intermorph crosses are equally fertile. The nectarless flowers are pollinated by female carpenter bees (Xylocopa cubaecola) that collect pollen, often by sonication, from two centrally positioned yellow feeding anthers. An inconspicuous deflected pollinating anther deposits pollen on the side of the bee thorax, which contacts the stigma of the mirror-image morph. A yellow-orange "guide" on the white tepals appears to be a visual attractant. Flowers emit methoxy benzenoid volatiles that may also attract bees.

Conclusions: Reciprocity of the style with a single pollinating stamen in C. xanthorrhizos appears to promote intermorph pollen export via "safe sites" on pollen-collecting bees. This novel case of dimorphic enantiostyly contributes to understanding of the evolution of floral polymorphisms.

Premise: Extreme events are an understudied aspect of ongoing anthropogenic climate change that could play a disproportionate role in the threat that rapid environmental shifts pose to natural populations.

Methods: We exposed plants originating from seeds that were harvested before (ancestors) and after (descendants) multiple extreme heat events from six populations across the range of Mimulus cardinalis (Phyrmaceae) to a short-term heat-wave treatment in controlled growth chamber environments. We assessed physiological, performance, and functional responses (stomatal conductance, leaf temperature deficit, photosystem II efficiency, relative growth rate, specific leaf area, and leaf dry matter content) to the heat-wave treatment, along with evolutionary responses (differences between ancestors and descendants) of M. cardinalis populations to the recent natural extreme heat event.

Results: Plants in the heat-wave treatment increased their overall performance, and the magnitude of increase was generally greatest among trailing-edge populations. Despite limited overall trait differences between ancestors and descendants, there was some evidence of divergent evolutionary responses among regions to the natural extreme heat event. However, we did not find evidence of adaptive evolution that affected how M. cardinalis populations responded to the heat-wave treatment.

Conclusions: These results demonstrate that many M. cardinalis populations may reside in environments that are below their optimum average temperature, revealing potential resiliency to future warming. However, limited evolutionary responses in M. cardinalis to the recent extreme heat wave could still indicate potential for future vulnerability to extreme climate events of increased intensity, frequency, and duration.

Premise: Understanding how plant populations adapt to water limitation through stomatal traits is key to predicting drought responses. The dominant C₄ grass Andropogon gerardi, distributed across sharp climate gradients in North America, offers an excellent focal species to study stomatal architecture (size and density). Using a common garden, we tested how stomatal architecture relates to home climate, how stomatal architecture influences gas exchange, and how experimental drought affects these responses in a greenhouse. We hypothesized that aridity drives stomatal architecture and that experimental drought reduces the size of stomata but increases their density to maintain photosynthesis.

Methods: We measured stomatal architecture and gas exchange in 25 populations sourced across temperature (4-21°C) and precipitation (350-1400 mm yr⁻¹) gradients under well-watered conditions. Eight populations (precipitation: 472-1356 mm yr⁻¹) were then subjected to drought (~15% moisture) or were well-watered (30% control) to assess trait plasticity. Stomatal traits were measured using epidermal peels and light microscopy, gas exchange with a LI-COR 6400, and network analyses were used to characterize adaptive strategies.

Results: Arid populations exhibited smaller, denser stomata compared to wet populations, and networks demonstrated a trade-off between stomatal size and density. In the experimental drought, stomatal size decreased. while density increased, with dry populations showing fewer changes than wet populations. Key traits in the network were stomatal size and water-use efficiency.

Conclusions: Andropogon gerardi demonstrated adaptive changes in stomatal architecture. Our findings emphasize the interplay between adaptation and climate, providing important insights into how plants may respond to increased droughts.

Premise: Hybridization is an important evolutionary process across all groups of embryophyte land plants, but relatively little is known about hybridization and introgression in plants with a dominant gametophyte life cycle stage. This paper focuses on hybridization between four closely related species of the moss genus Sphagnum.

Methods: Analyses utilized three types of molecular data: restriction-site-associated DNA sequencing (RADseq), RADseq-like data derived from in silico digestion of genome sequences, and species-specific barcode markers developed previously for this group. Sampling included 582 gametophytes from 79 collecting sites from 27° to 56°N. A range of analytical methods were employed: phylogeny reconstruction, genetic analyses using the program structure, demographic modeling, and comparative genomics.

Results: Gene flow was detected among all pairwise combinations of extant species and between ancestral lineages and those species. Hybridization between S. diabolicum and S. magniae was especially pronounced and plants in a regional zone from North Carolina to New Jersey were genetically admixed. Demographic analyses indicated that this admixture reflects hybridization. Introgressed SNPs were detected across all chromosomes, but introgressed SNPs fixed in genetically pure samples of the two species were concentrated on four autosomes: 2, 7, 14, and 19. Patterns of genomic admixture/introgression were significantly correlated with climate variation across collection sites within the hybrid zone.

Conclusions: The genomic structure of plants in a regional hybrid zone between S. magniae and S. diabolicum was structured by climate adaptation and strengthens the value of this group for learning more about speciation and climate adaptation.