Kyle G. Dexter

Sabal minor (Arecaceae): a New Northern Record of Palms in Eastern North America

Abstract We report a new Sabal minor county record for North Carolina that represents the furthest known northern population of the largely tropical family Arecaceae in eastern North America. We give a brief introduction to Sabal and explain why this S. minor population may represent a northward range expansion in response to climate warming in northeast North Carolina. Finally, we discuss the usefulness of both historical herbarium specimens and modern day botanical collections to research on climate change and plant population responses.

Radseq dataset with 90% missing data fully resolves recent radiation of Petalidium (Acanthaceae) in the ultra-arid deserts of Namibia

Abstract Deserts, even those at tropical latitudes, often have strikingly low levels of plant diversity, particularly within genera. One remarkable exception to this pattern is the genus Petalidium (Acanthaceae), in which 37 of 40 named species occupy one of the driest environments on Earth, the Namib Desert of Namibia and neighboring Angola. To contribute to understanding this enigmatic diversity, we generated RADseq data for 47 accessions of Petalidium representing 22 species. We explored the impacts of 18 different combinations of assembly parameters in de novo assembly of the data across nine levels of missing data plus a best practice assembly using a reference Acanthaceae genome for a total of 171 sequence datasets assembled. RADseq data assembled at several thresholds of missing data, including 90% missing data, yielded phylogenetic hypotheses of Petalidium that were confidently and nearly fully resolved, which is notable given that divergence time analyses suggest a crown age for African species of 3.6–1.4 Ma. De novo assembly of our data yielded the most strongly supported and well‐resolved topologies; in contrast, reference‐based assembly performed poorly, perhaps due in part to moderate phylogenetic divergence between the reference genome, Ruellia speciosa, and the ingroup. Overall, we found that Petalidium, despite the harshness of the environment in which species occur, shows a net diversification rate (0.8–2.1 species per my) on par with those of diverse genera in tropical, Mediterranean, and alpine environments.

The environmental triangle of the Cerrado Domain: Ecological factors driving shifts in tree species composition between forests and savannas

3. We used a dataset of 1,165 tree species inventories spread across the Cerrado Domain, which 22 come from six vegetation types that have a substantial arboreal component: woody savannas, 23 dystrophic cerradão, mesotrophic cerradão, seasonally dry tropical forests, semideciduous 24 forests and evergreen forests. We found three extremes in terms of tree species composition, 25 with clear underlying ecological drivers, which leads us to propose a ternary model, the 26 ‘Cerrado Vegetation Triangle’, to characterize woody vegetation in the Cerrado. At one 27 extreme, we found that semideciduous and evergreen forests are indistinguishable floristically 28 and are found in areas with high water availability. At another extreme lie seasonally dry 29 tropical forests which are found on more fertile soils. At the third extreme, we found that all 30 types of savanna, and dystrophic cerradão, are highly similar in tree species composition and 31 are commonly found in areas of poor soils and high flammability. Mesotrophic cerradão is 32 transitional in tree species composition between savannas and seasonally dry tropical forest. 33

Taxonomic Novelties in Namibian Ruellia (Acanthaceae)

Abstract n Recent fieldwork in Namibia has led to the discovery of two undescribed species of Ruellia, Ruellia acetabula and Ruellia kaokoana . These taxa are described and illustrated. Additionally, new lectotypifications are proposed for Ruellia marlothii and Ruellia diversifolia. Some specimens previously identified as Ruellia diversifolia are ascribed to the two new species. A revised checklist and a key to distinguish the nine species of Ruellia native to Namibia plus the Angolan R. diversifolia are provided.

Plant DNA barcodes and assessment of phylogenetic community structure of a tropical mixed dipterocarp forest in Brunei Darussalam (Borneo)

DNA barcoding is a fast and reliable tool to assess and monitor biodiversity and, via community phylogenetics, to investigate ecological and evolutionary processes that may be responsible for the community structure of forests. In this study, DNA barcodes for the two widely used plastid coding regions rbcL and matK are used to contribute to identification of morphologically undetermined individuals, as well as to investigate phylogenetic structure of tree communities in 70 subplots (10 × 10m) of a 25-ha forest-dynamics plot in Brunei (Borneo, Southeast Asia). The combined matrix (rbcL + matK) comprised 555 haplotypes (from ≥154 genera, 68 families and 25 orders sensu APG, Angiosperm Phylogeny Group, 2016), making a substantial contribution to tree barcode sequences from Southeast Asia. Barcode sequences were used to reconstruct phylogenetic relationships using maximum likelihood, both with and without constraining the topology of taxonomic orders to match that proposed by the Angiosperm Phylogeny Group. A third phylogenetic tree was reconstructed using the program Phylomatic to investigate the influence of phylogenetic resolution on results. Detection of non-random patterns of community assembly was determined by net relatedness index (NRI) and nearest taxon index (NTI). In most cases, community assembly was either random or phylogenetically clustered, which likely indicates the importance to community structure of habitat filtering based on phylogenetically correlated traits in determining community structure. Different phylogenetic trees gave similar overall results, but the Phylomatic tree produced greater variation across plots for NRI and NTI values, presumably due to noise introduced by using an unresolved phylogenetic tree. Our results suggest that using a DNA barcode tree has benefits over the traditionally used Phylomatic approach by increasing precision and accuracy and allowing the incorporation of taxonomically unidentified individuals into analyses.

The long-term ecology and evolution of marine reptiles in a Jurassic seaway

Marine reptiles flourished in the Mesozoic oceans, filling ecological roles today dominated by crocodylians, large fish, sharks and cetaceans. Many groups of these reptiles coexisted for over 50u2009million years (Myr), through major environmental changes. However, little is known about how the structure of their ecosystems or their ecologies changed over millions of years. We use the most common marine reptile fossils—teeth—to establish a quantitative system that assigns species to dietary guilds and then track the evolution of these guilds over the roughly 18-million-year history of a single seaway, the Jurassic Sub-Boreal Seaway of the United Kingdom. Groups did not significantly overlap in guild space, indicating that dietary niche partitioning enabled many species to live together. Although a highly diverse fauna was present throughout the history of the seaway, fish and squid eaters with piercing teeth declined over time while hard-object and large-prey specialists diversified, in concert with rising sea levels. High niche partitioning and spatial variation in dietary ecology related to sea depth also characterize modern marine tetrapod faunas, indicating a conserved ecological structure of the world’s oceans that has persisted for over 150u2009Myr.The teeth of Mesozoic marine reptiles are used to establish a dietary guild system for the species of the Jurassic Sub-Boreal Seaway over about 18 million years, revealing that niche partition and spatial distribution that varied following sea depth enabled species coexistence, as with marine faunas today.

Tracking of Host Defenses and Phylogeny During the Radiation of Neotropical Inga-Feeding Sawflies (Hymenoptera; Argidae)

Coevolutionary theory has long predicted that the arms race between plants and herbivores is a major driver of host selection and diversification. At a local scale, plant defenses contribute significantly to the structure of herbivore assemblages and the high alpha diversity of plants in tropical rain forests. However, the general importance of plant defenses in host associations and divergence at regional scales remains unclear. Here, we examine the role of plant defensive traits and phylogeny in the evolution of host range and species divergence in leaf-feeding sawflies of the family Argidae associated with Neotropical trees in the genus Inga throughout the Amazon, the Guiana Shield and Panama. Our analyses show that the phylogenies of both the sawfly herbivores and their Inga hosts are congruent, and that sawflies radiated at approximately the same time, or more recently than their Inga hosts. Analyses controlling for phylogenetic effects show that the evolution of host use in the sawflies associated with Inga is better correlated with Inga chemistry than with Inga phylogeny, suggesting a pattern of delayed host tracking closely tied to host chemistry. Finally, phylogenetic analyses show that sister species of Inga-sawflies are dispersed across the Neotropics, suggesting a role for allopatric divergence and vicariance in Inga diversification. These results are consistent with the idea that host defensive traits play a key role not only in structuring the herbivore assemblages at a single site, but also in the processes shaping host association and species divergence at a regional scale.

Inserting Tropical Dry Forests Into the Discussion on Biome Transitions in the Tropics

Tropical moist forests and savannas are iconic biomes. There is, however, a third principal biome in the lowland tropics that is less well known: tropical dry forest. Discussions on responses of vegetation in the tropics to climate and land-use change often focus on shifts between forests and savannas, but ignore dry forests. Tropical dry forests are distinct from moist forests in their seasonal drought stress and consequent deciduousness and differ from savannas in rarely experiencing fire. These factors lead tropical dry forests to have unique ecosystem function. Here, we discuss the underlying environmental drivers of transitions among tropical dry forests, moist forests and savannas, and demonstrate how incorporating tropical dry forests into our understanding of tropical biome transitions is critical to understanding the future of tropical vegetation under global environmental change.