Publications

Abstract Premise Staminodes are commonly studied in hermaphroditic flowers, in which a fraction of the androecium evolves into infertile structures, but few studies have addressed the evolution of staminodes as they occur through the loss of stamen function in carpellate flowers. Plants of Paronychia (Caryophyllaceae) are monoecious with hermaphroditic flowers with one staminodial whorl, except for the dioecious P. chartacea and P. minima. Dioecious species have carpellate flowers that evolved an additional whorl of staminodes, providing an exceptional opportunity to study a second origin of staminodes in the same flower. Methods Using scanning electron microscopy, we observed the development of carpellate and staminate flowers to determine whether the developmental pathway of the staminodes in hermaphroditic flowers was co-opted during the evolutionary transition to unisexual flowers. Results In carpellate flowers, antesepalous staminodes initiate as sterile anthers that develop similar to functioning stamens, but arrest before full development, leaving a rudimentary anther with lateral lobes that correspond to thecae. After antesepalous staminodes arrest, alternisepalous staminodes initiate as structures that correspond with filaments, as they do in staminate and hermaphroditic flowers. Conclusions The second origin of staminodes in carpellate flowers evolved using a different developmental pathway than what had previously evolved in the alternisepalous whorl. The two androecial whorls in the same flowers are serialogous as members of the androecium, but are paralogous as staminodes on the basis of structural and developmental differences.

How do xerophytic species thrive in environments that experience extreme annual drought? Although critical to the survival of many species, the genetic responses to drought stress in many non-model organisms has yet to be explored. We investigated this question in Mentzelia section Bartonia (Loasaceae), which occurs throughout western North America, including arid lands. To better understand the genetic responses to drought stress among species that occur in different habitats, the gene expression levels of three species from Mentzelia were compared across a precipitation gradient. Two de novo reference transcriptomes were generated and annotated. Leaf and root tissues were collected from control and drought shocked plants and compared to one another for differential expression. A target-gene approach was also implemented to better understand how drought-related genes from model and crop species function in non-model systems.

Premise of research. Staminodes are infertile stamens that have evolved numerous times in angiosperms and exhibit a vast array of forms and functions. Variation in staminodes suggests that numerous evolutionary processes underlie their origins, but to understand how and why they evolved, comparative studies of groups of closely related species are needed. Identifying structures as staminodes, however, is not always straightforward and sometimes requires corroborating phylogenetic and developmental evidence. Staminodial structures in Paronychia (Caryophyllaceae), for example, vary in shape and size and have been referred to as both petals and staminodes, rendering their homology uncertain.Methodology. The evolution and development of staminodes were compared across species of Paronychia. We tested the hypotheses that structures were either petals or staminodes by evaluating the floral development of 14 species with scanning electron and light microscopy and conducted ancestral state estimations across phylogenies to infer when staminodes evolved.Pivotal results. Staminodes developed between the fertile androecial whorl and carpel, indicating an androecial origin. In eight species, staminodes developed similar to filaments of a fertile stamen in shape, length, and time, suggesting homology to them. In four species, staminodes are highly reduced through the heterochronic termination of development following initiation. In two species, broader staminodes, compared with filaments in the same flower, were interpreted as functional co-options. A vascular strand was not observed in any species examined, indicating that staminodes are vestigial before co-option. Staminodes evolved before the origin of Paronychia and were lost at least three times.Conclusions. Staminodes in Paronychia began as vestigial stamens following the loss of anthers and were highly reduced, remained vestigial, or were co-opted; we call this the vestigial intermediate hypothesis. Our results illustrate a dynamic history of staminodial evolution in Paronychia and that selection on the function of staminodes can differ across closely related species.

Adaptive radiation is an evolutionary process that has been promulgated in some clades as an explanation for species richness and disparity in morphological forms across ecological gradients. Studies designed to elucidate the mechanisms and causes of adaptive radiation have largely focused on animal systems, but plant clades have tremendous potential to answer elusive questions regarding adaptive radiations. The goals of this review are to (1) produce a synthetic understanding of adaptive radiations through studies that have investigated plants systems, (2) critically reflect on contemporary studies to highlight how approaches have been successful as well as limiting, and (3) outline gaps in our understanding of adaptive radiations while emphasizing that plants have ideal characteristics to answer future questions. Thirty-five adaptive radiation clades are highlighted, of which several are supported with multiple lines of evidence, such as the Hawaiian silverswords, Hawaiian lobeliads, and columbines. Plant adaptive radiation examples are commonly insular, diversified in the Miocene or Pliocene, are associated with dispersal-mediated ecological opportunities, are polyploids, and have experienced hybridization. From those studies, a general model of plant insular adaptive radiation is proposed. The limitations of the current reliance on phylogenetic comparative approaches to detect adaptive radiations are considered, and an integrative approach that includes phylogenetics, genomics, and evolutionary ecology is advocated. The review concludes with a call for additional studies that are needed before we are to fully understand adaptive radiations, and they include the following: (1) how do biological interactions influence adaptive radiations, (2) what role does environmental change play in generating ecological opportunity, (3) how does genetic evolution drive adaptive radiation, (4) do models adequately explain the adaptive radiation process, (5) what is the role of hybridization, and (6) why do some groups not undergo adaptive radiation after ecological opportunity?

Background: Mentzelia (Loasaceae) is a genus of approximately 95 species that are largely distributed in western North America; however, much ambiguity remains regarding species in Mexico.Questions: What species of Mentzelia occur in Mexico and how can they be distinguished?Study species: MentzeliaMethods: Fieldwork, herbarium studies and scanning electron microscopy were carried out to determine the diversity of Mentzelia species in Mexico.Results: Twenty-five species of Mentzelia occur in Mexico, of which four taxa are endemic to the country. Five of the six sections of Mentzelia occur in Mexico. Mentzelia section Mentzelia was the most species rich in Mexico (8 spp.), followed by section Trachyphytum (7 spp.), section Bartonia (6 spp.), section Bicuspidaria (3 spp.), and section Dendromentzelia (1 sp.). The sections have different distribution patterns, with some restricted to few areas and one widespread across most of Mexico.Conclusions: This study is the first treatment of Mentzelia that encompasses all species and regions of Mexico, which includes approximately 26 % of the worldwide Mentzelia species. In-depth studies of the species in the region are needed to abate gaps in our knowledge on the extent of species distributions and to clarify species boundaries among some problematic species complexes.