NSF-DEB Bridging Ecology & Evolution (BEE):
Ecological and evolutionary processes affecting the co-existence of close relatives
Study system: North American Lobelia (Campanulaceae)
Fabulous Co-PIs: Chris Blackwood, Lynda Delph, Nico Cellinese & Grant Godden A key factor affecting biodiversity is the number of species that can live in the same place at the same time. However, not all species can co-exist and the rules regulating co-existence are not completely understood. This project investigates the co-occurence of closely related wildflower species in habitats throughout eastern North America. Closely related species are likely to have similar traits and similar ecological needs. On one hand, similarities may result in close relatives being more likely to live in the same environments. On the other hand, similarities may cause close relatives to compete or interfere with one another during growth and reproduction, making it difficult for close relatives to co-occur in the long term. |
This research will improve our understanding of how ecological and evolutionary processes affect co-existence and biodiversity. We will sample from multiple populations of 24 wildflower species in Lobelia sect. Lobelia (Campanulaceae) across their ranges in eastern North America to document where they live and how often they co-occur (see figure above). The study will determine how present-day patterns of co-occurrence are affected by ecological and evolutionary processes, such as degree of relatedness, trait similarity, habitat characteristics, or historical migration. Investigations will include determination of species relationships via phylogenomics, key components of each species’ niche via microsite and trait characterization, and the degree to which species interfere with one another’s growth or reproduction. Whether interference affects their likelihood of co-existing will be determined using field measurements of reproductive traits, experimental crosses, and transplant experiments.
Causes of variation in population sex ratio
NSF-DEB Evolutionary Processes (EP):
Understanding the causes of geographic variation in sex ratio of a gynodioecious plant (funded from 2009–2014 and still going!) Fabulous Co-PIs: Chris Caruso, Maia Bailey Variation in population sex ratio provides an excellent model for investigating the mechanisms of population differentiation because it is tightly linked to reproductive fitness and has clear consequences for patterns of genetic variation within populations. We investigated the evolutionary causes and consequences of variation in. population sex ratio in the sexually dimorphic wildflower, Lobelia siphilitica (Campanulaceae). L. siphilitica is gynodioecious, a relatively rare breeding system in which hermaphrodites and females co-exist within populations. L. siphilitica exhibits substantial variation in the frequency of female plants among populations (see figure to the right). Population sex ratios are also strongly geographically structured in this species, which we are still working to explain! However, our results indicate that population sex-ratio variation in this species reflects selective processes rather than stochastic ones (Madson 2012), that selection may act via variation in male rather than female fitness (Caruso & Case 2007, 2013; Case & Caruso 2010; Caruso et al. 2012), and high-female populations contain rare male-sterility genes (Adhikari et al. 2019)! |
Distribution and population sex ratios for 93 populations of L. siphilitica. Grey shading shows county-level presence data based on collection records. Pie charts show the proportion of plants in each population that are female (red) or hermaphrodite (black). All populations were censused in 2009 & 2011 (Madson, M.Sc. thesis, Kent State University, 2012)
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This grant has resulted in 10 publications to date. The grant and resulting data have supported 3 Masters theses, 2 dissertation projects, and engaged 22 undergraduate students in research!
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Evolutionary dynamics of mitochondrial male sterility in flowering plants
Fabulous Collaborators: Lila Fishman, Findley Finseth, Jeff Mower, John Willis
In eukaryotes, organellar genomes are typically uniparentally inherited, creating opportunity for intergenomic conflict with biparentally inherited nuclear genomes, despite the need for cooperation between these genomic components. For example, from the perspective of a maternally inherited mitochondrial genome, males are essentially expendable, and mutations that increase female but decrease male fertility spread readily within populations. This 'selfish' organellar evolution manifests in plants as mitochondrial male sterility (a.k.a. CMS), where carriers of expressed CMS genes are phenotypically female. Nuclear alleles have evolved to counteract CMS genes, restoring male function (and a hermaphroditic phenotype) to their carriers, but much is still unknown about the origins, dynamics and evolutionary consequences of this cyto-nuclear conflict over male fertility. It has potentially far-reaching consequences for organismal and genomic diversity, and may have profound effects on individual fitness, population differentiation, and even speciation. Our work on this has focused on populations of yellow monkeyflower (still affectionately called Mimulus guttatus, Phrymaceae) that carry CMS genes but also nuclear male-fertility restorers (Rf). Carrying both sets of genes means that populations in nature contain only hermaphrodite phenotypes, and female phenotypes are only seen in hybrid crosses between M. guttatus and close relatives (like M.nasutus; see figure to left) that do not carry the appropriate nuclear Rf. |