My research interests are in the ecology and evolution of plant reproductive systems and my research group focuses on features that promote outcrossing between individuals; namely, the evolution of separate (as opposed to combined) sexes and the evolution of physiological mechanisms that prevent self-fertilization in hermaphrodites. Such traits are important in controlling patterns of mating and affect the level of heterozygosity within individuals, the extent of genetic variation in populations, and the evolutionary potential of populations.

The lab is also interested in the inference and interpretation of phylogenetic histories, the impact of hybridization on plant speciation and reproductive strategies, and comparative studies of features that accompany transitions in sexual strategies, such as the evolution of floral sexual dimorphism or the temporal/spatial segregation of sexual function.  Finally, we are interested in the development of floral morphologies and the roles of phenotypic plasticity and plant architecture in molding reproductive phenotypes.

During my time at Amherst, my group has developed the plant genus Lycium as a useful natural system to study evolutionary transitions of reproductive traits.  Members of this genus vary both in the deployment of sexual function (i.e., some species and populations are hermaphroditic, whereas others have separate sexes), and in the presence of genetically controlled self-incompatibility systems.  This group is also interesting from a molecular systematic perspective given its cosmopolitan distribution, species richness, patterns of hybridization (coupled with variation in ploidy levels), and diverse reproductive systems.

Use the navigation bar (@ left) to link to publications from the lab.

Recent publications

Miller, JS, K Greenberg'2017, D Schneider'2020, RA Levin. 2021. Dimorphism, polyploidy, and genetic diversity in the Australian endemic Lycium australe (Solanaceae). International Journal of Plant Sciences. 182:356-376.

Whole-genome duplication is often associated with the evolution of dimorphic sexual systems; however, the association is not universal, and the evolutionary pathway(s) underlying the association remain unresolved. We report correlated variation in ploidy level, sexual system, and genetic structure in Lycium australe. Both gynodioecy and dioecy are documented and are associated with diploidy and polyploidy, respectively. Floral size dimorphism is also reported among morphs in both sexual systems. There is significant genetic structure associated with ploidy level and geography based on genome-wide SNPs and plastid haplotypes.

Levin, RA and JS Miller. 2021. Molecular signatures of long-distance oceanic dispersal and the colonization of Pacific islands in Lycium carolinianumAmerican Journal of Botany 108:694-710.

Long-distance dispersal has been key in explaining the present distributions of many plant species. Such dispersal events have important evolutionary consequences, as bottlenecks during colonization can result in reduced genetic diversity. We examine the phylogeographic history of Lycium carolinianum, a widespread species ranging from southeastern North America to several islands in the Pacific. Across its range, this species shows variation in sexual expression and mating systems, including self-compatibility in Hawaii. Genomic sequence data reveal that a single long-distance dispersal from North America to the Pacific islands via fleshy, bird-dispersed fruits best explains the unusually widespread distribution of this species. Lower genetic diversity in island versus mainland populations suggests that self-fertilization may have facilitated the subsequent colonization of several Pacific archipelagos.

Miller, JS, Blank, CM'2014, and RA Levin. 2019. Colonization, Baker's law, and the evolution of gynodioecy in Hawaii: implications from a study of Lycium carolinianum. American Journal of Botany 106:733-743.

As Baker first suggested, the successful colonization of oceanic islands is often associated with uniparental reproduction (self‐fertility).  However,  the high incidence of dimorphism (dioecy, gynodioecy) on islands complicates this idea. Lycium carolinianum has a widespread distribution, occurring on the North American mainland and the Hawaiian Islands. In this paper, we examine Baker's ideas for mainland and island populations of L. carolinianum and examined inbreeding depression as a possible contributor to the evolution of gynodioecy on Maui.

​Kamath, A'2011, RA Levin, and JS Miller. 2017. Floral size and shape evolution following the transition to gender dimorphism. American Journal of Botany 104:451-460.

The transition from cosexuality to separate sexes has occurred independently over a hundred times in angiosperms. When transitions take place in some but not all populations of a single species, they offer a unique opportunity to understand how selection through male and female function acts to shape floral morphology, while minimizing the confounding effects of phylogenetic history. 

We examine changes in flower size and shape following the transition from cosexuality to separate sexes in Lycium californicum (Solanaceae). While abiotic environmental gradients across the species’ range influence both overall flower size and shape, flower size dimorphism arises through selection for larger flowers in males but not smaller flowers in females. 

Miller, JS, A Kamath '2011, BC Husband, and RA Levin. 2016. Correlated polymorphism in cytotype and sexual system within a monophyletic species, Lycium californicumAnnals of Botany 117:307-317.

We document the perfect association of tetraploidy with gender dimorphism (or diploidy with cosexuality) across 36 populations spanning the geographic range of Lycium californicum.  Molecular sequence data strongly support the monophyly of Lycium californicum and that cosexuality and diploidy are ancestral traits.  Character mapping suggests that tetraploidy & separate sexes have arisen twice independently.

Levin, RA, EM Keyes '2012, and JS Miller. 2015. Evolutionary relationships, gynodioecy, and polyploidy in the Galápagos endemic Lycium minimum (Solanaceae)International Journal of Plant Sciences 176:197-210.

Lycium minimum is an endemic species native to the Galápagos Islands and the only species of Lycium occurring at the equator. We demonstrate the presence of male-sterility on two islands, which represents the first discovery of separate sexes in any South American Lycium.  The presence of pollen-sterile individuals is coincident with a reduction in flower size.  Though Lycium minimum is allied with both North and South American species, it has colonized the Galápagos from South America. 

Blank, CM'2014, RA Levin, and JS Miller. 2014. Intraspecific variation in gender strategies in Lycium (Solanaceae): Associations with ploidy and changes in floral form following the evolution of gender dimorphism. American Journal of Botany 101:2160-2168.

A study of a species with polymorphism in sexuality and ploidy reveals the convergent evolution of separate sexes in some diploid populations in Hawaii and in tetraploid populations in Mexico.  Changes in flower size and shape are reconstructed following transitions from hermaphroditism to separate sexes.

Research Awards

Faculty Research Award Program, Amherst College
2019; Restriction-site associated DNA sequencing (RADseq) in Lycium australe (Solanaceae)

National Science Foundation 0843364
2009-2018; RUI: Fine scale phylogenetic relationships in Lycieae (Solanaceae): A multilocus approach for understanding biogeography, polyploidy, and reproductive evolution.

Faculty Research Award Program, Amherst College
2009; Species-level evolutionary relationships in Old World Lycium (Solanaceae) using multiple nuclear COSII markers

National Science Foundation 0343735 
2004-08; RUI: Phylogenetic Relationships and Character Evolution in Lycieae (Solanaceae)

Faculty Research Award Program, Amherst College

2019; Restriction-site associated DNA sequencing (RADseq) in Lycium australe (Solanaceae)
2007; A tale of two continents: Long-distance dispersal of Lycium – an empirical test of Baker’s Law
2006; Phylogeography of southwestern US and Mexican Lycium californicum (Solanaceae)
2004; Too much of a good thing – redundancy and the evolution of separate sexes in Lycium (Solanaceae)

National Science Foundation 0343732
2004-09; Collaborative Research: Architectural Effects and the Analysis of Sexual Size Dimorphism