Maples

The native striped maple, Acer pensylvanicum, exhibits a rare sex determination system known as sexual plasticity in which individuals may change sex from year to year. We have been monitoring study populations in New Jersey since 2014. Populations are composed almost entirely of trees bearing either male or female flowers. With males outnumbering females by approximately 3 to 1.

Current projects

The underlying genetics of sexual plasticity

What are the genetic underpinings of environmental sex determination?

With the support of the National Science Foundation, we are investigating the transcriptomics of flexible sex expression between sexes and tissues and over time. We are also putting this in the context of larger sexual systems, using the reproductively diverse maple clade.

NSF: 2217891

Sexual plasticity - origin and development

How does sexual plasticity evolve in a population and how is it maintained?

In collaboration with Juan Bonachela of Rutgers, we are using multi-year field data to develop models that explore the development and persistence of sexual plasticity in the striped maple system.

Rare hermaphrodites

What role do trees exhibiting both sexes play in the plastic mating system?

An ongoing question in biology involves the evolution of separate sexes. In plants separate sexes have evolved many times, probably through many pathways. Using multiple years of field data, we are exploring the reproductive trajectory of the rare individuals expressing both sexes. We are curious to see whether this is an intermediate stage between separate sexes. We also seek to understand the ecological and physiological correlates of this rare phenotype.

Sex differences

What sex differences exist between males and females?

While sex differences are common and frequently obvious in animals, sex differences in plants are less well-understood. Often, because sexes may segregate and occupy different ecological niches it can be hard to disentangle habitat differences from sex differences.

Using this species we are examining differences in physiology between male-expressing and female-expressing individuals. We are particiularly interested in differences in phenology, photosynthetics functioning, stress, and nutrient acquisition.

Previous projects

Non-structural carbohydrates

The internal resource status of a tree (represented by concentrates of non-structural sugars) correlates with sex switching behavior. This is the only study at this time on the effect of carbohydrates on plastic sex expression.

Blake-Mahmud and Struwe 2020

Special Issue in American Journal of Botany

The influence of damage

Unlike what we see in most sexually plastic species, decreased health correlates with femaleness in striped maple. Moreover, manipulative studies show that extreme damage can cue female flowering.

Blake-Mahmud and Struwe 2020

Special Issue in American Journal of Botany

Patterns in sex expression

We investigated the patterns in sex expression over consecutive years in multiple populations. Using a machine learning technique we found that, while a tree's sex the previous year is the best predictor of its sex in the current year, other factors are important, including size and health of the tree.

Blake-Mahmud and Struwe 2019

Annals of Botany

Bud development

In combined field and greenhouse studies, we investigated the timing of floral development in striped maple buds. Unlike the long development of buds in most tree species, striped maple may switch the sex expression of its flowers within three weeks of flowering. This is unheard of in woody plants and opens the door for more investigations of floral morphology

Blake-Mahmud and Struwe 2018

Trees: Structure and Function

DOI: 10.1007/s00468-018-1655-6

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