Black and white video loop of an unusual, abstractly shaped flower of a cocoa plant turning on its own axis against a dark background.

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Cacao Pollination, The Sweet Science: A Study of Floral Morphology Using 3D Imaging

byZEISS Microscopy 6 November 2024 5 min read

Introduction

Investigating Cacao Trees and Tiny Pollinators to Protect the Future of Chocolate

Imagine enjoying a piece of chocolate: it melts on your tongue. A firework of serotonin goes off in your brain – provided you like this sweet treat. With a growing number of chocolate lovers worldwide, the global chocolate market size was estimated at $ 119.39 billion in 2023, with an expected compound annual growth rate (CAGR) of 4.1 % from 2024 to 2030.¹

Cocoa, the main ingredient in chocolate, is derived from the cacao tree, Theobroma cacao. The tree produces tiny flowers and only a few of these are successfully pollinated, probably by small insects. With insect pollinator populations in sharp decline globally due to an overdependence on pesticides, habitat loss, and the climate crisis, new strategies to increase and improve the pollination success of cacao trees are critical. Katherine Wolcott, a PhD candidate in the Department of Biology at the University of Miami, is actively researching this topic.

Close-up of a cacao pod growing from a tree branch, surrounded by small, delicate white and pink flowers. Lush green foliage in the blurred background. — Cacao plants' small, delicate flowers (less than 1 cm in diameter) with many curved structures.

Enhancing Comparative Morphology Studies: Overcoming Limitations With 3D Imaging

An important question that Katherine Wolcott wants to answer: which insects are small enough to reach the reproductive organs inside the flower and successfully pollinate the cacao plant? To find out, she is measuring the dimensions of the flowers. In this way, she hopes being able to draw conclusions about the functional size limitations of the pollinators. Put simply: which insects are small enough to get into the flower and therefore could be considered as possible pollinators?

Because the cacao plant's flowers have such small, intricate 3D structures that insect pollinators need to maneuver around, it is impossible to analyze them using conventional morphological methods such as calipers. However, using micro-computed tomography (micro-CT) and 3D surface modeling, Katherine Wolcott can accurately quantify the dimensions of cacao flowers and the functional size limits of potentially effective pollinators.
Acquired 3D datasets and measurements can be reused for further morphological studies of putative pollinators. Her research produces surface models and landmarks, which she can share directly with other scientists who wish to build on or replicate her work. In addition to comparative morphology, the research generates datasets to train a machine learning algorithm to accelerate future 3D morphology studies on flowering plants and other biological organisms.

Person picking a small flower with tweezers outdoors, surrounded by trees and sky. — Katherine Wolcott carefully collecting Byttneria flowers.

Discovering the World of Byttnerioideae with Phylogenetics and 3D Imaging

The laboratory studies the ecology and evolution of the Byttnerioideae, a subfamily of Malvaceae consisting mostly tropical and subtropical plants that includes the cacao plant. Its small- and bizarrely-flowered relatives include the endangered species of wild Colombian cacao (Herrania umbratica) and the Florida pine rockland endemic, the eyebright Ayenia (Ayenia euphrasiifiolia).

By combining phylogenetics, fieldwork, and 3D imaging, Katherine Wolcott and the lab team will be able to study key morphological and evolutionary features of these species and determine when, where and how they evolved. In doing so, they will not only find answers to questions about evolutionary history, but also information for future land management decisions to better conserve these unique plants.

In my PhD project, I am studying the three-dimensional flower morphology of six species of Byttnerioideae. They are growing in botanical collections throughout South Florida, so I can sample them any time they are flowering without even having to hop on a plane!

MSc. Katherine Wolcott PhD Candidate, Department of Biology, University of Miami

An Article about Advances in Plant Imaging across Scales

The article "3D pollination biology using micro-computed tomography and geometric morphometrics in Theobroma cacao" published in "Applications in Plant Sciences" is based on the first chapter of her dissertation. In it, Katherine Wolcott focuses extensively on the functional morphology of the best-studied representative of the Byttnerioideae: Theobroma cacao. She investigated the relationship between this morphology and the still poorly understood pollinators.

Using precise, high-resolution micro-CT imaging, the research team is able to quantify how small an insect must be to fit into the constricted petals of the cacao plant and reach its pollen. After developing a baseline of CT scanning protocols and analysis methods for cacao, the project will expand to study the morphology of cacao relatives with the ultimate goal of using machine learning to address some larger biodiversity questions using flowers and micro-CT.

Read the full article.

From Sea Spiders to Cacao Flowers: A Passion for 3D imaging

Katherine Wolcott has been, as she says, "in love" with 3D imaging technologies ever since she took her first CT scan of a sea spider (Pycnogonida) during her master’s program. She works with specimens from natural history museums, and being able to study the anatomy of tiny structures such as nerves, glands, and vasculature in situ in a non-invasive way is a dream come true for her.

Exploring Cacao Flowers: Pollen Access, Morphology, and Pollinator Compatibility

Detailed 3D render of a cacao flower with labeled parts: whole flower, petal side view, and petal bottom view. Pollen shown in yellow, petal side door marked in teal.. Katherine Wolcott — Katherine Wolcott

Cacao Flower's Pollen Access Mechanism

Cacao flower and petal with the petal side door (opening for pollen access, which were measured for the study) shown in teal and pollen shown in yellow. Note how the pollen is only visible when approaching the petal from below.

Diagram of a flower with measurements of petal dimensions and pollinator dimensions, including length, height, and width. Images of pollinators with annotated features are shown. — Katherine Wolcott

Morphology & Pollinator Dimensions

Cacao flower with surface landmarks used to compare floral morphology, petal side door dimensions, and putative pollinator dimensions. A ceratopogonid midge is shown to scale in the transparent white box.

Diagram showing putative pollinators ranked by likelihood, featuring Scatopsidae, Ceratopogonidae, Formicidae, and Sparasionidae in circular sections with a scale of 1 mm. — Katherine Wolcott

Ranking Cacao's Pollinators by Fit

Cacao’s putative pollinators are ranked if they fit in the petal side door in 3, 2, or < 2 dimensions from most likely to unlikely.

Transforming Cacao Farming? The Quest for Morphological Self-Compatibility Clues

The precise landmarking of her imaging results has raised a promising hypothesis that Katherine Wolcott is pursuing. She and the lab team may have found a morphological signature of self-compatibility.

Some cacao trees are self-compatible, meaning that they do not need to be outcrossed but are able to pollinate themselves. Other cacao trees are self-incompatible: they need to be outcrossed for successful pollination.

There are currently no reliable morphological or genetic markers to determine this. Farmers therefore have to wait until the plants are of reproductive age. Then, they try to see which of the cacao trees will bear fruit after self-pollination.

If we had a way to identify self-compatibility based on flower shape alone, it would be a huge step forward in cacao agriculture, one of the world’s most economically important crops.

Katherine Wolcott

Katherine Wolcott and her colleagues are now working out the details of the next field expedition. This will include a follow-up study of the findings on the morphological signature of self-compatibility in cacao.
In addition, Katherine Wolcott is working on the final part of her PhD project: She is applying machine learning to the micro-CT datasets she has generated over the past few years, with a noble goal: "Hopefully, the tools I develop will help drive the next generation of museum research efforts toward new discoveries about broad patterns of biodiversity", concludes Katherine Wolcott.

Website of Katherine Wolcott

LinkedIn profile of Katherine Wolcott

Instagram profile of Katherine Wolcott

X profile of Katherine Wolcott

About the Department of Biology at University of Miami

The University of Miami’s integrative Biology Department aims to foster work that transcends traditional disciplinary boundaries. To address biology’s most pressing questions with powerful approaches, scientists span scales of space, time, and complexity. Various interrelated programs focus on key biological issues and challenges facing humanity.

A variety of human stressors threaten biodiversity, including climate change, habitat fragmentation, invasive species, pollution, and changes in natural disturbance regimes. The Department’s Biodiversity and Global Change Biology Program examines how these human stressors affect biodiversity, seeks to understand their consequences and identifies strategies to address them.

3D imaging techniques, such as micro-CT, offer several advantages in the study of floral morphology. They allow for non-invasive visualization and analysis of intricate structures, enabling precise quantification of dimensions, detailed examination of complex shapes, and the generation of accurate 3D models for further analysis.
3D imaging techniques provide valuable insights into the pollination dynamics of cacao trees by revealing the intricate relationships between floral structures and potential pollinators. By accurately visualizing and measuring floral features, researchers can identify the functional size limits of effective pollinators and gain a deeper understanding of the complex mechanisms involved in cacao tree pollination.
3D imaging, combined with phylogenetics and fieldwork, allows researchers to explore the morphological and evolutionary characteristics of cacao trees and their relatives. By accurately capturing the three-dimensional structure of flowers, researchers can analyze and compare the morphology of different species, investigate evolutionary relationships, and gain insights into the origins, adaptations, and diversification of cacao trees and related plant species.
In English, "cacao" is usually shorthand to refer to the species, Theobroma cacao, along with the cacao pod (the fruit), cacao beans (the seeds), and a sweet, sticky pulp surrounding the seeds, which are harvested and then undergo a series of processes to transform them into cocoa and chocolate.
Cocoa and chocolate are the result of fermenting cacao beans and pulp (when the magic of different flavor profiles develops), then drying, roasting, and finely grinding them to separate cocoa solids from the cocoa butter. "Cocoa" usually refers to these solids, with little additional processing. "Chocolate" includes cocoa solids and cocoa butter, supplemented with oils, sugar, and often milk. Overall, cacao and cocoa are closely related but differ in terms of state and usage.

¹
https://www.grandviewresearch.com/industry-analysis/chocolate-market

¹
The images on this page are licensed under CC BY-NC-SA 4.0. The use of the images is permitted only for non-commercial purposes, and the author must be credited when used. Derivative works must be licensed under the same conditions.

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Download the E-Book

Cacao Pollination, The Sweet Science: A Study of Floral Morphology Using 3D Imaging

Investigating Cacao Trees and Tiny Pollinators to Protect the Future of Chocolate

Enhancing Comparative Morphology Studies: Overcoming Limitations With 3D Imaging

Discovering the World of Byttnerioideae with Phylogenetics and 3D Imaging

An Article about Advances in Plant Imaging across Scales

From Sea Spiders to Cacao Flowers: A Passion for 3D imaging

Exploring Cacao Flowers: Pollen Access, Morphology, and Pollinator Compatibility

Cacao Flower's Pollen Access Mechanism

Morphology & Pollinator Dimensions

Ranking Cacao's Pollinators by Fit

Transforming Cacao Farming? The Quest for Morphological Self-Compatibility Clues

About the Department of Biology at University of Miami

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