CAM Evolution in Succulents
ISEF Category: Plant Sciences
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Subcategory: Systematics and Evolution · Difficulty: Advanced · Setup: University Lab · Time: Full Year
The Hook
Some plants survive drought by changing when they open their gas exchange doors. That trick, CAM photosynthesis, can leave a genetic trail in their DNA. You can trace that trail across succulent families and ask when the trait appeared, and how many times it evolved. This turns plant evolution into a data puzzle you can actually solve.
What Is It?
CAM photosynthesis is a water-saving strategy. Most plants take in carbon dioxide during the day, but CAM plants often open their stomata, the tiny leaf pores, at night. That helps them lose less water in hot, dry places. Think of it like doing your grocery shopping after dark to avoid the heat.
Your project asks a bigger question, how did this strategy evolve across different succulent groups? You can compare DNA sequences from a gene linked to carbon metabolism, such as PEPCK, across species in NCBI. Then you can map traits onto a phylogenetic tree, which is a family tree for species, and use ancestral-state reconstruction to estimate where CAM likely appeared. The goal is not just to list species, but to test an evolutionary pattern.
Why This Is a Good Topic
This is a strong science fair topic because you can ask clear yes-or-no and compare-across-groups questions with public data. The project connects to drought tolerance, crop adaptation, and plant survival in harsh climates. You can learn real research skills, like sequence alignment, tree building, and trait mapping, without needing a wet lab. That makes the work advanced, but still doable if you are patient and organized.
Research Questions
- How does PEPCK sequence similarity vary among CAM and non-CAM succulent species?
- What is the effect of family membership on the inferred ancestral state of CAM photosynthesis?
- Does the placement of CAM species on the phylogenetic tree suggest one origin or multiple origins of CAM?
- To what extent do PEPCK sequence changes correlate with habitat aridity across succulent families?
- Which succulent lineages show the strongest signal for repeated CAM evolution?
- How does the choice of alignment method change the ancestral-state reconstruction for CAM traits?
Basic Materials
- Computer with internet access.
- Access to NCBI GenBank and NCBI Protein databases.
- Spreadsheet software such as Google Sheets or Excel.
- R installed with the phytools and ape packages.
- Sequence alignment tool such as MAFFT or Clustal Omega.
- Reference trait list for CAM and non-CAM species from peer-reviewed sources.
- Notebook for tracking species names, accession numbers, and trait labels.
Advanced Materials
- Computer with enough memory to handle multi-species alignments.
- R installed with phytools, ape, and geiger packages.
- MEGA or IQ-TREE for phylogenetic tree building.
- A curated set of PEPCK sequences downloaded from NCBI.
- Trait matrix with habitat, growth form, and CAM status from published literature.
- Optional access to a high-performance computing cluster for larger datasets.
- ImageJ or another image analysis tool if you add leaf anatomy comparisons from published images.
Software & Tools
- R: Runs phylogenetic analyses, ancestral-state reconstruction, and visualization with packages like phytools.
- NCBI GenBank: Provides public DNA and protein sequences for target species.
- MEGA: Helps you align sequences, inspect trees, and compare evolutionary models.
- MAFFT: Produces multiple sequence alignments that you can use before tree building.
- Google Sheets: Organizes species metadata, accession numbers, and trait coding.
Experiment Steps
- Define the species set and decide which succulent families you will compare.
- Gather PEPCK sequences and trait labels from NCBI and published sources.
- Align the sequences and check whether the gene region is comparable across species.
- Build a phylogenetic tree and choose a trait-coding scheme for CAM status.
- Map CAM and related traits onto the tree and run ancestral-state reconstruction in R.
- Compare alternate models or datasets to see how sensitive your conclusion is.
Common Pitfalls
- Mixing DNA and protein records, which makes the alignment meaningless for downstream tree building.
- Using species with weak or missing CAM evidence, which can corrupt the trait matrix.
- Comparing sequences that cover different gene regions, which creates false differences.
- Trusting one tree without checking support values, which can hide unstable branching.
- Treating one ancestral-state result as final, which ignores how model choice can change the answer.
What Makes This Competitive
A stronger project does more than make one tree. It tests how sensitive the evolutionary story is to gene choice, alignment method, and trait coding. You can also compare CAM-rich lineages against close non-CAM relatives instead of using random species. A top project explains uncertainty clearly and uses that uncertainty to test a real evolutionary hypothesis.
Project Variations
- Focus on one succulent family, such as Crassulaceae, and test whether CAM evolved once or several times within that group.
- Compare PEPCK with another photosynthesis-related gene to see whether both genes tell the same evolutionary story.
- Add habitat data, such as rainfall or temperature range, and test whether arid environments predict CAM more strongly than family history does.
Learn More
- NCBI Gene and GenBank: Search sequence records, gene summaries, and linked literature for plant genes and species.
- PubMed: Find review articles and primary papers on CAM evolution, PEPCK, and succulent physiology.
- MIT OpenCourseWare Biology courses: Review phylogenetics, molecular evolution, and tree-thinking concepts from free course materials.
- R phytools documentation: Learn how to run ancestral-state reconstruction and plot trait evolution on trees.
- USDA PLANTS Database: Check plant names, taxonomy, and distribution details for North American species when your dataset includes them.
- NOAA Climate Data Online: Pull climate context for habitat comparisons if you expand your project to environmental factors.