Geometric Morphometrics

Geometric morphometrics is one of the tools of phenomics, i.e. the analysis of high-dimensional phenotypic data. Geometric morphometrics go beyond the independent measurements of length, width and height and work with sets of point coordinates thus better capturing the geometry of objects.

The study of poppy seeds was a technical challenge, due to their small size (often <1mm in length). Nevertheless, a protocole was designed and its potential has been demonstrated in a previous publication (Jesus et al. 2021).

How does it work?

Papaver seeds are photographed from a lateral view, with the hilum to the right and the broader part of the seed at the bottom. Each seed is photographed with a digital microscope creating one mounted photo from several single photos that are stacked together to give depth of field to the seed and enable the counting of the number of seed cells. The photo is processed and a black and white mask is generated. Five landmarks are recorded using ImageJ (see Figure below).

Seed shape is analysed using outline analysis based on elliptic Fourier transforms (EFT).

Data acquisition and post-processing (a) Lateral view position; (b) Background removal and cleaning; (c) Mask; (d) Landmarked-mask (Jesus et al. 2021).

What are we planning to do?

We aim to study the same accessions (20-30 seeds per accession) of domesticated and wild species of poppy analysed in the DNA part of the project and historical samples from different European herbaria to 1) search for the most likely ancestor of opium poppy and where it could have grown, 3) better understand the evolution of the crop in recent times, and 3) generate a robust model to classify waterlogged archaeological seeds into wild or domestic opium poppy. Eventually, new material from archaeological sites will be added to the existing dataset, particularly expanding towards new regions (northern and eastern Europe) and chronologies (from the Bronze Age to the Medieval period) to build a new narrative on the complex history of this crop.

Jesus, A., Bonhomme, V., Evin, A., Ivorra, S., Soteras, R., Salavert, A., Antolín, F., Bouby, L., 2021. A morphometric approach to track opium poppy domestication. Scientific Reports 11, 9778.

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