Pod and seed defensive coloration (camouflage and mimicry) in the genus Pisum

Abstract

The small genus Pisum is composed of two annual species, P. fulvum and the domesticated pea P. sativum. The domesticated pea has two main wild-type taxa: P. elatius and P. humile. Members of the genus Pisum are not well defended from herbivory by high levels of toxins like the seeds of many other legume species. We studied the color patterns in the pods and seeds of these three wild taxa (P. fulvum, P. elatius and P. humile) in order to examine their potential for defensive coloration (camouflage and Batesian mimicry). All three taxa are polymorphic concerning pod and seed coloration. The mature pods of many individuals of P. humile and P. elatius mimic aposematic caterpillars, but some are plain green. The pods of some individuals of P. elatius have a zigzag or straight red marking along them that resembles the conspicuous dorsal markings of the local common venomous viper, potentially mimicking it. The pods of many individuals of P. fulvum have dark blotches that when compared to such patterns in animals, potentially function as camouflage. The seeds of all three species are camouflaged by either: (1) color matching with that of soil (especially P. fulvum and P. elatius), (2) disruptive coloration (especially P. humile), (3) variability in seed-coat color that may undermine the use of search images by visually oriented granivores that look for cryptic seeds (all taxa). The mature pods of P. fulvum are also defended in many inflorescences by degenerated flowers that develop into sharp thorns. It seems that this species is still in the process of evolving this mechanical defense as the response to millennia of strong grazing pressure.

Keywords:

• camouflage
• defense
• evolution
• herbivory
• mimicry
• Pisum
• pods
• seeds
• thorns

Acknowledgments

We thank Professor Shahal Abbo for giving us access to his seed collection, for illuminating discussions and collaboration.