Scientists have identified the evolutionary pathway that led some plants to turn carnivorous, a finding that explains why pitcher plants from different parts of the world appear strikingly similar despite having evolved independently.
Pitcher plants capture insects by luring them into a pitfall trap - a cupped leaf with a waxy, slippery interior that makes it difficult to climb out.
A soup of digestive fluids sits at the bottom of this chamber and breaks down the flesh and exoskeletons of prey.
The study probes the origins of carnivory in several distantly related plants - including the Australian, Asian and American pitcher plants, which appear strikingly similar to the human (or insect) eye.
Although each species developed carnivory independently, the research concludes that the biological machinery required for digesting insects evolved in a strikingly similar fashion in all three. The study hints that for a plant, the evolutionary routes to carnivory may be limited.
"It suggests that there are only limited pathways for becoming a carnivorous plant," said Victor A Albert from University at Buffalo in the US.
"These plants have a genetic tool kit, and they are trying to come up with an answer to the problem of how to become carnivorous. And in the end, they all come up with the same solution," said Albert.
The new study builds on this older work, conducting a deeper investigation into how unrelated pitcher plants came to share so much in common.
The path to carnivory was remarkably similar for the three species examined - Cephalotus follicularis (Australian pitcher plant, related to starfruit), Nepenthes alata (Asian pitcher plant, related to buckweat) and Sarracenia purpurea (American pitcher plant related to kiwifruit).
A genetic analysis, which included sequencing the entire genome of Cephalotus, found strong evidence that during their evolution into carnivores, each of the plants opted many of the same ancient proteins to create enzymes for digesting prey.
Over time, in all three species, plant protein families that originally assisted in self-defense against disease and other stresses developed into the digestive enzymes we see today, genetic clues suggest.
These enzymes include basic chitinase, which breaks down chitin-the major component of insects' hard, exterior exoskeletons-and purple acid phosphatase, which enables plants to obtain phosphorus, a critical nutrient, from victims' body parts.
Enzymes in a fourth carnivorous species, the sundew Drosera adelae, a relative of Nepenthes that is not a pitcher plant, also appeared to share this evolutionary road.
The study was published in the journal Nature Ecology and Evolution.
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