Carnivorous plant traps help scientists explain the evolution of complex 'composite' traits

5th January 2024. Story subject to Science X's stringent editorial procedures and reviewed for accuracy, reliability and credibility, with University of Bristol validating the information. The central focus is on a study by an international team of scientists led by Dr. Ulrike Bauer of the University of Bristol.

The team examined two species of tropical pitcher plant, separated by a vast 4,000 km of ocean – the Slender Pitcher Plant (Nepenthes gracilis) found in Borneo and the Nepenthes pervillei found in the Seychelles islands on Africa's East coast. They discovered both plants independently developed an uncommon "springboard" function for trapping insects. This action is triggered when raindrops strike the lid of a pitcher plant, and insects perched beneath this lid are flung into the trap underneath. These findings are reported in the prestigious Science journal.

The springboard trapping method requires three separate traits. Firstly, a horizontal lid is required for insects to fall within the trap. Secondly, this lid must possess a spring-like quality to adequately transfer the force from raindrops to insects, and last, the lid underside should have a layer of small wax crystals offering the perfect balance of traction—just enough for insects to traverse upside down while remaining slippery enough for insects to lose their footing when a raindrop strikes. These three attributes are all crucial for a successful trap.

According to Dr. Bauer, this setup is a "composite trait," the creation of which poses considerable difficulties for evolutionary biologists. Traditional evolutionary theories suggest that natural selection acts on existing variable traits, favoring those that offer an advantage and give a better chance of producing higher numbers of offspring. This basic principle has explained many aspects of evolution but struggles with explaining the birth of completely new traits, especially those resulting from previously unrelated components, like the pitcher plant's springboard mechanism.

In response, Dr. Bauer and her team propose an alternative explanation: The spontaneous coincidence or luck of the draw to create a beneficial new combination. Dr. Bauer explained, "We found that the critical traits in the majority of Nepenthes pitcher plant species are incredibly varied, creating a wealth of possible trait combinations, increasing the probability of a beneficial new combination. In this scenario, it's the lack of strong selection that aids evolution by allowing for greater trait variability or more 'entries' in the evolutionary lottery."

More details can be found in the research paper by Guillaume Chomicki and others titled 'Convergence in carnivorous pitcher plants reveals a mechanism for composite trait evolution' in the journal Science (2024). DOI: 10.1126/science.ade0529
Provided by University of Bristol.