Growth & Development

Dimorphism in cleistogamous flowers in Portulaca oleracea

A trade-off between outcrossing and self-pollination is due to an interplay between genes and environment.

Should you grow cleistogamous or chasmogamous flowers? Chasmogamous flowers open to the world, exposing their reproductive organs to pollinators, herbivores and pathogens. Cleistogamous flowers in contrast are closed, and tend to self-pollinate but protect their reproductive organs. Self-pollination is often a poor second to outcrossing, but under certain conditions the guarantee of some form of pollination can be valuable. What Tomoyo Furukawa and colleagues wanted to know was what drives the choice between open and closed flowers? Is it genetic, or is a plastic response to the environment?

Image: Furukawa et al.

To find out, Furukawa and colleagues grew Portulaca oleracea (Purslane) seedlings from sixteen different populations under two conditions, low temperature and high temperature. They found that offspring from CH (open-flower) plants also had open flowers, and the CL (closed-flower) plants produced offspring with closed flowers. They also found that temperature did not change flower production.

However, they did find that the open-flower plants were less successful under colder conditions. They conclude that the differences between the two strategies is due to genetic inheritance, and the difference between populations of P. oleracea is down to the environment having an effect on survival of the differing genotypes.

“Plants probably need less time to become large in high-temperature environments than in low-temperature environments. Thus, CH plants might produce more seeds than CL plants even though CH plants begin reproduction later than CL plants,” conclude the authors. “In fact, the number of seeds produced was greatest in the plants that began flower bud production at a larger plant size under high-temperature conditions. On the other hand, the low frequency of CH plants suggests that CL plants have more advantages than CH plants overall and thus that CL plants will become dominant in the future.”