Flowering plants welcome other life

Burst of evolution 100 million years ago opened new niches

A burst of flowering plant evolution some hundred million years ago may have served as an ecological stimulus package, spurring the radiation of ants, salamanders and other life. 

The evolution of members of the rosid clade (including roses, citrus, apples, figs, cotton and peaches, shown clockwise above) dramatically changed the forests around 100 million years ago. USDA/ARS

A new DNA analysis examines a prominent branch on the flowering plant family tree that includes the pea family; fruit-bearing trees such as apples, peaches and plums; and the birch, elm, and oak and beech families. The findings suggest that the arrival of these plants changed the face of Earth’s forests, which may have opened a suite of ecological nooks and crannies, ripe for colonization by beetles, mammals, frogs and ferns, the researchers report online February 9 in Proceedings of the National Academy of Sciences.

The research is in line with the fossil record, says paleobotanist William Crepet of Cornell University. Scientists have known there was a rapid radiation of these plants around this time, and there is fossil evidence of the plants’ flowers from 100 million and 94 million years ago. “This is a good, solid study,” Crepet says.

The largest section of the flowering plant family tree, known as the rosid clade, comprises about 140 families and 70,000 species. (It’s named after the rose family, a prominent member.) Though there have been previous studies of this angiosperm group, its size and diversity has made assessing evolutionary relationships difficult, especially in the deeper branches. To investigate, botanist Doug Soltis of the University of Florida in Gainesville and his colleagues looked at changes in DNA from more than 12 genes in more than 100 rosids. The researchers also looked at the number of mutations in the DNA to estimate the timing of the evolution of different rosid groups.

It appears that rosids arrived in a series of rapid bursts in the mid- to late-Cretaceous. The researchers’ timing model suggests an initial radiation around 93 million to 115 million years ago followed by two more bursts between 83 million and 107 million years ago. 

“We’re looking at the rise of forests that are dominant today,” says Soltis. “This is a landmark terrestrial evolutionary event that allowed a lot of other things to happen.”

The evolution of the rosids coincides with the diversification of several animal groups, including ants and plant-eaters such as beetles and hemipterans, the true bugs, the researchers report. A major radiation of amphibians, many of which live in forests today, is thought to date to 80 million to 85 million years ago, as does a major fern radiation. Even though these are both very old groups evolutionarily, the ferns and amphibians seem to have exploded with the rise of angiosperm-dominated forests.

Crepet cautions that there is a lot of debate about models that use molecules to infer timing of evolutionary events, but says the new time estimates aren’t unreasonable.

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