Just a few genetic differences tailor flowers to specific pollinators

A new study led by the University of South Carolina (USC) has found that distinct variations in the attributes of wildflowers, depending on their respective pollinators, are driven by a small number of key genetic differences.

Wildflowers exhibit unique sets of characteristics – termed “pollination syndromes” – that have evolved to cater to specific animal pollinators, such as insects or birds. 

Penstemons

While most species within the Penstemon genus present wide, blue flowers, serving as landing spots for bees, evolution has led some species to develop narrow, red, tubular flowers, catering to hummingbird pollination.

The North American wildflower genus Penstemon displays remarkable floral syndrome convergence, with at least 20 separate lineages that have evolved from ancestral bee pollination syndrome (wide blue-purple flowers that present a landing platform for bees and small amounts of nectar) to hummingbird pollination syndrome (bright red narrowly tubular flowers offering copious nectar). 

Focus of the study 

Related taxa that differ in floral syndrome offer an attractive opportunity to examine the genomic basis of complex trait divergence,” the authors explained.

The objective of this research was to explore how these distinctive pollination syndromes are preserved genetically. 

How the research was conducted 

The team sequenced the DNA of 229 plants from three related species of the Penstemon genus: P. neomexicanus and P. virgatus, which are bee-pollinated, and P. barbatus, adapted to hummingbird pollination.

What the researchers learned 

Despite the stark differences in floral attributes, the experts found a relatively small number of genetic differences between P. barbatus and its bee-pollinated relatives. 

Moreover, plants from the same geographical vicinity exhibited greater genetic similarity compared to those from varied locations, regardless of the species. These findings suggest that a genetic blending occurs between wildflowers adapted to both bee and hummingbird pollination. 

Varied pollinators 

However, the researchers identified 21 sites that showcased consistent differences among species with varied pollinators. These sites are dispersed throughout the genome, suggesting an increased likelihood of the disruption of complementary floral traits by recombination, resulting in hybrids with diminished success. 

Interestingly, three of these identified genetic variances were located proximal to genomic regions that determine flower color, width, and nectar volume – traits distinctive to different pollination syndromes.

 Flower traits

The study provides evidence of occasional hybridization between neighboring bee- and hummingbird-pollinated Penstemon species, alongside an intense selection pressure to retain flower traits adapted to each type of pollinator.

“Although bee- vs. hummingbird-pollinated species are easily distinguished in the field, based on unmistakable differences in flowers and the overall stature of the plant, a surprisingly small number of genetic regions distinguish these different species at the genetic level,” concluded Carolyn Wessinger, an assistant professor of Evolution and Plant Biology at USC.

The study is published in the journal PLoS Biology.

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