A Thousand Acres of Silphiums

Until this spring, I assumed that spring ephemerals, like Claytonia virginica (spring beauty) and others that begin flowering in early spring, did not provide much sustenance for early season pollinators. For no reason in particular, I assumed that most of these plants preferred selfing versus providing the resources to attract insect pollinators.

After taking a closer look at the blankets of C. virginica that lie on the slopes of Beckemeier Conservation Area near our house, my eyes were opened. I found pollinators everywhere on multiple trips during this long and cool spring. Unfortunately many species were so quick that they eluded me and my camera. However, I managed to nab a few of the more cooperative and with some help of those smart folks at BugGuide.Net, I got as close to the right identifications as I could.

Have you heard of oligolecty? Until doing this research, I had not either. Oligolectic is a term that describes certain bees species that have specialized preference to pollen from only specific plant groups – plants from a small group of genera, a single genus, or in this case, one single species.

The spring beauty bee (Andrena erigenidae) is a mining bee (Andrenidae) that feeds exclusively on the pollen and nectar of C. virginica. In fact, the larvae of this species cannot grow optimally on any other pollen source. So, it may not come as a surprise that this was the most common bee I found foraging on the fields of spring beauty.

These mining bees will take the pollen during a flight run that may last up to more than an hour and then bring it back to their self-constructed nursery hole in the ground. There they will turn the pollen into cakes and lay a single egg on each. This will be all the material needed for an individual larvae to develop into an adult.

The next pollinator is a bee from the same genus, Adrena. This is a huge genus, comprised of more than 450 species in the U.S. Most often they are impossible to identify to species without having the bee in-hand and available for close inspection.

This beautiful and hairy ginger was considerably larger than the previous Andrena. I estimate this bee was about two-thirds the size of the domesticated honeybee.

I’m not sure if this individual was a male, or if it was only interested in getting nectar, but I never saw this species actively collecting pollen from C. virginica.

The long tongue on this one will allow for it to collect nectar from a larger variety of flowers, while the hairs on this bee definitely help it meet its pollinator status.

I found a couple cuckoo bees foraging amoung the C. virginica as well. This “nomad cuckoo” pictured below is a cleptoparasite, meaning the female will lay its egg inside the nest of a different host species. The cleptoparisitc larvae will hatch first and will often kill the eggs or larvae of its host and then use the pollen provisions the host mother left to complete its development. This particular genus, the Nomada, is known to primarily use species in the above discussed Andrena genus as its host.

The cuckoo wasp, like this metalic green beauty in the Chrysididae family are also cleptoparasites that likely will use Adrena bees as hosts.

Bees and wasps were not the only pollinators I found on spring beauty. I also found a couple species of ants (not pictured because they never stand still long enough) and a couple of dipteran species, like this tachinid fly.

I now want to introduce what was probably the most interesting thing I learned about spring beauty this year. Having been able to work on Asian Soybean Rust for a couple years during my career, I have since been very interested in the complex life-cycles of plant rusts. I suppose due to the dense population of C. virginica at this location and the cool and wet spring we have had, I found that many plants were infected with spring beauty plant rust (Puccinia mariae-wilsoniae). With just taking a cursory estimation of the hillsides, I think that as many as 50% of this population was infected with this rust. When I took the succeeding photo ( I so wish I had taken more and better photos of this), little did I know that my investigation would take me into a complex relationship that not only involved this plant host and rust relationship, but would also involve slugs (yes slugs) and the very pollinators that enticed me to bend the knee in the first place.

I am sure that anyone who has taken the time to appreciate spring beauty more than during one season and/or place has noticed the variability in flower parts coloration.  The majority of what is to follow here comes from an intriguing bit of work by Frank Frey (2004). C. virginica can vary from almost completely white to being mostly colored with pink to mauve to crimson stripes and other floral parts. Frank describes that plants that with higher levels of theses reddish pigments are preferred by pollinators and therefore, “…floral redness was associated with higher percentage fruit set.”  Well then, this should beg the question, if this is the case why are there still plenty of individuals and populations of the less-fecund whitish pigmented flowers? Shouldn’t selection have taken care of this by now?

Here is where the slugs and rust comes into the story. These two, surprisingly, affect opposing selective forces on the coloration of C. virginica flowers. Plants with more white-colored flowers hold up better against predation by slugs due to the anti-herbivore properties of the flavonol pigments that produce the white coloration in these plants. In addition, for reasons that are not completely understood, the rust pathogen does better at infecting and propagating new spores on plants with redder-colored flowers. This was eye-opening for me to learn that something besides pollinator preference was manifesting a selective force on floral morphologies.

This is a highly simplified summary of the story this paper holds. I highly encourage you to check it out for yourself by following the link below.

I love the never ending stories that can be learned from a single, common and seemingly simple spring ephemeral wildflower. I’m sure that spring beauty still has a number of stories to tell. I wish I had taken more photos of the rust and I will try and see if I can find plants with telia, the next form of spore-producing legion by this rust. It occurs later in the lifecycle of the plant. I just hope I’m not too late to get it this season.

Thanks for the visit!

-OZB

Citations

Frey, Frank M. 2004. Opposing natural selection from herbivores and pathogens may maintain floral-color variation in Claytonia virginica (Portulacaceae). Evolution, 58: 2426-2437.