This week, the molecular ecology lab took a field trip to Mt. Tamalpais to visit several wild populations of our focal plant species, Mimulus guttatus (=Erythranthe guttata).
On Tuesday, September 10, 2019 at 1:00PM, the class left in two passenger vans, and headed to the Rock Springs Trailhead on Mt. Tamalpais, Marin County. To get to the site, we left San Francisco on 101 North, crossing the Golden Gate Bridge into Marin County. We took exit 450B and merged onto Sir Francis Drake Blvd. We turned left onto Pacheco Avenue, then right onto Broadway, and then left onto Bolinas Rd. We followed Bolinas Rd for approximately 10 miles, and then took a left on West Ridgecrest Blvd. Four miles up this road, the parking lot is on the right.
After parking in the lot, the class headed northwest on the Cataract Trail. This trail soon led us to a bridge over Cataract Creek. The class paused here, under a dense oak riparian canopy, to observe a population of Mimulus guttatus growing in the dry creek bed. The plants were in their vegetative state, forming mats of rhizomatous rosettes, which were patchily distributed along the creak bed. We talked about their morphological variation, and the research that Dr. Paul’s grad student, Alec Chiono, is conducting about the climate variability hypothesis using M. guttatus.
Figure 1. Dry bed of Cataract Creek with M. guttatus plants growing in it.
The class spread out here to collect samples of M. guttatus leaves. We each tried to collect distinct individuals, based on spatial separation. We each took a small sample of our plant, approximately 2-3 leaves of new growth, and dropped them into tubes full of silica powder. We immediately inverted the tubes several times to make sure the sample was covered in silica, to help dry out the tissue. We labelled the tubes with our initials, the date, and the population code CATB.
Figure 2. Collection vial with M. guttatus sample and silica in it.
After each person made their collection, we walked back down the trail toward the parking lot, but diverted north at the trail split to observe a population of M. guttatus along a different stretch of Cataract Creek. This population’s habitat lacked the dense canopy, and instead occurred in a sunny, nonnative grassland. The Mimulus plants in this location were mostly brown and drying out, but some fruits were left on the stalk, full of seeds for us to observe. Dr. Paul crushed some of the fruits, exposing tiny black seeds. We discussed dispersal hypotheses for this species.
Next we went back to the cars and drove back down West Ridgecrest Blvd for a few minutes, before pulling off on the side of the road, just past a gate on the left. We headed to the west side of the road, to observe a serpentine outcrop. We discussed the harsh, dry characteristics of this substrate and the general ecology of species that occur here. Not many species occurred in this rocky area (mostly Arctostaphylos sp. and Adenostoma fasciculatum around the edges). I observed a few dried up individuals of the genus Streptanthus.
Figure 3. Serpentine outcrop on a hillside off W Ridgecrest Blvd.
We crossed the street, and walked past a gate to an old mining area. On an exposed serpentine outcrop near the trail, we observed another population of M. guttatus. Here, it could be seen that the M. guttatus plants grew along a small drainage, where water flows ephemerally along the surface of the rock.
Figure 4. M. guttatus population on a serpentine outcrop.
We next headed back down West Ridgecrest Blvd to another trailhead. Walking west on this trail for about 5 minutes, we got to an intermittent creek with a small riparian corridor, running down an otherwise dry, grassy hillside. The riparian corridor, with its dense green vegetation was contrasted sharply by the surrounding dry grass. In this drainage, running with shallow water, a population of M. guttatus was in bloom. We observed the flowers and discussed potential pollinator hypotheses.
Figure 5. M. guttatus in flower in a wet creek bed.
This completed our tour of the variable habitats of M. guttatus. After enjoying the view and the fresh air for a bit longer, we headed back to campus.
Figure 6. A view of the city from up high on Mt. Tamalpais.