The first case discussed how populations become individual species which for these animals that do not travel big distances- seems to rely on local geological events. He discussed how allotropic isolation which is caused by land barriers was responsible for creating two distinct populations of the California Giant Salamander. About two million years ago the California Giant Salamander broke in two separate populations as the Sacramento river drained to the ocean and create the San Francisco Bay. The root of Dr. Girman’s research was to determine if the two populations had a healthy genetic diversity. It was fascinating to learn about electroshocking ponds to make it easier to catch the salamanders and how he would analyze their DNA extracted from their mitochondria. What was concluded were that there were actually three distinct populations. How this was able to occur was due to prezygotic isolation, the Wilson Grove formation in Mt. Tamailpais and Sonoma County, and the Petaluma Gap (a phenomenon where there is a constant movement of air between regions). In all of the locations sampled there was a healthy genetic diversity except those in Sierra Azul. Here the salamanders looked dry and unhealthy. The cause of this is unknown, but it should be a concern. Was it due to the close mercury mine? Who knows, but further research should be conducted to figure out how we as people from California can protect our indigenous species.
The next scenario was about the California Tiger Salamander and what influences them to leave their birthplace. The eggs of the California Tiger Salamander are found in vernal pools (wetland depressions that fill in rainy season). After the larvae complete their underwater development then they must undergo metamorphosis in order to leave the pools and spend their adult life on land. Once on land, they take residence in squirrel burrows. When they detect a change in air moisture level the salamanders know that it is time for rain and; thus, must lay their eggs. Because seasons are vital to the life span of vernal pools the change of rainy seasons to a dry season was an evolutionary factor that allowed the salamanders to change and adapt from water to land. The change in their shape is a factor that determines survival in their environment and, thus, the question that spurred this research was: what affects the timing of metamorphosis? There are several various factors that make contributions, but the best way to find an answer was to estimate the events of metamorphosis. Dr. German and his research team measured the largest larvae in each pool each week. If there was a decrease in growth size, then the largest larvae have either stopped growing or have already left making the largest larvae in the water slightly smaller. In conclusion to the experiment, Dr. Girman and his team determined that prey density, predator density, and population numbers are not factors to metamorphosis. Evidence suggested that metamorphosis is related to the drop of pool depth. When the depth decreases metamorphosis increases due to the beginning of the dry season. If the depth increases then the pressure to change is less urgent. This demonstrates phenotypic plasticity or an organism's ability to adjust to the environmental conditions.
The third case of salamander biology involved newts. They are a different species from the salamanders, but they do have similar reproductive cycles. The main reproductive difference is that they undergo amplexus where the male grabs the female for reproduction, then he would drop a sperm packet and if she is interested the female will bury her eggs in it. The question that drove the research was: how do newts find their mates? The study revolved around the California Newt, the Rough-Skinned Newt, and the Red-Bellied Newt that all reside in Sonoma county. Due to reproductive isolation these three species do not hybridize with each other. These mechanisms that prevent reproduction are temporal and habitat isolation. Prior research indicated that newts do not use visual stimuli in choosing mates, but do they use chemical signals? The research was done in the Galbreath Wildland Preserve where all three species overlap. Based on what was known, Dr. Girman and his team hypothesized whether smell was a possibility. The experiment was done by leaving individuals to decide who their mates are in a controlled environment. After many trials using Y mazes with different scents applied to each branch, the data indicated that Rough- Skinned females did not have a preference for males of their own species but had a definite aversion to males from other species. When given the option between their own males or water they choose water 50% of the time. In contrast, males would choose any scent that was female regardless of species. Because of this they drive the mating process. Females are, thus, given the responsibility of installing a reproductive barrier between species to prevent hybridization.
If newts choose a mate based on smell, do humans do the same? In the after cafe there was an activity where 12 individuals were given cologne samples and based on their smelling abilities were given the task to find their partner with the same scent. After a few minutes of sniffing each other's card, they all failed to find their correct partner. This showed us that despite what we were supposed to do we tended to choose the smell that appealed to us the most.
Dr. Girman taught the Piner community that protecting these unique animals is important. Many of them are endangered due to the destruction of vernal pools. It is our duty to protect their habitat and rebuild the homes we have destroyed to ensure the future of our diverse, independent, and picky salamanders and newts.
By: Lindsey Tah- STEAM Club President