My research interests are centered around the processes that shape species relationships. One facet of biology that influences species in numerous ways is the evolution of chemical defenses and I am interested in understanding how such traits influence the ecology and evolution of species.
The current research I do investigates how toxins in poisonous newts may influence ecological, behavioral, and evolutionary dynamics, and whether such phenomena occur at multiple spatial and temporal scales.
The approach I take to answering these research questions is interdisciplinary. I rely on methods from analytical chemistry, genetics, and field biology, as well as theory that is central to conservation biology, community ecology, and animal behavior to shape and design experimental work. I enjoy collaborating and learning with fellow researchers to achieve solutions to broader or more large scale projects. My work is done in the laboratory and field, both locally and in more distant locations.
My research experiences and the projects I am working on are outlined below. Contact me if you have questions or any thoughts you would like to share.
Phenotypic variation of chemical defenses in newts
Newts of the genus Taricha possess a neurotoxin, tetrodotoxin (TTX) that is considered to have evolved as a means of chemical defense. However, very little is known about newt TTX, such as how they maintain it, if they produce it, and whether it varies not only between populations, but also within individuals over time. Over the last five years, I have used this system as a model to explore potential ecological roles of chemical defenses. I have also characterized the phenotypic variation of TTX in newts across most of California and experimentally manipulated environments to test the stability of the trait.
Sampling newts in the wild
I modified and improved a previous sampling method so that individuals could be sampled non-destructively from their breeding site. As a result, I can track individual TTX levels through time.
Collecting a skin sample from an adult newt
I use this method to take a non-destructive 2mm skin sample from a newt. The animal is released at the point of capture in the stream and is never brought into the laboratory.
I take a lot of observational notes, from densities of newts to newt morphological characteristics and abiotic data like water temperature and pH.
A field observation of tail damage that is caused by nonnative crayfish that have spread into this site.
Water quality data
Waiting as the water quality meter logs data at a newt breeding site. Unfortunately, no newts.
Sadly, a more common site as California progresses through the drought. At this specific site, there was no water and approximately 25 newts looking for a stream.
Amphibian behavior in response to increased ultraviolet radiation
This was a project I worked on in Costa Rica with Andy Blaustein, Barbara Han, and Lee Kats. I studied the calling behavior of male strawberry poison dart frogs (Dendrobates pumilio) in response to increased ultraviolet (UV) radiation. Ambient radiation is known to harm amphibians, yet this species of frog is diurnal and spends most of the day actively calling. The study examined whether males would abandon calling site locations sooner if UV levels were increased. The study led to my mentoring undergraduates on research projects further related to UV and amphibians in Costa Rica.
Strawberry poison dart frogs
Males like this one are often heard calling as you walk through the forest. They usually call from exposed locations, where UV would be relatively high, but often take cover under vegetation where UV is lower .
Experimentally manipulating and measuring UV levels
I mentored Nicholas on this project, along with a handful of other undergraduates. Here we're attempting to reduce UV levels with filters to test if calling males will call longer when UV is reduced.
Cloud forest team
Working with Alan Pounds and undergraduates in Monteverde to understand amphibian declines at high elevation sites.
Helping undergraduates with a research project that involved quantify the amount of UV that red-eyed tree frog eggs experience in a swamp at La Selva Preserve in Costa Rica.
The Sarapiqui River
The end of a long day of field work on a number of great undergraduate student projects.
A night hike
Always a must after a hard day of field work. We found a sock headed snake, along with a ton of other herps!
Macroinvertebrate foraging behavior in response to amphibian chemical cues and defense toxins
This work centered around my interest in learning whether chemical defense compounds from toxic California newts (Taricha torosa) have any ecological effects upon the aquatic community. The toxin newts have, tetrodotoxin (TTX) will elicit antipredator behavior in conspecific larvae because adults can be cannibalistic, but what effect TTX may have upon lower trophic levels, such as the macroinvertebrate community was not clear. Using field bioassays, I found that newt chemical cues affected macroinvertebrate foraging behavior. Using TTX in the laboratory, I found that predatory nymphs exposed to TTX reduced their mean angular velocities 4 fold and strike velocities 3 fold relative to controls.
Ephemeropterans are one of the species that compose the macroinvertebrate community. They live in streams as aquatic nymphs before hatching out of the water as a flying insect.
Conducting a preliminary feeding experiment with dragonfly nymphs and newt larvae.
Experimental flow-through chambers
I used these small experimental chambers to test how dragonfly nymphs would respond to waterborne chemical cues. I've just introduced fluorescein dye to determine flow dynamics.
Mayflies in the laboratory
I fabricated these small mesocosms for experimental bioassays with macroinvertebrates to test dose responses to waterborne TTX.
A dragonfly nymph in one of the experimental chambers. The nymph was exposed to waterborne TTX or a control prior to the prey being introduced. I recorded the trial, then analyzed velocities from the video.
I have worked with agencies, local researchers, and undergraduate students to research and manage aquatic invasive species in southern California. This work has primarily focused on introduced crayfish (Procamburas clarkii) and New Zealand mud snails (Potamopyrgus antipodarum) and researching what effects they may have on local amphibians, specifically California newts (Taricha torosa) and tree frog species (Pseudacris cadaverina and P. regilla) as well as native turtles (Emys pallida) and freshwater macroinvertebrates.
Crayfish and amphibians
The results of collaborative research projects have shown that native amphibian breeding and recruitment are negatively affected by crayfish predation and aggressive behaviors.
Crayfish and trapping
Collaborators and I have found that trapping improves amphibian breeding and reproductive success, especially in above average rainfall years when many crayfish are washed out of streams.
Mentoring undergraduates in field techniques
Newts and crayfish coexist in this stream, which is rare in southern California. Here, I'm showing students how to estimate crayfish density, sample for newts, and set crayfish traps.
Characterizing and evaluating the effects of invasive aquatic species through removal and restoration
I am working on two projects that focus on understanding how introduced aquatic species impact native species. One project is at a local set of ponds that are in the process of being restored. I am working with students and researchers to study how removal of these species affects native amphibians, reptiles and macroinvertebrates. For the other project, I will lead a study to characterize conditions of streams and test the effects nutrients and the removal of introduced species have on macroinvertebrate communities.
A mayfly nymph
Mayflies are considered indicator species of a streams biological integrity. In conjunction with other macroinvertebrates, they can be used to understand how well a stream is doing.
Field sampling for macroinvertebrates
During this project, undergraduates and I have spent time working in streams, where they have become pros at sampling macroinvertebrates.
At a restoration site where many red-eared slider turtles have been introduced. The pond they live in is also filled with introduced fishes. I am working to understand how their removal will affect native species.
Weighing a southwestern pond turtle
This is a native turtle that is coexisting with introduced fishes and turtles. We collect turtle morphological and survival data to determine how the population is doing as restoration progresses.
Native turtles have been captured and marked so that their growth and survival can be tracked. Here, I'm out on the water taking individuals from traps and taking mass and carapace measurements.
A conservation management plan for amphibians of the Santa Monica Mountains, Los Angeles, California
The goal of this project is to understand how amphibians are using the landscape and to potentially identify breeding populations of concern. I will use next-generation sequencing techniques to capture numerous genetic loci from three amphibian species and use those genetic markers to assess diversity, connectivity, and gene flow between breeding sites. In collaboration with the National Park Service, these data will help identify habitat and breeding populations that may be of conservation priority.
The Santa Monica Mountains
A montage of images I put together; the Pacific side of the range as viewed from Piuma Canyon, looking southeast.
A focal species of the study
This is one of the tree frog species that will be studied in this project, Pseudacris cadeverina. It is a stream-breeding specialist, and its patterns will be compared to a generalist breeder.
Spring in the coastal area of the Santa Monica Mountains. The bright yellow of Coreopsis gigantea is electrifying.
This individual is close to completing metamorphosis and leaving the water. This Pseudacris species is a generalist breeder. Here, eggs were laid in an ephemeral pool in the mountains.
Desert tortoise conservation genomics
I am assisting the Shaffer Laboratory and UCLA graduate student Evan McCartney-Melstad with a research project that is evaluating how desert tortoise genomics can be used to understand and model the movement of genes on the desert landscape. As solar energy becomes increasingly popular in the desert regions of the southwest, Evan's research will help to inform land management agencies of the corridors that are most
critical to protect and ensure continued gene flow. You can check out Evan's website for more details.
The desert tortoise
This one was found near the Kelso Dunes. Desert tortoises are facing challenges as the desert continues to be developed for solar power and people keep taking them as pets.
Collecting blood samples for DNA extraction and analyses
The potential for transmission of infectious disease is so severe that you wear two gloves - remove one and throw it out if you touch anything. Phil Spinks finding the cavity to draw a blood sample from this tortoise.
Bleeding desert tortoises
Evan schooling the boss! Brad got it on the first try.
Janet Vu was a great help keeping the tortoise under control while I took the sample. She is also great with GIS and has done a solid amount of work on this project.
Janet drawing a blood sample for subsequent DNA extraction.
Desert tortoise project