Pterygoplichthys up close

Research in the Nutritional Physiology Lab


Our primary research goal is to understand how organisms are specialized to use specific resources and the consequences of specialization to ecosystem fluxes.  Our research integrates isotopic, molecular, biochemical, and physiological approaches to gain insight into the nutritional physiology of a range of taxa from microbes to vertebrates.  By understanding the resource acquisition strategies of a range of organisms within a given ecosystem, we can better understand fluxes within that system.  Our longterm goal to use this information to make more informed management decisions for natural systems, conservation, and aquaculture.

Current Projects:

Evolution of dietary specialization in prickleback fishes
Digestive adaptations for herbivory
Digestion in seagrass-eating, juvenile bonnethead sharks
Impacts of environmental perturbations on animal microbiome & phys
Abalone disease and aquaculture in a changing world
  

San Simeon
Field collection site:
San Simeon, CA
picture by M.H. Horn

Peru_wood
Field collection site:
Rio Maranon, Peru
picture by A.S. Flecker

Evolution of dietary specialization in prickleback fishes
Using physiological genomics, transcriptomics, microbiome sequencing, enzyme biochemistry, tissue histology, and whole animal physiology, we are investigating what it takes to make a living on different diets. The family Stichaeidae features dietary diversity in sympatric species, convergent evolution of herbivory, sister taxa with different diets, and ontogenetic dietary shifts, making them a dream system in which to understand dietary specialization in vertebrates. This is the focus of Dr. German, and PhD candidate Michelle Herrera. We collaborate with former lab member Dr. Joseph Heras, now a faculty member at CSU San Bernardino. This work has relevance to aquaculture, as we seek to develop sustainable aquaculture targets and feeds. A parallel project using experimental evolution with Danio rerio is also underway. The Danio work is becoming the focus of PhD Student Daniel Rankins. 

Ap
A. purpurescens (carnivore) picture by M.H. Horn


Cv
C. violaceus (herbivore)
picture by M.H. Horn

Digestive adaptations for herbivory
In 1971, Nevo transplanted five breeding pairs of the insectivorous lizard Podarcis sicula from Pod Kopiste to Pod Mrcaru in the Croatian Adriatic.  36 years later, Herrel et al. (2008, PNAS) revealed that the transplanted lizards on Pod Mrcaru had become largely herbivorous.  The transplanted P. sicula were larger, had greater bite force, and perhaps most interesting, had developed valves in their large intestines typically only observed in highly derived herbivorous lizards (e.g., Iguanids, Agamids).  So, in just ~30 generations, P. sicula had developed morphological adaptations for consumption of a plant diet that we previously thought only evolved over longer time scales.  In collaboration with Anthony Herrel and Zoran Tadic, we received a NSF grant to investigate the digestive physiology of P. sicula from the two islets, and this formed the foundation of Beck Wehrle's dissertation research.  See Beck's pagefor more detail. This work continues as an international collaboration, and PhD Student Daniel Rankins is using metagenomic sequencing of the enteric micrbiome to examine the pathways the microbes may use in the lizard hindgut.        


P. sicula
P. sicula (from Pod Mrcara)
picture by B.A. Wehrle













Pod Kopiste
Pod Kopiste, with few plants
picture by D.P. German









Digestion in seagrass-eating, juvenile bonnethead sharks
Herbivorous sharks? Bonnethead sharks (Sphyrna tiburo) appear to consume a fair amount of seagrass as juveniles (up to 62% index of relative importance in some young-of-the-year; Bethea et al. 2007).  In collaboration with Yannis Papastamatiou (Florida International University) we have shown that these sharks have the capability to assimilate nutrients from seagrass (Jhaveri et al. 2015; Leigh et al. 2018, and may have some microbial help in the process; Leigh et al. 2021).  This was the work of former PhD student Samantha Leigh (now at CSU Dominguez Hills), and her webpage has more detail on this exciting project.

bonnethead
Sphyrna tiburo
(image from marinebio.org)


Shark gut
S. tiburo with its gut.


The impacts of environmental perturbations on animal microbiomes and physiology
Animals do not roam this world alone. They are a collection of the animal and all of the microorganisms that reside on and within their bodies. This "holobiont" is what really interacts with the world, and thus, when we examine how animals respond to perturbations, we must also consider how their microbiomes respond, and perhaps whether the microbes provide resilience to specific stressors. PhD Candidates Karina Brocco French and Matea Djokic are studying how pollutants impact animals and their microbiomes, the former in sea urchin larvae, the latter in mosquitofish.
PhD Candidate Nefertiti Smith Christman is similarly studying how suspended sediment impacts the  gut microbiome and physiology of zebrafish. This is exciting work that has the potential to push the field of fish physiology forward.  

Zebrafish
Danio rerio from control (top) and suspended sediment treatments (bottom). Note the clay in the mucus of the sediment-exposed fish. Suspended sediment is an issue for fish globally. Photo by N. Smith Christman.


Mosquitofish
Mosquitofish (Gambusia affinis) are planted all over Orange County for mosquito abatement. By taking advantage of gradients in pollution at various sites, we are examining how pollution levels impact the fish physiology and microbiome. Photo by M. Djokic.   

Abalone disease and aquaculture in a changing world
Abalone are amazing megagastropods. They are massive, herbivorous, marine snails that have a large ecological and cultural significance globally.  Work on abalone began in our laboratory with Dr. Alyssa Frederick's dissertation work, and we continue to collaborate with her in these endeavors, as she is now the director of the White Abalone Captive Breeding Program at Bodega Marine Laboratory (UC Davis). We are examining the best feeds for abalone in a changing world and PhD Candidate Newton Hood is exploring abalone reproduction in conjunction with BML and The Cultured Abalone Farm (Goleta, CA). See Alyssa Frederick's webpage for more detail.    

abalone
Haliotis fulgens, green abalone
picture by A.R. Braciszewski