About

Eva K. Fischer is the principal investigator of the Fischer Lab at the University of California, Davis, where she studies brain and behavior with a particular enthusiasm for baked goods. Her current scientific questions focus on understanding behavior across different levels of biological organization and investigating whether cell types are truly distinct entities. Eva follows a mentoring strategy inspired by her PhD advisor, which includes boosting lab morale and productivity through intermittent food rewards. She values the people in her lab, affectionately known as the LABradors, as her favorite lab item. Her research approach reflects a deep interest in the neural and biological bases of behavior, emphasizing both the complexity of social interactions and the underlying cellular mechanisms.

Research topics

• Biology
• Ecology
• Genetics
• Physiology
• Neuroscience
• Psychology
• Developmental psychology
• Evolutionary biology
• Endocrinology

Selected publications

• Author response for "Consequences of developmental and growth-rate plasticity within and across life stages in wood frogs ( <i>Rana sylvatica</i> )"

  2025-01-28

  peer-review
  PublisherDOI

• Author response for "Partner cues and individual variation underlie sex-reversed parental care in poison frogs"

  2025-10-29

  peer-reviewSenior author
  PublisherDOI

• Early development of the glucocorticoid stress response in dyeing poison frog tadpoles

  General and Comparative Endocrinology · 2025-06-26 · 3 citations

  articleSenior author
  PublisherDOI

• Why not both? A case study in measuring cortisol and corticosterone

  Integrative Organismal Biology · 2025-01-01 · 1 citations

  articleOpen accessSenior author

  Synopsis A general tenet in stress physiology is that the hypothalamic-pituitary-adrenal axis predominantly produces one glucocorticoid (GC) in response to stressors. However, most vertebrates produce both cortisol and corticosterone, these steroids show variation across species in absolute levels, relative proportions, and stress responsivity, and they regulate much more than just stress physiology. In the present commentary, we argue that focusing on a single GC may not capture the whole story, presenting an overview of previous studies and an example from our own work on poisons frogs—a group relatively new to endocrinological studies. We originally set out to validate non-invasive waterborne hormone measurements in our focal species, the dyeing poison frog Dendrobates tinctorius. In pursuing this goal, we uncovered unexpected patterns of GC abundance within and across species. Dendrobates tinctorius had higher amounts of corticosterone than cortisol in both plasma and waterborne samples, and corticosterone was responsive to adrenocorticotropic hormone as canonically assumed. However, corticosterone and cortisol levels were surprisingly similar in D. tinctorius, and cortisol was more abundant than corticosterone in water samples from four additional poison frog species. Alongside those of other studies, these results challenge the broadly accepted assumption that corticosterone is always more abundant in amphibians and add to the growing literature highlighting the importance of measuring both GCs to understand (stress) physiology.

  PublisherOA PDFDOI

• Author response for "Partner cues and individual variation underlie sex-reversed parental care in poison frogs"

  2025-10-15

  peer-reviewSenior author
  PublisherDOI

• Consequences of developmental and growth-rate plasticity within and across life stages in wood frogs ( <i>Rana sylvatica</i> )

  Royal Society Open Science · 2025-05-01 · 1 citations

  articleOpen access

  Increased trait responsiveness to the environment can provide short-term benefits but may induce delayed costs. Anurans (frogs and toads) provide an excellent system to examine phenotypic plasticity and developmental carry-over effects given their ecologically distinct life stages, which have distinct development and growth opportunities. Previous research has predominantly assessed phenotype at metamorphosis rather than within and across life stages. To address this knowledge gap, we reared wood frogs ( Rana sylvatica ) at two densities and assessed morphology and survival at multiple larval and post-metamorphic timepoints. As expected, the high-density rearing environment depressed early larval size and survivorship and delayed metamorphosis. However, compensatory growth-rate plasticity enabled high-density tadpoles to metamorphose at a similar size as low-density tadpoles. Regardless of rearing density, larval duration was negatively correlated with metamorphic mass for the earliest developers and influenced post-metamorphic survivorship and morphology, but we found evidence for a trade-off between compensatory growth and later-life survival. Our results reinforce the need to sample at multiple timepoints and life stages to understand interactions between phenotype and developmental environment. More broadly, this study contributes to understanding trade-offs and compensation associated with phenotypic plasticity, which will become even more critical given accelerating rates of global environmental change.

  PublisherDOI

• Partner cues and individual variation underlie sex-reversed parental care in poison frogs

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-09-04

  preprintOpen accessSenior author

  Abstract Flexible parental care strategies are widespread in nature and factor into conflict between the sexes and the realization of sex roles. While adaptive explanations abound, the mechanisms underlying flexible ‘sex-reversal’ of care are less clear. We enlist a biparental frog ( Ranitomeya imitator ) with flexible parental care to investigate the extrinsic and intrinsic mechanisms underpinning parental decisions. Using mate removal experiments in the laboratory, we show that members of the primary caregiving sex (males) show less variation than the flexible sex (females) in their propensity to provide care, and that care propensity in females is affected by extrinsic partner cues as well as individual variability. Indeed, individual repeatability in parental effort is high in both typically caregiving and flexible parents. To investigate the underpinnings of differences in care propensity, we sequenced RNA from whole brains of caregiving and non-caregiving frogs of both sexes. While actively caregiving females showed minimal differential gene expression compared to actively caregiving males, females that failed to provide care showed distinct patterns of gene expression. Our findings offer an initial glimpse into the environmental and genetic regulation of individual variation in sex-reversed parental care.

  PublisherOA PDFDOI

• Flexibility in Gene Coexpression at Developmental and Evolutionary Timescales

  Molecular Biology and Evolution · 2025-08-06

  articleOpen access1st authorCorresponding

  The explosion of next-generation sequencing technologies has allowed researchers to move from studying single genes to studying thousands of genes, and thereby to also consider the relationships within gene networks. Like others, we are interested in understanding how developmental and evolutionary forces shape the expression of individual genes, as well as the interactions among genes. In pursuing these questions, we confronted the central challenge that standard approaches fail to control the Type I error and/or have low power in the presence of high dimensionality (i.e. large number of genes) and small sample size, as in many gene expression studies. To overcome these challenges, we used random projection tests and correlation network comparisons to characterize differences in network connectivity and density. We detail central challenges, discuss sample size guidelines, and provide rigorous statistical approaches for exploring coexpression differences with small sample sizes. We apply these approaches in a species known for rapid adaptation-the Trinidadian guppy (Poecilia reticulata)-and find evidence for coexpression network differences at developmental and evolutionary timescales. Our findings suggest that flexibility in gene coexpression relationships could promote evolvability.

  PublisherDOI

• An Evolutionary Loss of Parental Care in Stickleback Is Associated with Differences in the Activity, but Not the Number, of Neuropeptidergic Neurons in the Preoptic Area

  Brain Behavior and Evolution · 2025-03-28 · 5 citations

  articleOpen access

  INTRODUCTION: A central question about the evolution of social behavior is how extensive diversity can arise when behaviors depend on shared neural, molecular, and hormonal mechanisms. Comparing close relatives can offer insights into which components of shared mechanisms are most evolvable. METHODS: We discriminate between two nonexclusive hypotheses by which conserved neural mechanisms might evolve to generate differences in social behavior: changes in the number or activity of neurons. We test these hypotheses in two recently diverged ecotypes of threespine stickleback (Gasterosteus aculeatus); the common ecotype provides parental care, while the white ecotype does not. We used double-label fluorescent immunohistochemistry with pS6, a marker of transcriptionally active neurons, to quantify the number and activity of two preoptic neuropeptidergic cell types that affect parental care across vertebrates: galanin (Gal) and oxytocin (OXT). RESULTS: Ecotypes did not differ in the overall activity of the preoptic area or the number of Gal and OXT neurons but did differ in the activity of Gal and OXT neurons. The activity of these neurons changed across reproductive stages in the common but not the white ecotype. Activity peaked after mating in commons when males began to care for their offspring, suggesting that changes in the activity of these specific preoptic neurons are required to transition from courtship to parenting. CONCLUSION: Overall, our study suggests that rapid behavioral evolution occurred via changes in the activity but not the number of specific preoptic neuropeptidergic neurons.

  PublisherOA PDFDOI

• Author response for "Partner cues and individual variation underlie sex-reversed parental care in poison frogs"

  2025-11-04

  peer-reviewSenior author
  PublisherDOI

Frequent coauthors

• Lauren A. O’Connell

  Stanford University

  27 shared

• Faith O. Hardin

  University of Illinois Urbana-Champaign

  16 shared

• Kim L. Hoke

  Colorado State University

  16 shared

• Katharina M Soto

  University of Illinois Urbana-Champaign

  16 shared

• Alexandre B. Roland

  15 shared

• Nora A. Moskowitz

  Stanford University

  13 shared

• Andrea Colton

  12 shared

• Devin Edmonds

  University of Illinois Urbana-Champaign

  12 shared

Labs

• Fischer LabPI

Education

• PhD, Biology

  Colorado State University

  2015

• BA

  Cornell University

  2007