About

Karen Sears is a professor in the Department of Ecology and Evolutionary Biology at UCLA. Her research focuses on harnessing the diversity of mammals to identify processes driving change in organisms during their lives and in lineages over time, with the aim of informing challenges in human health. Her current topics of study include the developmental basis of bats' and marsupials' unique phenotypes, as well as the developmental, cellular, and molecular basis of aging in bats. Her work involves understanding the developmental biology and evolutionary processes of mammals, contributing to the broader fields of developmental biology, evolution, paleobiology, and tropical biology.

Research topics

• Genetics
• Biology
• Evolutionary biology
• Zoology

Selected publications

• Validating wing biopsies for blood-borne pathogen characterization in bats

  bioRxiv (Cold Spring Harbor Laboratory) · 2026-03-13

  articleOpen access

  Abstract Wildlife surveillance is critical for tracking disease emergence, characterizing pathogen diversity, and assessing spillover risks. Blood-borne pathogens are of particular interest for such efforts due to their global distribution, broad host taxa, and zoonotic potential. Despite the need to monitor blood-borne pathogens, blood collection efforts are costly for both biologists and the wildlife being sampled (i.e., time-consuming and stressful), hindering our ability to expand and enhance surveillance efforts. There is thus a pressing need for reliable methods for detecting blood-borne pathogens that minimize sampling efforts and wildlife stress. Vascular tissues can contain enough blood to detect infections while minimizing sampling effort and stress on wildlife, but it is unclear how pathogen detection and characterization from these tissues compared to blood. To evaluate the reliability of using vascular tissues for detecting blood-borne pathogens in wildlife, we collected paired samples of blood and wing biopsies from individual common vampire bats ( Desmodus rotundus ) and molecularly screened them for bartonellae, hemotropic mycoplasmas (hemoplasmas), and trypanosomes. The probability of detection was consistently lower in wing tissues than in blood for all pathogens, possibly due to blood vessel avoidance when collecting the former. However, we detected infection in wing tissues of at least two individual bats for each blood-borne pathogen. Paired-positive individuals mostly showed high sequence concordance between tissues, indicating frequent detection of the same infections. Estimated sample sizes needed to detect a single infection and the reported prevalences were similar (i.e., n = 10–39). Due to the lower probability of infection in wing tissues compared to blood, we suggest that using these samples to estimate infection prevalence of blood-borne pathogens is not ideal. However, our results demonstrate that vascular tissues are viable for initial pathogen assessment and discovery to help target surveillance efforts in the future.

  PublisherOA PDFDOI

• Gene co-expression networks reveal differential developmental modularity in Mammalian limbs

  bioRxiv (Cold Spring Harbor Laboratory) · 2026-05-08

  articleOpen accessSenior author

  Abstract Mammalian limb development is a complex system involving several signaling centers and coordinated cell behaviors to sculpt a functioning limb capable of the diverse locomotory strategies that mammals exhibit. To investigate the changes in development that facilitate the generation of the wide array of limb phenotypes across mammals, we take a correlation network approach to investigate the developing limbs of mice, bats, and opossums, which represent typical limb development, a novel limb phenotype, and a shift in developmental timing, respectively. Using transcriptomic data of early limb development across these taxa, we build module correlation networks and identify a difference in network connectivity and the distribution of limb development genes across bat limb development. We identify a unique signature of increased modularity in the bat forelimb that is not detected in mouse or opossum. This modularity is not associated with increased specialization of limb development modules, but rather is marked by target limb development genes being spread evenly across several modules. The opossum, with its standard phenotype but altered developmental timing, does not show a difference in modularity relative to mouse. This work points toward the benefit of a network-minded approach to transcriptomic networks, which reveals developmental modularity and potential gene targets for exploration of developmental system evolution.

  PublisherDOI

• Postnatal Development of the Gray Short-Tailed Opossum ( <i>Monodelphis domestica</i> ): Implications for Metatherian Decline at the K–Pg

  bioRxiv (Cold Spring Harbor Laboratory) · 2026-03-08

  articleOpen accessSenior author

  Abstract Marsupials give birth to extremely altricial offspring which must be reared externally for an extended period, often in a pouch. Despite often being considered a defining feature of marsupials, around a third of living species lack a pouch. Here, we describe the postnatal development of the gray short-tailed opossum, Monodelphis domestica , a small pouchless South American didelphid and consider its implications for life history evolution within Metatheria. We find that at birth, ossification and chondrogenesis in neonatal M. domestica is more extensive than in basal pouched Australidelphian marsupials like the dunnart. Key precocial milestones such as tarsal ossification, eye opening, growth of body fur, and chewing tooth eruption occur earlier and more rapidly. Principal component analysis of life history and reproductive traits reveals a pronounced r- to K-selected gradient across living marsupial species. Stochastic character-mapping based ancestral state reconstruction suggests that absence of the pouch, and by inference possession of an r-selected life history strategy characterised by large litters, short attachment phases, and accelerated weaning was likely ancestral amongst crown-group marsupials. The more K-selected reproductive strategy of pouched marsupials wherein there is a prolonged postnatal development window, and relative few young are produced, likely evolved during the early Cenozoic, and separately amongst australidelphian and ‘ameridelphian’ marsupials. Rather than making early marsupials more sensitive to environmental disturbances, we hypothesis that their possession of an ‘r-selected’ life history strategy may have been a key factor in their persistence through the K–Pg extinction.

  PublisherOA PDFDOI

• Getting a head start: Craniofacial heterochrony in marsupials involves dynamic changes to molecular and cellular mechanisms underlying neural crest development

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-09-25

  preprintOpen access

  Abstract The neural crest is a vertebrate innovation central to craniofacial development and evolution. While the gene regulatory networks guiding neural crest development are well characterized, the mechanisms generating species-specific craniofacial diversity remain poorly understood. Marsupials provide a unique model for studying neural crest plasticity, having evolved accelerated patterns of craniofacial development during embryogenesis. This adaptation arises in response to marsupials being born altricial after a short gestation yet require well-developed mouthparts to attach to a teat and continue development in the pouch. However, how marsupials achieve this heterochronic shift in neural crest development is largely unknown. In this study, we investigate the cellular and molecular mechanisms underlying their distinct heterochrony, revealing that marsupials produce dense pre-migratory aggregates of neural crest cells which undergo collective migration as epithelial-like sheets, potentially facilitating rapid establishment of the facial prominences. These cellular behaviours are unique amongst amniotes but resemble patterns in anamniotes which similarly exhibit accelerated craniofacial development to support early feeding. Marsupials appear to have evolved a similar mechanism of neural crest migration to facilitate their developmental heterochrony. These findings suggest that vertebrate neural crest migration may be shaped by the pace of craniofacial development during embryogenesis rather than phylogeny, providing new perspectives on neural crest plasticity and the developmental mechanisms driving craniofacial diversity across vertebrates.

  PublisherOA PDFDOI

• Conservation and alteration of mammalian striatal interneurons

  Nature · 2025-11-05 · 16 citations

  articleOpen access

  Mammalian brains vary in size, structure and function, but the extent to which evolutionarily novel cell types contribute to this variation remains unresolved1–4. Previous studies suggest that there is a primate-specific population of striatal inhibitory interneurons—the TAC3 interneurons5. However, broader taxonomic and developmental characterization is required to address novelty in cell-type evolution. Here we examine gene expression in inhibitory neurons across 10 mammalian species, spanning 160 million years of divergence from primates. We find that the initial class of newborn TAC3 interneurons specified during development represents an ancestral, medial ganglionic eminence (MGE)-derived striatal population that is also present in pig and ferret cortex. This discovery prompted a re-examination of Glires, including mice, which are thought to lack the TAC3 type5,6. Targeted enrichment of MGE precursors in mice revealed conservation of the TAC3 initial class, camouflaged by reduced expression of Tac2 (the mouse orthologue of TAC3) and a gain of Th expression. Extending our analysis to the adult striatum further supported the homology of primate TAC3 and mouse Th striatal interneurons, and also uncovered a rare Tac2 subpopulation in the mouse ventromedial striatum. This study suggests that initial classes of telencephalic inhibitory neurons are largely conserved, and that during evolution, neuronal types in the mammalian brain change through redistribution and fate refinement, rather than by derivation of novel precursors early in development. An analysis of cell-type diversity in brain samples from a variety of mammalian species, both during development and in adult animals, reveals that the TAC3 initial class of striatal interneurons is conserved across placental mammals and is homologous to Th striatal interneurons in rodents.

  PublisherOA PDFDOI

• Author response for "Natural mutants in mammalian facial morphology: A review of palate clefting in bats"

  2025-03-10

  reviewSenior author
  PublisherDOI

• Author Correction: Conservation and alteration of mammalian striatal interneurons

  Nature · 2025-12-11

  articleOpen access
  PublisherOA PDFDOI

• Natural mutants in mammalian facial morphology: A review of palate clefting in bats

  Annals of the New York Academy of Sciences · 2025-04-27

  reviewOpen accessSenior author

  Bats (order Chiroptera) exhibit great diversity in the size and shape of their palates. One palate characteristic in particular that diverges from other mammals is the presence of a natural and nonpathological cleft palate in roughly half of the ∼1500 species of bats. Despite being typically detrimental when present in other mammals, bats have repeatedly evolved a midline cleft palate in at least 10 lineages and a bilateral cleft palate at least once and, based on observations presented, possibly more. Additionally, some bats that typically do not have a nonpathological cleft palate have been shown to develop pathological palate clefting. Palate clefting in bats therefore has the potential to offer new perspectives on palate development and morphology. In this review, we discuss some of what is currently known regarding the evolution and development, proposed adaptive significance, biomechanics, and diversity of cleft palate in bats and explore avenues for further research on this important topic.

  PublisherOA PDFDOI

• Different orthology inference algorithms generate similar predicted orthogroups among Brassicaceae species

  Applications in Plant Sciences · 2024-12-25 · 1 citations

  articleOpen access

  Premise: Orthology inference is crucial for comparative genomics, and multiple algorithms have been developed to identify putative orthologs for downstream analyses. Despite the abundance of proposed solutions, including publicly available benchmarks, it is difficult to assess which tool is most suitable for plant species, which commonly have complex genomic histories. Methods: We explored the performance of four orthology inference algorithms-OrthoFinder, SonicParanoid, Broccoli, and OrthNet-on eight Brassicaceae genomes in two groups: one group comprising only diploids and another set comprising the diploids, two mesopolyploids, and one recent hexaploid genome. Results: The composition of the orthogroups reflected the species' ploidy and genomic histories, with the diploid set having a higher proportion of identical orthogroups. While the diploid + higher ploidy set had a lower proportion of orthogroups with identical compositions, the average degree of similarity between the orthogroups was not different from the diploid set. Discussion: Three algorithms-OrthoFinder, SonicParanoid, and Broccoli-are helpful for initial orthology predictions. Results produced using OrthNet were generally outliers but could still provide detailed information about gene colinearity. With our Brassicaceae dataset, slight discrepancies were found across the orthology inference algorithms, necessitating additional analyses such as tree inference to fine-tune results.

  PublisherOA PDFDOI

• Author response for "Bats as instructive animal models for studying longevity and aging"

  2024-09-03

  peer-review
  PublisherDOI

Recent grants

• Collaborative research: Understanding the role of developmental bias in the morphological diversification of bat molars

  NSF · $661k · 2020–2023

• Dimensions: Collaborative Research: Discovering genomic and developmental mechanisms that underlie sensory innovations critical to adaptive diversification

  NSF · $231k · 2017–2020

• NIH Grant R21OD02298803

  NIH · $157k · 2020

• NIH Grant R21OD022988

  NIH · $269k · 2019

• Collaborative Research: Genetic Determinants of MammalianLlimb Biodiversity

  NSF · $520k · 2013–2016

Frequent coauthors

• Alexa Sadier

  University of California, Los Angeles

  30 shared

• Daniel J. Urban

  28 shared

• Laurel R. Yohe

  Planetary Science Institute

  27 shared

• Lisa Noelle Cooper

  Northeast Ohio Medical University

  22 shared

• Jennifer A. Maier

  University of California, Los Angeles

  17 shared

• Neal Anthwal

  STMicroelectronics (United Kingdom)

  17 shared

• Liliana M. Dávalos

  Stony Brook University

  14 shared

• Sharlene E. Santana

  Burke Museum of Natural History and Culture

  13 shared

Labs

• Sears LabPI

Education

• Ph.D., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2000

• M.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  1996

• B.A., Environmental Science

  University of California, Los Angeles

  1994