About

Neil D. Tsutsui is a Professor and Michelbacher Chair at the UC Berkeley Rausser College of Natural Resources, serving as Faculty Director of the UC Berkeley Central Sierra Field Research Stations. He holds a PhD in Ecology, Behavior, and Evolution from UC San Diego and a BA in Biology, specializing in Marine Science, from Boston University. His research focuses on social insects, primarily ants, exploring their communication, behavior, ecology, and evolution. His work involves both field and laboratory studies, examining chemical communication, behaviors, and the genetics of individuals, populations, and species. Tsutsui is also dedicated to the preservation of biodiversity and open spaces, actively engaging in public talks, educational outreach to public schools, and professional service to cities and the East Bay Regional Parks.

Research topics

• Biology
• Ecology
• Evolutionary biology
• Zoology
• Communication

Selected publications

• Social Organization Is Associated With Relaxed Selection on Worker Genes in Highly Polygyne Ants

  Ecology and Evolution · 2025-07-01 · 1 citations

  articleOpen accessSenior author

  ABSTRACT Ants display a diversity of social structures reflected by differences in caste, nest, and colony organization. Previous research has shown that highly eusocial insects (Hymenoptera) exhibit genome‐wide signatures of relaxed selection due to their smaller effective population sizes. However, it is unknown how the colony structure itself may shape the evolution of eusocial species through its effects on the worker caste. Worker ants are typically sterile or produce only male offspring, so traits affecting their behavior evolve mainly through kin selection. Kin selection is predicted to be strongest when relatedness within the colony is high, as in species with a single queen per colony (monogyne). In these cases, the reproductive individuals who are the recipients of worker helping behavior are more likely to carry the same allele for that behavior, with probability proportional to relatedness between worker and reproductive. In contrast, in species with multiple queens and lower relatedness, like weakly or highly polygyne ants, there is a higher chance that altruistic behavior benefits non‐relatives. These colony structures are predicted to weaken kin selection, leading to more relaxed selection on worker‐biased genes. We find some evidence in highly polygyne species that genes with worker‐biased expression experience more relaxed selection compared to queen‐biased or non‐differentially expressed genes. However, this pattern does not appear to hold consistently across species with lower or more variable queen numbers, where the degree of relaxed selection in worker genes shows no clear association with average queen number per nest. This may point to possible compensatory mechanisms present in these contexts to counteract relaxed selection in workers or that these predicted patterns are too subtle to be detected with current methods, highlighting areas of future study.

  PublisherOA PDFDOI

• Social organization shapes worker gene evolution in unicolonial ants

  2025-02-07

  preprintSenior author

  Ants display a diversity of social structures reflected by differences in caste, nest, and colony organization. Previous research has shown that highly eusocial insects (Hymenoptera) exhibit genome-wide signatures of relaxed selection due to their smaller effective population sizes. However, it is unknown how colony structure itself may shape the evolution of eusocial species though its effects on the worker caste. Worker ants typically either produce only male offspring or are sterile, thus worker traits evolve primarily through kin selection. Here, we predict that workers should be subject to selective forces of varying strength according to the social context of their species. This follows from kin selection theory, which predicts that kin selection should be more effective in contexts of high relatedness between the altruist (worker) and beneficiary (nestmates), such as in single-queen (monogyne) contexts. Alternatively, in species with many queens and low intra-nest relatedness, such as polygyne or unicolonial species, kin selection should be less effective, ie. more relaxed on genes controlling worker traits. We show that worker-specific genes in unicolonial species show significantly more relaxed selection compared to queen-specific or non-differentially expressed genes. Interestingly, we also find that levels of relaxed selection in worker genes and average queen number per nest do not have a strong correlation in species with only several or varying numbers of queens per nest. This may point to possible compensatory mechanisms present in these contexts to counteract relaxed selection in workers, or that these predicted patterns are too subtle to be detected with current methods, highlighting areas of future study.

  PublisherDOI

• Chemical species recognition in an adaptive radiation of Hawaiian <i>Tetragnatha</i> spiders (Araneae: Tetragnathidae)

  Proceedings of the Royal Society B Biological Sciences · 2024-04-09 · 6 citations

  articleOpen access

  Studies of adaptive radiations have played a central role in our understanding of reproductive isolation. Yet the focus has been on human-biased visual and auditory signals, leaving gaps in our knowledge of other modalities. To date, studies on chemical signals in adaptive radiations have focused on systems with multimodal signalling, making it difficult to isolate the role chemicals play in reproductive isolation. In this study we examine the use of chemical signals in the species recognition and adaptive radiation of Hawaiian Tetragnatha spiders by focusing on entire communities of co-occurring species, and conducting behavioural assays in conjunction with chemical analysis of their silks using gas chromatography-mass spectrometry. Male spiders significantly preferred the silk extracts of conspecific mates over those of sympatric heterospecifics. The compounds found in the silk extracts, long chain alkyl methyl ethers, were remarkably species-specific in the combination and quantity. The differences in the profile were greatest between co-occurring species and between closely related sibling species. Lastly, there were significant differences in the chemical profile between two populations of a particular species. These findings provide key insights into the role chemical signals play in the attainment and maintenance of reproductive barriers between closely related co-occurring species.

  PublisherOA PDFDOI

• Variable viral loads and immune response in an invasive ant's native and introduced ranges

  Diversity and Distributions · 2024-06-01 · 2 citations

  articleOpen access

  Abstract Aim Pathogens can play an important role in biological invasions. Introduced populations may be particularly vulnerable to pathogens due to factors such as low genetic diversity and high population density. However, introduced populations that escape their natural pathogens may reallocate resources away from immunity and towards growth and reproduction. Interestingly, introduced ants have been suggested to have increased tolerance to new pathogens, contributing to their success as introduced species. In this study, we aimed to investigate whether introduced Argentine ant populations harbour different viral loads compared to native populations and if these differences were related to immunity‐related gene expression. Location The study was conducted across the native range of Argentine ants in Argentina and four introduced regions in California, France, Australia and New Zealand. Methods We used RT‐qPCR to quantify viral loads and gene expression in the ants. We analysed 15 different potentially pathogenic viruses across the Argentine ant's native and introduced ranges. Results We found that five viruses, LhuPcV1, LhuPiLV1, LhuCV1, Kashmir Bee virus and LHUV‐1, presented high loads in Argentine ants compared to the other viruses we screened. We found a significant effect of range on viral infections: high viral loads were commonly found in ants from introduced populations, which also exhibited increased immune gene expression. We found highly significant correlations between viral loads and expression of immune and metabolic genes. However, these associations were not fully consistent across the studied regions, indicating the complexity of eco‐immunological phenomena. Main Conclusions Our results suggest that introduced Argentine ant populations host different viral communities compared to native populations and that these differences are correlated with changes in immunity‐related gene expression. The study highlights the complex role of pathogens in biological invasions and the importance of considering eco‐immunological factors when assessing the impact of introduced species.

  PublisherDOI

• Reference genome of the kidnapper ant, <i>Polyergus mexicanus</i>

  Journal of Heredity · 2024-09-09

  articleOpen accessSenior author

  Polyergus kidnapper ants are widely distributed, but relatively uncommon, throughout the Holarctic, spanning an elevational range from sea level to over 3,000 m. These species are well known for their obligate social parasitism with various Formica ant species, which they kidnap in dramatic, highly coordinated raids. Kidnapped Formica larvae and pupae become integrated into the Polyergus colony where they develop into adults and perform nearly all of the necessary colony tasks for the benefit of their captors. In California, Polyergus mexicanus is the most widely distributed Polyergus, but recent evidence has identified substantial genetic polymorphism within this species, including genetically divergent lineages associated with the use of different Formica host species. Given its unique behavior and genetic diversity, P. mexicanus plays a critical role in maintaining ecosystem balance by influencing the population dynamics and genetic diversity of its host ant species, Formica, highlighting its conservation value and importance in the context of biodiversity preservation. Here, we present a high-quality genome assembly of P. mexicanus from a sample collected in Plumas County, CA, United States, in the foothills of the central Sierra Nevada. This genome assembly consists of 364 scaffolds spanning 252.31 Mb, with contig N50 of 481,250 kb, scaffold N50 of 10.36 Mb, and Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness of 95.4%. We also assembled the genome of the Wolbachia endosymbiont of P. mexicanus-a single, circular contig spanning 1.23 Mb. These genome sequences provide essential resources for future studies of conservation genetics, population genetics, speciation, and behavioral ecology in this charismatic social insect.

  PublisherDOI

• Genome assembly of the winter ant, <i>Prenolepis imparis</i>

  Journal of Heredity · 2024-12-09

  articleOpen accessSenior author

  The winter ant, Prenolepis imparis, is one of the most common, widespread, and conspicuous ant species in North America. P. imparis is well adapted to cold climates, and consequently, is often noted as the only active ant species during colder months. This specialized life history makes P. imparis a useful model organism for exploring thermal physiology and understanding the potential impacts of a warming climate on insects. Phylogeographic studies have revealed deeply divergent lineages across North America, as well as a single collection of an apparent social parasite in California. In light of its distinctive cold adaptation and recently discovered geographic diversity, a better understanding of the underlying genetic patterns of the winter ant is valuable to future conservation efforts for this species. Here, we present a high-quality genome assembly of P. imparis from Santa Clara County, California. This genome assembly consists of 787 scaffolds spanning 327.3 Mb, with contig N50 of 901.9 kb, scaffold N50 of 18.7 Mb, and BUSCO completeness of 96.5%. This genome assembly provides an essential foundation for future studies of the winter ant and will be particularly useful for understanding the genetic basis of thermal adaptation, cold resistance, chemical ecology, and the resilience of organisms in response to a changing climate.

  PublisherOA PDFDOI

• Author response for "Variable viral loads and immune response in an invasive ant's native and introduced ranges"

  2024-04-30

  peer-review
  PublisherDOI

• Colony discrimination and competition in the eusocial trematode, Himasthla rhigedana

  Research Square · 2024-02-20

  preprintOpen accessSenior author

  Abstract The California horn snail ( Cerithideopsis californica ) hosts a diverse community of trematode parasite species, yet these species rarely co-occur in the same host. Some trematodes in this community competitively exclude conspecifics and heterospecifics using a soldier caste. How these trematodes can distinguish colonymates from competitors is unknown. Here we examine patterns of colony discrimination in Himasthla rhigedana , a marsh-dwelling species of parasitic trematode that possesses a soldier caste in their intermediate snail hosts. Aggression assays pairing colonies against multiple opponents demonstrate that H. rhigedana distinguish between conspecific colonies, consistently directing more attacks towards colonies collected from a distant marsh. We demonstrate that conspecific interactions between colonies are predominantly symmetrical (both colonies attack during encounters), and that the likelihood of aggression is the same whether the attacker soldier is “sterile” (soldier redia with no germinal balls) or an “intermediate” (soldier redia with developing germinal balls). Recognizing heterospecific or conspecific threats is a necessary function for the evolution of soldier castes, which almost exclusively occur within eusocial insects. By finding parallels in disparate phyla, our results in H. rhigedana provide a foundation for understanding the evolution of colony discrimination generally, as well as in trematode species and other parasite taxa with similar competitive interactions.

  PublisherOA PDFDOI

• Author response for "Variable viral loads and immune response in an invasive ant's native and introduced ranges"

  2024-02-21

  peer-review
  PublisherDOI

• An assemblage-level comparison of genetic diversity and population genetic structure between island and mainland ant populations

  Evolution · 2024-07-09 · 1 citations

  article

  Island biotas provide unparalleled opportunities to examine evolutionary processes. Founder effects and bottlenecks, e.g., typically decrease genetic diversity in island populations, while selection for reduced dispersal can increase population structure. Given that support for these generalities mostly comes from single-species analyses, assemblage-level comparisons are needed to clarify how (i) colonization affects the gene pools of interacting insular organisms, and (ii) patterns of genetic differentiation vary within assemblages of organisms. Here, we use genome-wide sequence data from ultraconserved elements (UCEs) to compare the genetic diversity and population structure of mainland and island populations of nine ant species in coastal southern California. As expected, island populations (from Santa Cruz Island) had lower expected heterozygosity and Watterson's theta compared to mainland populations (from the Lompoc Valley). Island populations, however, exhibited smaller genetic distances among samples, indicating less population subdivision. Within the focal assemblage, pairwise Fst values revealed pronounced interspecific variation in mainland-island differentiation, which increases with gyne body size. Our results reveal population differences across an assemblage of interacting species and illuminate general patterns of insularization in ants. Compared to single-species studies, our analysis of nine conspecific population pairs from the same island-mainland system offers a powerful approach to studying fundamental evolutionary processes.

  PublisherDOI

Recent grants

• LTREB Collaborative Proposal: Large-scale removal of introduced ants as a test of community reassembly

  NSF · $178k · 2017–2022

• Collaborative Research: Scents of Self: How Trade-offs Shape Self/Non-self Recognition Cues in a Supercolonial Insect

  NSF · $605k · 2016–2020

Frequent coauthors

• Andrew V. Suarez

  University of Illinois Urbana-Champaign

  55 shared

• David A. Holway

  University of California, San Diego

  26 shared

• Ted J. Case

  University of California, San Diego

  23 shared

• Brian R. Johnson

  The Aerospace Corporation

  20 shared

• Deborah R. Smith

  17 shared

• Lori Lach

  James Cook University

  16 shared

• J. Spencer Johnston

  Texas A&M University

  15 shared

• Susanta K. Behura

  University of Missouri

  14 shared

Education

• Ph.D., Biology

  University of California San Diego

  2008

• B.A.

  Boston University

  1995