ANNA TSIOULIAS/THE HOYA | The Department of Biology hosted Jen White, an insect ecology professor at the University of Kentucky, for a guest lecture on the ways that bacteria affect spider reproduction March 20.
An insect ecology professor at the University of Kentucky explored her research on how bacteria affects spider reproduction during a March 20 lecture.
The researcher, Jen White, presented her findings on bacterial endosymbionts, microbes that live inside their host’s body and pass from parent to offspring. The department of biology hosted White’s conversation as part of their seminar series, which brings scholars from other universities to discuss their research.
White said people often only imagine bacteria in terms of diseases or microbes, but her research illustrates how bacteria can impact hosts like insects.
“All eukaryotes are dependent on ancient symbioses that have become internalized and part of our bodies, like mitochondria or chloroplasts if you happen to be a plant,” White said during the event. “But some bacteria take this relationship further, embedding themselves within their hosts in ways that dramatically alter their biology.”
Unlike contagious bacteria, White said, the microbes passed from parent to offspring are locked within their hosts, making the bacteria in the spiders entirely dependent on transmission.
“They’re obligate from the perspective of the bacteria but not from the perspective of the spider host,” White said. “The bacteria can’t live outside the host, they have reduced amount of genetic information, they haven’t been out and about in the world, they can’t cope without their host.”
While the bacteria needs male and female spiders to reproduce, male hosts are evolutionary dead-ends, meaning that because their sperm cells lack the necessary cytoplasm for bacterial transmission, male spiders cannot pass the genetic information.
White said these bacteria have evolved ways that manipulate their hosts’ reproductive systems to favor infected female spiders instead of males.
“These endosymbionts can feminize genetic males into functional phenotypic females,” White said. “They can cause parthenogenesis, where they just turn off sex altogether and make every offspring a clonal female. You can have male killing, which seems counterproductive at first, but if you can kill those boys in a way that benefits the fitness of their infected sisters, then it becomes genetically advantageous.”
White said one manipulation strategy bacteria employ is cytoplasmic incompatibility, where the bacteria sabotage infected males’ sperm so they can only produce viable offspring with infected females.
“You can think about it almost as a sabotage and rescue system,” White said. “Bacteria sabotage the sperm as it’s being produced in a way that will not create fertile, viable offspring unless that sperm unites with an egg that also contains the same bacteria or some other bacteria that has the same rescue factor.”
Over time, this process allowed infected female spiders and their bacteria to dominate the population — a pattern White explored in her research on the spider species Mermessus fradeorum, which can host up to five different endosymbionts.
Through controlled breeding experiments, White and her team discovered that spiders infected with all five bacteria were almost exclusively female. Among them, they identified one strain of bacteria as a necessary component for feminization.
Eliza Zaroff (CAS ’25) said these findings about bacteria reshape how we should think about ecology and evolution.
“They actively shape their hosts’ biology and, as a result, entire populations,” Zaroff told The Hoya. “As climate change alters temperature patterns, understanding these microbial relationships could give us insight into broader ecological shifts.”
White found that spiders reared in warmer conditions produced more males, and the effect even carried over to the next generation, saying the findings suggest temperature plays a critical role in spider sex determination.
“We saw the uninfecteds has a nice even sex ratio, and the offspring of the feminized were majority female,” White said. “This shows that high temperature suppresses feminization.”
Emma Lederer, a fourth-year doctorate in biology student who attended the event, said these findings highlight a crucial intersection between microbial ecology and climate change.
“A lot of ecology research is really focused on how things are going to adapt to climate change,” Lederer told The Hoya. “Normally, it’s like everything is bad with climate change, but maybe with this species it’s neither good nor bad, it’s already existing in this range of temperatures.”
Zaroff said the lecture highlighted the microbial world’s powerful yet underappreciated influence over other organisms.
“I think it’s really cool how the bacteria are changing how their hosts reproduce; they’re not just passively living in them,” Zaroff said. “This lecture really made me think about how microbes can have a much bigger impact on biological processes than we often appreciate.”