8.29.26

Time flies when you turn up the heat

A member of Richard’s lab recording data on the fruit fly population.

Aging is a natural process that happens in all living things. As organisms get older, their cells and DNA slowly become damaged. Some of this wear and tear happens naturally as cells do their jobs. Other damage can be brought on by stressful environmental conditions, such as high temperatures. 

Richard is a scientist interested in factors that affect aging. He is curious about why some individuals of the same species live longer than others. Similarly, some individuals reach maturity faster, or in other words, have shorter development time. These topics can be tricky to study because lifespan, or how long an organism lives, can take a long time to observe. For this reason, Richard studies aging in flies. Flies are especially useful for questions like these because they are small, easy to raise, and have short life cycles. This allows researchers to study growth, development, and aging in a short amount of time.

Each fruit fly is placed in their own container that is labeled with an assigned ID number, their sex, and the date they emerged as an adult. 

To start, Richard, along with members of his lab, wanted to look at how temperature affects development time and lifespan. Every organism has a range of temperatures where it grows and functions best. If the environment is much warmer or colder than that range, it can cause stress. Temperature also affects how quickly many biological processes happen. For example, in warmer temperatures, metabolism, or the process of turning food into energy, usually speeds up. Because of this, young organisms often grow and develop faster in warmer conditions. Faster development and metabolism can cause cell damage to build up more quickly.

Richard’s lab includes scientists at all stages – from undergraduates to graduate students, and researchers who already have advanced degrees. They worked together to investigate how temperature affects the development time and lifespan in a fruit fly species. They knew from previous studies that female fruit flies usually live longer than males. Richard’s lab wanted to build on past work and figure out how temperature affects this pattern. 

The vials with fruit flies inside are kept in incubators set to either 18°C or 22°C.

To test the effects of temperature, the research team raised fruit flies in two conditions: 18°C and 22°C. Female flies laid eggs, each in their own container, and the eggs were allowed to develop. Each day, the team recorded when adult flies emerged from their pupal cases and whether they were male or female. Development time was measured as the number of days it took each fly to grow from an egg into an adult.

After the flies emerged, they were moved to a separate container and kept at the same temperature treatment. This ensured the team could keep track of how long each fly lived. The adult flies were all given the same food and kept at the temperatures that they were raised in. Each day, members of the team would carefully check each vial and look for deaths. By knowing the dates that each fly had emerged as an adult and their death date, they could calculate lifespan. Throughout his experiment, the team measured lifespan and development time in thousands of male and female fruit flies!

Featured scientist: The Richard Meisel lab at the University of Houston

Flesch–Kincaid Reading Grade Level = 9.1

Additional Teacher Resources

4.29.26

The chromosome advantage: Lifespan differences across sexes

Nicole Riddle looking at fruit flies under the microscope

The activities are as follows:

Many factors affect lifespan, or how long an organism lives. Different species, and individuals within a species, will all live to different ages. Across species, things like body size, rate of metabolism, and genetics can all come into play. For example, larger animals tend to live longer than smaller organisms. Within a species, genetics and environmental conditions, such as being able to find food, the presence of predators, and disease, will also impact survival.

Scientists have also noticed that in many animal species, one sex tends to live longer than the other. Sometimes it is the males, and sometimes it is the females. Why might this be? To better understand aging differences across sexes, a group of scientists decided to work together. Each scientist studies a different species, so by combining their knowledge, they can look for patterns and see if there are consistent factors that are the cause.

Jamie Walters running DNA extractions in the lab.

Nicole and Jamie are two scientists in this group. Nicole studies fruit flies, while Jamie studies moths and butterflies. Even though fruit flies and moths are both insects, sex is determined differently. In most animals, biological sex is determined by specific chromosomes. These structures are inside cells and carry genetic information. Individuals usually have two sex chromosomes. Whether those two chromosomes are the same or different often determines whether their bodies develop as male or female.

In fruit flies, females have two of the same sex chromosomes (XX), while males have two different sex chromosomes (XY). In moths and butterflies, the pattern is reversed. Males have two of the same sex chromosomes (ZZ), while females have two different ones (ZW).

Nicole and Jamie wondered if having two different sex chromosomes might affect lifespan. When an individual has only one copy of a particular chromosome—like the X in XY males or the Z in ZW females—there is no second copy for the genes on that chromosome. If that single copy contains a harmful mutation or becomes damaged, the organism cannot rely on a second copy to make up for it. On the other hand, individuals with two of the same sex chromosomes (XX or ZZ) have a kind of “genetic backup”. This extra protection might reduce the risk of problems that could lead to an earlier death.

To test their idea about sex chromosomes and lifespan, Nicole and Jamie designed an experiment called a survival assay. A survival assay is a laboratory experiment in which scientists carefully track how long organisms live under controlled conditions. By keeping the environment consistent, scientists can focus on the specific factor they want to study.

Nicole works with fruit flies (left) and Jamie studies pantry moths (right). 
 
Plodia interpunctella female by Pekka Malinen, Luomus is licensed under CC BY-SA 4.0.

Nicole performed her survival assay with the fruit fly species, Drosophila melanogaster. Jamie worked with a pantry moth species called Plodia interpunctella. Both scientists already raise these species in their labs and carefully document the life cycles and age of each individual.

To set up their assays, Nicole and Jamie chose individuals that had emerged from the pupae stage around the same time. This step was important because they wanted to make sure all individuals had the same starting point. If some individuals had emerged a lot sooner, the results would not be accurate.

Nicole collected 100 female and 100 male fruit flies, and Jamie collected 60 male and 60 female moths. The insects were given plenty of food and kept in good environmental conditions, such as appropriate temperature and humidity. By reducing stress, they could better observe natural lifespan differences between males and females, rather than differences caused by harsh conditions.

Each day, Nicole and Jamie recorded how many males and females were still alive. This careful daily tracking allowed them to see how survival changed over time. The survival assay continued until the last individual had died. By the end of the experiment, Nicole and Jamie had detailed data showing how long males and females lived in each species. These results would help them test whether having two identical sex chromosomes—or two different ones—might influence lifespan.

Featured scientists: Nicole Riddle (she/her) from the University of Alabama at Birmingham and Jamie Walters (he/him) from the University of Kansas.

Flesch–Kincaid Reading Grade Level = 9.9

Additional Teacher Resources:

  • Scientist profiles: Nicole Riddle and Jamie Walters both have scientist profiles to supplement this activity. Have students read more about their research, personal lives, and advice they have as a way to share contemporary scientist role models with students!
  • You can learn more about the IISAGE (Integration Initiative: Sex, Aging, Genomics, and Evolution) project here. This initiative is a collaborative effort to learn more about the mechanisms of sex-specific differences in aging and features research with a variety of organisms.
  • Visit this page for additional scientist profiles and Data Nuggets featuring IISAGE research.