Effects of inbreeding in crickets

Illinois State University dual contributors.

Featured Scientist: Kylie Hampton, M.S. 2020, School of Biological Sciences, Illinois State University

An image of Kylie Hampton at a research laboratory, looking into a microscope.

Birthplace: Chicago, IL

My Research: I am interested in understanding how the female immune system is impacted by mating in decorated crickets. 

Research Goals: I hope to continue to work in the field of Behavioral Ecology because it provides the opportunity to ask really exciting research questions. I am specifically interested in mating behavior and the study of the insect immune system. However, I have diverse research interests and would be excited to gain experience in other fields as well! 

Career Goals: I hope to be a research assistant in a lab that has similar research interests. I really enjoy doing lab work involving microscopy and microbiology but I’d be excited to give field work a try, too! 

Hobbies: I love listening to true crime podcasts, drinking wine, reading, and painting!

Favorite Thing About Science: I love science because it’s an entire field devoted to understanding the world. Every project that I have been a part of has been my personal attempt to contribute something new or to support existing knowledge, which I find to be a really rewarding experience. 

Featured Scientist: Ian Rines, PhD (Anticipated Spring 2023), School of Biological Sciences, Illinois State University

An image of Ian Rines at a research laboratory. There is a transparent box in front of him and room is illuminated in red light.

Birthplace: Charleston, SC

My Research: Male crickets produce compounds that they feed to females during mating. I study how male crickets use these compounds to manipulate female behaviors during and after reproduction. 

Research Goals: I’m interested in the study of animal behavior and am broadly interested in continuing to work with insects. I would like to use molecular techniques to change how genes are expressed in crickets. These techniques should help me to understand what causes certain behaviors. 

Career Goals: I’m not entirely sure what I’d like to do in the future, but right now, I’m hoping to do research in an academic setting.

Hobbies: I enjoy reading, watching movies, and (mild) hiking. 

Favorite Thing About Science: My favorite thing about science is actually doing the science itself. It’s fulfilling to design and carry out experiments to get at an answer to a question. 

Organism of Study: We study the decorated cricket, Gryllodes sigillatus

An image of a female decorated cricket. She is crouching down to grasp a clear, globular, object attached to her body. The male is in the distance, walking away from the female.
G. sigillatus, or the decorated cricket. Pictured is a male (left) and a female (center). This pair has just finished mating and the female is bending around to remove the gift (the clear capsule she is grasping). 

Field of Study: Behavioral Ecology 

What is Behavioral Ecology? Animal behavior is shaped over time based on ancestry and environmental surroundings. Good behaviors, those that help animals to survive, become more common. Bad behaviors, those that do not help animals survive, become less common. Behavioral ecology is the study of how these behaviors are formed. 

Check Out My Original Paper: “Effects of inbreeding on life-history traits and sexual competency in decorated crickets” 

A QR code that links to the original publication.
QR code to original publication

Citation: S.K. Sakaluk, J. Oldzej, C.J. Hodges, C.L. Harper, I.G. Rines, K. J. Hampton, K.R. Duffield, J. Hunt, B.M. Sadd, Effects of inbreeding on life-history traits and sexual competency in decorated crickets. Anim. Behav. 155: 241-248 (2019). 

Research at a Glance: This paper presents the results of two undergraduate research projects from several years ago. We helped to write the results of their work for publication. We studied how inbreeding affects mating and offspring production in decorated crickets. The crickets were originally collected in New Mexico in 2001. They were mated several times to siblings to create genetically distinct lineages of crickets. To see the impact of extreme inbreeding, we measured the number of offspring that the female crickets produced. Not surprisingly, we found that inbred crickets had fewer offspring. Here, inbred crickets were from the lineages that experienced inbreeding. These offspring took longer to hatch and grow into adults. We also did another experiment to see how inbreeding impacts mating success. From that study, we found that inbred males are less successful at completing their steps in mating, which involve attaching a sperm package to the female’s genitalia. Surprisingly, we found that inbred females preferred inbred males from within their own line, that is, the males that were most closely related to them. This result seemed to contradict all the previous results found in the literature, which indicated that inbreeding had negative effects in these crickets. In general, inbreeding is considered a bad strategy for reproduction, as it can lead to inbreeding depression. Inbreeding depression is a reduction of reproductive output due to mating between relatives. 

Highlights: Experiment 1: In the first experiment, we examined the effects of inbreeding on the offspring. We looked at hatching and development times, the number of offspring produced, the offspring size, and various other outcomes of mating. In Figure 1, we compared the number of days that it took to hatch for inbred and outbred crickets. Here, outbred crickets are from lineages that did not experience inbreeding. We found that inbred crickets take longer to hatch. 

Figure 1. Hatching time of inbred and outbred offspring. The x-axis shows whether the crickets were inbred or outbred, while the y-axis is the average number of days that crickets took to hatch. Hatching time was the time from when the egg was laid to when the cricket emerged from the egg. Figure adapted from Sakaluk et al.2019.

In Figure 2, we compared the number of offspring that were produced from inbred and outbred crickets. We found that inbred crickets have fewer offspring than outbred crickets. 

Figure 2. Number of offspring from inbred and outbred matings. Again, the x-axis shows whether the crickets were inbred or outbred. The y-axis is the average number of offspring produced by females. Figure adapted from Sakaluk et al. 2019. 

In Figure 3, we looked at the amount of time that it took male and female offspring to develop into adults because sex is known to affect development time. We then compared development time for inbred and outbred crickets. We found that, regardless of sex, inbred crickets took longer to develop into adults. Overall, these results show that inbreeding can have negative impacts on the cricket offspring. 

Figure 3. Development time of inbred and outbred offspring by sex. The x-axis shows the sex of the crickets, while the y-axis indicates the average development time in days. Development time was characterized by how long it took crickets to reach sexual maturity. Figure adapted from Sakaluk et al. 2019.

Experiment 2: Our second experiment, where we studied the effects of inbreeding on mating success, yielded very surprising results. We observed the behaviors of several cricket mating pairs. We paired inbred males with inbred females and outbred males with outbred females, then watched them mate. Next, we paired inbred males with outbred females and outbred males with inbred females. We did this to make sure that we had all possible mating combinations (Table 1). To observe mating, we placed males and females into small plastic containers in a dark, warm room. We had the room illuminated by red light because crickets can’t see red light and it allowed us to observe them. 

A table of Mating Pairs. Pairs are as follows: 1. Inbred female by inbred male, 2. Inbred female by outbred male, 3. Outbred female by inbred male, and 4. Outbred female by outbred male.
Table 1. Layout of all mating combinations we observed. 

To successfully mate, male crickets must attach the sperm package to the female. We found that inbred males had a lower chance of successfully attaching the sperm package, regardless if they were paired with inbred or outbred females. We think that inbred males are just bad at mating. This is because previous research shows that males are more likely to experience the negative effects of inbreeding when it comes to the steps in mating. 

Surprisingly, inbred females were more likely to mate with inbred males. Given these results, we cannot simply conclude that “inbreeding is bad”, because inbred females seem to prefer mating with inbred males. While our experiments don’t tell us why this is happening, we have several ideas. Our inbred lineages of crickets have been isolated within their inbred lines from a long time. It is possible that females don’t recognize males from outside of their lineages. They may not see these outsider males as acceptable mates because they are only ever exposed to one type of male, that is, their inbred counterparts.

What My Science Looks Like: The image the below is a mating chamber. We illuminate the room in red light, then observe the mating behavior through this observation chamber.

An image of the cricket mating chamber. It is a translucent plastic box with air holes on the sides.
Image of a mating observation chamber. 

The Big Picture: Studying the effects of inbreeding in crickets may not seem like an important thing to research. Our cricket species is not endangered or declining, but the same cannot be said for many other insect species. Substantial declines have been reported in bees, moths, butterflies, dragonflies, and other insects. There are approximately 1.5 million species on our planet, and insects account for more than half of those species. Compared to most vertebrates, it is much harder to determine whether an insect species is declining. When species go into decline, they are more likely to experience inbreeding and this can negatively impact the species. Inbreeding can harm offspring by shortening their lifespans, damaging their health, and reducing their reproductive output. Given these negative effects, we would expect inbred individuals to avoid mating each other. However, our research shows that animals may not always avoid inbreeding. This is particularly important because we also find that inbred males are less successful at mating. Our study has led to surprising results and further unanswered questions. Future research should help to unravel these mysteries, and focus on the effects of inbreeding on multiple traits (such as mating), not just life history traits

Decoding the Language: 

Compound: A chemical compound is made up of two or more elements. For example, table salt (NaCl) is a chemical compound because it is made up of both sodium (Na) and chlorine (Cl). 

Gryllodes sigillatus (G. sigillatus): The scientific name for the decorated cricket.

Inbreeding: Reproduction between closely related animals. 

Inbreeding depression: The reduction of reproductive output due to mating between relatives. 

Life history traits: Traits that may influence the fitness of an organism, specifically those involved in growth, survival, and reproduction. 

Mating success: In the context of our study, mating success refers to the successfully completing all the steps in copulation, starting with a male courting and a female terminating sperm transfer. 

Molecular techniques: A method used to manipulate and understand DNA, RNA, or protein. 

Outbred: In the context of this study, these are crickets that were not subjected to full-sibling matings and were allowed to mix freely. 

Reproductive output: The number of offspring produced by a female. 

Sperm package: To mate, male decorated crickets will attach a sperm package to the genitalia of the female. The package contains a combination of proteins that the female will feed on after it is attached to her body. As she feeds, sperm from the package will enter the female’s reproductive tract. The longer the package is attached to her body, the more likely it is for the female to be fertilized by the male’s sperm. It is in the male’s best interest to successfully attach the package and to make it as tasty as possible. This lengthens the amount of time that the female feeds and the amount of time that the sperm has access to her reproductive tract. 

Learn More: 

Insect decline

Synopsis edited by: Rosario Marroquin-Flores (she/her/hers), PhD (Anticipated Spring 2022), School of Biological Sciences, Illinois State University 

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