Naturally Inspiring

April 16, 2023April 17, 2023

What makes a fly attractive?

By Dexter Lowe

A review of the research article Divergent selection on behavioural and chemical traits between reproductively isolated populations of Drosophila melanogaster, by Jin, Barbash, and Castillo

(image credit ScienceSourceimages)

Why the Fly?

The unassuming fruit fly is to many people merely a nuisance; however, it has led to breakthroughs so significant to human life it has won numerous Nobel prizes (McKie). Drosophila melanogaster is a species of fly that belongs to the genus Drosophila. These flies have a short lifespan, mature very quickly, and have a genetic make-up that is very similar to humans. Because of these traits the fruit fly is known as a model organism, used in empirical studies to help us understand a wide range of biological phenomena. One such study was conducted in 2022 by researchers from Cornell University and the University of Nebraska, and could possibly provide insight into the factors of divergent intrasexual and intersexual selection (Jin et al., 2022).

Sexual selection is an important evolutionary factor because it can produce new genetic variation, and can be just as crucial to an organism’s success as natural selection. It can be further broken down into intrasexual and intersexual selection. The former pertains to competition between individual organisms of the same sex, with the goal of accessing a mate of the other sex. The latter is closely intertwined, and refers to whom members of differing sexes choose to mate with. Together, these selection factors can work together to create a more genetically diverse population.

Going further, when a population becomes separated, whether it is by physical separation (geographic isolation), different times of reproduction (temporal isolation), or different behaviors (behavioral isolation) it can become reproductively isolated. This isolation can happen relatively quickly, due to sexual selection creating expeditious changes in mating preferences. But what changes are being made, and why do they matter? These are the questions being pursued with fruit flies (Jin et al. 2022).

What’s more important? Behavior or Chemical Traits?

The researchers in this study attempted to determine what traits were under divergent selection by using strains of fruit flies that modeled larger populations that had asymmetrical reproductive isolation. Reproductive isolation is the process of preventing matings between individuals from different populations. This can be achieved by a number of different mechanisms such as geographic isolation, behavioral isolation, or physiological differences. You may ask, how can reproductive isolation be asymmetrical? This occurs when one strain mates without preference, while the other strain has preference for partners of the same strain only. Examining asymmetrical isolation can help researchers pinpoint which traits, whether it is chemical or behavioral, makes the difference in preference.

In this case, Drosophila melanogaster populations from around the world are reproductively isolated by differing behavioral and chemical traits. This is a result of divergent selection, which occurred when two strains of fruit flies were separated geographically. Because of this separation they began to develop different diverse behaviors and chemical signals. Knowing this, the goal of the research was to determine “which specific male traits are females selecting, and are these traits under divergent sexual selection?” (Jin et al., 2022).

Evidence

The two strains that were used in this research study were denoted as M-type and Z-type, and were from different territories. The Z-type stayed in the ancestral territory of southern Africa. The M-type strains were those that had left Africa 10,000 to 15,000 years ago to locations in Europe and North America. With a physical separation of this nature the two strains became geographically isolated. Courtship traits and cuticular hydrocarbons (CHCs) have been under divergent selection during this separation, creating diversity in both Z-type and M-type strains. Geographic isolation over a time period this large for a species with a relatively quick lifespan resulted in an incompatibility to mate between strains (Jin et al., 2022). The reproductive isolation between these strains was asymmetric, meaning that M-type females would mate with both M- and Z-type males, while Z-type females preferred to mate with only Z-type males.

To examine whether divergent selection is currently ongoing, researchers examined cuticular hydrocarbons, for differences in compound abundance. Cuticles are present in many insects and are a main component of the exoskeleton. CHCs are thought to have waterproofing functions, but to also act as a type of communication signal (Menzel et al., 2017). By determining the abundance of different compounds found on the CHCs of different strains, researchers can narrow in on commonalities and differences. These differences could play a role in why one strain may have successful copulation amongst members of the same strain, and unsuccessful encounters with a different strain.

They also sorted mating behaviors they put into the categories of “separate, engaging, singing, singing-2, scissoring, circling, attempted copulation, and copulating” (Jin et al., 2022). It was established that courtship initiation would be recorded after non “separate” behaviors occurred. In other words, if the fly’s were interacting in any capacity it was considered a courtship behavior.

Once data was compiled, it was statistically analyzed to examine courtship behavior and plasticity. They concluded that courtship of Z-type and M-type males is significantly different, and that geographic strains are reproductively isolated. In addition, they found that male courtship behavior and cuticular hydrocarbons are plastic. A plastic trait is one that has the ability to change when presented with different conditions in the environment. In other words, the CHCs and courtship behavior changed in different settings. One example of behavior that Z-type strains used and was not found in M-type flies was scissoring, which is quick opening and closing of the wings. They also observed Z-type males spending less time singing on average (Jin et al., 2022). CHC compound amounts varied when males were presented with different strains of females, displaying that they are plastic and could play a role in courtship.

The conclusion of reproductive isolation arose from M-type males and Z-type females producing larvae much less than crosses between Z-type males and Z-type females (Jin et al., 2022). This exhibits that if two individuals cannot produce viable offspring with one another they have become reproductively isolated.

Now What?

While the results of the study did show divergent selection and asymmetrical reproductive isolation, more experiments need to be conducted to determine the role of traits under selection. For example, it was unclear whether African male behaviors (Z-type) had developed different behaviors. It was also expressed several times that sample sizes were too low, resulting in an inability to determine if some male strains were significantly different from one another (Jin et al., 2022). It may be beneficial to revisit these crosses with a larger sample size to increase the confidence of any significant results.

It was determined that four out of the five examined CHC compounds had differences among strains, but the role of these differences was not explained. Furthermore, without knowing what job the traits or compounds in the CHCs do, further exploration into the significance of different CHC compounds is needed to figure out their role in the courtship puzzle. This experiment could be easily replicated with greater sample sizes, and further emphasis on cuticular hydrocarbon analysis, to corroborate the results of Jin et al,. 2022 and increase the importance Drosophila melanogaster has in modern evolutionary biology.

Further Reading

Dean M Castillo, Daniel A Barbash, Moving Speciation Genetics Forward: Modern Techniques Build on Foundational Studies in Drosophila, Genetics, Volume 207, Issue 3, 1 November 2017, Pages 825–842, https://doi.org/10.1534/genetics.116.187120

This journal article from 2017 provides a larger perspective on the discoveries that can be achieved with the genus drosophila. It was compiled by two of the authors from this research article; Dean Castillo and Daniel Barbash.

Mirzoyan Z, Sollazzo M, Allocca M, Valenza AM, Grifoni D and Bellosta P (2019) Drosophila melanogaster: A Model Organism to Study Cancer. Front. Genet. 10:51. doi: 10.3389/fgene.2019.00051

This review article provides a comprehensive list of the cancer research that Drosophila melanogaster has played a part in. Similar development of cancer in flies and humans are described. The relevance of fruit flies in scientific research for human disease is dramatic.

References

Jin, B., Barbash, D. A., & Castillo, D. M. (2022). Divergent selection on behavioural and chemical traits between reproductively isolated populations of Drosophila melanogaster. Journal of Evolutionary Biology, 35, 693 – 707. https://doi.org/10.1111/jeb.14007

Leslie, M. (2020, April 2). Proteins that sense light also sense taste, at least in fruit flies. Science. Retrieved March 4, 2023, from http://dx.doi.org/10.1126/science.abc0403

Markow, T. A. (2015, June 4). The natural history of model organisms: The secret lives of drosophila flies. eLife. Retrieved March 23, 2023, from http://dx.doi.org/10.7554/eLife.06793

McKie, R. (2017, October 7). Six Nobel prizes – what’s the fascination with the fruit fly? The Guardian. Retrieved March 23, 2023, from https://www.theguardian.com/science/2017/oct/07/fruit-fly-fascination-nobel-prizes-genetics

Menzel Florian, Blaimer Bonnie B., & Schmitt Thomas (2017). How do cuticular hydrocarbons evolve? Physiological constraints and climatic and biotic selection pressures act on a complex functional traitProc. R. Soc. B.284: 20161727. 20161727. Retrieved April 14th, 2023, from http://doi.org/10.1098/rspb.2016.1727

April 13, 2023April 13, 2023

Sizing up Salmon

By Grace Veenstra

This article covers the 2020 study by Ulaski, Finkle and Westley on the direction and magnitude of natural selection of body size among age-classes of seaward-migrating sockeye salmon.

“Bigger Isn’t Always Better”

The idea that “bigger is better” is a prevalent one in biology. Body size has a significant impact on fitness, the ability of organisms to survive and reproduce, across all branches of life. In wolves, a larger body size gives them greater success in grappling and subduing large prey like moose or elk (MacNulty et al., 2009). In dall sheep, a larger body size gives males a reproductive advantage when they compete for the right to mate, and since adult sheep may lose up to 16% of their body mass during winter, those with a higher body mass are more likely to survive (U.S. National Park Service, 2020). However, “bigger” is not always a “better” lifestyle method for some animals, and can be actively harmful to their chances of survival.

Insects and arthropods are limited in their body size because they breathe by soaking in oxygen like a sponge. If they are too large, they cannot absorb sufficient oxygen and die of hypoxia. It was only during the Paleozoic, when oxygen concentrations reached as high as 35% during the Carboniferous period, that insects were capable of gigantism, with some dragonflies as large as seagulls (Harrison et al., 2010). Furthermore, it is costly to support a large body mass: the larger the body, the greater the energy requirements and the more food is required to sustain the animal. There are also factors of predation, where a larger body size may reduce agility, increase detection by predators, or increase costs to reproduction (Blanckenhorn, 2000). In essence, how natural selection acts on size is complex. Understanding how size correlates with survival is important, particularly when we are examining the salmon populations of Alaska.

April 11, 2022April 14, 2022

Finish your antibiotics completely, the future depends on it!

Background

You’ve most likely had an infection that required treatment with antibiotics. At the time that you were prescribed antibiotics, you probably heard that familiar spiel about needing to take the entire course of antibiotics even if you feel better before finishing them. You might be wondering, why does it matter? Hopefully after reading this post you will be able to answer that question for yourself.

As you might imagine, bacteria developing the ability to survive antibiotic treatment is bad news for us. This means that over time, our commonly used antibiotics are becoming less effective at killing bacteria. As bacteria evolves more antibiotic resistance, we may no longer be able to treat common infections unless we come up with another alternative treatment. It is important that we try to delay the evolution of antibiotic resistance as much as we can to buy time to develop other effective treatments. So what are the driving forces of bacterial evolution and what can we do about it?

October 22, 2021October 26, 2021

Rat Microbiomes and Metabolites; a Way to Learn About the Human Stress Response?

Stress, Development, and the Microbiome

Stress, the sort that persists and comes from sources beyond our control, can be detrimental to our health, and even more so to the young (Luna R. et al. 2015). When outside sources of stress are present from a young age, normal development and the adult stress response is impacted in a way that makes healthy coping with stress more difficult throughout life (McEwen et al. 2011) (Eliand L. et al. 2013). Environmental stressors can not only cause developmental changes and impact overall health but can also cause changes to a person’s microbiome or the sum of microbes that coexist with an individual. Which could in-turn alter the sort of metabolites a person secretes (Verbeke K et al. 2015).

Sprague Dawley rat from Charles River Laboratories Source: crivier.com

October 22, 2021

Mental to Dental Connection

Background

Mental health diseases like depression and anxiety have plagued humans presumably since we achieved sentience, and lately it seems like the mental health crisis in America is getting worse and worse. Everyone blames this rise on something different; social media, the pandemic, tumultuous politics, or just the dramatics of younger generations. No matter where the blame is placed, statistics show that the rise in the number of diagnoses is real. Almost all mental health diseases show growth, but anxiety and depression have skyrocketed (ADAA). Even before the COVID 19 pandemic, anxiety was at an all time high, as shown in the figure below.

Fig. 1: These graphs show the number of people diagnosed with anxiety in 1990 (left) and 2017 (right). The United States shows a drastic increase. Darker areas indicate higher numbers of anxiety diagnoses. Image sourced from Our World in Data.

October 22, 2021

Athletes Have Unique Gut Microbial Communities

Background

People may be familiar with products that claim to impact gut health via probiotics and prebiotics, like kombucha and supplements. Prebiotics are plant fibers that encourage growth of beneficial gut bacteria, while probiotics are usually live bacteria that are associated with good gut health (Mayo Clinic Staff, 2021). Diversity comes up often in discussions about gut microbes. Diversity refers to the amount of different species present in a sample, and more diverse samples contain a wider range of microbes. We know that a less diverse community of gut microbes is associated with inflammatory bowel diseases (Cénit et al., 2014) and obesity (Turnbaugh et al., 2008). However, relatively little is known about how the performance of endurance exercise might impact the microbes living within the gut.

October 22, 2021October 26, 2021

Gutsy Irish Cricket Players Remarkably Transformed by Their Travels

Background:

International travel is part of modern life, your life. Whether that is visiting family in Europe, business trips to Asia, or a dream vacation to the tropics, these all have something in common. The microbes and germs in these places are different and not what your body is used to at home.

Your body is covered, inside and out, with little microbes that influence your health both mentally and physically (Beaumont et al. 2018. Hathaway et al. 2021). These symbionts (organisms that coexist and interact closely with another organism) are not the same for every person, especially at a global scale. Recent advancements in global sampling of microorganisms has shown that novel and unknown microbes are not only common in the cities of the world but often differ based on the climate, country, and various other environmental factors. Consequently, when a person travels to a new part of the globe, they are exposed to microbes that their bodies may never have seen before and contact with microbes like these can lead to some uncomfortable conditions (Danko et al. 2021).

October 22, 2021

The Future of Predicting Cancer Could Involve Microbes

Background

Colorectal Cancer (CRC) makes up a large proportion of cancer in the United States. CRC occurs in two locations, the colon and rectum. It is the 3rd most diagnosed type of cancer in the U.S., and in 2021 it is estimated there will be just over 100,000 cases of colon cancer and around 45,000 cases of rectal cancer leading to more than 50,000 deaths (American Cancer Society, 2021).

Colorectal cancer causes the third most cancer-related deaths among men and women separately, and if you combine into one population it causes the second most. The actual death rate of CRC has decreased in the last couple of decades due to increase in effectiveness and quantity of screenings (e.g. colonoscopy) which look for signs of CRC, including polyps (small clump of cells that can be cancerous) located in the rectum/colon (Stewart and Carter-Templeton, 2017). Even with the ability to screen and look for physical changes in the colon/rectum, many people still die from CRC and it is a major problem facing the field of oncology and medicine in general.

October 22, 2021October 26, 2021

Are Your Microbes Making You Anxious?

Background:

Anxiety and depression are at an all-time high, with more diagnoses and higher disability ratings (Spitchak, 2020). Mental health disorders like this have been linked to inflammation in the gut, as the immune system is activated by stress (Spitchak, 2020). Cognitive Behavioral Therapy and anxiety-reducing medications like benzodiazepines are the current gold standard for managing long-term chronic stress and anxiety, as well as short-term needs like panic or anxiety attacks (Ballenger, 2000). These methods do help, but some people have drug-resistant depression, and others simply prefer a greater variety of options to manage their symptoms. Getting outside more has long been accepted as a mental health boost, both from the calming peaceful environment to the vitamin D exposure, to the clean air, and even the soil microbes (Asprey, 2021). A less conventional option than a simple walk may exist and appears to be emerging after 16 plus years of research by Chris Lowry, who has been working with the soil bacterium M. vaccae since the early 2000s.

October 22, 2021

The way to one’s heart is through their stomach

Background:

Over the pasting years, atherosclerosis continues to be the number one killer in the United States (Heart disease facts 2021). This chronic inflammatory disorder is the foundation of heart disease (CVD) and happens when dietary cholesterol builds up in our arteries. With the accumulation of cholesterol comes arterial wall damage and the prevention of oxygen-rich blood circulating smoothly throughout the body. Fatty streaks then progress into advanced lesions followed by strokes, heart attacks, and death.

There have been several suggestions to decrease the illness and mortality of CVD. Statins have been prescribed to patients to reduce the production of cholesterol. Alternatively, stents have been surgically inserted in patients to keep blood flowing through narrowed arteries. Yet, the mortality rate from CVD continues to rise. Researchers propose to tackle this issue at a different angle: the gut microbiome. Does your gut health play a role in promoting CVD? You bet it does. Previous studies have suggested that the excessive consumption of animal products along with their interactions with the gut microbiome can play a substantial role in the progression of CVD (Witkowski et al., 2020).