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). 


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.


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

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.

Continue reading “Sizing up Salmon”

When Environments Change

Can Algae save the world?

In today’s world with an increasing human footprint across the natural world, scientists believe we may be entering a sixth mass extinction. Fragmented habitats, introduction of invasive species, and climate change are just some of the factors leading to this mass extinction.  A lot of species still have yet to be recorded, so the number of extinctions of populations and species documented by scientists are likely to be large underestimates (Barnosky et al. 2011).  Climate change is one factor among many that is leading to the loss of biodiversity. Therefore, it is important for scientists to understand how populations respond to rapid environmental change. It is known that evolutionary history may affect risk of extinction within populations due to the accumulation of mutations, or pleiotropy. In one environment certain mutations will be favored, but in others they may have detrimental effects that reduce fitness, or reproductive success of a certain genotype in a population. (genotype being the genetic makeup of an individual) This would lower a population’s ability to withstand environmental change due to the accumulation of mutations which aren’t suited for the new environment. (MacLean et al. 2004) Understanding evolutionary history is crucial for understanding how populations will respond to environmental change caused by climate change. In the October edition of the Journal of Evolutionary Biology there was a study looking at how evolutionary history affects extinction probability.  Its title is “The effect of selection history on extinction risk during severe environmental change’. This study looked at how the extinction risk of populations of the green algae Chlamydomonas reinhardtii changed with various stressful environments (Lachapelle et al. 2017).

Continue reading “When Environments Change”

Parasitic Limitations on the Size of American Cliff Swallows

Introduction to the Role of the Parasite:

A parasite is an organism that lives in or on another organism at that organism’s expense. For most people, the thought of a parasite is usually in the form of leeches, tapeworms, or ticks. Within populations, parasites have the power to dictate the health of a population and which individuals survive. From an evolutionary standpoint, this can determine who in a population survives due to a parasites ability to kill off the defenseless, and therefore allow individuals with only specific traits to survive. Under the basic concept of natural selection: those who survive, pass on their traits, while the unfit individuals die and fail to pass their traits to the next generation. Parasites act as a controlling factor for which hosts and genes survive for reproduction. With this in mind, Charles R. Brown and Mary Bomberger Brown began a study to investigate the effect of parasitic cimicid bugs on the brood size of cliff swallows (Brown and Brown 2017).

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Do girls rule the world? They just might in finch hybridization!

Background: what’s happening, and where?

Map of the Galapagos Islands, Floreana is present at lower center
Figure 1. Galápagos Islands, image from Google Maps

In 1998, one of Charles Darwin’s famous finches, the medium tree finch, was classified as threatened on the International Union for Conservation of Nature’s (ICUN) red list (BirdLife, 2018). The medium tree finch, otherwise known as Camahynchus pauper, was named for the size of its short, curved beak. It can be found living only on Floreana island, an island that is part of the Galapágos Islands archipelago (bottom center of fig. 1). Over the last couple hundred years, this finch has faced numerous threats to its survival in the form of habitat fragmentation and destruction, predation, and now specifically parasitism (Kleindorfer et al., 2014). In 2009, the species was bumped all the way up to being labelled as critically endangered, after its population numbers dipped, largely due to threats caused by humans (BirdLife, 2018).

Continue reading “Do girls rule the world? They just might in finch hybridization!”

Attractive Dads Make Poor Parents

An overview of Alissa et al. (2017)

The debate over parental responsibility is a contentious one in our human society. Who should get parental leave? Whose responsibility is child protection and education? Such questions are often aimed at trying to get men more involved in the caring of a child or to split responsibility more evenly between two parents. Who would have thought that similar questions are being asked about spider societies?

It turns out that those intriguing 8-legged creatures that have plagued people’s nightmares and inspired fantasy from Charlotte’s Web to Harry Potter, also have very complex family dynamics. For most wild creatures the main purpose in life is to reproduce as successfully as possible. Thus, in some species, such as the harvestman spider, Serracutisoma proximum, investigated by Alissa et al. (2017), we see a trade-off between energy and time investment in mating effort and offspring care. Continue reading “Attractive Dads Make Poor Parents”

The Chronicles of Evolutionary Weight in the Fight Against Cancer


“Dad, you have to try it, don’t you?’ Mary insists again.

Enrique doesn’t answer his daughter. What she’s implying will make him spend even more time in the hospital, to help someone in the distant future whom he will never meet, maybe. When he was 70, Enrique was diagnosed with acute myeloid leukemia (AML). As he understands it, some of his blood cells will never mature and perform the correct functions in his body. This cancer can be cured through chemotherapy in 25% of cases, but in most cases cannot be treated or reversed (Kornblau 2014). Enrique is contemplating joining a drug trial. In any given trial there is only a 10% chance that a patient will respond to the specific drug tested (Kornblau 2014). Some therapeutic drugs work for some patients, but how to match a patient to a drug is unknown; this is what the study Enrique might join is trying to figure out. Continue reading “The Chronicles of Evolutionary Weight in the Fight Against Cancer”

Evolutionary advantage of learning to cope with change


Whether migratory birds will respond successfully to rapid climate change is unclear.  Birds migrate to take advantage of seasonal peaks in resource availability: Food and habitat become abundant quickly during summer at northern latitudes, but decline quickly in the fall.  Timely arrival on the summer range is vital for many species (Alerstam and Hedenström 1998). Continue reading “Evolutionary advantage of learning to cope with change”

All is fair in (insect) love and war

Let’s rock! (freakingnews.com)

Musicians alike, from Roy Orbison and Gram Parsons to Rod Stewart and classic rockers Nazareth have crooned woefully on that most powerful of feelings: Love hurts. Each of these fellas, though, had at least one thing going for him. Although they may have been jilted by former lovers, they can be thankful that none of them was a praying mantis! Scientists (and Tina Turner) may rightly question What’s love got to do with it? But there can be no doubt, mantis mating can be a very painful experience for the males involved. That’s because female predatory mantises practice sexual cannibalism, or the act of consuming a male mate before, during, or following a reproductive event. As many as one in four mantis sexual encounters may involve cannibalistic behavior. And while this bit of trivia knowledge has been known for quite some time now, two questions have continued to perplex evolutionary biologists:
How did sexual cannibalism evolve and why has it persisted in the face of natural selection? Continue reading “All is fair in (insect) love and war”

Does it even matter that you’re not a monkey? Host Species vs Immunocompetence


Viruses and their hosts influence each other’s evolution. As selection acts on viruses to increase their ability to infect hosts, selection is acting on hosts to decrease their susceptibility to viruses, and the next generation of viruses is less effective at infecting hosts. But the viruses continue to evolve, as do the hosts–they coevolve and often demonstrate this pattern:

RQ dynamics

This is called the Red Queen Effect, after the Red Queen from Through the Looking Glass by Lewis Carroll.

“Now, here, you see, it takes all the running you can do just to keep in the same place. If you want to get somewhere else, you must run at least twice as fast!”

Continue reading “Does it even matter that you’re not a monkey? Host Species vs Immunocompetence”