Fishing through genes: the unique relationship between cavefish and Autism Spectrum Disorder

By: Matthew Mesiti, Trevor Tubbs, Nicholas Poli (Stonehill College, BIO323 Evolution, Fall 2018)

Today, autism spectrum disorder (ASD) affects a large portion of the world and is very prevalent in our lives. The well-known developmental disorder has been known to cause reduced social interaction, repetitive behavior, sleep deficits, hyperactivity, adherence to a particular stimulus, and higher anxiety level in humans. However, Mosato Yoshizawa and his research team discovered these same behaviors overlapping with Mexican teleost, a type of fish that is scientifically called Astyanaz mecixanus. More specifically, the research team found similarities in the genes of Astyanaz mecixanus cave-dwelling morphs and human ASD risk genes. Although the cave-dwelling fish did have a relationship with human ASD risk genes, the morphs also displayed positive selection and a positive response to human ASD drugs.

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One of the most common psychiatric disorders today is Autism Spectrum Disorder, a worldwide disorder causing reduced social interaction, repetitive behavior, sleep deficits, hyperactivity, adherence to a particular stimulus, and higher anxiety level in humans. Although it is known to affect many humans today, there has also been a newly discovered relationship with a species of fish. Evolution is known to be an ongoing process causing changes in many places to many species. According to Masato Yoshizawa and his research team, the fish species Astyanaz mexicanus has displayed evolutionary changes which have been linked to Autism Spectrum Disorder (ASD).
In their research, the team discovered cave-dwelling and surface-dwelling morphs that showed opposing behavior characteristics. The surface-dwelling morphs readily schooled, did not have repetitive behaviors or hyperactivity, had normative sleep patterns, did not show adherence to a vibration stimulus, and had lower cortisol levels. However, the cave-dwelling morphs did not readily school, performed repetitive behaviors and hyperactivity, were sleepless, showed adherence to a vibration stimulus, and higher cortisol levels. Core ASD symptoms, like those that were previously mentioned, show a great similarity to the behaviors of the cave-dwelling morphs.
Based on these observations, the research team studied the relationship between human ASD-risk genes and cavefish ASD-risk genes under molecular evolution. To accomplish this, they investigated shifts in orthologs, relationships of homologous gene sequences between organisms after speciation, of the ASD-risk genes. Additionally, due to similar behavior traits to the cave-dwelling fish, the team also tested genes involved in schizophrenia. Nonetheless, the research found a greater relationship with ASD-risk genes. Specifically, the team discovered that 92.5% of 493 human ASD-risk genes are within the genomes of cave-dwelling fish, further indicating that there is a strong relationship between the Astyanaz mexicanus cave-dwelling morphs and human ASD.

Not only did the research team conclude this relationship but they found that the cave-dwelling morphs experienced positive selection due to the following additional effects of the ASD-risk genes: improved pathways of digestive system development and function, and improved lipid and energy metabolism. Additional traits developed by the cavefish were eye degeneration, pigment-loss, widened jaws and increased number of teeth, increase in fat tissue, and enhancement of non-visual sensory systems.

To conclude their study, the research team further showed the relationship between ASD patients and the cavefish as a result of similar neural pathways. They discovered that ASD approved drugs such as aripiprazole, risperidone, and clozapine had positive effects on the cavefish reducing their hyperactivity and adherence to particular stimuli, and increasing sleep duration. The altered behavior of cave-dwelling fish proves that there are similar neurological pathways between ASD patients and cave-dwelling fish.

Overall, this study shows that there is a clear relationship between Astyanaz mexicanus cave-dwelling morphs and human Autism Spectrum Disorder. The research team concluded, using a recent study, that many animals’ species such as honeybees also exhibit behavioral traits similar to ASD patients and contain enriched ASD-risk genes. Thus, determining that there may be more relationships regarding the evolution of animal behaviors and human ASD.

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Citation: Yoshizawa, Masato, et al. “The Evolution of a Series of Behavioral Traits Is Associated with Autism-Risk Genes in Cavefish.” BMC Evolutionary Biology, vol. 18, no. 1, 18 June 2018, doi:10.1186/s12862-018-1199-9.

Masato Yoshizawa’s email: