Something Fishy Going On - The Impact of Nanoplastics on the Behaviour of Fish

With the enormous rise in plastic use and production within the last century, we are now coming to terms with the impact plastics are having on our environment.

As a result, an expanding area of research that is the study of how microscopic plastic particles less than 100nm in size, referred to as “nanoplastics” (NPs), could potentially be the most hazardous form of marine litter [1]. Due to their small size and therefore high surface area, toxic chemicals can be retained by NPs and could lead to an accumulation of these toxins in marine organisms once the NP pass through membranes and into cells [2].

Krill, Source: Wikimedia Commons

With the ability of NPs to cross from the blood and into the brain, plastic deposits were found in the brains of the tiny crustaceans Daphnia magna, which were kept in water enriched with nano- and micro- sized particles [3]. The direct effect of these NPs can be seen in the behaviour of Daphnia: those who consumed the plastics showed a dose-dependent higher incidence of death; at lower, less fatal concentrations, NPs slowed the eating and preying behaviours [4].
Another question that researchers are investigating is whether NPs can be passed up the food chain as smaller creatures like Daphnia are eaten in large numbers by bigger fish. It has been found that NPs administered to algae become accumulated in fish and have a profound effect on their eating and shoaling behaviour, as well as changes in their metabolism [5].

Can plastic nanoparticles alter behaviour?

It is important to note that the occurrence of NPs in the natural marine environment has not yet been proven, and the above mentioned studies used much higher concentrations that would be found in nature [1]. However, these results can be seen as a wakeup call to start thinking of the impact our plastic use has on the environment.

Joanne Falck
PhD Student, AG Garner

[1] Koelmans et al., Marine anthropogenic litter, 2015
[2] Velzeboer et al., Environ. Sci. Technol. 2014
[2] Mattsson et al., Scientific Reports, 2017
[3] Mattsson et al., Environ. Sci. Technol, 2015
[4] Mattsson et al., Environ. Sci. Technol, 2014

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Tracing the Roots of Aggression

Many evolutionary theories explain the development of human aggression as a necessary trait for survival. However, aggression rarely has practical use in contemporary society. When exhibited, it is often in a violent and illegal context and therefore it is incriminated. Sometimes, it can even be considered part of someone’s temperament.

Aggression is thought to be the result of a complex corticolimbic interaction between subcortical neural systems, decision-making circuits, and frontoparietal regions [1]. Strong genetic and hormonal influences, in addition to the various environmental stimuli, seem to regulate these networks. This raises questions regarding the degree of responsibility that violent people bear.

Aggression Is a Male Phenomenon
According to statistics, the ratio of crimes committed by males compared to females is greater than 10:1. The more aggressive behavior of males starts to manifest itself even before adolescence, with boys being more likely to be involved in some kind of antisocial conduct [2].
Hormones are among the first suspects for male aggression. Exposure to androgens in the early stages of adolescence is thought to constitute a possible cause. However, according to a recent meta-analysis, the association between testosterone levels and antisocial behavior is weak [3]. Next is the stress hormone cortisol, whose action is regulated through the hypothalamus and adrenal axis. Lower cortisol concentration was found in the saliva of males with antisocial conduct [4]. Finally, low levels of the serotonin metabolite 5-HIAA and low blood sugar are other messengers implicated in the regulation of aggressive behavior.

Is It You Y?
More than four decades have passed since males with XYY syndrome, known also as supermales, were associated with criminal behavior. A higher percentage of XYY men was found in prisons and in institutions for criminally insane people than was found among the normal population. This hypothesis has been significantly weakened after the publication of epidemiological studies that suggested otherwise [5], although it has not been totally refuted as emerging evidence still supports the initial claim [6].
Taking a closer look at the genes, recent knockout studies in mice have excluded any contribution of the Y-linked loci to aggression [7]. Nevertheless, the investigation of other chromosome loci revealed genes that might explain the sex-related difference in aggression and should be interpreted along with the hormone hypothesis. A shorter GAG repeat in the Androgen receptor in Swedish and Indian males accused of aggressive behavior has been associated with it [8]. Certain polymorphisms of the monoamine oxidase (MAOA, MAOB)-coding genes have been linked with functional differences in expression. A plethora of enzyme-coding genes (COMT, dopamine-β-hydroxylase and tryptophan hydroxylase) has been linked to male aggressive behavior [9].

Environmental Interactions
Stressful events, especially in the first years of life, confer a higher risk for manifesting antisocial conduct. Interestingly, it seems that stress triggers aggressive behavior in males with a “vulnerable” genetic background and more specifically a low-activity polymorphism in the MAOA gene. The causality in this case is not clear yet, as evidence suggests that an initial stressful event down-regulated the activity of the MAOA genes later on [2].

The Role of Recreational Substances
Substance use is closely related to offending behavior in both sexes, with alcohol being the most common culprit. It is not only widespread alcohol use, but also its high correlation with violent behavior that make it one of the most significant perpetrators of aggression. Drug users on the other hand, rarely exhibit such behavior, with cocaine users being the only exception [10]. 
Aggressive behavior, like every behavior, is difficult to approach and explain with molecular and genetic mechanisms. However, there seems to be a notable interaction between the environment and one's genetic background. This requires further investigation, as the potential implications for preventing the development of an aggressive behavior, even in a small portion of the population, could improve dramatically the fabric of our societies.

[1] Coccaro et al, Biol Psychiatry, 2011
[2] Craig and Halton, Hum Genet, 2009
[3] Book et al, Aggress Violent Behav, 2001
[4] Shirtcliff et al, Dev Psychopathol, 2005
[5] Noël et al, Clin Genet, 1974
[6] Stochholm et al, BMJ Open, 2012
[7] Gatewook et al, J Neurosci, 2006
[8] Rajender et al, Int J Legal Med, 2008
[9] Pavlov et al, J Appl Genetics, 2012
[10] Lammers et al, Tijdschr Psychiatr, 2014

by Andreas A. Diamantaras, MSc student
This article originally appeared in CNS Volume 7, Issue 3, Nature vs Nurture