We have previously seen how a mother’s environment or her behaviors might epigenetically affect her offspring. Now we have results that hint at the epigenetic effect fathers may pass on through generations.
In a previous article we explored the heritability of alcoholism and how dad’s drinking could epigenetically affect a son’s preference for alcohol. In a new study conducted at the University of Illinois at Urbana-Champaign, researchers found that stickleback fish fathers may potentially alter their young epigenetically through increased attentive behaviors. Fish dads who paid more attention to their offspring essentially made them act in a way where they were less likely to be consumed by predators. This was then discovered to be accompanied with a change in gene expression found in the offspring’s brain.
The findings were reported in the Proceedings of the Royal Society B: Biological Sciences and highlight how giving paternal care to the stickleback offspring could increase their chances of survival. This increased survival could have been a result of the epigenetic alteration the father fish had on the offspring’s expression of a DNA methyltransferase, DNMT3A, involved in de novo methylation.
“There is lots of evidence that moms are very important for their offspring,” said Alison Bell, University of Illinois animal biology professor who conducted the study along with fellow researcher Katie McGhee. “But we know much less about fathers.”
Other studies that have assessed mice, voles, and monkeys, for example, demonstrate the influence maternal attentiveness and care can have on newborns, changing the offsprings’ future behavior even when the maternal care is not given by a mom that is related to them genetically. According to Bell, the changes to their behavior are often associated with alterations in gene expression due to methylation, reducing the rate of translation of specific genes into proteins.
Bell and McGhee investigated the small, three-spined stickleback fish (Gasterosteus aculeatus). In this species the father is the sole caretaker of the offspring, making these fish an ideal subject for a study investigating fatherly influence, according to Bell.
“Everybody loves to eat fish eggs; caviar is totally delicious, so you can imagine how in the wild everybody and their mother is trying to eat the stickleback’s clutch of eggs,” she explained. “So males are very aggressive towards intruders, and they spend a lot of time just hanging out at their nest and defending it.”
The stickleback fathers differ in the way they care for their young, said Bell. Some fathers are more aggressive and chase intruders away more than they interact with their young, whereas other less aggressive stickleback dads will hover, using their fins to fan the nest to increase oxygen as well as retrieve young stickleback babies known as fry, who roam too far from the nest.
“The dad is actually handling the fry in his mouth,” she said. “He’ll chase them down, suck them up into his mouth and then spit them back into his nest. Early studies in sticklebacks suggested that fry are learning about predators by having their dad chase after them.”
Bell and McGhee researched the way stickleback fathers cared for their young and the effect this had on fry behavior. They separated the fathers from half of their fry before the youngsters hatched.
“This allowed us to compare these offspring that were orphans with their siblings, who were raised by their father,” Bell added.
While tracking the sticklebacks’ behavior near the nest when presented with a predator, McGhee found that of the very attentive fathers, the offspring who were orphaned were generally more active, especially when around a predator. When the predator fish – a pike – was nearby, the sticklebacks swam and pecked at the sides of the tank in an attempt to escape. This behavior is noted to make them more likely to be spotted and consumed by a predator pike.
When reared by their attentive fathers, however, the fry reduced this frantic and anxious behavior. The offspring that were reared by their attentive fathers were much less active compared to their orphaned siblings, according to the researchers.
The fathers that were less attentive, however, showed no significant influence on their offspring. The fry that were orphaned versus the ones that were raised by their less attentive fathers acted similarly when around a predator.
Overall, these findings suggest that there is a difference in fish families’ responses to stress, according to Bell. There is an ability of the father to change their behavior which could impact their offspring’s behavior, compensating for inherent vulnerabilities.
The research team also found that the difference in paternal care was linked with changes to an enzyme that promotes DNA methylation in the offspring. After the behavioral assessment of the fish, the researchers used qRT-PCR to measure the expression of DNMT3A in the sticklebacks’ brains.
The offspring of fathers that provided a lot of direct care had elevated DNMT3A expression compared to their orphaned siblings, wrote the researchers. On the other hand, the offspring of the fathers that behaved in a defensive manner at the expense of direct care had lower DNMT3A expression than their orphaned siblings.
The scientists collected evidence they deemed “consistent with the hypothesis that high levels of direct offspring care during development increases de novo methylation in offspring leading to changes in gene expression and behaviour.” Even though they obtained interesting results, Bell and McGhee warned against jumping to conclusions and indicated that “although paternal care might lead to methylation induced repression of genes associated with anxiety, this is one of many possibilities.”
“Our study is important because, one, we show that dads can be like moms in that their care can influence their offspring; two, we show that dads can be like moms in that it looks like it could be mediated by gene expression changes due to differences in methylation; and three, we find this funky thing where the amount of methylation and the amount of care seems to vary among families,” Bell said.
Source: Learn all about it and read more about their findings here: K. McGhee, A. Bell. Paternal care in a fish: epigenetics and fitness enhancing effects on offspring anxiety. Proceedings of the Royal Society B: Biological Sciences, 2014.
References: University of California Santa Cruz. Study shows how epigenetic memory is passed across generations. 2014.