//
you're reading...

Fisheries

You look like your mom: parental effects in Atlantic salmon

Van Leeuwen, T.E., McLennan, D., McKelvey, S., Stewart, D.C., Adams, C.E., Metcalfe, N. B. (2016). The association between parental life history and offspring phenotype in Atlantic salmon. J. Exp. Biol. 219: 374-382. doi: 10.1242/jeb.122531

Parental effects are sometimes called maternal effects. Since mom is the one to carry the eggs or young in her body, her condition usually has a much greater influence on the offspring.

Parental effects are sometimes called maternal effects. Since mom is the one to carry the eggs or young in her body, her condition usually has a much greater influence on the offspring. [Wikimedia]

We can all agree that both our personal experiences (nurture) and our genes (nature) have a role in shaping our personality, behaviour, looks, and other traits. The environment you grow up in has a big influence on your talents, interests, and life trajectory. The genes and gene variants you are born with form the basic blueprint of every protein and cell in your body.

But the story is more complicated than nature vs. nurture. The environment the parents experienced during reproduction will also influence the development of their offspring. On a similar note, the environment the parents experienced during their development, and their life history, is also gaining traction as an important predictor of offspring performance and life history pathway.

Parental effects are part of the concept of epigenetics, inheritable traits that are not due to changes in the actual gene or gene variants. Epigenetics are effectively changes in how genes are “read” by cells, and whether they are “on” (active) or “off” (silenced). Such mechanisms are one of the reasons why identical twins, with the same genetic code and raised in the same household, can have very different lifestyles.

Atlantic salmon life history

Atlantic salmon (Salmo salar) spawn in freshwater rivers and streams. Alevin (newly hatched fish with their yolk sac still attached) hide in the gravel for a few weeks, slowly absorbing nutrients from their yolk sac. Once the yolk sac is exhausted, the fish leave the safety of the river bottom and start to feed. They quickly develop into young juveniles called parr, and will grow in their native streams from some time.

Parr typically smolt after 1 to 3 years of growth in their native stream. Smolting is a series of complex physiological and morphological changes that prepare the parr for entering the ocean. As the age of seaward migration is partially determined by growth rate, faster-developing fish spend less time in freshwater. Once at sea, salmon may not return to spawn for years. The amount of time mature salmon spend at sea before returning home to spawn (1 to 6 years) is one source of variation in life history within the population.

The basic life history of sea-run Atlantic salmon. Unlike some other species, a minority of spawners are able to make it back to the ocean to return ad spawn again.

The basic life history of sea-run Atlantic salmon. Unlike some other species, a minority of spawners are able to make it back to the ocean to return ad spawn again. [Wikimedia]

A pre-smolt parr. Some male salmon never get much beyond this life stage. [Flickr]

A pre-smolt parr. Some male salmon never get much beyond this life stage. [Flickr]

Some male fish never smolt and remain stuck in the parr stage. Somehow, these males are able to become sexually mature without migrating seaward. Because of their small size, these “precocious parr” can’t compete directly with the larger, sea-run males during spawning to monopolize mates. Instead, they cruise around the spawning grounds, and participate as sneaker males. Instead of battling for their babes, sneaker males… sneak around spawning pairs and indiscriminately fertilize any eggs they can approach closely. This alternative life history strategy is another source of variation in the population.

Atlantic salmon are excellent models for studying the concept of parental effects in a natural setting because they have multiple potential life histories that not only lead to successful reproduction, but interbreed with each other. Life history routes (e.g. time at sea, sneaker vs. sea-run) in salmon are thought to arise from a mix of genetic and non-genetic factors. Sneaker and sea-run males can develop at the same river site, but go on to lead very different lives.

Life history determination, fish rearing, and metabolism

To investigate how parent life history may influenced offspring traits, Van Leeuwen et al. needed to systematically breed Atlantic salmon with a variety of life history pathways. Mature, sea-run salmon and precocious parr were captured from the River Blackwater, Scotland.

A printing of a scale of a large salmon captured in the summer. [Wikimedia]

A printing of a scale of a large salmon captured in the summer. [Wikimedia]

By examining the rings on the scales of their wild-caught breeding fish (a technique called “scalimetry”), the researchers were able to determine the rough age of the each fish, and number of years they had spent in freshwater and saltwater prior to capture. This is because scales grow in a ring-like pattern, producing bands called annuli. Bands are thicker in the summer than in the winter (since they grow faster when food is plentiful), and differ between pre-smolt freshwater and post-smolt seawater salmon.

After capture, the mature females (1 or 2 years at sea) were bred with either sea-run males (1 or 2 years) or sneaker males (0 years at sea). The eggs, separated into family groups, were raised in a hatchery for ~8 months, during which their growth rates and condition were monitored. The following autumn, once the salmon had developed into juveniles (parr), the resting and maximum metabolic rates of the young were tested to get a sense of their overall energy budget and performance. The authors then analyzed the relationships between offspring traits and the life history traits of their parents.

Mother knows best

Mothers that had spent a longer time at sea were larger, and produced larger eggs and larger and stronger offspring at the time of first feeding (even after accounting for the effects of larger egg mass). Marine environments tend to be more productive than freshwater environments, so the larger mothers that spent more time at sea probably have more energy available to invest into their offspring.

Even after accounting for the fact that larger fish tend to hatch out of larger eggs, the relationship between egg mass, maternal life history, and offspring size remained, suggesting difference in other factors, like maternal hormones or individual egg position in the ovary (some eggs are closer to blood vessels and in a better position to received nutrients), may also play a role.

Young alevin of a Pacific species, the chum salmon.

Young alevin of a Pacific species, the chum salmon.

These relationships weren’t as strong once the offspring were no longer dependent on their yolk sacs for nutrients, suggesting maternal investment (and maternal effects) had a major influence on these traits.

While maternal environment leading up to egg production influenced early offspring traits, this study is unable to rule out the influence of genetic effects. Traits that correlated with the father’s life history, such as the greater body condition in sneaker male offspring fry, demonstrate that genetics also has a role in determining offspring traits (since father’s play no role in egg provisioning).

Now when I was your age…

By the time fry had been feeding on their own for some time, the early life history of the mother in freshwater was a better indicator of their developmental trajectory – mothers that left freshwater early produced offspring with higher maximum metabolic rates and aerobic scope, and that grew faster.

A large adult male Atlantic salmon. [Flickr]

A large adult male Atlantic salmon. [Flickr]

The father’s life history also had an effect, though it was less prominent than the role of the mother. Male salmon adopt two major reproductive strategies: the territorial strategy (adopted by sea-run males), where the male defends a single female; and the non-territorial/sneaker strategy, where the male cruises around the spawning ground looking for opportunities to steal fertilizations from larger males.

While both strategies produce viable offspring, no one really knows whether one strategy is more successful than the other in either the quantity or quality of offspring. However, data here suggests that sneaker males produce offspring with relatively high growth rates, in better condition, and maximum metabolic rate (though mother also influenced this). How this shakes down in terms of offspring success and fitness is not known.

Conclusions

The duration of key developmental stages (time in freshwater before seaward migration, length of time at sea before spawning) of the mother, and to a lesser extent the father, are important predictors of offspring metabolic and growth-related traits. It is possible that parents may be adjusting the life history trajectory of their offspring to perform best in the environments that they themselves experienced as juveniles.

 

Discussion

Trackbacks/Pingbacks

  1. […] posted about salmon parenting on Monday and covered the contributions of each parent. Salmon (Fig. 3) are anadromous fishes: born in freshwater, they migrate to the ocean where they […]

Post a Comment

Instagram

  • by oceanbites 5 days ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 2 weeks ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 weeks ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 1 month ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 3 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 3 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 4 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 4 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 5 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 5 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 6 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 6 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 7 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
  • by oceanbites 7 months ago
    Have you seen a remote working setup like this? This is a photo from one of our Oceanbites team members Anne Hartwell. “A view from inside the control can of an underwater robot we used to explore the deep parts
  • by oceanbites 8 months ago
    Today is the day of  #shutdownacademia  and  #shutdownstem  and many of us at the Oceanbites team are taking the day to plan solid actions for how we can make our organization and the institutions we work at a better place
  • by oceanbites 8 months ago
    Black lives matter. The recent murders of Ahmaud Arbery, Breonna Taylor, and George Floyd have once again brought to light the racism in our country. All of us at Oceanbites stand with our Black colleagues, friends, readers, and family. The
WP2Social Auto Publish Powered By : XYZScripts.com