This blog post is provided by Zoe Almeida and tells the #StoryBehindThePaper for the paper “Lingering legacies: Past growth and parental experience influence somatic growth in a fish population” which was recently published in the Journal of Animal Ecology. In their study, Zoe and colleagues find that growth in Walleye fish is more affected by growth in the previous year and parental experience than by recently experienced environmental conditions.  

Body growth is one of those deceitfully simple values that we frequently use in ecology. It seems so straightforward. All you need to know is how big they were last time and how big they are now, right? Growth is used as a proxy for health and condition of individuals – as an integrator of environmental experiences. Because of this, we often use growth to track responses to environmental changes, such as temperature and food availability. However, as an integrator, growth may be responsive to a greater suite of experiences than just those in the most recent environments. Family history and genetics, early life environments, and the experiences from previous periods can all be integrated into growth.

Despite the potentially consequential influence of these legacies to populations, we expect that the most recent environmental conditions would still have strong effects on growth rates.  

In our recent study, we wanted to better understand how a variety of legacy and recent environmental effects influenced growth. Specifically, we wanted to tease apart the roles of the following 5 factors (we call them ‘hypothesized pathways’) in affecting growth: 1) recent environmental conditions, such as food availability and temperature; 2) traits and experiences, including growth, in the previous year; 3) competition for food experienced in early life; 4) body size achieved in early life; and 5) parental condition and their recent environmental experiences.

Tracking of individuals over generations for a long enough period to gain information on all these hypothesized pathways is logistically challenging; however, long-term monitoring programs can provide a wealth of information beyond what they were initially designed for. We used data from a long-term monitoring program in Lake Erie to investigate correlates of adult Walleye (Sander vitreus)growth rates. Lake Erie is one of the premiere Walleye fisheries in the world and, because of this, has long-term records of sizes and ages of adults, densities and sizes in early life stages, and environmental conditions throughout the year.

We used these long-term records of Walleye to determine which hypothesized pathways were most important for affecting body growth at the annual cohort-level (i.e., change in mean body size in a cohort from one year to the next) from 1982 to 2015. We focused on young adult Walleye (ages 3-5), a period during which individuals show considerable growth before their growth slows at later ages.

Because these hypothesized pathways can affect growth simultaneously (they are not mutually exclusive) and through multiple life stages, we examined different combinations of these pathways with piecewise structural equation models (SEMs).

The piecewise SEMs that were most supported by our data included traits and experiences, specifically growth, in the previous year (hypothesized pathway 2) and parental condition and environmental experiences (hypothesized pathway 5). Interestingly, we found a negative relationship between growth in the previous year and recent growth, meaning that when cohort body growth was higher than average in one year, it was lower than average in the following year. We explored a few different explanations for this and the only one we couldn’t exclude was that growth may increase after periods of slowed growth or reduced biomass, a phenomenon called ‘compensatory growth’ that is not uncommon in fishes. However, since we were looking at growth in cohorts and not among individuals, we cannot truly determine if compensatory growth explained the pattern we observed.

Parental experience influenced growth in multiple ways. Perhaps the most interesting is that when parents experienced more severe winters before spawning, their offspring growth was enhanced later in life. The influence of the parental experience on cohorts of Walleye 3 to 5 years after they hatched was in many ways surprising. Our results indicate that parental contributions to offspring affects cohorts into adulthood and has important implications for the effects of climate change on warming winters.

We were surprised that recently experienced environmental conditions (hypothesized pathway 1), such as the recent prey, temperature, and fishing pressure experienced, were not included in any of the most-supported models. In designing this study, we had initially included these recent environmental conditions because we assumed they would have the strongest effects. Temperature is known to have a strong influence on growth in fishes, how could we not see an effect of it? At least at the cohort-level, however, these recent conditions are not as influential as the legacy effects of earlier experiences and parental experiences.

Overall, our results have important implications for the broader understanding of how animals respond to their environments. While recently experienced environments certainly do affect animals, we also must account for legacy effects. If not, legacy effects will likely appear as unaccounted for variation that will prevent a greater understanding of environmental effects and may delay our ability to manage and conserve populations under changing climates.

Read the paper

Read the full paper here: Almeida, L. Z., Ludsin, S. A., Faust,M. D., & Marschall, E. A. (2024). Lingering legacies: Pastgrowth and parental experience influence somatic growth ina fish population. Journal of Animal Ecology, 00, 1–13. https://doi.org/10.1111/1365-2656.14143