How Maternal Age and Diet Impact Fitness and Reproductive Timing in Rotifers

By Dr. Chinta SidharthanReviewed by Lily Ramsey, LLMDec 9 2024

Life history traits, such as reproduction and lifespan, are shaped by the interplay of individual characteristics and environmental factors. Among the microscopic aquatic species of rotifers, maternal age, and food availability significantly influence survival and reproductive timing.

A recent study published in the Journal of Animal Ecology investigated how maternal affect senescence, which is the decline in offspring fitness due to maternal aging, and how caloric restriction impacts population dynamics in rotifers.

Using detailed demographic modeling, the researchers explored the interactions between these factors and their effect on reproductive patterns, lifespan, and fitness outcomes.

​​​​​​​Study: Maternal effect senescence and caloric restriction interact to affect fitness through changes in life history timing. Image Credit: William Edge/Shutterstock.com

Background

Intrinsic factors, such as age and genetic traits, and extrinsic factors, including food availability, influence an organism's survival and reproductive success. Caloric restriction, which is often associated with extended lifespans, can delay reproduction but might shift fertility to older ages.

In many species, maternal age impacts offspring performance, with older mothers often producing offspring with reduced survival and reproductive potential — a phenomenon known as maternal effect senescence.

While lifespan extension through caloric restriction is well-documented, its interactions with maternal age and fitness outcomes are less understood.

Studies have suggested that food limitation alters reproduction timing and life history traits in ways that differ across generations. However, the broader ecological consequences of these interactions on population structure and growth remain unclear.

The Current Study

In this study, the researchers examined the effects of maternal age and food availability on rotifer population dynamics using experimental and modeling approaches.

Life table experiments were conducted on Brachionus manjavacas, a rotifer species, under two feeding conditions — ad libitum or free-fed, and caloric restriction with lower food quantities.

The study established maternal cohorts at specific ages to cover various reproductive stages, and the offspring were raised under controlled conditions.

The researchers recorded survival and daily reproduction data across the lifespan of the individual rotifers in the study. They also developed matrix population models to assess demographic parameters.

Each model incorporated individual attributes, including age and maternal age, along with environmental treatment. Furthermore, fertility and survival rates were estimated using non-parametric methods to ensure flexibility and precision.

For ad libitum conditions, fertility rates were determined through observed cumulative reproduction curves.

For the low-food group, the same methodology was used but modified to reflect reduced nutritional intake. Additionally, survival probabilities were interpolated and extrapolated to align with observed maternal age trends.

Furthermore, life table response experiments (LTRE) were used to analyze differences in population growth rates between feeding treatments. These analyses identified the contributions of changes in survival and fertility across age and maternal age classes.

Additional hypothetical scenarios were also modeled to simulate stationary populations while adjusting fertility or survival to match natural constraints. The researchers aimed to highlight how caloric restriction and maternal age influence individual life histories, including lifespan extension, delayed reproduction, and shifts in fertility timing.

Major Findings

The findings showed that maternal age and caloric restriction interact in complex ways to influence rotifer population dynamics. Caloric restriction was found to extend the lifespan but delay reproduction, leading to a decrease in the population growth rate.

Individuals' reproductive value was observed to shift under low food conditions, with higher contributions from older maternal and offspring ages. Furthermore, fertility and survival exhibited trade-offs across ages and maternal ages, with caloric restriction mitigating some negative effects of maternal effect senescence.

The population growth rates were significantly lower (1.8789) under caloric restriction as compared to ad libitum conditions (1.9363). The study also found that the lifetime reproductive output remained consistent across treatments, but the timing of reproductive events had shifted.

Fertility contributions under low food conditions were higher at older ages and maternal ages. Survival rates showed similar compensatory patterns, with decreased early-age survival and increased longevity at older maternal ages.

Moreover, the LTRE analyses revealed that differences in population growth rates between feeding treatments were primarily due to reduced fertility at young maternal ages under caloric restriction.

The findings emphasized the interaction between maternal age and caloric restriction and demonstrated how life history traits adapt to environmental constraints. The delayed reproduction under caloric restriction while extending lifespan led to complex trade-offs that affected overall fitness and population structure.

Conclusions

Overall, the study drew attention to the intricate balance between environmental factors and individual life history traits in shaping population dynamics.

The results showed that caloric restriction in rotifers extended lifespan but delayed reproduction, altering population growth rates and reproductive timing. The findings highlighted the compensatory effects of maternal age and survival in mitigating fitness losses under nutritional stress.

By integrating demographic models with experimental data, the study provided insights into how environmental conditions and biological attributes jointly influence evolutionary and ecological processes.