Species survival in abruptly changing environment: Founder traits in evolutionary rescue
- Indian Entomologist
- 19 hours ago
- 4 min read
by Rahul Kumar
The red flour beetle, Tribolium castaneum, is a serious pest of storage grains. A female red flour beetle, can lay 300 to 600 eggs during its lifespan. This explosive growth in population combined with its appetite for wheat and wheat products cause huge economic losses to the farmers, traders as well as households. Therefore, it is important to study how pests evolve and adapt to different environments. The species is optimally adapted to grow on wheat. What would happen if these beetles are forced to grow on suboptimal food resources it is not familiar with?
Deepa Agashe and team from NCBS, Bengaluru, collected ten different wild populations of red flour beetles from different parts of India. They changed the diet of the beetles from their favourite food, wheat flour, to corn flour which is not its preferred food. Out of the ten source populations, they maintained 30 selection lines, for 70 generations over five years. They observed that all populations initially declined when transferred to corn flour from wheat flour. Out of 30 populations, one even went extinct. But then, within 20 generations, some started recovery showing the classic U-shaped curve of evolutionary rescue. In evolutionary rescue, as also observed in the present work, populations shrink dramatically before recovering through the rise of beneficial traits. Between decline and recovery phases, the species may remain in a “bottleneck” phase characterized by consistently low population size.
There are many studies on the factors influencing successful evolutionary rescue. But, so far, we lack studies about the demographic factors and traits that dictate population size during and after successful evolutionary rescue. Could the speed at which a population adapts during evolutionary rescue predict its future dynamics and adaptations? To address this question, the researchers collected data points on population size and fitness-related traits such how fast larvae grew into adults, lifespan, starvation resistance, number of offspring and larval cannibalism from the original founding population and from each subsequent generation over the span of five years. They analysed the data points statistically and modelled it. The model suggested that the populations founded by fast developing beetles ended up with larger and more stable populations. Populations where the original females lived longer tended to have larger populations later, probably because long-lived females produced more offspring over time. But this correlation applies only to the number of larvae rather than adults, that too, in the later phases of the experiment. The other traits showed poor correlations with long-term population performance. The development rate of the original founders or how fast their larvae grew into adults, therefore, was the single best predictor of whether populations would thrive or not in the long-term. Although founder traits like development rate have long-term associations with population size or reproductive fitness, these were not found to have effects on declines and rebounds during evolutionary rescue. This is attributed to high levels of demographic stochasticity or the random fluctuations in population size during rescue. Surprisingly, populations that experienced slower declines or faster bottleneck recoveries did not outperform others in overall growth in future generations. Instead, ancestral traits such as development rate and female lifespan mattered more in context of overall population growth. Interestingly, the first generation of beetles reared on corn flour showed adaptive shifts in fitness-related traits. These shifts were driven by both plasticity and selection. However, they showed poor correlations with population performance during the rescue phase.
Irrespective of early differences, after 70 generations, beetles across all populations had parallelly evolved faster development and higher reproductive success. What could be the reason behind such parallelism in trait evolution? The researchers suggest the possibility of many factors. One may be the species specific negative density dependent population growth characteristic of red flour beetles. Maladaptation to the changed environment could be another. The alleles that confer better adaptation will have large-effects, of course. Polygenic inheritance could lead to convergence in traits. One cannot neglect the effect of external factors or the environmental forcing also, say the researchers.
In any case, the results from this study suggests that some pest populations are difficult to eradicate because of their fast juvenile development rate followed by rapid evolutionary rescue under novel suboptimal resources or even pesticides. Species with faster development may have better chances of survival under abrupt environmental changes. The results have implications in species conservation and pest control in a constantly changing and unpredictable environment such as global climate change and rapid urbanization. This work also offers an explanation for why arthropods dominate the planet.
For more details, please refer:
V. Ravi Kumar, S. Buddh, S. Singhal, A. Prakash, & D. Agashe (2025). Founders predict trait evolution and population performance after evolutionary rescue in the red flour beetle. Proc. Natl. Acad. Sci. U.S.A. 122 (36). e2506244122. https://doi.org/10.1073/pnas.2506244122.
About the author:
Dr Rahul Kumar is one of the associate editors of “Indian Entomologist.” He is currently working as an Assistant Professor and Head of the Department of Zoology at Sheodeni Sao College (Magadh University), Kaler-824127, India. His ongoing research primarily addresses the behavioural, evolutionary, and taxonomic aspects of insects and spiders. Additionally, he has worked on molecular biology (eukaryotic gene regulation) at JNU, New Delhi; nanotechnology (nano-therapeutics and diagnostics) at AIIMS, New Delhi; science education (activity-based teaching-learning) at NCERT, New Delhi and insect taxonomy (micro-moths) at ICAR-IARI, New Delhi as a research fellow.
Disclaimer: The contents, style, language, plagiarism, references, mention of any products if any, etc., are the sole responsibility of the author
Comments