Over half of the world’s human population lives in cities. Are species adapting to life in these novel urban environments? A global team of researchers (including Tiffany Longo, Jesse Bragger, and Summer Shaheed, shown in in the photo) used white clover as a study system to find out. They measured the production of a compound called hydrogen cyanide (HCN) in rural and urban clover plants. Production of HCN deters herbivores and increases tolerance to drought but has a cost: Clover must expend energy to produce HCN.
Compare how evolution by inheritance of acquired characters and the theory of evolution by natural selection would explain the observation that HCN production is often high in rural environments with many herbivores and low in urban environments with few herbivores.

Verified step by step guidance

1. Identify the key concepts involved in the problem: inheritance of acquired characters, evolution by natural selection, and the environmental factors influencing traits in organisms.
2. Explain the theory of inheritance of acquired characters: This theory suggests that traits acquired or modified during an organism's lifetime can be passed on to its offspring. In the context of the problem, this theory would imply that clover plants in rural areas might develop higher HCN production due to the presence of more herbivores and then pass this trait to their offspring.
3. Discuss the theory of evolution by natural selection: This theory posits that traits that increase an organism's chances of survival and reproduction will become more common in the population over generations. For clover plants, those in rural areas with high herbivore pressure that produce more HCN might be more likely to survive and reproduce, passing on the high HCN production trait genetically.
4. Compare how each theory would explain the lower HCN production in urban environments: According to the inheritance of acquired characters, urban clover might not develop high HCN production due to fewer encounters with herbivores and thus not pass this trait to offspring. In contrast, natural selection would suggest that urban clover with lower HCN production is more energetically efficient and better suited to environments with fewer herbivores, thus they are more likely to survive and reproduce.
5. Evaluate the implications of each theory on the adaptation of species to urban environments: Consider how each theory supports or challenges the observed patterns of trait development in clover plants in different environments and the broader implications for understanding adaptation in urban settings.

Key Concepts

Evolution by Inheritance of Acquired Characters

This concept, often associated with Lamarckism, suggests that organisms can pass on traits acquired during their lifetime to their offspring. For example, if a clover plant develops a higher production of hydrogen cyanide (HCN) due to increased herbivore pressure, it is believed that this trait could be inherited by its progeny. However, this theory has largely been discredited in favor of natural selection, as it lacks empirical support and does not account for genetic inheritance.

Natural Selection

Natural selection is a fundamental mechanism of evolution proposed by Charles Darwin. It posits that individuals with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to the next generation. In the case of clover plants, those in rural areas with high herbivore presence may produce more HCN to deter herbivores, while urban clovers may not need to invest energy in HCN production due to lower herbivore pressure, illustrating how environmental factors shape evolutionary adaptations.

Trade-offs in Resource Allocation

In ecology and evolutionary biology, trade-offs refer to the balance organisms must strike between competing demands for resources. For clover plants, producing HCN can deter herbivores and enhance drought tolerance, but it requires significant energy investment. In urban environments, where herbivore pressure is lower, the energy spent on HCN production may not yield sufficient benefits, leading to lower HCN levels. Understanding these trade-offs is crucial for explaining the observed differences in HCN production between rural and urban clover populations.