Question

Two species of fish had recently undergone sympatric speciation. The males of each species had a different coloring through which females could identify and choose a partner from her own species. After some time, pollution made the lake so cloudy it was hard for females to distinguish colors. What might take place in this situation?

Short answer

Hybrids may form due to difficulty in mate selection, impacting speciation.

Step-by-step solution

Understand Sympatric Speciation

Sympatric speciation occurs when new species arise from a single population without geographic barriers separating them. In this case, the two fish species have evolved in the same environment and developed distinct male coloration for mating purposes.

Evaluate the Role of Coloring in Mating

The coloration of male fish plays a crucial role in mate selection by females. This trait ensures reproductive isolation, as females prefer mates from their own species based on color differences.

Assess the Impact of Pollution

Pollution has made the water cloudy, which interferes with the ability of female fish to see and distinguish male coloration. This environmental change affects the primary mechanism of mate selection of the fish.

Predict the Consequences

With reduced visibility, females may struggle to select partners from their own species, leading to interbreeding between the two species. This could result in hybrid offspring and potentially reduce the genetic differentiation between the species.

Key concepts

Environmental Impact on Speciation

Environmental changes can have significant implications for the process of speciation, especially in sympatric scenarios where species arise without geographic barriers. In many ecosystems, specific environmental conditions are crucial in maintaining the distinctiveness of species.
When pollution occurs, it can dramatically alter these conditions. For instance, in the case of the two fish species, water pollution caused the lake to become cloudy. This change in environment disrupts the clear visual signaling that females rely on to choose mates from their own species.

• Cloudy water reduces the contrast between colors.
• The disruption in mate selection can lead to increased interbreeding.
• Over time, this can erode species distinctions.

Hence, with environmental interference, the specific adaptations that facilitated sympatric speciation may be undermined. This scenario can result in the fusion of previously distinct species or the emergence of hybrid populations.

Mate Selection Mechanisms

Mate selection is a critical driver in the process of speciation, particularly in sympatric environments. In our example, male fish of each species have developed distinct coloration, which females utilize for choosing their mates. This type of selection is a crucial mechanism for promoting reproductive isolation.
Successful mate selection mechanisms rely on clear and recognizable traits, like visual or auditory signals. However, these signals can be susceptible to environmental changes.

• Females may choose mates based on multiple sensory inputs, such as color and movement.
• When the primary signal (i.e., color) is obscured, reliance on secondary signals may increase.

When the water turned cloudy due to pollution, females lost the ability to see the males' colors, making the visual cues ineffective. As a result, females might resort to other, less precise signals, leading to mixed-species pairings. This indicates the interplay between mate selection mechanisms and environmental factors, emphasizing the complexity in speciation maintenance.

Reproductive Isolation

Reproductive isolation acts as a vital mechanism that keeps species distinct even when they coexist in the same geographical area. For the fish, the separate coloring of males serves as prezygotic isolation. With females only choosing males of the same species based on this trait, genetic integrity is maintained.
However, when pollution caused reduced visibility, this isolation mechanism was compromised.

• Without visual cues, females may inadvertently choose partners from different species.
• This decision can lead to hybridization, where offspring inherit genetic material from both species.
• Over successive generations, hybridization can diminish the genetic differences that define the species.

Reproductive isolation is not only about prezygotic barriers like mate choice but also involves postzygotic mechanisms that ensure offspring viability. Yet, in polluted environments, these pre-reproductive barriers become ineffective, potentially blurring the lines between once separate species.