A fish species is sexually dimorphic: males possess ultraviolet (UV) s...
Females assess males from long distances
The plausible reason for the fish species' ultraviolet (UV) spots being colored ultraviolet is that females assess males from long distances. Here's an explanation of why this is the correct answer:
Importance of sexual dimorphism
Sexual dimorphism, the differences in physical characteristics between males and females of the same species, often plays a crucial role in mate selection and reproduction. In this particular fish species, the presence of UV spots on the males but not on the females is an example of sexual dimorphism.
Females' preference for larger and more intense UV spots
The question states that females prefer males with larger and more intense UV spots as mates. This indicates that the UV spots serve as a visual cue for the females to assess the quality of potential mates.
Long-distance assessment
The fact that females prefer males with larger and more intense UV spots suggests that they use these spots to evaluate the fitness and attractiveness of potential mates. However, in order for the UV spots to serve as a reliable indicator from a distance, they need to be visually conspicuous.
Ultraviolet as a visible signal
Ultraviolet light is outside the range of human vision, but many animals, including birds and some fish, can perceive UV light. Therefore, it is plausible that the fish species in question can also see UV light.
Conspicuousness of UV spots
UV spots are likely to be more visually conspicuous than spots of other colors, especially in aquatic environments. Water absorbs many colors of light, but UV light penetrates water more effectively than longer wavelengths. This means that UV spots would be relatively more visible to both potential mates and predators in the underwater environment.
Conclusion
Considering that females prefer males with larger and more intense UV spots, it is plausible that the spots are colored ultraviolet to enable long-distance assessment. The UV spots would stand out against the background, making them more easily visible to females and potentially helping them make informed decisions about their choice of mates.