Guppy Color Variation and Selection

Modelling of Sexual and Natural Selection

• Modelling sexual and natural selection is based on experimentally controlling selection pressures.
• John Endler studied wild guppies (Poecilia wingei) in Trinidad, which inhabit small pools associated with mountain streams.

Endler's Investigation of Selection in Guppy Fish

• Guppies are native to the Caribbean and South America.
• Male guppies are colourful and variable, while females are large and typically plain.
• Endler studied the wide variation between male guppies in different pools and within the same stream, measuring their size, colour, and spot patterns.
• Endler observed a strong link between a guppy's habitat within a stream and whether a guppy was flashy or drab.

Selection Pressures on Guppy Color Variation

• Guppy males are categorized as "Drab," "Average," or "Flashy," based on their coloration.
• "Drab" males have only modest colour dots near their tails.
• "Average" males have a few spots along their body and tail.
• "Flashy" males have vivid blue and orange splotches along their sides.

Models of Endler's Investigation of Selection

• A computer model simulates Endler's experiments, manipulating female preference for flashy males, the number of predators, and the initial number of guppies.
• Students use the model to investigate the impact of predators and female preference on the number of spots on male guppies.
• Use natural selection to explain the effects of predators on guppy spots and sexual selection for the effects of female preference.

Endler's Investigation of Selection in Guppy Fish (Selective Pressures)

• Flashy males are more likely to be eaten by predators.
• In areas with high predator density, male guppies tend toward a drab colouration as camouflage to avoid predation.
• Flashy coloration attracts females, allowing males to pass their genes to the next generation.
• Bright colours might indicate "good genes" in the same way the strong physique of a human athlete shows health and vitality.

Predation Pressures on Guppy Color Variation

• Different stream sections have varying predator species.
• Rivulus ("killifish") are found at higher elevations and primarily feed on young guppies.
• Pike cichlids are found at lower elevations and are the most voracious predators, consuming significant numbers of guppies daily.

Models of Endler's Investigation of Selection (Further Exploration)

• The computer model allows students to study how different predator numbers affect the average number of spots on guppies.
• The model can simulate how relocating fish from areas with cichlid predators to areas without them influences their evolution.

Endler's Investigation of Selection in Guppy Fish (Experiment Results)

• In areas with low predation, sexual selection leads to an increase in the number of flashy males. "Dull" allele genes are removed from the population due to lack of reproduction.
• In areas with high predation pressure, predator selection reduces the number of flashy males, as they are more readily preyed upon. The "flashy" alleles are removed.

Endler's Investigation of Selection in Guppy Fish (Transplanted Guppies)

• Dull-colored male guppies were transplanted to areas with fewer predators.
• Over 15 guppy generations, the transplanted population evolved to have more brightly coloured males, with more colored areas and more spots.

Scientific Models (General Concepts)

• Models are helpful for simplifying complex processes or structures, changing the scale of study subjects, or manipulating time rates of phenomena.
• Models assist communication by making complex systems or concepts more accessible.
• Scientists employ models to test predictions about processes not easily observed.

Types of Scientific Models

• Experimental Models: control experimental conditions to study processes in complex natural scenarios.
• Mathematical Models: use mathematical language to describe system behaviours.
• Computer Models: computer programs simulating system behaviour.
• Physical Models: tangible models of structures.
• Images/Graphs: visual representations of phenomena.
• Analogies: comparisons highlighting similarities between systems.

Limitations of Models

• No model can provide a complete representation of a phenomenon.
• Models are not perfect copies but simplified representations of aspects of a target system.
• Models should be as simple as possible while encompassing as many characteristics of reality as possible.
• Model accuracy relies on the current state of scientific knowledge and might require modification with new data.

References (Source Material)

• Includes specific scientific articles/papers. (These are noted, but not fully transcribed.)