Rapid evolution and plasticity of genitalia

Area of Science:

• Evolutionary biology
• Animal reproductive morphology
• Developmental plasticity

Background:

• Genital morphology varies significantly and influences fitness.
• Sexual selection, natural selection, and neutral forces are known drivers of genital divergence.
• Genitalia may also exhibit developmental plasticity influenced by environmental factors.

Purpose of the Study:

• To investigate rapid genital evolution in Trinidadian guppies introduced to a low-predation environment.
• To test for developmental plasticity of the male intromittent organ (gonopodium) in response to environmental cues.
• To determine if plasticity itself evolved in the introduced guppy populations.

Main Methods:

• Experimental introduction of guppies to streams with reduced predation.
• Laboratory rearing of source and introduced populations for two generations to control for environmental effects.
• Measurement of gonopodium length relative to body size under different feeding and predator cue treatments.

Main Results:

• Introduced guppy populations evolved shorter gonopodia relative to body size within 8-12 generations.
• Gonopodium length showed plasticity, with longer relative lengths observed in individuals reared on low food levels.
• No significant difference in gonopodium length was found in response to predator cues.
• The plastic response to food levels was consistent between source and introduced populations, indicating no evolution of plasticity.

Conclusions:

• Rapid evolution of genital morphology can occur in response to environmental changes, such as reduced predation.
• Developmental plasticity plays a role in maintaining gonopodium length relative to body size under varying nutritional conditions.
• This study highlights the interplay between rapid evolution and developmental plasticity in shaping genital variation.