Sperm competition experiments between lines of crickets producing different sperm lengths

Area of Science:

• Evolutionary Biology
• Reproductive Biology
• Animal Behavior

Background:

• Sperm number is a key factor in fertilization success during sperm competition.
• The role of sperm size variation in fertilization success remains less understood.
• Sperm size varies significantly across and within species, potentially influenced by sperm competition.

Purpose of the Study:

• To investigate the consequences of sperm length variation on fertilization precedence.
• To determine if sperm size influences competitive ability in controlled sperm competition experiments.
• To examine the relationship between sperm length and fertilization success in the field cricket Gryllus bimaculatus.

Main Methods:

• Controlled sperm competition experiments were conducted using the field cricket Gryllus bimaculatus.
• Cricket lines with distinct short, medium, and long sperm lengths were selectively bred.
• Two-male sperm competitions were established through sequential mating, with paternity assessed using an irradiated male technique.

Main Results:

• No evidence was found linking sperm length variation to differences in fertilization success.
• Males producing longer sperm did not exhibit a fertilization advantage over males producing shorter sperm.
• Sperm length, whether diverged or near the population mean, did not confer a competitive advantage.

Conclusions:

• Sperm size does not appear to be a significant determinant of fertilization success in Gryllus bimaculatus under these experimental conditions.
• The study suggests that factors other than sperm length may play a more critical role in sperm competition outcomes in this species.
• Further research is needed to explore other potential drivers of variation in fertilization success in species with sperm competition.