Competitive gametic traits and their coevolution with strong and slight anisogamy

Area of Science:

• Evolutionary biology
• Reproductive biology
• Biophysics

Background:

• Gamete dynamics (GD) theory models the evolutionary transition from isogamy to anisogamy.
• This transition involves gamete limitation, competition, and provisioning requirements.
• Recent models incorporating competitive gamete traits yield different predictions.

Purpose of the Study:

• To re-evaluate gamete trait evolution within conventional GD theory.
• To investigate the impact of competitive gamete traits on anisogamy evolution.
• To compare findings with recent alternative models.

Main Methods:

• Developing mathematical models for gamete traits (motility, target size) under GD assumptions.
• Analyzing the conditions for trait evolution in male versus female gametes.
• Comparing model outcomes with existing theories and recent developments.

Main Results:

• Competitive gamete traits tend to evolve in the male gamete unless gamete limitation is strong and the trait benefits the larger gamete.
• Gamete trait evolution does not change the fundamental conditions for anisogamy evolution.
• Discrepancies with Siljestam & Martinossi-Allibert stem from their assumptions on zygote survival.
• Coevolution of gamete size with traits like motility can drive the evolution of slight anisogamy.

Conclusions:

• Conventional GD theory predicts male-biased evolution of competitive gamete traits.
• The evolution of anisogamy is robust to the inclusion of these traits under standard GD assumptions.
• Novel findings suggest coevolutionary pathways to anisogamy involving multiple gamete traits.