Microbes as manipulators of egg size and developmental evolution.

Area of Science:

• Evolutionary Biology
• Marine Biology
• Microbial Ecology

Background:

• Marine invertebrates exhibit two main reproductive strategies: energy-poor eggs developing into feeding larvae, or energy-rich eggs into non-feeding larvae.
• Evolutionary transitions between these developmental modes are known, but the driving factors remain unclear.
• Microbial manipulators influencing host reproduction are common in terrestrial systems and increasingly found in marine taxa that have undergone developmental transitions.

Purpose of the Study:

• To investigate the potential role of microbes in driving evolutionary transitions in marine invertebrate development.
• To present theoretical models demonstrating how microbial manipulation could alter reproductive strategies.
• To provide a framework for comparing marine and terrestrial microbe-host evolutionary dynamics.

Main Methods:

• Theoretical modeling of host-microbe interactions.
• Analysis of sex ratio shifts and egg size selection.
• Identification of marine invertebrate genera potentially fitting the model.

Main Results:

• Microbial manipulators can induce a sperm-limited environment by shifting host sex ratios toward female dominance.
• This sperm limitation selects for larger eggs, facilitating a transition to non-feeding larvae.
• Loss of microbial manipulation can lead to the recovery of ancestral egg size and feeding larval development.

Conclusions:

• Microbial manipulators are a plausible factor driving evolutionary transitions in marine invertebrate developmental modes.
• This mechanism offers a new perspective on invertebrate developmental evolution and parallels with terrestrial systems.
• Further research is needed to confirm these microbial influences and compare mechanisms across environments.