Size-dependent sex allocation in a simultaneous hermaphrodite parasite

Area of Science:

• Evolutionary Biology
• Reproductive Biology
• Parasitology

Background:

• Traditional sex allocation models often focus on sequential and simultaneous hermaphrodites.
• Size-dependent sex allocation is a known phenomenon, particularly in plants.
• Simultaneous hermaphrodites, like the tapeworm Schistocephalus solidus, exhibit variable adult sizes, making them ideal for studying size-dependent allocation.

Purpose of the Study:

• To investigate sex allocation patterns in the simultaneous hermaphrodite tapeworm Schistocephalus solidus.
• To determine the relationship between individual body volume and the allocation of resources to reproductive tissues.
• To explore the implications of size-dependent sex allocation in animals compared to plants.

Main Methods:

• Utilized stereological techniques to measure somatic and reproductive tissue volumes.
• Employed an allometric model to analyze the relationship between individual volume and reproductive tissue allocation.
• Quantified yolk gland volume (female allocation) and testis volume (male allocation).

Main Results:

• Yolk gland volume (female allocation) increased disproportionately with individual volume.
• Testis volume (male allocation) showed a tendency to increase less than proportionally with individual volume.
• Sex allocation was strongly correlated with individual volume, with larger tapeworms showing a greater bias towards female allocation.

Conclusions:

• Schistocephalus solidus exhibits significant size-dependent sex allocation, with larger individuals favoring female reproduction.
• These findings extend the concept of size-dependent sex allocation beyond plants to simultaneous hermaphrodite animals.
• The results contribute to a broader understanding of reproductive strategies in organisms with variable adult sizes.