Sex-ratio evolution in sex changing animals.

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Zoology

Background:

• Sex allocation theory predicts facultative offspring sex ratio adjustments based on local conditions.
• Consequences for overall population sex ratios are less understood, except in sequential hermaphrodites (sex-changing organisms).

Purpose of the Study:

• To test theoretical predictions regarding population sex ratios in sex-changing animals.
• Specifically, to examine the bias towards the first sex, the effect of partial sex change, and differences between protogynous and protandrous species.

Main Methods:

• A comparative study was conducted using data from 121 species of sex-changing animals.
• Species spanned five phyla: fish, arthropods, echinoderms, molluscs, and annelid worms.
• Predictions were tested across these diverse taxa.

Main Results:

• The study found support for the prediction that sex-changing organisms bias their sex ratio towards the first sex.
• A stronger bias was observed in species where all individuals change sex compared to partially sex-changing ones.
• Sex ratios were more biased in protogynous (female-first) species than in protandrous (male-first) species.

Conclusions:

• The findings support key predictions of sex allocation theory in sex-changing organisms.
• The degree of sex ratio bias is influenced by the mode of sex change and the initial sex.
• These results highlight the importance of studying sequential hermaphrodites to understand population-level sex allocation.