Same-Sex Sexual Behavior in Invertebrates: A Systematic Synthesis of Prevalence, Study Type, and Interpretation

Area of Science:

• Zoology
• Ethology
• Evolutionary Biology

Background:

• Same-sex sexual behavior (SSB) encompasses diverse interactions between individuals of the same sex in the animal kingdom.
• Published evidence indicates SSB occurs across a wide range of invertebrate taxa, including arthropods, mollusks, and annelids.

Purpose of the Study:

• To systematically synthesize existing literature on same-sex sexual behavior in invertebrates.
• To assess the prevalence, reported behaviors, and proposed explanations for SSB across different invertebrate groups.

Main Methods:

• Systematic synthesis of 222 primary studies and 12 reviews on invertebrate SSB.
• Categorization of reported behaviors and explanatory frameworks provided by the original studies.

Main Results:

• Evidence of SSB was found in approximately 207 invertebrate species, with insects being the most frequently reported group.
• Copulation-like interactions were the most common SSB, followed by courtship and mounting.
• Explanations for SSB included mistaken identity and indiscriminate mating, with adaptive and social functions also noted; fitness consequences were context-dependent.

Conclusions:

• Same-sex sexual behavior in invertebrates is a widespread and heterogeneous phenomenon, not reducible to a single cause.
• The expression of SSB is influenced by factors such as mating systems, study methodologies, and taxonomic history.
• Further research is needed to fully understand the diverse evolutionary and ecological roles of SSB in invertebrates.