Frequency-dependent Batesian mimicry maintains colour polymorphism in a sea snake population

Area of Science:

• Evolutionary Biology
• Animal Behavior
• Ecology

Background:

• Polymorphic traits persist in populations via mechanisms like negative frequency-dependent selection or heterozygote advantage.
• Non-venomous turtle-headed sea snakes (Emydocephalus annulatus) in New Caledonia display three distinct color morphs: black, black-and-white banded, and grey-banded.
• These morphs are hypothesized to be Batesian mimics of venomous sea snakes found in the same habitat.

Purpose of the Study:

• To investigate the maintenance mechanisms of color morph frequencies in Emydocephalus annulatus populations.
• To test the hypothesis of negative frequency-dependent selection acting on these morphs.
• To evaluate the role of Batesian mimicry in the survival of these sea snakes.

Main Methods:

• Conducted 18 consecutive years of population surveys to record sea snake morph frequencies.
• Analyzed recruit numbers (neonates and immigrants) in relation to existing morph frequencies.
• Observed behavioral responses of predatory fish to different sea snake morphs.

Main Results:

• Morph frequencies are maintained by negative frequency-dependent selection, with rarer morphs showing increased recruitment.
• Mimetic (banded) morphs are less frequent than the cryptic melanic morph, aligning with evolutionary predictions.
• Behavioral studies indicated differential predation, with banded snakes being avoided and black snakes attacked by smaller fish.

Conclusions:

• Negative frequency-dependent selection is the primary mechanism maintaining color polymorphism in Emydocephalus annulatus.
• Batesian mimicry of venomous sea snakes likely provides a survival advantage against predators like fish and sea eagles.
• The observed morph frequencies and anti-predator behaviors support the mimicry hypothesis in this sea snake population.