The Role of Mimicry in Orchid Pollination

Cryptostylis orchids do not offer nectar or food rewards. Instead, they rely on mimicry—specifically, their flowers look and smell like the females of their pollinator wasps. This mimicry is so precise that male wasps are attracted to the flowers, believing them to be potential mates. When a male wasp attempts to copulate with the flower, the unique shape of the orchid’s anther and stigma ensures that pollen is attached to the wasp in a species-specific manner. The wasp then inadvertently transfers this pollen to another Cryptostylis flower during its next mating attempt, facilitating pollination.

Behavioural Isolation as a Prezygotic Barrier

This strategy exemplifies a prezygotic reproductive barrier—a mechanism that prevents fertilization between different species before the formation of a zygote. In Cryptostylis, the barrier is not mechanical, temporal, or based on habitat, but rather behavioural. The orchids exploit the innate mating behaviors of their pollinator wasps through visual and olfactory mimicry. This ensures that each wasp species is attracted only to flowers that mimic its own females, preventing cross-pollination between different orchid species even when they grow side by side.

Why This Is Not Mechanical, Temporal, or Habitat Isolation

• Mechanical isolation involves physical incompatibility between reproductive structures, which is not the case here; the wasps can physically interact with the flowers.

• Temporal isolation refers to differences in breeding or flowering times, which is not the main mechanism in this scenario.

• Habitat isolation occurs when species occupy different environments, but Cryptostylis species often coexist in the same habitats.

Instead, the key isolating mechanism is the wasp’s behavior, manipulated by the orchid’s mimicry, making behavioural isolation through mimicry the best explanation.

Evolutionary Significance

This highly specialized pollination system not only maintains species boundaries but also drives the evolution of both the orchid and the wasp. The orchids benefit from precise pollen transfer, while the wasps, despite being deceived, continue to play their role in the reproductive cycle of the orchids. Such systems highlight the complexity and creativity of evolutionary solutions to the challenge of reproductive isolation.

Conclusion

The prezygotic barrier that prevents inter-species cross-pollination in Cryptostylis orchids is best explained by behavioural isolation through mimicry. By mimicking female wasps, these orchids ensure that only specific pollinators are attracted and that pollen transfer remains species-specific, thereby maintaining reproductive isolation and promoting speciation.

Correct answer:
(1) behavioural isolation through mimicry