Previous Year Questions

Question :

Directions : Read the following passage carefully and answer the questions that follow.

Mantis shrimp (e.g., Gonodactylaceus falcatus) possess a rare ability to reflect and detect circularly polarised light, a signal modality nearly unique in the animal kingdom. Scientists at the University of Queensland observed that these shrimps display circular polarisation patterns, especially on their legs, head, and armoured tail, when they curl defensively. This visual code seems to function as a ___A____ signal to competitors, effectively conveying occupancy of a burrow without revealing itself to predators or rivals. Controlled experiments revealed that mantis shrimp avoided burrows reflecting circularly polarised light in 68 percent of trials, suggesting they perceive such signals as a sign that another shrimp occupies the space.

The mantis shrimp's visual system is extraordinarily sophisticated. With compound eyes containing many photoreceptor types, these shrimps can process both linear and circular polarisation simultaneously, making them the only known animals with such a capability. Specialised microstructures in their eyes act like natural quarter-wave plates, converting circular into linear polarised light for analysis. Moreover, dynamic eye movements, torsional rotations help align visual receptors to optimise polarisation contrast. Such active alignment enhances the detection of polarisation signals within the shrimps' visual field. These adaptations also influence how shrimps choose a hiding position, given that polarisation visibility depends on orientation.

In Mediterranean marine environments and beyond, another communication channel involves snapping shrimp (family Alpheidae). These shrimps generate loud, broadband snapping sounds through rapid closure of an oversized claw, causing cavitation bubbles, to signal territory, interact socially, hunt, or respond to disturbances. Their snaps dominate underwater high-frequency soundscapes, peaking between 2 kHz and 20 kHz, and are often the most audible source in reef acoustic measurements. Snapping patterns follow daily and lunar rhythms, typically increasing around dawn and dusk and varying by location.

Scientists have begun using passive acoustic monitoring to study snapping shrimp populations and assess habitat health in the Mediterranean and globally. By deploying hydrophones, researchers can detect snapping rates and frequencies, estimate shrimp abundance, and infer seabed or reef conditions without disturbing habitats. In the Mediterranean Sea, snapping shrimp acoustic activity forms a key component of the marine soundscape; such sound patterns are now considered valuable biodiversity indicators and tools for ecosystem monitoring.

These discoveries in Australia and the Mediterranean regions have sparked renewed scientific curiosity across sensory ecology, communication, and technology. The mantis shrimp's use of polarised light signals challenges traditional understanding of animal communication and inspires optical technologies, including advanced polarising imaging for medical or remote-sensing purposes. Meanwhile, snapping shrimp acoustic signatures offer non-invasive, scalable tools for marine habitat assessment and conservation, especially as ocean conditions change. Together, visual and acoustic modalities in shrimps continue to open interdisciplinary research avenues in biology, engineering, and environmental monitoring.

Which of the following is the most appropriate to fill the blank 'A' as given in the passage?