Q.86 Which one of the following animals develops adaptive predator avoidance
morphology because of the presence of high predator number in its habitat?
(A) Daphnia sp.
(B) Scaphiopus sp.
(C) Wolbachia sp.
(D) Rhodnius sp.

Daphnia sp. is the correct answer.

Daphnia, a freshwater crustacean, exhibits inducible morphological defenses like neckteeth, helmets, and crests in response to high predator densities, enhancing survival against gape-limited predators.​

Option Analysis

(A) Daphnia sp.
Daphnia develops predator-specific morphological changes, such as elongated spines and body shape alterations, triggered by chemical cues (kairomones) from predators like Chaoborus or Triops when predator numbers are high. These adaptive defenses reduce handling time and gape limitation for predators, directly matching the question criteria.​

(B) Scaphiopus sp.
Scaphiopus (spadefoot toads) tadpoles show behavioral adaptations like increased activity or burst swimming in ephemeral pools but lack inducible morphological changes for predator avoidance; instead, they rely on rapid development or omnivory without predator-cued morphology shifts.​

(C) Wolbachia sp.
Wolbachia is an endosymbiotic bacterium that manipulates host reproduction (e.g., cytoplasmic incompatibility) but does not develop morphology itself; studies show it may alter host spider behavior like boldness, not adaptive prey morphology.​

(D) Rhodnius sp.
Rhodnius (kissing bugs) are blood-feeding vectors responding to host cues or repellents via behavior (e.g., avoidance of VOCs), with no evidence of predator-induced morphological plasticity; they focus on host-seeking, not anti-predator defenses.​

Daphnia sp. exemplifies adaptive predator avoidance morphology, forming inducible defenses such as neckteeth, crests, and body widening in habitats with high predator densities like Chaoborus larvae. This phenotypic plasticity allows rapid adaptation to predation risk via kairomones, reducing gape-limited predation success.​

Phenotypic Plasticity Mechanism

Daphnia detects predator cues, triggering morphological shifts within days: helmets against piercing predators (Notonecta) and spines against engulfers (Triops). These changes increase escape probability by 50% without permanent costs in low-risk environments.​

Comparisons with Other Species

• Scaphiopus sp.: Relies on behavioral escape, not morphology.​

• Wolbachia sp.: Bacterial symbiont; no prey defenses.​

• Rhodnius sp.: Behavioral host avoidance only.​