Q. Consider the following statements regarding Darwin’s bark spider and its silk:
Only large adult female Darwin’s bark spiders produce the toughest natural silk due to higher ecological and energetic demands.
The exceptional toughness of the silk is mainly due to high proline content in dragline silk, making its production metabolically expensive.
To optimise energy use, adult females build sparser webs with stronger threads, while males and juveniles build denser webs with weaker silk.
Silk elasticity varies significantly between males, females, and juveniles, reflecting adaptive genetic differences.
Which of the statements given above are correct?
(a) 1, 2 and 3 only
(b) 1 and 2 only
(c) 2, 3 and 4 only
(d) 1, 2, 3 and 4
Correct Answer:
(a) 1, 2 and 3 only
Detailed Explanation:
Statement 1 is correct: The study shows that only large adult females of Caerostris darwini produce ultra-tough silk because they are 3–5 times larger than males and face greater ecological pressures such as building massive webs over rivers.
Statement 2 is correct: The silk’s extraordinary strength (≈1.6 GPa, about three times stronger than iron) comes from high proline content in dragline (major ampullate) silk, which enhances elasticity and toughness but is energetically costly to produce.
Statement 3 is correct: To manage this high energy cost, adult females spin fewer but stronger threads, while males and juveniles use denser webs made of cheaper, weaker silk, reflecting adaptive energy optimisation.
Statement 4 is incorrect: The study explicitly notes that silk elasticity remains constant across all individuals, indicating it is a genetically conserved trait and does not vary adaptively.