How do copulatory pads develop during frog maturation

Copulatory pads (or nuptial pads) are specialized secondary sexual characteristics that develop on the thumbs and forelimbs of male frogs. Their growth is a hormonally-driven process tied to sexual maturity and the breeding season.

The development occurs as follows:

1. Hormonal Trigger: As a male frog reaches sexual maturity and the breeding season begins, its testes are stimulated to produce high levels of androgen hormones, primarily testosterone.
2. Cellular Response: These androgens circulate in the blood and bind to receptors in the skin cells of the thumb pads.
3. Epidermal Thickening: The hormones trigger rapid cell division (proliferation) in the epidermis (outer skin layer), causing it to become thick and rough.
4. Formation of Spines: The surface develops numerous tiny, hard, conical projections made of keratin. These keratinized papillae (spines) give the pad its sandpaper-like texture, which is essential for gripping.
5. Glandular Enlargement: The mucous glands beneath the skin also enlarge and secrete a sticky mucus, further aiding adhesion.

After the breeding season, androgen levels drop, and the pads regress and become smooth again until the next year.