A nuptial pad is a secondary sex characteristic

Secondary sex characteristic

Secondary sex characteristics are features that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which give an individual an advantage over its rivals in courtship and aggressive...

 present on some mature male frog

Frog

Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...

s and salamander

Salamander

Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...

s. Triggered by androgen

Androgen

Androgen, also called androgenic hormone or testoid, is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors...

 hormones, this breeding gland (a type of mucus gland) appears as a spiked epithelial swelling on the forearm

Forearm

-See also:*Forearm flexors*Forearm muscles...

 and prepollex that aids with grip, used primarily by males to grasp (or clasp) females during amplexus

Amplexus

Amplexus is a form of pseudocopulation in which a male amphibian grasps a female with his front legs as part of the mating process...

. They can also be used in male-male combat in some species.

Historical background

Austrian biologist Paul Kammerer

Paul Kammerer

Paul Kammerer was an Austrian biologist who studied and advocated the now abandoned Lamarckian theory of inheritance – the notion that organisms may pass to their offspring characteristics they have acquired in their lifetime...

 experimented on midwife toad

Midwife toad

Midwife toads are a genus of frogs in the Discoglossidae family, and are found in most of Europe and northwestern Africa. Characteristic of these toad-like frogs is their parental care: the males carry a string of fertilised eggs on their back, hence the name "midwife". The female expels a strand...

s' nuptial pads. He used the offsprings' apparent enlargening from generation-to-generation as evidence of Lamarckian evolution.

Species examples

Many amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

 species manifest nuptial pads for use in amplexus, an example being the Rough-skinned newt

Rough-skinned Newt

The rough-skinned newt is a North American newt known for its strong poison.- Toxicity :Many newts produce toxins to avoid predation, but the toxins of the genus Taricha are particularly potent...

, Taricha granulosa.