Amplexus

Amplexus (Latin "embrace") is a type of mating behavior exhibited by some externally fertilizing species (chiefly amphibians and horseshoe crabs) in which a male grasps a female with his front legs as part of the mating process, and at the same time or with some time delay, he fertilizes the eggs, as they are released from the female's body.

[1] In amphibians, females may be grasped by the head, waist, or armpits, and the type of amplexus is characteristic of some taxonomic groups.

In order for amplexus to be initiated, male frogs must first find a mate by attracting one through calls, typically in the evening.

[4] After conducting experiments, researchers confirmed that amplexus does decrease a female's locomotor performance (e.g., swimming, walking) as well as the feeding rates.

[5] These two types of amplexus have been classified based on the position of the male amphibian relative to the female.

[2] In addition to those forelimb muscles being larger in males, male frogs also typically have keratin pads or nuptial pads, which are located on their thumbs and contribute to the success of amplexus by assisting in gripping the female for the duration of amplexus.

[7] Additionally, amplexus is thought to help with the alignment of the reproductive tracts of both males and females, which furthermore contributes to successful fertilization.

The hormone arginine vasotocin (AVT) has been identified as having an effect on the calling behaviours produced by these male amphibians when searching for a female mate, as AVT increased the amount of calling behaviour produced in male amphibians.

[7] Furthermore, both arginine vasotocin and gonadotropin-releasing hormone have been found to be involved in the sexual behaviour of male amphibians.

A study conducted on red-spotted newts found an acute increase in corticosterone for both males and females who were engaged in the behaviour of amplexus.

Other anurans (the Archaeobatrachia, Sooglossidae and Myobatrachidae), show the ancestral state which is inguinal or lumbar amplexus (abdominal, in front of the hindlegs).

In the Western USA, for example, this time is typically soon after the onset of the winter rainy season, when intermittent streams and vernal pools become available as a breeding habitat.

Horseshoe crabs typically go ashore for amplexus in high tide, and end up on beaches where the eggs are more protected.