Amplexus

Many types of amplexus are identified in the literature. However, two types of amplexus are more common than others, known as inguinal and axillary amplexus. These two types of amplexus have been classified based on the position of the male amphibian relative to the female. When a male amphibian clasps a female around her waist (inguinal region) using his forelimbs, this is considered inguinal amplexus. By contrast, when a male amphibian clasps behind the forelimbs (axillary region) of the female, this is considered axillary amplexus. == Physiological and hormonal function ==

Physiology Amplexus has been found to involve different muscles in both male and female amphibians. The forelimb muscles in both males and females have been identified as the key muscles for amplexus that most species use. This amplexus behaviour allows the amphibians' cloacae to be in close contact, while gametes are released. Additionally, amplexus is thought to help with the alignment of the reproductive tracts of both males and females, which furthermore contributes to successful fertilization. A female amphibian may not always be receptive to a male amphibian who is trying to initiate amplexus, as the female may not be ready to produce eggs. However, overall it was found that males have a higher level of corticosterone compared to females, as amplexus is seen as more energetically costly to males. The increase in corticosterone found in females could be attributed to amplexus preventing them from foraging for food. ==Amphibians==

(Bufo bufo). mating ball (multiple amplexus). (Agalychnis callidryas), Costa Rica Anurans Amplexus chiefly occurs aquatically, but some terrestrial anurans (frogs and toads) like the disc-tongued frogs (Discoglossidae) perform amplexus on land. In crown-group anurans, like the true frogs (Ranidae), the tree frogs (Hylidae), and the true toads (Bufonidae), amplexus is axillary (in the armpits). Other anurans (the Archaeobatrachia, Sooglossidae and Myobatrachidae), show the ancestral state which is inguinal or lumbar amplexus (abdominal, in front of the hindlegs). Some species show cephalic amplexus where the head of the female is held while others show complete lack of amplexus. However, multiple amplexus is not common among anurans, which could indicate that the costs associated with multiple amplexus are higher than the advantages associated with it. Newts In the case of newts, the process of amplexus is often observed soon after the newts become seasonally active. 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. The rough-skinned newt is a specific widespread example of a newt in the western USA that can be observed in quiet stream pools and shallow ponds engaging in amplexus. During amplexus in newts, males will typically show the behaviour of tail fanning and chin rubbing which is thought to prompt the mating receptivity of the female newt. Studies have shown that male newts who have deeper tail-fins have better control of females during amplexus and are also more successful in catching the females for amplexus. A study examining the wrestling behaviour of newts found that of the observed wrestling encounters, 90% were "won" by the paired male, meaning he would retain the female newt. The study found that the invading unpaired newt rarely successfully displaces the paired male newt, engaged in amplexus. ==Horseshoe crabs==

''. The male is the smaller individual. Amplexus occurs in all four species of horseshoe crab. Horseshoe crabs typically go ashore for amplexus in high tide, and end up on beaches where the eggs are more protected. The first pair of walking legs is used to tightly clasp the female in all species, and the second pair is also employed in all but Limulus polyphemus. A male horseshoe crab develops modified claspers during sexual maturity when the male moults; these modified claspers can then help during the process of amplexus. The male's pair of posterior claspers are known for having the ability to maintain long-term amplexus which have been found to always attach to the female's opisthosoma during amplexus. If a male horseshoe crab has a damaged or missing clasper, then that puts the male at a disadvantage and increases the probability of being displaced by other competing male crabs. == Other animals ==

Fossil evidence suggests that a certain euthycarcinoid (an extinct arthropod) from the Cambrian may also have mated by amplexus. Crustaceans of the order Amphipoda engage in amplexus. ==See also==