Amplexus
Amplexus (Latin "embrace") is a type of
Amplexus involves direct contact between male and female, distinguished from other forms of external fertilization, such as
The competition for a female mate among males is considered intense, and it is not uncommon for a male amphibian to attack an already-amplexed pair of amphibians.[3] When a male amphibian attacks an amplexed pair of amphibians, he is trying to force the other male to release its grasp of the female, so he can then mate with her.[3] Male amphibians are also known to show mate-guarding behaviour, which is shown after amplexus, and it is the male's attempt to prevent the female amphibian from mating with other males.[3]
The duration of amplexus has been found to vary across species. In some species it may last for many days, while in others it may last a few hours.[4] Despite the variation in the duration of amplexus across species, typically all species that exhibit this behaviour have to use their forelimb muscles for the duration of amplexus.[4] Studies have found that this reproductive behaviour of amplexus can come with different fitness costs, due to the fact that amplexus can occur for prolonged periods of time. For instance, a study found that when a male amphibian is grasping and holding onto a female amphibian, this can lead to the impairment of the female's ability to move or to feed.[5] 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] With regard to the cost to the male engaged in amplexus, male amphibians have been found to not feed at all during amplexus.[5]
Types
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.[6] These two types of amplexus have been classified based on the position of the male amphibian relative to the female.[6] When a male amphibian clasps a female around her waist (inguinal region) using his forelimbs, this is considered inguinal amplexus.[6] By contrast, when a male amphibian clasps behind the forelimbs (axillary region) of the female, this is considered axillary amplexus.[6]
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.[4] These forelimb muscles that are used during amplexus are typically larger in males than females, and for males these muscles contain more oxidative fibers, which could mean that amplexus involves an increased rate of aerobic metabolism.[4] 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] This amplexus behaviour allows the amphibians' cloacae to be in close contact, while gametes are released.[8] Additionally, amplexus is thought to help with the alignment of the reproductive tracts of both males and females, which furthermore contributes to successful fertilization.[1] 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.[1] When the female is not ready to engage in amplexus, she will simply vibrate her body, which will then be felt by the male who is clasped to her and he will then stop the amplexus behaviour.[1]
Hormones
Two major hormones have been identified to be involved in amplexus. 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.[8] Additionally, it is believed that the gonadotropin-releasing hormone (GnRH) has an influence on amplexus in amphibians, as it has been found to produce or initiate this behaviour in many anuran amphibians.[8] Furthermore, both arginine vasotocin and gonadotropin-releasing hormone have been found to be involved in the sexual behaviour of male amphibians.[8] The stress hormone corticosterone has also been identified as associated with the sexual behaviour of amplexus. 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.[9] 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.[9] The increase in corticosterone found in females could be attributed to amplexus preventing them from foraging for food.[9]
Amphibians
![](http://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Mating_pair_of_common_frogs_in_amplexus.jpg/220px-Mating_pair_of_common_frogs_in_amplexus.jpg)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Common_toad_Bufo_bufo_multiple_amplexus_mating_ball.jpg/220px-Common_toad_Bufo_bufo_multiple_amplexus_mating_ball.jpg)
Anurans
Amplexus chiefly occurs aquatically, but some terrestrial
In most anurans, the males deposit sperm onto the eggs as they are being laid, however males of the genus
Newts
In the case of
Horseshoe crabs
Amplexus occurs in all four species of
Other animals
Fossil evidence suggests that a certain
See also
- Nuptial pad – Secondary sex characteristic on some mature male frogs and salamanders
References
- ^ a b c d e f Mollov, Ivelin; Popgeorgiev, Georgi; Naumov, Borislav; Tzankov, Nikolay; Stoyanov, Andrei (2010). "Cases of abnormal amplexus in anurans (Amphibia: Anura) from Bulgaria and Greece". Biharean Biologist.
- ^ doi:10.1139/Z03-013.
- ^ PMID 23162205.
- ^ doi:10.1139/Z03-013.
- ^ S2CID 83622844.
- ^ JSTOR 3891845.
- PMID 24698093.
- ^ S2CID 41855944.
- ^ PMID 25157790.
- ^ a b Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill Publishing Company.
- ^ S2CID 21612515.
- ^ Linzey, D. 2001. Vertebrate Biology, McGraw Hill Publishers, New York.
- ^ C. Michael Hogan (2008) Rough-skinned Newt (Taricha granulosa) Archived 2009-05-27 at the Wayback Machine, Globaltwitcher, ed. N. Stromberg
- ^ S2CID 34638425.
- ^ S2CID 53183312.
- ISSN 0173-9565.
- S2CID 85269977.
- ^ S2CID 85269977.
- ^ S2CID 1398829.
- S2CID 129234373.
External links
![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)