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. Amplexus involves direct contact between male and female, distinguished from other forms of external fertilization such as broadcast spawning, where sperm and eggs are freely shed into water without direct contact by individuals. In order for amplexus to be initiated, male frogs must first find a mate by attracting one through calls, typically in the evening.[2] Once a male has successfully attracted a mate the process of amplexus begins while the unsuccessful males are forced to continue their search for a mate through further calls.[2] The competition for a female to mate with among males is considered intense as it is not uncommon for a male amphibian to attack an already-amplexed pair of amphibians.[3] When a male amphibian attacks an already-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.[4] Male amphibians are also known to show mate-guarding behaviour, which is shown after amplexus and it is the males attempt to prevent the female amphibian from mating with other males.[4] The duration of amplexus has been found to vary across different species as in some species it has been found to last for many days but in other species, it has been found to last a few hours.[5] Despite the variation in the duration of amplexus across different species, typically all the species that exhibit this behaviour have to use their forelimb muscles for the whole duration of amplexus.[5] 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.[6] After conducting experiments, researchers confirmed that amplexus does decrease a female's locomotor performance (e.g. swimming, walking) as well as decrease the feeding rates of females engaged in amplexus.[6] With regards to the cost of a male engaged in amplexus, male amphibians have been found to not feed at all during amplexus.[6] Additionally, amplexus is thought to help with the alignment of the reproductive tracts of both males and females which furthermore contributes to the achievement of successful fertilization.[1]
There are two different types of amplexus known as inguinal and axillary amplexus.[7] These two types of amplexus have been classified based on the position of the male amphibian to the female it is mating with.[7] When a male amphibian clasps a female around their waist (inguinal region) using his forelimbs, this is then considered inguinal amplexus.[7] Contrastingly, when a male amphibian clasps behind the forelimbs (axillary region) of a female amphibian, this is then considered axillary amplexus.[7]
Physiological and Hormonal Function
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 key muscles for amplexus that most species use.[8] 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.[8] 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.[9] This amplexus behaviour allows the amphibians cloacae to be in close contact while gametes are being released.[10] Additionally, amplexus is thought to help with the alignment of the reproductive tracts of both males and females which furthermore contributes to the achievement of successful fertilization.[11] 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.[11] 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.[11]
Amphibians
Anurans
Amplexus chiefly occurs aquatically, but some more 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.[12]
In most anurans, the males deposit sperm onto the eggs as they are being laid, however males of the genus Ascaphus possess an intromittent organ, unique among anurans, for internal fertilization. Internal fertilization does occur in a few other genera, including Nectophrynoides, Mertensophryne, and Eleutherodactylus.[12][13]
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 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.[14]
Horseshoe crabs
Amplexus occurs in all four species of horseshoe crab. 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.[15]
Other animals
Fossil evidence suggests that a certain euthycarcinoid (an extinct arthropod) from the Cambrian may also have mated by amplexus.[16]
See also
References
- ^ a b 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.
- ^ a b McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". NRC Canada. doi:10.1139/Z03-013.
- ^ Sztatecsny, Marc; Preininger, Doris; Freudmann, Anita; Loretto, Matthias-Claudio; Maier, Franziska; Hödl, Walter (2012-09-23). "Don't get the blues: conspicuous nuptial colouration of male moor frogs (Rana arvalis) supports visual mate recognition during scramble competition in large breeding aggregations". Behavioral Ecology and Sociobiology. 66 (12): 1587–1593. doi:10.1007/s00265-012-1412-6. ISSN 0340-5443.
- ^ a b Sztatecsny, Marc; Preininger, Doris; Freudmann, Anita; Loretto, Matthias-Claudio; Maier, Franziska; Hödl, Walter (2012-09-23). "Don't get the blues: conspicuous nuptial colouration of male moor frogs (Rana arvalis) supports visual mate recognition during scramble competition in large breeding aggregations". Behavioral Ecology and Sociobiology. 66 (12): 1587–1593. doi:10.1007/s00265-012-1412-6. ISSN 0340-5443.
- ^ a b McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". NRC Canada. doi:10.1139/Z03-013.
- ^ a b c Bowcock, Haley; Brown, GregoryP.; Shine, Richard (2009-02-23). "Beastly Bondage: The Costs of Amplexus in Cane Toads (Bufo marinus)". Copeia. 2009 (1): 29–36. doi:10.1643/ce-08-036. ISSN 0045-8511.
- ^ a b c d Nussbaum, Ronald A. (1980). "Phylogenetic Implications of Amplectic Behavior in Sooglossid Frogs". Herpetologica. 36 (1): 1–5. ISSN 0018-0831.
- ^ a b McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". NRC Canada. doi:10.1139/Z03-013.
- ^ Chakraborti, S.; Nag, T.C.; Das, D.; Sanyal Chatterjee, T.; De, S.K. (2014). "Cytokeratin localization in toe pads of the anuran amphibian Philautus annandalii (Boulenger, 1906)". Tissue and Cell. 46 (3): 165–169. doi:10.1016/j.tice.2014.03.001. ISSN 0040-8166.
- ^ Propper, Catherine R.; Dixon, Timothy B. (1997). "Differential Effects of Arginine Vasotocin and Gonadotropin-Releasing Hormone on Sexual Behaviors in an Anuran Amphibian". Hormones and Behavior. 32 (2): 99–104. doi:10.1006/hbeh.1997.1408.
- ^ a b c Mollov, Ivelin; Popgeorgiev, Georgi; Naumov, Borislav; Tzankov, Nikolay; Stoyanov, Andrei (2010). "Cases of abnormal amplexus in anurans (Amphibia: Anura) from Bulgaria and Greece" (PDF). Biharean Biologist.
- ^ a b Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill Publishing Company.
- ^ 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
- ^ Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (February 1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science. 13 (1): 151–159. doi:10.2108/zsj.13.151.
- ^ Collette, Joseph H.; Gass, Kenneth C.; Hagadorn, James W. (May 2012). "Protichnites eremita Unshelled? Experimental Model-Based Neoichnology and New Evidence for A Euthycarcinoid Affinity for This Ichnospecies". Journal of Paleontology. 86 (3): 442–454. doi:10.1666/11-056.1.
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