Amplexus

<h2 id="types">Types</h2>
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.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> These two types of amplexus have been classified based on the position of the male amphibian relative to the female.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> When a male amphibian clasps a female around her waist (inguinal region) using his forelimbs, this is considered inguinal amplexus.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> By contrast, when a male amphibian clasps behind the forelimbs (axillary region) of the female, this is considered axillary amplexus.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>

<h2 id="physiological-and-hormonal-function">Physiological and hormonal function</h2>
<h3>Physiology</h3>
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.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a> 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.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a> 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.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> This amplexus behaviour allows the amphibians' cloacae to be in close contact, while gametes are released.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a> 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 class="footnote-ref" id="fnref:20" href="#fn:20">20</a> 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.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> 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.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a>

<h3>Hormones</h3>
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.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a> 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.<a class="footnote-ref" id="fnref:24" href="#fn:24">24</a> Furthermore, both arginine vasotocin and gonadotropin-releasing hormone have been found to be involved in the sexual behaviour of male amphibians.<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a> 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.<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a> 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.<a class="footnote-ref" id="fnref:27" href="#fn:27">27</a> The increase in corticosterone found in females could be attributed to amplexus preventing them from foraging for food.<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a>

<h2 id="amphibians">Amphibians</h2>

<h3>Anurans</h3>
Amplexus chiefly occurs aquatically, but some terrestrial <a href="/facts/Frog/IxYhbeda">anurans</a> (frogs and toads) like the <a href="/facts/Disc-tongued_frog/4BH2cp5R">disc-tongued frogs</a> (<a href="/facts/Discoglossidae/4BH2cp5R">Discoglossidae</a>) perform amplexus on land. In crown-group anurans, like the true frogs (<a href="/facts/Ranidae/zKlDcL4Q">Ranidae</a>), the <a href="/facts/Tree_frog/D7LhXSTX">tree frogs</a> (Hylidae), and the true toads (<a href="/facts/Bufonidae/ETrzsg2f">Bufonidae</a>), amplexus is axillary (in the armpits). Other anurans (the <a href="/facts/Archaeobatrachia/6269Ts2m">Archaeobatrachia</a>, <a href="/facts/Sooglossidae/RcrCmF6o">Sooglossidae</a> and <a href="/facts/Myobatrachidae/QhMGj4rt">Myobatrachidae</a>), 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.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a> Additionally, anurans species have been observed to engage in multiple amplexus, which can also be referred to as a mating ball, as many toads attach themselves to a female trying to initiate amplexus.<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a> 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.<a class="footnote-ref" id="fnref:31" href="#fn:31">31</a> For female anurans, the idea of multiple amplexus would probably be more advantageous, because mating with more than one male would increase fertilization chances or increase offspring genetic diversity.<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> Multiple amplexus would typically be common in explosive breeding amphibians, when there is a larger number of adults ready to breed at a breeding site in a short period of time.<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a> When this occurs female amphibians are viewed as a very important resource for males, as there are typically more males present than females, thus leading to more chances for multiple amplexus to occur.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a>
In most anurans, the males deposit sperm onto the eggs as they are being laid, however males of the genus <a href="/facts/Ascaphus/T8ULEobk">Ascaphus</a> possess an <a href="/facts/Intromittent_organ/0bhhQ2hY">intromittent organ</a>, unique among anurans, for internal fertilization. Internal fertilization does occur in a few other genera, including <a href="/facts/Nectophrynoides/AuxFw3bm">Nectophrynoides</a>, <a href="/facts/Mertensophryne/s04G6Xjf">Mertensophryne</a>, and <a href="/facts/Eleutherodactylus/XFwVTsET">Eleutherodactylus</a>.<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a><a class="footnote-ref" id="fnref:36" href="#fn:36">36</a>

<h3>Newts</h3>
In the case of <a href="/facts/Newt/2KNMYeSn">newts</a>, 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 <a href="/facts/Intermittent_stream/UIPqg1S7">intermittent streams</a> and <a href="/facts/Vernal_pools/ztyFdarU">vernal pools</a> become available as a breeding habitat. The <a href="/facts/Rough-skinned_newt/TIjRgSGY">rough-skinned newt</a> 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.<a class="footnote-ref" id="fnref:37" href="#fn:37">37</a> 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.<a class="footnote-ref" id="fnref:38" href="#fn:38">38</a> 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 class="footnote-ref" id="fnref:39" href="#fn:39">39</a> Additionally, it has been found that the probability of a male newt who has a deeper tail-fin to achieve amplexus is greater than those newts who do not contain a deeper tail-fin, as male newts tend to use their tails during male-male competition.<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a> When a male newt, who is unpaired, encounters a female and male newt engaged in amplexus, the unpaired newt will try to displace the paired male newt by using wrestling tactics.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a> 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.<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a> The study found that the invading unpaired newt rarely successfully displaces the paired male newt, engaged in amplexus.<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a>

<h2 id="horseshoe-crabs">Horseshoe crabs</h2>

Amplexus occurs in all four species of <a href="/facts/Horseshoe_crab/IuaBGa9T">horseshoe crab</a>. Horseshoe crabs typically go ashore for amplexus in high tide, and end up on beaches where the eggs are more protected.<a class="footnote-ref" id="fnref:44" href="#fn:44">44</a> 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 <a href="/facts/Limulus_polyphemus/lJlYkhfC">Limulus polyphemus</a>.<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a> A male horseshoe crab develops modified <a href="/facts/Clasper/RR2Q0HAT">claspers</a> during sexual maturity when the male moults; these modified claspers can then help during the process of amplexus.<a class="footnote-ref" id="fnref:46" href="#fn:46">46</a> 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 <a href="/facts/Opisthosoma/rXmmsVrX">opisthosoma</a> during amplexus.<a class="footnote-ref" id="fnref:47" href="#fn:47">47</a> In contrast, the male's anterior claspers have been found to attach to the female's opisthosoma as well, but on the lateral edges of the opisthosoma and function to resist displacement from environmental factors.<a class="footnote-ref" id="fnref:48" href="#fn:48">48</a> Uniquely, amplexus is most likely to occur between horseshoe crabs when the female horseshoe crab has a hard shell.<a class="footnote-ref" id="fnref:49" href="#fn:49">49</a> Additionally, males who inhabit a clean shell are more likely to enter amplexus, compared to males who contain a dirty shell, as it seems that females have a preference for clean shells on males.<a class="footnote-ref" id="fnref:50" href="#fn:50">50</a> A male horseshoe crab's claspers may also be an important factor of consideration for the initiation of amplexus. Since claspers are used for the attachment to the female, claspers that are in good condition are more successful for the initiation of amplexus.<a class="footnote-ref" id="fnref:51" href="#fn:51">51</a> 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.<a class="footnote-ref" id="fnref:52" href="#fn:52">52</a>

<h2 id="other-animals">Other animals</h2>
Fossil evidence suggests that a certain <a href="/facts/Euthycarcinoid/uJ6o1Smz">euthycarcinoid</a> (an extinct arthropod) from the <a href="/facts/Cambrian/jIfzKtod">Cambrian</a> may also have mated by amplexus.<a class="footnote-ref" id="fnref:53" href="#fn:53">53</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Nuptial_pad/IaYvx0zF">Nuptial pad</a> – Secondary sex characteristic on some mature male frogs and salamanders</li></ul>

<h2 id="external-links">External links</h2>

Wikimedia Commons has media related to Amphibia pairs.

<ul><li><a href="https://web.archive.org/web/20090703075359/http://fvc3.com/tadpoles.html">Amplexus in Action</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">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 href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". Canadian Journal of Zoology. 81 (3): 388–394. doi:10.1139/Z03-013. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". Canadian Journal of Zoology. 81 (3): 388–394. doi:10.1139/Z03-013. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">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. Bibcode:2012BEcoS..66.1587S. doi:10.1007/s00265-012-1412-6. ISSN 0340-5443. PMC 3496481. PMID 23162205. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3496481" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3496481</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">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. Bibcode:2012BEcoS..66.1587S. doi:10.1007/s00265-012-1412-6. ISSN 0340-5443. PMC 3496481. PMID 23162205. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3496481" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3496481</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">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. Bibcode:2012BEcoS..66.1587S. doi:10.1007/s00265-012-1412-6. ISSN 0340-5443. PMC 3496481. PMID 23162205. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3496481" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3496481</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". Canadian Journal of Zoology. 81 (3): 388–394. doi:10.1139/Z03-013. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". Canadian Journal of Zoology. 81 (3): 388–394. doi:10.1139/Z03-013. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">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. S2CID 83622844. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">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. S2CID 83622844. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">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. S2CID 83622844. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Nussbaum, Ronald A. (1980). "Phylogenetic Implications of Amplectic Behavior in Sooglossid Frogs". Herpetologica. 36 (1): 1–5. ISSN 0018-0831. JSTOR 3891845. <a href="/wiki/ISSN_(identifier)" target="_blank">/wiki/ISSN_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Nussbaum, Ronald A. (1980). "Phylogenetic Implications of Amplectic Behavior in Sooglossid Frogs". Herpetologica. 36 (1): 1–5. ISSN 0018-0831. JSTOR 3891845. <a href="/wiki/ISSN_(identifier)" target="_blank">/wiki/ISSN_(identifier)</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Nussbaum, Ronald A. (1980). "Phylogenetic Implications of Amplectic Behavior in Sooglossid Frogs". Herpetologica. 36 (1): 1–5. ISSN 0018-0831. JSTOR 3891845. <a href="/wiki/ISSN_(identifier)" target="_blank">/wiki/ISSN_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Nussbaum, Ronald A. (1980). "Phylogenetic Implications of Amplectic Behavior in Sooglossid Frogs". Herpetologica. 36 (1): 1–5. ISSN 0018-0831. JSTOR 3891845. <a href="/wiki/ISSN_(identifier)" target="_blank">/wiki/ISSN_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". Canadian Journal of Zoology. 81 (3): 388–394. doi:10.1139/Z03-013. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">McLister, James (2003). "The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success". Canadian Journal of Zoology. 81 (3): 388–394. doi:10.1139/Z03-013. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">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. PMID 24698093. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">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. PMID 9367717. S2CID 41855944. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">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 href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">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 href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">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 href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">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. PMID 9367717. S2CID 41855944. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">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. PMID 9367717. S2CID 41855944. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
<li id="fn:25">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. PMID 9367717. S2CID 41855944. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></li>
<li id="fn:26">Reedy, Aaron M.; Edwards, Alex; Pendlebury, Chloe; Murdaugh, Laura; Avery, Ryan; Seidenberg, Jake; Aspbury, Andrea S.; Gabor, Caitlin R. (2014). "An acute increase in the stress hormone corticosterone is associated with mating behavior in both male and female red-spotted newts, Notophthalmus viridescens". General and Comparative Endocrinology. 208: 57–63. doi:10.1016/j.ygcen.2014.08.008. ISSN 0016-6480. PMID 25157790. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></li>
<li id="fn:27">Reedy, Aaron M.; Edwards, Alex; Pendlebury, Chloe; Murdaugh, Laura; Avery, Ryan; Seidenberg, Jake; Aspbury, Andrea S.; Gabor, Caitlin R. (2014). "An acute increase in the stress hormone corticosterone is associated with mating behavior in both male and female red-spotted newts, Notophthalmus viridescens". General and Comparative Endocrinology. 208: 57–63. doi:10.1016/j.ygcen.2014.08.008. ISSN 0016-6480. PMID 25157790. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></li>
<li id="fn:28">Reedy, Aaron M.; Edwards, Alex; Pendlebury, Chloe; Murdaugh, Laura; Avery, Ryan; Seidenberg, Jake; Aspbury, Andrea S.; Gabor, Caitlin R. (2014). "An acute increase in the stress hormone corticosterone is associated with mating behavior in both male and female red-spotted newts, Notophthalmus viridescens". General and Comparative Endocrinology. 208: 57–63. doi:10.1016/j.ygcen.2014.08.008. ISSN 0016-6480. PMID 25157790. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></li>
<li id="fn:29">Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill Publishing Company. <a href="#fnref:29" class="footnote-back-ref">↩</a></li>
<li id="fn:30">Lod, Thierry; Lesbarr, David (2004). "Multiple paternity in Rana dalmatina , a monogamous territorial breeding anuran". Naturwissenschaften. 91 (1): 44–47. Bibcode:2004NW.....91...44L. doi:10.1007/s00114-003-0491-7. ISSN 0028-1042. PMID 14740104. S2CID 21612515. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:30" class="footnote-back-ref">↩</a></li>
<li id="fn:31">Lod, Thierry; Lesbarr, David (2004). "Multiple paternity in Rana dalmatina , a monogamous territorial breeding anuran". Naturwissenschaften. 91 (1): 44–47. Bibcode:2004NW.....91...44L. doi:10.1007/s00114-003-0491-7. ISSN 0028-1042. PMID 14740104. S2CID 21612515. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:31" class="footnote-back-ref">↩</a></li>
<li id="fn:32">Lod, Thierry; Lesbarr, David (2004). "Multiple paternity in Rana dalmatina , a monogamous territorial breeding anuran". Naturwissenschaften. 91 (1): 44–47. Bibcode:2004NW.....91...44L. doi:10.1007/s00114-003-0491-7. ISSN 0028-1042. PMID 14740104. S2CID 21612515. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:32" class="footnote-back-ref">↩</a></li>
<li id="fn:33">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 href="#fnref:33" class="footnote-back-ref">↩</a></li>
<li id="fn:34">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 href="#fnref:34" class="footnote-back-ref">↩</a></li>
<li id="fn:35">Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. New York: McGraw-Hill Publishing Company. <a href="#fnref:35" class="footnote-back-ref">↩</a></li>
<li id="fn:36">Linzey, D. 2001. Vertebrate Biology, McGraw Hill Publishers, New York. <a href="#fnref:36" class="footnote-back-ref">↩</a></li>
<li id="fn:37">C. Michael Hogan (2008) Rough-skinned Newt (Taricha granulosa) Archived 2009-05-27 at the Wayback Machine, Globaltwitcher, ed. N. Stromberg <a href="http://www.globaltwitcher.com/artspec_information.asp?thingid=43182" target="_blank">http://www.globaltwitcher.com/artspec_information.asp?thingid=43182</a> <a href="#fnref:37" class="footnote-back-ref">↩</a></li>
<li id="fn:38">Able, David J. (1999-11-04). "Scramble competition selects for greater tailfin size in male red-spotted newts (Amphibia: Salamandridae)". Behavioral Ecology and Sociobiology. 46 (6): 423–428. Bibcode:1999BEcoS..46..423A. doi:10.1007/s002650050638. ISSN 0340-5443. S2CID 34638425. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:38" class="footnote-back-ref">↩</a></li>
<li id="fn:39">Able, David J. (1999-11-04). "Scramble competition selects for greater tailfin size in male red-spotted newts (Amphibia: Salamandridae)". Behavioral Ecology and Sociobiology. 46 (6): 423–428. Bibcode:1999BEcoS..46..423A. doi:10.1007/s002650050638. ISSN 0340-5443. S2CID 34638425. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:39" class="footnote-back-ref">↩</a></li>
<li id="fn:40">Able, David J. (1999-11-04). "Scramble competition selects for greater tailfin size in male red-spotted newts (Amphibia: Salamandridae)". Behavioral Ecology and Sociobiology. 46 (6): 423–428. Bibcode:1999BEcoS..46..423A. doi:10.1007/s002650050638. ISSN 0340-5443. S2CID 34638425. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:40" class="footnote-back-ref">↩</a></li>
<li id="fn:41">Verrell, Paul A. (1986). "Wrestling in the red-spotted newt (Notophthalmus viridescens): resource value and contestant asymmetry determine contest duration and outcome". Animal Behaviour. 34 (2): 398–402. doi:10.1016/s0003-3472(86)80108-7. ISSN 0003-3472. S2CID 53183312. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:41" class="footnote-back-ref">↩</a></li>
<li id="fn:42">Verrell, Paul A. (1986). "Wrestling in the red-spotted newt (Notophthalmus viridescens): resource value and contestant asymmetry determine contest duration and outcome". Animal Behaviour. 34 (2): 398–402. doi:10.1016/s0003-3472(86)80108-7. ISSN 0003-3472. S2CID 53183312. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:42" class="footnote-back-ref">↩</a></li>
<li id="fn:43">Verrell, Paul A. (1986). "Wrestling in the red-spotted newt (Notophthalmus viridescens): resource value and contestant asymmetry determine contest duration and outcome". Animal Behaviour. 34 (2): 398–402. doi:10.1016/s0003-3472(86)80108-7. ISSN 0003-3472. S2CID 53183312. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:43" class="footnote-back-ref">↩</a></li>
<li id="fn:44">Leschen, Alison S.; Grady, Sara P.; Valiela, Ivan (2006). "Fecundity and spawning of the Atlantic horseshoe crab, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA". Marine Ecology. 27 (1): 54–65. Bibcode:2006MarEc..27...54L. doi:10.1111/j.1439-0485.2005.00053.x. hdl:1912/906. ISSN 0173-9565. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:44" class="footnote-back-ref">↩</a></li>
<li id="fn:45">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. S2CID 85269977. <a href="https://doi.org/10.2108%2Fzsj.13.151" target="_blank">https://doi.org/10.2108%2Fzsj.13.151</a> <a href="#fnref:45" class="footnote-back-ref">↩</a></li>
<li id="fn:46">Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science. 13 (1): 151–159. doi:10.2108/zsj.13.151. ISSN 0289-0003. S2CID 85269977. <a href="https://doi.org/10.2108%2Fzsj.13.151" target="_blank">https://doi.org/10.2108%2Fzsj.13.151</a> <a href="#fnref:46" class="footnote-back-ref">↩</a></li>
<li id="fn:47">Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science. 13 (1): 151–159. doi:10.2108/zsj.13.151. ISSN 0289-0003. S2CID 85269977. <a href="https://doi.org/10.2108%2Fzsj.13.151" target="_blank">https://doi.org/10.2108%2Fzsj.13.151</a> <a href="#fnref:47" class="footnote-back-ref">↩</a></li>
<li id="fn:48">Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science. 13 (1): 151–159. doi:10.2108/zsj.13.151. ISSN 0289-0003. S2CID 85269977. <a href="https://doi.org/10.2108%2Fzsj.13.151" target="_blank">https://doi.org/10.2108%2Fzsj.13.151</a> <a href="#fnref:48" class="footnote-back-ref">↩</a></li>
<li id="fn:49">Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science. 13 (1): 151–159. doi:10.2108/zsj.13.151. ISSN 0289-0003. S2CID 85269977. <a href="https://doi.org/10.2108%2Fzsj.13.151" target="_blank">https://doi.org/10.2108%2Fzsj.13.151</a> <a href="#fnref:49" class="footnote-back-ref">↩</a></li>
<li id="fn:50">Botton, Mark L.; Shuster, Carl N.; Sekiguchi, Koichi; Sugita, Hiroaki (1996). "Amplexus and Mating Behavior in the Japanese Horseshoe Crab, Tachypleus tridentatus". Zoological Science. 13 (1): 151–159. doi:10.2108/zsj.13.151. ISSN 0289-0003. S2CID 85269977. <a href="https://doi.org/10.2108%2Fzsj.13.151" target="_blank">https://doi.org/10.2108%2Fzsj.13.151</a> <a href="#fnref:50" class="footnote-back-ref">↩</a></li>
<li id="fn:51">Duffy, Erin E.; Penn, Dustin J.; Botton, Mark L.; Brockmann, H. Jane; Loveland, Robert E. (2005-08-11). "Eye and clasper damage influence male mating tactics in the horseshoe crab, Limulus polyphemus". Journal of Ethology. 24 (1): 67–74. doi:10.1007/s10164-005-0163-5. ISSN 0289-0771. S2CID 1398829. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:51" class="footnote-back-ref">↩</a></li>
<li id="fn:52">Duffy, Erin E.; Penn, Dustin J.; Botton, Mark L.; Brockmann, H. Jane; Loveland, Robert E. (2005-08-11). "Eye and clasper damage influence male mating tactics in the horseshoe crab, Limulus polyphemus". Journal of Ethology. 24 (1): 67–74. doi:10.1007/s10164-005-0163-5. ISSN 0289-0771. S2CID 1398829. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:52" class="footnote-back-ref">↩</a></li>
<li id="fn:53">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. Bibcode:2012JPal...86..442C. doi:10.1666/11-056.1. S2CID 129234373. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:53" class="footnote-back-ref">↩</a></li>
</ol>

Amplexus open-in-new

Amplexus