Penile Anatomy and Hypotheses of Erectile Function in the American Alligator (Alligator mississippiensis): Muscular Eversion and Elastic Retraction

Kelly, Diane A.

doi:10.1002/ar.22644

Cited by 24 publications

(17 citation statements)

References 26 publications

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“…Anatomical studies have proposed a different mechanism for crocodilia, in which the penis is protruded from the vent by adjacent cloacal musculature; both the sphincter cloacae and levator cloacae muscles have been implicated in this process [Powell, 1999;Kelly, 2013]. In squamates, the transversus penis muscle acts to evert the hemipenes, whereas the retractor penis magnus functions in retraction [Ruiz and Wade, 2002].…”

Section: Diversity Of Amniote External Genitaliamentioning

confidence: 99%

Evolution of External Genitalia: Insights from Reptilian Development

Gredler¹,

Larkins²,

Leal³

et al. 2014

Sex Dev

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External genitalia are found in each of the major clades of amniotes. The phallus is an intromittent organ that functions to deliver sperm into the female reproductive tract for internal fertilization. The cellular and molecular genetic mechanisms of external genital development have begun to be elucidated from studies of the mouse genital tubercle, an embryonic appendage adjacent to the cloaca that is the precursor of the penis and clitoris. Progress in this area has improved our understanding of genitourinary malformations, which are among the most common birth defects in humans, and created new opportunities for comparative studies of other taxa. External genitalia evolve rapidly, which has led to a striking diversity of anatomical forms. Within the past year, studies of external genital development in non-mammalian amniotes, including birds, lizards, snakes, alligators, and turtles, have begun to shed light on the molecular and morphogenetic mechanisms underlying the diversification of phallus morphology. Here, we review recent progress in the comparative developmental biology of external genitalia and discuss the implications of this work for understanding external genital evolution. We address the question of the deep homology (shared common ancestry) of genital structures and of developmental mechanisms, and identify new areas of investigation that can be pursued by taking a comparative approach to studying development of the external genitalia. We propose an evolutionary interpretation of hypospadias, a congenital malformation of the urethra, and discuss how investigations of non-mammalian species can provide novel perspectives on human pathologies.

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Section: Diversity Of Amniote External Genitaliamentioning

confidence: 99%

Evolution of External Genitalia: Insights from Reptilian Development

Gredler¹,

Larkins²,

Leal³

et al. 2014

Sex Dev

View full text Add to dashboard Cite

show abstract

“…Two regions of erectile tissue are present; the corpus spongiosum is flexible, fibrous tissue that surrounds the penile sulcus in non-mammalian amniotes and the penile urethra in mammals, and the corpora cavernosa are large, paired regions of highly vascularized tissue that expand upon increased blood flow [Reese, 1915;Zug, 1966;King, 1979;Powell, 2000;Kelly, 2004Kelly, , 2013Cabrera et al, 2007]. The base of the alligator penis is formed from paired penile bodies called crura [Gadow, 1887;Reese, 1924;Kelly, 2013]. Proximally, each crus is connected to the pelvic girdle and adjacent cloacal muscles; distally, the crura fuse to form the shaft of the corpus cavernosum [Powell, 2000;Kelly, 2013].…”

mentioning

confidence: 99%

“…Erection and eversion by hydrostatic pressure and muscle contraction function to achieve turgor and to create a functional channel for sperm transfer [Hart and Melese-D'Hospital, 1983;Schmidt and Schmidt, 1993;Andersson and Wagner, 1995;Kelly, 2002Kelly, , 2004Kelly, , 2013Hsu et al, 2005;Cabrera et al, 2007]. Hydrostatic pressure is produced by blood vasculature in penises of crocodilians, turtles and mammals [Zug, 1966;King, 1979;Kelly, 2004;Moore et al, 2012], by lymphatic vessels in bird penises, when present [King, 1979], and by both blood and lymph in squamates [Dowling and Savage, 1960].…”

mentioning

confidence: 99%

“…Internally, crocodilian, turtle, and mammalian penises have large fibroelastic, vascular, and lacunar tissues that support vascular erection [Zug, 1966;King, 1979;Kelly, 2004]. Two regions of erectile tissue are present; the corpus spongiosum is flexible, fibrous tissue that surrounds the penile sulcus in non-mammalian amniotes and the penile urethra in mammals, and the corpora cavernosa are large, paired regions of highly vascularized tissue that expand upon increased blood flow [Reese, 1915;Zug, 1966;King, 1979;Powell, 2000;Kelly, 2004Kelly, , 2013Cabrera et al, 2007]. The base of the alligator penis is formed from paired penile bodies called crura [Gadow, 1887;Reese, 1924;Kelly, 2013].…”

mentioning

confidence: 99%

“…The base of the alligator penis is formed from paired penile bodies called crura [Gadow, 1887;Reese, 1924;Kelly, 2013]. Proximally, each crus is connected to the pelvic girdle and adjacent cloacal muscles; distally, the crura fuse to form the shaft of the corpus cavernosum [Powell, 2000;Kelly, 2013]. In crocodilians, eversion of the phallus is achieved by muscle contraction [Reese, 1915;Powell, 2000;Kelly, 2013], and vascular dilation inflates the distal portion of the penis (glans) and the tissue adjacent to the penile sulcus [Gadow, 1887;Reese, 1915;Cabrera et al, 2007;Ziegler and Olbort, 2007;Moore et al, 2012].…”

mentioning

confidence: 99%

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Morphogenesis and Patterning of the Phallus and Cloaca in the American Alligator, Alligator mississippiensis

Gredler¹,

Seifert²,

Cohn³

2014

Sex Dev

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In most animals, reproduction by internal fertilization is facilitated by an intromittent organ, such as the penis in amniote vertebrates. Recent progress has begun to uncover the mechanisms of mammalian external genital development; however, comparatively little is known about the development of the reptilian penis and clitoris. Here, we describe the development of the phallus and cloaca in the American alligator, Alligator mississippiensis. The embryonic precursor of the penis and clitoris is the genital tubercle, which forms by the budding of genital mesenchyme beneath the ventral body wall ectoderm, adjacent to the cloacal membrane. The cloacal lips develop from another pair of outgrowths, the lateral swellings. Early development of the alligator phallus, cloaca, and urogenital ducts generally resembles that of other reptiles, suggesting that differences in adult reptilian phallus and cloacal anatomy arise at later stages. The phallic sulcus is derived from the cloacal endoderm, indicating that the crocodilian sulcus is functionally and developmentally homologous to the mammalian urethra. Initial external genital outgrowth and patterning occur prior to temperature-dependent sex determination. Our analysis of alligator phallus and cloaca development suggests that modifications of an ancestral program of urogenital development could have generated the morphological diversity found in the external genitalia of modern amniotes.

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Genital anatomy and copulatory interactions in the broad snouted Caiman (Caiman latirostris)

Moore

Kelly

Piva

et al. 2021

The Anatomical Record

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The broad snouted caiman is a crocodylian native to South America that is subject to extensive conservation management in both wild and farming environments. Although reproductive behaviors like egg laying and clutch care have been examined in this species, little else is known about their copulatory system. We examined the anatomy of male and female cloacal and genital tissues ex vivo to build hypotheses of their interactions during copulation and the effects of that interaction on insemination. Male phallic glans tissues were artificially inflated to expand into their copulatory state, allowing the examination and quantification of structural changes at the gross and tissue levels. Digital reconstruction of MRI stacks yielded three‐dimensional tissue compartment specific glans models of the inflated state. Silicone molds of female cloacae and oviducts in conjunction with dissection and diceCT analysis allowed us to assess internal geometry and infer how male and female features interact in copulo. We observed glans expansion within the female proctodeum would result in a copulatory lock limiting deeper intromission or retraction. Intromission and subsequent creation of the copulatory lock produces extensive clitoral compression, providing a possible mechanism for female assessment of male copulatory performance. Further, glans expansion forms a distal lumen that positions the glans tip in or near the vaginal openings. A coiled, muscular vagina provides a possible mechanism for postcopulatory sexual selection by excluding semen. Together, the complex male–female interaction supports evidence for cryptic selection by female choice, which can act as a driver of genital coevolution.

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Penile Anatomy and Hypotheses of Erectile Function in the American Alligator (Alligator mississippiensis): Muscular Eversion and Elastic Retraction

Cited by 24 publications

References 26 publications

Evolution of External Genitalia: Insights from Reptilian Development

Evolution of External Genitalia: Insights from Reptilian Development

Morphogenesis and Patterning of the Phallus and Cloaca in the American Alligator, <b><i>Alligator mississippiensis</i></b>

Genital anatomy and copulatory interactions in the broad snouted Caiman (Caiman latirostris)

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