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Male ducks in the genus Oxyura produce bill-drumming displays, sometimes called "bubbling display." We recorded high-speed video and sound of the bill-drumming display in ≥4 captive Ruddy Ducks (Oxyura jamaicensis) to ask: how is the sound produced? Our videos showed that, while floating in the water adjacent to a conspecific, the male struck his bill against his upper breast approximately 8.6 times over the course of 1 s. The breast, which had been inflated with air via both tracheal and interclavicular air sacs, visibly recoiled from each impact, producing motion in the water, including bubbles. These bill-to-breast collisions produced an atonal thumping sound; the display then ended with a vocalization as the tracheal air sac deflated. We recorded males performing this display on land and producing the normal sound, thus, the bubbling of the water is not integral to the acoustic qualities of the display. Histology on 4 birds showed that the tracheal air sac became more developed in breeding males, allowing males to inflate it, creating a stretched membrane that is struck with the bill (i.e., a drum). The entire structure in the neck of the Ruddy Duck male during the breeding season may develop to enhance sound production and/or protect the male against this constant beating created by the display. [ABSTRACT FROM AUTHOR]

Quantification of genital variation in males and females can inform our understanding of likely copulatory interactions and evolution of genital diversity. However, no studies have quantified genital shape variation within a single snake species or examined the shape and size of both the vaginal pouch and hemipenes. Here, we examine the shape and size of the genitalia of female and male diamondback water snakes, Nerodia rhombifer , using a three-dimensional automated landmark geometric morphometric approach on models of the lumen of the vaginal pouch and inflated hemipenes, applying these techniques for the first time to the genital shape of vertebrates. Vaginal pouch shape is significantly associated with body size and reproductive status. As females grow larger and become reproductive, the vaginal pouch enlarges, widens and becomes more bifurcated. In reproductive males, the shape of the hemipenes is also significantly associated with body size. As males grow larger, the hemipenes enlarge and widen; their bifurcation becomes more defined and the spines at the base become more prominent. Vaginal pouch and hemipenial centroid size are isometric with respect to body length. The centroid sizes of the hemipenes and vaginal pouch are not significantly different from one another, hence the genitalia match in size. Reproductive females and males covary in the degree of bifurcation and size of their genitalia. We demonstrate the utility of three-dimensional analysis in studies of the shape of soft tissues and advocate its use in future studies of genitalia. [ABSTRACT FROM AUTHOR]

Copulatory behavior and genital morphology interact to deliver sperm more effectively during mating, but the nature of this interaction has not been explored in depth in most vertebrates. Alpacas have unusually long copulations lasting 15–20 min, and a unique copulatory behavior, where the penis intromits all the way past the cervix, into the uterine horns. Here we describe the morphology of male and female genitalia and report unique morphological characteristics that may be associated with this unusual insemination mode. Vaginal shape is highly variable, and seemingly not associated with age or parity. The cranial vagina varies between bulbous and cylindrical, while the caudal vagina is typically narrower and always cylindrical. The cervix consists of a series of two to three spirals or rings, and it is often found in a relaxed state that may prevent damage caused by the cartilaginous penis tip as it pushes through the cervix to reach the uterine horns. The uterus and uterine horns have a complex shape with multiple constrictions. The cartilaginous penis tip has a sharp urethral process that may help to push against these constrictions. The diameter of the vaginal lumen is much greater than the diameter of the penis suggesting that there is little direct interaction between them, and that female vaginal shape is not under strong copulatory selection. In effect, the entire female reproductive tract of the female is interacting with the penis during copulation. [ABSTRACT FROM AUTHOR]

The morphological differences in female genitalia within and between species are little studied and poorly understood, yet understanding patterns of variation in female genitalia can provide insights into mechanisms of genital evolution. The present study aimed to explore the patterns of intraspecific and interspecific variation in female genitalia in two sister taxa of watersnake ( Nerodia sipedon and Nerodia fasciata) that have similar genital shape. We used a geometric morphometric ( GM) approach to study variation in shape of the vagina between and within two sister species. We examined genital shape in female watersnakes ranging from small, sexually immature females to large reproductive females that had recently given birth. We found that shape variation of genitalia is strongly correlated with body size, where larger but not smaller females have a bifurcation in the vagina. However, we also found significant shape variation in the structure of the vagina between the two species, where N. fasciata has narrower genitalia with more prominent bifurcation, whereas N. sipedon has wider genitalia with less marked bifurcation. Using GM allowed us to detect significant differences in genital shape that were not apparent upon visual examination alone, suggesting that shape variation in female genitalia may be greater than previously assumed. Additional study of morphological differences in male reproductive organs for these species would help to determine whether there has been genital co-evolution, and potentially mechanical reproductive isolation, in these two closely-related and occasionally sympatric species. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 183-191. [ABSTRACT FROM AUTHOR]

What is the vagina? This seemingly simple question has a rather complex answer, depending on whether we use a functional or a developmental definition. The terminal portion of the female reproductive tract that opens to the environment initially served as a conduit for eggs to be laid, and in species with external fertilization the distal oviduct may be specialized for oviposition but there is no vagina. In animals with internal fertilization, this terminal section of the oviduct interacts with the sperm and the intromittent organ leading to functional specialization of this region that we often call a vagina in insects and some vertebrates. Here we address the evolution, morphology and diverse functions of the vagina and some of the unknown questions that remain to be addressed in the study of this remarkable structure., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)