External reproductive structures of male Surfperches (Embiotocidae): Urogenital papilla

Abstract

Fishes exhibit a dynamic array of reproductive diversity. Among the various forms of reproduction, internal fertilization has evolved at least 13 times and has been observed in 2–3% of teleost species, half of which are marine. Internal fertilization has led to the evolution of male intromittent organs to aid in sperm transfer during copulation. The intromittent organs of poeciliids have been widely investigated, but little research has focused on the intromittent organs of marine fishes. The surfperches are internally fertilizing, viviparous fishes with a ventrally located papilla. In this article, the external morphology of 19 Embiotocidae species was examined. Additionally, paraffin histology was used to investigate the walleye surfperch (Hyperprosopon argenteum), black perch (Embiotoca jacksoni), and dwarf perch (Micrometrus minimus) papilla to aid in the identification of tissue composition to determine its function. External morphology was documented via macro photography and males were dissected to observe the relationship between the testes, spermatic duct, and papilla. We provide histological evidence that the urogenital papilla is directly connected to the spermatic duct and testis and likely involved in spermatozeugmata transfer. Our research also determined that the papillae were composed of both urinary and reproductive tissues, thus we propose the papilla be referred to as a urogenital papilla. Our study contributes to an overall understanding of intromittent organs of marine fishes, particularly in the surfperches, which has not been previously documented.

Morphology of the urogenital papilla of the male marine teleost Black Rockfish, Sebastes schlegelii (Hilgendorf, 1880), and its role in internal fertilization

“…The male rockfish has a UGP to ensure the safe transfer of sperm to the female (Iida, 2019). Previous studies have shown that the morphology of male external genitalia varies among taxa (Bond & Forsgren, 2022). In some bony fishes, specifically poeciliids and anablepids, the external genitalia develop from the median anal fin in the form of intromittent organs or genitalia (Rosa-Molinar & Burke, 2002).…”

“…Males of viviparous teleost fish have evolved special intromittent organs that protrude externally from the reproductive tract and transport sperm into females for internal fertilization. The shift from external to internal fertilization in teleost fishes has led to changes in the sperm transfer mechanism correlated with the evolution of intromittent organs (Bond & Forsgren, 2022).…”

“…Males of viviparous teleost fish have evolved special intromittent organs that protrude externally from the reproductive tract and transport sperm into females for internal fertilization. The shift from external to internal fertilization in teleost fishes has led to changes in the sperm transfer mechanism correlated with the evolution of intromittent organs (Bond & Forsgren, 2022). For example, males of viviparous Poeciliidae possess hook‐like extensions on the third, fourth, and fifth rays of the anal fin, called a gonopodium (Langerhans et al, 2005; Rosen & Tucker, 1961), that acts as an intromittent organ for the transmission of male gametes during breeding.…”

“…Previous studies of intromittent organ have focused on freshwater fishes, and few have investigated marine teleosts. To our knowledge, and before a study on male embiotocids by Bond and Forsgren (2022), the morphology of the intromittent organ of marine teleosts has only addressed in clinid fishes (Fishelson et al, 2006), which have an ampulla‐like structure in the abdominal cavity, the outer layer of which contains a large number of muscles. The inner layer contains a large number of sperm as well as an external fleshy bulge that is an extension of the ampulla structure (Fishelson et al, 2006; Rosen & Gordon, 1953).…”

Developmental regulation of the male urogenital papilla in the male marine teleost black rockfish, Sebastes schlegelii (Hilgendorf, 1880)

“…Most teleosts (about 97%) exhibit external fertilization, in which males and females release gametes into the water [1]. Teleosts with internal fertilization have evolved different mating apparatuses for sperm transport in males in order to survive and reproduce [2]. These are mostly fin specializations or external extensions of the reproductive tract.…”