Occurrence of abnormal sexual dimorphic structures in the gonochoristic crustacean, Upogebia major (Thalassinidea: Decapoda), inhabiting mud tidal flats in Japan

Abstract

Normal females of the mud shrimp, Upogebia major, have a pair of pleopods on the first abdominal segment, while normal males do not. We have investigated nine populations in the Seto-Inland Sea, Japan, and found morphological disorders on the first abdominal segments of both males and females. In males, the first pleopods occurred. Morphology and arrangement of these additional pleopods were classified into four types. The pleopods of Types M-1 and M-2 were similar in structure to those of normal females. These males could be considered as de-masculinized individuals, and the occurrence of males with these morphological disorders showed local variation: while their frequency was high in two specific sites in Kasaoka Inlet (11.5% in Site 6 and 5.5% in Site 7), it was less than 3.5% in other sites. Other types had abnormal additional appendages similar to the walking legs (pereiopods) (Type M-3) or biramous leaf-like pleopods (Type M-4), but their frequency was extremely low (only 3 out of 1558 males inspected). Morphological disorders in males (Types M-1 and M-2) occurred independently of gonadal development, and did not affect the sexual characteristics as revealed by analyses of allometric growth and gonadal index. In females, morphological disorders were classified into five types: incomplete first pleopods (Type F-1); lack of the first pleopods (Type F-2 and F-3); transformation into the pereiopod-like pleopods (Type F-4); and biramous leaf-like pleopods (Type F-5). The frequency of Types 1–3 was especially high in Site 6 in Kasaoka Inlet (24.4%), but was less than 9.4% in other sites. A feature was that cuticular lesions often co-occurred with the morphological disorders. Possible causal factors of these abnormalities are discussed.

Definition of a new unbiased gonad index for aquatic invertebrates and fish: its application to the sea urchin Paracentrotus lividus

“…In accordance with previous studies carried out on various species (Gonor 1972, Roff 1983, Stoltz et al 2005, Nanri et al 2011, the gonads of Paracentrotus lividus can grow at a different rate than its body, and this process may vary between populations. While in Ardeleiro the gonads increased in size at the same rate as the diameter, the gonadal growth in the population of Queiruga was much slower.…”

“…Furthermore, this index assumes the relationship between the 2 measures is isometric, meaning that both the gonad and body weight increase at the same rate. Consequently, we will refer to this index as the linear gonad index (LGI): (1) Most previous studies that use the LGI assume that these statements are true without first verifying them, even though they have been shown to be false for several marine species (Russell 1998, Stoltz et al 2005, Nanri et al 2011. In these cases, the LGI, or any other GI that assumes isometric gonad growth, should not be used to compare individuals with different sizes, since it could lead to erroneous conclusions about their reproductive cycle (Devlaming et al 1982, Erickson et al 1985, Bonardelli and Himmelman 1995, Somarakis et al 2004.…”

Morphological study for understanding the sexual pattern in ghost shrimp Callichirus major (Crustacea: Axiidea)

“…This phenomenon was observed by Kang et al () in Upogebia major . Nanri et al () also observed an ovotestis gonad in U. major , as well as some morphological disorders in the pleopods and dimorphic sexual structures, finding female attributes in males and male attributes in females.…”

“…The limitation for mating maybe would occur even for Callianassids under high densities because only a limited number of individuals are available surrounding any single individual with a solitary underground habit. It has been reported in the literature that species with this cryptic lifestyle can present a low population density in their burrows ( C. major = 6.07 galleries/m 2 ) and may display characteristics of intersexuality and hermaphroditism (Almeida & Buckup, ; Botter‐Carvalho, Santos, & Carvalho, ; Kang et al, ; Nanri et al, ; Oliveira et al, ; Rudolph, ; Rudolph & Almeida, ; Rudolph & Verdi, ; Silva‐Castiglioni et al, ). In addition, the occurrence of these characteristics in genus Callichirus is described by Hernáez Bové () and Souza et al () for C. seilacheri and C. major , respectively.…”

“…Several cases of sexual abnormalities in species with ecological aspects related to C. major have also been reported in the literature. Among those, intersexuality in Upogebia stellata (see Pinn, Atkinson, & Rogerson, ), as well as the occurrence of abnormal sexual structures in U. major (see Nanri et al, ), can be highlighted.…”