Sexual Systems and Life History of Barnacles: A Theoretical Perspective

Abstract

Thoracican barnacles show one of the most diverse sexual systems in animals: hermaphroditism, dioecy (males and females), and androdioecy (males and hermaphrodites). In addition, when present, male barnacles are very small and are called "dwarf males". The diverse sexual systems and male dwarfism in this taxon have attracted both theoretical and empirical biologists. In this article, we review the theoretical studies on barnacles' sexual systems in the context of sex allocation and life history theories. We first introduce the sex allocation models by Charnov, especially in relation to the mating group size, and a new expansion of his models is also proposed. We then explain three studies by Yamaguchi et al., who have studied the interaction between sex allocation and life history in barnacles. These studies consistently showed that limited mating opportunity favors androdioecy and dioecy over hermaphroditism. In addition, other factors, such as rates of survival and availability of food, are also important. We discuss the importance of empirical studies testing these predictions and how empirical studies interact with theoretical constructs.

The unexpected mating system of the androdioecious barnacle Chelonibia testudinaria (Linnaeus 1758)

“…; Yamaguchi et al . ), a notion not supported in C. testudinaria . The dwarfism of males has been hypothesized to indicate early maturation and higher relative survival to maturity (Crisp ; Yamaguchi et al .…”

“…The dwarfism of males has been hypothesized to indicate early maturation and higher relative survival to maturity (Crisp ; Yamaguchi et al . ). Early maturation would increase the relative fitness of males, especially if overall mortality rates were high.…”

“…Males differ from hermaphrodites in two aspects: they are attached to hermaphrodites and are dwarfed relative to hermaphrodites. Proximity was proposed to lead to a male mating advantage (Charnov 1987;Urano et al 2009;Yamaguchi et al 2012), a notion not supported in C. testudinaria. The dwarfism of males has been hypothesized to indicate early maturation and higher relative survival to maturity (Crisp 1983;Yamaguchi et al 2012).…”

“…Proximity was proposed to lead to a male mating advantage (Charnov 1987;Urano et al 2009;Yamaguchi et al 2012), a notion not supported in C. testudinaria. The dwarfism of males has been hypothesized to indicate early maturation and higher relative survival to maturity (Crisp 1983;Yamaguchi et al 2012). Early maturation would increase the relative fitness of males, especially if overall mortality rates were high.…”

Structural specialties, curiosities, and record‐breaking features of crustacean reproduction

“…(B) Ventral view of female Zonophryxus quinquedens with attached male (arrow; from Raupach and Thatje, Polar Biol, , 29, 439–443, reproduced by permission). (C) Female gooseneck barnacle Trianguloscalpellum regium with several tiny males (arrowhead) in receptacle inside scutal edge (frame; from Yusa et al, Proc R Soc Lond B, , 279, 959–966, reproduced by permission). (D) Ventral aspect of posterior body part of female Chondracanthus lophii with tiny male (arrow) attached between egg sacs (es; from Østergaard and Boxshall, Zool Anz, 2004, 243, 65–74, reproduced by permission).…”