Sex determination in the androdioecious barnacleScalpellum scalpellum(Crustacea: Cirripedia)

Abstract

How androdioecy (coexistence of hermaphrodites and males) is maintained is still poorly understood. Therefore, sex determination was studied in the androdioecious barnacle Scalpellum scalpellum L. First, 247 cypris larvae from seven broods were investigated for sexual dimorphism in larval morphology and found to be all identical. Second, experiments with cyprids showed that males and hermaphrodites differ distinctly in morphology as soon as 4-5 days after settlement. Third, 14 252 cyprids were allowed to settle on the bottom of their culture cages, and all surviving larvae developed into hermaphrodites and none into dwarf males. Fourth, larvae settled in hermaphrodite receptacles (i.e. future males) were removed at increasing intervals after settlement to study if the male and hermaphrodite sexual expressions are fixed or plastic. All larvae became dwarf males if allowed to stay there for more than 8 h after settlement. But if removed within 3 h after settlement, half of them developed into hermaphrodites. We conclude that an environmental sex determination mechanism operates in S. scalpellum. Together with a 1:1 hermaphrodite/male ratio observed in previously reported experiments offering a free choice of settlement, we suggest that all larvae are potential hermaphrodites, but only 50% can settle in hermaphrodite receptacles and yield males.

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

“…Scalpellid dwarf males are lecithotrophic and non‐feeding. They are shorter lived than their carrying females or hermaphrodites, and thus, the females must repeatedly acquire new males during their lifetime (Høeg et al, ). It is largely unknown how these dwarf males fertilize the females but males of Verum brachiumcancri and Gymnoscalpellum indopacificum were shown to possess a long penis that reaches the mantle cavity of the female (Buhl‐Mortensen and Høeg, ; Chan et al, ).…”

In the footsteps of Darwin: dwarf male attachment sites in scalpellid barnacles (Crustacea: Cirripedia: Thoracica) – implications for phylogeny and the evolution of sexual systems

“…The precise location, size and shape of the receptacle area varied with species. Only in very exceptional cases were settled cyprids or metamorphosed dwarf males found elsewhere along the mantle rim (Spremberg et al, 2012;Høeg et al, 2016). In specimens where no males have yet settled, there are no clear morphological characteristics in external morphology that identify the receptacle area.…”

“…Ever since, cirripedes have attracted special attention as promising model species from both theoretical and experimental approaches, which, in particular, have addressed questions on the evolution of reproductive systems (e.g. Charnov, 1982Charnov, , 1987Høeg, 1995;Yamaguchi et al, 2007Yamaguchi et al, , 2012Yamaguchi et al, , 2014Kelly & Sandford, 2010;Hoch & Levington, 2012;Yusa et al, 2012;Høeg, Yusa & Dreyer, 2016).…”

Diversity of sexual expressions in barnacles

“…Conopea galeata Gomez, 1975 Octolasmis warwickii S. scalpellum Wijayanti and Yusa, 2016;Høeg et al, 2016Svane, 1986Beukeboom and Perrin, 2014 Darwin, 1851a …”