Data from: Functions of bidirectional sex change and simultaneously hermaphroditic phase gonads in the monogamous goby Lubricogobius exiguus

Hermaphroditism has been widely confirmed in fish and includes four
recognized types: protogyny, protandry, bidirectional sex change, and
simultaneous hermaphroditism. Among these, bidirectional sex change and
simultaneous hermaphroditism are considered the most flexible sexual
patterns, due to their frequent switching of functional sexes. They are
predicted to evolve under conditions of limited mating opportunities, such
as low population density and mobility, and are thought to share common
evolutionary factors. The goby Lubricogobius exiguus exhibits
bidirectional sex change, with simultaneously hermaphroditic (SH) phase
gonads, containing both developed testicular and ovarian tissues,
particularly in females and solitary individuals. In this study, we
conducted field observations to examine the mating system in L. exiguus
and investigate the significance of its plastic sexual patterns. The
results revealed that the goby randomly formed mating pairs, regardless of
body size. Although a few pairs maintained long-term mating relationships
over 70 days, approximately half of the pairs dissolved within 11 days.
Under frequent partner changes in the non-size-assortative monogamy, the
goby individuals rapidly established new mating pairs through
bidirectional sex change using SH phase gonads. This sexual plasticity
enabled L. exiguus to initiate reproduction quickly regardless of the sex
of the partner, supporting the evolutionary predictions underlying
bidirectional sex change and simultaneous hermaphroditism. In addition to
the characteristics of the mating system, ecological traits such as being
a microhabitat specialist on sandy-bottom substrates with a short lifespan
may have influenced the evolution of the sexual pattern in L. exiguus.