In the junior research group, funded by the Leibniz association since 2017, we focus on a novel reproductive strategy, called pelvic brooding, which evolved within ricefishes (Actinopterygii: Adrianichthyidae) from Sulawesi, Indonesia. To tackle the morphological and genomic bases of pelvic brooding as well as the evolution and adaptive value of this novel reproductive strategy we use a holistic approach linking comparative morphology, gene expression, whole genome and field data.
Of special interest in evolutionary biology are phenotypic changes that allow the use of ecological opportunities (or niches) that were previously not available. These traits, often called evolutionary (key-) innovations or adaptive breakthrough, are mostly a complex suite of characters that can entail severe changes in the most fundamental life history traits, such as feeding, reproduction, locomotion or behavior. Putative key innovations can opennovel routes of evolutionary diversification, leading to adaptive divergence in many traits that permit adaptation to different aspects of the environment.
Novel reproductive strategies are especially interesting, as this complex adaptations, are often connected with changes in morphology, physiology and life-history traits and may even involve the origin of novel organs, like the mammalian placenta.
Studying the genetic basis of complex traits requires a system with different trait characteristics in closely related species, which can – ideally – still interbreed. In this respect, ricefishes are an ideal model. At least two lineages of ricefishes on Sulawesi evolved anextraordinary reproductive system, called “pelvic brooding”.
Female of the pelvic brooding species Oryzias eversi with eggs.
In contrast to most other ricefishes that deposit fertilized eggs shortly after spawning, females of pelvic brooding species carry an egg-clutch until the fry hatches. The eggs are connected with the female by attaching filaments and are anchored inside the abdomen by a unique structure, called plug. The plug is a transient tissue that forms after spawning, becomes vascularized and finally dissolved after the juveniles have hatched. Further obvious morphological adaptationsare a ventral concavity and elongated pelvic fins, present only in pelvic brooding females.
f.l.t.r. Jana Flury, Tabias Spanke, Leon Hilgers, Julia Schwarzer and Alina Schüller.
