Morphological measurements Oryzias eversi, Oryzias nigrimas and hybrids

The evolution of complex phenotypes like reproductive strategies is challenging to understand as they often depend on multiple adaptations, which only jointly result in a specific functionality. Sulawesi ricefishes (Adrianichthyidae) evolved a reproductive strategy termed pelvic brooding. In contrast to the more common transfer brooding, female pelvic brooders carry an egg-bundle connected to their body for weeks until the fry hatches. To examine the genetic architecture of pelvic brooding, we crossed the pelvic brooding Oryzias eversi and the transfer brooding O. nigrimas (species divergence time: ~ 3.6 my). We hypothesize, that a low number of loci and modularity have facilitated the rapid evolution of pelvic brooding. Traits associated to pelvic brooding, like rib length, pelvic fin length and morphology of the genital papilla were correlated in the parental species but correlations were reduced or lost in their F1 and F2 hybrids. Using the Castle-Wright estimator, we found that gene...