This period of incubation can take much longer than the production of another clutch of eggs by the female, especially in temperate regions where pregnancies last longer, leading to a reproductive environment in which sexual selection can be stronger on females than on males due to increased male parental investment. This reversal of traditional sex roles has only been found in pipefishes, whereas seahorses have largely been accepted as monogamous. Some pipefish species display classical polyandry because of this unique situation. Male syngnathids usually prefer females with large body size and prominent ornaments such as blue skin pigmentation or skin folds. Syngnathid males in some species are apparently capable of absorbing eggs or embryos while in the brood pouch. In these cases, embryos with the highest survival rate are those whose mothers display the preferred phenotype.