then takes up with her cloaca. The eggs are fertilised internally, and the female deposits them individually, usually folding them into leaves of aquatic plants. A female takes around five minutes for the deposition of one egg. They usually lay around 200 eggs per season. Embryos are usually light-coloured, 1.8–2 mm in diameter with a 6 mm jelly capsule, which distinguishes them from eggs of other co-existing newt species that are smaller and darker-coloured. A genetic particularity shared with other Triturus species causes 50% of the embryos to die. Larvae hatch after two to five weeks, depending on temperature. As in all salamanders and newts, forelimbs develop first, followed later by the back legs. Unlike smaller newts, crested newt larvae are mostly nektonic, swimming freely in the water column. Just before the transition to land, the larvae resorb their external gills; they can at this stage reach a size of . Metamorphosis into terrestrial efts takes place two to four months after hatching, again depending on temperature. Survival of larvae from hatching to metamorphosis has been estimated at a mean of roughly 4%. In unfavourable conditions, larvae may delay their development and overwinter in water, although this seems to be less common than in the small-bodied newts. Evolution The northern crested newt sometimes hybridises with other crested newt species where their ranges meet, but overall, the different species are reproductively isolated. In a case study in the Netherlands, genes of the introduced Italian crested newt (T. carnifex) were found to introgress into the gene pool of the native northern crested newt. The closest relative of the northern crested newt, according to molecular phylogenetic analyses, is the Danube crested newt (T. dobrogicus). In western France, the northern crested newt's range overlaps with that of the marbled newt (T. marmoratus), but the two species in general prefer different habitats. When they do occur in the same breeding ponds, they can form hybrids, which have intermediate characteristics. Hybrids resulting from the cross of a crested newt male with a marbled newt female are much rarer due to increased mortality of the larvae and consist only of males. In the reverse cross, males have lower survival rates than females. Overall, viability is reduced in these hybrids and they rarely backcross with their parent species. Hybrids made up 3–7% of the adult populations in different studies. Little genetic variation was found over most of the