Sympatric speciation:

only occurs in bacteria.
occurs whenever a physical barrier between two species is removed (i. e., a river dries up) and the two species start to interbreed.
can occur instantaneously through formation of polyploid offspring.
whenever hybrids mate with parental species.
can occur instantaneously through formation of polyploid offspring.

can occur instantaneously through formation of polyploid offspring.

Explanation:

In Sympatric speciation, species are not geographically isolated but reproductively isolated from each other as two varying types of species is observed to have emerged from one original. Take for example, in Fruit Flies where each species have different food choices, making each one to feed on separate fruits.

"SYMPATHETIC SPECIATION do occur instantaneously through formation of polyploid offspring (it has double the normal amount of chromosomes)". And it's most likely take place due to natural selection. It relies on the process of disruptive selection acting against hybrids.

layer 3 is younger than layer 6.