The mechanism promotes tightly coupled evolutionary pressure, which causes the host and symbiont to function as a holobiont.
[10] Since the egg contributes the organelles and has more space and opportunity for intracellular symbionts to be passed to subsequent generations, it is a very common method of vertical transmission.
[12] Alternatively, endophytes can be transmitted directly when reproductive organs are developing in the shoot apical meristem.
When other actions, such as Caesarian delivery, bottle feeding, or maternal antibiotics during nursing occur, these modes of vertical transmission are disrupted.
[18] This type of vertical transmission does not always occur via the behavior of the genetic parent; instead, other members of a social or family groups may transmit the microbial community, resulting in kin selection.
[23] In order to maintain the infection within a host species, it must enter the forming egg cell and be transmitted through the germline.
To improve the rate of vertical transmission, Wolbachia can alter its host's reproductive system[23] in a diverse array of mechanisms, such as induced parthenogenesis, male killing, or feminization.
[28][29][30][31] Through the "milk" the youngsters receive parent microflora including Wigglesworthia glossinidia, the bacteria providing host with vitamins B scarce in the tsetse fly's blood-only diet.
[34] Offspring hatch symbiont-free, and bacterial symbionts are transmitted vertically across generations by social interactions with the onset of regurgitation feeding by (foster) mothers early in the development.
[35] The mother's skin is adapted for this purpose, thickening beforehand and regenerating quickly after being consumed to continue providing for her young.
Bornean foam‑nesting frogs Leptomantis harrissoni tadpoles receive microbes from both their parents (vertically) and environment (horizontally).
[36] By doing so, they help youngsters to have the ability to digest fat and protein in the mother egg versus plant debris in the mini pond they live in.