Final answer:
Vertebrate sexual reproduction involves several strategies: ovipary (external egg development), ovovivipary (internal egg development without significant maternal connection), and vivipary (internal development with maternal connection). External fertilization is common in aquatic environments, while internal fertilization is the norm for terrestrial settings. A rare form of asexual reproduction, parthenogenesis, is also observed in some vertebrates.
Step-by-step explanation:
Vertebrates reproduce sexually, and this involves various reproductive strategies. Generally, sexual reproduction involves the joining of male and female gametes during fertilization, resulting in genetically unique offspring. There are three main strategies observed in vertebrates: ovipary, ovovivipary, and vivipary.
In ovipary, the development of the embryo occurs within an external egg, a method commonly seen in many amphibians, reptiles, and all birds. The strategy of ovovivipary is where the egg develops within the mother's body but without significant maternal connection, as seen in some species of fish, reptiles, and amphibians. Lastly, vivipary is where the development takes place inside the female, connected to the mother for sustenance, as observed in most mammals.
Aquatic vertebrates often have external fertilization, while terrestrial vertebrates usually have internal fertilization. External fertilization is advantageous in water due to the medium's supportive nature for the diffusion of gametes. In contrast, internal fertilization protects the gametes in a terrestrial environment from desiccation and other external factors.
Some vertebrates can also reproduce through parthenogenesis, an asexual method where unfertilized eggs develop into offspring. This has been observed in select reptiles, amphibians, and fish under certain conditions, such as isolation from males. However, this phenomenon is rare and typically happens in response to unusual circumstances.