Question

Start with a description of oviparity and viviparity as reproductive strategies, giving example lineages of turtles, tuataras, and/or squamates that utilize each strategy. Then, summarize temperature-dependent sex determination and parthenogenesis as reproductive strategies, naming the groups that utilize these strategies as well.  

Discuss the reasons why TDSD or parthenogenesis might be helpful and/or detrimental for a species in decline.

Answer 1

Oviparous(egg laying):

Oviparous reptiles lay amniotic eggs. Amniotic eggs have a hard shell which protects the embryo, and a special membrane to prevent the embryo from drying out.

In simple words, the females deposit eggs, that develop and hatch in the external environment.

Turtles, crocodiles, and tuatara are all examples of oviparity.

Viviparous (live bearing):

Viviparity is a reproductive pattern in which females retain developing eggs inside their reproductive tracts and give birth to their offsprings capable of a free living existence.Some snake and lizard species are viviparous.

Temperature dependent sex determination (TDSD):

It is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring.It is only observed in reptiles and teleost fish. It is the most popular and most studied type of environmental sex determination (ESD). Some other conditions, e.g. density, pH, and environmental background color, are also observed to alter sex ratio.

Squamates and turtles are also examples of temperature dependant sex determination.

Parthenogenesis:

It is a form of reproduction in which an egg can develop into an embryo without being fertilized by a sperm. Parthenogenesis is derived from the Greek words for “virgin birth,” and several insect species including aphids, bees, and ants are known to reproduce by parthenogenesis.

TDSD and parthenogenesis have been long proposed to be helpful in a species of decline, some proposed examples are TDSD in certain populations of spotted skink (Niveoscincus ocellatus), a small lizard in Tasmania, where it is advantageous to have females early in the season. The warmth early in the season ensures female-biased broods that then have more time to grow and reach maturity and possibly reproduce before they experience their first winter, thereby increasing fitness of the individual.

By this way, the turtles were also incubated at temperatures that produce solely males, both sexes, and solely females, depending on their requirements for a species.

Parthenogenesis have been used in stem cell culture research in laboratories which can be very helpful for a species in decline.