
Concept explainers
To review:
The relationship between viviparity and cold climates, based on the given phylogenetic tree.
Given:
The evolution of viviparity in different lineages of the lizard Sceloporus living in different temperature ranges is shown in Figure 1 of the phylogenetic tree given below:
Introduction:
Animals like birds, reptiles, and amphibians in which the development of the young ones takes place inside the eggs laid by the female are known as oviparous animals. In viviparous animals like mammals, the development of the young ones takes place inside the body of the female who gives birth to the offspring.

Explanation of Solution
It can be observed from the given phylogenetic tree that viviparous mode of reproduction has evolved in the lineages which live in the 19.0–23.4°C temperature range during the warmest months (cool temperature areas).
According to the ‘cold-climate’ hypothesis, animals living in colder climates are more likely to evolve viviparity. In viviparous animals, the development of the young one takes place inside the body of the female and the parent invests more in the development of its offspring.
In areas with a cold climate (high altitudes), the female basks in the sun during the day and move to safe and warm places to take cover during the night. The female can thus regulate the temperature of its body by behavioral thermoregulation. This provides an ambient temperature for the growth and development of the embryo.
An increased parental investment leads to the birth of a few large-sized offspring, which are more capable of surviving to maturity, especially under adverse environmental conditions.
Therefore, it can be concluded that the lizards living in cold areas evolved viviparity because it helped in the better survival of the offspring till maturity.
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Chapter 32 Solutions
Life: The Science of Biology
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