Ch. 47 - Animal Reproduction and Development

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch. 47 - Animal Reproduction and Development

Problem 6

Chapter 47, Problem 6

Many frogs and mice are similar in size, yet a frog egg is vastly larger than a mouse egg. Propose a plausible explanation for this difference in the egg size.

Verified step by step guidance

Understand the reproductive strategies: Frogs are external fertilizers, meaning they lay their eggs in water and fertilization occurs outside the female's body. Mice, on the other hand, are internal fertilizers with fertilization occurring inside the female's body.

Consider the survival rates: Since frog eggs are laid in water and are exposed to predators and environmental conditions, they are produced in large quantities with each being relatively large to house more yolk to sustain the embryo until it can fend for itself.

Analyze the development process: The larger size of frog eggs is also due to the need for more yolk to support the development of the embryo directly into a tadpole, which must be somewhat self-sufficient. In contrast, mouse embryos develop internally and are nourished directly by the mother through the placenta.

Examine the maternal investment: Mice invest in fewer eggs but provide prolonged internal protection and postnatal care, which increases the survival chance of each offspring. This allows mouse eggs to be smaller as the embryo relies less on the egg's initial yolk content.

Reflect on evolutionary adaptations: The differences in egg size between frogs and mice reflect their evolutionary adaptations to their respective environments and reproductive strategies, optimizing their survival and reproductive success.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oviparity vs. Viviparity

Oviparity refers to the reproductive strategy where organisms lay eggs that develop outside the mother's body, as seen in frogs. In contrast, viviparity involves live birth, typical of many mammals like mice. The differences in reproductive strategies can influence egg size, with oviparous species often producing larger eggs to provide sufficient nutrients for the developing embryo.

Nutritional Investment in Eggs

The size of an egg often correlates with the amount of yolk it contains, which serves as a nutrient source for the developing embryo. Frogs, which lay eggs in aquatic environments, produce larger eggs with more yolk to support the embryo during its early development stages, while mice, which give live birth, invest in fewer but more developed offspring.

Environmental Adaptations

Different species adapt their reproductive strategies based on environmental conditions. Frogs typically lay eggs in water, where larger eggs can help ensure survival against predation and environmental challenges. Mice, being terrestrial and nurturing their young internally, have evolved to produce smaller eggs that develop into more complex organisms before birth, reflecting their different ecological niches.

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Related Practice

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True or false: The corpus luteum is retained upon implantation due to the presence of the hormone human chorionic gonadotropin (hCG).

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Give examples of negative and positive feedback in hormonal control of the human menstrual cycle. Why can a high estradiol level be considered a 'readiness' signal from a follicle?

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Summarize the experimental evidence that Daphnia require three cues to trigger sexual reproduction. Discuss what these cues indicate about the environment.

Textbook Question

Which of the following statements regarding animal development is/are correct? Select True or False for each statement.

T/FThe neural tube forms after organogenesis is complete

T/FThe blastocyst is formed during cleavage

T/FDuring cleavage, the zygote divides rapidly without growth, forming a mass of cells

T/FAnimals have two germ layers

Textbook Question

How do spermatogenesis and oogenesis in humans differ with respect to numbers of cells produced, gamete size, and timing of the second meiotic division?

Textbook Question

In sperm competition, what is 'second-male advantage'?

a. The observation that when females mate with two males, each male fertilizes the same number of eggs

b. The observation that when females mate with two males, the second male fertilizes most of the eggs

c. The observation that females routinely mate with at least two males before laying eggs or becoming pregnant

d. The observation that accessory fluids prevent matings by second males—for example, by forming copulatory plugs

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