Chapter 42 Animal Development Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc Chapter 41 At a Glance 42 1 What Are the Principles of Animal Development 42 2 How Do Indirect and Direct Development Differ 42 3 How Does Animal Development Proceed 42 5 How Do Humans Develop 42 6 Is Aging the Final Stage of Human Development Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 1 What Are the Principles of Animal Development is the process by which multicellular organisms grow and increase in organization and complexity Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 1 What Are the Principles of Animal Development Three principle mechanisms contribute to development First Second some of their daughter cells or specialize in both structure and function for example as nerve cells or muscle cells Third as they differentiate groups of cells move about and into multicellular structures such as a brain or a biceps muscle Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 1 What Are the Principles of Animal Development All of the cells of an individual animal s body are How then can they differentiate into different structures with distinct functions The solution is to use different genes in different places in an animal s body and at different times during an animal s life Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Baby mammals and reptiles including birds are miniature versions of the adults of their species undergoing a process called The majority of animals species however undergo in which the newborn has a very different body structure than the adult Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ During indirect development animals undergo a radical change in body form Indirect development occurs in amphibians such as frogs and toads and in most invertebrates The females of animals that undergo indirect development typically produce huge numbers of eggs each containing a small amount of food reserve called The yolk nourishes the developing embryo until it hatches into a small sexually immature feeding stage called a plural larvae Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Indirect development continued Because the parents usually provide these vulnerable offspring with neither food nor protection from predators most die in their larval stage After feeding for a few weeks to several years the handful of survivors undergo a revolution in body form or and become sexually mature adults Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Indirect development continued Most larvae not only from the adults but also in their ecosystems For instance most adult butterflies sip nectar from flowers and unintentionally pollinate the flower in return Their caterpillar larvae munch on leaves often of specific host plants Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Indirect development continued Although we tend to regard the adult form as the and the larval stage as most of the life span of some animals especially insects is spent in the larval form An extreme example is provided by the North American periodical cicadas Periodical cicadas spend 12 or 16 years as underground larvae sucking juices from plant roots and only 4 to 6 weeks as adults mostly mating and laying eggs Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Newborn animals that undergo direct development resemble miniature adults Other animals including some snails and fish and all mammals and reptiles including birds undergo direct development in which the newborn animal closely resembles the adult As the young animal matures it may grow bigger but does not fundamentally change its body form Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Direct development continued Juveniles of directly developing species are typically much larger than larvae so they need much more nourishment before emerging into the world Two strategies have evolved that meet the embryo s food requirement Birds most other reptiles and many fish Mammals some snakes and a few fish have relatively little yolk in their eggs and Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 2 How Do Indirect and Direct Development Differ Direct development continued Providing food for directly developing embryos places great demands on the mother Many of these offspring such as those of birds and mammals require additional care and feeding after birth placing additional demands on one and often both parents Relatively few offspring are produced but a higher proportion reach adulthood because the parents devote more resources to each individual Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 3 How Does Animal Development Proceed Most of the mechanisms of are fundamentally similar in vertebrates and invertebrates and in animals with indirect or direct development Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 3 How Does Animal Development Proceed Cleavage of the zygote begins development The formation of an embryo begins with a series of mitotic cell divisions of the fertilized egg or The zygote is a very large cell Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 3 How Does Animal Development Proceed Cleavage of the zygote begins development continued During cleavage there is cell growth between cell divisions so as cleavage progresses the available cytoplasm is split up into ever smaller cells that gradually approaches the size of cells in the adult Eventually a solid ball of small cells the is formed Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 42 3 How Does Animal Development Proceed Cleavage of the zygote begins development continued As cleavage continues a cavity opens within the morula and the cells become the outer covering of a hollow structure called the The details of cleavage differ by species and are partly determined by the amount of yolk which hinders cytokinesis cytoplasmic division Eggs with extremely large yolks such as a hen s egg don
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