Justify the statement. Q10 How important is the presence of air bladder in Pisces? Q11 What are the modifications that are observed in birds that help them fly?
Q12 Could the number of eggs or young ones produced by an oviparous and viviparous mother be equal? Q13 Segmentation in the body is first observed in which of the following: a Platyhelminthes b Aschelminthes c A Q15 Prepare a list of some animals that are found parasitic on human beings.
Question 5 What is the difference between direct and indirect development? Previous Question Next Question. Q:- Why are living organisms classified? Q:- State two economically important uses of: a Heterotrophic bacteria b Archaebacteria Q:- Define a taxon. Give some examples of taxa at different hierarchical levels.
Q:- Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal. Q:- Bile juice contains no digestive enzymes, yet it is important for digestion. The larva undergoes a drastic metamorphosis in order to achieve its adult stage. Animals that undergo indirect development lay numerous eggs. Because the eggs are small, they have relatively little yolk. Due to the small amount of yolk, the larva develops and hatches rapidly.
Reptiles, birds and mammals tend to experience direct development. This means that the young of these species are hatched looking like a miniature version of their adult parents. The survival of these creatures on land is due in part to the construction of the egg from which the offspring come.
The series of four extra-embryonic membranes of the egg allow for exchange of gasses, containment of waste material and protection of the fetus.
Some echinoderms, amphibians and insects undergo indirect development: butterflies, dragonflies, frogs and so forth. The larva or young form of these creatures often fulfill a different ecological niche than the adult animal does. Therefore, more young can exist and thrive together than would be possible for the adult form. This is called incomplete metamorphosis.
The gist of it is that in regular development, the babies look like the adult. In metamorphosis, the organism post-change will look nothing like the organism pre-change. When babies look like the adults, it is called "direct development" rather than metamorphosis. A full grown mouse for the most part looks like a larger baby mouse. However, insects and frogs they can undergo metamorphosis which is rapid and really obvious changes. An example is how a tadpole looks very different than frog.
Or how a caterpillar looks very different than a butterfly. Animals that go through metamorphosis mainly some orders of insects undergo a complete rearrangement of the tissues inside of the animal's body. Direct development, which is what mammals and most other animals do, have the underlying body parts grow and change shape as the animal develops, but do not go through a complete resorption and rebirth as a new body. Alternative hypotheses relating the expression of patterning genes to the development of the derived body plan in the parasitic form.
Each color represents the expression territory of a single patterning gene. A The expression of patterning genes is not altered. The novel morphology must be caused by modifications to downstream developmental events. B The relative boundaries and relative sizes of gene expression territories are altered, resulting in an alteration of the body plan. C A subset of gene expression territories is deleted, resulting in an alteration of the body plan. Given the plethora of gene expression work reported from N.
For example, mef2 , soxD1 , and m - LIM are 3 genes with spatially segregated expression in the tentacles of N. Studying these genes in E. If the genes were not expressed in the tentacles during polyp development, but they are not expressed during parasite development, this would suggest that these gene expression territories have been deleted concordant with the absence of tentacles hypothesis 3.
Alternatively, if the expression of these genes is altered relative to other patterning genes during parasite versus polyp development, this would support hypothesis 2. Studying gene expression between stages of E. The evolution of parasitism, particularly endoparasitism, results in the necessity for the infecting species to 1 locate the appropriate host s , 2 infect the host by entering and establishing at appropriate location s , and 3 extract nutrition from the host, either through feeding on the host's tissues or the host's ingested food.
Thus, many parasites fulfill a number of criteria for a metamorphic life history in that a stage parasitic on 1 host usually differs from the free-living stage or parasitic stage on another host in habitat, food sources, and morphology. Endoparasitic flatworms, particularly digenean trematodes, exhibit remarkable evolutionary innovations resulting from the origin of obligate parasitism.
Their life histories typically involve a series of stages miracidium, sporocyst, redia, cercaria, metacircaria, reproductive adult , with 2 or more hosts, and at least 2 infective stages. Developmental transitions between these stages generally involve events characteristic of metamorphosis miracidium to sporocyst: neodermis formation, shift to host habitat; cercaria to metacircaria: tail, digestive tract, and suckers formation, shift to free-living environment Ruppert and others Cribb and others mapped various digean life cycles on phylogenies and found changes in life cycles and hosts is common and related.
If each host gain is accompanied by the addition of a new parasitic stage adapted to living in the new host, then parasitism is an engine for the evolution of new metamorphoses. We suggest that the evolution of endoparasitism was the precondition for the evolution of a novel metamorphosis in the life history of E. Prior to the origin of its parasitic life history, predation by M. Once E. Regardless of the scenario that favored the evolution of parasitism, the insertion of a successful parasitic stage required coordinated spatio-temporal development in a specific ctenophore species.
Although the suite of morphological characters exhibited by the parasite does not differ drastically from other stages in the life history, this may reflect the evolutionary recency of this novel stage.
If the parasitic stage is maintained in E. Similar arguments have been used in describing the evolution of the diversity in holometabolous insects where more radical metamorphic life histories may permit differential selection on different life history stages Yang The genus Peachia belongs to the family Haloclavidae, and the parasitism exhibited by these anemones almost certainly evolved independently from the parasitism of E.
Like E. However, Peachia differs from E. In addition, Peachia differs from E. Future studies on the development of Peachia species would provide an informative comparison with E.
The evolution of indirect and direct life histories is a central question in organismal life history evolution, but studies on the transition from indirect to direct development greatly outnumber studies on the transition from direct to indirect.
In addition, E. A major challenge to understanding the evolution of indirect development is the following. How can exceedingly distinctive novel life history stages, requiring the evolution of complex new developmental pathways, become interposed in the ontogeny of a direct developing ancestor?
If an existing life history stage for example, a planula can establish itself as a parasite through fortuitous preadaptations, subsequent selection on the parasite can lead to the evolution of a novel stage that may require a metamorphic transition. Ancient indirect developing lineages do not allow us to track the evolutionary mechanisms underlying the origin of novel metamorphoses. However, in the case of E. By leveraging the molecular and genomic tools developed for the closely related anemone N.
Future studies addressing expression of developmental regulatory genes in different life history stages as well as endogenous and exogenous signaling to coordinate the changes between stages will aid in identifying mechanisms for how the novel stage develops.
In addition, such study may help elucidate steps in the evolution of indirect life history; a critical innovation acquired in many dominant animal taxa but something thought difficult to study.
We would like to thank the symposium organizers for organizing this symposium. We would like to thank all audience-members from the platform and associated-sessions for constructive discussions. We would also like to thank 2 anonymous reviewers for insightful comments that improved this manuscript. Google Scholar. Google Preview. Oxford University Press is a department of the University of Oxford.
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Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume Article Contents Abstract. Introduction: defining metamorphic criteria. Evolutionary shifts between direct and indirect development. Metamorphosis in the Cnidaria. Family Edwardsiidae: direct to indirect development? Molecular mechanisms underlying changes in ontogeny. Metamorphosis and endoparasitism.
Qualitative shift to indirect development in the parasitic sea anemone Edwardsiella lineata. Reitzel , Adam M. Reitzel 1. Department of Biology, Boston University. Oxford Academic. James C. John R.
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