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Wayne Leibel 11 September Introduction: Neotropical fish of the family Cichlidae are a widespread and diverse group of freshwater fish which, through adaptive radiation, have exploited various niches in freshwater ecosystems.
One such evolutionary adaptation employed by numerous taxa is miniaturization, an evolutionary process in which a large ancestral form becomes reduced in size to exploit alternative niches.
A considerable amount of research has been conducted on the effects of miniaturization on amphibians Hankenbut although miniaturization has been found to occur in 85 species of freshwater South American fish, little has been done to investigate the effects which miniaturization imposes on the anatomy of the fish Hanken master thesis pdf biology campbell Wake Evolution is the process by which species adapt to environmental stresses over time.
Nature imposes various selective pressures on ecosystems causing adaptive radiation, where species expand and fill new niches. One such adaptation for a new niche is miniaturization. Miniaturization is observed in a variety of taxa, and evolutionary size decreases are observed in mammals and higher vertebrates, but it is more common and more pronounced in reptiles, amphibians and fish Hanken and Wake Miniaturization evolved as a specialization which allowed the organisms to avoid selective pressures and occupy a new niche.
Miniaturization as a concept is dependent on the phylogenetic assumption that the organism evolved from a larger predecessor.
Over time, the miniature organism had to adapt to the new conditions as a tiny species. All of the same basic needs had to be met, but with a smaller body.
In miniature species there is a critical relationship between structure of the body and body size, and frequently this downsizing results in structural and functional changes within the animal Harrison Within the concept of miniaturization is the assumption that the species evolved from a larger progenitor.
It is necessary then to explore the effects of the miniaturization process. Hanken and Wake found that the adult skulls of the salamander Thorius were lacking several bones, others were highly underdeveloped, and many species within the genus were toothless.
Several invertebrate species display the wholesale loss of major organs systems as a result of the drastic reduction in body size Hanken and Wake Hanken and Wake also have shown that morphological novelty is a common result of miniaturization.
Morphological novelty, in essence, is the development of new structures in the miniature organism. For example, as body size decreases, certain vital organs will only be able to be reduced by a certain amount and still function.
As a result organs such as the inner ear remain large relative to the size of the miniature skull, and structural innovations have to occur in order to support the proportionately large inner ear.
InJames Hanken, at the University of Colorado determined that the adult skull of the Plethodontid salamanders could be characterized by three observations: In his experiments, Hanken found that cranial miniaturization of the Thorius skull was achieved at the expense of ossification.
Much of the ossified skeleton was lost or reduced, especially in the anterior elements, which are seen typically in larger adult salamanders Hanken In contrast to this ossified downsizing, many of the sensory organs were not diminished in size — therefore present in greater proportion to the rest of the reduced head.
Hanken proposed that paedomorphosis was the mode of evolution of the plethodontid salamanders Hanken Paedomorphosis is the state where the miniaturized structures of the adult salamanders can be described as arrested juvenile states.
To support this theory, Hanken showed data where cranial skeletal reduction was less extreme in the posterior regions of the skull. One of the hallmarks of paedamorphosis is the lack of conservation in structures derived late in development.
Early developed structures are highly conserved, and the latter derivations become either lost, or greatly reduced. Again, Hanken has shown that elements appearing late in development exhibit greater variation among species than do elements appearing earlier in ontogeny Hanken But the presence of novel morphological features cannot be accounted for merely by truncated development and the retention of juvenile traits.
Miniature Plethodontid salamanders display features that are not present in other species, juvenile or adult. These novel morphological features are associated with the evolution of decreased size and are postulated to compensate for the reductions occurring in other areas Hanken InTrueb and Alberch published a paper presenting similar results in their experiments with frogs.
Trueb and Alberch examined three morphological variables: Size and snout length were measured, and the data showed that the more heavily ossified frogs tended to be smaller, whereas the less-ossified species were of average size, contrary to what was hypothesized.
Very little research has been done on the effects of miniaturization on fish.EDUCATIONAL PSYCHOLOGY INTERACTIVE Readings in Educational Psychology. Developed by: W. Huitt Last updated: November 2 UNCG Undergraduate Bulletin 4 Notices Equality of Educational Opportunity The University of North Carolina at Greensboro is com-mitted to equality of educational opportunity and does not.
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Senior Honors Thesis Research Proposal. Albert B. Ulrich III Thesis Advisor: Dr. Wayne Leibel 11 September Introduction: Neotropical fish of the family Cichlidae are a widespread and diverse group of freshwater fish which, through adaptive radiation, have .
Beginning graduate school is overwhelming. Graduate programs are not simply continuations of undergraduate degrees, but an introduction into academia- it is a process of acculturation. Master of Science in Biology: Thesis Option The thesis option should be strongly considered by students interested in eventually applying to Ph.D.
programs. A thesis student may take fewer courses but more research credit .