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The preceding explanation is also consistent with the fossil record of amphisbaenians foods dietary cholesterol found vytorin 20mg free shipping. Although not fossorial cholesterol medication welchol side effects generic vytorin 30mg visa, the Cuban gecko Tarentola americana may have arrived in a similar way from the Mediterranean. The initial diversification of blindsnakes (Typhlopidae) followed a vicariant event, the separation of East and West Gondwana about 150 Ma. Like amphisbaenians, these burrowing animals spend much of their lives underground. Nevertheless, later diversification involved both vicariant and oceanic dispersal events, including a westward transatlantic one. Historical Biogeography of Malagasy Reptiles Some Malagasy reptiles appear to have biogeographic patterns consistent with Gondwana vicariance. Ninety Ma, the combined Madagascar and India plates likely had subaerial connections with Antarctica. Madagascar was connected to Antarctica via the Gunnerus Ridge, and India was connected via the Kerguelen Plateau. The phylogeny demonstrates that these clades are outside (sister to) other ranoids. Molecular dating places the origin of the clades containing these four subfamilies in the Cretaceous. Malagasy boid snakes, podocnemid turtles, and pleurodont iguanian lizards date to at least 75, 80, and 67 Ma, respectively, indicating that dispersal origins for these taxa were highly unlikely, and these taxa were likely isolated as the result of a single vicariant event during the Late Cretaceous. Other estimates of the ages of these taxa place their divergences slightly earlier. The taxa would have to be much older (about 160 Ma) to have arisen from an African vicariant event and much younger (65 Ma) to have arisen from Laurasian vicariance. The single iguanid genus in Fiji (Brachylophus), which is nested within the South American iguanids, does represent a much later dispersal event from South America. If vicariance accounts for presence of boid snakes, podocnemid turtles, and pleurodont iguanian lizards on Madagascar, then they should also occur in India and Australia. Iguanids (fossils) and the sister group to podocnemids (the extinct Bothremydidae) did occur in India. The absence of extant podocnemids and iguanids in India has been attributed to the effect of the Deccan Traps volcanism, but keep in mind that some frog taxa were able to survive on the Indian continent during this time period. At some point, bufonids dispersed into the Old World and diversified into the Eurasian and African clades, likely across Beringia. Although at least three possible routes existed (Berengia, DeGeer, and Thulean land bridges), the Thulean land bridge is most likely because it provided a much milder climatic regime. Many examples exist, and similar to studies dealing with deep history, these studies are expanding rapidly because we can often tie divergence events to landscape changes. These salamanders are tied to stream systems and can be common in many localities. Phylogeographic divergence in these salamanders is linked with historical drainage patterns (mid-Miocene and Pleistocene) rather than current 9 8 7 6 5 2 1 3 4 N. Horizontal bars and shaded rectangles indicate 95% credibility intervals of estimates of divergence times. Graphic on the left (A) shows phylogenetic relationships of taxa and graphic on right (B) shows distributions of each clade. Terrarana now includes the families Eleutherodactylidae, Craugastoridae, Ceuthomantidae, Strabomantidae, and Brachycephalidae. Shifts in the drainage patterns during glacial events split populations, resulting in the fragmentation that we see today. In this case, interruption of historic stream patterns was the vicariant event leading to separation of populations. Diversity of dendrobatid frogs in the Neotropics has been interpreted as originating in the Amazon Basin followed by dispersal out of the basin and into Central America. This deep divergence accounts for the presence of caecilians on most southern continents today.

Finally cholesterol medication reactions generic vytorin 30mg, we showcase several phylogeography studies to show how the combined use of well-supported phylogenetic hypotheses and geological-fossil data is rapidly improving our understanding of the history of patterns of distribution and diversification in amphibians and reptiles cholesterol lowering diet ppt vytorin 20mg sale. The circle represents the globe, and shades of color represent latitudinal zones with the latitude zero across the center. On the left, black points represent individual species, and clearly the number of species is correlated with latitude; tropical habitats have more species than temperate habitats. Explanations for higher diversity in tropical regions center on correlations between numbers of species and environmental variables such as temperature and moisture. On the right, evolutionary relationships of species are shown (lines) with a hypothetical monophyletic clade represented. This graphic stresses a history of diversification indicating that more clades originated in the tropics, and because of niche conservatism, few clades were able to evolve ecological traits allowing them to disperse to temperate climates. The flora and fauna of any given area differs compared with the flora and fauna of adjacent areas. The flora and fauna can persist over large or small areas and then gradually or abruptly change to new flora and fauna. Geographical ecology (ecological biogeography) examines geographic patterns in the structure of different communities from a perspective of resource utilization. Island biogeography fits into this category but emphasizes immigration and extinction. Ecological biogeography emphasizes overall structure of communities across space and has resulted in descriptions of biomes, biogeographic realms, and other ecologically based categories. Historical biogeography focuses on the relationships and origins of taxa, emphasizing the phylogenetic affinities of the species (their evolutionary histories) and how those tie in with the history of distributional patterns. The key difference between the ecological and historical approaches to animal distributions is that ecological approaches center on extant or relatively recent correlates of present-day distributions, whereas modern historical biogeography emphasizes the evolutionary history of the organisms of interest. Both approaches predict similar numbers of species at various latitudes, but the biogeographical approach traces the origins of the faunas tying together phylogeny, ecology, and microevolution. The ecological approach pays little attention to the underlying evolutionary relationships of organisms at any particular place on the planet, whereas the historical biogeography approach interprets patterns of species richness in the context of evolutionary relationships. It is clear that most species and clades originated in tropical environments, with relatively few moving into colder regions. This can be nicely illustrated by examining two commonly discussed ecological parameters from a phylogenetic perspective, niche conservatism and niche evolution. Niche conservatism refers to individual species maintaining ecological traits similar to those of their sister taxon and ancestors, whereas niche evolution refers to divergence in niche characteristics. Populations represent a distribution of the requirements of their individual members. Survival of individuals does not necessarily ensure survival of the population; individuals must reproduce and so must their offspring for a population to persist. At one season or year, conditions allow reproduction and survival of young and the population grows; in the next, reproduction could be unsuccessful and the population could drift toward extinction. Factors affecting these population cycles are climate (micro- and macro-) relative to physiological tolerances, availability and access to resources, and interspecific interactions. Many amphibians are resilient to relatively long-term (several years) environmental fluctuations, such as extended droughts. As a result, we often see drastic reductions in amphibian and reptile abundance at the local level followed by rapid increases in abundance when conditions change. The ability to withstand long time periods when resources are low is largely a consequence of physiological correlates of ectothermy. Amphibians and reptiles can persist on relatively little energy for long time periods when compared with endothermic mammals and birds. Other factors, such as historical accident and dispersal ability, determine which species are likely to occur in one area and the probability of their reaching another area. Needless to say, amphibian and reptile species are not randomly distributed across the planet. Examples include increase in abundance of numerous exotic lizards in Miami, Florida; the marine toad (Rhinella marina) in the West Indies, Australia, and the southwest Pacific; the various species of Mediterranean geckos (Hemidactylus) that have colonized the New World; and the brown tree snake (Boiga irregularis) in Guam. Thus, physiological tolerances are not the only factors limiting and determining distributions. Two clades (blue and green) have retained ancestral niche characteristics and have distributions restricted to tropical and subtropical environments.

Although unisexual reproduction maximizes reproductive rates (no investment in males) foods to keep cholesterol down buy 30mg vytorin mastercard, sexual reproduction provides the raw material on which natural selection operates-heritable variation among individuals cholesterol test requires fasting generic 30 mg vytorin. Individual females cannot predict the environments that their offspring will encounter during their lifetimes. Consequently, production of numerous, slightly different offspring that results from reshuffling of genes during sexual reproduction provides the opportunity for adaptation to changing environments. Individuals best able to survive and reproduce given the abiotic and biotic environments at the time will send the most descendants into the next generation. Amphibians and reptiles enhance reproductive output and offspring survival in many ways. Fertilization can occur inside or outside the body of the female and development can be direct or indirect. Their complex life histories, which usually include a larval stage and radical metamorphosis, no doubt set the stage for the evolution of the great diversity of reproductive modes observed today. Two major reproductive modes are generally recognized in reptiles: oviparity, the deposition of eggs, and viviparity, the birth of fully formed individuals. However, much variation occurs within oviparous species in terms of egg retention and development prior to egg deposition. Some species have no placenta, others have a simple placenta, and yet others have a placenta that rivals that of eutherian mammals. Although most amphibians and reptiles reproduce sexually, some species consist entirely of females that reproduce unisexually. In some cases, females "steal" the genomes of sexual species with which they live but do not pass them on; in others, females produce identical daughters clonally, eliminating involvement of males entirely. Parental care is widespread in amphibians and reptiles, varying from attendance of eggs to protection and/or feeding of offspring. These and many other fascinating phenomena comprise reproduction and reproductive modes of amphibians and reptiles. Chapter 4 Reproduction and Life Histories Chapter Outline Gametogenesis and Fertilization Gamete Structure and Production Fertilization-Transfer and Fusion of Gametes Reproductive Behaviors Associated with Mating Reproductive Ecology Ecology of Nesting Amphibians Reptiles Sex Determination Number and Size of Offspring Reproductive Productivity Seasonality in Reproduction Amphibians 117 117 120 121 123 123 123 124 126 129 132 132 132 Reptiles Sexual versus Unisexual Reproduction Hybridogenesis Kleptogenesis Parthenogenesis Life Histories Reproductive Effort and Costs of Reproduction Life History Variation Amphibians Reptiles Seasonal versus Aseasonal Environments Growth as a Life History Trait Phenotypic Plasticity in Life History Traits 133 136 136 139 140 142 146 149 149 150 150 152 152 the transition from a totally aquatic life to living at least part of the time on land presented a major challenge in vertebrate evolution and led to an explosion of reproductive adaptations. Because external fertilization was the ancestral condition of the first amphibians, standing water was required for reproduction. The evolution of internal fertilization allowed some amphibians independence from standing water for breeding. Direct development (no free-living larval stage) or attendance of eggs in moist microhabitats permitted development away from water. The evolution of the amniotic egg characterized one clade of tetrapod vertebrates, the Amniota (reptiles [including birds] and mammals). Amniotic structures allow respiration and storage of nitrogenous waste within the egg, making it possible for development to occur on land in "dry," although not desiccating, egg deposition sites. These factors, among others, ultimately led to the successful and broad diversification of tetrapod vertebrates. Internal (hormonal) controls mediate reproductive timing, but ultimately reproduction is triggered directly or indirectly by environmental cues, such as temperature, rainfall, or photoperiod. Hormonal changes cause gametogenesis, the production of sex cells or gametes (ova in females, sperm in males), a process that is similar in all vertebrates. In addition to gamete production, gonads produce hormones that feed back on the brain, pituitary, and other organs and ultimately influence the physiology and behavior of reproduction. Gamete Structure and Production Male gametes (spermatozoa) are produced by cells (spermatogonia) in the seminiferous tubules of the testes during spermatogenesis. Spermatogonia undergo mitotic divisions to produce additional spermatogonia, which differentiate into primary spermatocytes. As primary spermatocytes differentiate into secondary spermatocytes, the chromosome number is halved by two meiotic events, ultimately producing four 1N spermatids. Within species, reproductive activity between sexes is usually synchronous, although some Herpetology. Diagrammatic representation of a crosssection through a seminiferous tubule in a typical reptile testis. Androgens not only effect development of secondary sexual structures but also feed back on sexual behavior and the brain. The acrosome produces proteolytic enzymes that digest the egg capsule and allow the spermatozoon to penetrate into an egg.

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