Spelling suggestions: "subject:"coldclimate hypothesis"" "subject:"andclimate hypothesis""
1 |
Physiological and Ecological Constraints on the Evolution of Viviparity in Sceloporine LizardsParker, Scott Landsborough 16 February 2006 (has links)
The purpose of this study was to evaluate putative physiological and ecological constraints on the evolution of viviparity in sceloporine lizards. In Chapters one and two, I investigated the role of in utero oxygen availability as a constraint on the capacity to support embryonic development during extended egg retention. I incubated eggs of sceloporine lizards under conditions that simulated retention in the oviduct under a range of oxygen partial pressures. In Chapter one, I tested the hypothesis that embryos of the oviparous lizard Sceloporus undulatus from a high-latitude population are laid at more advanced developmental stages and have a higher developmental rate at low partial pressure oxygen (pO2) under simulated in utero conditions than embryos from a low-latitude population. This hypothesis was rejected; embryos from the two populations did not differ in embryonic stage at oviposition or developmental rate when incubated under simulated in utero conditions at low pO2. In Chapter two I tested the hypothesis that the degree of embryonic development attained by reptilian embryos in utero is directly related to in utero pO2. The species chosen for the study differed in their capacity to support embryonic development during egg retention and were characterized by developmental arrest (Urosaurus ornatus), retarded development (Sceloporus virgatus), and normal development (Sceloporus scalaris) when eggs are retained past the normal time of oviposition. The estimated in utero pO2's for the three species increased in the order of U. ornatus (5-6 kPa) < S. virgatus (9-11 kPa) < S. scalaris (> 11 kPa). These results indicate that in utero oxygen availability is associated with interspecifc differences in the capacity to support embryonic development during extended egg retention.
In Chapter three I tested the hypothesis that embryo thermal requirements determine the northern distributional limit of Sceloporus undulatus. I incubated eggs of S. undulatus under temperature treatments that simulated the thermal environment that eggs would experience if located in nests within their geographic range at 37 °N and at latitudes north of the species present geographic range at 42 and 44 °N. Incubation temperatures simulating nests at 44 °N prolonged incubation and resulted in hatchlings with shorter tails, shorter hind limb span, slower growth and lower survival than hatchlings from eggs incubated at temperatures simulating nests at 37 and 42 °N. I also predicted that the northernmost distributional limit of S. undulatus would be associated with locations that provide the minimum heat sum (degree-days) required to complete embryonic development. Eighty-four percent of location between 37-40 °N had > 495 degree-days above a threshold of 17 °C accumulated during June-September compared to eleven percent of locations between 41-50 °N. These results are consistent with the hypothesis that incubation temperature is an important factor limiting the geographic distributions of oviparous reptile species at high latitudes and high elevations. / Ph. D.
|
2 |
Evolução da viviparidade nas serpentes da tribo Hydropsini / Evolution of viviparity in snakes of the tribe HydropsiniBraz, Henrique Bartolomeu Pereira 29 August 2013 (has links)
A oviparidade é o modo reprodutivo ancestral dos répteis e a viviparidade surgiu diversas vezes independentemente nos Squamata. O cenário evolutivo mais aceito para a evolução da viviparidade em répteis Squamata propõe que ela é uma adaptação a baixas temperaturas e que resulta de aumentos graduais e progressivos na quantidade de desenvolvimento embrionário ocorrendo dentro do útero antes da postura dos ovos. Essa transição é frequentemente tida como irreversível. No presente trabalho as cobras-dágua da tribo Hydropsini foram utilizadas como modelo para testar de forma comparativa diversas predições derivadas desse cenário. Especificamente, foi avaliado se a evolução da viviparidade na tribo (1) seria um fenômeno irreversível, (2) se ela seria associada a modificações na morfologia uterina e na espessura da casca do ovo e (3) se ela seria correlacionada a regiões de climas frios. Diferentes métodos de análise não corroboram a suposta irreversibilidade da viviparidade e sugerem que a oviparidade em algumas espécies possa ser resultado de reversões. A aquisição da viviparidade em Hydropsini foi acompanhada de modificações importantes na morfologia uterina que incluem a diminuição das dimensões das glândulas uterinas que secretam o material que compõe a casca de ovo. A hipótese de que os aumentos na retenção uterina são acompanhados por diminuição na espessura da casca do ovo não foi corroborada. Por fim, o teste das predições da hipótese do clima frio não obteve suporte para baixas temperaturas como pressão seletiva favorecendo a origem da viviparidade nos Hydropsini. Hipóteses alternativas para explicar a origem da viviparidade na tribo são exploradas. / Oviparity is the ancestral reproductive mode of reptiles and viviparity evolved multiple times independently in Squamata. The most accepted evolutionary scenario for the evolution of viviparity in squamate reptiles suggests that it is an adaptation to low temperatures and that it arises from progressive and gradual increases in the amount of intrauterine embryonic development before egg-laying. In this study, the water snakes of the tribe Hydropsini were used as model system to test, within a comparative framework, several predictions derived from the gradualist scenario for the evolution of viviparity in Squamata. Specifically, it was evaluated if the evolution of viviparity in the tribe (1) is an irreversible phenomenon, (2) if it is associated with changes in uterine morphology and eggshell thickness and (3) if it is correlated to cold climates. The different analytical methods used did not corroborate the irreversibility of viviparity and suggest that oviparity may be revolved in some species. The evolutionary acquisition of viviparity in Hydropsini was accompanied by important uterine changes, including the reduction of the glands that secrete the shell components. The hypothesis that the increases in egg retention are accompanied by decreasing eggshell thickness was not corroborated. Finally, it was not found support for the test of the predictions derived from the cold climate hypothesis for the evolution of viviparity in Hydropsini. Alternative hypothesis explaining this reproductive mode in the group were explored.
|
3 |
Evolução da viviparidade nas serpentes da tribo Hydropsini / Evolution of viviparity in snakes of the tribe HydropsiniHenrique Bartolomeu Pereira Braz 29 August 2013 (has links)
A oviparidade é o modo reprodutivo ancestral dos répteis e a viviparidade surgiu diversas vezes independentemente nos Squamata. O cenário evolutivo mais aceito para a evolução da viviparidade em répteis Squamata propõe que ela é uma adaptação a baixas temperaturas e que resulta de aumentos graduais e progressivos na quantidade de desenvolvimento embrionário ocorrendo dentro do útero antes da postura dos ovos. Essa transição é frequentemente tida como irreversível. No presente trabalho as cobras-dágua da tribo Hydropsini foram utilizadas como modelo para testar de forma comparativa diversas predições derivadas desse cenário. Especificamente, foi avaliado se a evolução da viviparidade na tribo (1) seria um fenômeno irreversível, (2) se ela seria associada a modificações na morfologia uterina e na espessura da casca do ovo e (3) se ela seria correlacionada a regiões de climas frios. Diferentes métodos de análise não corroboram a suposta irreversibilidade da viviparidade e sugerem que a oviparidade em algumas espécies possa ser resultado de reversões. A aquisição da viviparidade em Hydropsini foi acompanhada de modificações importantes na morfologia uterina que incluem a diminuição das dimensões das glândulas uterinas que secretam o material que compõe a casca de ovo. A hipótese de que os aumentos na retenção uterina são acompanhados por diminuição na espessura da casca do ovo não foi corroborada. Por fim, o teste das predições da hipótese do clima frio não obteve suporte para baixas temperaturas como pressão seletiva favorecendo a origem da viviparidade nos Hydropsini. Hipóteses alternativas para explicar a origem da viviparidade na tribo são exploradas. / Oviparity is the ancestral reproductive mode of reptiles and viviparity evolved multiple times independently in Squamata. The most accepted evolutionary scenario for the evolution of viviparity in squamate reptiles suggests that it is an adaptation to low temperatures and that it arises from progressive and gradual increases in the amount of intrauterine embryonic development before egg-laying. In this study, the water snakes of the tribe Hydropsini were used as model system to test, within a comparative framework, several predictions derived from the gradualist scenario for the evolution of viviparity in Squamata. Specifically, it was evaluated if the evolution of viviparity in the tribe (1) is an irreversible phenomenon, (2) if it is associated with changes in uterine morphology and eggshell thickness and (3) if it is correlated to cold climates. The different analytical methods used did not corroborate the irreversibility of viviparity and suggest that oviparity may be revolved in some species. The evolutionary acquisition of viviparity in Hydropsini was accompanied by important uterine changes, including the reduction of the glands that secrete the shell components. The hypothesis that the increases in egg retention are accompanied by decreasing eggshell thickness was not corroborated. Finally, it was not found support for the test of the predictions derived from the cold climate hypothesis for the evolution of viviparity in Hydropsini. Alternative hypothesis explaining this reproductive mode in the group were explored.
|
Page generated in 0.0555 seconds