Diversificação de anuros no Chaco Sul-Americano
Carregando...
Data
2016-01-28
Autores
Estrada, Francisco Adolfo Brusquetti [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Os processos de diversificação biológica na América do Sul têm sido foco de vários estudos nos últimos tempos; porém, nota-se um marcado viés para os biomas florestados como a Amazônia e a Mata Atlântica. Nesse contexto, o Chaco é um dos biomas que tem recebido menor atenção. Nesta tese apresentamos o primeiro esforço por entender quais eventos e processos têm sido responsáveis pela diversificação de anuros endêmicos deste bioma, incluindo Lepidobatrachus asper, Lepi. laevis, Lepi. llanensis e Leptodactylus bufonius. Para atingir esse objetivo utilizamos sequências de DNA mitocondrial e nuclear de uma ampla amostragem de cada uma das espécies. Nos primeiros dois capítulos investigamos a diversificação do gênero Lepidobatrachus, sendo que no primeiro deles nossos objetivos foram analisar a estrutura genética e delimitar um período de tempo de diversificação que nos permita associá-la com eventos históricos e assim gerar as primeiras hipóteses sobre diversificação de anuros no Chaco. A estrutura genética identificada corresponde à distribuição geográfica dos espécimes analisados, assim como também revela algumas quebras ao longo da paisagem. A principal dessas barreiras corresponde à área central do Chaco, que por sua extrema aridez poderia estar atuando como uma barreira climática para a dispersão desses animais. Por outro lado, a dinâmica histórica dos rios da região poderia ter influenciado na estrutura genética das espécies do gênero Lepidobatrachus. Sugerimos uma antiga e rápida radiação para este gênero, com introgressões marinhas e períodos de alta temperatura e aridez como os principais responsáveis por sua diversificação. No segundo capítulo, aprofundamos no estudo da estrutura genética usando frequência alélica. Investigamos a história demográfica e usamos modelos de isolamento com migração para testar as hipóteses propostas no primeiro capítulo e entender os processos que resultaram na diversidade que hoje conhecemos dentro do gênero Lepidobatrachus. Nossos resultados sugerem que as antigas formações continentais estáveis, como os arcos estruturais e os crátons, tiveram um importante papel na diversificação do gênero Lepidobatrachus, atuando como refúgios durante as introgressões marinhas. A barreira climática do Chaco central é confirmada para uma das espécies do gênero. Adicionalmente, encontramos que os rios exerceram diferentes efeitos nas diferentes espécies do gênero, o que pode estar relacionado ao tempo de persistência de cada uma das espécies na área de influência desses rios. A maior persistência de Lept. llanensis resultou num padrão genético modelado pela dinâmica desses rios alóctones. No terceiro e último capítulo analisamos a estrutura genética e demografia histórica de Lept. bufonius, uma espécie de ampla distribuição, para ter acesso a história evolutiva mais recente do Chaco. Os resultados suportam eventos de expansão recente e constante fluxo gênico entre as populações. As expansões estão relacionadas aos períodos interglaciais, enquanto o fluxo gênico é mantido por dispersões curtas que seguem um modelo “steppingstone”, permitindo assim uma alta conectividade, inclusive entre as populações mais distantes. Esse mesmo padrão foi registrado em anuros de outras regiões semiáridas pelo mundo.
Diversification processes in South America have been the focus of several studies in recent times; however, with a marked bias towards the forested biomes such as the Amazon and the Atlantic Forest. In this context, the Chaco has been one of the biomes that have received less attention. In this thesis we present the first effort to understand the events and processes that have been responsible for the diversification of endemic frogs in this biome, including Lepidobatrachus asper, Lepi. laevis, Lepi.llanensis, and Leptodactylus bufonius. For this purpose we used DNA sequences, both mitochondrial and nuclear, of a large sample of each species. In the first two chapters we investigate the diversification of the genus Lepidobatrachus. In the first one, our goals were to assess genetic structure and to delimit a diversification timeframe, which allow us to do associations with historical events and, thereby, generate the first hypotheses about diversification within the Chaco. The identified genetic structure is concordant with the geographic distribution of sampled specimens as well as shows some breaks along the landscape. The most important of these breaks matches with the central area of the Chaco, which due to the extreme aridity may act as a climatic barrier for the dispersal of these animals. On the other hand, the historical dynamics of the rivers of this region has influenced the genetic structure of these species. We suggest an old and rapid radiation for Lepidobatrachus, with marine introgressions and periods of high temperature and aridity as the main responsible in the genus diversification. In the second chapter, we deepen the genetic structure using allele frequency, we investigated the demographic history and used isolation-with-migration models to test hypotheses proposed in the first chapter and to understand the processes that resulted in the current diversity of the genus Lepidobatrachus. Our results support that old and stable continental formations, such as structural arches and cratons, have played an important role in the genus diversification, acting as refuges during marine introgressions. The central Chaco climatic barrier is confirmed for one species of the genus. Additionally, we find different effects of the rivers on the species of the genus, related to the time of persistence of each one in the area of influence of these rivers. The longer persistence of Lepi. llanensis resulted in a genetic pattern shaped by dynamics of allochthonous rivers. In the third and last chapter we analyzed the genetic structure and historical demography of the widely distributed species Lept. bufonius in order to access the recent evolutionary history of this biome. Our results support recent expansion events and current gene flow among populations. The expansions are related to interglacial periods. Gene flow is maintained by short dispersions that follow a "stepping-stone" model enabling high connectivity, even among the most remote populations. The same pattern was registered in frogs in other semiarid regions of the world.
Diversification processes in South America have been the focus of several studies in recent times; however, with a marked bias towards the forested biomes such as the Amazon and the Atlantic Forest. In this context, the Chaco has been one of the biomes that have received less attention. In this thesis we present the first effort to understand the events and processes that have been responsible for the diversification of endemic frogs in this biome, including Lepidobatrachus asper, Lepi. laevis, Lepi.llanensis, and Leptodactylus bufonius. For this purpose we used DNA sequences, both mitochondrial and nuclear, of a large sample of each species. In the first two chapters we investigate the diversification of the genus Lepidobatrachus. In the first one, our goals were to assess genetic structure and to delimit a diversification timeframe, which allow us to do associations with historical events and, thereby, generate the first hypotheses about diversification within the Chaco. The identified genetic structure is concordant with the geographic distribution of sampled specimens as well as shows some breaks along the landscape. The most important of these breaks matches with the central area of the Chaco, which due to the extreme aridity may act as a climatic barrier for the dispersal of these animals. On the other hand, the historical dynamics of the rivers of this region has influenced the genetic structure of these species. We suggest an old and rapid radiation for Lepidobatrachus, with marine introgressions and periods of high temperature and aridity as the main responsible in the genus diversification. In the second chapter, we deepen the genetic structure using allele frequency, we investigated the demographic history and used isolation-with-migration models to test hypotheses proposed in the first chapter and to understand the processes that resulted in the current diversity of the genus Lepidobatrachus. Our results support that old and stable continental formations, such as structural arches and cratons, have played an important role in the genus diversification, acting as refuges during marine introgressions. The central Chaco climatic barrier is confirmed for one species of the genus. Additionally, we find different effects of the rivers on the species of the genus, related to the time of persistence of each one in the area of influence of these rivers. The longer persistence of Lepi. llanensis resulted in a genetic pattern shaped by dynamics of allochthonous rivers. In the third and last chapter we analyzed the genetic structure and historical demography of the widely distributed species Lept. bufonius in order to access the recent evolutionary history of this biome. Our results support recent expansion events and current gene flow among populations. The expansions are related to interglacial periods. Gene flow is maintained by short dispersions that follow a "stepping-stone" model enabling high connectivity, even among the most remote populations. The same pattern was registered in frogs in other semiarid regions of the world.
Descrição
Palavras-chave
Diversificão de anuros, Bioma Chaco, Lepidobatrachus, Leptodactylus bufonius