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| Author(s): |
Gisele Pires de Mendonça Dantas
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2007-10-05 |
| Examining board members: |
Joao Stenghel Morgante;
Maria Alice dos Santos Alves;
Maria Cristina Arias;
Joaquim Olinto Branco;
Cristina Yumi Miyaki
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| Advisor: | Joao Stenghel Morgante |
| Abstract | |
Larus dominicanus is a widely distributed species in the Southern Hemisphere, and it breeds on islands close to the continents. In the last few decades this species presented great population expansions, due to its generalist habits and its great competitive capacity. These populations expansions ended up leading to the displacement of other seabirds and marine mammals of the breeding sites. In this sense, studies that seek understanding the biology and evolution of L. dominucanus are fundamental to create management and conservation plans to the seabird assemblage on the Brazilian coast. The primary aim of this study was to characterize the reproductive biology of Larus dominicanus, in order to determine the species reproductive success. In addition we evaluated the sex ratio of the populations throughout the Brazilian coast. In order to accomplish this we studied the reproductive biology of the species in one breeding colony in São Paulo state. We observed that L. dominicanus presented high reproductive success with about 70% of the eggs hatching and 50% of the chicks surviving until the flight phase. The chicks present a fast growth and within 30 days were mature enough to fly, making them able to escape from the predators. We also observed that before the flight phase, during the egg phase and mainly the first 15 days of life, the eggs and the chicks were more susceptible to vulture attacks, the main predator of the species in São Paulo state. In this sense, with a 50% rate survival and low predation rates after the flight phase, we can infer that the populations of L. dominicanus must be going through high increments per year. The secondary sex ratio analyzed to all populations sampled through the Brazilian coast did not show deviation from the 1:1 proportion. This result indicated that the L. dominicanus populations are stable, a characteristic expected to be found in populations that breed in sites with good environmental conditions. In a case like this, the parents do not need to favor the gender that needs less energy to survive, what would lead to a deviation in the sex ratio. In this scenario of high reproductive success and equal proportion of males and females in a widely distributed species, we expected to find high levels of genetic variability both among and in the populations. Nevertheless, our mitochondrial DNA (mtDNA) data revealed an opposite situation. We studied two mitochondrial genes (cytb, ATPase 8 and 6) and observed that throughout the whole Brazilian coast the 11 genetic diversity for the group was practically null. We found only one haplotype to the cytb and two haplotypes for the ATPase 8 and 6, these last two were different for one base pair. The low differentiation was maintained when we extended the sampling to the whole species\' distribution , with samples from the Antarctic Peninsula and the Marion Islands, and sequences from the Genbank from Australia and Kerguelen Islands. We proposed two scenarios that could explain this extremely low variability, either the populations of L. dominicanus went through a severe demographic event, or through selection events. In order to distinguish among this processes, we development 13 not linked nuclear markers, searching for a common pattern between the nuclear markers and the mtDNA genes. If the L. dominicanus populations had gone through demographic events, we expected to find the same expansion signal in the nuclear markers, once demographic events would be marked in the whole genome, both nuclear and mitochondrial. On the other hand, if the low genetic variability observed resulted from selective events, we expected to find variation in the nuclear DNA, and not to find an expansion signal. Our results showed exactly the last scenario, with high genetic diversity in all 13 nuclear not linked loci and no expansion signal. Even in more detailed analyses, with a higher number of individuals, the same pattern of neutrality, and not of population expansion, for the nuclear markers was found. Therefore, we concluded that L. dominicanus is an extremely well adapted species for the new environmental conditions generated by antropic activities. The species showed great reproductive success and no deviation of the 1.1 sex ratio. The low genetic diversity observed in mitochondrial DNA compared with the high variability found in different nuclear loci, indicate that this species has gone through selective processes on the mitochondrial molecule. To the conservation point of view, the high genetic variability found in nuclear markers is in agreement with the wide distribution of the species. Apparently, this species do not present diversity levels low enough to generate worries regarding its maintenance. In addition, the low levels of diversity found on the mitochondrial DNA open new frontiers to understand how evolution has acted on marine organisms and what are the processes that lead to the diversification of this group. (AU) | |
| FAPESP's process: | 03/01599-1 - Breeding biology, population structure and genetic variability of Larus dominicanus |
| Grantee: | Gisele Pires de Mendonça Dantas |
| Support Opportunities: | Scholarships in Brazil - Doctorate |