Author(s): Cunha, Luis Filipe das Neves
Date: 2012
Persistent ID: http://hdl.handle.net/10400.3/3968
Origin: Repositório da Universidade dos Açores
Project/scholarship: info:eu-repo/grantAgreement/FCT/3599-PPCDT/115713/PT ;
Subject(s): Pontoscolex corethrurus; Bioindicator; Earthworm; Mitochondrial DNA; Volcanic Crater; Domínio/Área Científica::Ciências Naturais::Ciências Biológicas
Tese de Doutoramento, Biologia (Biologia Celular e Molecular), 18 de Maio de 2012, Universidade dos Açores.
Understanding how living processes persist under the challenges of intense physical or chemical stress emanating from diverse geogenic sources, such as those originated by volcanic activity have increasingly gained importance mainly compelled by biotechnology imperatives. Volcanically active regions, such as Furnas, a geothermal field located in São Miguel Island (Azores), often have a high-density of human inhabitants due to the elevated natural fertility of its soils, despite of creating significant risk scenarios of exposure to a wide range of chemical substances. The volcanic gases at the Furnas caldera create a hypoxic and hypercapnia environment combined with 10˚ C elevated soil temperatures and acidic conditions promoting bioavailability of heavy metals. These tripartite stress factors combine to create an in-hospitable challenge to the resident biota; therefore, it is surprising that this extreme soil environment supports a viable earthworm population. In fact, the epidermis of Amynthas gracilis resident on Furnas soil is ~50% thinner than the respiratory exchange surface in conspecifics resident on inactive volcanic soils. This was also found in resident Pontoscolex icorethrurus. This leads to the plausible conclusion that the earthworm’s responses to the multi-stressor challenges in active volcanic soils are, like the adaptations of arthropods and vertebrates to hypoxic conditions, multifactorial and involve integrated modifications ranging from genetic and biochemical, to cellular and physiological levels of organization. Analyses of mitochondrial data using different approaches corroborate the existence of two different genetic lineages living in São Miguel Island. Furnas population showed lower genetic diversity when compared to the populations living within pineapple plantations. Molecular markers included the mitochondrial regions of the cytochrome c oxidase subunit I gene (COI), small ribosomal unit (s- rRNA), the NADH desidrogenase subunit 2 and 3. The importance of genetic reduction in the population genetic structure of earthworms living under the stress of the volcanic environment is further discussed. Analysis using AFLP markers showed Pontoscolex corethrurus to be a genetically heterogeneous complex with direct association with the previous results of mitochondrial divergence. The complete congruence between molecular markers suggests that cryptic speciation is a plausible explanation for the deep mitochondrial divergence in P. corethrurus in São Miguel Island. Four pairs of primers generated 425 loci. The average ratio of polymorphic loci among the studied populations was of 84%. Shannon information index was 0.28 with a higher value of 0.3 in Furnas. These results show that the genetic diversity detected with AMOVA was mainly caused by individual differences within a population. In fact, three different ancestral clusters were identified among populations. One cluster showed to be almost exclusive to Furnas individuals showing and confirming the genetic differentiation of this apparently isolated geographic group. On the one hand it is plausible to consider that the homogenizing effect of selection on genomic diversity would intensify in populations successfully inhabiting intensely stressful environmental conditions, such as actively volcanic soils. In contrast, an intriguing alternative scenario may pertain where chemical contaminants increase genetic diversity by causing genomic mutation which could explain why Furnas population showed the highest number of private bands. Microbial populations associated with the earthworms revealed some conspicuous results. Some bacteria were found in both earthworm populations as resident microbial flora (e.g. Nitrobacter, Serratia, Bradyrhizobium, and Methylobacterium) while others seem to be restrict to one of the studied populations. The Azorean P. corethrurus has some conspicuous genera such Anaeromyxobacter and Desulfovibrio that may result of adaptations to the environment in which the host lives. This is also the first report of Verminephrobacter phylotypes within the Pontoscolex genus. With this project was possible to elucidate some of functional mechanisms employed by annelids that allow it to maintain viable populations in soil exhibiting elevated heavy metal availability, low oxygen/high CO2 content and a high ambient temperature (~37˚C) as well the consequences of living under such environment revealed at genetics level from the individual to the population.
This study was financially supported by CIRN (University of the Azores), DRCT (Government of the Azores) and by the research grant PTDC/AAC-AMB/115713/2009 from Fundação para a Ciência e Tecnologia (FCT). Luis Cunha was supported by a Doctoral grant from DRCT (M312/F/029/2007).
