Dispersão de sementes de Marantaceae: o papel da heterogeneidade ambiental nas interações planta-dispersor e nos padrões de distribuição de ervas de sub-bosque na Amazônia central

We investigated aspects of seed dispersal of four Marantaceae species related to the complexity of multiple dispersers and a terra firme heterogeneous landscape in Central Amazonia. In Chapter 1 we compared seed dispersal by ants and crickets among herb species and found that there is no difference between the number of seeds removed by crickets and ants. However, crickets remove seeds mainly at night and tend to move large seeds further. We emphasize that crickets, like ants, may play an important role in the dispersion of arilate seeds. In Chapter 2 we used the seed dispersal effectiveness framework (SDE) to compare the role of different disperser groups in the dispersion and recruitment of herbs within a heterogeneous landscape. We specifically asked whether there was a relationship between the seed dispersal assigned to the herb and the relative contribution of the different dispersers to herb SDE; How the SDE and dispersers assemblage changed due to the habitat type; and if there was a match between the SDE, germination and recruitment within habitat types. We found that the seed dispersion is mainly carried out by invertebrates, many of them unexpected. For three of the four species studied there was a relationship between the assigned dispersion syndrome and the most effective group of seed disperser. However, among different habitats, sometimes the second most effective disperser contributed disproportionately to the SDE. In addition, the habitat with higher SDE is not always better for germination and recruitment. Therefore, the complementary roles of seed dispersers at local scale, combined with changes in the match pattern between SDE and the suitable recruitment habitat, should hold the changes in community structure of animal dispersed understory herbs in tropical heterogeneous landscapes. In Chapter 3 we investigated changes in population structure, patterns of abundance and their relationships with light and hydrology, to understand processes of limitation of dispersion and recruitment along a landscape. Herbs with small diaspores were more restricted to one type of environment, suggesting dispersion limitation and recruitment more associated with more enlightened environments. Herbs with large diaspores were more distributed in the landscape suggesting no dispersion limitation, and with recruitment strongly associated with hydrology. Therefore, the landscape spatial pattern of the herb species emerges from the combination of dispersion and recruitment limitation acting on different spatial scales. In this thesis, we demonstrate that the seed dispersal process of understory herbs is much more complex than previously considered and involves numerous seed dispersers not previously recognized. The shade tolerance condition of the species studied is not related to the type of seed disperser as seen previously. Dispersion is an important process to allow the studied species to occupy different habitats; however, environmental filters seem to refine patterns of abundance long the heterogeneous landscape.Investigamos aspectos da dispersão de sementes de quatro espécies de Marantaceae relacionados à complexidade dos múltiplos dispersores e de uma paisagem heterogênea de terra firme na Amazônia Central. No capítulo 1 comparamos a dispersão de sementes por formigas e grilos entre as espécies de ervas e descobrimos que não há diferença entre o número de sementes removidas por grilos e formigas. Porém grilos removem sementes principalmente no período da noite e tendem a mover as sementes grandes mais longe. Ressaltamos que os grilos, assim como as formigas, podem ter papel importante na dispersão de sementes ariladas. No capítulo 2 utilizamos o framework de efetividade de dispersão (SDE) para comparar o papel de diferentes grupos de dispersores na dispersão e recrutamento das ervas dentro de uma paisagem heterogênea. Perguntamos especificamente se existia relação entre o modo de dispersão atribuído à erva e a contribuição relativa dos diferentes dispersores à efetividade; como a efetividade de dispersão e assembleia de dispersores mudava com relação ao tipo de ambiente; e se existia uma associação entre os locais com maior efetividade, germinação e recrutamento. Encontramos que a dispersão de sementes é realizada principalmente por invertebrados, muitos deles inesperados. Para três das quatro espécies estudadas houve relação entre a síndrome de dispersão atribuída e o grupo dispersor mais efetivo. Entretanto, entre ambientes diferentes, o segundo dispersor mais efetivo pode contribuir desproporcionalmente para o SDE. Além disso, nem sempre o ambiente com maior SDE é também melhor para a germinação e recrutamento. Portanto, os papéis complementares dos dispersores de sementes à escala local de ervas, combinados com as mudanças no padrão de correspondência da SDE e habitat adequado para o recrutamento, devem ajudar a impulsionar a estrutura da comunidade de ervas de sub-bosque dispersas em animais em ambientes heterogêneos tropicais. No capítulo 3 investigamos mudanças na estrutura das populações, padrões de abundância e suas relações com luz e hidrologia, para entender processos de limitação de dispersão e de estabelecimento ao longo de uma paisagem. As ervas com diásporos pequenos foram mais restritas a um tipo de ambiente, sugerindo limitação de dispersão e recrutamento mais associados a ambientes mais iluminados. Ervas com diásporos grandes estiveram mais distribuídas na paisagem sugerindo ausência de limitação de dispersão, e com recrutamento fortemente associado à hidrologia. Portanto, o padrão espacial da paisagem das espécies de ervas emerge da combinação de dispersão e limitação de recrutamento que atuando em diferentes escalas espaciais. Nesta tese, demonstramos que o processo de dispersão de sementes das ervas de sub-bosque é muito mais complexo do que considerado anteriormente e envolve inúmeros dispersores de sementes não antes reconhecidos. A condição de tolerância à sombra das espécies estudadas não está relacionada ao tipo de dispersor de sementes como visto anteriormente. A dispersão é um processo importante para permitir que as espécies estudadas ocupem diferentes habitats, no entanto, os filtros ambientais parecem refinar os padrões de abundância ao longo da paisagem heterogênea

In situ short-term responses of Amazonian understory plants to elevated CO₂

The response of plants to increasing atmospheric CO2 depends on the ecological context where the plants are found. Several experiments with elevated CO2 (eCO2) have been done worldwide, but the Amazonian forest understory has been neglected. As the central Amazon is limited by light and phosphorus, understanding how understory responds to eCO2 is important for foreseeing how the forest will function in the future. In the understory of a natural forest in the Central Amazon, we installed four open-top chambers as control replicates and another four under eCO2 (+250 ppm above ambient levels). Under eCO2, we observed increases in carbon assimilation rate (67%), maximum electron transport rate (19%), quantum yield (56%), and water use efficiency (78%). We also detected an increase in leaf area (51%) and stem diameter increment (65%). Central Amazon understory responded positively to eCO2 by increasing their ability to capture and use light and the extra primary productivity was allocated to supporting more leaf and conducting tissues. The increment in leaf area while maintaining transpiration rates suggests that the understory will increase its contribution to evapotranspiration. Therefore, this forest might be less resistant in the future to extreme drought, as no reduction in transpiration rates were detected.</p

In situ short-term responses of Amazonian understory plants to elevated CO₂

The response of plants to increasing atmospheric CO2 depends on the ecological context where the plants are found. Several experiments with elevated CO2 (eCO2) have been done worldwide, but the Amazonian forest understory has been neglected. As the central Amazon is limited by light and phosphorus, understanding how understory responds to eCO2 is important for foreseeing how the forest will function in the future. In the understory of a natural forest in the Central Amazon, we installed four open-top chambers as control replicates and another four under eCO2 (+250 ppm above ambient levels). Under eCO2, we observed increases in carbon assimilation rate (67%), maximum electron transport rate (19%), quantum yield (56%), and water use efficiency (78%). We also detected an increase in leaf area (51%) and stem diameter increment (65%). Central Amazon understory responded positively to eCO2 by increasing their ability to capture and use light and the extra primary productivity was allocated to supporting more leaf and conducting tissues. The increment in leaf area while maintaining transpiration rates suggests that the understory will increase its contribution to evapotranspiration. Therefore, this forest might be less resistant in the future to extreme drought, as no reduction in transpiration rates were detected.</p

High frequency of WNT-activated medulloblastomas with CTNNB1 wild type suggests a higher proportion of hereditary cases in a Latin-Iberian population

PurposeMedulloblastomas are the most common primary malignant brain tumors in children. They are divided into molecular subgroups: WNT-activated, SHH-Activated, TP53 mutant or wild type, and non-WNT/non-SHH (Groups 3 and 4). WNT-activated medulloblastomas are usually caused by mutations in the CTNNB1 gene (85%–90%), and most remaining cases of CTNNB1 wild type are thought to be caused by germline mutations in APC. So far, the frequencies of CTNNB1 have been reported mainly in North American and European populations. The aim of this study was to report the frequency of CTNNB1 mutations in WNT-activated medulloblastomas in a Latin-Iberian population and correlate with their clinicopathological characteristics.MethodsA total of 266 medulloblastomas from seven different institutions from Brazil (n=211), Portugal (n=38), and Argentina (n=17) were evaluated. Following RNA and DNA isolation from formalin-fixed, paraffin-embedded (FFPE) tumor tissues, the molecular classification and CTNNB1 mutation analysis were performed by nCounter and Sanger sequencing, respectively.ResultsWNT-activated medulloblastomas accounted for 15% (40/266) of the series. We observed that 73% of WNT-activated medulloblastomas harbored CTNNB1 mutations. CTNNB1 wild-type cases (27%) were more prevalent in female individuals and suggested to be associated with a worse outcome. Among the CTNNB1 wild-type cases, the available analysis of family history revealed two cases with familiar adenomatous polyposis, harboring APC germline variants.ConclusionWe observed a lower incidence of CTNNB1 mutations in WNT-activated medulloblastomas in our Latin-Iberian cohort compared to frequencies previously described in other populations. Considering that CTNNB1 wild-type cases may exhibit APC germline mutations, our study suggests a higher incidence (~30%) of hereditary WNT-activated medulloblastomas in the Latin-Iberian population

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Sensitivity of South American tropical forests to an extreme climate anomaly

The tropical forest carbon sink is known to be drought sensitive, but it is unclear which forests are the most vulnerable to extreme events. Forests with hotter and drier baseline conditions may be protected by prior adaptation, or more vulnerable because they operate closer to physiological limits. Here we report that forests in drier South American climates experienced the greatest impacts of the 2015–2016 El Niño, indicating greater vulnerability to extreme temperatures and drought. The long-term, ground-measured tree-by-tree responses of 123 forest plots across tropical South America show that the biomass carbon sink ceased during the event with carbon balance becoming indistinguishable from zero (−0.02 ± 0.37 Mg C ha −1 per year). However, intact tropical South American forests overall were no more sensitive to the extreme 2015–2016 El Niño than to previous less intense events, remaining a key defence against climate change as long as they are protected

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Busy nights: High seed dispersal by crickets in a neotropical forest

Among invertebrates, ants are the most abundant and probably most important seed dispersers in both temperate and tropical environments. Crickets, also abundant in tropical forests, are omnivores and commonly attracted to fruits on the forest floor. However, their capability to remove seeds has been reported only once. We compared Marantaceae seed removal by crickets and ants to assess the role of crickets as secondary seed dispersers in Amazonia. Compared with ants, crickets dispersed an equivalent number of seeds and tended to disperse larger seeds farther. However, seed removal by crickets occurs mostly at night, suggesting that removal of arillate seeds by crickets on the tropical forest floor is probably being overlooked or wrongly attributed to other invertebrate groups. One potential consequence of seed dispersal by crickets may be a change in the local spatial distribution of arillate-seed species, due to lower aggregation around ant nests. © 2016 by The University of Chicago