Galhas de insetos em habitats xérico e mésico em região de transição Cerrado-Caatinga no norte de Minas Gerais, Brasil

Galls are morphological changes caused by endoparasites on plants, mainly related to insects. Several hypotheses have been proposed to explain the patterns of gall richness. In this study, we tested the harsh environment hypothesis, which suggests higher galling richness in xeric habitats when compared to mesic habitats. In addition, we describe the richness of gall induced-insects on their host plants in a transition Cerrado-Caatinga, Brazil. Sampling was performed along of five trajectory of an “imaginary line,” traveled at a natural walking pace over the course of one hour in each of the three adjacent habitats (cerrado, dry forest and riparian forest). We found 98 different morphospecies of galling insects on 70 plant species belonging to 20 families. Gall richness was higher in the xeric habitats (cerrado and dry forest) when compared to mesic habitat (riparian forest). Gall richness differed significantly among the gall-inducing taxa; most galls morphospecies were induced by the Diptera (Cecidomyiidae). In general, richness of all gall-inducing taxa was higher in the xeric habitats than in the mesic habitat. The highest gall richness was found on leaves of the host plants of the riparian forest and cerrado, while the stem represented the organ most attacked in the dry forest. Although there is lower availability of sites for oviposition by female galling in the dry forest during the dry season, we found higher gall richness in this environment when compared to riparian forest. In this way, confirming the harsh environment hypothesis despite the absence of leaves. Likely, there was high gall irradiation on organ exposed continuously to gall attack during ecological time in dry forest. However, further studies are needed to clarify the forces related to differential gall performance among habitats, particularly in threatened Cerrado-Caatinga transition.Key words: Cerrado, seasonally dry tropical forests, harsh environment hypothesis, galling insects, host plants.Galhas são modificações morfológicas provocadas por endoparasitas, principalmente insetos, em tecidos vegetais. Várias hipóteses têm sido propostas para explicar os padrões observados para a riqueza de galhas. Nesse cenário, testou-se a hipótese do estresse ambiental, que prediz que a riqueza de galhas é maior em habitats xéricos quando comparados a habitats mésicos, além de descrever a riqueza de galhas induzidas por insetos sobre suas plantas hospedeiras em habitats de transição Cerrado-Caatinga. A amostragem de galhas e plantas hospedeiras foi realizada por meio de caminhadas ao longo de cinco transectos, com duração de uma hora cada, em cada um dos três habitats adjacentes (cerrado, mata ciliar e mata seca). Foram observadas 98 morfoespécies de galhas sobre 70 espécies de plantas (20 famílias). A riqueza de galhas foi maior em habitats xéricos (cerrado e mata seca) quando comparados ao habitat mésico (mata ciliar). Foi verificada uma variação significativa quanto à riqueza de galhas em função do táxon indutor, ocorrendo uma maior riqueza de galhas formadas por insetos da ordem Diptera (família Cecidomyiidae). No geral, todos os táxons indutores de galhas apresentaram maior riqueza em habitats xéricos do que no habitat mésico. A folha foi o órgão vegetal mais atacado na mata ciliar e no cerrado, enquanto o caule foi o órgão mais atacado na mata seca. Apesar de existir menor disponibilidade de sítios para oviposição por galhadores na mata seca durante o período seco, foi encontrada maior riqueza de galhas nesse ambiente, quando comparado à mata ciliar, corroborando, portanto, a hipótese do estresse ambiental. Possivelmente, na mata seca existiu forte pressão evolutiva de galhadores sobre órgãos continuamente expostos durante o tempo ecológico. Entretanto, ressalta-se a necessidade de estudos mais amplos sobre os mecanismos responsáveis pela performance diferencial de galhadores em regiões de transição, particularmente entre o Cerrado e a Caatinga.Palavras-chave: Cerrado, floresta tropical seca, hipótese do estresse ambiental, insetos galhadores, plantas hospedeiras

Galling inducing insects associated with a tropical shrub : The role of resource concentration and species interactions

Os insetos galhadores são herbívoros sedentários sofsticados que apresentam alto nível de especialização com sua planta hospedeira, mas sua performance pode ser afetada por fatores bióticos e abióticos. Neste estudo nós testamos duas hipóteses: a) plantas que possuem maior número de vizinhos coespecífcos apresentam maior riqueza e abundância de insetos galhadores, e b) a competição interespecífca é uma força capaz de molda a organização das comunidades de insetos herbívoros associados com uma planta super-hospedeira. O sistema Copaifera oblongifolia (Fabaceae)/insetos galhadores associados foi usado para testar estas hipóteses. Os trabalhos de campo foram desenvolvidos em áreas de Cerrado do norte de Minas Gerais, Brasil. Para testar a primeira hipótese, nós avaliamos, com modelos lineares generalizados de efeitos mistos, os efeitos do número de vizinhos coespecífcos na riqueza e abundância de galhas associadas com 67 arbustos de C. oblongifolia pertencentes a duas populações. Para testar a segunda hipótese, nós usamos modelos nulos para avaliar se um arbusto de C. oblongifolia colonizado por uma espécie de inseto galhador é preferido ou evitado por uma outra espécie de inseto galhador. Um total de 2901 insetos galhadores pertencentes a 15 diferentes espécies foi coletado nos 67 arbustos de C. oblongifolia. Nós observamos uma relação negativa entre o número de vizinhos coespecífcos e a riqueza e a abundância de insetos galhadores associados com C. oblongifolia. Assim, nossos resultados não corroboraram a hipótese da concentração do recuro e nós usamos a teoria da diluição do recurso para explicar este resultado. Nossos resultados também mostraram que o padrão de co-ocorrência dos insetos galhadores na planta hospedeira não diferiu daquele esperado pelo acaso. Portanto, a estrutura da comunidade de insetos galhadores associada com C. oblongifolia não pode ser atribuída a eventos determinísticos com a competição interespecífca.Gall-forming insects are sophisticated sedentary herbivores that present high level of specificity with host plant, but their performance can be affected by biotic and abiotic factors. In this study we have tested two predictions: a) plants that have a greater number of conspecific neighbors have greater richness and abundance of gall-forming insects, and b) interspecific competition is a force capable of shaping the organization of gall-forming insect communities in super-host plants. We used the Copaifera oblongifolia (Fabaceae)/galling insects’ system to test these predictions. Fieldwork was carried out in areas of Cerrado (Brazilian Savanna) in northern Minas Gerais, Brazil. To test the first hypothesis, we evaluated with generalized linear mixed models, the effects of the number of conspecific neighbors on the richness and abundance of galls associated with 67 C. oblongifolia individual plants belonging to two populations. To test the second hypothesis, we used null models to evaluate whether a plant of C. oblongifolia colonized by a species of gall is preferred or avoided by another species of gall. A total of 2901 gall-forming insects belonging to 15 species were collected from the host plant C. oblongifolia. We observed negative relationships between the number of conspecific neighbors and the abundance and richness of gall-forming insects associated C. oblongifolia. Thus, our data did not support the resource concentration hypothesis. Instead, we used the resource dilution theory to explain the negative relation between resource concentration and frequency of attack by galling insects. Our results also showed that the co-occurrence pattern of gall-forming insects in the host plant did not differ from those expected by chance. Therefore, the structure of the gall-forming insect community associated to single C. oblongifolia plants cannot be attributed to deterministic factors such as interspecific competition

Biotic and Abiotic Interactions Shape Seed Germination of a Fire-Prone Species

Both biotic and abiotic environmental filters drive the occurrence, distribution, and persistence of plant species. Amongst drivers that influence the distribution of plants in harsh environments, seed predation and temperature are particularly important in habitats that are prone to fire. In this study, we highlight the combined effects of predation and high temperature simulating fire to understand its effects on the germination percentage and germination speed of the fire prone species Copaifera oblongifolia. Groups of seeds attacked by the beetles Rhinochenus brevicollis and Apion sp., seeds manipulated by the ant Atta laevigata, and seeds left intact were put to germinate in controlled environments. To evaluate the effects of abiotic filters, seeds with intact elaiosomes and seeds with elaiosomes removed by the ant Atta laevigata were exposed to temperatures of 27, 60, 100, and 200 °C. The results showed that only 2.8% of the seeds attacked by R. brevicollis germinated. Seeds attacked by Apion sp. germinated faster, followed by seeds with their elaiosomes removed and seeds with intact elaiosomes. Seeds attacked by Apion sp. had the lowest germination percentage. The temperature of 200 °C killed seed embryos, whereas seeds exposed to 100 °C took longer to germinate than seeds exposed to other temperatures. Our results reveal that fire intensity and seed damage are important drivers of seed germination of C. oblongifolia

Soil fertility and rainfall during specific phenological phases affect seed trait variation in a widely distributed Neotropical tree, Copaifera langsdorffii

[Premise]: Knowledge of intra-specific variation in seed traits and its environmental determinants is important for predicting plant responses to environmental changes. Here, we tested the hypothesis that differences in soil fertility and rainfall during specific phenological phases drive variation in seed traits in a widely distributed tree, Copaifera langsdorffii. We also tested the hypothesis that climatic heterogeneity increases within-plant variation in seed traits. [Methods]: Inter- and intra-population and within-plant variation in seed mass, number, and seed size/seed number were evaluated for 50 individuals from five populations distributed along a rainfall gradient and occurring on varying soil types. Using multivariate approaches, we tested the effects of soil fertility characteristics and rainfall in five reproductive phenological phases on seed traits. [Results]: The seed traits varied greatly both among populations and within plants. Inter-population variation in seed mass was driven by total rainfall during fruit development, and variation in seed number was influenced by total rainfall during the dry season before the reproductive phase. Phosphorus levels and potential acidity of the soil also explained the variations in seed mass and seed mass/seed number, respectively. A positive association between intra-annual variation in rainfall and within-plant variation in seed mass and seed number was found. [Conclusion]: Both rainfall during specific reproductive phases and soil conditions shape the variation in the seed mass and number of C. langsdorffii. Environment-driven seed trait variation may contribute to this species' broad niche breadth, which in turn may determine the species' persistence under future climatic conditions.This study was conducted with financial support from the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and with a scholarship from the International Doctoral Sandwich Program (PDSE), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Variations in leaf flushing time, leaf phenol content, branch growth and abundance of 24 species of gall-inducing insects associated with 102 Copaifera langsdorffii plants

Climatic factors shaping intraspecific leaf trait variation of a neotropical tree along a rainfall gradient.

Intraspecific trait variation has been singled out as an important mechanism by which individuals can cope with environmental variations and avoid local extinctions. Here we evaluate variation in metamer traits (i.e., traits associated with internodes, petioles and their corresponding leaves) and parameters of chlorophyll fluorescence within and among populations of a neotropical tree, Copaifera langsdorffii. We also evaluated phenotypic plasticity in natural settings comparing traits between shade and sun-exposed metamers. We selected six populations along a climatic gradient ranging from semi-arid to humid and representing three different biomes (Caatinga, Cerrado, and Atlantic Forest). Local climatic conditions significantly affected the morphological and physiological traits of populations. Trait variation among populations was explained mainly by aridity index and evapotranspiration. Individuals from drier regions had lower specific leaf area (SLA), lower investment in leaf area per total dry mass of metamer (LARm), lower specific petiole length (SPL) and lower potential quantum yield (Fv/Fm, only for sun-exposed metamers). Populations from locations with greater environmental heterogeneity (interannual variation) had greater plasticity in response to light for Fv/Fm and electron transport rate (ETR) and morphological traits related to the hydraulic and biomechanical aspects of the leaves (petiole length, internode length and SPL). High intraspecific variation in metamer traits in C. langsdorffii coupled with its ability to modify these traits in response to different climate conditions can explain the success of the species over a range of different habitats and represent important factors for the persistence of this species in the face of climate change

Data from: Plant phenological asynchrony and community structure of gall-inducing insects associated with a tropical tree species

The dynamics of occurrence of target-organs in plant populations produces windows of opportunity that directly and indirectly affect the structure of herbivore communities. However, mechanisms that drive herbivore specialization between resource patches are still poorly known. In the present study, we tested three hypotheses related to variation in host plant phenology and community structure (i.e. composition, richness and abundance) of gall-forming species: (i) plants with early leaf-flushing in the season will have greater vegetative growth and high contents of secondary chemical compounds; (ii) gall-inducing insect community structure changes among temporary resource patches of the host and (iii) interspecific competition is a probable mechanism that drives gall-inducing insect community structure on Copaifera langsdorffii. We monitored daily a total of 102 individuals of the super-host C. langsdorffii from August 2012 to May 2013, to characterize the leaf flushing time of each host plant. The leaf flushing time had a positive relationship with the number of folioles per branch and a negative relationship with branch growth. We sampled a total of 4,906 galls belonging to 24 gall-inducing insect species from 102 individuals of C. langsdorffii. In spite of some gall-inducing species presented high abundance on early leaf-flushing plants, direct and indirect effects of plant phenology on galling insect abundance was species-dependent. At the community level, our study revealed that the quality and quantity of plant resources did not affect the richness and abundance of gall-inducing insects associated with C. langsdorffii. However, the richness and composition of gall-inducing species varied according to the variation in leaf flushing time of the host plant. The results of null model analysis showed that galls co-occurrence on C. langsdorffii trees differ more than expected by chance and that interspecific competition can be one potential mechanism structuring this gall-inducing insect community

Climatic factors shaping intraspecific leaf trait variation of a neotropical tree along a rainfall gradient

Intraspecific trait variation has been singled out as an important mechanism by which individuals can cope with environmental variations and avoid local extinctions. Here we evaluate variation in metamer traits (i.e., traits associated with internodes, petioles and their corresponding leaves) and parameters of chlorophyll fluorescence within and among populations of a neotropical tree, Copaifera langsdorffii. We also evaluated phenotypic plasticity in natural settings comparing traits between shade and sun-exposed metamers. We selected six populations along a climatic gradient ranging from semi-arid to humid and representing three different biomes (Caatinga, Cerrado, and Atlantic Forest). Local climatic conditions significantly affected the morphological and physiological traits of populations. Trait variation among populations was explained mainly by aridity index and evapotranspiration. Individuals from drier regions had lower specific leaf area (SLA), lower investment in leaf area per total dry mass of metamer (LARm), lower specific petiole length (SPL) and lower potential quantum yield (Fv/Fm, only for sun-exposed metamers). Populations from locations with greater environmental heterogeneity (interannual variation) had greater plasticity in response to light for Fv/Fm and electron transport rate (ETR) and morphological traits related to the hydraulic and biomechanical aspects of the leaves (petiole length, internode length and SPL). High intraspecific variation in metamer traits in C. langsdorffii coupled with its ability to modify these traits in response to different climate conditions can explain the success of the species over a range of different habitats and represent important factors for the persistence of this species in the face of climate change.This study was carried out with financial support from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, 303154/2013-6, Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG, APQ 01727-17) and Pró-Reitoria de Pesquisa, Universidade Federal de Minas Gerais (001).Peer Reviewe