Cecília Lomônaco

Variações fenotípicas e potencial plástico de Eugenia calycina Cambess. (Myrtaceae) em uma área de transição cerrado-vereda

The aims of this work were to verify the incidence of phenotypic variation and the plastic potential of Eugenia calycina in a transitional savanna/palm swamp area. Subpopulations were characterized by seed weight, number of seeds per fruit and number of flowers per plant. Moreover, density of occurrence and the rate of parasitism on fruits by larvae of flies (Diptera: Tephritidae) in each area were significantly different. Asynchronism of the flowering period, being late for the savanna area, was also observed. A genetic quantitative model was used to measure phenotypic plasticity based on a reciprocal transplantation experiment of sibling-seeds into soils collected from each area. Three aspects of plastic potential were evaluated: height of steam and number and length of the seedlings leaves. Observed differences in these characters were attributed not only to genetic divergences but also to phenotypic plasticity. The individuals showed different plastic responses, diverging in their ability to respond to environmental influences. The data confirm the role of phenotypic plasticity in the adaptive and evolutionary process involved with ecotype formation in savanna/palm swamp transitional vegetation.

Variações fenotípicas em Musca domestica L. (Diptera: Muscidae) em resposta à competição larval por alimento

Phenotypic variations on developmental period, size and fluctuating asymmetry (FA) of Musca domestica L., induced by larval competition for food were described and correlated. Ten densities, varying from 100 to 1000 larvae per 75 g of wheat medium, were established in the laboratory and observed until adult emergence. The adjusted curve of survival was similar to a hyperbola. The developmental period extended with increasing densities, and the size was inversely proportional to the degree of larval crowding. Males and females responded differently to the selection pressures of competition, being size of the males much more variable than those of the females. Although morphological and physiological adjustments caused by environmental interaction were detected, the levels of fluctuating asymmetry remained invariable. Genetic correlation between these types of phenotypic variation was not detected. It can be supposed, however, that levels of FA, which are stress indicative, were minimized by the considerably plastic potential of the species. Thus, physiological and morphological adjustments reduced developmental difficulties and promoted survival of a greater number of individuals.

Phenotypic plasticity of Myzus persicae (Hemíptera: Aphididae) raised on Brassica oleracea L. var. acephala (kale) and Raphanus sativus L. (radish)

The study of variability generated by phenotypic plasticity is crucial for predicting evolutionary patterns in insect-plant systems. Given sufficient variation for plasticity, host race formation can be favored and maintained, even simpatrically. The plasticity of size and performance (assessed by the lifetime fitness index rm) of six clones of Myzus persicae was tested, with replicates allowed to develop on two hosts, kale (Brassica oleracea var. acephala) and radish (Raphanus sativus). The clones showed significant variability in their plasticity. Reaction norms varied through generations and negative genetic correlation, although not significant, tend to increase with the duration of host use. The lack of plasticity in lifetime fitness among generalist clones occurred as an after-effect of the highly plastic determinants. Significant morphological plasticity in host used was observed, but no variation in the plastic responses (GxE interaction) was detected. Strong selection for a larger size occurred among individuals reared on radish, the most unfavorable host. Morphological plasticity in general body size (in a multivariate sense) was not linear related to fitness plasticity. These observations suggest that a high potential for the evolution of host divergence favors host race formation.

Developmental stress by diflubenzuron in Haematobia irritans (L.) (Diptera: Muscidae)

This study aimed to assess the effect of sub-lethal concentrations of the insect growth regulator (IGR), diflubenzuron, on the body size of the horn fly Haematobia irritans (L.) and on its developmental stability, by fluctuating asymmetry (FA) analysis. Breeding media with different sub-lethal diflubenzuron concentrations and a control medium, were prepared to obtain morphometric measures on adult individuals. Principal component analysis was used to generate an index of general body size, using the correlation matrix of the original characters. Levels of FA and the multivariate index of size were compared among treatments. Contrary to the expectations, the exposure to diflubenzuron did not result in a significant and concomitant increase in the level of FA across treatments or in the number of individuals showing developmental instability. Nevertheless, a significant reduction of size due to the diflubenzuron may reflect the ability of H. irritans to perform physiological and morphological adjustments allowing phenotype compensation, at least to some extent, for stressful environmental conditions. On the other hand, the IGR may be selecting more symmetrical and resistant individuals. From the pest control point of view, the reduction of size may be a positive effect of the IGR since size is usually directly related to fitness.

Plasticidade morfológica, reprodutiva e assimetria flutuante de Myzus persicae (Sulzer) (Hemiptera: Aphididae) sob diferentes temperaturas

Four clones of the aphid Myzus persicae (Sulzer) were used to assess the magnitude of their responses to seven different temperatures (15.0, 17.5, 20.0, 22.5, 25.0, 27.5 and 30.0oC). A multivariate index of size was obtained using five morphological characteristics simplified by PCA. Among these characteristics, four were measured bilaterally both sides in order to evaluate the fluctuating asymmetry (FA). Fertility was estimated according to the number of nymphs in the reproductive female apparatus. The variability attributed to the environmental and genetic components was estimated using a genetic quantitative model. A large part of the total variability found for size distribution was attributed to differences in temperature (environmental component), but genetic components of variation were also detected. The plastic potential was considered adaptive, since it increases clone survival in unstable environments and allows new habitat exploitation. However, 30oC temperature did not permit clone development and survival. Lower variability in one morphological character, the rostrum, in comparison with the other traits may be the result of a stabilizing selection, in relation to its adaptive value to obtain food. The aphids presented FA in some of the measured characteristics. However, no linear relation was detected for the levels of FA and temperature values and no general pattern of variability was found. The data corroborate the hypothesis that size is more effectively affected than FA by external influences, and consequently, is a much more efficient indicator of environmental stress.

Effects of sublethal concentrations of diflubenzuron and methoprene on Aedes aegypti (Diptera: Culicidae) fitness.

The effects of sublethal concentrations of the insect growth regulators (IGRs) diflubenzuron and methoprene on some fitness components of an Aedes aegypti (L.) population in south-eastern Brazil were investigated. The fourth instar larvae of the mosquito were exposed to 20ppb methoprene and 3ppb diflubenzuron, and adult survivors were evaluated for fitness parameters, including body size and biomass, fecundity, fertility, longevity and symmetry. The sublethal concentrations had negative effects on longevity, but biomass, fecundity and fertility were not affected by either IGR. In separate experiments, A. aegypti individuals’ surviving concentrations of 2, 3 and 3.5 ppb diflubenzuron and 5, 10 and 20ppb methoprene were used for morphological analyses (size and symmetry). Diflubenzuron had negative effects on the mosquito’s body symmetry. The observed decreases in longevity and symmetry may have negative impacts on the population dynamics of A. aegypti.

Potencial plástico de Cabralea canjerana subsp. polytricha (Adr. Juss.) Penn. (Meliaceae) e seu papel na formação de ecótipos em áreas de cerrado e vereda, Uberlândia, MG

The ecotype formation of Cabralea canjerana subsp. polytricha in areas of savanna and palm swamp in an ecological reserve in Uberlândia, MG, was studied, using a quantitative genetic model to measure phenotypic plasticity. Ecotypes were characterised by the height of the individuals, weight of fruits and seeds, number of viable seeds per fruit and synchronization of the flowering period. There is great genetic variability in important fitness characters of the subspecies. The genotypes respond phenotypically to the environmental heterogeneity produced by the savanna/palm swamp gradient in two of the three measured characters. The plastic responses were distinct among genotypes in both direction and intensity. Asynchrony of the flowering period and the action of seed dispersers may contribute to increase the divergences of the ecotypes in the study area.

Plasticidade fisiológica e comportamental de Brevicoryne brassicae (L.) (Hemiptera: Aphididae) em duas variedades de Brassica oleraceae L.

Interactions between phytophagous insects and their host plants can produce physiological, morphological and behavioural changes on the population of the parasites. Such changes due to phenotypic plasticity may be relevant in both the specialisation process and host races or ecotypes formation. In this work the occurrence of phenotypic plasticity (physiological and behavioural) on distinct aphids clones of Brevicoryne brassicae (L.) was investigated utilising two different hosts: cabbage (Brassica oleraceae var. acephala) and broccoli (B. oleraceae var. italica). Nimphs, with approximately the same age, were placed individually on the underneath leaf surface on each tested host. Their developmental time and fecundity were observed daily in order to calculate a fitness index (rm) or performance. Experiments to determine preference (behavioural plasticity) were done inside the laboratory, basing on the choice of eighty aphids (20 per clone) for a particular host. Measurements of variability on plastic responses among clones were done following a quantitative genetic model. Clones demonstrated low physiological plasticity (F=3.412; P=0.067) probably due to the great genetic similarity between the two variety of plants used as hosts. Small variability was verified for this kind of plasticity among the performance of the analysed clones (F=1.281; P=0.283). Nevertheless, the clones presented significant preference for a particular host (c2=4.66; P<0.05), which demonstrates the conditioning behaviour (individuals choosing the hosts were they fed during their development). Aparently the selection pressure was not hard enough to promote biotype or race formation in B. brassicae adapted to the host varieties tested.

HABITAT PARTITION, AND VARIATIONS OF SIZE AND SYMMETRY OF THREE SYMPATRIC SPECIES OF ALPHEUS (DECAPODA: CARIDEA) ALONG AN INTERTIDAL GRADIENT IN THE SOUTHWESTERN ATLANTIC

Abstract Species assemblages of Alpheus of similar morphology occur along the tropical and subtropical margins of all world oceans. We studied sympatric populations of Alpheus belonging to three color morphs recognized along an intertidal gradient at Cabo Branco beach, State of Paraíba, Brazil. Morphological measurements of populations sampled monthly during a year were used to obtain indexes of size and fluctuating asymmetry. Standard statistical analyses were used in order to verify if the stress gradient established along the intertidal region affects spatial distribution, size and body symmetry in these three sympatric populations. Alpheus armillatus sensu stricto, the most frequent species, was predominant in the upper meso-littoral zone, being significantly smaller in the lower zone. A. cf. angulosus was predominant in the middle zone, while A. cf. heterochaelis was restricted to the upper zone. Individuals of A. cf. angulosus were significantly smaller than those of the other two morphs. Males were larger than females in all morphotypes, while cheliped dimensions show allometric growth. Couples invariably belong to a same morph. We obtained indications that competition between morphs are favoring the establishment of larger individuals in the most disputed zones of the middle and upper meso-littoral, although we were not able to confirm whether wave action was the main environmental factor responsible for these gradients in body size and symmetry along the intertidal region. Our data provide further ecological and biological evidence for the three color morphs representing distinct species, whose sympatric populations may be further recognized by additional morphological criteria. However, we are unsure about the constancy of these auxiliary distinguishing characters for allopatric populations from throughout their full western Atlantic ranges.

Respostas fisiológicas, morfológicas e comportamentais de Zabrotes subfasciatus (Boheman) (Coleoptera: Bruchidae) associadas ao consumo de diferentes variedades de feijão (Phaseolus vulgaris)

This study was developed aiming to verify physiological, morphological and behavioral responses of two different Zabrotes subfasciatus (Boheman) populations to different beans varieties (Phaseolus vulgaris) (Fabaceae). Female longevity, fertility and oviposition preference site, as well as size and levels of fluctuating asymmetry for males and females were described. Zabrotes subfasciatus displayed physiological plasticity in response to the diet, which was considered an important adaptive ability to maintain the insect generalist habit for food consumption and oviposition sites. The populations studied had different responses to the same treatments, indicating genetic, physiological and behavioral variation on their plastic potential. The Hopkins principle, which determines the influence of previous female experience in the choice of oviposition sites, was not confirmed. The occurrence of fluctuating asymmetry in males and females was variable, probably as a consequence of genomic factors determining this trait.