Alexandre A. Peixoto

Morphological variation in a natural population of Drosophila mediopunctata: altitudinal cline, temporal changes and influence of chromosome inversions

To characterize the morphological variation in a natural population of Drosophila mediopunctata, males were collected on three occasions at a single locality. From each wild-caught male 14 body measures were taken and the karyotype for inversions on chromosomes X and II was determined. Through a principal components analysis, two sources of variation, identified as size and shape, accounted for approximately 80 and 6 per cent of the total morphological variability, respectively. The shape component was determined primarily by variations in the position of the wing second longitudinal vein. Differences between collections were detected both for size and shape. An altitudinal cline was observed in respect of wing shape, although altitude explained only a small part of the shape variation. Size and shape were affected by chromosome II inversions. However, in respect of size, no direct differences were detected between karyotypes but a significant interaction between collecting date and karyotype was found. This suggests that karyotypes might differ in their norms of reaction in the field.

Sex-ratio in Drosophila mediopunctata

The occurrence of sex-ratio in Drosophila mediopunctata is described. The sex-ratio trait, affected males producing progenies with a large excess of females, is known also in eight other Drosophila species. It has X-linked inheritance, being apparently always associated with particular X chromosome inversions. The expression of the sex-ratio trait in D. mediopunctata is very variable.

Chromosomal inversion polymorphism in Drosophila mediopunctata: seasonal, altitudinal, and latitudinal variation

The most polymorphic chromosome for inversions in Drosophila mediopunctata is the chromosome II, where 17 inversions have been found, eight of which occurring in the distal region and nine in the proximal region. We present an analysis of the chromosome II inversion polymorphism with respect to seasonal, altitudinal and latitudinal variation. In D. mediopunctata from the Parque Nacional do Itatiaia (southeastern Brazil), the frequencies of three of the distal inversions (namely DA, DS, and DP) vary seasonally. These inversions also show altitudinal clines in their frequencies. This microgeographic pattern was not observed on a macrogeographic scale. D. mediopunctata from Porto Alegre are less polymorphic for inversions than other populations, the most remarkable reduction occurring in the proximal region of chromosome II. There is a considerable difference between D. mediopunctata from Campinas and specimens from Serra do Japi, which are separated by only 50 km. In contrast, D. mediopunctata from Serra do Japi are much more similar to specimens from the Parque Nacional do Itatiaia, which is 200 km far.

Fine Structure of the Male Reproductive System and Reproductive Behavior of Lutzomyia longipalpis Sandflies (Diptera: Psychodidae: Phlebotominae)

Background The male reproductive system of insects can have several tissues responsible for the secretion of seminal fluid proteins (SFPs), such as testes, accessory glands, seminal vesicles, ejaculatory duct and ejaculatory bulb. The SFPs are transferred during mating and can induce several physiological and behavioral changes in females, such as increase in oviposition and decrease in sexual receptivity after copulation. The phlebotomine Lutzomyia longipalpis is the main vector of visceral leishmaniasis. Despite its medical importance, little is known about its reproductive biology. Here we present morphological aspects of the male L. longipalpis reproductive system by light, scanning and transmission electron microscopy, and compare the mating frequency of both virgin and previously mated females. Results The male L. longipalpis reproductive system is comprised by a pair of oval-shaped testes linked to a seminal vesicle by vasa deferentia. It follows an ejaculatory duct with an ejaculatory pump (a large bulb enveloped by muscles and associated to tracheas). The terminal endings of the vasa deferentia are inserted into the seminal vesicle by invaginations of the seminal vesicle wall, which is composed by a single layer of gland cells, with well-developed endoplasmic reticulum profiles and secretion granules. Our data suggest that the seminal vesicle acts both as a spermatozoa reservoir and as an accessory gland. Mating experiments support this hypothesis, revealing a decrease in mating frequency after copulation that indicates the effect of putative SFPs. Conclusion Ultrastructural features of the L. longipalpis male seminal vesicle indicated its possible role as an accessory gland. Behavioral observations revealed a reduction in mating frequency of copulated females. Together with transcriptome analyses from male sandfly reproductive organs identifying ESTs encoding orthologs of SFPs, these data indicate the presence of putative L. longipalpis SFPs reducing sexual mating frequency of copulated females.

Effects of Light and Temperature on Daily Activity and Clock Gene Expression in Two Mosquito Disease Vectors

Most organisms feature an endogenous circadian clock capable of synchronization with their environment. The most well-known synchronizing agents are light and temperature. The circadian clock of mosquitoes, vectors of many pathogens, drives important behaviors related to vectoral capacity, including oviposition, host seeking, and hematophagy. Main clock gene expression, as well as locomotor activity patterns, has been identified in Aedes aegypti and Culex quinquefasciatus under artificial light-dark cycles. Given that these mosquito species thrive in tropical areas, it is reasonable to speculate that temperature plays an important role in the circadian clock. Here, we provide data supporting a different hierarchy of light and temperature as zeitgebers of two mosquito species. We recorded their locomotor activity and quantified mRNA expression of the main clock genes in several combinations of light and temperature cycles. We observed that A. aegypti is more sensitive to temperature, while C. quinquefasciatus is more responsive to light. These variations in clock gene expression and locomotor activity may have affected the mosquito species’ metabolism, energy expenditure, fitness cost, and pathogen transmission efficiency. Our findings are relevant to chronobiology studies and also have epidemiological implications.

Cryptic diversity in an Atlantic Forest malaria vector from the mountains of South-East Brazil

BackgroundAnopheles (Kerteszia) cruzii is the primary vector of human and simian malarias in Brazilian regions covered by the Atlantic Rainforest. Previous studies found that An. cruzii presents high levels of behavioural, chromosomal and molecular polymorphisms, which led to the hypothesis that it may be a complex of cryptic species. Here, An. cruzii specimens were collected in five sites in South-East Brazil located at different altitudes on the inner and coastal slopes of two mountain ranges covered by Atlantic Rainforest, known as Serra do Mar and Serra da Mantiqueria. Partial sequences for two genes (Clock and cpr) were generated and compared with previously published sequences from Florianópolis (southern Brazil). Genetic diversity was analysed with estimates of population structure (FST) and haplotype phylogenetic trees in order to understand how many species of the complex may occur in this biome and how populations across the species distribution are related.ResultsThe sequences from specimens collected at sites located on the lower coastal slopes of Serra do Mar (Guapimirim, Tinguá and Sana) clustered together in the phylogenetic analysis, while the major haplotypes from sites located on higher altitude and at the continental side of the same mountains (Bocaina) clustered with those from Serra da Mantiqueira (Itatiaia), an inner mountain range. These two An. cruzii lineages showed statistically significant genetic differentiation and fixed characters, and have high FST values typical of between species comparisons. Finally, in Bocaina, where the two lineages occur in sympatry, we found deviations from Hardy-Weinberg equilibrium due to a deficit of heterozygotes, indicating partial reproductive isolation. These results strongly suggest that at least two distinct lineages of An. cruzii (provisorily named “Group 1” and “Group 2”) occur in the mountains of South-East Brazil.ConclusionsAt least two genetically distinct An. cruzii lineages occur in the Atlantic Forest covered mountains of South-East Brazil. The co-occurrence of distinct lineages of An. cruzii (possibly incipient species) in those mountains is an interesting biological phenomenon and may have important implications for malaria prevalence, Plasmodium transmission dynamics and control.

Speciation in Brazilian Atlantic Forest Mosquitoes: A Mini-Review of the Anopheles cruzii Species Complex

Anopheles (Kerteszia) cruzii s.l. (Diptera: Culicidae) has long been known as the primary vector of human and simian malaria parasites in southern and southeastern Brazil (Deane et al., 1970; 1971; Rachou, 1958). Between 1930 and 1960, An. cruzii together with Anopheles (Kerteszia) bellator and Anopheles (Kerteszia) homunculus were considered the main vectors of malaria once endemic in southern Brazil. Vector control has reduced or even interrupted malaria transmission in some areas, but An. cruzii is still responsible for several oligosymptomatic malaria cases in southern and southeastern Brazil. This mosquito is also a vector of simian malaria in Rio de Janeiro and Sao Paulo States (Deane et al., 1970). Studies on seasonal and vertical distribution of An. cruzii demonstrated high vertical mobility from ground level to tree tops and this behavior could be responsible for human infection by simian Plasmodium species (Deane et al., 1984; Marrelli et al., 2007; Ueno et al., 2007).