Intraspecific variation ofDrosophila buzzatii larval breeding success onOpuntia: A yeast-plant-insect relationship

The cactophilic species,Drosophila buzzatii, normally breeds in decaying pockets ofOpuntia cladodes, in which there is a complex interaction with the microbial flora, especially yeast species. Isofemale lines were used to estimate genetic variation among larvae reared on their natural feeding substrate. Four naturally occurring cactophilic yeast species isolated from the same Tunisian oasis as theDrosophila population were used. Two fitness components were studied for each line, viability and developmental time. Genetic variations amongD. buzzatii lines were observed for both traits. A significant yeast species x isofemale line interaction for viability was also evidenced, suggesting the occurrence of specialized genotypes for the utilization of breeding substrates. This genetic heterogeneity in the natural population may favor a better adaptation to the patchily distribution of yeasts.     

Developmental Time and Thorax Length Differences Between the Cactophilic Species Drosophila Buzzatii and D. Koepferae Reared in Different Natural Hosts

Drosophila buzzatii and Drosophila koepferae are two cactophilic sibling species whose ranges partially overlap in Northwestern and Western Argentina. Both species can utilize the decaying tissues of both Opuntia and columnar cacti as breeding sites. Though D. buzzatii and D. koepferae are not differentially attracted to Opuntia and columnar hosts, the composition of the communities of flies emerging from natural substrates of both cacti differed significantly in a natural population. The objective of this paper is to analyze whether intra and/or interspecific competition affects development time and thorax length in D. buzzatii and D. koepferae when both species are reared in single and mixed species culture and fed with semi-natural media prepared with fermenting materials of Opuntia sulphurea(tuna) and Trichocereus terschekii(cardón). Our results showed that both traits differ significantly between flies raised in different hosts and that differences between D. koepferae and D. buzzatii species for both thorax length and development time depend on the type of culture (mixed vs. single species). In addition, the host by type of culture interaction was significant. We also observed thorax length differences between Drosophila species and type of culture. Our present data suggest that the effect of intra and interspecific competition varied between the two traits investigated and between species. However, competition alone cannot explain the differential pattern of resource utilization shown by D. buzzatii and D. koepferae in the natural population studied.     

Molecular Population Genetics of the α<Emphasis Type="Italic">-Esterase5</Emphasis> Gene Locus in Original and Colonized Populations of <Emphasis Type="Italic">Drosophila buzzatii</Emphasis> and Its Sibling <Emphasis Type="Italic">Drosophila koepferae</Emphasis>

Several studies have suggested that esterase-2 (EST-2) may be the target of natural selection in the cactophilic fly Drosophila buzzatii. In this work, we analyzed nucleotide variation in a fragment of α-esterase5 (αE5), the gene encoding EST-2, in original (Argentinian) and colonized (Australian) populations of D. buzzatii and in its sibling D. koepferae. Estimates of nucleotide heterozygosity in D. buzzatii were similar in Australia and Argentina, although we detected a loss of singletons in colonized populations, suggesting a moderate founder effect. Interspecific comparisons revealed that D. buzzatii was more polymorphic for nonsynonymous variation, whereas D. koepferae was more variable for synonymous and noncoding sites. The two major chromosomal arrangements (2st and 2j) in D. buzzatii displayed similar levels of nucleotide variation, whereas 2jz ³ was monomorphic. The sequenced region allowed the discrimination of a greater number of EST-2 protein variants in the Australian sample than in the Argentinean sample. In D. koepferae, nucleotide variation in αE5 does not depart from neutral expectations, although tests of population structure were significant for silent variation. In contrast, D. buzzatii has probably undergone a recent population expansion in its South American range. In addition, the McDonald and Kreitman test revealed an excess of nonsynonymous polymorphism in both original and colonized populations of this species. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Richard Kliman]     

Microsatellite allele sequencing in population analyses of the South American cactophilic species Drosophila antonietae (Diptera: Drosophilidae)

Drosophila antonietae belongs to the Drosophila buzzatii cluster, a cactophilic group of species naturally endemic to South America. Morphological and genetic analyses indicate that its populations are the most homogenous in the cluster and that the diversity observed is mainly a result of variation within populations. Seven polymorphic microsatellite loci were described for this species and used in the present study to investigate the genetic diversity of natural populations of D. antonietae by both length and sequence variation. The study aimed to understand how homoplasy and null alleles affect inferences about the population history of this species and to obtain an accurate interpretation of population inferences where these loci could be applied. The results provide useful information on the interpretation of genetic data derived from the microsatellite loci described for D. antonietae and on evolutionary aspects of cactophilic Drosophila. Importantly, the results indicate that size homoplasy and null alleles do not represent significant problems for the population genetics analyses because the large amount of variability at microsatellite loci compensate the low frequency of these problems in the populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 573–584.     

Coexistence of ecologically similar colonising species. II. Population differentiation in Drosophila aldrichi and D. Buzzatii for competitive effects and responses at different temperatures and allozyme variation in D. aldrichi

Drosophila aldrichi and D. buzzatii are cactophilic species that colonised Australia about 55–60 years ago. They are sympatric only in Australia. Thus they may be in the process of adapting to new environments and to each other, and diversifying among local, possibly isolated, populations. Larval competitive effects for three populations of each species (Roma, Planet Downs, and Binjour) were measured on semi-natural cactus rots at three temperatures, with preadult viability, developmental time and adult body weight scored for each sex and species. Populations of both species varied in their responses to the other species as competitor, and one D. buzzatii population (Roma) reduced larval performance of D. aldrichi significantly more than did other D. buzzatii populations. Geographic divergence for the three traits was similar in both species, with a relative performance index derived from these traits highest for Roma, second for Binjour, and least for the Planet Downs population of each species. The Roma D. aldrichi population was the most different from the other populations for the performance index and in terms of genetic distances derived from allozyme frequencies. Additionally, comparisons of climatic variables among the population localities showed that the Roma environment was most different from the others. Differential natural selection in different areas of the cactus distribution may be a major cause of population divergence in both species. Drosophila aldrichi is superior for some fitness components at the highest temperature. Thus temperature variation throughout the cactus distribution may contribute to the different ranges of these two species, with competitive exclusion of D. aldrichi in the southern, cooler region of the cactus distribution, but coexistence in the northern, warmer region.     

Rapid Divergent Evolution of Male Genitalia Among Populations of Drosophila buzzatii

Increasing evidence from multiple animal systems suggests that genital evolution and diversification are driven by rapid and strong evolutionary forces. Particularly, the morphology of male genital structures is considered to be among the fastest evolving traits in animal groups with internal fertilization. In this study, we investigated patterns of male genital variation within and between natural populations of the cactophilic fly Drosophila buzzatii in its original geographic distribution range in the Neotropics. We detected significant morphological differences among populations and distinguished five differentiated groups. Moreover, among population differentiation in genital morphology was associated with the degree of geographic isolation among populations and clearly contrasted with the general homogeneity detected for the putatively neutral mitochondrial gene COI. Integrating our present data with previous molecular population genetic surveys, our results suggest that male genital morphology has rapidly diverged after the recent demographic expansion that D. buzzatii has undergone in the arid zones of South America. Because the “lock and key” hypothesis failed to explain the present pattern, we explored alternative explanations for the observed pattern of genital diversification including drift-facilitated sexual selection.     

The evolutionary history of Drosophila buzzatti. XXVI. Macrogeographic patterns of inversion polymorphism in New World populations

Inversion polymorphisms in the second and fourth chromosomes of the cactophilic Drosophila buzzatti in the native distribution range of the species are described. Over 5,000 flies from 26 localities were scored revealing interesting geographic structuring of arrangement frequencies. Multiple regression and partial correlation approaches showed that the frequencies of second and fourth chromosome arrangements vary clinically along latitudinal and altitudinal gradients and to a lesser extent with longitude. Although many non selective explanations can account for this pattern, its resemblance to the clinal pattern described in recently established Australian populations of Drosophila buzzatii, strongly suggests a selective explanation. Additionally, the correlated variation observed between the frequencies of arrangements 2St on the second chromosome and 4St on the fourth suggests a pattern of interchromosomal association, which, when considering the vast area surveyed, might be explained as the result of epistatic interactions. The analysis of population structure revealed a significant regional pattern, concordant with previously described phytogeographic regions. F-statistics showed that the patterns of variation were different not only between the second and fourth chromosomes, but also between second chromosome arrangements, suggesting that selective differentiation might have contributed to population structure. Since D. buzzatii breeds and feeds on the decaying tissues of diverse cactus species present in different phytogeographic regions, it is difficult to distinguish the underlying causes of the geographic patterns observed. However, inversion heterozygosity is not correlated with the diversity of potential cactus hosts. The evidence presented suggests that differential selection may be the main cause for the population structure. It is also possible to conclude that the inversion polymorphism of D. buzzatti is flexible rather than rigid.     

Yeast communities as descriptors of habitat use by the Drosophila fasciola subgroup (repleta group) in Atlantic rain forests

Yeast communities associated with four species of the Drosophila fasciola subgroup (repleta group) in tropical rain forests were surveyed in an abandoned orchard, and rain forest sites of Rio de Janeiro and Ilha Grande, State of Rio de Janeiro, Brazil. Adult flies of Drosophila carolinae, Drosophila coroica, Drosophila fascioloides and Drosophila onca frequently carried Candida colliculosa, Geotrichum sp, Kloeckera apiculata and a Pichia membranaefaciens-like species. The most frequent yeasts in the crop of flies included Candida collicullosa, C. krusei, Pichia kluyveri and a P. membranaefaciens-like species. The physiological abilities and species composition of these yeast communities differed from those of other forest-inhabiting Drosophila. The narrow feeding niches of the fasciola subgroup suggested the use of only part of the substrates available to the flies as food in the forest environment, as noted previously for cactophilic Drosophila serido (mulleri subgroup of the repleta group) in a sand dune ecosystem. The cactophilic yeasts that were isolated have not been previously found in forests. The fasciola subgroup probably used epiphytic cactus substrates as breeding and feeding sites in the forest. The physiological profile of yeasts associated with the fasciola flies was broader than that of yeasts associated with the cactophilic Drosophila serido, suggesting that the fasciola subgroup represents an older lineage from which the South American repleta species evolved.     

Evolution of male genitalia: environmental and genetic factors affect genital morphology in two <Emphasis Type="Italic">Drosophila</Emphasis> sibling species and their hybrids

Background  

The rapid evolution of genital morphology is a fascinating feature that accompanies many speciation events. However, the underlying patterns and explanatory processes remain to be settled. In this work we investigate the patterns of intraspecific variation and interspecific divergence in male genitalic morphology (size and shape) in the cactophilic sibling species Drosophila buzzatii and D. koepferae. Genital morphology in interspecific hybrids was examined and compared to the corresponding parental lines.     

Phenotypic plasticity in Drosophila cactophilic species: the effect of competition,density, and breeding sites

Changes in the environmental conditions experienced by naturally occurring populations are frequently accompanied by changes in adaptive traits allowing the organism to cope with environmental unpredictability. Phenotypic plasticity is a major aspect of adaptation and it has been involved in population dynamics of interacting species. In this study, phenotypic plasticity (i.e., environmental sensitivity) of morphological adaptive traits were analyzed in the cactophilic species Drosophila buzzatii and Drosophila koepferae (Diptera: Drosophilidae) considering the effect of crowding conditions (low and high density), type of competition (intraspecific and interspecific competition) and cacti hosts (Opuntia and Columnar cacti). All traits (wing length, wing width, thorax length, wing loading and wing aspect) showed significant variation for each environmental factor considered in both Drosophila species. The phenotypic plasticity pattern observed for each trait was different within and between these cactophilic Drosophila species depending on the environmental factor analyzed suggesting that body size‐related traits respond almost independently to environmental heterogeneity. The effects of ecological factors analyzed in this study are discussed in order to elucidate the causal factors investigated (type of competition, crowding conditions and alternative host) affecting the election of the breeding site and/or the range of distribution of these cactophilic species.     

Differential Rates of Male Genital Evolution in Sibling Species of <Emphasis Type="Italic">Drosophila</Emphasis>

Genital morphology in animals with internal fertilization is considered to be among the fastest evolving traits. Sexual selection is often proposed as the main driver of genital diversification but the exact selection mechanisms involved are usually unclear. In addition, the mechanisms operating may differ even between pairs of sibling species. We investigated patterns of male genital variation within and between natural populations of the cactophilic fly Drosophila koepferae ranging its entire geographic distribution and compared them with those previously observed in its sibling species, D. buzzatii. Using both mtDNA and nDNA markers we found that genital shape variation in D. koepferae is more restricted than expected for neutral evolution, suggesting the predominance of stabilizing selection. We also detected dissimilar patterns of divergence between populations of D. koepferae that were allopatric and sympatric with D. buzzatii. The constrained evolution inferred for D. koepferae’s genitalia clearly contrasts with the rapid divergence and higher morphological disparity observed in the populations of D. buzzatii. Finally, different possible scenarios of male genital evolution in each species and within the radiation of D. buzzatii cluster are discussed.     

Conservation of pBuM–2 satellite DNA sequences among geographically isolated Drosophila gouveai populations from Brazil

In this study, we have compared 34 repetition units of pBuM-2 satellite DNA of individuals from six isolated populations of Drosophila gouveai, a cactophilic member of Drosophila buzzatii cluster (repleta group). In contrast to the results of previous morphological and molecular data, which suggest differentiation among the D. gouveai populations, the sequences and the cluster analysis of pBuM-2 monomers showed that this repetitive element is highly conserved among the six D. gouveai populations (97.8% similarity), indicating a slow rate of evolution of pBuM-2 sequences at the population level. Probably, some homogenization mechanisms of tandem sequences, such as unequal crossing or gene conversion, have maintained the sequence similarity of pBuM-2 among D. gouveai populations. Alternatively, such a result may be associated with a functional role of pBuM-2 sequences, although it is not understood at present.     

Geographical distributions,relative abundance and coexistence of Drosophila aldrichi and Drosophila buzzatii in Australia

Abstract Climatic data and collection records for the cactophilic Drosophila aldrichi and Drosophila buzzatii for 97 localities were used to examine the effects of geographical location, season, host plant species and climatic factors on their range and relative abundance. Temporal variation in relative abundance was assessed from monthly collections over 4 years at one locality. Effects of weather variables over the 28 days before each collection were examined. A generalized linear model of the spatial data showed significant geographical variation in relative abundance, and significant climatic effects, with the proportion of D. aldrichi higher in the warm season, and increasing as temperature variation decreased and moisture indices increased. The temporal data gave generally concordant results, as D. aldrichi proportion was higher in summer and autumn, and increased as maximum and minimum temperatures increased, and as variation in maximum temperature decreased. In a laboratory competition experiment, D. aldrichi eliminated D. buzzatii at 31°C, but was itself eliminated at 18°C and 25°C. The range of D. buzzatii is constrained only by availability of its host plant, Opuntia species, although its relative abundance is reduced in the northern part of its distribution. The range of D. aldrichi, from central Queensland to northern NSW, Australia, is entirely within that of D. buzzatii, and its relative abundance decreases from north to south. Both climate and weather, particularly temperature variability, have direct effects on the relative abundances of the two species, and both likely act indirectly by influencing the outcome of interspecific competition.     

The evolutionary history of Drosophila buzzatii XXVII

The correlation between body size and longevity was tested in an Argentinian natural population of Drosophila buzzatii. Mean thorax length of flies newly emerging from rotting cladodes of Opuntia vulgaris was significantly smaller than that of two samples of flies caught at baits. The present results which might be interpreted as directional selection for longevity favoring larger flies are in agreement with previous results achieved in a Spanish natural population of D. buzzatii. Flies emerging from different substrates showed significant differences in thorax length, suggesting that an important fraction of phenotypic variance can be attributed to environmental variability. However, laboratory and field work in different populations of D. buzzatii showed a significant genetic component for thorax length variation.     

Genetic history of a colonizing population: Drosophila buzzatii (Diptera: Drosophilidae) in Australia

Drosophila buzzatii Patterson & Wheeler, a cactophilic species that feeds and breeds in the rotting tissues of various Opuntia cactus species, was inadvertently introduced to Australia from Argentina sometime during the period 1931–1936. After a bottleneck at introduction, its spread through the cactus distribution was probably very rapid as a result of natural dispersal from the site of introduction and from three other foci colonized from the introduction site by human intervention. By 1940, the Opuntia distribution and consequently that of D. buzzatii was reduced to spatially isolated populations, with probable further bottlenecking of at least some of the D. buzzatii populations. Allozyme data (primarily six polymorphic loci) from flies collected during April 1972 to February 1996 at 67 localities were used to examine current population differentiation and relationships, as well as to infer aspects of their demographic history. Although there is significant isolation‐by‐distance, genetic relationships among the populations are not simply related to geographical distance, implying that genetic drift has contributed to population differentiation. However, the biotic and, to an extent, the physical environment are not the same in Australia as in Argentina. Consequently, exposure to novel environments has led to local adaptation and further population differentiation. Genetic variation and the structure of Australian populations apparently are determined by founder effects (drift) at the level of individual breeding sites (cactus rots), by diversifying selection among rots within a locality, as well as by drift and geographically varying selection among localities. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 682–698.     

Quantitative genetic analysis of the body size and shape of Drosophila buzzatii

Summary Body size in Drosophila is known to be closely related to a number of traits with important life history consequences, such as fecundity, dispersal ability and mating success. We examine the quantitative genetic basis of body size in three populations of the cactophilic species Drosophila buzzatii, which inhabit climatically different areas of Australia. Flies were reared individually to eliminate any common environmental component in a full-sib design with families split between two temperatures (18° and 25 °C). The means of several size measures differ significantly among populations while the genetic correlations among these traits generally do not differ, either among populations from different natural environments or between the different laboratory temperatures. This stability of correlation structure is necessary if laboratory estimates of genetic correlations are to have any connection with the expression of genetic variation in the field. The amount of variance due to genotype-by-environment interactions (family x temperature of development) varied among populations, apparently in parallel with the magnitudes of seasonal and diurnal variation in temperature experienced by the different populations. A coastal population, inhabiting a relatively thermally benign environment, showed no interaction, while two inland populations, inhabiting thermally more extreme areas, showed interaction. This interaction term is a measure of the amount of genetic variation in the degree of phenotypic plasticity of body size in response to temperature of development. Thus the inland flies vary in their ability to attain a given body size at a particular temperature while the coastal flies do not. This phenotypic plasticity is shown to be due primarily to differences among genotypes in the amount of response to the change in temperature. A possible selective basis for the maintenance of genetic variation for the levels of phenotypic plasticity is proposed.     

Genetic and phenotypic variation for flight ability in the cactophilicDrosophila species,D. aldrichi andD. buzzatii

The flight ability ofDrosophila aldrichi (Patterson & Crow) andD. buzzatii (Patterson & Wheeler) using tethered flights, was measured with respect to age-related changes, genetic variation and adult body size variation induced by rearing at different larval densities.Drosophila buzzatii flew for much longer thanD. aldrichi, especially females, but age-related changes in flight duration were significant only forD. aldrichi. Effects of body size on flight ability were significant inD. buzzatii, but not inD. aldrichi. InD. buzzatii, there was a significant genotype-environment interaction (larval density × line) for flight duration, with short and average flight duration isofemale lines showing longer flights, but a long flight duration line shorter flights as body size decreased (i.e., as larval density increased). Heritability estimates for flight duration were similar in the two species, but flight duration showed no significant genetic correlations with developmental time, body size or wing dimensions (except for one wing dimension inD. buzzatii). Although not significantly different between the species, heritabilities for life-history traits (adult size and developmental time) showed contrasting patterns — with higher heritability for body size (body weight and thorax length) inD. buzzatii, and higher for developmental time inD. aldrichi. In agreement with limited previous field evidence,D. buzzatii is better adapted for colonization than isD. aldrichi.     

Phylogenetic utility of the mitochondrial cytochrome oxidase gene: Molecular evolution of the Drosophila buzzatii species complex

Phylogenetic relationships among eight species of the Drosophila buzzatii species complex (D. mulleri subgroup; D. repleta species group) and D. hamatofila were determined by sequencing the mitochondrial cytochrome oxidase subunit 1, II, and III genes. The species examined included members of the martensis cluster (D. martensis, D. starmeri, D. venezolana), the buzzatii cluster (D. buzzatii, D. serido, D. borborema), and the stalkeri cluster (D. stalkeri, D. richardsoni). The molecular phylogeny was found to be congruent with the chromosomal inversion phylogeny. Analyzing the cytochrome oxidase subunits separately revealed that not all the subunits seem to have the same phylogenetic information content. Parameters are discussed that might explain these differences. Correspondence to: G. Spicer     

Geographic distribution of the bathypelagic genus paraeuchaeta (Copepoda,Calanoida)

The geographic distribution of the bathypelagic calanoid genus Paraeuchaeta was investigated by examining midwater trawl and plankton net samples collected mostly from depths exceeding 1000 m throughout the world's oceans. Of the 81 species referred to Paraeuchaeta, the geographic ranges of about 50 species could be defined with reasonable certainty. Contrary to early authors, the number of species having a worldwide distribution was surprisingly small (12 species or 15% of the 81 species of the genus) as compared to common species endemic to various geographic regions (34 species or 42% of the total of 81). Almost twice as many species were found in the Indo-Pacific Ocean as in either the Atlantic or the Southern Ocean. Faunistically, the northern Atlantic, mid-Atlantic, northern Pacific, East Pacific, Indo-West Pacific, and Southern Ocean were distinct in terms of endemic species. A number of species were found to be endemic to highly productive areas, where they were usually very abundant. Rare species, on the other hand, were generally found to be widely distributed, although some were too rare for their range to be determined with certainty. To explain these findings, the following hypothesis is proposed: Bathypelagic calanoids endemic to and abundant in eutrophic areas are those adapted to eutrophic conditions of their habitats and therefore cannot expand their ranges into contiguous oligotrophic waters even if the other environmental conditions are favorable. Other species, on the other hand, generally have extensive geographic ranges because of their survival ability in widely expanding oligotrophic conditions and the absence of physicochemical barriers at bathypelagic depths of the world's oceans.     

Host alkaloids differentially affect developmental stability and wing vein canalization in cactophilic Drosophila buzzatii

Host shifts cause drastic consequences on fitness in cactophilic species of Drosophila. It has been argued that changes in the nutritional values accompanying host shifts may elicit these fitness responses, but they may also reflect the presence of potentially toxic secondary compounds that affect resource quality. Recent studies reported that alkaloids extracted from the columnar cactus Trichocereus terscheckii are toxic for the developing larvae of Drosophila buzzatii. In this study, we tested the effect of artificial diets including increasing doses of host alkaloids on developmental stability and wing morphology in D. buzzatii. We found that alkaloids disrupt normal wing venation patterning and affect viability, wing size and fluctuating asymmetry, suggesting the involvement of stress–response mechanisms. Theoretical implications are discussed in the context of developmental stability, stress, fitness and their relationship with robustness, canalization and phenotypic plasticity.