Coexistence of ecologically similar colonising species III. Drosophila aldrichi and D. buzzatii: larval performance on,and adult preference for,three Opuntia cactus species

Two Drosophila species, D. buzzatti and D. aldrichi, coexist on several species of Opuntia cacti in Australia, primarily on O. tomentosa and O. streptacantha in the northern part of the cactus distribution, and on O. stricta in the south. Thorax length of field-collected adults was less, and the variance in length greater, than that for flies reared on simulated rots in the laboratory, indicating that these species are affected by crowding in nature. A larval performance index, measured on simulated cactus rots at low, moderate and high densities in single-species cultures, and at moderate and high densities in mixed-species cultures, was used to compare the relative intensity of intra- and interspecific competition at the same total larval density per 5 g necrotic cactus. Larval performance of both fly species was greatest on O. streptacantha, intermediate on O. tomentosa, and least on O. stricta in both single-species and mixed-species cultures. On O. stricta, the performances of D. aldrichi and D. buzzatii were not different when in single-species cultures, but that of D. aldrichi decreased significantly in mixed-species cultures. On the other two cactus species, the performances of D. aldrichi and D. buzzattii were not different in mixed-species cultures. The order of preferences by adult females for the cacti differed from that for larval performance, with females of both species prefering O. stricta. Analysis of microbial numbers growing on the cacti showed little difference among cacti at the rot age used for testing adult preference, but later growth was greater on O. tomentosa and O. streptacantha, the cacti that best supported larvae. Differential larval performance on O. stricta may contribute to the rare presence of D. aldrichi in the southern part of the cactus distribution, while the superior quality of O. tomentosa and O. streptacantha (larger rot size and higher microbial concentration) may reduce competition and facilitate cocxistence of the fly species in the north.     

Larval age differences and competition between Drosophila aldrichi and D.buzzatii

Abstract.

• 1 Competitive interactions among larvae of Drosophila species using the same habitat will usually involve individuals varying in age and size. Older, larger larvae might be expected to outcompete younger, smaller larvae.
• 2 Newly hatched laryae of Drosophila aldrichi and D.buzzatii were placed on induced cactus necroses (simulating the natural habitat), either simultaneously, or with a 1 or 2 day difference in the time at which individuals of the other species were added.
• 3 Evidence for competitive differences with larval age were found. In both species, body weight was significantly higher for those larvae added first than for later addition larvae, and a longer time to complete development was required for those larvae added 2 days later. However, pre-adult viability of D.aldrichi was significantly higher for larvae started 1 or 2 days after larvae of D.buzzatii. For D.buzzatii, viability was lowest for larvae started simultaneously with D.aldrichi, but not different between those started either before or after D.aldrichi.
• 4 Considering all three traits, no clear advantage for the early addition larvae was observed.

     

Reaction norms across and genetic parameters at different temperatures for thorax and wing size traits in Drosophila aldrichi and D. buzzatii

Reaction norms across seven constant and one fluctuating temperature of development were measured for thorax length and several wing size traits for up to 10 isofemale lines of each of the cactophilic Drosophila species, D. aldrichi and D. buzzatii, originating from the same locality. Maximum thorax length was reached at different low to intermediate temperatures for the two species, whereas wing length was highest at the lowest temperature in both species. Various ratio parameters showed pronounced species differences. The reaction norm for the wing loading index (wing length/thorax length) decreased monotonically with temperature in both species, but was much steeper and spanned a wider range in D. aldrichi than in D. buzzatii, suggesting either that wing loading is not a good characterization of flight capacity or, more likely, that flight optimization does not occur in the same manner in both species. The vein ratio (distal length/proximal length of the third vein) increased with temperature in D. buzzatii but decreased in D. aldrichi. Wing development in the two species thus is very different, with the proximal part of the wing in D. buzzatii more closely allied to the thorax than to the distal part. Among line variation was significant for all traits in both species, and most pronounced for thorax length and the ratio parameters. Coefficients of variation were significantly different between the species for all traits, with those in D. aldrichi higher than in D. buzzatii. Genetic variance in plasticity was significant for all traits in D. buzzatii, but only for seven out of 12 in D. aldrichi. Additive genetic variances for all traits in both species were significantly larger than zero. Genetic correlations between thorax length and several wing length parameters, and between these and wing area, were positive and generally significant in both species. The genetic correlation between the distal and the proximal length of the third vein was not significantly different from zero in D. aldrichi, but negative and significant in D. buzzatii. Heritabilites varied significantly among temperatures for almost all traits in both species. Phenotypic variances were generally higher in D. aldrichi than in D. buzzatii, and commonly highest at the extreme temperatures in the former species. At the high temperature the genetic variances also were usually highest in D. aldrichi. The data clearly suggest that the process of thermal adaptation is species specific and caution against generalizations based on the study of single species.     

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.     

Oviposition preference and life history traits in cactophilic Drosophila koepferae and D. buzzatii in association with their natural hosts

Drosophila koepferae and D. buzzatii are two closely related cactophilic species inhabiting the arid lands of southern South America. Previous studies have shown that D. buzzatii breeds primarily on the necrotic cladodes of several Opuntia cacti and D. koepferae on the rotting stems of columnar cacti of the genera Trichocereus and Cereus. In this paper, we analyze the patterns of host plant utilization in a locality where both Drosophila species are sympatric. Field studies showed an absence of differential attraction of adult flies to the rots of two major host cacti: O. sulphurea and T. terschekii. However, the proportion of D. buzzatii flies emerged from the rotting cladodes of O. sulphurea was significantly higher than in T. terschekii. In laboratory experiments, egg to adult viability in single species cultures varied when both Drosophila species were reared in media prepared with O. sulphurea or T. terschekii. In addition, between-species comparisons of flies emerged from single species cultures showed that D. buzzatii adults were smaller and developed faster than D. koepferae. Furthermore, analysis of flies emerged in mixed species cultures showed differences in oviposition preference and oviposition behavior. We discuss the observed between-species differences and suggest that these traits are the result of adaptation to specific patterns of spatial and temporal predictability of their respective preferred host plants: columnar are less dense and less ephemeral resources, whereas the opuntias are more abundant, and fast rotting cacti. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation and differentiation at microsatellite loci in Drosophila simulans. Evidence for founder effects in new world populations.

Drosophila simulans isofemale lines from Africa, South America, and two locations in North America were surveyed for variation at 16 microsatellite loci on the X, second, and third chromosomes, and 18 microsatellites, which are unmapped. D. simulans is thought to have colonized New World habitats only relatively recently (within the last few hundred years). Consistent with a founder effect occurring as colonizers moved into these New World habitats, we find less microsatellite variability in North and South American D. simulans populations than for an African population. Population subdivision as measured at microsatellites is moderate when averaged across all loci (FST = 0.136), but contrasts sharply with previous studies of allozyme variation, which have showed significantly less differentiation in D. simulans than in D. melanogaster. There are substantially fewer private alleles observed in New World populations of D. simulans than seen in a similar survey of D. melanogaster. In addition to possible differences in population size during their evolutionary histories, varying colonization histories or other demographic events may be necessary to explain discrepancies in the patterns of variation observed at various genetic markers between these closely related species.     

Divergence of water balance mechanisms in two sibling species (Drosophila simulans and D. melanogaster): effects of growth temperatures

Drosophila simulans is more abundant under colder and drier montane habitats in the western Himalayas as compared to its sibling D. melanogaster but the mechanistic bases of such climatic adaptations are largely unknown. Previous studies have described D. simulans as a desiccation sensitive species which is inconsistent with its occurrence in temperate regions. We tested the hypothesis whether developmental plasticity of cuticular traits confers adaptive changes in water balance-related traits in the sibling species D. simulans and D. melanogaster. Our results are interesting in several respects. First, D. simulans grown at 15 °C possesses a high level of desiccation resistance in larvae (~39 h) and in adults (~86 h) whereas the corresponding values are quite low at 25 °C (larvae ~7 h; adults ~13 h). Interestingly, cuticular lipid mass was threefold higher in D. simulans grown at 15 °C as compared with 25 °C while there was no change in cuticular lipid mass in D. melanogaster. Second, developmental plasticity of body melanisation was evident in both species. Drosophila simulans showed higher melanisation at 15 °C as compared with D. melanogaster while the reverse trend was observed at 25 °C. Third, changes in water balance-related traits (bulk water, hemolymph and dehydration tolerance) showed superiority of D. simulans at 15 °C but of D. melanogaster at 25 °C growth temperature. Rate of carbohydrate utilization under desiccation stress did not differ at 15 °C in both the species. Fourth, effects of developmental plasticity on cuticular traits correspond with changes in the cuticular water loss i.e. water loss rates were higher at 25 °C as compared with 15 °C. Thus, D. simulans grown under cooler temperature was more desiccation tolerant than D. melanogaster. Finally, desiccation acclimation capacity of larvae and adults is higher for D. simulans reared at 15 °C but quite low at 25 °C. Thus, D. simulans and D. melanogaster have evolved different strategies of water conservation consistent with their adaptations to dry and wet habitats in the western Himalayas. Our results suggest that D. simulans from lowland localities seems vulnerable due to limited acclimation potential in the context of global climatic change in the western Himalayas. Finally, this is the first report on higher desiccation resistance of D. simulans due to developmental plasticity of both the cuticular traits (body melanisation and epicuticular lipid mass) when grown at 15 °C, which is consistent with its abundance in temperate regions.     

Genetics of esterases in Drosophila. VII. Genetic control of the activity level of juvenile hormone (JH)-esterase and heat resistance in D. virilis at high temperatures

The heat-resistant subline 147S was obtained in Drosophila virilis by selecting for viability individuals of heat-sensitive stock 147. It was shown that in the heat-treated 147S pupae the activity of juvenile hormone (JH)-esterase is decreased and, consequently, the titer of juvenile hormone is increased compared with those in the control pupae. These changes are consistent with those observed earlier for resistant stock 101. Heat-resistant stocks 101 and 147S were crossed with heat-sensitive stock 147, whose heat-treated larvae show earlier activation and higher activity of JH-esterase than control larvae. The viability and electrophoretic esterase patterns were analyzed in the F₁ and F₂ hybrids at different temperatures. It was found that the F₁ hybrid is resistant to the effect of high temperature and its activity level of JH-esterase is lower compared with controls. In the F₂ hybrid, there was a 3:1 segregation of viability and a 1:2:1 segregation of the activity level of JH-esterase at high temperatures. It is concluded that the activity level of JH-esterase and heat resistance in D. virilis are monogenically controlled at high temperatures.     

Evolutionary responses of Drosophila melanogaster to selection at different larval densities: changes in genetic variation,specialization and phenotypic plasticity

Abstract We studied the evolutionary response to novel environments by applying artificial selection for total progeny biomass in populations of Drosophila melanogaster maintained at three different larval population densities. We found the relative amount of genetic variability for characters related with biomass to be lower and the correlation between them more negative at the intermediate density, and that selection resulted in changes in phenotypic plasticity and in patterns of resource allocation between traits. We found some evidence for tradeoffs between densities, which suggests that populations living at heterogeneous densities might be subject to disruptive selection. Our results show that adaptation to new environments may be a complex process, involving not only changes in trait means, but also in correlations between traits and between environments.     

DNA variation at the rp49 gene region in Drosophila madeirensis and D. subobscura from Madeira: inferences about the origin of an insular endemic species

An ~1.6 ‐ kb fragment spanning the rp49 gene was sequenced in 16 lines of Drosophila subobscura from Madeira and in 22 lines of the endemic species D. madeirensis. Nucleotide diversity in D. subobscura from Madeira (π=0.0081) was similar to that in lines from Spain carrying the O₃₊₄ chromosomal arrangement (π=0.0080). No significant genetic differentiation was detected between insular and continental O₃₊₄ lines of D. subobscura. These results are compatible both with a rather recent and massive colonization, and with multiple colonization events from the continent. Nucleotide diversity in D. madeirensis (π=0.0076) was similar to that in D. subobscura, which deviates from the expectation, under strict neutrality, of a lower level of variation in an insular species with a small population size. The observed numbers of shared polymorphisms and of fixed differences between D. madeirensis and D. subobscura are compatible with the isolation model of speciation, where shared polymorphisms are due to common ancestry.     

The effects of ambient flow velocity,colony size,and upstream colonies on the feeding success of Bryozoa. II. Conopeum reticulum (Linnaeus), an encrusting species

The effects of ambient flow velocity, colony size, and the presence of an actively-feeding colony upstream on the feeding success of the encrusting bryozoan Conopeum reticulum (Linnaeus) were studied. Zooids from both large and small colonies showed a reduction in feeding as flow velocity increased, however, the reduction in feeding was less for zooids from large colonies except at very fast ambient flow velocities. The greater pumping capacity of large colonies may result in a relatively greater per zooid feeding success from moving water. The presence of an actively-feeding colony upstream was found to enhance the feeding of zooids on downstream colonies. Diversion of flowing water by actively-feeding colonies upstream may account for the observed enhancement of feeding by zooids on colonies downstream.The results from this study on an encrusting species are compared with results from a previous study on feeding from flow by an arborescent bryozoan, and the feeding performances of these two colony types are related to their respective flow microhabitats.     

Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic Forest of SE-Brazil II. Spatial and ontogenetic dynamics in Andira legalis, a deciduous legume tree

Andira legalis Vell. Toledo (Leguminosae, Papilionoideae) is a deciduous tree of the coastal vegetation of Brazil. It was studied in the restinga ecosystems of the Atlantic coast along a moisture gradient of open dry restinga (annual precipitation 800 mm, water table high at 0.9–1.2 m but partially saline), intermediate restinga (annual precipitation 1164 mm, water table low at 2–3 m) and wet restinga (annual precipitation 1000 mm, water table high at 0.5–1 m). In addition, a comparison of the ecophysiological performance was made of A. legalis in the wet restinga and a dune forest (water table low at 2–6 m). Plants of A. legalis at a given site and even within clonal stands show considerable phenological plasticity, where especially timing of leaf shedding and new bud break, leaf expansion and maturation varies between neighbouring individuals and all stages can be observed at the same time. We used analyses of soluble carbohydrate carbon compounds, soluble non-protein nitrogen compounds, stable isotope signatures (¹³C, ¹⁵N) and parameters of fluorescence of chlorophyll a for describing metabolic relations and photosynthetic behaviour and to deduce possible variations in ecophysiological strategies in response to site conditions. The phenological plasticity is described in relation to predominant metabolite levels in leaves, roots, xylem and phloem, but its ecological advantage—perhaps related to staggered resource acquisition and susceptibility to predators—remains an open question. For overall ecophysiological performance among the environmental factors root access to the ground water table appeared to be more essential than significantly different precipitation regimes, as plants in the intermediate restinga appeared to be more stressed than those in the other two open restingas. Shading in the dune forest was also an important environmental constraint.     

CHMetal(II) axial interaction in planar complexes (metal = Cu, Pd) and implications for possible environmental effects of alkyl groups at biological copper sites

Intramolecular M(II)H–C interactions (M(II)=Cu(II), Pd(II)) involving a side chain alkyl group of planar d⁸ and d⁹ metal complexes of the N-alkyl (R) derivatives of N,N-bis(2-pyridylmethyl)amine with an N₃Cl donor set were established by structural and spectroscopic methods. The methyl group from the branched alkyl group (R = 2,2-dimethylpropyl and 2-methylbutyl) axially interacts with the metal ion with the MC and MH distances of 3.056(3)–3.352(9) and 2.317(1)–2.606(1) Å, respectively, and the M–H–C angles of 122.4–162.3°. The Cu(II) complexes showing the interaction have a higher redox potential as compared with those without it, and the ¹H NMR signals of the interacting methyl group in Pd(II) complexes shifted downfield relative to the ligand signals. Dependence of the downshift values on the dielectric constants of the solvents used indicated that the M(II)H–C interaction is mainly electrostatic in nature and may be regarded as a weak hydrogen bond. Implications for possible environmental effects of the leucine alkyl group at the type 1 Cu site of fungal laccase are also discussed.