Papers by Michele Schiffer
Divergence among populations can occur via additive genetic effects and/or because of epistatic i... more Divergence among populations can occur via additive genetic effects and/or because of epistatic interactions among genes. Here we use line-cross analysis to compare the importance of epistasis in divergence among two sympatric Drosophila species from eastern Australia, one (D. serrata) distributed continuously and the other (D. birchii) confined to rainforest habitats that are often disjunct. For D. serrata, crosses indicated that development time and wing size differences were due to additive genetic effects, while for viability there were digenic epistatic effects. Crosses comparing geographically close populations as well as those involving the most geographically distant populations (including the southern species border) revealed epistatic interactions, whereas crosses at an intermediate distance showed no epistasis. In D. birchii, there was no evidence of epistasis for viability, although for development time and wing size there was epistasis in the cross between the most geographically diverged populations. Strong epistasis has not developed among the D. birchii populations, and this habitat specialist does not show stronger epistasis than D. serrata. Given that epistasis has been detected in crosses with other species from eastern Australia, including the recently introduced D. melanogaster, the results point to epistasis not being directly linked to divergence times among populations.
There is increasing interest in comparing species of related organisms for their susceptibility t... more There is increasing interest in comparing species of related organisms for their susceptibility to thermal extremes in order to evaluate potential vulnerability to climate change. Comparisons are typically undertaken on individuals collected from the field with or without a period of acclimation. However, this approach does not allow the potential contributions of environmental and carry-over effects across generations to be separated from inherent species differences in susceptibility. To assess the importance of these different sources of variation, we here considered heat and cold resistance in Drosophilid species from tropical and temperate sites in the field and across two laboratory generations. Resistance in field-collected individuals tended to be lower when compared with F1 and F2 laboratory generations, and species differences in field flies were only weakly correlated to differences established under controlled rearing conditions, unlike in F1–F2 comparisons. This reflected large environmental
effects on resistance associated with different sites and conditions experienced within sites. For the 8 h cold recovery assay there was no strong evidence of carry-over effects, whereas for the heat knockdown and 2 h cold recovery assays there was some evidence for such effects. However, for heat these were species specific in direction. Variance components for inherent species differences were substantial for resistance to heat and 8 h cold stress, but small for 2 h cold stress, though this may be a reflection of the species being considered in the comparisons. These findings highlight that inherent differences among species are difficult to characterise accurately without controlling for environmental sources of variation and carry-over effects. Moreover, they also emphasise the complex nature of carry-over effects that vary depending on the nature of stress traits and the species being evaluated.
The Drosophila serrata species complex from Australia and New Guinea has been widely used in evol... more The Drosophila serrata species complex from Australia and New Guinea has been widely used in evolutionary studies of speciation and climatic adaptation. It is believed to consist of D. serrata, D. birchii and D. dominicana, although knowledge of the latter is limited. Here we present evidence for a previously undescribed cryptic member of the D. serrata species complex. This new cryptic species is widespread in far north Queensland, Australia and is likely to have been previously mistaken for D. serrata. It shows complete reproductive isolation when crossed with both D. serrata and D. birchii. The cryptic species can be easily distinguished from D. serrata and D. birchii using either microsatellite loci or visual techniques. Although it occurs sympatrically with both D. serrata and D. birchii, it differs from these species in development time, viability, wing size and wing morphology. Its discovery explains patterns of recently described mitochondrial DNA divergence within D. serrata, and may also help to clarify some ambiguities evident in early evolutionary literature on reproductive incompatibility within the D. serrata species complex.
An unknown Drosophila montium subgroup species was collected on Cape York Peninsula in 1992, a li... more An unknown Drosophila montium subgroup species was collected on Cape York Peninsula in 1992, a live culture of the same species was established from flies collected in the vicinity of Lake Placid near Cairns in 2001. From these specimens we now have sufficient information to describe a new species—Drosophila bunnanda. It differs morphologically from the four other montium subgroup species already known from northern Queensland—D. serrata, D. birchii, D. kikkawai, and D. sp. cf. jambulina, and from one very similar species—D. dominicana—known from Papua New Guinea. Molecular data support the taxonomic findings. Additional information and a key for all Australian montium subgroup species is provided to allow clear differentiation between them and D. bunnanda.
Three new Drosophila species are described in the ananassae subgroup from Australia, New Guinea a... more Three new Drosophila species are described in the ananassae subgroup from Australia, New Guinea and Samoa. Drosophila pandora sp.nov. and D. anomalata sp.nov. are morphologically very similar to the circumtropical species D. ananassae and are classified together in the ananassae complex. For 40 years D. pandora has been incorrectly identified as D. ananassae in the Australian tropics. The results of a detailed examination of the morphology of 1649 wild-caught ananassae-like male specimens, sampled from 60 islands from Southeast Asia to French Polynesia and 94 localities of northern Australia and western, central and eastern New Guinea, are reported. Comparisons are made with Afrotropical and Oriental samples to confirm the identity of D. ananassae s.str. Photomicrographs of the male terminalia and sex combs of D. ananassae and D. pandora from geographically distant localities demonstrate the stability of the important diagnostic characters. Males of D. anomalata, known only from three localities in Queensland, Australia, have a unique bobbing behaviour when courting, and they have the lowest total number of teeth in the sex combs. The distinctive male terminalia of related species D. atripex, D.monieri, D. ochrogaster, D. parapallidosa and D. pallidosa are figured for comparison. Among them, a species from Samoa, closely resembling the Fijian endemic species D. phaeopleura, is described here as Drosophila schugi sp.nov.
Evolution, 1998
... ARY A. HOFFMANN1 AND MICHELE SCHIFFER School of Genetics and Human Variation, La Trobe Univer... more ... ARY A. HOFFMANN1 AND MICHELE SCHIFFER School of Genetics and Human Variation, La Trobe University, Bundoora, Victoria 3083, Australia 1E-mail: genaah @gen. latrobe. edu.au ... IMASHEVA, AG, V. LOESCHCKE, LA ZHIVOTOVSKY, AND 0. E. LAZENBY. 1997. ...
Molecular Ecology, 2007
Although fragmented rainforest environments represent hotspots for invertebrate biodiversity, few... more Although fragmented rainforest environments represent hotspots for invertebrate biodiversity, few genetic studies have been conducted on rainforest invertebrates. Thus, it is not known if invertebrate species in rainforests are highly genetically fragmented, with the potential for populations to show divergent selection responses, or if there are low levels of gene flow sufficient to maintain genetic homogeneity among fragmented populations. Here we use microsatellite markers and DNA sequences from the mitochondrial ND5 locus to investigate genetic differences among Drosophila birchii populations from tropical rainforests in Queensland, Australia. As found in a previous study, mitochondrial DNA diversity was low with no evidence for population differentiation among rainforest fragments. The pattern of mitochondrial haplotype variation was consistent with D. birchii having undergone substantial past population growth. Levels of nuclear genetic variation were high in all populations while F ST values were very low, even for flies from geographically isolated areas of rainforest. No significant differentiation was observed between populations on either side of the Burdekin Gap (a long-term dry corridor), although there was evidence for higher gene diversity in low-latitude populations. Spatial autocorrelation coefficients were low and did not differ significantly from random, except for one locus which revealed a clinal-like pattern. Comparisons of microsatellite differentiation contrasted with previously established clinal patterns in quantitative traits in D. birchii , and indicate that the patterns in quantitative traits are likely to be due to selection. These results suggest moderate gene flow in D. birchii over large distances. Limited population structure in this species appears to be due to recent range expansions or cycles of local extinctions followed by recolonizations/expansions. Nevertheless, patterns of local adaptation have developed in D. birchii that may result in populations showing different selection responses when faced with environmental change.
Immunology and Cell Biology, 2003
The prospect for successful biocontrol using immunocontraception is threatened if there is adapta... more The prospect for successful biocontrol using immunocontraception is threatened if there is adaptation to the vaccine through natural selection of individuals that are genetically resistant to the contraceptive agent. To assess this possibility we examined the literature and found that little relevant data are available for any species on the appropriate trait, fertility variation among immunized individuals, or about appropriate population and genetic parameters influencing the likelihood of a selection response. Some data are available on variation in antibody response to immunocontraceptives, but the relationship between antibody response and fertility levels is poorly documented. The antibody response data indicate low heritability for this trait suggesting that fertility levels of contraceptive-resistant individuals will also have a low heritability. Slow evolution of contraception resistance might therefore be anticipated. The absence of information about relevant parameters makes the construction of quantitative models premature. We discuss factors in particular need of investigation if predictions about resistance evolution are to be made. These include: 1. the genetic basis of fertility retention, 2. the proportion of the population resistant to the contraceptive agent and how this is affected by gene flow from refuge populations, 3. the geneticallybased fitness tradeoffs of resistant individuals that often accompany selection, 4. cross-generation effects that can thwart the effects of selection, and 5. the efficiency of delivery of the contraceptive agent. An understanding of the above for particular species, and the development of appropriate divergently acting multiple vaccines that can be used in temporal rotation or in mixtures, should facilitate the development of management options to minimize resistance evolution.
Annals of Applied Biology, 2009
ABSTRACT The wheat curl mite (WCM), Aceria tosichella, is an eriophyid pest of cereals, and the v... more ABSTRACT The wheat curl mite (WCM), Aceria tosichella, is an eriophyid pest of cereals, and the vector responsible for the transmission of wheat streak mosaic virus (WSMV). In a previous study, the taxonomic status of A. tosichella in Australia was assessed using molecular markers. A. tosichella was shown to consist of two genetically distinct lineages likely to represent different species. Here we show that both lineages occupy similar distributions, occurring throughout the entire Australian wheat belt, and that the lineages are often found in sympatry. CLIMEX analysis suggests that tolerance to heat and desiccation limit the distribution of A. tosichella. In the laboratory, only one WCM lineage transmitted WSMV virus under controlled conditions. These results have implications for the management of WCM and WSMV within Australia.
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Papers by Michele Schiffer
effects on resistance associated with different sites and conditions experienced within sites. For the 8 h cold recovery assay there was no strong evidence of carry-over effects, whereas for the heat knockdown and 2 h cold recovery assays there was some evidence for such effects. However, for heat these were species specific in direction. Variance components for inherent species differences were substantial for resistance to heat and 8 h cold stress, but small for 2 h cold stress, though this may be a reflection of the species being considered in the comparisons. These findings highlight that inherent differences among species are difficult to characterise accurately without controlling for environmental sources of variation and carry-over effects. Moreover, they also emphasise the complex nature of carry-over effects that vary depending on the nature of stress traits and the species being evaluated.
effects on resistance associated with different sites and conditions experienced within sites. For the 8 h cold recovery assay there was no strong evidence of carry-over effects, whereas for the heat knockdown and 2 h cold recovery assays there was some evidence for such effects. However, for heat these were species specific in direction. Variance components for inherent species differences were substantial for resistance to heat and 8 h cold stress, but small for 2 h cold stress, though this may be a reflection of the species being considered in the comparisons. These findings highlight that inherent differences among species are difficult to characterise accurately without controlling for environmental sources of variation and carry-over effects. Moreover, they also emphasise the complex nature of carry-over effects that vary depending on the nature of stress traits and the species being evaluated.