Electrophoretic variation at three enzyme loci‐alcohol dehydrogenase (Adh), glycerophosphate dehy... more Electrophoretic variation at three enzyme loci‐alcohol dehydrogenase (Adh), glycerophosphate dehydrogenase (Gpdh), triosephosphate isomerase (Tpi)‐ is compared in Australian Drosophila melanogaster populations at three levels of spatial heterogeneity; among breeding sites, within populations, and between populations at the geographic level. Heterogeneity at the breeding site level greatly exceeds that among adults within populations, indicating greater intermixing at the mobile adult stage than at the developmentally immature and less migratory larval stage. Heterogeneity at the microspatial level is large relative to the geographic level at two of these loci.Spatial patterns of variation in ecological phenotypes are also considered. It is argued that electrophoretic variants may contribute little to an understanding of this quantitative variation, and that a more useful approach in ecological genetics is to consider ecological phenotypes as primary data.
Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extreme... more Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extremes, yet responses to aridity may be equally important. Here we focus on plasticity in desiccation resistance, a key trait shaping distributions of <i>Drosophila</i> species and other small ectotherms. We examined the extent to which 32 <i>Drosophila</i> species, varying in their distribution, could increase their desiccation resistance via phenotypic plasticity involving hardening, linking these responses to environment, phylogeny and basal resistance. We found no evidence to support the seasonality hypothesis; species with higher hardening plasticity did not occupy environments with higher and more seasonal precipitation. As basal resistance increased, the capacity of species to respond via phenotypic plasticity decreased, suggesting plastic responses involving hardening may be constrained by basal resistance. Trade-offs between basal desiccation resistance and plasticity were not universal across the phylogeny and tended to occur within specific clades. Phylogeny, environment and trade-offs all helped to explain variation in plasticity for desiccation resistance but in complex ways. These findings suggest some species have the ability to counter dry periods through plastic responses, whereas others do not; and this ability will depend to some extent on a species' placement within a phylogeny, along with its basal level of resistance.
Wolbachia bacteria are being widely released for suppression of dengue transmitted by Aedes mosqu... more Wolbachia bacteria are being widely released for suppression of dengue transmitted by Aedes mosquitoes. Walker, Quek, Jeffries and colleagues present robust evidence for natural Wolbachia infections in malaria-vectoring Anopheles mosquitoes, paving the way for new Wolbachia-based interventions.
Spodoptera frugiperda has been reported in China since the beginning of 2019, threatening maize p... more Spodoptera frugiperda has been reported in China since the beginning of 2019, threatening maize production and raising questions about interactions with indigenous pests on maize. Spodoptera frugiperda is in the same feeding guild as the indigenous species Ostrinia furnacalis , with both pests attacking maize plant tissues such as whorls and tassels. In this study, the interaction of these species was assessed under laboratory and field conditions by examining the survival and predation rate of larvae in maize whorls and tassels. Intraspecific and interspecific interactions of larvae were assessed to characterize movements in arenas in the presence and absence of food. When S. frugiperda and O. furnacalis were present at an equal ratio, S. frugiperda prevailed over O. furnacalis with a high survival rate (over 90%) and predation rate of O. furnacalis (over 40%) under most scenarios in both laboratory and field conditions. When both species occurred at different ratios in the field, S. frugiperda had on average almost 16 times the number of survivors as O. furnacalis on whorls, and 8.3 times the number on tassels, highlighting a substantial advantage in these environments. Spodoptera frugiperda larvae undertook a low frequency of lethal attacks (strikes) and showed a higher incidence of defensive movements compared to O. furnacalis . A field survey showed that S. frugiperda larvae can colonize vegetative plant stages in maize, but it remains to be seen if competitive interactions can be linked to population dynamics of both species though they are expected to favor S. frugiperda .
We have started to test the effects of environmental extremes on the expression of genetic variat... more We have started to test the effects of environmental extremes on the expression of genetic variation for traits likely to be under selection in natural populations. We have shown that field heritability may be high for stress response traits in contrast to morphological traits, which tend to show lower levels of heritable variation in nature compared with the laboratory. Selection for increased stress resistance can lead to a number of other evolutionary changes, and these may underlie trade-offs between favourable and stressful environments. Temperature extremes can have a marked influence on the heritability of life history traits. Heritabilities for fecundity can be high when parental flies are reared at low temperatures and under field conditions. The expression of genetic variation for development time is somewhat more complex when temperature extremes are considered. Populations at species margins may be ideal for studying the effects of environmental stress on evolution.
The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution... more The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution and a predominance of species in Australia, but there is little information on the presence and impacts of Wolbachia endosymbionts in this group. Here we describe the first Wolbachia infection from this group, wClay isolated from Scaptodrosophila claytoni (van Klinken), a species from the east coast of Australia. The infection is polymorphic in natural populations, occurring at a frequency of around 6%–10%. wClay causes male killing, producing female‐biased lines; most lines showed 100% male killing, though in 1 line it was &lt;80%. The lines need to be maintained through the introduction of males unless the infection is removed by tetracycline treatment. wClay is transmitted at a high fidelity (98.6%) through the maternal lineage and has been stable in 2 laboratory lines across 24 generations, suggesting it is likely to persist in populations. The infection has not been previously described but is closely related to the male‐killing Wolbachia recently described from Drosophila pandora based on multilocus sequence typing and the wsp gene. Male‐killing Wolbachia are likely to be common in drosophilids but remain difficult to detect because the infections can often be at a low frequency.
Electrophoretic variation at three enzyme loci‐alcohol dehydrogenase (Adh), glycerophosphate dehy... more Electrophoretic variation at three enzyme loci‐alcohol dehydrogenase (Adh), glycerophosphate dehydrogenase (Gpdh), triosephosphate isomerase (Tpi)‐ is compared in Australian Drosophila melanogaster populations at three levels of spatial heterogeneity; among breeding sites, within populations, and between populations at the geographic level. Heterogeneity at the breeding site level greatly exceeds that among adults within populations, indicating greater intermixing at the mobile adult stage than at the developmentally immature and less migratory larval stage. Heterogeneity at the microspatial level is large relative to the geographic level at two of these loci.Spatial patterns of variation in ecological phenotypes are also considered. It is argued that electrophoretic variants may contribute little to an understanding of this quantitative variation, and that a more useful approach in ecological genetics is to consider ecological phenotypes as primary data.
Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extreme... more Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extremes, yet responses to aridity may be equally important. Here we focus on plasticity in desiccation resistance, a key trait shaping distributions of <i>Drosophila</i> species and other small ectotherms. We examined the extent to which 32 <i>Drosophila</i> species, varying in their distribution, could increase their desiccation resistance via phenotypic plasticity involving hardening, linking these responses to environment, phylogeny and basal resistance. We found no evidence to support the seasonality hypothesis; species with higher hardening plasticity did not occupy environments with higher and more seasonal precipitation. As basal resistance increased, the capacity of species to respond via phenotypic plasticity decreased, suggesting plastic responses involving hardening may be constrained by basal resistance. Trade-offs between basal desiccation resistance and plasticity were not universal across the phylogeny and tended to occur within specific clades. Phylogeny, environment and trade-offs all helped to explain variation in plasticity for desiccation resistance but in complex ways. These findings suggest some species have the ability to counter dry periods through plastic responses, whereas others do not; and this ability will depend to some extent on a species' placement within a phylogeny, along with its basal level of resistance.
Wolbachia bacteria are being widely released for suppression of dengue transmitted by Aedes mosqu... more Wolbachia bacteria are being widely released for suppression of dengue transmitted by Aedes mosquitoes. Walker, Quek, Jeffries and colleagues present robust evidence for natural Wolbachia infections in malaria-vectoring Anopheles mosquitoes, paving the way for new Wolbachia-based interventions.
Spodoptera frugiperda has been reported in China since the beginning of 2019, threatening maize p... more Spodoptera frugiperda has been reported in China since the beginning of 2019, threatening maize production and raising questions about interactions with indigenous pests on maize. Spodoptera frugiperda is in the same feeding guild as the indigenous species Ostrinia furnacalis , with both pests attacking maize plant tissues such as whorls and tassels. In this study, the interaction of these species was assessed under laboratory and field conditions by examining the survival and predation rate of larvae in maize whorls and tassels. Intraspecific and interspecific interactions of larvae were assessed to characterize movements in arenas in the presence and absence of food. When S. frugiperda and O. furnacalis were present at an equal ratio, S. frugiperda prevailed over O. furnacalis with a high survival rate (over 90%) and predation rate of O. furnacalis (over 40%) under most scenarios in both laboratory and field conditions. When both species occurred at different ratios in the field, S. frugiperda had on average almost 16 times the number of survivors as O. furnacalis on whorls, and 8.3 times the number on tassels, highlighting a substantial advantage in these environments. Spodoptera frugiperda larvae undertook a low frequency of lethal attacks (strikes) and showed a higher incidence of defensive movements compared to O. furnacalis . A field survey showed that S. frugiperda larvae can colonize vegetative plant stages in maize, but it remains to be seen if competitive interactions can be linked to population dynamics of both species though they are expected to favor S. frugiperda .
We have started to test the effects of environmental extremes on the expression of genetic variat... more We have started to test the effects of environmental extremes on the expression of genetic variation for traits likely to be under selection in natural populations. We have shown that field heritability may be high for stress response traits in contrast to morphological traits, which tend to show lower levels of heritable variation in nature compared with the laboratory. Selection for increased stress resistance can lead to a number of other evolutionary changes, and these may underlie trade-offs between favourable and stressful environments. Temperature extremes can have a marked influence on the heritability of life history traits. Heritabilities for fecundity can be high when parental flies are reared at low temperatures and under field conditions. The expression of genetic variation for development time is somewhat more complex when temperature extremes are considered. Populations at species margins may be ideal for studying the effects of environmental stress on evolution.
The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution... more The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution and a predominance of species in Australia, but there is little information on the presence and impacts of Wolbachia endosymbionts in this group. Here we describe the first Wolbachia infection from this group, wClay isolated from Scaptodrosophila claytoni (van Klinken), a species from the east coast of Australia. The infection is polymorphic in natural populations, occurring at a frequency of around 6%–10%. wClay causes male killing, producing female‐biased lines; most lines showed 100% male killing, though in 1 line it was &lt;80%. The lines need to be maintained through the introduction of males unless the infection is removed by tetracycline treatment. wClay is transmitted at a high fidelity (98.6%) through the maternal lineage and has been stable in 2 laboratory lines across 24 generations, suggesting it is likely to persist in populations. The infection has not been previously described but is closely related to the male‐killing Wolbachia recently described from Drosophila pandora based on multilocus sequence typing and the wsp gene. Male‐killing Wolbachia are likely to be common in drosophilids but remain difficult to detect because the infections can often be at a low frequency.
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Papers by Ary Hoffmann