Developmental conservation among related species is a common generalization known as von Baer's t... more Developmental conservation among related species is a common generalization known as von Baer's third law and implies that early stages of development are the most refractory to change. The "hourglass model" is an alternative view that proposes that middle stages are the most constrained during development. To investigate this issue, we undertook a genomic approach and provide insights into how natural selection operates on genes expressed during the first 24 h of Drosophila ontogeny in the six species of the melanogaster group for which whole genome sequences are available. Having studied the rate of evolution of more than 2,000 developmental genes, our results showed differential selective pressures at different moments of embryogenesis. In many Drosophila species, early zygotic genes evolved slower than maternal genes indicating that mid-embryogenesis is the stage most refractory to evolutionary change. Interestingly, positively selected genes were found in all embryonic stages even during the period with the highest developmental constraint, emphasizing that positive selection and negative selection are not mutually exclusive as it is often mistakenly considered. Among the fastest evolving genes, we identified a network of nucleoporins (Nups) as part of the maternal transcriptome. Specifically, the acceleration of Nups was driven by positive selection only in the more recently diverged species. Because many Nups are involved in hybrid incompatibilities between species of the Drosophila melanogaster subgroup, our results link rapid evolution of early developmental genes with reproductive isolation. In summary, our study revealed that even within functional groups of genes evolving under strong negative selection many positively selected genes could be recognized. Understanding these exceptions to the broad evolutionary conservation of early expressed developmental genes can shed light into relevant processes driving the evolution of species divergence.
Drosophila buzzatii and Drosophila koepferae are two cactophilic sibling species whose ranges par... more 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 (cardo´n). 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.
Developmental conservation among related species is a common generalization known as von Baer's t... more Developmental conservation among related species is a common generalization known as von Baer's third law and implies that early stages of development are the most refractory to change. The "hourglass model" is an alternative view that proposes that middle stages are the most constrained during development. To investigate this issue, we undertook a genomic approach and provide insights into how natural selection operates on genes expressed during the first 24 h of Drosophila ontogeny in the six species of the melanogaster group for which whole genome sequences are available. Having studied the rate of evolution of more than 2,000 developmental genes, our results showed differential selective pressures at different moments of embryogenesis. In many Drosophila species, early zygotic genes evolved slower than maternal genes indicating that mid-embryogenesis is the stage most refractory to evolutionary change. Interestingly, positively selected genes were found in all embryonic stages even during the period with the highest developmental constraint, emphasizing that positive selection and negative selection are not mutually exclusive as it is often mistakenly considered. Among the fastest evolving genes, we identified a network of nucleoporins (Nups) as part of the maternal transcriptome. Specifically, the acceleration of Nups was driven by positive selection only in the more recently diverged species. Because many Nups are involved in hybrid incompatibilities between species of the Drosophila melanogaster subgroup, our results link rapid evolution of early developmental genes with reproductive isolation. In summary, our study revealed that even within functional groups of genes evolving under strong negative selection many positively selected genes could be recognized. Understanding these exceptions to the broad evolutionary conservation of early expressed developmental genes can shed light into relevant processes driving the evolution of species divergence.
Drosophila buzzatii and Drosophila koepferae are two cactophilic sibling species whose ranges par... more 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 (cardo´n). 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.
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Papers by Julián Mensch