ABSTRACTWith the realization that much of the biological diversity on Earth has been generated by... more ABSTRACTWith the realization that much of the biological diversity on Earth has been generated by discrete evolutionary radiations, there has been a rapid increase in research into the biotic (key innovations) and abiotic (key environments) circumstances in which such radiations took place. Here we focus on the potential importance of population genetic structure and trait genetic architecture in explaining radiations. We propose a verbal model describing the stages of an evolutionary radiation: first invading a suitable adaptive zone and expanding both spatially and ecologically through this zone; secondly, diverging genetically into numerous distinct populations; and, finally, speciating. There are numerous examples of the first stage; the difficulty, however, is explaining how genetic diversification can take place from the establishment of a, presumably, genetically depauperate population in a new adaptive zone. We explore the potential roles of epigenetics and transposable elements (TEs), of neutral process such as genetic drift in combination with trait genetic architecture, of gene flow limitation through isolation by distance (IBD), isolation by ecology and isolation by colonization, the possible role of intra‐specific competition, and that of admixture and hybridization in increasing the genetic diversity of the founding populations. We show that many of the predictions of this model are corroborated. Most radiations occur in complex adaptive zones, which facilitate the establishment of many small populations exposed to genetic drift and divergent selection. We also show that many radiations (especially those resulting from long‐distance dispersal) were established by polyploid lineages, and that many radiating lineages have small genome sizes. However, there are several other predictions which are not (yet) possible to test: that epigenetics has played a role in radiations, that radiations occur more frequently in clades with small gene flow distances, or that the ancestors of radiations had large fundamental niches. At least some of these may be testable in the future as more genome and epigenome data become available. The implication of this model is that many radiations may be hard polytomies because the genetic divergence leading to speciation happens within a very short time, and that the divergence history may be further obscured by hybridization. Furthermore, it suggests that only lineages with the appropriate genetic architecture will be able to radiate, and that such a radiation will happen in a meta‐population environment. Understanding the genetic architecture of a lineage may be an essential part of accounting for why some lineages radiate, and some do not.
ABSTRACT Eight polymorphic microsatellites were developed in the perennial herbaceous Aster amell... more ABSTRACT Eight polymorphic microsatellites were developed in the perennial herbaceous Aster amellus L. (Asteraceae) and characterized on three populations from France and Switzerland. The number of alleles ranged between four and 30 depending on the locus, and the mean number of effective alleles was 5.8. The average gene diversity equalled 0.744 (range: 0.419–0.957) and the overall differentiation was found significant (θ = 0.092, P < 0.01). Three loci displayed significant heterozygote deficiencies, which might indicate the presence of null alleles. Amplifications were detected on eight loci in Aster alpinus L.
Sperm form and size is tremendously variable within and across species. However, a general explan... more Sperm form and size is tremendously variable within and across species. However, a general explanation for this variation is lacking. It has been suggested that sperm size may influence sperm competition, and there is evidence for this in some taxa but not others. In addition to normal fertilizing sperm, a number of molluscs and insects produce nonfertile sperm that are also extremely morphologically variable, and distinct from fertilizing forms. There is evidence that nonfertile sperm play an indirect role in sperm competition by decreasing female remating propensity in Lepidopterans, but in most taxa the function of parasperm is unknown. We investigated the role of nonfertile (oligopyrene) sperm during sperm competition in the fresh water snail Viviparus ater. Previous studies found that the proportion of oligopyrene sperm increased with the risk of sperm competition, and hence it seems likely that these sperm influence fertilization success during competitive matings. In mating experiments in which females were sequentially housed with males, we examined a range of male characteristics which potentially influence fertilization success. We found that the size of oligopyrene sperm was the best predictor of fertilization success, with males having the longer sperm siring the highest proportion of offspring. Furthermore, we found a positive shell size and sperm concentration effect on paternity, and females with multiply sired families produced more offspring than females mating with only one male. This result suggests polyandry is beneficial for female snails.
La discussion generale organisee a la fin de la deuxieme journee a fait ressortir les points suiv... more La discussion generale organisee a la fin de la deuxieme journee a fait ressortir les points suivants: 1- Les participants se sont declares satisfaits de la tenue de la reunion, tant dans son deroulement, que dans les echanges d'informations auxquels elle a donne lieu. La quantite et la qualite des resultats presentes a permis de mettre en evidence la puissance d'analyse que represente le travail en reseau. 2-L'importance de la valorisation des resultats a ete soulignee a plusieurs reprises. La diffusion de l'information devrait se faire dans un premier temps par la voie de rapport internes a la DRV, puis par la voie d'articles publies dans des revues scientifiques. Sur le programme C. gigas triploides , une premiere diffusion des resultats obtenus en Normandie est d'ores et deja envisagee (communication au congres CIEM de Dublin, Octobre 1993). 3-La question de la formalisation du Reseau a ete posee. Les participants ont convenu d'un commun accord de con...
Cette etude a ete menee dans le but de reintroduire, par la selection, la culture du millet setar... more Cette etude a ete menee dans le but de reintroduire, par la selection, la culture du millet setaria italica en alsace. L'objectif principal etait de preciser les bases genetiques de la variation et de creer une variabilite nouvelle. L'etude de 15 lignees d'origines differentes en 2 lieux et 2 densites puis pour 4 dates de semis montre une grande sensibilite du millet au conditions experimentales et souligne l'importance des interactions ge. L'analyse des correlations genetiques met en evidence des liaisons potentiellement valorisables dans le cadre d'un schema de selection multivariable. L'analyse des correlations environnementales permet une approche plus physiologique de l'integration des caracteres. L'etude des generations f2 et f3 d'un demi-diallele 66 sans diagonale souligne, pour tous les caracteres, l'importance de l'epistasie et la reduction des heterosis residuels au niveau f2 et f3. L'heterosis est souvent fonction de la ...
SummaryRhizobia, soil bacteria of the Rhizobiales, enter the roots of homologous legumes, where t... more SummaryRhizobia, soil bacteria of the Rhizobiales, enter the roots of homologous legumes, where they induce the formation of nitrogen‐fixing nodules. Signals emanating from both symbiotic partners control nodule development. Efficient nodulation requires precise, temporal regulation of symbiotic genes. Roots continuously release flavonoids that interact with transcriptional activators of the LysR family. NodD proteins, which are members of this family, act both as sensors of the environment and modulate the expression of genes preceded by conserved promoter sequences called nod‐boxes. The symbiotic plasmid of the broad host‐range Rhizobium sp. NGR234 caries 19 nod‐boxes (NB1 to NB19), all of which were cloned upstream of a lacZ‐reporter gene. A flavonoid, daidzein was able to induce 18 of the 19 nod‐boxes in a NodD1‐dependent manner. Interestingly, induction of four nod‐boxes (NB6, NB15, NB16 and NB17) is highly dependent on NodD2 and was delayed in comparison with the others. ...
ABSTRACTWith the realization that much of the biological diversity on Earth has been generated by... more ABSTRACTWith the realization that much of the biological diversity on Earth has been generated by discrete evolutionary radiations, there has been a rapid increase in research into the biotic (key innovations) and abiotic (key environments) circumstances in which such radiations took place. Here we focus on the potential importance of population genetic structure and trait genetic architecture in explaining radiations. We propose a verbal model describing the stages of an evolutionary radiation: first invading a suitable adaptive zone and expanding both spatially and ecologically through this zone; secondly, diverging genetically into numerous distinct populations; and, finally, speciating. There are numerous examples of the first stage; the difficulty, however, is explaining how genetic diversification can take place from the establishment of a, presumably, genetically depauperate population in a new adaptive zone. We explore the potential roles of epigenetics and transposable elements (TEs), of neutral process such as genetic drift in combination with trait genetic architecture, of gene flow limitation through isolation by distance (IBD), isolation by ecology and isolation by colonization, the possible role of intra‐specific competition, and that of admixture and hybridization in increasing the genetic diversity of the founding populations. We show that many of the predictions of this model are corroborated. Most radiations occur in complex adaptive zones, which facilitate the establishment of many small populations exposed to genetic drift and divergent selection. We also show that many radiations (especially those resulting from long‐distance dispersal) were established by polyploid lineages, and that many radiating lineages have small genome sizes. However, there are several other predictions which are not (yet) possible to test: that epigenetics has played a role in radiations, that radiations occur more frequently in clades with small gene flow distances, or that the ancestors of radiations had large fundamental niches. At least some of these may be testable in the future as more genome and epigenome data become available. The implication of this model is that many radiations may be hard polytomies because the genetic divergence leading to speciation happens within a very short time, and that the divergence history may be further obscured by hybridization. Furthermore, it suggests that only lineages with the appropriate genetic architecture will be able to radiate, and that such a radiation will happen in a meta‐population environment. Understanding the genetic architecture of a lineage may be an essential part of accounting for why some lineages radiate, and some do not.
ABSTRACT Eight polymorphic microsatellites were developed in the perennial herbaceous Aster amell... more ABSTRACT Eight polymorphic microsatellites were developed in the perennial herbaceous Aster amellus L. (Asteraceae) and characterized on three populations from France and Switzerland. The number of alleles ranged between four and 30 depending on the locus, and the mean number of effective alleles was 5.8. The average gene diversity equalled 0.744 (range: 0.419–0.957) and the overall differentiation was found significant (θ = 0.092, P < 0.01). Three loci displayed significant heterozygote deficiencies, which might indicate the presence of null alleles. Amplifications were detected on eight loci in Aster alpinus L.
Sperm form and size is tremendously variable within and across species. However, a general explan... more Sperm form and size is tremendously variable within and across species. However, a general explanation for this variation is lacking. It has been suggested that sperm size may influence sperm competition, and there is evidence for this in some taxa but not others. In addition to normal fertilizing sperm, a number of molluscs and insects produce nonfertile sperm that are also extremely morphologically variable, and distinct from fertilizing forms. There is evidence that nonfertile sperm play an indirect role in sperm competition by decreasing female remating propensity in Lepidopterans, but in most taxa the function of parasperm is unknown. We investigated the role of nonfertile (oligopyrene) sperm during sperm competition in the fresh water snail Viviparus ater. Previous studies found that the proportion of oligopyrene sperm increased with the risk of sperm competition, and hence it seems likely that these sperm influence fertilization success during competitive matings. In mating experiments in which females were sequentially housed with males, we examined a range of male characteristics which potentially influence fertilization success. We found that the size of oligopyrene sperm was the best predictor of fertilization success, with males having the longer sperm siring the highest proportion of offspring. Furthermore, we found a positive shell size and sperm concentration effect on paternity, and females with multiply sired families produced more offspring than females mating with only one male. This result suggests polyandry is beneficial for female snails.
La discussion generale organisee a la fin de la deuxieme journee a fait ressortir les points suiv... more La discussion generale organisee a la fin de la deuxieme journee a fait ressortir les points suivants: 1- Les participants se sont declares satisfaits de la tenue de la reunion, tant dans son deroulement, que dans les echanges d'informations auxquels elle a donne lieu. La quantite et la qualite des resultats presentes a permis de mettre en evidence la puissance d'analyse que represente le travail en reseau. 2-L'importance de la valorisation des resultats a ete soulignee a plusieurs reprises. La diffusion de l'information devrait se faire dans un premier temps par la voie de rapport internes a la DRV, puis par la voie d'articles publies dans des revues scientifiques. Sur le programme C. gigas triploides , une premiere diffusion des resultats obtenus en Normandie est d'ores et deja envisagee (communication au congres CIEM de Dublin, Octobre 1993). 3-La question de la formalisation du Reseau a ete posee. Les participants ont convenu d'un commun accord de con...
Cette etude a ete menee dans le but de reintroduire, par la selection, la culture du millet setar... more Cette etude a ete menee dans le but de reintroduire, par la selection, la culture du millet setaria italica en alsace. L'objectif principal etait de preciser les bases genetiques de la variation et de creer une variabilite nouvelle. L'etude de 15 lignees d'origines differentes en 2 lieux et 2 densites puis pour 4 dates de semis montre une grande sensibilite du millet au conditions experimentales et souligne l'importance des interactions ge. L'analyse des correlations genetiques met en evidence des liaisons potentiellement valorisables dans le cadre d'un schema de selection multivariable. L'analyse des correlations environnementales permet une approche plus physiologique de l'integration des caracteres. L'etude des generations f2 et f3 d'un demi-diallele 66 sans diagonale souligne, pour tous les caracteres, l'importance de l'epistasie et la reduction des heterosis residuels au niveau f2 et f3. L'heterosis est souvent fonction de la ...
SummaryRhizobia, soil bacteria of the Rhizobiales, enter the roots of homologous legumes, where t... more SummaryRhizobia, soil bacteria of the Rhizobiales, enter the roots of homologous legumes, where they induce the formation of nitrogen‐fixing nodules. Signals emanating from both symbiotic partners control nodule development. Efficient nodulation requires precise, temporal regulation of symbiotic genes. Roots continuously release flavonoids that interact with transcriptional activators of the LysR family. NodD proteins, which are members of this family, act both as sensors of the environment and modulate the expression of genes preceded by conserved promoter sequences called nod‐boxes. The symbiotic plasmid of the broad host‐range Rhizobium sp. NGR234 caries 19 nod‐boxes (NB1 to NB19), all of which were cloned upstream of a lacZ‐reporter gene. A flavonoid, daidzein was able to induce 18 of the 19 nod‐boxes in a NodD1‐dependent manner. Interestingly, induction of four nod‐boxes (NB6, NB15, NB16 and NB17) is highly dependent on NodD2 and was delayed in comparison with the others. ...
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