Stratégies reproductives et transmission des gènes: grâce aux femmes et malgré les hommes ?

Study of animal behavior reveals that the main concern of every living organism is gene transmission, whatever the society in which it lives. Different reproductive strategies exist according to species, type of gamete production, and also sex. In mammals, some kind of reproductive antagonism may exist between males and females. The differential expression of some genes according to their parental origin has led to the conflict theory of genomic imprinting.     

Comparaison des croisements au hasard,prère-sœur et demi frère-sœur par le coefficient de dépression

The chromosomal theory of inbreeding based on a gametic interaction system lead us to define a depression coefficientD. Comparison of random, sib and half-sib matings (with inbreeding coefficientF=0, 1/4 and 1/8) shows thatD depends on the structure of the starting population and on values of the model parameters. This result accounts for responses of lines whose depression does not depend directly on the inbreeding coefficient and which theories of inbreeding based on increasing homozygosity fail to explain.     

Activité des pyrophosphatases inorganiques acide et alcaline après traitement avec divers herbicides

Various herbicides are applied on seventeen-day-old cucumber seedlings growing in a nutrient solution. After 1 and 3 days, acid and alkaline pyrophosphatase activities are measured in the leaves and the roots of seedlings treated with lethale dosis of atrazine, chlortoluron, ioxynil, MCPA, dicamba, alachlor. The same enzymes are determined after 5 h in seedlings on which previously paraquat and DNOC were pulverised. In the leaves, acid pyrophosphatase activity is stimulated by almost all the herbicides, especially by ioxynil, paraquat and DNOC while alkaline pyrophosphatase remains similar to the controls. The alkaline and acid pyrophosphatase activity in the roots is either unchanged or stimulated or inhibited without any correlation with the various modes of action of the herbicides.     

Écologie comparée des entomophthoracées pathogènes de pucerons en france littorale et continentale

Résumé Le r?le des Entomophthorales dans la dynamique des populations de pucerons infestant la végétation spontanée est comparé d'une part en zone littorale (Basse-Normandie) et d'autre part en zone continentale (Vosges). En Basse-Normandie, le comportement anholocyclique de nombreuses espèces de pucerons contribue à la permanence des populations aphidiennes et, en conséquence, à la persistance de la mycose. Dans les Vosges, en raison des dures conditions hivernales, les pucerons ont un développement holocyclique et leurs colonies se développent pendant 6 ou 7 mois seulement; en 1974, la mycose appara?t au moment du maximum de la population aphidienne et une situation épizootique détermine le rapide déclin des populations. Dans les 2 régions,Erynia neoaphidis Remaud. & Henn.,Entomophthora planchoniana Cornu,Neozygites fresenii (Nowak.) Remaud. & Kell. etConidiobolus obscurus (Hall & Dunn) Remaud. & Kell sont les pathogènes les plus communs. La fréquence deZoophthora phalloides Batko sur le littoral normand contraste avec sa rareté dans les Vosges.Conidiobolus osmodes Drechsler, occasionnellement observé en Normandie, n'a jamais été rencontré dans les Vosges.E. neoaphidis etE. planchoniana sont présents toute l'année. La première espèce est plus abondante au printemps, la seconde en automne.C. obscurus etZ. phalloides semblent mieux adaptés aux conditions fra?ches du printemps et de l'automne et sont très rarement rencontrés pendant la période chaude de l'été. En revanche,N. fresenii est trouvé surtout en été etC. osmodes presque exclusivement en hiver.Z. phalloides montre une préférence marquée pour des h?tes tels queMyzus ascalonicus Donc. etTubaphis ranunculina Wlk.;E. planchoniana attaque préférentiellement les espèces du genreCavariella. Les profils dynamiques des différents pathogènes des pucerons les plus communs sont donnés et les particularités écologiques de chaque pathogène sont précisées; les situation épizootiques se manifestent exclusivement en présence de populations aphidiennes de haut niveau. Toutes les espèces agissent comme de bons facteurs de régulation et, saufN. fresenii, sont capables de se maintenir aux dépens de populations aphidiennes très basses et clairsemées.

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Summary The role of entomophthorosis in the dynamics of aphid populations infesting natural vegetation in northern littoral France (Basse-Normandie) and in northeastern continental France (Vosges) is compared. In Basse-Normandie, anholocyclic behavior of numerous aphid species contributes to the permanent presence of aphid populations and consequently, the persistence of mycosis. In the Vosges, severe winter, conditions result in holocyclic development whereby aphid colonies are present for only 6 to 7 months; during 1974 diseased specimens appeared when aphid populations were maximum, subsequent epizootic development caused a rapid decline of populations. In the 2 regions,Erynia neoaphidis Remaud. & Henn.,Entomophthora planchoniana Cornu,Neozygites fresenii (Nowak). Remaud. & Kell. andConidiobolus obscurus (Hall & Dunn) Remaud. & Kell. are most common. The frequent occurrence ofZoophthora phalloides Batko in littoral Normandy contrasts with an apparent rarity in the Vosges.Conidiobolus osmodes Drechsler is occasionally encountered in Normandy, but is not found in the Vosges.E. neoaphidis andE. planchoniana are present throughout the year. The former is most abundant in the spring, the latter in the autumn.C. obscurus andZ. phalloides seem better adapted to cooler spring and fall conditions as their occurrence is exceedingly rare during the host summer period. In contrast,N. fresenii is found in the summer whileC. osmodes almost always occurs in the winter.Z. phalloides appears to prefer such asMyzus ascalonicus Donc. andTubaphis ranunculina Wlk.;E. planchoniana prefersCavariella spp. Dynamic profiles of the various pathogens of the most common aphids at different times of the year are given; ecological features of each pathogen are described; epizootics only occur in high aphid populations. All species act as good regulating factor and, with the exception ofN. fresenii, persist in very low aphid populations.

     

Diatomées épilithiques et qualité biologique des ruisseaux du mont Stratonikon,Chalkidiki (Grèce)

During two sampling periods (lowflow and highflow) epilithic diatoms were collected in two hydrographic sectors of Stratonikon mountain. In the study 162 taxa were identified from which 42 species, one sub-species and nine varieties are first records for the Greek flora. Running waters present a high species richness and most of the dominant species found in the study area are cosmopolitan, alkaliphilous, prefering well oxygenated waters. The species Achnanthes minutissima var. minutissima, Amphora pediculus, Cocconeis placentula, Rhoicosphenia abbreviata, and Nitzschia dissipata var. dissipata were dominant during both sampling periods. Under highflow conditions, the species Gomphonema olivaceum var. olivaceum and G. tergestinum became also dominant. The Shannon's index values varied from 0.6 to 5.0 and evenness from 0.15 to 0.86. Dendrograms and MDS plots showed the floristic particularities of sites due to human activities and environmental conditions.The values of IPS diatomic index showed that the biological quality of the water was very good during the study period.     

Beltrania penzig : B. magnoliae sp. nov., avec clé d'identification des espèces

Beltrania Penzig : B. magnoliae sp. nov., with a taxonomic key to species. Beltrania magnoliae sp. nov., from decaying leaves of Magnolia gradiflora L. (Magnoliaceae) from south-west of France, is described in vivo and in vitro. It can be distinguished by having one kind of setae, straight sparsely verrucose, conidiophores often branched from the base, separating cells not observed in vivo. A taxonomic key to species in the genus is proposed.