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The Influence of Dispersal Pattern On the Evolution of Fecundity
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A model was made of the effect of natural selection on fecundity within species and fecundity differences between species on the dynamics of a population. The population has a life history involving one pool of freely dispersing random mating adults and many local groups of competing juveniles. The adults disperse over the patches of juvenile food, and lay one clutch of eggs in a patch. The resulting sib competition leads to maximization of relative fitness at an intermediate ("optimal") fecundity. This optimal fecundity does not necessarily lead to superiority in interspecific competition. At optimal fecundity neither number of adults nor number of juveniles will be maximized. This is a consequence of individual selection from adult to next geueration adult opposing selection from juvenile to juvenile.
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The Development of a Mouth-Opening Mechanism in a Generalized Haplochromis Species: H. Elegans Trewavas 1933 (Pisces, Cichlidae)
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A system of staging has been devised, resolving the buccal development of the mouth-brooding cichlid fish Haplochromis elegans1 into 13 stages, with intervals increasing with age. A high resolution is required only when the rate of shape-change is high in younger animals. A reconstruction technique has been formulated producing rotated views of plastic embedded specimens. Of buccal development, stages 5 and 6 proved to be of special interest because of an important kinematical transition. This transition is relatively fast and demonstrates a synchrony in the development of elements constituting a mouth-opening mechanism. The effects of this transition on movement-patterns during respiration have been understood in the light of changes in the proportions of the head.
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Duration of the Developmental Stages and Timing of the End of the Reproductive Season of Pterostichus Oblongopunctatus (Fabricius) (Col., Carabidae) and Philonthus Decorus (Gravenhorst) (Col., Staphylinidae)
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The duration of the development of the pre-adult stages of Pterostichus oblongopunctatus and Philonthus decorus was investigated at different temperatures in the laboratory and in a field experiment. The development in the field was simulated using the relation between temperature and rate of development as observed in the laboratory. Comparison of the calculated and the observed duration of development was used to adjust the parameters. With the adjusted parameters it was possible to determine the exact period in which eggs would have to be laid if they were to complete their development before the winter period. It was concluded that in 1979 Pterostichus stopped laying eggs "in time", whereas Philonthus continued its egg production for about one month "too long". The results are discussed in relation to the life-strategies of these species.
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X-Ray Radiographic Examination of Dart Formation in Helix Aspersa
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Formation of the dart in the snail Helix aspersa occurs following loss of the dart during mating behavior. The new dart is formed during a period of 5-6 days within a dart sac lined with epithelium, and the stages of its development can be followed by x-ray radiography. CaCO3 deposition is initiated at the tip of a conical tubercle covered with epithelium and proceeds anteriorly forming a shaft with blades and then posteriorly with the formation of a flared region bearing pleated rods. The form of the dart appears to be governed by the conformation of the epithelium lining the dart sac. The calcium content of the dart is approximately 0.5 mg. The dart sac tissue (excluding the collar spherules) contains less than 5% of this amount, indicating that the calcium used for dart formation comes from other body or shell sources.
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Melanochromis Crabro Sp. Nov.: a Cichlid Fish From Lake Malawi Which Feeds On Ectoparasites and Catfish Eggs
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Melanochromis crabro sp. nov., a member of the "Mbuna" group, is described from Lake Malawi. It feeds upon a variety of foods, but appears to be adapted to feed on Argulus africanus, a branchiuran parasite commonly found on the catfish, Bagrus meridionalis. It is suggested that the host-cleaner association also facilitates an egg-stealing habit, since M. crabro robs B. meridionalis of its eggs which are laid on the substratum.
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Genetic Variation in the Pattern of Initial Oviposition Behaviour of Leptopilina Heterotoma Thomson (=Pseudeucoila Bochei Weld), a Parasite of Drosophila Melanogaster
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Females of the strains Leiden and Storrs and of the F 1 and F2 offspring of the cynipid wasp Leptopilina heterotoma Thomson (= Pseudeucoila bochei Weld) were compared in parasitization behaviour during 15 successive ovipositions in larvae of the fruit fly Drosophila melanogaster. Host mortality was high in the Leiden strain, low in the Storrs strain and intermediate in the F1. The F2 generations tended to their female parental strain, which indicates additive genetic effects on mortality. The success of reproduction estimated by the number of parasite eggs related to the number of larvae presented showed the same kind of variation between the strains. The strains did not differ in mean duration of searching before oviposition. Experience obtained during the successive parasitizations did not influence the mean searching time. A number of larvae was not accepted for oviposition by the wasps in all groups. The rejection frequency increased in all groups during the experiment; probably by the improvement of the capacity to examine the host. The duration of an oviposition act decreased during the experiment in all groups. The sequences of two ovipositions resulting in dead larvae (D-D) or living larvae (L-L) were more frequent than might be expected, except for the Storrs strain. The clustering was related to the experience obtained. Preening of abdominal parts was more frequent in the Storrs- than in the Leiden strain. It appeared to be an element of the oviposition behaviour and occurred most frequently immediately upon an oviposition act and in particular if the larva stayed alive. Frequencies of preening in the hybrid generations may be explained by dominance of the high preening tendency in the Storrs strain.
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Etude Morphologique Des Pterygopodes De Alopias Vulpinus (Bonnaterre, 1788) (Pisces, Alopiidae)
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L'armature squelettique des ptérygopodes de Alopias vulpinus (Bonnaterre, 1788) est composée de trois cartilages: "stem" ou axial, terminal externe et terminal interne.
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Early Parasitation of Oak-Apple Galls (CΥNips Quercusfolii L., Hymenoptera)
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Early parasitation of oak-apple galls may lead to an aberrant appearance. It induces a food-web similar to that of Cynips divisa Hartig rather than to normal galls of Cynips quercusfolii L.
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Photoperiodic Response Curve for ΥPonomeuta Vigintipunctatus (Retz.) (Lepidoptera: Yponomeutidae)
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Yponomeuta vigintipunctatus exhibits a facultative diapause in the pupal stage. Induction of diapause is governed by photoperiod, and the photoperiodic reaction is of the long-day type. The critical daylength of the Dutch strain tested is 17 hr at 19° C. Ecological implications of the photoperiodic response found in this strain are briefly discussed.
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