LOPHOSTEUS SUPERBUS PANDER, EIN TELEOSTOME AUS DEM SILUR OESELS

Numerous scales as well as fragments of spines and bones of Lophosteus superbus Pander 1856, a fish which has not been re-studied since 1893, were found in a rock specimen of Ohesaare Beds (marine Downtonian) from the Isle of Oesel (Estonia). The various remains have been studied morphologically and histologically. The structure of the remains demonstrates the close relationship of L. superbus with Andreolepis hedei Gross 1968. Both genera have been placed in the new family Lophosteidae and the new order Lophosteiformes. The position of this order within the Teleostomi will remain unclear until connected remains or intact fish specimens are found. The scales of both genera indicate a possible connection with the Actinopterygii. In addition, the morphology and histology of some bone fragments covered with small teeth and tubercles are described. These fragments may also belong to L. superbus.
Schuppen und Bruchstücke von Stacheln und Knochen des seit 1893 nicht mehr untersuchten Fisches Lophosteus superbus Pander 1856 wurden zahlreich in einem Handstück der Ohesaare Schichten (marines Downton) der Insel Oesel (Estland) gefunden. Die verschiedenen Reste wurden morphologisch und histologisch untersucht. Intakte Schuppen und der histologische Bau der Reste erwiesen die nahe Verwandschaft von L. superbus mit Andreolepis hedei Gross 1968. Beide Gattungen wurden in der neuen Familie der Lophosteidae und der neuen Ordnung Lophosteiformes vereinigt, deren Stellung innerhalb der Teleostomi (Osteichthyes) unklar bleibt, solange keine zusammenhängenden Fischreste oder intakte Fische gefunden werden. Die Schuppen beider Gattungen weisen auf mögliche Beziehungen zu den Actinopterygiern. – Angefügt wird die morphologische und histologische Beschreibung einiger Knochenreste, die mit zahlreichen konischen Zähnchen und Tuberkeln pflasterförmig besetzt sind. Vielleicht gehören auch diese Reste zu L. superbus.     

Social control of egg-laying rate in queens of the fire ant, Solenopsis invicta*

ABSTRACT Social control of egg-laying rate in queens of the fire ant (Solenopsis invicta Buren) was studied by experimental manipulation of the number of larvae, pupae and workers in colonies, and the age and size of larvae and workers. Workers and pupae do not stimulate oviposition by queens. The number of fourth instar larvae, on the other hand, bears a positive log-log relationship to the queen's egg-laying rate. Such larvae are needed both to stimulate and maintain oviposition. Their withdrawal results, within 48 h, in a decline in queen oviposition almost to zero. Their addition to broodless nests results in peak laying in about 4 days. Larvae in the first three stadia and early in the fourth stadium have a much lower effect upon queen fecundity. Sexual larvae are only c. 5% as stimulating on a weight basis, but equivalent on an individual basis. Several associated measures are positively correlated to egg-laying rate: weight of the queen, the number of her vitellogenic follicles per ovariole, total vitellogenic follicles, the time she spends feeding and (usually) the number of workers in the retinue that cares for her. The egg volume is negatively correlated with laying rate, so that queens lay more eggs for the same expenditure of material as laying rate increases. As body size of workers increases, they become less effective in transmitting the larval stimulation to the queen, but worker age has no effect on this ability. For a given number of larvae, queens in small, naturally growing colonies lay fewer, larger eggs than do queens in experimental colonies, but their fecundity increases more rapidly in relation to number of larvae. When larvae are fed vital-dyed food in one experimental colony, and then transferred to an undyed colony, the dye is rapidly transferred to worker crops, and into the queen's eggs, indicating bulk movement of material from larvae to workers to the queen and eggs. Large larvae are more effective at this than small larvae. Fourth instar larvae may be a digestive and metabolic caste that processes protein for egg production by the queen. If that is the case, the queen and fourth instar larvae are linked in a positive feedback loop. Either the logarithmic relation of fecundity to larval numbers or physical limits of the queen may set the maximum egg-laying rate, and thus determine maximum colony size. The data do not allow a clear choice between these alternatives.     

Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden

1. Plants from different populations often display a variation in herbivore resistance. However, it is rarely understood what plant traits mediate such differences. 2. It was tested how leaf phenology affects herbivore populations in a 15‐year‐old common garden of valley oaks (Quercus lobata Née) with different populations and maternal parents from throughout the Q. lobata range. 3. The abundance of leaf miners (Stigmella sp. Shrank) and leaf phenology of oaks in the common garden was measured. 4. Leaf miner abundance varied among provenance locations (population), but not among maternal parents within populations. Leaf phenology varied by provenance location and maternal parent, and trees that leafed out earlier accrued higher leaf‐miner abundance. Path analysis indicated that leaf phenology was the likely driver of provenance and parental differences in resistance to leaf miners. 5. Understanding population differences is particularly important when considering transport of genotypes for ornamental or restoration purposes. The present study suggests that similarity in leaf phenology may be one factor that could be used to find genotypes with a similar herbivore resistance to local genotypes.     

Promitosis and Rod Occurrence in the Limax Ameba Vahlkampfia lobospinosa*

SYNOPSIS. Nuclear division and trophozoite structure and function were investigated in Vahlkampfia lobospinosa. During karyokinesis the nucleolus remained present and divided to form polar masses. Chromatids separated and were directed to the polar masses by spindle fibers within an intact nuclear membrane. No interzonal body was formed. Trophozoites consistently contained and extruded a rod-like structure 10–15 × 1–2 μm. Although it was found in other areas of the cell within the cytoplasm, this rod most frequently protruded from the uroid.