Altitudinal differentiation in the diapause response of two species of dung flies

1. Seasonality is a prime selective factor promoting genetic differentiation of populations. Local adaptation in diapause response was investigated in the two geographically and altitudinally widespread dung flies Scathophaga stercoraria (Diptera: Scathophagidae) and Sepsis cynipsea (Diptera: Sepsidae).
2. Replicate sibships from three sites in Switzerland with low and high altitude dung fly populations were raised in a common laboratory environment simulating the natural decreasing photoperiod and temperature regimen before winter. From field phenologies, the critical photoperiod inducing diapause was predicted to be longer for high than for low altitude populations (12 vs. 10 h for Sc. stercoraria , and 12.25 vs. 11 h for Se. cynipsea ) if they are locally adapted.
3. Contrary to expectation and to Sc. stercoraria , which diapauses in the pupal stage, Se. cynipsea diapauses in the adult stage.
4. Low but significant levels of genetic differentiation in pre-winter adult emergence were evident between low and high altitude populations of both species, but they were far from the differences predicted. Scathophaga stercoraria also showed geographical differentiation independent of altitude.
5. Sepsis cynipsea females stopped reproducing at some point before winter, but altitude did not affect the timing of adult diapause. High altitude females and females that did not initiate reproduction before winter survived the simulated winter better.
6. Both species largely used temperature rather than photoperiod as a cue inducing winter diapause, an untypical case of phenotypic plasticity. The hypothesis that Sc. stercoraria , whose generation times are much longer than those of Se. cynipsea , responds to a greater extent to temperature rather than photoperiod only was rejected.     

Occurrence and Significance of Vitellogenins in Female Castes of Social Hymenoptera

A female specific protein is found in queens, workers, and gvnandromorphsof several species of social Hymenoptera. Possibly it is presentalso in experimentally produced diploid males, but it couldnot be found in normal haploid drones. A high tiler of the femalespecific protein (vitellogenin) is found in the hemolymph ofhoneybee queens during periods of oviposition and even duringperiods when no eggs are laid. A high titer is also observedin egg-laying workers of the honeybee and the stingless bees.Rates of synthesis of vitellogenin are negatively correlatedwith the concentration in the hemolymph. In nursing workersrates of vitellogenin synthesis are twice as high as in egg-layingworkers. In non-laying workers vitellogenin normally only occurs in thehemolymph of nursing workers; this period of nursing is moreextended in A. florea than in A. mellifica, a fact which maysignal a more primitive level of female caste differentiationin A. florea. Aspects of genetic, endocrine, and social regulationof vitellogenin synthesis are discussed.     

Ontogeny of cephalic volatile patterns in queens and mating biology of the neotropical stingless bee,Scaptotrigona postica

Summary

Chemical communication is an ancient yet still immensely important part of reproduction. Amongst all invertebrates, the most sophisticated “chemical languages” are used by social insects. Here the sex- and caste-specific pheromonal messages consist of multicomponent mixtures. In the neotropical stingless bee Scaptotrigona postica, an inhabitant of dense tropical rain forests, the cephalic volatiles of a queen transmit information on her reproductive status to males. A distinct ontogenetic pattern of the queen pheromone composition allows drones to discriminate receptive virgins which are then chased during the short nuptial flight through the forest understorey. By means of gas chromatographic/mass spectroscopic analyses, the numerous volatile compounds found in pentane extracts of individual bee heads could be identified. Qualitative as well as quantitative changes of these volatiles in the course of imaginal development could be determined, and bioassays with synthetic compounds were undertaken in order to decode the chemical signals used during the short encounter of a young queen and her mate.     

Myxosoma cerebralis (Myxozoa: Myxosporea) Etiologic Agent of Salmonid Whirling Disease Requires Tubificid Worm (Annelida: Oligochaeta) in its Life Cycle

Studies of the life cycle of Myxosoma cerebralis showed that development of infectivity did not occur endogenously but that the spore “aging” process required participation of an aquatic tubificid oligochaete. Data suggestive of such involvement were derived from trials in which spores were “aged” in an array of inert, sterilized, pasteurized, or natural aquatic substrates and from examination of aquatic soils from trout hatcheries in which whirling disease was epizootic. The role of the aquatic oligochaete was confirmed two ways. First, signs of whirling disease developed, and M. cerebralis spores were produced in young rainbow trout (Salmo gairdneri) that had been fed oligochaetes harvested from pond soil taken from two hatcheries where whirling disease was epizootic. Second, when containers of pasteurized soil were populated with four genera of oligochaetes–Aeolosoma, Dero, Stylaria, or Tubifex– from a biological supply house, or with tubificid worms from trout hatcheries free of whirling disease, and then seeded with M. cerebralis spores and “aged” for 4 months, whirling disease occurred only in trout held with Tubifex and with hatchery tubificids.     

QUANTIFICATION OF THE SINUSOIDAL TRAJECTORY IN TISSUE MASS AND CONDITION INDICES OF A BIVALVE (EGERIA RADIATA) IN THE CROSS RIVER, NIGERIA

Variation in monthly values of dry tissue mass (DTM) and twodifferent types of condition indices of the bivalve Egeria radiata(Lamarck, 1804) was studied for 32 consecutive months. To quantifythe seasonal trajectory of variation these data were fittedto one- and two-compartment sinusoidal models; and also to aquadratic, cubic and quartic models. The cyclic events in thevariation of the DTM and both indices of condition were adequatelydescribed by the one-compartment sinusoidal model whose parametersare biologically interpretable. The fit of the data is progressivelyimproved as one moves from the quadratic through the cubic tothe quartic model whose fit was best. Although biological meaningcould be found for the one-compartment sinusoidal model, thebiological meaning of the coefficients of the parabolic-basedmodels are obscure. Multiple regression analysis shows thatof all the four environmental parameters (temperature, salinity,pH and phytoplankton) tested, temperature has the greatest effecton DTM and one of the condition indices, while pH has the greatestimpact on the other condition index. This implies that the twoindices are not only intrinsically different, but that theyrespond to different sets of factors. Inter- and intra-specificcomparison of the many recommended ‘standard’ indicesof condition found in the literature, especially with regardto their innate sensitivity to seasonal variation in internal(e.g. state of gravidity) and external (physicochemical parametersof water) factors is necessary. (Received 1 May 1996; accepted 30 August 1996)