THE EFFECTS OF STEADY AND CYCLING TEMPERATURES ON THE ACTIVITY OF THE SLUG DEROCERAS RETICULATUM

At constant temperatures, crawling activity in the slug Derocerasreticulatum has an optimum at 13°C in late winter, and 17°Cin early summer. The optimum for feeding remains at 14°C.Activity has anendogenous basis, but daytime activity increaseswith temperature and long daylengths. Cycling temperatures producemore locomotor activity and less feeding in 24 h than constanttemperatures, even when the temperature is higher at night.However, cooling stimulates and warming inhibits activity duringthe period of change and when cooling occurs at dusk, over halfthe 24 h activity occurs in the next three hours. Faster ratesof cooling produce greater responses, but can result in loweroverall activity because the slugs remain longer at low temperatures. (Received 25 May 1984;     

Ecological,morphological and genetic divergence of sympatric North Atlantic killer whale populations

Ecological divergence has a central role in speciation and is therefore an important source of biodiversity. Studying the micro‐evolutionary processes of ecological diversification at its early stages provides an opportunity for investigating the causative mechanisms and ecological conditions promoting divergence. Here we use morphological traits, nitrogen stable isotope ratios and tooth wear to characterize two disparate types of North Atlantic killer whale. We find a highly specialist type, which reaches up to 8.5 m in length and a generalist type which reaches up to 6.6 m in length. There is a single fixed genetic difference in the mtDNA control region between these types, indicating integrity of groupings and a shallow divergence. Phylogenetic analysis indicates this divergence is independent of similar ecological divergences in the Pacific and Antarctic. Niche‐width in the generalist type is more strongly influenced by between‐individual variation rather than within‐individual variation in the composition of the diet. This first step to divergent specialization on different ecological resources provides a rare example of the ecological conditions at the early stages of adaptive radiation.     

Can intra‐specific genetic variation in arbuscular mycorrhizal fungi (Glomus etunicatum) affect a mesophyll‐feeding herbivore (Tupiocoris notatus Distant)?

Abstract.  1. Arbuscular mycorrhizal fungal (AMF) infection can have negative, positive or neutral effects on insect herbivore populations, but patterns are difficult to predict.
2. Intra-specific genetic variation in nutrient uptake ability between fungal isolates may also have indirect effects on insect herbivores due to changes in plant quality. In preliminary studies mirid ( Tupiocoris notatus ) populations were significantly reduced on tobacco ( Nicotiana rustica ) colonised by AMF but it was unknown if same-species fungal isolates differed in their effect.
3. An experiment was performed as a first test of the effect of intra-specific genetic variation in the mycorrhizal fungus Glomus etunicatum on mirid nymphal population structure, dynamics, and growth rate.
4. Mirid nymphal populations were lower on mycorrhizal fungal-infected plants. Population size, however, did not differ between the mycorrhizal isolates. While no statistical difference in population between isolates was found, one isolate consistently had 1.7–2.4 times lower mirid populations compared with the controls, indicating that the magnitude of effect is different between mycorrhizal isolates.
5. The significantly negative effect of AMF on mirid populations likely resulted from AMF-induced changes in plant quality (e.g. increased defence). This study lends further support to recent demonstrations that below-ground symbionts significantly influence above-ground processes. In addition, mycorrhizal fungi can affect insect population structure, which may have consequences for future herbivory.