Early exposure to predation risk carries over metamorphosis in two distantly related freshwater insects

1. Predation and competition play a central role in ecological communities, and it is increasingly recognised that animals use early warning cues to reduce the impact of these antagonistic interactions. 2. Strategies to avoid risk can occur during embryo development through plasticity in egg hatching time. This strategy, and its associated costs and carryover effects on adults are little understood in insects. In this study, these are explored in two distantly related freshwater insects: the damselfly Ischnura elegans and the mosquito Aedes albopictus. 3. As predicted, damselfly eggs hatched earlier in response to larval predators cues, a treatment that also affected adult size. Risk cues did not affect mosquito egg hatching time, but they did affect larval development time in a sex‐dependent manner. 4. The results suggest that responses aimed at avoiding risks can be triggered during the egg stage, and although they can vary dramatically among species, they are likely to be widespread in insects. Early warning responses can be particularly important to understand the ecology of aquatic insects, some of them global vectors of human diseases.     

Sharing the same space: foraging behaviour of saproxylic beetles in relation to dietary components of morphologically similar larvae

1. Saproxylic beetles (Coleoptera) have particular requirements for dead wood. Little is known about their larval development, especially within intermediate and late stages of dead wood decay. 2. We studied the natural foraging behaviour of three saproxylic beetles with morphologically similar (i.e. convergent) larvae and similar habitat requirements –Cucujus cinnaberinus Scopoli (Cucujidae), Pyrochroa coccinea L., and Schizotus pectinicornis L. (Pyrochroidae) – examining dietary components using visual gut content analysis. 3. There were few significant differences in diet among the study species, but there were significant differences for the different dietary components in individual species. Guts of all three species included more plant and fungal material than animal. We also observed that with increasing body size larvae foraged significantly less on fungal material. We observed significant differences among species and selection with respect to body size during the overwintering period. Larvae swallowed more animal and less fungal material with increasing body size. 4. The study species seem to be opportunistic foragers, varying their foraging capability according to seasonality and age. They probably generally foraged woody material infested by filamentous fungi (i.e. xylomycetophagy), swallowing other material that is in their way while foraging, including animal parts and small arthropods. 5. We found that morphologically similar larvae do not differ much in their foraging behaviour even when sharing the same habitat. Larval size seems to be a useful predictor for foraging behaviour of saproxylic beetles within the same guild. The study species are probably occasional predators with less ability to forage on other animals than previously suggested.     

Trophic specialization in Arctic charr Salvelinus alpinus (Pisces; Salmonidae): morphological divergence and ontogenetic niche shifts

Lake Thingvallavatn supports four trophic morphs of Arctic charr, Salvelinus alpinus (L.); two of the morphs are benthic (small and large benthivorous charr) one exploits pelagic waters (planktivorous charr) and the fourth is found in both habitats (piscivorous charr). The morphological variation among these morphs was analysed by use of principal component analysis and canonical discriminant analysis. The benihic morphs have a short lower jaw and long pectoral fins. The benthic fish also have fewer gillrakers than the other morphs. Small and large benthivorous charrs attain sexual maturity from 2 and 6 years of age, and at fork lengths from 7 and 22 cm, respectively. Small benthivorous charr retain their juvenile parr marks as adults, have beige ventral colours, and are frequently melanized under the lower jaw. Planktivorous and piscivorous charr attain sexual maturity from 4 and 6 years of age, from fork lengths of 15 and 23 cm, respectively. This phenotypic polymorphism is associated with habitat utilization and diet of the fish, and has probably arisen within the lake system through diversification and niche specialization. The pelagic morphs apparently stem from a single population, and are possibly diversified through conditional niche shifts which affect ontogeny. Juveniles reaching a body length of 23 cm may change from zooplankton to fish feeding. Asymptotic length increases thereby from 20.5 cm in planktivorous charr to 30.2 cm in piscivorous charr. The benthic morphs appear to represent separate populations, although both feed chiefly on the gastropod Lymnaea peregra. Their co-existence seems to be facilitated by size dependent constraints on habitat use. The small morph (asymptotic length 13.3 cm) exploit the interstitial crevices in the lava block substratum, whereas the large morph (asymptotic length 55.4 cm) live epibenthically.