Potential for Powered Flight Neared by Most Close Avialan Relatives,but Few Crossed Its Thresholds

Media player

Status and Breeding Sites of Three Presumed Endangered Scottish Saproxylic Syrphids (Diptera, Syrphidae)

From 1987 to 1999 efforts were made to understand the status and breeding sites of three presumed endangered flies in Britain: Blera fallax (Linnaeus), Hammerschmidtia ferruginea (Fallén) and Callicera rufa Schummel (Diptera, Syrphidae). Historical data on flight periods, localities and breeding sites were collated from the literature and captured specimens in museums and other collections. Using these data, life cycles were investigated, and cited and other localities searched for adults and early stages. Looking for early stages was more productive than looking for adults. B. fallax is the most endangered. It has declined in abundance, is restricted to two localities and, in 1999, breeding sites were destroyed at one of these localities. In contrast C. rufa is widespread and not uncommon throughout northern Scotland. H. ferruginea is not as endangered as B. fallax but adverse factors such as habitat destruction affect most of its sites.     

A rapid altitudinal range expansion in the pine processionary moth produced by the 2003 climatic anomaly

Climatic anomalies may produce, or accelerate, geographic range expansions of species limited by temperature or other climatic variables. Most such expansions are only temporary, before the prevailing climatic conditions drive the founder populations extinct. In contrast, here, we report a recent rapid shift of the range limit during the record hot summer of 2003 in southern Europe that has the potential to be both permanent, and to have important implications on species range dynamics in general. The winter pine processionary moth (Thaumetopoea pityocampa), an important pine defoliator whose larvae feed in colonies during the winter, is limited in its distribution by winter temperatures. In the last three decades, warmer winters have led to a gradual but substantial expansion of its range both latitudinally and altitudinally. In the summer of 2003, T. pityocampa underwent an extraordinary expansion to high elevation pine stands in the Italian Alps; its altitudinal range limit increased by one third of the total altitudinal expansion over the previous three decades. In an experiment, we found flight activity of newly emerged females to increase with temperature. By determining a threshold temperature for flight take‐offs under controlled conditions, we calculated that the nights above the threshold temperature were over five times more frequent, and considerably warmer, at the range limit in 2003 than in an average year. We therefore attribute the colonization of extreme, high‐elevation sites to increased nocturnal dispersal of females during the unusually warm night temperatures in June – August 2003. Importantly, the colonies established at extreme sites survived the winter and produced offspring in 2004, although the range did not expand further because of low night temperatures that year. We discuss several life‐history characteristics of T. pityocampa that maximize the likelihood of population persistence at the new range limit. As global warming continues and climatic anomalies are predicted to become more frequent, our results draw attention to the importance of extreme climatic events in the range formation of phytophagous insects.     

Stable isotopes identify dispersal patterns of stonefly populations living along stream corridors

1. Populations in different locations can exchange individuals depending on the distribution and connectivity of suitable habitat, and the dispersal capabilities and behaviour of the organisms. We used an isotopic tracer, ¹⁵N, to label stoneflies (Leuctra ferruginea) to determine the extent of adult flight along stream corridors and between streams where their larvae live. 2. In four mass, mark‐capture experiments we added ¹⁵NH₄Cl continuously for several weeks to label specific regions of streams within the Hubbard Brook Experimental Forest, NH, U.S.A. We collected adult stoneflies along the labelled streams (up to 1.5 km of stream length), on transects through the forest away from labelled sections (up to 500 m), and along an 800‐m reach of adjacent tributary that flows into a labelled stream. 3. Of 966 individual adult stoneflies collected and analysed for ¹⁵N, 20% were labelled. Most labelled stoneflies were captured along stream corridors and had flown upstream a mean distance of 211 m; the net movement of the population (upstream + downstream) estimated from the midpoint of the labelled sections was 126 m upstream. The furthest male and female travelled approximately 730 m and approximately 663 m upstream, respectively. We also captured labelled mature females along an unlabelled tributary and along a forest transect 500 m from the labelled stream, thus demonstrating cross‐watershed dispersal. 4. We conclude that the adjacent forest was not a barrier to dispersal between catchments, and adult dispersal linked stonefly populations among streams across a landscape within one generation. Our data on the extent of adult dispersal provide a basis for a conceptual model identifying the boundaries of these populations, whose larvae are restricted to stream channels, and whose females must return to streams to oviposit.     

Sexual dimorphism in the pyrgomorphid grasshopper Phymateus morbillosus: from wing morphometry and flight behaviour to flight physiology and endocrinology

Abstract In the field, adult males of the grasshopper Phymateus morbillosus are able to fly for up to 1 min and cover up to c. 100 m, whereas females, although fully winged, are apparently unable to get airborne. Morphometric data indicate that the males are lighter, have longer wings, a higher ratio of flight muscles to body mass, and a lower wing load value than females. It was investigated whether this inability of females to fly is related to fuel storage, flight muscle enzymatic design and/or the presence and quantitative capacity of the endocrine system to mobilize fuels. In both sexes, readily available potential energy substrates are present in the haemolymph in similar concentrations, and the amount of glycogen in flight muscles and fat bodies does not differ significantly between males and females. Mass-specific activities of the enzymes GAPDH (glycolysis), HOAD (fatty acid oxidation) and MDH (citric acid cycle) in flight muscles are significantly lower in females compared with males, and mitochondria are less abundant in the flight muscles of females. There is no significant difference between the ability of the two sexes to oxidize various important substrates. Both sexes contain three adipokinetic peptides in their corpora cardiaca; the amount of each peptide in female grasshoppers is higher than in males.
Thus, despite some differences listed above, both sexes appear to have sufficient substrates and the necessary endocrine complement to engage in flight. It seems more likely, from the morphometric data above, that the chief reason for flightlessness is that P. morbillosus females cannot produce sufficient lift for flight; alternatively, the neuronal functioning associated with the flight muscles may be impaired in females.     

The implications of function on the origin and homologies of the dipterous wing

Abstract The origin of Diptera, and the homologies of the dipteran wing, are re-examined in the light of recent studies on the flight biomechanics and functional wing morphology of Diptera and of Panorpa. Significant Diptera apomorphies are identified, relevant fossils discussed, and a hypothetical wing ground-plan figured.
The arculus, the modified clavus and the anteroposterior asymmetry of the fly wing seem to be adaptations to a mode of flight in which instantaneous wing pitch and camber are controlled automatically, rather than by muscular action; probably in association with the development of asynchronous power musculature.
Tillyard's Cu2 (=CUP) is believed to be a secondary pseudo-vein, his 1A to be the true CuP and 2A to be 1A.
The late Permian fossil Permotipula Patricia is almost certainly a member of the Diptera stem-group, possibly even of the crown-group. The Mesozoic Laurentipteridae and the Permian Permotanyderidae are other possible, but not certain, stem-group members.