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Head Capsule (head + capsule)
Selected AbstractsWHEN ONTOGENY REVEALS WHAT PHYLOGENY HIDES: GAIN AND LOSS OF HORNS DURING DEVELOPMENT AND EVOLUTION OF HORNED BEETLESEVOLUTION, Issue 11 2006Armin P. Moczek Abstract How ecological, developmental and genetic mechanisms interact in the genesis and subsequent diversification of morphological novelties is unknown for the vast majority of traits and organisms. Here we explore the ecological, developmental, and genetic underpinnings of a class of traits that is both novel and highly diverse: beetle horns. Specifically, we focus on the origin and diversification of a particular horn type, those protruding from the pronotum, in the genus Onthophagus, a particularly speciose and morphologically diverse genus of horned beetles. We begin by documenting immature development of nine Onthophagus species and show that all of these species express pronotal horns in a developmentally transient fashion in at least one or both sexes. Similar to species that retain their horns to adulthood, transient horns grow during late larval development and are clearly visible in pupae. However, unlike species that express horns as adults, transient horns are resorbed during pupal development. In a large number of species this mechanisms allows fully horned pupae to molt into entirely hornless adults. Consequently, far more Onthophagus species appear to possess the ability to develop pronotal horns than is indicated by their adult phenotypes. We use our data to expand a recent phylogeny of the genus Onthophagus to explore how the widespread existence of developmentally transient horns alters our understanding of the origin and dynamics of morphological innovation and diversification in this genus. We find that including transient horn development into the phylogeny dramatically reduces the number of independent origins required to explain extant diversity patters and suggest that pronotal horns may have originated only a few times, or possibly only once, during early Onthophagus evolution. We then propose a new and previously undescribed function for pronotal horns during immature development. We provide histological as well as experimental data that illustrate that pronotal horns are crucial for successful ecdysis of the larval head capsule during the larval-to-pupal molt, and that this molting function appears to be unique to the genus Onthophagus and absent in the other scarabaeine genera. We discuss how this additional function may help explain the existence and maintenance of developmentally transient horns, and how at least some horn types of adult beetles may have evolved as exaptations from pupal structures originally evolved to perform an unrelated function. [source] Interactions between the stem-mining weevils Ceutorhynchus napi Gyll. and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) in oilseed rapeAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2004Georg Dechert Abstract 1,The rape stem weevil Ceutorhynchus napi Gyll. and the cabbage stem weevil Ceutorhynchus pallidactylus (Marsh.) share the same habitat and food resource within the stems of oilseed rape, Brassica napus L. var. oleifera. Interactions occurring between these two sympatric species on this host were studied under both field and laboratory conditions. 2,The oviposition preference of C. pallidactylus and the within-plant distribution of eggs and larvae were examined in field plots of oilseed rape. Female C. pallidactylus tended to lay their eggs in plants already infested by eggs and larvae of C. napi rather than in uninfested plants. The within-plant distribution of the egg batches of C. pallidactylus did not differ significantly between uninfested plants and those preinfested by C. napi. Ovipositing females of C. napi and C. pallidactylus generally showed a significant preference for plants with larger stem diameter. 3,Laboratory choice tests provided further evidence for the oviposition preference of C. pallidactylus. Females laid significantly more eggs in leaves of plants that had been previously infested by C. napi than in leaves of previously uninfested plants. 4,Larvae of C. pallidactylus showed a significant shift of their feeding niche towards the stem base when feeding in individual plants attacked by both species. This possibly indicates ressource partitioning between C. pallidactylus and C. napi. The within-plant distribution of C. napi larvae was not affected by the simultaneous attack of C. pallidactylus. 5,The size of the head capsule of full-grown larvae of C. napi and C. pallidactylus was not significantly correlated with the diameter of the stem of their host plant or with the number of conspecific larvae within individual plants. [source] Short-term environmental changes in Lake Morenito (41°S, 71°W, Patagonia, Argentina) from the analysis of sub-fossil chironomidsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2005Julieta Massaferro Abstract 1.A short sediment core from Lake Morenito was studied to assess the impact of environmental changes on chironomid communities occurring during the last ca 100 yr. 2.Lake Morenito (41°S, 71°W) is located 20 km west of the city of Bariloche, in northern Patagonia, Argentina. Before 1960, this lake was a branch of Lake Moreno; by that time, an artificial dam closed the system, establishing the new lake. Another human disturbance that took place during the time span of the core was the introduction of salmonids to the area ca 1910. 3.The most important natural events that occurred in the area during the last 100 yr were related to volcanic episodes. One of them, occured in Chile in 1960 affecting the Argentinian side, coincided with the dam's construction. 4.Changes in the chironomid community were recorded by studying the sub-fossil remains (the chitinized head capsule of the larvae) present in the sedimentary sequence. The results show that volcanic tephra layers deposited along the core led to a sharp instantaneous drop in the diversity and abundance of chironomid assemblages. Human activities are also associated with a change in chironomid community composition. 5.Chironomus reached its maximum abundance values in 1910 and 1960. The organic matter content also increased at the same time. The increase of Chironomus after 1910 is clearly related to an increase in the trophic status of the lake. However, owing to the synchronicity of events in 1960, i.e. the volcanic event and the dam's construction, it is difficult to establish whether the change in the chironomid assemblage was in response to an increase in trophic enrichment, to natural disturbance, or both. Copyright © 2004 John Wiley & Sons, Ltd. [source] Interglacial Chironomidae (Diptera) from Thule, Northwest Greenland: matching modern analogues to fossil assemblagesBOREAS, Issue 4 2003KLAUS PETER BRODERSEN An analysis of subfossil insect remains (Diptera, Chironomidae) from an interglacial site at Narsaarsuk near Thule Air Base, NW Greenland, was undertaken to complement our understanding of last interglacial environments in the Arctic by analogue matching to modern chironomid assemblages. The subfossil larval midge head capsules were well preserved and 82% of the chironomid remains were identified as eight different extant chironomid taxa. The assemblage was dominated by the lotic Diamesa (43.8%), a number of lentic taxa (Hydrobaenus, Psectrocladius, Cricotopus/Orthocladius) and a few semi-aquatic taxa (Smittia, Chaetocladius). A single black fly head capsule (Diptera, Simuliidae) was registered. The interglacial sample was compared to subfossil chironomid assemblages from 42 lakes in West Greenland, two glacier lakes (with and without river influence) and a quantitative zoobenthos study from Narsaq Elv. Similarity analysis, analogue matching and multidimensional scaling suggest a lotic, cold, glacier-fed interglacial palaeo-biotope. Quantitative temperature reconstruction was not possible owing to a high dissimilarity to modern lentic chironomid assemblages from West Greenland. However, the simple numerical methods convincingly managed to reflect an interglacial river and stream environment, which can be difficult to document from other palaeoecological data. [source] Early Jurassic Coleopterans from the Mintaja Insect Locality, Western AustraliaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2010Sarah K. MARTIN Abstract: Beetles (Coleoptera) are the most common insects recovered from the Lower Jurassic Mintaja insect locality of Western Australia, with over half of the fossils recorded from this site being isolated coleopteran elytra. A range of partial beetle bodies and other isolated beetle sclerites have also been recovered from the locality; much of this material is taxonomically unidentifiable due to its disarticulation and poor preservation. A number of the Mintaja coleopterans are assigned to the archostematan family Ommatidae, including Zygadenia westraliensis (Riek, 1968) comb. nov, previously placed in the morphogenus Mesothoris, and an unnamed species of Tetraphalerus. Also recorded is a new species of elaterid, Lithomerus wunda sp. nov., along with other fragments likely attributable to the same family. The remaining material is assigned into morphospecies, separated primarily on preserved body parts , specifically, there are three morphospecies based on partially articulated coleopteran bodies, two morphospecies based on isolated head capsules, three morphospecies based on isolated thoracic sclerites, three morphospecies based on isolated abdominal sclerites, and 13 morphospecies based on isolated elytra. Overall, the ecology of these fossils is difficult to interpret due to poor preservation, although some of the beetles were likely aquatic, and the Ommatidae and Elateridae were both likely xylophilous. There is a strong similarity between the Mintaja coleopterans and those from the Late Triassic Denmark Hill locality of Queensland, though many of these similarities are based on morphotaxa and may be superficial in nature. Of the species that have been assigned to named taxa, all are generally typical of the Late Mesozoic worldwide, with Zygadenia, Tetraphalerus and Lithomerus all long-ranging, cosmopolitan genera. [source] | |||||||||||||