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      One proboscis, two tasks: Adaptations to blood-feeding and nectar-extracting in long-proboscid horse flies (Tabanidae, Philoliche)

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          Abstract

          Female Pangoniinae in the tabanid fly genus Philoliche can display remarkably elongated proboscis lengths, which are adapted for both blood- and nectar-feeding. Apart from their role as blood-sucking pests, they represent important pollinators of the South African flora. This study examines the morphology of the feeding apparatus of two species of long-proboscid Tabanidae: Philoliche rostrata and Philoliche gulosa – both species display adaptations for feeding from a diverse guild of long-tubed flowers, and on vertebrate blood. The heavily sclerotised proboscis can be divided into two functional units. The short, proximal piercing part is composed of the labrum-epipharynx unit, the hypopharynx and paired mandible and maxilla. The foldable distal part is composed of the prementum of the labium which solely forms the food canal and is responsible for nectar uptake via the apical labella. The proboscis works as a drinking straw, relying on a pressure gradient provided by a two-part suction pump in the head. Both proboscis and body lengths and suction pump dimensions show a significantly correlated allometric relationship with each other. This study provides detailed insights into the adaptations for a dual diet using an elongated sucking proboscis, and considers these adaptations in the context of the evolution of nectar feeding in Brachycera.

          Highlights

          • The proboscis of female long-proboscid Philoliche consists of two functional units.

          • This proximal region composes the piercing, blood sucking part of the mouthparts.

          • Only the distal proboscis is adapted to feeding nectar from long-spurred flowers.

          • Body and proboscis length show a significant positive relationship in Philoliche rostrata.

          • Suction pump size and proboscis length show a significant positive relationship.

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          Most cited references55

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          Pollinator shifts drive increasingly long nectar spurs in columbine flowers.

          Directional evolutionary trends have long garnered interest because they suggest that evolution can be predictable. However, the identification of the trends themselves and the underlying processes that may produce them have often been controversial. In 1862, in explaining the exceptionally long nectar spur of Angraecum sesquipedale, Darwin proposed that a coevolutionary 'race' had driven the directional increase in length of a plant's spur and its pollinator's tongue. Thus he predicted the existence of an exceptionally long-tongued moth. Though the discovery of Xanthopan morgani ssp. praedicta in 1903 with a tongue length of 22 cm validated Darwin's prediction, his 'race' model for the evolution of long-spurred flowers remains contentious. Spurs may also evolve to exceptional lengths by way of pollinator shifts as plants adapt to a series of unrelated pollinators, each with a greater tongue length. Here, using a species-level phylogeny of the columbine genus, Aquilegia, we show a significant evolutionary trend for increasing spur length during directional shifts to pollinators with longer tongues. In addition, we find evidence for 'punctuated' change in spur length during speciation events, suggesting that Aquilegia nectar spurs rapidly evolve to fit adaptive peaks predefined by pollinator morphology. These findings show that evolution may proceed in predictable pathways without reversals and that change may be concentrated during speciation.
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            An uncorrelated relaxed-clock analysis suggests an earlier origin for flowering plants.

            We present molecular dating analyses for land plants that incorporate 33 fossil calibrations, permit rates of molecular evolution to be uncorrelated across the tree, and take into account uncertainties in phylogenetic relationships and the fossil record. We attached a prior probability to each fossil-based minimum age, and explored the effects of relying on the first appearance of tricolpate pollen grains as a lower bound for the age of eudicots. Many of our divergence-time estimates for major clades coincide well with both the known fossil record and with previous estimates. However, our estimates for the origin of crown-clade angiosperms, which center on the Late Triassic, are considerably older than the unequivocal fossil record of flowering plants or than the molecular dates presented in recent studies. Nevertheless, we argue that our older estimates should be taken into account in studying the causes and consequences of the angiosperm radiation in relation to other major events, including the diversification of holometabolous insects. Although the methods used here do help to correct for lineage-specific heterogeneity in rates of molecular evolution (associated, for example, with evolutionary shifts in life history), we remain concerned that some such effects (e.g., the early radiation of herbaceous clades within angiosperms) may still be biasing our inferences.
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              When is it Coevolution?

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                Author and article information

                Contributors
                Journal
                Arthropod Struct Dev
                Arthropod Struct Dev
                Arthropod Structure & Development
                Elsevier Science Ltd
                1467-8039
                1873-5495
                1 September 2014
                September 2014
                : 43
                : 5
                : 403-413
                Affiliations
                [a ]Department of Integrative Zoology, University of Vienna, Faculty of Life Science, Althanstrasse 14, 1090 Vienna, Austria
                [b ]South African National Biodiversity Institute, Kirstenbosch Research Centre, Private Bag X7, Claremont, Cape Town, South Africa
                [c ]VetCore Facility for Research, University of Veterinary Medicine, Vienna, Austria
                [d ]Department of Theoretical Biology, University of Vienna, Faculty of Life Science, Althanstrasse 14, 1090 Vienna, Austria
                Author notes
                []Corresponding author. Department of Integrative Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria. Tel.: +43 1 4277 54519; fax: +43 1 4277 9544. florian.karolyi@ 123456univie.ac.at
                Article
                S1467-8039(14)00067-X
                10.1016/j.asd.2014.07.003
                4175409
                25066540
                8fbaa83c-b254-4fe3-a895-6b5c44295a40
                © 2014 The Authors
                History
                : 27 May 2014
                : 9 July 2014
                Categories
                Article

                Developmental biology
                diptera,philoliche,functional morphology,blood sucking,nectar-feeding,mouthparts
                Developmental biology
                diptera, philoliche, functional morphology, blood sucking, nectar-feeding, mouthparts

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