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      Moth versus fly: a preliminary study of the pollination mode of two species of endemic Asteraceae from St Helena ( Commidendrum robustum and C. rugosum ) and its conservation implications

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          Abstract

          Commidendrum robustum (Roxb.) DC. (St Helena gumwood) and C. rugosum (Dryand.) DC. (St Helena scrubwood) are ecologically important, endemic woody Asteraceae from the isolated South Atlantic island of St Helena. Once very abundant, they now exist in sparse fragmented populations due to 500 years of environmental destruction. They are sister taxa that evolved on the island and are reported to hybridise. Commidendrum rugosum has a saucer-like erect capitulum, whereas C. robustum has a somewhat globular hanging capitulum. Using daytime timelapse photography to follow capitula through their life cycle, we found that C. rugosum appears to be myophilous, visited largely by flies (including the endemic syrphid, Sphaerophoria beattiei Doesburg & Doesburg) and occasionally by Lepidoptera . Commidendrum robustum , on the other hand, although visited by flies, strongly attracts moths (especially noted at the Millennium Forest site). Our data suggest that moth visits may reduce visits from flies due to the sensitivity of flies to interference by other insects. We conclude that C. robustum may have a mixed syndrome of myophily/phalaenophily and that there is apparently some divergence of the pollination niche between the two species. Its potential in attracting moths, coupled with its former abundance, suggests that it may have been a major food source for adults of the numerous endemic moths. Pollinator activity was measured by insect visitation rates (mean visits per capitulum per day, V) and insect residence time (mean pollinator kiloseconds per capitulum per day, R). Both are higher for C. robustum ( C. rugosum , V = 16.4, R = 3.101; C. robustum , V = 34.0, R = 8.274), reflecting the abundance of moths on the capitula at the Millennium Forest site. The conservation implications of the pollination mode are that: (1) there is considerable pollinator activity on the capitula and pollination is not currently a limiting factor for plant reproduction; (2) gene exchange between geographically-isolated populations of C. rugosum is likely to be minimal due to the apparent reliance of the species for pollination on small flies (especially Sphaerophoria beattiei ), which are believed to be not effective as pollinators over long distances (> 1 km). A possible exception is the strong-flying drone-fly, Eristalis tenax Linn. which, although not as abundant as Sphaerophoria , does visit the flowers; (3) there is considerable overlap between the two species in flower visitors and interspecific pollen transfer is possible where the two species grow intermixed (which has potential positive and negative implications for species survival).

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          Most cited references 19

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          Hybridization and extinction

          Abstract Hybridization may drive rare taxa to extinction through genetic swamping, where the rare form is replaced by hybrids, or by demographic swamping, where population growth rates are reduced due to the wasteful production of maladaptive hybrids. Conversely, hybridization may rescue the viability of small, inbred populations. Understanding the factors that contribute to destructive versus constructive outcomes of hybridization is key to managing conservation concerns. Here, we survey the literature for studies of hybridization and extinction to identify the ecological, evolutionary, and genetic factors that critically affect extinction risk through hybridization. We find that while extinction risk is highly situation dependent, genetic swamping is much more frequent than demographic swamping. In addition, human involvement is associated with increased risk and high reproductive isolation with reduced risk. Although climate change is predicted to increase the risk of hybridization‐induced extinction, we find little empirical support for this prediction. Similarly, theoretical and experimental studies imply that genetic rescue through hybridization may be equally or more probable than demographic swamping, but our literature survey failed to support this claim. We conclude that halting the introduction of hybridization‐prone exotics and restoring mature and diverse habitats that are resistant to hybrid establishment should be management priorities.
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            Flies and flowers: taxonomic diversity of anthophiles and pollinators

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              Adaptive introgression as a resource for management and genetic conservation in a changing climate.

              Current rates of climate change require organisms to respond through migration, phenotypic plasticity, or genetic changes via adaptation. We focused on questions regarding species' and populations' ability to respond to climate change through adaptation. Specifically, the role adaptive introgression, movement of genetic material from the genome of 1 species into the genome of another through repeated interbreeding, may play in increasing species' ability to respond to a changing climate. Such interspecific gene flow may mediate extinction risk or consequences of limited adaptive potential that result from standing genetic variation and mutation alone, enabling a quicker demographic recovery in response to changing environments. Despite the near dismissal of the potential benefits of hybridization by conservation practitioners, we examined a number of case studies across different taxa that suggest gene flow between sympatric or parapatric sister species or within species that exhibit strong ecotypic differentiation may represent an underutilized management option to conserve evolutionary potential in a changing environment. This will be particularly true where advanced-generation hybrids exhibit adaptive traits outside the parental phenotypic range, a phenomenon known as transgressive segregation. The ideas presented in this essay are meant to provoke discussion regarding how we maintain evolutionary potential, the conservation value of natural hybrid zones, and consideration of their important role in adaptation to climate.
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                Author and article information

                Contributors
                Journal
                Biodivers Data J
                Biodivers Data J
                1
                urn:lsid:arphahub.com:pub:F9B2E808-C883-5F47-B276-6D62129E4FF4
                urn:lsid:zoobank.org:pub:245B00E9-BFE5-4B4F-B76E-15C30BA74C02
                Biodiversity Data Journal
                Pensoft Publishers
                1314-2836
                1314-2828
                2020
                06 May 2020
                : 8
                Affiliations
                [1 ] University of British Columbia, Vancouver, Canada University of British Columbia Vancouver Canada
                Author notes
                Corresponding author: Mikko Pasi Tapani Paajanen ( mikko.paajanen@ 123456botany.ubc.ca ).

                Academic editor: Torsten Dikow

                Article
                52057 13087
                10.3897/BDJ.8.e52057
                7220971
                Mikko Pasi Tapani Paajanen, Quentin Cronk

                This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Figures: 6, Tables: 2, References: 25
                Categories
                Research Article

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