TY - JOUR A1 - Joschinski, Jens A1 - Hovestadt, Thomas A1 - Krauss, Jochen T1 - Coping with shorter days: do phenology shifts constrain aphid fitness? JF - PeerJ N2 - Climate change can alter the phenology of organisms. It may thus lead seasonal organisms to face different day lengths than in the past, and the fitness consequences of these changes are as yet unclear. To study such effects, we used the pea aphid Acyrthosiphon pisum as a model organism, as it has obligately asexual clones which can be used to study day length effects without eliciting a seasonal response. We recorded life-history traits under short and long days, both with two realistic temperature cycles with means differing by 2 °C. In addition, we measured the population growth of aphids on their host plant Pisum sativum. We show that short days reduce fecundity and the length of the reproductive period of aphids. Nevertheless, this does not translate into differences at the population level because the observed fitness costs only become apparent late in the individual's life. As expected, warm temperature shortens the development time by 0.7 days/°C, leading to faster generation times. We found no interaction of temperature and day length. We conclude that day length changes cause only relatively mild costs, which may not decelerate the increase in pest status due to climate change. KW - Homoptera aphididae KW - clock reproduction ecology KW - phenotypic plasticity KW - phenology shifts KW - insect timing KW - physiological constraints KW - day length KW - circadian rhythms KW - Acyrthosiphon pisum KW - climate change Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148382 VL - 3 IS - e1103 ER - TY - THES A1 - Böll, Susanne T1 - Ephemere Laichgewässer: Anpassungsstrategien und physiologische Zwänge der Gelbbauchunke (Bombina variegata) in einem Lebensraum mit unvorhersehbarem Austrocknungsrisiko T1 - Temporary ponds: Adaptations and physiological constraints of the yellow-bellied toad (Bombina variegata) living in a habitat with an unpredictable risk of desiccation N2 - Die Gelbbauchunke Bombina variegata gilt als eine typische Pionierart, die bevorzugt vegetationslose, ephemere Gewässer mit hohem Austrocknungsrisiko als Laichgewässer nutzt. Kleinstgewässer dieser Art zeichnen sich durch hohe Fluktuationen abiotischer (Temperatur, Ionenkonzentration, Wasserstand), aber auch biotischer Faktoren (Dichte, Räuberdruck) aus. In Anpassung an das zeitlich und räumlich unvorhersehbare Auftreten dieser Gewässer hat die Gelbbauchunke eine für eine temperate Art außergewöhnlich lange Fortpflanzungsperiode (April - August). Die Weibchen zeigten während der Saison eine kontinuierliche Eientwicklung, die es ihnen erlaubt, opportunistisch mehrfach abzulaichen und damit eine zeitliche Risikostreuung der Gelege zu betreiben. Darüber hinaus nutzt Bombina variegata alle Möglichkeiten der räumlichen Risikostreuung, indem sie ihre Gelege in kleinen Portionen innerhalb von Pfützen, aber auch auf verschiedene Pfützen verteilt. Die hohe Variabilität in den produzierten Eigrößen, besonders zwischen den Gelegen verschiedener Weibchen, ließ auf den ersten Blick eine weitere Strategie zur Risikostreuung vermuten; allerdings war die Eigröße von der Kondition der Weibchen abhängig: während gut konditionierte Weibchen in der Lage waren, sowohl größere Eier als auch größere Gelege zu produzieren, gingen schlechter konditionierte Weibchen einen „trade-off“ zugunsten einer möglichst hohen Fekundität ein. Unter günstigen Bedingungen greift diese Strategie, während die Produktion überdurchschnittlich großer Eier unter Austrocknungsbedingungen von Vorteil ist: Kaulquappen großer Eier hatten eine entsprechend größere Schlupfgröße und zeigten gegenüber Quappen kleinerer Eier eine beschleunigte Entwicklung. Auch bei den Labor- und Freilanduntersuchungen, die sich mit der Frage be-schäftigten, wie Bombina variegata auf kritische Veränderungen des Wasservo-lumens reagiert, war eine enorme Variabilität in den Wachstums- und Entwicklungsverläufen der Kaulquappen der verschiedenen Ansätze zu beobachten, die sich nur bedingt auf abweichende Versuchsbedingungen zurückführen ließ; vielmehr dürfte die qualitative Ausstattung der Quappen eine wesentliche Rolle gespielt haben. Dabei kristallisierten sich in den verschiedenen Versuchen zwei unterschiedliche Entwicklungsstrategien heraus: Kaulquappen, die eine insgesamt relativ lange Entwicklungszeit benötigten, zeigten eine hohe phänotypische Plastizität und reagierten adaptiv auf abnehmende Wasserstände, indem sie ihre Entwicklung auf Kosten ihres Wachstums beschleunigten. Bei Quappen, die im Durchschnitt eine wesentlich schnellere Entwicklungszeit besaßen, war diese per se günstige hohe Entwicklungsrate dagegen fixiert, unabhängig davon, während welcher Entwicklungsphase die Quappen auf veränderte Bedingungen umgestellt wurden. Unter verschlechterten Bedingungen zeigten sie lediglich Wachstumseinbußen. Ähnlich reagierten Kaulquappen auf zunehmende Ionenkonzentrationen bzw. sinkende Wasserstände. Dagegen wirkte sich Ammoniak, Exkretionsprodukt von Amphibienlarven, in erhöhten Konzentrationen stark negativ aus und beeinträchtigte sowohl das Wachstum als auch die Entwicklung der Quappen. Auf Räuber, die im Vergleich zum Austrocknungsrisiko temporärer Gewässer eine eher untergeordnete Rolle spielen, reagierten Bombina variegata-Quappen nur bedingt. Erst nach Fütterung der Libellenlarven mit Unkenquappen schränkten sie vorübergehend ihre Aktivität ein und mieden den räubernahen Bereich, ohne dass dadurch die Entwicklungsgeschwindigkeit oder das Wachstum der Quappen beeinträchtigt wurde; allerdings war eine erhöhte Mortalität zu beobachten. N2 - The yellow-bellied toad, Bombina variegata, lives in highly dynamic habitats, where she predominantly uses shallow pools with no vegetation as breeding sites. These temporary ponds have a high risk of desiccation and show strong fluctuations in abiotic (e.g. temperature, ion concentration, water level) as well as biotic factors (e.g. density, predation pressure). In accordance with the unpredictability of breeding sites in time and space, Bombina variegata has an unusually long breeding season for a temperate zone species lasting from April to August. During this period females showed continuous egg development, allowing for repeated opportunistic spawning bouts as a temporal risk spreading strategy. Besides, B. variegata uses all opportunities of spacial risk spreading by distributing her eggs within as well as between different pools. A high variability of egg sizes, especially between clutches of different females was observed indicating another risk spreading strategy. However, mean egg size was dependent on the condition of the female: while females with an above average condition were able to produce both, large eggs as well as large clutches, females of lower condition were forced to undergo a trade-off, aiming at a high fecundity but at the cost of reduced egg size. This is a successful strategy under favourable conditions, however under drying conditions the pro-duction of large eggs is of major advantage: tadpoles from large eggs had larger hatching sizes and metamorphosed earlier than tadpoles from small eggs. Furthermore, an enormous variability in mean size at metamorphosis and devel-opmental time was observed in a series of lab and field experiments where tad-poles were exposed to varying water volumes. These findings cannot fully be attributed to differences in experimental design, but rather indicate inherent differences of tadpoles of different cohorts. Basically, two developmental strategies were observed: tadpoles exhibiting a long larval period had a high phenotypic plasticity and showed an adaptive trade-off under decreasing water levels, ac-celerating their development at the cost of reduced growth. On the other hand, tadpoles that developed at a faster rate in the first place showed a fixed devel-opment and merely reduced their growth, no matter at which developmental stage the change to unfavourable conditions occurred. Similar results were ob-tained when tadpoles were exposed to increases in ion concentrations or to wa-ter level reductions. However, increased levels of ammonia, the excretion prod-uct of tadpoles, led to a major negative impact on both, growth and development of the tadpoles. In comparison to the risk of desiccation, predators play only a minor role in temporary ponds. Accordingly, Bombina variegata tadpoles reduced their activity and avoided the area of the dragonfly larvae only temporarily, after these were fed with tadpoles. Neither growth nor development of the larvae were impaired; however, a higher mortality was observed. KW - Bombina variegata KW - Risikostreuung KW - phänotypsche Plastizität KW - Entwicklungsgeschwindigkeit KW - Räuberdruck KW - Bombina variegata KW - risk spreading KW - phenotypic plasticity KW - developmental time KW - predation pressure Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-5268 ER - TY - JOUR A1 - Grözinger, Franziska A1 - Thein, Jürgen A1 - Feldhaar, Heike A1 - Rödel, Mark-Oliver T1 - Giants, Dwarfs and the Environment - Metamorphic Trait Plasticity in the Common Frog JF - PLOS ONE N2 - In order to understand adaptation processes and population dynamics, it is central to know how environmental parameters influence performance of organisms within populations, including their phenotypes. The impact of single or few particular parameters in concert was often assessed in laboratory and mesocosm experiments. However, under natural conditions, with many biotic and abiotic factors potentially interacting, outcomes on phenotypic changes may be different. To study the potential environmental impact on realized phenotypic plasticity within a natural population, we assessed metamorphic traits (developmental time, size and body mass) in an amphibian species, the European common frog Rana temporaria, since a) larval amphibians are known to exhibit high levels of phenotypic plasticity of these traits in response to habitat parameters and, b) the traits' features may strongly influence individuals' future performance and fitness. In 2007 we studied these metamorphic traits in 18 ponds spread over an area of 28 km 2. A subset of six ponds was reinvestigated in 2009 and 2010. This study revealed locally high variances in metamorphic traits in this presumed generalist species. We detected profound differences between metamorphing froglets (up to factor ten); both between and within ponds, on a very small geographic scale. Parameters such as predation and competition as well as many other pond characteristics, generally expected to have high impact on development, could not be related to the trait differences. We observed high divergence of patterns of mass at metamorphosis between ponds, but no detectable pattern when metamorphic traits were compared between ponds and years. Our results indicate that environment alone, i.e. as experienced by tadpoles sharing the same breeding pond, can only partly explain the variability of metamorphic traits observed. This emphasizes the importance to assess variability of reaction norms on the individual level to explain within-population variability. KW - rana temporaria populations KW - prey growth rate KW - phenotypic plasticity KW - larval density KW - amphibian metamorphosis KW - ambystoma opacum KW - predation risk KW - life history KW - developmental plasticity KW - adaptive plasticity Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117203 SN - 1932-6203 VL - 9 IS - 3 ER -