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Generalists and specialists along a latitudinal transect: patterns of thermal adaptation in six species of damselflies
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2012 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 93, no 6, 1340-1352 p.Article in journal (Refereed) Published
Abstract [en]

Tropical organisms colonizing temperate environments face reduced average temperatures and dramatic thermal fluctuations. Theoretical models postulate that thermal specialization should be favored either when little environmental variation is experienced within generations or when among-generation variation is small relative to within-generation variation. To test these predictions, we studied six temperate species of damselflies differing in latitudinal distribution. We developed a computer model simulating how organisms experience environmental variation (accounting for diapause and voltinism) and performed a laboratory experiment assaying thermal sensitivities of growth rates. The computer model showed opposing latitudinal trends in among-and within-generation thermal variability: within-generation thermal variability decreased toward higher latitudes, whereas relative levels of among-generation thermal variability peaked at midlatitudes (where a shift in voltinism occurred). The growth experiment showed that low-latitude species were more thermally generalized than mid- and high-latitude species, supporting the prediction that generalists are favored under high levels of within-generation variation. Northern species had steeper, near-exponential reaction norms suggestive of thermal specialization. However, they had strikingly high thermal optima and grew very slowly over most of the thermal range they are expected to experience in the field. This observation is at present difficult to explain. These results highlight the importance of considering interactions between life history and environmental variation when deriving expectations of thermal adaptation.

Place, publisher, year, edition, pages
2012. Vol. 93, no 6, 1340-1352 p.
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:umu:diva-57156DOI: 10.1890/11-1910.1ISI: 000305296600012OAI: oai:DiVA.org:umu-57156DiVA: diva2:540315
Available from: 2012-07-09 Created: 2012-07-09 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Thermal adaptation along a latitudinal gradient in damselflies
Open this publication in new window or tab >>Thermal adaptation along a latitudinal gradient in damselflies
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding how temperature affects biological systems is a central question in ecology and evolutionary biology. Anthropogenic climate change adds urgency to this topic, as the demise or success of species under climate change is expected to depend on how temperature affects important aspects of organismal performance, such as growth, development, survival and reproduction. Rates of biological processes generally increase with increasing temperature up to some maximal temperature. Variation in the slope of the initial, rising phase has attracted considerable interest and forms the focus of this thesis. I explore variation in growth rate-temperature relationships over several levels of biological organization, both between and within species, over individuals’ lifetime, depending on the ecological context and in relation to important life history characteristics such as generation length and winter dormancy.

      Specifically, I examine how a clade of temperate damselflies have adapted to their thermal environment along a 3,600 km long latitudinal transect spanning from Southern Spain to Northern Sweden. For each of six species, I sampled populations from close to the northern and southern range margin, as well from the center of the latitudinal range. I reared larvae in the laboratory at several temperatures in order to measure indiviudal growth rates. Very few studies of thermal adaptation have employed such an extensive sampling approach, and my finding reveal variation in temperature responses at several levels of organization.

      My main finding was that temperature responses became steeper with increasing latitude, both between species but also between latitudinal populations of the same species. Additional genetic studies revealed that this trend was maintained despite strong gene flow. I highlight the need to use more refined characterizations of latitudinal temperature clines in order to explain these findings. I also show that species differ in their ability to acclimate to novel conditions during ontogeny, and propose that this may reflect a cost-benefit trade-off driven by whether seasonal transitions occur rapidly or gradually during ontogeny.

      I also carried out a microcosm experiment, where two of the six species were reared either separately or together, to determine the interacting effects of temperature and competition on larval growth rates and population size structure. The results revealed that the effects of competition can be strong enough to completely overcome the rate-depressing effects of low temperatures. I also found that competition had stronger effects on the amount of variation in growth rates than on the average value.

      In summary, my thesis offers several novel insights into how temperature affects biological systems, from individuals to populations and across species’ ranges. I also show how it is possible to refine our hypotheses about thermal adaptation by considering the interacting effects of ecology, life history and environmental variation.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2012. 35 p.
Keyword
Growth rate, metabolic theory of ecology, universal temperature dependence, environmental gradients, thermal performance, thermal sensitivity, environmental variability, optimality theory, life history, acclimation, size structure, competition, cannibalism, intraguild predation
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-62276 (URN)978-91-7459-529-1 (ISBN)
Public defence
2013-01-18, N450, Umeå Universitet, Johan Bures väg 14, Umeå, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Available from: 2012-12-21 Created: 2012-12-14 Last updated: 2017-02-01Bibliographically approved

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