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- Karlsson, Bengt, et al.
(författare)
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Test of a developmental trade-off in a polyphenic butterfly: direct development favours reproductive output
- 2008
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 22:1, s. 121-126
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Tidskriftsartikel (refereegranskat)abstract
- 1.Evolutionary theory predicts that resource allocation decisions taken during development are adjusted to an organism's life-history. These decisions may have irreversible effects on body design and strong fitness consequences. Holometabolous insects that have a long expected life span typically postpone reproduction, and so are expected to allocate resources for somatic maintenance prior to investing in reproduction. In contrast, insects that have a short expected life span are expected to allocate relatively less to soma and more to reproduction. In support of this theory, an earlier investigation of resources allocated to soma vs. reproductive reserves in the comma butterfly, Polygonia c-album, revealed that short-lived females indeed allocate more resources to reproductive reserves as compared to longer lived females that hibernate before reproduction suggesting that short-lived females should have higher fecundity. 2. Here we test this prediction, using the comma butterfly as our study organism. Depending on daylength and temperature this butterfly produces one of two morphs: (i) a light summer morph that reproduces directly after adult eclosion and has a short expected life span of a couple of weeks; or (ii) a darker winter morph that normally lives for 8–9 months before the onset of reproduction. Our test is based on experimental manipulation that allowed us to induce reproduction without prior hibernation in winter morph comma butterflies, and comparing lifetime fecundity among three groups: (i) directly reproducing summer morph commas; (ii) directly reproducing winter morph commas; and (iii) winter morph commas reproducing after overwintering. This protocol allowed us to tease apart trade-offs during development and the hibernation period. 3. The results showed that the short-lived summer morph had a substantially higher fecundity (total number of eggs = 586 ± 19, mean ± SE) than the winter morph females manipulated to reproduce without hibernation (total number of eggs = 334 ± 42). We argue that this is a consequence of a resource allocation trade-off during early development observed in this species; females with a short expected life as adults allocate relatively more of their resources to reproductive parts and thereby reach a higher reproductive output compared to females predisposed for a long adult life. 4. There was no significant difference in lifetime fecundity between winter morph females that did, or did not, hibernate before reproduction. This suggests that the cost of hibernation per se is small and hence corroborates our conclusion that the life-history implemented trade-off made during early development underlies the lower reproductive output of the winter morph butterflies.
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- Stjernholm, Fredrik, 1973-
(författare)
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Allocation of body resources to reproduction in butterflies
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The life-history of an organism can be studied and understood in terms of acquisition and expenditure of resources. In butterflies, the use of resources for reproduction has been the focus of much research due to the possibility to easily quantify both the input of resources from different sources over the life-cycle as well as the partitioning of these resources to reproduction. In the first part of my thesis we studied how the pattern of partitioning of resources between somatic tissue, such as muscles, wings and exoskeleton, and storage of resources for reproductive purposes during metamorphosis affects reproduction. Theory predicts that reproduction should be strongly dependent on the relative investments in soma and reproductive reserves, but this has generally proven difficult to show empirically. Butterflies are eminently suited for testing this prediction, and our results show that fecundity of female comma butterflies (Polygonia c-album) is strongly influenced by allocation priorities. One aspect of resource use that has not attracted attention until recently is the possibility that butterflies during the reproductive stage can break down flight muscles in the thorax and use muscle nutrients for reproduction. Since butterflies are generally resource limited this could alleviate the costs resulting from somatic investment found in paper I. Through a series of studies we show that thorax mass and nitrogen content decreases over the adult lifespan in a manner consistent with the hypothesis that thorax resources are used for reproduction. In order to determine if these resources could actually come from the flight muscles, something that is known to occur in other insects, the reduction in flight muscle size over the lifespan was studied in the green-veined white butterfly (Pieris napi). The results showed that flight muscle size decreased with on average 75% in long-lived females, suggesting that breakdown of flight muscles could indeed influence reproduction. Taken together, the work in this thesis shows that resource allocation during metamorphosis strongly influences the reproductive potential, but that butterflies can overcome some of the costs of somatic investment by reallocating resources from thoracic tissue to reproduction.
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