Body size & cold resistance in flies

#Posted by Maren Wellenreuther

Next week we will be reading something that is at the heart of our groups interest. The paper will deal with insects, body size, resistance to temperature and will discuss the evolutionary implications of phenotype divergence on the genetic architecture.

I will bring German cheesecake for fika!

Here is the abstract and download link

The effect of developmental temperature on the genetic architecture underlying size and thermal clines in Drosophila melanogaster and D. simulans from the east coast of Australia.
van Heerwaarden B, Sgrò CM.

Body size and thermal tolerance clines in Drosophila melanogaster occur along the east coast of Australia. However the extent to which temperature affects the genetic architecture underlying the observed clinal divergence remains unknown. Clinal variation in these traits is associated with cosmopolitan chromosome inversions that cline in D. melanogaster. Whether this association influences the genetic architecture for these traits in D. melanogaster is unclear. Drosophila simulans shows linear clines in body size, but nonlinear clines in cold resistance. Clinally varying inversions are absent in D. simulans. Line-cross and clinal analyses were performed between tropical and temperate populations of D. melanogaster and D. simulans from the east coast of Australia to investigate whether clinal patterns and genetic effects contributing to clinal divergence in wing centroid size, thorax length, wing-to-thorax ratio, cold and heat resistance differed under different developmental temperatures (18 °C, 25 °C, and 29 °C). Developmental temperature influenced the genetic architecture in both species. Similarities between D. melanogaster and D. simulans suggest clinally varying inversion polymorphisms have little influence on the genetic architecture underlying clinal divergence in size in D. melanogaster. Differing genetic architectures across different temperatures highlight the need to consider different environments in future evolutionary and molecular studies of phenotypic divergence.

http://onlinelibrary.wiley.com/doi/10.1111/j.1558-5646.2010.01196.x/pdf

On the evolution of large insects

Posted by Erik Svensson

Our last lab-meeting contained an interesting discussion about the evolutionary significance of large body size in insects, stimulated by the excellent talk by Yuma Takahashi about his ongoing research on Ischnura-damselflies. I thought we should continue on the theme of body size evolution and its drivers in insects, by reading two recent papers that should hopefully be entertaining and interesting.

Both papers discuss the rise and fall of large insects, such as gigantic dragonflies during the Carboniferous Period, and the biotic and abiotic factors driving selection on both body size and wing size. Among the most discussed (but also controversial) idéas is that atmospheric oxygen levels might have been important, but predation has also been suggested to play a role.

Time and place of lab-meeting as usual: "Argumentet" (2nd floor, Ecology Building) at 10.30 on Tuesday September 18 2012. 

Below, you will find the title of the papers and Abstracts and links that should allow you to download the paper if you are on the Lund University network. You can also download them here and here. You might also be interested in the short comment on the latter paper by Steven Chown, which you can download here. 

Environmental and biotic controls on the evolutionary history of insect body size

Author(s): Clapham, ME (Clapham, Matthew E.)1; Karr, JA (Karr, Jered A.)1

Source: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA  Volume: 109   Issue: 27   Pages: 10927-10930   DOI:10.1073/pnas.1204026109   Published: JUL 3 2012

Abstract: Giant insects, with wingspans as large as 70 cm, ruled the Carboniferous and Permian skies. Gigantism has been linked to hyperoxic conditions because oxygen concentration is a key physiological control on body size, particularly in groups like flying insects that have high metabolic oxygen demands. Here we show, using a dataset of more than 10,500 fossil insect wing lengths, that size tracked atmospheric oxygen concentrations only for the first 150 Myr of insect evolution. The data are best explained by a model relating maximum size to atmospheric environmental oxygen concentration (pO(2)) until the end of the Jurassic, and then at constant sizes, independent of oxygen fluctuations, during the Cretaceous and, at a smaller size, the Cenozoic. Maximum insect size decreased even as atmospheric pO(2) rose in the Early Cretaceous following the evolution and radiation of early birds, particularly as birds acquired adaptations that allowed more agile flight. A further decrease in maximum size during the Cenozoic may relate to the evolution of bats, the Cretaceous mass extinction, or further specialization of flying birds. The decoupling of insect size and atmospheric pO(2) coincident with the radiation of birds suggests that biotic interactions, such as predation and competition, superseded oxygen as the most important constraint on maximum body size of the largest insects.

Atmospheric oxygen level and the evolution of insect body size

Harrison, JF (Harrison, Jon F.)1; Kaiser, A (Kaiser, Alexander)2; VandenBrooks, JM (VandenBrooks, John M.)1

Source: PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES  Volume: 277   Issue: 1690   Pages: 1937-1946   DOI: 10.1098/rspb.2010.0001   Published:JUL 7 2010

Abstract: Insects are small relative to vertebrates, possibly owing to limitations or costs associated with their blind-ended tracheal respiratory system. The giant insects of the late Palaeozoic occurred when atmospheric PO(2) (aPO(2)) was hyperoxic, supporting a role for oxygen in the evolution of insect body size. The paucity of the insect fossil record and the complex interactions between atmospheric oxygen level, organisms and their communities makes it impossible to definitively accept or reject the historical oxygen-size link, and multiple alternative hypotheses exist. However, a variety of recent empirical findings support a link between oxygen and insect size, including: (i) most insects develop smaller body sizes in hypoxia, and some develop and evolve larger sizes in hyperoxia; (ii) insects developmentally and evolutionarily reduce their proportional investment in the tracheal system when living in higher aPO(2), suggesting that there are significant costs associated with tracheal system structure and function; and (iii) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of aPO(2) on larger insects. Together, these provide a wealth of plausible mechanisms by which tracheal oxygen delivery may be centrally involved in setting the relatively small size of insects and for hyperoxia-enabled Palaeozoic gigantism.

New lab-meeting on micro- and macroevolution of body size

Since this week's lab-meeting discussion about Anna's presentation took longer time than planned, we will discuss the paper by Uyeda et al. in PNAS this coming Tuesday instead, in "Argumentet" (13.00-15.00). Hope to see you all there, and I recommend you to read this important paper in detail before the meeting to have a good and productive discussion. Also, do not forget to take a look at Jerry Coyne's blogpost about the paper which you can find here.