Category Archives: Published paper

Low genetic variation in cold tolerance linked to species distributions in butterflies

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Authors: Jonathan MP Davis, Belinda van Heerwaarden, Carla M Sgrò, Jennifer A Donald, and Darrell J Kemp

Published in: Evolutionary Ecology, volume 28, issue 3 (May 2014)

Abstract

Species with restricted distributions make up the vast majority of biodiversity.

Recent evidence from Drosophila suggests that species with restricted distributions may simply lack genetic variation in key traits, limiting their ability to adapt to conditions beyond their current range. Specifically, tropical species of Drosophila have been shown to have low means and low genetic variation for cold tolerance and desiccation tolerance.

It has therefore been predicted that these species will be limited in their response to future climatic changes. However whether these results extend beyond Drosophila is not known.

Eurema hecabe, one of three congeneric butterflies with contrasting Australian distributions. Image credit: AntanO [CC-BY-SA-3.0] via Wikimedia Commons.

Eurema hecabe, one of three congeneric butterflies with contrasting Australian distributions. Image credit: AntanO [CC-BY-SA-3.0] via Wikimedia Commons.

We assess levels of quantitative genetic variation for cold tolerance and body size in three species of butterfly from the genus Eurema that can be classified as tropically restricted (E. laeta), tropical/subtropical (E. hecabe) and widespread (E. smilax) in their distribution.

Compared to the more widely distributed species, we show that the tropically restricted E. laeta has significantly lower mean cold tolerance and lacks genetic variation for this trait. Thus, we empirically confirm in non-model organisms that low levels of genetic variation in a key ecological trait may play a role in limiting the distribution of tropically restricted species.

Citation

Davis J, van Heerwaarden B, Sgrò CM, Donald J, Kemp DJ (2014) Low genetic variation in cold tolerance linked to species distributions in butterflies. Evolutionary Ecology PDF DOI

Latitudinal clines in heat tolerance, protein synthesis rate and transcript level of a candidate gene in Drosophila melanogaster

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Authors: Fiona E Cockerell, Carla M Sgrò, and Stephen W McKechnie

Published in: Journal of Insect Physiology, volume 60 (January 2014)

Highlights

  • We investigate heat tolerance in D. melanogaster reared at 18 and 25 °C from populations collected over a range of latitudes.
  • Tropical flies are more heat tolerant than temperate region flies after heat hardening.
  • Total protein synthesis rates vary clinally depending on temperature conditions.
  • Levels of a major transcript of the heat-stress hsr-omega gene vary clinally.

Abstract

The occurrence of climatic adaptation in Drosophila melanogaster is highlighted by the presence of latitudinal clines in several quantitative traits, particularly clines in adult heat knockdown tolerance that is higher in tropical populations. However the presence of latitudinal patterns in physiological characteristics that may underlie these traits have rarely been assessed.

Protein synthesis has been implicated as an important physiological process that influences thermal tolerance, and this has not been examined in a clinal context.

Here, we characterise latitudinal variation in D. melanogaster from eastern Australia in both adult heat knockdown tolerance and rates of protein synthesis following rearing at both 25 °C, approximating summer conditions, and 18 °C, approximating winter development.

We also examined clinal variation in the predominant nuclear transcript of the heat-inducible RNA gene hsr-omega, which has been implicated in regulating protein synthesis.

We find significant clines in heat-hardened tolerance when cultured at both 18 and 25 °C — tolerance increased towards the low latitude tropics. Rates of protein synthesis measured in ovarian tissue also associated negatively with latitude, however the presence of the clines depended on rearing temperature and heat stress conditions.

Finally, omega-n levels measured without heat stress showed a positive linear cline. When measured after a mild heat stress higher levels of omega-n were detected and the clinal pattern became parabolic — mid-latitude populations had lower levels of the transcript.

While congruent latitudinal trends were detected for these three traits, only a low level of positive association was detected between protein synthesis and thermal tolerance providing little evidence that these traits are related at the level of cellular physiology. However the new clinal patterns of protein synthesis and hsr-omega variation suggest that these variables exert important influences on traits involved with latitudinal climatic adaptation.

Citation

Cockerell FE, Sgrò CM, McKechnie SW (2014) Latitudinal clines in heat tolerance, protein synthesis rate and transcript level of a candidate gene in Drosophila melanogaster. Journal of Insect Physiology PDF DOI

A comparison of inbreeding depression in tropical and widespread Drosophila species

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Authors: Jesper S Bechsgaard, Ary A Hoffmann, Carla M Sgrò, Volker Loeschcke, Trine Bilde, and Torsten N Kristensen

Published in: PLOS ONE, volume 8, issue 2 (February 2013)

Abstract

The evolutionary history of widespread and specialized species is likely to cause a different genetic architecture of key ecological traits in the two species groups. This may affect how these two groups respond to inbreeding.

Here we investigate inbreeding effects in traits related to performance in 5 widespread and 5 tropical restricted species of Drosophila with the aim of testing whether the two species groups suffered differently from inbreeding depression. The traits investigated were egg-to-adult viability, developmental time and resistance to heat, cold and desiccation.

Our results showed that levels of inbreeding depression were species and trait specific and did not differ between the species groups for stress resistance traits. However, for the life history traits developmental time and egg-to adult viability, more inbreeding depression was observed in the tropical species.

The results reported suggest that for life history traits tropical species of Drosophila will suffer more from inbreeding depression than widespread species in case of increases in the rate of inbreeding e.g. due to declines in population sizes.

Citation

Bechsgaard JS, Hoffmann AA, Sgrò CM, Loeschcke V, Bilde T, Kristensen TN (2013) A comparison of inbreeding depression in tropical and widespread Drosophila species, PLoS ONE PDF DOI