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Behavioural field experiments assessing the habitat and host preference of D. sechellia in the wild

Harris, Rebecca (2015) BIOP01 20142
Degree Projects in Biology
Abstract
The extensive studies on D. sechellia have made it a familiar example of chemosen-sory evolution and speciation. This specialist drosphilid species is well-known for its ability to tolerate and actively seek out its toxic host Morinda citrifolia (noni). It was originally thought that this toxic fruit was the exclusive host of D. sechellia because most drosophilids cannot tolerate and are deterred by the characterizing odour components, hexanoic and octanoic acid, given off by noni. However, the origins of noni are questionable and it has been proposed that D. sechellia may have evolved on an older endemic pandanus in the Seychelles. This study tests the viability of this claim by comparative behavioural field studies of D. sechellia... (More)
The extensive studies on D. sechellia have made it a familiar example of chemosen-sory evolution and speciation. This specialist drosphilid species is well-known for its ability to tolerate and actively seek out its toxic host Morinda citrifolia (noni). It was originally thought that this toxic fruit was the exclusive host of D. sechellia because most drosophilids cannot tolerate and are deterred by the characterizing odour components, hexanoic and octanoic acid, given off by noni. However, the origins of noni are questionable and it has been proposed that D. sechellia may have evolved on an older endemic pandanus in the Seychelles. This study tests the viability of this claim by comparative behavioural field studies of D. sechellia abundances in various habitats and chemcial analysis of two pandanus sp. (P. tec-torius and P. hornei) in The Seychelles. The results revealed that despite extensive research D. sechellia is not exclusive to noni as a host or noni groves as a habitat. Furthermore, it questions the possiblity of P. tectorius and P. hornei as the original hosts. (Less)
Popular Abstract
Habitat and host assessment of D. sechellia in the wild

General introduction
Drosophila sechellia is endemic to the Seychelles and is part of a diverse family of flies called Drosophilidae. It is unique because of its ability to locate and tolerate a toxic host called noni. The toxicity of the noni is mostly attributed to the high concentrations of hexanoic and octanoic acid, which repel and even terminate oogenesis in other drosophilids. These aliphatic acid act as an attractant for D. sechellia and as a results it has developed some notable chemosensory differences to its siblings allowing it to locate its scare and widely dispersed host in the Seychelles. The origins of noni are controversial and it is speculated that the fruit was... (More)
Habitat and host assessment of D. sechellia in the wild

General introduction
Drosophila sechellia is endemic to the Seychelles and is part of a diverse family of flies called Drosophilidae. It is unique because of its ability to locate and tolerate a toxic host called noni. The toxicity of the noni is mostly attributed to the high concentrations of hexanoic and octanoic acid, which repel and even terminate oogenesis in other drosophilids. These aliphatic acid act as an attractant for D. sechellia and as a results it has developed some notable chemosensory differences to its siblings allowing it to locate its scare and widely dispersed host in the Seychelles. The origins of noni are controversial and it is speculated that the fruit was not native or present in the Seychelles during D. sechellia’s speciation from D. simulans. Therefore it has been proposed that perhaps an older and more abundant plant such as a pandanus species was the original host and if this is the case D. sechellia should still be present in this habitat type and bait.

Methods
I conducted behavioural field experiments in three different locations (a residential site, noni groves site and pandanus groves site) and on various bait types (banana, cultivated noni, wild noni, pandanus and banana spiked with acetic acid or hexanoic acid). In each trial I collected flies that had chosen between two bait types (banana vs noni, banana vs wild noni, noni vs wild noni, acetic acid vs hexanoic acid, noni vs pandanus). In addition I collected the chemical odour profiles of two pandanus species (P. tectorius and P. hornei), cultivated noni and wild noni using an oven bag, tenax filter and pump (standard headspace collection). The chemicals attained from the filters were analysed in a gas chromatograph mass spectrometer which separated the chemicals according to their mass to charge ratio.

Results and Discussion
The comparative behavioural results showed that D. sechellia was significantly more abundant in the noni groves compared to the residential site as expected but not significantly different from the pandanus groves site. This suggest that D. sechellia is not exclusive to the noni habitat as originally thought. In addition, D. sechellia was present in all baits types, but only dominant in noni and wild noni baited traps further suggesting that D. sechellia is likely an opportunistic specialist rather than an obligate specialist. There was no significant preference for pandanus or the pandanus habitat and neither of the pandanus species odour profiles were similar to noni or advantageously suitable for D. sechellia.

Conclusion
Therefore this study found that D. sechellia is not exclusive to its current host, noni, as originally thought and that it is wild noni rather than a pandanus species that is the original host of D. sechellia.





Advisor: Marcus Stensmyr
Master´s Degree Project: 60 credits 2015
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Harris, Rebecca
supervisor
organization
course
BIOP01 20142
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
5468664
date added to LUP
2015-06-08 10:20:44
date last changed
2015-06-08 10:20:44
@misc{5468664,
  abstract     = {The extensive studies on D. sechellia have made it a familiar example of chemosen-sory evolution and speciation. This specialist drosphilid species is well-known for its ability to tolerate and actively seek out its toxic host Morinda citrifolia (noni). It was originally thought that this toxic fruit was the exclusive host of D. sechellia because most drosophilids cannot tolerate and are deterred by the characterizing odour components, hexanoic and octanoic acid, given off by noni. However, the origins of noni are questionable and it has been proposed that D. sechellia may have evolved on an older endemic pandanus in the Seychelles. This study tests the viability of this claim by comparative behavioural field studies of D. sechellia abundances in various habitats and chemcial analysis of two pandanus sp. (P. tec-torius and P. hornei) in The Seychelles. The results revealed that despite extensive research D. sechellia is not exclusive to noni as a host or noni groves as a habitat. Furthermore, it questions the possiblity of P. tectorius and P. hornei as the original hosts.},
  author       = {Harris, Rebecca},
  language     = {eng},
  note         = {Student Paper},
  title        = {Behavioural field experiments assessing the habitat and host preference of D. sechellia in the wild},
  year         = {2015},
}