Master Project: April 2008 Archives

Braconid parasitoids of Drosophila lay their eggs in the larvae of Drosophila. They are represented on all continents. As Drosophila melanogaster has now a cosmopolitan distribution this species has become an important host for many Asobara species. Currently we keep 5 species in our laboratory: Asobara tabida, a palearctic species, A. citri, an African species, A. japonicus from Japan, A. pleuralis from Indonesia and A. persimilis from Australia.  Although D. melanogaster has the same developmental period from egg to adult in worldwide, the 5 Asobara species differ markedly in developmental time, from 21 days in A.tabida to 12 days in A. pleuralis, measured at 25 C, with the other species having intermediate developmental times. This poses the question which selective pressures act on developmental time, and which constraints prevent species to have shorter developemental times. Our hypothesis is that a shorter developmental time has costs, because it is traded off against other life-history characters, like fecundity or longevity.
The practical work involves measuring of size, weight, egg load, fecundity and lipoprotein contents of Asobara wasps reared under standard laboratory conditions.

This project can be done as BSc stage (4 months), or be extended to a MSc research project.

 

Supervision: Majeed Askari Seyahooei & Jacques van Alphen

Contact: m.a.seyahooei@biology.leidenuniv.nl      

 

Leptopilina boulardi is a Drosophila parasitic wasp originating from Africa, which can now be found in many subtropical and Mediterranean regions as a parasitoid of Drosophila melanogaster. We collect 10 populations of this parasitoid from five different climatic zone in Iran. We culture these lines in our lab since their collection in the summer of 2006. We have measured a number of life history traits of these lines, which show significant variation between lines from different climatic zones. We want to investigate the hypothesis that the observed differences in longevity and metabolic rate for these lines are adaptations to the local climate. Several lines originated from the Caspian coast with a very wet and mild climate, while others originate from the hot and dry desert and Mediterranean climates found in the interior of Iran. Coastal and interior collection sites differ enormously in rainfall and seasonal temperatures.
To study if metabolic rate is an adaptation to local climateto and to study how metabolic rate affects the trade-off between longevity and fecundity we will measure longevity of different lines at a constant temperature and measuring the metabolic rate of individuals in a group of 20 wasps with a sensitive respirometer at different ages of the wasps, at time of emerging, 5, 10, 15 and 20 days after emerging. The egg loads of the wasps will be measured at the time of dead.
Longevity of the wasp will be measured in the presence of food and without food and egg load of the wasps will be measured at the time of death when the body is still fresh by dissection of the ovarioles and by counting the eggs on photographs of dissected ovarioles.

Supervision: Majeed Askari Seyahooei & Jacques van Alphen

Contact: m.a.seyahooei@biology.leidenuniv.nl      

Asobara species are Braconid larval parasitoids of Drosophila. The genus has a cosmopolitan distribution and can be found in all major climatic zones. Larval feeding and genetic background of different species strongly affects the energy allocation of these parasitoids. Our studies on five species of Asobara, A. tabida, A. citri, A. pleuralis, A. persimilis and A. japonica show significant variation on lipid resources and egg mass(egg load & egg size) of these parasitoids at emergence from the host's puparium. The parasitoids can either allocate resources to reproduction or to the maintenance of its own body. The best strategy of allocation depends on, climatic conditions and the spatial and temporal distribution of hosts in their country of origin. Our hypothesis is that different sources of energy, lipids, glycogen and sugars may play a different role in the trade-off between longevity and fecundity of the parasitoids. To study the allocation of these resources to reproduction and longevity we plan to do a series of experiments with these five species to measure energy reserves and egg loads in the course of their adult lives. These measurements will be done for a group of 30 wasps reared under the same conditions at different times after emergence: directly after emerging, after five days, 10 days, and 15 days of adult age and at the time of dead. The energy reserve will be measured by colorimetric methods and egg loads will be recorded by photography of dissected ovariols.

 

Supervision: Majeed Askari Seyahooei & Jacques van Alphen

Contact: m.a.seyahooei@biology.leidenuniv.nl                  

Biodiversity of nocturnal Lepidoptera in the dunes

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The Dutch dunes have and exceptional biodiversity of moth species. Research projects carried out during the field course Animal Ecology revealed that the moth fauna of the Dunes in Wassenaar is far less well known that that of the dunes in the province of North Holland.  In addition it is not well understood which factors govern moth biodiversity. Recently the alarming decrease of moth biodiversity in the British Isles was headline news. The dune ecosystem has been changing a lot over the past 50 years. Likewise, the climate in western Europe is changing. To implement good nature management is of paramount importance to understand how moth diversity responds to all these changes.
The dune vegetation in the Netherlands has been severely affected by nitrogen deposit, which has resulted in an large increase of tall grasses. In addition, the rabbit populations, in the past severely reduced by myxomatosis have now succumbed to a calcivirus and have been reduced to 10% of their former densities. This has allowed scrubs and trees to expand in area at the expense of open short vegetation. Current management of the dunes is directed at recreating wet dune slacks and to increase short open vegetation again.
 It is desirable to know how the changes in vegetation have affected moth biodiversity, and how future management can be optimized to in respect to moth diversity.
 We seek BSc and MSc students who are willing to study existing data on moths distribution in the dutch dunes and measure moth diversity in different vegetation types in the Dunes near Wassenaar.

The practical work will consist of running moth light traps during the night in the dunes and to study the existing data on moth distribution and abundance in relation to changes in vegetation.

Contact: Jacques van Alphen

j.j.m.van.alphen@biology.leidenuniv.nl

Insects can defend themselves against pathogens and parasites by a cellular immune response. Recognition of a foreign body in the hemolymph results in aggregation of certain types of blood cells around the foreign body. These cells form a dense capsule in which melanine is secreted and the foreign body is killed either by asphyxiation or by poisoning.

Endoparasitoids often place their eggs in the body cavity of insect larvae and are vulnerable to the cellular immune response of the host. Endo-parasitoids have evolved a number of mechanisms to escape encapsulation. In several species the egg is placed inside the brain, or under the cells lining of the gut and escape in such a manner exposure to the host's immune response. Other parasitoids produce viruslike particles, which are injected into the host at oviposition. The viruslike particles are instrumental in killing blood cells and preventing their multiplication. Yet other parasitoids have a protein coating on the outside of the egg, which makes that the egg is not recognized as foreign. Finally, some parasitoids have a coating of sticky proteins on the egg, which make the egg adhere to gut and fat tissue of the host. Blood cells can no longer reach the parts of the egg covered by fat tissue or gut, and encapsulation of the egg is no longer possible.

To escape encapsulation for parasitoids is often a race against the clock and the outcome of the battle between the immune system of the host and the ploys of the parasitoid to escape encapsulation may therefore depend on the temperature. In the parasitoid-host relation between Drosophila melanogaster and Asobara tabida, an increase in rearing temperature from 20°C to 25°C resulted in a significant increase in encapsulation of the parasitoid's eggs (van Alphen & Drijver, 1982) In western Europe, the preferred host of Asobara tabida is D.subobscura. This species lacks the ability to encapsulate parasitoid eggs and is therefore a high quality host for

A.tabida. The cosmopolitan D.melanogaster, of African origin, is also used as host. In northern Europe, this host is only accepted when D.subobscura is rare. In southern Europe, D.subobscura is often absent during the warm summer months, and D.melanogaster is more often used as host. Southern populations of A.tabida are better in evading the immune response of D.melanogaster, but still may suffer significant egg mortality by encapsulation of the eggs (Kraaijeveld & van Alphen, 198?).

 

In this project we want to investigate the potential effects of a warmer climate on the rate of encapsulation of A.tabida eggs by Drosophila melanogaster. We predict that encapsulation rate will increase with temperature, as found before. If indeed we find that encapsulation of A.tabida eggs varies with temperature, we can use the finding that the profitability of D.melanogaster as host varies with temperature to predict host species selection. A.tabida females are most often time limited (Ellers et al., 200?) hence they can maximize their fitness by maximizing the number of offspring per unit of time. We can now calculate whether an A.tabida female should accept or reject D.melanogaster larvae when foraging on a patch containing a mixture of both species of larvae. Optimal host species selection depends on the encounter rates with both D.subobscura larvae and D.melanogaster larvae, on oviposition and recognition times and on host profitability. To test the predictions of this simple host selection model We measure profitability of D.subobscura larvae and D. melanogaster larvae at 18°C, 21°C and 24°C for the Sospel strain of A.tabida. Next we allow A.tabida females of the Sospel strain to search at 21°C for D.subobscura and/or D.melanogaster larvae at different densities and measure s and m. Similar experiments at 18°C and 24°C will show if encounter rates increase with temperature or not. Using the optimal host selection model, we then calculate at which density they should begin to accept D.melanogaster larvae.

Next we do host selection experiments offering equal numbers of D.melanogaster and D.subobscura at the density where they should switch. Stochastic variation in encounter rates with both species will cause partial acceptance and partial rejection of D.melanogaster larvae in this experiment. We then repeat the experiments at 18°C and 24°C. The predicted outcome

is that rejection rates will be higher at 24°C and lower at 18°C. This tells us that A.tabida responds or not to temperature with a switch in host selection behaviour. Although finding a response would be spectacular, establishing that such a response is lacking is also useful to predict the change in impact of A.tabida on D.melanogaster populations when the climate becomes warmer.

 

Contact: Jacques van Alphen

(http://132.229.50.4/~alphen/)

Korte beschrijving: Fruitvlieg larven worden vaak blootgesteld aan sluipwesp aanvallen. Als de sluipwesp zijn eitje gelegd heeft in de larven, dan kan de larven deze inkapselen, mits hij resistent is. Resistent zijn is niet altijd een voordeel, omdat het kostbaar is: resistente larven bewegen hun kaken minder snel, waardoor ze ook minder snel voedsel opnemen en minder snel groeien. Dit is één trade-off van resistentie. Mogelijk zijn er meer trade-offs, waaronder het vermogen om als man een vrouwtje te bevruchten. Fruitvlieg vrouwtjes paren meerdere keren in hun leven. Tussen twee paringen zit een aantal dagen. Dit komt doordat tijdens het overbrengen van sperma, er ook eiwitten bij het vrouwtje binnen komen die tijdelijk voorkomen dat het vrouwtje herpaart met een mannetje. Dit vermogen om te voorkomen dat een vrouwtje herpaart varieert tussen mannen. Ook zou het mogelijk zijn dat niet resistent fruitvlieg mannen daar beter in zijn dan resistente mannen, puur omdat het produceren van deze eiwitten mogelijk kostbaar is. Resistent zijn is duur, dus misschien heb je minder energie om deze eiwitten te maken.  

 

Vraagstelling: Herparen vrouwtjes eerder als ze eerst gepaard hebben met een resistente fruitvlieg man vergeleken met vrouwtjes die eerst gepaard hebben met en niet resistente man?

 

Technieken: a) het onderhouden van fruitvlieg lijnen, b)het opzetten van paringen en het paringsgedrag observeren c) data analyse met de daarbij behorende statistiek d) wordt er een verschil gevonden dan kunnen we met moleculaire technieken bepalen of de hoeveelheid eiwitten verschilt tussen controle (niet-resistent) en resistente mannen.

 

Periode: Vanaf Juni 2006 tot en met December 2008.

Bachelor of Masterstage: Kan allebei. Duur in overleg.

Vereist: Interesse in seksuele selectie en life-history trade-offs.

 

Contact: Femmie Kraaijeveld-Smit

 

 (http://biology.leidenuniv.nl/~smit/index.html)

Korte beschrijving: In het veld worden de larven van fruitvliegen vaak geparasiteerd door sluipwespen. Als de larve niet resistent is, ontwikkeld zich uit de fruitvlieg larve een sluipwesp i.p.v. een fruitvlieg. De mate van resistentie tegen een sluipwesp aanval varieert over heel Europa. Ook is bekend dat het paringssucces van resistente fruitvlieg mannen hoger is dan van mannen die niet immuun zijn. Dit was getest met vrouwtjes uit een gebied waar resistentie belangrijk is, omdat sluipwespen vaak aanvallen. Het is niet bekend of dit verschil in succes veroorzaakt wordt doordat vrouwtjes een voorkeur hebben voor die resistente mannen op basis van morfologische verschillen, of doordat het paringsgedrag verschilt tussen resistente en niet resistente mannen. Door vrouwtjes te manipuleren kan bepaald worden of dit gedrag verschilt. Deze gedragsobservaties zullen uitgevoerd worden in het lab van Dr. Ferveur in Dijon, Frankrijk.

 

Vraagstelling: Is het hogere paringsucces van resistente mannen gebaseerd op gedragsverschillen tussen resistente en niet resistente fruitvlieg mannen?

 

Technieken: a) het onderhouden van fruitvlieg lijnen, b) het opzetten en uitvoeren van gedragsobservaties van parende vliegen (daarbij gebruik makende van resistente en niet resistente mannen), waaronder ook video opnames, c) het analyseren van deze (video) data.

 

Periode: Vanaf Juli 2006 en in overleg met Dr. Ferveur.

Bachelor of Masterstage: Minimale duur van 3 maanden, waarvan 1 maand in Dijon.

Vereist: Interesse in gedragsbiologie en zin in een tripje naar Frankrijk. Het spreken van de Franse taal zou een voordeel zijn.

 

Contact: Femmie Kraaijeveld-Smit

 

 (http://biology.leidenuniv.nl/~smit/index.html)

Correlatie tussen resistentie en feromoon concentratie

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Ik ben al een tijdje bezig om uit te zoeken of fruitvliegen die resistent zijn tegen sluipwesp aanvallen anders ruiken dan fruitvliegen die niet resistent zijn (Gas Chromatograaf analyses van de feromonen). Het probleem met de resistente lijnen is dat ze nooit 100% resistent worden (maar 60%). Dus alle schijnbare verschillen tussen de controle en resistente lijnen zijn bijna nooit significant. Het mooiste zou zijn als de feromoon samenstelling van de mannetjes gecorreleerd  kon worden met hun resistentie niveau. Dit zou haalbaar zijn door mannetjes te laten paren met niet resistente vrouwtjes. Daarna de GC analyse uit te voeren op de mannetjes plus het resistentie niveau van de nakomelingen bepalen. Vervolgens zou een correlatie analyse (met nakomelingen resistentie op de x - as en feromoon concentratie op de y-as) moeten aantonen of resistente mannen inderdaad meer of minder van een bepaald feromoon hebben.

 

Periode: Vanaf October 2007

Mogelijk als Bachelor of Master stage

 

Contact: Femmie Kraaijeveld-Smit

 

 (http://biology.leidenuniv.nl/~smit/index.html)

Korte beschrijving: De mate van resistentie onder fruitvliegen tegen parasitisme door sluipwespen varieert over heel Europa. Ook is bekend dat het paringssucces van resistente fruitvlieg mannen hoger is dan van mannen die niet immuun zijn. Dit was getest met vrouwtjes uit een gebied waar resistentie belangrijk is, omdat sluipwespen vaak aanvallen. We weten dat de feromoonsamenstelling op de huid van de mannetjes verschilt tussen resistente en niet resistente mannen. Het zou dus kunnen zijn dat vrouwtjes aan de hand van deze feromonen (koolwaterstofverbindingen) kunnen inschatten of het een geschikte partner is (geschikt is dan in het geval waar resistent zijn van belang is de resistente man). Om dit te testen zullen we proberen de feromonen van resistente mannen over te brengen op niet resistente mannen. Vrouwtjes mogen dan vervolgens kiezen tussen deze geparfumeerde man en een ongeparfumeerde controle man (niet resistent). 

 

Vraagstelling: Is het verschil in paringsucces van resistente en niet resistente fruitvlieg mannen gebaseerd op het verschil in de koolwaterstoffen op de huid van deze mannetjes?

 

Technieken: a) het onderhouden van fruitvlieg lijnen, b) het uittesten van de beste parfumeer techniek, c) gas chromatografie om koolwaterstofverbindingen vast te stellen en ook het uitwerken van de gegevens, d)het opzetten van paringen en het paringsgedrag observeren d) data analyse met de daarbij behorende statistiek

 

Periode: Het gehele jaar door, vanaf Juni 2006 tot en met December 2008.

Bachelor of Masterstage: De duur van de stage is minimaal 3 maanden.

Vereist: Interesse in en verstand van seksuele selectie en soortsvorming

 

Contact: Femmie Kraaijeveld-Smit

Modelling an adaptive radiation in a single gene

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lands.jpgWe are looking for a enthusiastic master student to help us build a computer model to be used in the development and interpretation of an evolution experiment with bacteria. The student will (i) learn to program in R or another language of choice (ii) learn the relevant ecological, evolutionary, and biochemical theory, and (iii) develop and validate the mathematical model in cooperation with us.

 

Understanding the evolutionary origins of patterns of biodiversity is a major problem in biology. We are currently designing an experiment to examine the role of genetic constraints in the evolution of patterns of biodiversity. The project will make use of experimental evolution of bacteria.

     There are two major theoretical obstacles to developing this experiment that have to be overcome. Firstly, we have to find the right experimental conditions under which  adaptive radiations occur. Secondly, we wish to be able to interpret the data in quantitatively terms of key variables of the organisms and the environment.

     In order to meet these challenges, we will build a computer model of our experimental system that models the evolution of patterns of diversity. The model will make use of empirically determined parameter values.

 

Contact Bertus Beaumont (h.j.e.beaumont@biology.leidenuniv.nl) or Tom Van Dooren (t.j.m.van.dooren@biology.leidenuniv.nl) for more information.

 

 

 

Chromosome evolution in Austrolebias killifish

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gymno.jpg 

 Recent genomics studies confirm that as much genetic variation is due to structural genetic changes such as differences in gene copy number and chromosome rearrangements than as to single-nucleotide polymorphisms.  In order to understand the evolution of that kind of genetic variation, one needs to investigate which chromosome arrangements occur in different species, and whether rearrangements are associated with life history differences between species or not.

 

  karyo.jpg 

In this project, we investigate the evolution of chromosomal structural genetic changes using South-American annual Austrolebias killifish as a model system.

The putative ancestral number of chromosomes for the genus is 2N = 48 acrocentric chromosomes (number of arms NF = 48). Austrolebias prognathus has  2N = 36 chromosomes, with NF = 48 arms, implying that several chromosome fusions have occurred. There are several more changes documented in the Austrolebias genus, but the picture is incomplete. We keep over 25 species of the genus in the lab, and already have a molecular phylogeny. The student can make karyotypes of all those species using cells from fin-clips, and map chromosomal changes observed in the karyotypes on the molecular phylogeny.

 

This is a project for a Master student.

Prerequisites: Some familiarity with handling fish and with lab techniques is advantageous, but not strictly necessary.

Supervisors: Tom Van Dooren (t.j.m.van.dooren@biology.leidenuniv.nl), Kees Hofker and Gerda Lamers (IBL Visualization).

About this Archive

This page is a archive of entries in the Master Project category from April 2008.

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