Science by mePosted by Susanne den Boer Fri, March 19, 2010 14:21:55Our science paper on sperm competition came out yesterday, yay!:
S.P.A. den Boer, B. Baer & J.J. Boomsma (2010). Seminal fluid mediates ejaculate competition in social insects. Science 327, 1506-1509.
We got a great response so far, with many people reporting about our research (tv / radio / newspapers / blogs). I found a really nice blog written by Ed Yong (view here), that I would like to share with you. Ed writes in a very clear and amusing way about our science. Below you can read what Ed wrote, I have added the pictures myself.
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SPERM WARS - THE SPERM OF ANTS AND BEES DO BATTLE INSIDE THE QUEENS by Ed Yong, March 18 2010, 2PM
One night of passion and you're filled with a lifetime full of sperm with no need to ever mate again. As sex lives go, it doesn't sound very appealing, but it's what many ants, bees, wasps and termites experience. The queens of these social insects mate in a single "nuptial flight" that lasts for a few hours or days. They store the sperm from their suitors and use it to slowly fertilise their eggs over the rest of their lives. Males have this one and only shot at joining the Mile High Club and they compete fiercely for their chance to inseminate the queen. But even for the victors, the war isn't over. Inside the queen's body, their sperm continue the battle.
If the queen mates with several males during her maiden flight, the sperm of each individual find themselves swimming among competitors, and that can't be tolerated. Susanne den Boer from the University of Copenhagen has found that these insects have evolved seminal fluids that can incapacitate the sperm of rivals while leaving their own guys unharmed. And in some species, like leafcutter ants, the queen steps into the fray herself, secreting chemicals that pacify the warring sperm and ease their competition.
Queens of the bumblebee Bombus terrestris only mate with a single male (photo by Boris Baer)
The amazing thing about this chemical warfare is that it has evolved independently several times. Social insects evolved from ancestors that observed strictly monogamous relationships. Even now, the queens from many species mate with just one male during their entire lives. With just one set of sperm in their bodies, they have no problem with sperm conflict. The trouble starts when species start mating with several males during their nuptial flights, as honeybees, social wasps, leafcutter ants, army ants, and others do today.
A virgin queen of the leafcutter ant species Atta colombica. These queens will store the sperm of around 3 males in a special storage organ, the spermatheca, and they will use this sperm supply to internally fertilize eggs throughout their lives (photo by Boris Baer).
To understand the sperm wars, den Boer exposed sperm from different species to their own seminal fluids, those of brothers, or those of unrelated males. In two species of bees and three species of ants, she found that a male's seminal secretions are a boon to his own sperm. Even at small concentrations, they managed to boost the survival of sperm that had been stored in saline.
In species where queens mate with a single male, like bumblebees and Trachymyrmex zeteki ants, the seminal fluids had the same beneficial effect on the sperm of unrelated individuals. But these chemicals weren't so benign in species where queens store sperm from several males, like honeybees and the ants Atta colombica and Acromyrmex echinatior. There, they significantly reduced the survival rates of competitor sperm, slashing them from 6-18% after just 30 minutes.
An assay to determine the viability of sperm cells after being exposed to the seminal fluid of the same male or of a competitor. Shown is honeybee sperm, live sperm are green, dead are red (photo by Susanne den Boer)
How seminal fluids know to attack other sperm is a mystery. The fact that a brother's sperm also suffers, even though it shares much of the same DNA, suggests that the method involves a blanket attack on anything that isn't recognised as "self". And as with many wars, both sides suffer. It turns out that the protective chemicals from one set of seminal fluids can't counteract the destructive chemicals from another. If the two are mixed, no set of sperm survives very well.
From the queen's point of view, these battles are positively counter-productive. The more sperm she has, the more eggs she can fertilise and the more young she can raise. It's in her interest to stop the sperm from killing each other. Den Boer found that the queens of the leafcutter Atta colombica do just that. The fluids from a queen's spermathecae (the organ where she keeps her sperm supplies) can quell the destructive effect of rival seminal fluids. If they're added to the mix, survival rates for all the stored sperm shoot back up to normal levels. If the sperm wars get too heated, the queen evolves to restores peace for the sake of her future kingdom.
Science by mePosted by Susanne den Boer Fri, March 19, 2010 13:32:13Below you can read the Danish press release for our paper that just appeared in Science. I will post an English version soon.
S.P.A. den Boer, B. Baer & J.J. Boomsma (2010). Seminal fluid mediates ejaculate competition in social insects. Science 327, 1506-1509.
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SOCIALE INSEKTER GÅR AFTER DEN BEDSTE SÆD
Sociale insekter er intet mindre end geniale til at bevare den allerbedste sædkvalitet og sørge for, at der er nok af den. Afhængig af arten formerer dronninger af myrer og bier sig som unge jomfruer med en eller flere hanner og gemmer sæden resten af livet. Hunnerne opbevarer sæden i et særligt organ, så den kan bruges efter behov. Det betyder, at hannernes sæd benyttes langt tid efter, at de selv er afgået ved døden. Ny forskning på Københavns Universitet om dette emne offentliggøres nu i det anerkendte videnskabelige tidsskrift Science.
Det er en kendt sag, at vi mennesker mange steder på jorden har problemer med dårlig sædkvalitet.
Sådan er det ikke blandt sociale insekter såsom myrer og bier. I det seneste nummer af tidsskriftet Science viser et førende dansk forskerhold fra Danmarks Grundforskningsfonds Center for Social Evolution (CSE), Biologisk Institut på Københavns Universitet under ledelse af professor Jacobus Boomsma, hvorledes myrer og bier sørger for, at også på sædcelleniveau er det de stærkeste, der overlever og dermed sikrer koloniens fremtid.
Tidligere havde videnskaben en teori om, at hunnerne blandt de sociale insekter valgte den bedste sæd. Denne teori er nu bekræftet med forskningsresultaterne fra Københavns Universitet. Den samme teori har også optrådt i forbindelse med os mennesker, hvis en kvinde i løbet af sin ægløsning har forhold til flere forskellige mænd, men denne teori er aldrig blevet videnskabeligt bevist.
Det er den nu hos sociale insekter. At de er så sofistikerede hænger sammen med, at dronninger af avancerede myrer, nogle gedehamse og honningbier har et specielt organ, der opbevarer adskillige hanners sæd samme sted. Når disse dronninger parrer sig med hannerne er deres sæd ledsaget af en sædvæske, som beskytter den enkelte hans sæd.
De nye forskningsresultater viser, at sædvæsken fra hannerne indeholder stoffer, som genkender andre hanners sædceller, hvilket kan føre til en regulær ”spermkrig” sædcellerne imellem. Hannernes indbyrdes konkurrence er dermed med til at sikre deres egen genetiske arv. Men endnu mere opsigtsvækkende viser de nye forskningsresultater, at det i sidste ende er ”mor”, der bestemmer, hvilken sperm, hun vil befrugte sine æg med – trods den indbyrdes konkurrence mellem de mandlige sædceller. Det hænger sammen med, at hunnernes specielle organ er en slags ”sædbank”, hvori der produceres et ukendt stof, som kan neutralisere det maskuline ”konkurrence-stof”. Det er altså hunnerne som i sidste ende bestemmer, hvilken sæd, der skal benyttes, og hvor meget der skal opbevares i hendes sædbank.
100 millioner æg
En honningbi-dronning kan leve i op til syv år. Hendes eneste opgave er at lægge æg, og gennem hele hendes liv er hun stand til at befrugte op til en million æg. Men det er ingenting i forhold til den store bladskærermyre, hvor dronningen befrugter op til 100 millioner af sine æg hvis hun kommer til at leve hendes 20 leveår ud. Dermed kan hun opretholde en kæmpe koloni på ca. fem millioner arbejdermyrer, hvis liv ikke blot er hårdt, men også ganske kort. Myredronningen har i denne proces stor gavn af sit organ, hvor al sæd er samlet og bevaret. Hun bruger ganske lidt sæd ved hver befrugtning af sine æg, fordi mængden af sæd skal holde hele hendes liv. Hun er derfor særdeles interesseret i at eliminere hannernes interne ”sæd-kamp”, så hun har så meget sæd til rådighed som muligt.
Myre-dronningens hemmeligheder er langsomt ved at blive afsløret. Forskningen, der i dag offentliggøres i Science, løfter sløret for flere af dem. Først og fremmest viser resultaterne, at sociale insekter indretter sig efter behov – sandsynligvis kontrolleret og styret af dronningen. Det er ikke blot et spørgsmål om kvalitet, når sæden skal udvælges, men også om kvantitet for at opretholde en livslang og stor konto i dronningens egen sædbank.
”Det er utroligt, at vi mennesker skal bruge flydende nitrogen for at opbevare sædceller i lang tid, hvorimod myrerne har opfundet naturlige sædbanker, som fungerer ved stuetemperatur. På den måde er de langt mere sofistikerede end os mennesker,” siger Jacobus Boomsma, som har stået i spidsen for forskerholdet med de opsigtsvækkende resultater.
FAKTABOKS:
Forskningen er lavet i samarbejde med Susanne den Boer, en hollandsk Ph.d-studerende som fik sin grad i sidste år, og Boris Baer, som tidligere var postdoc ansat på CSE, men nu arbejder med sit eget team i Perth, Australien. Boris Baers forskning bidrager blandt andet med, hvilke proteiner og cellulære mekanismer, der regulerer dronningernes ”sædbank” (Baer et al, 2009 a,b). I september drager Susanne den Boer til Perth, støttet af et internationaliseringsstipendium fra Københavns Universitet og en EU Marie Curie ”outgoing postdoctoral fellowship”, som vil bringe hende tilbage til CSE i foråret 2013.
KONTAKTDATA:
Susanne P.A. den Boer & Jacobus J. (Koos) Boomsma, Center for Social Evolution, Biologisk Institut, Københavns Universitet, Universitetsparken 15, 2100 København Ø
Telefon: Professor Jacobus J. Boomsma: 35321340 (kontor), 20436771 (mobiltlf.) /
Susanne den Boer +45 41188436 (mobiltlf.)
Boris Baer, Centre (ARC Centre of Excellence in Plant Energy Biology UWA); Tlf: +61 8 6488 4495 / +61 4 24 652 9111
