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Tykanie biologicznego zegara u samic sikorek zależy od samców

2011-01-26 11:48
Foto. Krzysztof Merski

Płodność samic ptaków, podobnie jak u kobiet, pogarsza się z upływem czasu. Niektóre samice mogą jednak spowolnić tykanie biologicznego zegara wybierając odpowiednich partnerów - informują naukowcy w piśmie "Oikos".

Wraz z wiekiem samice ptaków stają się coraz mniej płodne - zauważa jeden z autorów badania, Josh Auld z National Evolutionary Synthesis Center w Durham (USA). Starsze samice nie tylko składają mniej jaj, ale też zaczynają je składać na późniejszym etapie sezonu lęgowego. Kiedy zaś młode się wylęgną i wymagają karmienia, samicom trudniej jest zdobyć mniej wówczas dostępny pokarm.

Mimo licznych dowodów na pogarszającą się płodność samic naukowcy niewiele jednak wiedzieli, jaką rolę grają w tej sytuacji samce. "Myślano, że się nie liczą" - mówi Auld, cytowany przez serwis ScienceDaily.

Aby tę tezę zweryfikować, naukowcy analizowali gromadzone od wielu lat dane na temat sikor modrych. Obserwacje i badania tysięcy tych leśnych ptaków z populacji zajmującej wyspę Korsykę prowadzono od końca lat 70.

Sikory modre rozmnażają się raz w roku, często co roku znajdując sobie coraz to innego partnera. Obrączkując ptaki i obserwując ich gniazda naukowcy są w stanie ustalić, które osobniki łączą się ze sobą, ile składają jajek i kiedy oraz jak z biegiem czasu rozwijają się ich młode.

Analizując dane na temat niemal sześciuset samic i tyluż samców (gromadzone przez 28 lat) naukowcy ze zdziwieniem dostrzegli, iż to, jak szybko z biegiem czasu samica traci płodność, po części zależy od jej partnerów.

Samiczki, decydując się na wybór samców, zwracają uwagę nie tyle na ich wiek czy tożsamość, co na ojcowską przeszłość. "Liczy się historia samca" - zwraca uwagę Anne Charmantier z National Center for Scientific Research we Francji.

U sikorek, których partnerem zostaje stosunkowo młody samiec-debiutant, płodność spada stosunkowo wolniej. "Samice, które raz po raz łączą się z młodymi samcami, mają się lepiej. Nie starzeją się tak szybko" - dodaje Auld.

Samce, które wcześniej zaczynają się rozmnażać, jako partnerzy okazują się zdrowsze lub bardziej zaradne niż te, które z ojcostwem zwlekają. Mogą być w lepszej formie lub mieć mniej pasożytów - spekuluje Charmantier.

Te cechy sprawiają, że samce okazują się lepsze w roli ojców, dzięki czemu samica mniej się eksploatuje. U sikor modrych samiec pomaga bowiem budować gniazdo, przynosi też samicy pokarm podczas składania i wysiadywania jaj. Później pomaga w opiece nad pisklętami - wylicza Auld. ZAN

 

 

źródło: www.naukawpolsce.pl

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