Are hybrid albatrosses the result of rape? The case of Laysan and Black-foots in the Northern Pacific

Sievert Rohwer (Department of Biology and Burke Museum of Natural History, University of Washington, Seattle, USA) and colleagues have “pre-published” in the on-line open-access resource PeerJPrePrints on the link between hybridization and rape in Black-footed Phoebastria nigripes and Laysan P. immutabilis Albatrosses.

The paper’s abstract follows:

“Conspecific rape often increases male reproductive success.  However, the haste and aggression of forced copulations suggests that males may sometimes rape heterospecific females, thus making rape a likely, but undocumented, source of hybrids between broadly sympatric species.  We present evidence that heterospecific rape may be the source of hybrids between Black-footed and Laysan Albatrosses (Phoebastria nigripes, and P. immutabilis, respectively).  Extensive field studies have shown that paired (but not unpaired) males of both of these albatross species use rape as a supplemental reproductive strategy.  Between species differences in size, timing of laying, and aggressiveness suggest that Black-footed Albatrosses should be more successful than Laysan Albatrosses in heteropspecific [sic] rape attempts, and male Black-footed Albatrosses have been observed attempting to force copulations on female Laysan Albatrosses.  Nuclear markers showed that six hybrids we studied were F1s and mitochondrial markers shoed that male Black-footed Albatrosses sired all six hybrids.  The siring asymmetry found in our hybrids may have long persisted because an IM analysis suggests that long-term gene exchange between these species has been from Black-footed Albatrosses into Laysan Albatrosses.  If hybrids are sired in heterospecific rapes, they presumably would be raised and sexually imprinted on Laysan Albatrosses, and two unmated hybrids in a previous study courted only Laysan Albatrosses.

Laysan-Black-footed Albatross hybrid, photograph by Lindsay Young

Click here and here to read two previous postings in ACAP Latest News on hybrid Black-footed and Laysan Albatrosses.

Reference:

Rohwer, S., Harris, R.B. & Walsh, H.E. 2014.  Rape and the prevalence of hybrids in broadly sympatric species: a case study using albatrosses.  PeerJPrePrints  27 pp.

John Cooper, ACAP Information Officer, 21 May 2014