Population differentiation on islands: a case study using blue titsin habitat mosaics

Blue Tit (Cyanistes caeruleus) Science Article 3

abstract

We hypothesized that changes in life history traits of populations on islands, especially the components of nicheenlargement, habitat tenacity and reduced dispersal of the ‘insular syndrome’, would result in greater rather than smallerphenotypic variation in populations on islands as compared to mainland counterparts. We tested these predictions with longterm studies of blue tits (Parus c ruleus) on Mediterranean mainland and insular habitats. These habitats are particularlysuitable for investigating the causes and consequences of phenotypic variation affected by spatially variable selection regimesbecause they are mosaics of patches in which strongly divergent selection pressures result from major habitat-specific differencesin the timing and abundance of food. Considerable inter-habitat phenotypic variation was found in a series of lifehistory traits (demographic, morphometric, behavioral) in the tits, variation that was much higher on the island of Corsica, inparticular, than the adjacent mainland. Birds there synchronized their breeding more tightly to local seasonal variations in foodthan on the mainland as a result of low dispersal and strong site tenacity. Two populations only 25 km apart and subject tostrongly divergent resource-based selection regimes became so differentiated that they reached reproductive isolation. Localdifferentiation in blue tits on Corsica supports the divergence-with-gene-flow model of speciation, which is central to theevolution of reproductive isolation.

Jacques Blondel, Anne Charmantier, Acta Zoologica Sinica 52(Supplement): 267-270, 2006

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