Fluctuating asymmetry is a function of population isolation in island lizards

Abstract

We measured the level of fluctuating asymmetry (FA) in head shape, head scalation and femoral pores in two lizard species (Podarcis bocagei and Podarcis hispanica) from 13 islands and 15 mainland localities in the Ria de Arosa archipelago of north-western Spain. Given the recent geological history of the region, the degree of isolation to which lizard populations have been subjected can be ordered along a spatio-temporal gradient, yielding the following hypotheses to be tested: FA will be higher (1) in island populations than in mainland populations; (2) on remote islands than on islands close to the mainland; (3) on small islands than on large islands. Molecular genetic data suggest that P. hispanica is autochthonous in the Ria de Arosa, whereas P. bocagei is a more recent arrival. Therefore, we predict also (4) a higher level of FA in P. hispanica than in P. bocagei. Statistically significant results were obtained for head-shape asymmetry, supporting the second and the fourth hypotheses. With an overall meristic asymmetry index, none of the hypotheses were corroborated, whereas for certain independent meristic traits, the first, the third and the fourth hypotheses were partially supported. Both head shape and meristic traits constitute precise measures of FA, but FA is more convincingly expressed in head shape and in single meristic traits than in overall meristic traits asymmetry. We conclude that FA reflects population isolation and may be a good indicator of developmental instability. It seems worthwhile to test for FA in a landlocked system under environmental and genetic stress, for the purpose of conservation biological assessments.