Microsatellite and mitochondrial DNA homogeneity among phenotypically diverse crossbill taxa in the UK

Genetic differentiation within and between the three morphologically diverg ent crossbill species extant in the UK was assessed by comparison of allele frequencies at five unlinked microsatellite loci and DNA sequence variatio n across the mitochondrial control region. No significant differences in mi crosatellite allele frequency were found either between different populatio ns of the same species or between the crosshill species themselves. A simil ar lack of genetic divergence was apparent from the mitochondrial sequence data. We resolved 33 different haplotypes; separated by low levels of seque nce divergence (0-0.15%). Levels of divergence within and between species w ere not significantly different. Haplotypes formed a polyphyletic phylogeny , indicating that the crossbill species do not form genetically separate cl ades. Discordance between neutral DNA polymorphisms and adaptive morphologi cal variation is discussed in relation to defining the systematic relations hip between crossbill forms. If adaptive differences have arisen without a concomitant divergence in neutral DNA then attempting to define crossbill t ypes from microsatellite and mitochondrial DNA without recourse to ecology and behaviour may be misleading.