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

Genetic differentiation within and between the three morphologically divergent crossbill species extant in the UK was assessed by comparison of allele frequencies at five unlinked microsatellite loci and DNA sequence variation across the mitochondrial control region. No significant differences in microsatellite allele frequency were found either between different populations of the same species or between the crossbill species themselves. A similar lack of genetic divergence was apparent from the mitochondrial sequence data. We resolved 33 different haplotypes, separated by low levels of sequence divergence (0-0.15%). Levels of divergence within and between species were not significantly different. Haplotypes formed a polyphyletic phylogeny, indicating that the crossbill species do not form genetically separate clades. Discordance between neutral DNA polymorphisms and adaptive morphological variation is discussed in relation to defining the systematic relationship between crossbill forms. If adaptive differences have arisen without a concomitant divergence in neutral DNA then attempting to define crossbill types from microsatellite and mitochondrial DNA without recourse to ecology and behaviour may be misleading.

A note on eggshell porosity, nest humidity and the effects of DDE in the grey heron (Ardea cinerea).

Water vapour conductance (GH2O) was determined for 25 grey heron Ardea cinerea eggs in the laboratory, and in nests during natural incubation at two Scottish colonies. The mean GH2O of eggs measured in the nest which successfully hatched was 9.0 mgH2O/mmHg/day and the mean water vapour pressure gradient between egg and nest (delta PH2O), measured using "calibrated" duck eggs, averaged at 31 mmHg (4.13 kPa). Based on eggshell porosity results, from the eggs which hatched, such a gradient would result in a loss of water from the eggs during incubation equivalent to 11% of their fresh weight. Shell thickness, the number of pores/cm2 of eggshell and DDE content were also determined for the 25 eggs measured in the laboratory. Eggs containing high levels of DDE had thinner shells, more pores in the eggshell and a higher overall eggshell porosity. The main problem posed by a high level of DDE would appear, however, not to be an excessive water loss from the egg during incubation, but rather eggshell thinning leading to a loss of the egg due to breakage in the nest.