Inheritance and variation in eggshell patterning in the great tit Parus major

Area of Science:

• Evolutionary Biology
• Genetics
• Ornithology

Background:

• The inheritance and function of avian eggshell patterns remain poorly understood.
• Eggshell pattern mimicry is crucial for brood parasitism, like that seen in cuckoos.
• Previous theories suggested female sex chromosome (W) linkage for egg pattern evolution, but this was unproven.

Purpose of the Study:

• To investigate the inheritance patterns of eggshell pigment patterns in a wild great tit population.
• To determine if eggshell patterns are genetically linked to sex and maternally inherited.
• To provide evidence for or against the hypothesis of female sex-linked inheritance of eggshell patterning.

Main Methods:

• Quantified three measures of egg-pigment patterns in a wild great tit population.
• Analyzed the resemblance of egg patterns between daughters, mothers, and grandmothers (maternal and paternal).
• Assessed the influence of female age and condition, and environmental factors on egg patterns.

Main Results:

• Eggshell pigment patterns were found to be female specific.
• No significant relationship was observed between egg patterns and female age or condition.
• Weak environmental effects were detected, but patterns showed strong maternal inheritance.
• Daughters' egg patterns resembled their mothers' and maternal grandmothers', but not paternal grandmothers'.

Conclusions:

• This study provides the first evidence for female sex-linked inheritance of avian eggshell patterning.
• The findings increase the likelihood that similar genetic systems are involved in egg mimicry.
• This mechanism could explain how egg patterns are passed down in species exhibiting egg mimicry and their hosts.