Abstract
Prenatal mortality is typically overlooked in population studies, which biases evolutionary inference by confounding selection and inheritance. Birds represent an opportunity to include this ‘invisible fraction’ if each egg contains a zygote, but whether hatching failure is caused by fertilization failure versus prenatal mortality is largely unknown. We quantified fertilization failure rates in two bird species that are popular systems for studying evolutionary dynamics and found that overwhelming majorities (99.9%) of laid eggs were fertilized. These systems thus present opportunities to eliminate the invisible fraction from life-history data.
Highlights
Study populations of wild animals offer great insight into the ecological and evolutionary processes operating under natural conditions, based on the ability to observe sampled individuals throughout their lives [1]
Assuming these rates of fertilization failure are consistent with those of unhatched eggs that were not examined, we estimate that 9 of 10 047 (0.1%) eggs laid by blue tits, and 9 of 6788 (0.1%) eggs laid by great tits over the course of the study were unfertilized
If we had relied on non-microscopic examination of egg contents for diagnosis, we would have found that approximately 52% of unhatched blue tit eggs and 33% of unhatched great tit eggs were unfertilized
Summary
Study populations of wild animals offer great insight into the ecological and evolutionary processes operating under natural conditions, based on the ability to observe sampled individuals throughout their lives [1]. Hatching failure in both wild and domestic birds results from either fertilization failure (i.e. the egg formed in the absence of a zygote) or prenatal mortality, and researchers typically rely on visual inspection of eggs’ contents to distinguish between these fates
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