Global warming has shifted phenological traits in many species, but whether species are able to track further increasing temperatures depends on the fitness consequences of additional shifts in phenological traits. To test this, we conducted a genomic selection experiment on wild great tits from the Hoge Veluwe study population (The Netherlands) to obtain great tits (Parus major) with genotypes for extremely early and late egg lay dates and measured phenology and fitness of selected great tit females under wild conditions.

Females with early genotypes advanced lay dates relative to females with late genotypes, but not relative to non-selected females. Females with early and late genotypes did not differ in the number of fledglings produced, in line with the weak effect of lay date on the number of fledglings produced by non-selected females in the years of the experiment. Our study is the first application of genomic selection in the wild and led to an asymmetric phenotypic response that indicates the presence of constraints toward early, but not late, lay dates.

See the associated article for materials and methods.

Open-source software was used. All analyses were performed in R (R package rethinking (https://github.com/rmcelreath/rethinking) was used for statistical analysis).