Plasticity in female timing may explain earlier breeding in a North American songbird

Abstract

1. Many species have shifted their breeding phenology in response to climate change. Identifying the magnitude of phenological shifts and whether climatemediated selection drives these shifts is key for determining species' resilience to climate change. Birds are a strong model for studying phenological shifts due to numerous long-term research studies; however, generalities pertaining to drivers of phenological shifts will emerge only as we add study species that differ in life history and geography.2. We investigated 32 years of reproductive timing in a non-migratory population of dark-eyed juncos Junco hyemalis. We predicted that plasticity in reproductive timing would allow females to breed earlier in warmer springs. We also predicted that selection would favour earlier breeding and asked whether the temperatures throughout the breeding season would predict the strength of selection.3. To test these predictions, we examined temporal changes in the annual median date for reproductive onset (i.e. first egg date) and we used a sliding window analysis to identify spring temperatures driving these patterns. Next, we explored plasticity in reproductive timing and asked whether selection favoured earlier breeding. Lastly, we used a sliding window analysis to identify the time during the breeding season that temperature was most associated with selection favouring earlier breeding. 4. First egg dates occurred earlier over time and strongly covaried with April temperatures. Furthermore, individual females that bred in at least 3 years typically bred earlier in warmer Aprils, exhibiting plastic responses to April temperature.We also found significant overall selection favouring earlier breeding (i.e. higher relative fitness with earlier first egg dates) and variation in selection for earlier breeding over time. However, temperature across diverse climatic windows did not predict the strength of selection. 5. Our findings provide further evidence for the role of phenotypic plasticity in shifting phenology in response to earlier springs. We also provide evidence for the role of selection favouring earlier breeding, regardless of temperature, thus setting the stage for adaptive changes in female breeding phenology. We | 1989

The biotic and abiotic drivers of timing of breeding and the consequences of breeding early in a changing world

“…Lay date may also vary due to intraindividual variation, whereby females adjust lay date to match environmental conditions through plastic responses (Hoover and Schelsky 2020, Burant et al 2022, Kimmitt et al 2022). Phenotypic plasticity, when a single genotype can produce multiple phenotypes in response to environmental conditions (Pigliucci 2005), can contribute to variation in lay date between years (Nussey et al 2005, Brommer et al 2008).…”

Complex relationships between climate and reproduction in a resident montane bird

“…We conducted sliding window analyses to test which climate variables best-predicted variation in timing of breeding and reproductive performance across years [ 13 , 18 , 27 , 61 – 63 ]. We ran separate sliding window analyses for each combination of climate and breeding variables to determine the climatic periods associated with variation in each breeding variable [ 61 ].…”