Climate change outpaces adaptive potential via hybridization in nesting female Saltmarsh and Nelson’s Sparrows

Hybridization and introgression can promote adaptive potential and evolutionary resilience in response to increased pressures of climate change; they can also disrupt local adaptation and lead to outbreeding depression. We investigated female fitness consequences of hybridization in two sister species that are endemic to a threatened tidal marsh ecosystem: Saltmarsh (Ammospiza caudacutus) and Nelson’s Sparrows (A. nelsoni). We found increasing nest flooding rates due to rising sea levels are outpacing potential adaptive benefits of hybridization due to very low overall nesting success in both the Nelson’s and Saltmarsh Sparrows. In the center of the hybrid zone across two years, we determined the success of 201 nests of 104 pure and admixed Saltmarsh and Nelson’s Sparrow females, genotyped using a panel of Single Nucleotide Polymorphisms (SNPs) from double digest restriction-site associated DNA (ddRAD) Sequencing. We evaluated five metrics of female fitness and modeled nesting success i..., We captured, banded, and genotyped a total of 104 female sparrows across the two sites and years. We monitored 202 nests (including 301 nestlings) of pure and admixed Saltmarsh and Nelson’s Sparrows across the two sites across the 2016 and 2017 breeding seasons. We conducted nest monitoring at both sites during May-August, encompassing three nesting cycles each in 2016 and 2017, as described in Maxwell et al. 2021 and following protocols from Saltmarsh Habitat and Avian Research Program (SHARP, www.tidalmarshbirds.org). Nests were visited every 3–4 days until completed and assigned an overall fate (fledged, failed due to flooding, failed due to predation, or failed due to unknown causes), following established standardized protocols (Ruskin et al., 2017). We calculated date of nest initiation based on known duration of egg-laying (3–5 days), incubation (11–12 days), and chick development (8–11 days) to determine first egg date following methods developed by Shriver et al. (2007).
We col..., Data files are provided as CSV spreadsheet files and do not require any special software to open or use. From here, data can be used for modeling or for creation of capture histories for survival analysis.Â