Changing climate mediates sapsucker (Aves: Sphyrapicus) hybrid zone movement.

Shawn M Billerman,Matthew D Carling,Melanie A Murphy

doi:10.1002/ece3.2507

Abstract

Hybrid zones, where two divergent taxa meet and interbreed, offer unique opportunities to investigate how climate contributes to reproductive isolation between closely related taxa and how these taxa may respond to climatic changes. Red‐naped (Sphyrapicus nuchalis) and Red‐breasted (Sphyrapicus ruber) sapsuckers (Aves: Picidae) hybridize along a narrow contact zone that stretches from northern California to British Columbia. The hybrid zone between these species has been studied extensively for more than 100 years and represents an excellent system for investigations of the evolution of reproductive isolation. Shifts in the proportions of phenotypes at hybrid localities since 1910 that were inferred using specimens from museum collections were confirmed using species distribution models. We predicted the historical, current, and future distributions of parental and hybrid sapsuckers using Random Forests models to quantify how climate change is affecting hybrid zone movement in the Pacific Northwest. We found observed distribution shifts of parental sapsuckers were likely the result of climate change over the past 100 years, with these shifts predicted to continue for both sapsuckers over the next 80 years. We found Red‐breasted Sapsuckers are predicted to continue to expand, while Red‐naped Sapsuckers are predicted to contract substantially under future climate scenarios. As a result of the predicted changes, the amount of overlap in the distribution of these sapsuckers may decrease. Using hybrid phenotypes, we found the climate niche occupied by the hybrid zone is predicted to disappear under future conditions. The disappearance of this climate niche where the two parental species come into contact and hybridize may lead to a substantial reduction in genetic introgression. Understanding the impacts of global climate change on hybrid zones may help us to better understand how speciation has been shaped by climate in the past, as well as how evolution may respond to climate change in the future.

Highlights

The processes that generate biodiversity are inextricably linked with climate
We seek to address the following questions: (1) How well do climate data predict the current distribution of sapsuckers and the region where they hybridize? (2) Is there evidence that past climate change has impacted the observed shifts in the distributions of parental species, impacting where they come into contact and might hybridize? and (3) Will future climate change lead to predicted movement of the Red-breasted and Red-naped sapsucker hybrid zone? We predict that climate has led to the expansion of Red- breasted Sapsuckers and subsequent range retraction of Red-naped Sapsuckers and that this is an ongoing process that will continue to drive similar distribution changes in this system
We were able to accurately predict historical and current distributions for both Red- naped and Red-breasted sapsuckers (Figures 5a,b,d,e and 6a,b) and the extent of the hybrid zone based on hybrid locality data (Figure 6e)

Summary

| INTRODUCTION

The processes that generate biodiversity are inextricably linked with climate. As such, climate can be a strong predictor of species distributions (Pearson & Dawson, 2003), impacting species either directly through physiological tolerance (e.g., Pörtner, 2002) or indirectly through community interactions such as habitat suitability (e.g., Hirzel & Lay, 2008). Photographed in Fremont National Forest, Lake County, Oregon, May 2013.Photograph used with permission and copyright Thomas B Johnson these two species overlap, individuals with hybrid phenotypes are frequently encountered (Figure 1; Cicero & Johnson, 1995; Howell, 1952; Johnson & Johnson, 1985; Trombino, 1998). Recent museum collections from 2012 show birds with predominantly Red-breasted Sapsucker phenotypes with some hybrids, but no Red-naped Sapsuckers (Billerman and Carling, in prep). (2) Is there evidence that past climate change has impacted the observed shifts in the distributions of parental species, impacting where they come into contact and might hybridize? (3) Will future climate change lead to predicted movement of the Red-breasted and Red-naped sapsucker hybrid zone?

| METHODS

Findings

| DISCUSSION