Exploring the hybrid speciation continuum in birds.

Jente Ottenburghs

doi:10.1002/ece3.4558

Abstract

Hybridization is increasingly recognized as a creative evolutionary force contributing to adaptation and speciation. Homoploid hybrid speciation—the process in which hybridization results in a stable, fertile, and reproductively isolated hybrid lineage where there is no change in ploidy—has been documented in several taxa. Hybridization can directly contribute to reproductive isolation or reinforce it at a later stage. Alternatively, hybridization might not be related to the evolution of reproductive isolation. To account for these different scenarios, I propose to discriminate between two types of hybrid speciation: type I where reproductive isolation is a direct consequence of hybridization and type II where it is the by‐product of other processes. I illustrate the applicability of this classification scheme with avian examples. To my knowledge, seven hybrid bird species have been proposed: Italian sparrow, Audubon's warbler, Genovesa mockingbird, Hawaiian duck, red‐breasted goose, golden‐crowned manakin, and a recent lineage of Darwin's finches on the island of Daphne Major (“Big Bird”). All studies provide convincing evidence for hybridization, but do not always confidently discriminate between scenarios of hybrid speciation and recurrent introgressive hybridization. The build‐up of reproductive isolation between the hybrid species and their parental taxa is mainly driven by premating isolation mechanisms and comparable to classical speciation events. One hybrid species can be classified as type I (“Big Bird”) while three species constitute type II hybrid species (Italian sparrow, Audubon's warbler, and golden‐crowned manakin). The diversity in hybrid bird species across a range of divergence times also provides an excellent opportunity to study the evolution of hybrid genomes in terms of genome stabilization and adaptation.

Highlights

The Greek philosopher Aristotle extensively described hybrids in his Historia Animalium and even called upon hybridization to explain the species richness in Africa: “And the proverb about Libya [Africa], that ‘Libya is always producing something new,’ is said to have originated from animals of different species uniting with one another in that country, for it is said that because of the want of water all must meet at the few places where springs are to be found, and that even differ‐ ent kinds unite in consequence.” Linnaeus considered hy‐ bridization as a creative force in the origin of new species (Linnaeus, 1751)
I will focus on the first category, homoploid hybrid speciation, which results in a stable, fertile, and reproductively isolated hybrid lineage in which there is no change in ploidy level (Mallet, 2007; Mavarez & Linares, 2008)
Rosenthal, and Andolfatto (2014) ar‐ gued that three criteria should be satisfied in order to indisputably demonstrate HHS: (a) genetic or morphological evidence for hy‐ bridization, (b) reproductive isolation of the hybrid lineage from its parental species, and (c) evidence that reproductive isolation is a di‐ rect consequence of past hybridization

Summary

Introduction

The Greek philosopher Aristotle extensively described hybrids in his Historia Animalium and even called upon hybridization to explain the species richness in Africa: “And the proverb about Libya [Africa], that ‘Libya is always producing something new,’ is said to have originated from animals of different species uniting with one another in that country, for it is said that because of the want of water all must meet at the few places where springs are to be found, and that even differ‐ ent kinds unite in consequence.” Linnaeus considered hy‐ bridization as a creative force in the origin of new species (Linnaeus, 1751). Seven bird species have been proposed to have hybrid origins: Italian sparrow (Passer italiae), Audubon’s warbler (Setophaga auduboni), Genovesa mockingbird (Mimus parvulus bauri), Hawaiian duck (Anas wyvilliana), red‐breasted goose (Branta ruficollis), golden‐crowned manakin (Lepidothrix vilasboasi), and a recent lineage of Darwin’s finches on the island of Daphne Major (originally referred to as “Big Bird”).

Results

Conclusion