Adaptive introgression as a resource for management and genetic conservation in a changing climate

Abstract

Current rates of climate change require organisms to respond through migration, phenotypic plasticity, or genetic changes via adaptation. We focused on questions regarding species' and populations' ability to respond to climate change through adaptation. Specifically, the role adaptive introgression, movement of genetic material from the genome of 1 species into the genome of another through repeated interbreeding, may play in increasing species' ability to respond to a changing climate. Such interspecific gene flow may mediate extinction risk or consequences of limited adaptive potential that result from standing genetic variation and mutation alone, enabling a quicker demographic recovery in response to changing environments. Despite the near dismissal of the potential benefits of hybridization by conservation practitioners, we examined a number of case studies across different taxa that suggest gene flow between sympatric or parapatric sister species or within species that exhibit strong ecotypic differentiation may represent an underutilized management option to conserve evolutionary potential in a changing environment. This will be particularly true where advanced-generation hybrids exhibit adaptive traits outside the parental phenotypic range, a phenomenon known as transgressive segregation. The ideas presented in this essay are meant to provoke discussion regarding how we maintain evolutionary potential, the conservation value of natural hybrid zones, and consideration of their important role in adaptation to climate.

Genetic conservation and management of the California endemic, Torrey pine (Pinus torreyanaParry): Implications of genetic rescue in a genetically depauperate species

“…Ex situ plantings of mainland and island individuals will both conserve native germplasm and provide a means to empirically test fitness of Torrey pine populations in a range of environments, particularly important as Torrey pine is a candidate for assisted migration. Furthermore, as the signature of heterosis is often short‐term, it will be important to evaluate whether fitness advantages observed in the F1 are maintained in the F2 generation, resulting in adaptive introgression (Hamilton & Miller, 2016; Rieseberg, Archer, & Wayne, 1999; Whitely et al., 2015). In addition to establishing ex situ plantings of pure parents, progeny with mixed ancestry produced from mainland and F1 individuals within this experiment provide ideal material to test the longer‐term consequences of genetic rescue.…”

“…If standing genetic variation and mutation alone provide limited adaptive capacity, rarity and isolation may contribute to increased risk of species’ extirpation (Frankham, 1998; Tallmon et al., 2004). In these scenarios, genetic or evolutionary rescue via managed introduction of genetic variation between populations may be required to conserve evolutionary potential of a species (Carlson, Cunningham, & Westley, 2014; Hamilton & Miller, 2016; Miller & Hamilton, 2016; Rius & Darling, 2014). …”

“…(2004) suggested that even limited gene flow may contribute to increased fitness of small, inbred populations by increasing adaptive potential. However, outbreeding depression or the loss of unique genotypes following the introduction of novel variation remains a concern to conservation efforts, particularly where it leads to reduced fitness of recombinant individuals (Frankham et al., 2011; Hamilton & Miller, 2016; Rhymer & Simberloff, 1996). Even in cases where increased fitness attributable to heterosis is observed in an F1 generation, this advantage may not be maintained in later generations (Keller et al., 2001).…”

Łeghágots'enetę (learning together): the importance of indigenous perspectives in the identification of biological variation

“…Variation below the species level is an important component of biodiversity because it provides the genetic variation required for incipient speciation and local genetic adaptation (Wood et al 2014, Mee et al 2015, Hamilton and Miller 2016. Cryptic intraspecific diversity, as is displayed between caribou ecotypes and subspecies (Pond et al 2016), can be especially contentious because it is not always clear how to best identify, delimit, or maintain genetic lineage diversity (Mace 2004, Wood et al 2014, Fitzpatrick et al 2015.…”

Guidelines for planning genomic assessment and monitoring of locally adaptive variation to inform species conservation

“…Identifying hybridization: Although not strictly a conservation action, identifying hybrids has direct relevance for conservation managers, because hybridization can be both a conservation problem, threatening species identity and genetic integrity (Bohling, 2016; Wayne & Shaffer, 2016), and a conservation opportunity, enhancing evolutionary potential in changing environments through adaptive introgression (Hamilton & Miller, 2016). In both cases, NGS provides both improved resolution to identify hybridization and the data needed to develop monitoring panels (Hohenlohe et al., 2011).…”