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

Abstract

Rare species present a challenge under changing environmental conditions as the genetic consequences of rarity may limit species ability to adapt to environmental change. To evaluate the evolutionary potential of a rare species, we assessed variation in traits important to plant fitness using multigenerational common garden experiments. Torrey pine, Pinus torreyana Parry, is one of the rarest pines in the world, restricted to one mainland and one island population. Morphological differentiation between island and mainland populations suggests adaptation to local environments may have contributed to trait variation. The distribution of phenotypic variances within the common garden suggests distinct population‐specific growth trajectories underlay genetic differences, with the island population exhibiting substantially reduced genetic variance for growth relative to the mainland population. Furthermore, F1 hybrids, representing a cross between mainland and island trees, exhibit increased height accumulation and fecundity relative to mainland and island parents. This may indicate genetic rescue via intraspecific hybridization could provide the necessary genetic variation to persist in environments modified as a result of climate change. Long‐term common garden experiments, such as these, provide invaluable resources to assess the distribution of genetic variance that may inform conservation strategies to preserve evolutionary potential of rare species, including genetic rescue.

Hybridization as a conservation management tool

“…Genetic adaptation is one way by which a population or species may avoid extinction caused by rapid environmental change (Hamilton & Miller ; Hoffmann et al., ; Hoffmann & Sgrò ). Whether a species will adapt in time to escape extinction depends on factors such as the rate of environmental change, the amount of adaptive genetic variation present, and generation time (Hamilton, Royauté, Wright, Hodgskiss, & Ledig, ; Hoffmann et al., ; Hoffmann & Sgrò ). Globally, temperature has increased and continues to increase at a rate not previously experience by life on Earth for at least 50 (if not hundreds of) million years (Gaffney & Steffen, ; Hönisch et al., ).…”

“…Since it is not possible to provide experimental data for every species, results of a subset of species or populations may provide proof‐of‐concept for groups that share similar biological and ecological characteristics. Research to inform decision making should involve multi‐generation testing of hybrids in the laboratory and in the wild (Hamilton et al., ). Our review shows that long‐term studies are rare for hybridization research related to conservation, and most data have been obtained for the F1 and F2 generations (Table ).…”

“…It increases heterozygosity and creates new genetic combinations, potentially reducing extinction risk by increasing adaptive potential and masking deleterious alleles. Hybridization may lead to new adaptive traits, allowing species to invade new niches and expand their distribution ranges (Becker et al, 2013;Carlson et al, 2014;Hamilton & Miller 2016;Hamilton et al, 2017;Hoffmann & Sgrò 2011;Meier et al, 2017;van Oppen et al, 2015). Genetic rescue or evolutionary rescue can be achieved when a population is successfully restored via hybridization (Table 2).…”

“…Research to inform decision making should involve multigeneration testing of hybrids in the laboratory and in the wild (Hamilton et al, 2017). Our review shows that long-term studies are rare for hybridization research related to conservation, and most data have been obtained for the F1 and F2 generations (Table 2).…”

Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass

“…Heterosis is the result of a non-additive phenotypic expression for one or more transgressive hybrid traits [7], which might be genetically and epigenetically controlled [8]. Best-parent heterosis may result in hybrids with extreme phenotypes that have higher fitness under stressful conditions than their parental species [5,9,10]. In this context, natural and artificial hybrid zones may play an important role in maintaining the conservation of genetic variation within and among species under rapidly changing conditions [11,12].…”