Torrey Pine

Dr. Stephanie Steele, San Diego Zoo Global 

The Torrey pine (Pinus torreyana) is a rare, iconic species that occurs naturally in only two locations in Southern California: in coastal San Diego County and on Santa Rosa Island. The species is of particular conservation concern due to prolonged drought which has increased susceptibility of trees to attack by the bark beetle Ips paraconfusus. The Ips beetle has posed a significant challenge for trees in the mainland population in recent years. While Torrey pines harbor a remarkably low level of genetic diversity, it is possible that genetic variation underlies resistance to beetles and thus determines, at least partially, which trees survive. To test this, we are using RNA-Seq to survey functional genetic diversity in Torrey pines that either succumb to mortality by bark beetles or remain asymptomatic. We aim to 1) characterize functional genetic diversity in the species, particularly in defense-related genes, 2) test for genetic differentiation between affected and asymptomatic trees, and 3) identify whether specific genetic variants are associated with survival. This work will offer insight into the adaptive potential of Torrey pines to respond to continued bark beetle outbreaks and will inform future restoration efforts for this iconic species.

Contributing Author(s): 
Date Recorded: 
Wednesday, September 11, 2019

Jill Hamilton, North Dakota State University

Species evolutionary potential is tightly linked to both the amount and distribution of genetic variation available through which natural selection may act. Rare species present particular challenges under rapidly changing conditions where the genetic consequences of rarity may limit species ability to adapt to ongoing change. Thus in a rapidly changing environment, maintenance of genetic variation within and across populations becomes an increasingly important target for species conservation. Here, I examine the role genetic rescue may play in the maintenance of a rare species' evolutionary potential. Exhibiting exceptionally low levels of genetic variation, endangered Torrey pine, one of the rarest pines in the world and endemic to California, may represent a candidate for genetic rescue. Restricted to just one island and one mainland population, preliminary evaluation of fitness traits in Torrey pine indicate F1 hybrids, representing a cross between mainland and island trees, are more fit relative to parental populations when grown in a common environment. This suggests that in the short-term, gene flow between populations may provide necessary genetic variation to persist in changing conditions. However, there remain gaps in our understanding of the long-term consequences of genetic rescue. Torrey pine, a poster child for rarity in forest trees, provides an ideal system for which to track the short and long-term consequences of genetic rescue.

Date Recorded: 
Wednesday, September 11, 2019