did hybridization save a species of galapagos giant tortoise? Flashcards
define hybridization
• Interbreeding of two different genetic lineages
• Spectrum - from within species to between species
• Middle is hybrids
• Between species does occur in nature
○ Ex mallard x black duck
• Evolutionary context
Outcomes of hybridization?
reinforcement, introgression, hybrid speciation
describe reinforcement
§ Commonly - reinforcement - incapable of reproducing or progeny are sterile - “evolutionary dead end”
describe introgression
§ Introgression - f1 progeny - hybrid that can mate back to either one of its parental lineages - brings back some diversity
describe Hybrid speciation
§ Hybrid speciation - progeny is its own novel evolutionary trajectory - does not breed back, novel species
conservation context - describe outbreeding depression and genetic swamping
○ Outbreeding depression - ex. All of one kind of offspring are sterile, but over time the frequency of the lineage that we are worried about decreases - lose genetic lineage entirely
§ outbreeding depression happens when crosses between two genetically distant groups or populations result in a reduction of fitness. § Negative! Genetic swamping- ex two lineages, the hybrids can reproduce - as we move through time, uniqueness lost/ rare and protected species gone - now all hybrid
issues w hybrids and conservation?
• Increasing rates of hybridization with time
○ Factors:
§ Unintentional introductions - due to globalization
§ Climate induced range shifts - changes in species ranges - potential for new hybridization due to increased contact
• Benefits of hybridization?
- Genetic rescue
* Genetic preservation - focus of this lecture
• Galapagos giant tortoise morphs?
two morphs - domed and saddleback
•
• Saddleback has large opening at the front
• Associated with different lifestyles
○ Domed - tropical, rainforest, tunnel in understory
○ Saddlebacked - dry, desert like conditions, cactus trees, extend neck far up and access cactus pads
where do the galapagos torts. live?
- Occur on all major islands and some minor
* 15 different species of tortoises
conservation threats to gal. tort.
• Introduction of pests
○ Cats and rats eat tortoise eggs and babies
• Habitat destruction
○ Human settlements and developments
• Being consumed
○ In 1800s they were consumed as a source of food by explorers - fresh meat bc of how long they live
• Since darwins time, 4 species have gone extinct
• 90% decline in tortoise abundance
why is norther isabela different?
• Norther part of isabela island has both saddleback and domed - unusual compared to rest
why does isabela have both morphs? hypothesis?
• “alien” individuals
• Those with genetic profiles very different from others collected at same location
• Where from and how did they get here?
○ Ancient DNA (museums) revealed tortoises with ancestry from pinta and floreana
§ These two species were declared extinct!!! Rediscovered
• Hypothesis:
○ Sailors would go to pinta and floreana and pick up tortoises, would sail to isabela and decide to leave some there
2008 expedition goals and results
- How prevalent are the hybrids?
- Are there pure individuals?
- Tortoises can live for over 150 yrs
- Extensive sampling in isabela - found 89 with DNA floreana and 17 w DNA pinta
- Hotspot where these tortoises tend to be found
2015 expedition goals and results
• Goals
○ Find individuals w known or likely ancestry
§ Pinta and floreana are saddleback - all other species on isabela are domed
○ Remove individuals to a captive breeding center
• Airlifted tortoises away from active volcano
○ Found 1300 total, 140 blood samples, and moved 32 to breeding center
• Now, confirm ancestry
• Genetic markers
○ Mitchondrial dna
○ Dinucleotide microsatellites
○ Reference database of extant and extinct species
• Analysis methods
• Haplotype sharing
• Individual ancestry
