describe methods of assisted reproduction used in the conservation of endangered mammals, limited to IVF, embryo transfer and surrogacy

Conservation – Assisted Reproduction (Topic 18: Classification, Biodiversity & Conservation)

Context Box – How this case‑study fits into the Cambridge 9700 syllabus

• Topic 18 links genetics, evolution and ecosystems to the practical challenge of conserving biodiversity.
• This note focuses on Assisted Reproductive Technologies (ART) as a specialised conservation tool, but it is situated within the wider framework of:

  • Classification & phylogenetics (Topics 12‑13)
  • Biodiversity indices and population genetics (Topic 14‑15)
  • Broad conservation strategies (habitat protection, ex‑situ gene banks, re‑introduction – Topic 16‑19)

• Assessment Objectives addressed:

  • AO1 – recall and define key terms (IVF, embryo transfer, surrogacy, heterozygosity, effective population size, etc.).
  • AO2 – interpret data tables, calculate success rates and discuss genetic implications.
  • AO3 – evaluate the benefits, limitations and ethical considerations of ART in conservation.

1. Why Maintaining Genetic Diversity Is Central to Conservation

• Genetic bottlenecks: sudden reductions in population size cause loss of alleles and raise inbreeding risk.
• Inbreeding depression: reduced fitness (lower birth rates, higher disease susceptibility) when deleterious recessive alleles become homozygous.
• Population‑genetic goal: maximise heterozygosity H and retain rare alleles.

  
  H = 1 – Σp_i² where p_i is the frequency of allele *i*.

• Effective population size (Nₑ): the number of breeding individuals that contribute genes to the next generation; ART aims to increase Nₑ by spreading gametes from more individuals.
• Role of ART: enables use of gametes from isolated, non‑breeding, or aged individuals, thereby widening the genetic base.

2. Classification & Phylogenetic Background (Brief Overview)

Understanding the taxonomic position of an endangered species helps to choose appropriate surrogate species and to assess phylogenetic compatibility.

• Hierarchy: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.
• Phylogenetic trees illustrate evolutionary relationships; the closer two species are on the tree, the more similar their reproductive physiology and placental structure tend to be – a key factor when selecting a surrogate.
• Example: Rhinoceros unicornis (Indian white rhino) and Ceratherium simum (southern white rhino) belong to the same genus, making inter‑species embryo transfer feasible.

3. Biodiversity Metrics Relevant to ART

4. Assisted Reproductive Technologies (ART) Used in Mammalian Conservation

4.1 In Vitro Fertilisation (IVF)

Fertilisation of oocytes by sperm in a laboratory culture system, producing embryos for transfer.

Procedure

1. Hormonal stimulation of the donor female (e.g., FSH + LH) to induce multiple mature oocytes.
2. Ultrasound‑guided or laparoscopic aspiration of oocytes.
3. Collection of fresh or cryopreserved sperm from the donor male.
4. Co‑incubation of oocytes and sperm in a defined medium (37 °C, 5 % CO₂).
5. Assessment of fertilisation (two pronuclei) and early cleavage (2‑cell → 4‑cell).
6. Selection of viable embryos for immediate transfer or cryopreservation.

Caveat Note

• Culture conditions are highly species‑specific; protocols that work for domestic species often fail for wildlife.
• Success rates reported for many endangered mammals remain < 30 % at the blastocyst stage.

Advantages

• Access to gametes from individuals that cannot breed naturally (old, injured, or geographically isolated).
• Embryos can be genetically screened (microsatellites, SNP panels) before transfer.
• Creates a “genetic bank” for future use.

Limitations

• Requires sophisticated labs and trained personnel.
• Repeated use of a few donors can still narrow the gene pool.
• High cost and limited success for many large‑mammal species.

Illustrative Data

4.2 Embryo Transfer (ET)

Placement of a viable embryo into the uterus of a recipient female (conspecific or closely related) that will carry the pregnancy.

Procedure

1. Synchronise the recipient’s estrous cycle with the donor using hormonal protocols (e.g., prostaglandin + progesterone).
2. Insert the embryo transcervically (non‑surgical) or via laparoscopy into the appropriate uterine horn.
3. Monitor pregnancy by trans‑abdominal ultrasound (from ~day 30).
4. Allow natural parturition or intervene if obstetric complications arise.

Caveat Note

• Precise hormonal synchronisation is technically demanding; mismatches reduce implantation success.
• Immunological or placental incompatibility can occur, especially in inter‑species transfers.

Advantages

• Amplifies the reproductive output of limited donor gametes.
• High‑fertility surrogates can reduce the time endangered females spend in captivity.
• Facilitates sharing of embryos between institutions.

Limitations

• Stress from handling may affect surrogate health.
• Logistical complexity when surrogates are housed at a different facility.

Illustrative Data

4.3 Surrogacy (Cross‑Species Gestational Carrying)

Use of a female from a closely related, more abundant species to gestate an embryo of the endangered species.

When Surrogacy Is Used

• Very few breeding females of the endangered species are available.
• Gestation length or physiological demands exceed the capacity of captive facilities.
• Embryos are known to be viable in the surrogate’s uterine environment (phylogenetic proximity is essential).

Key Considerations

• Phylogenetic proximity – reduces immunological rejection and placental incompatibility.
• Size & uterine capacity – surrogate must accommodate the embryo’s growth.
• Behavioural acceptance – surrogate should not reject or harm the newborn.

Caveat Note

• Hybrid embryos are not viable for most taxa; successful cases involve embryos that remain genetically pure of the endangered species.
• Legal and ethical frameworks often restrict the use of certain surrogate species.

Examples of Successful Surrogacy

• European bison (Bison bonasus) embryos carried by domestic cattle – 3 live calves from 5 transferred embryos.
• Black‑and‑white ruffed lemur (Varecia variegata) embryos carried by common brown lemur – 2 births from 4 embryos.

Illustrative Data

5. Population‑Genetic Implications of Using ART

• Each embryo transferred represents a new genotype entering the managed population, potentially raising heterozygosity H.
• Genetic management plans use pedigree analysis to avoid repeatedly using the same donor pair, thereby minimising the increase in the inbreeding coefficient F and protecting the effective population size Nₑ.
• Allele‑frequency models (Hardy–Weinberg expectations) can incorporate ART‑derived births to predict long‑term genetic health.

Worked Example (using the data‑interpretation table below)

For the black‑footed ferret: 3 donor females produced 36 embryos.

1. Assume each donor contributes an equal number of unique alleles (simplified). If the original population had 10 alleles at a locus, and each donor carries 4 private alleles, the addition of 12 live births could raise the allele count to 14.
2. Calculate the change in heterozygosity:

   
   H₁ = 1 – Σpᵢ² (before ART) = 1 – (0.1² × 10) = 0.90.

   
   After adding the new alleles (assuming equal frequencies), H₂ ≈ 1 – (0.07² × 14) ≈ 0.93.

   
   Thus, ART can increase heterozygosity by ≈0.03 (3 %).

6. Data‑Interpretation Exercise (AO2)

1. IVF success rate (embryos produced ÷ oocytes collected) – use the “Oocytes Collected” figures from Table 4.1 (48 for ferret, 22 for elephant, 24 for panda).
   

   • Ferret: 36 ÷ 48 = 75 %
   • Elephant: 22 ÷ 22 = 100 % (note: all collected oocytes fertilised, but blastocyst development is low)
   • Panda: 24 ÷ 24 = 100 %

2. Embryo‑to‑birth conversion efficiency (live births ÷ embryos transferred).
   

   • Ferret: 12 ÷ 30 = 40 %
   • Elephant: 2 ÷ 18 = 11 %
   • Panda: 9 ÷ 20 = 45 %

3. Species with greatest potential for rapid population increase – the giant panda shows the highest combined IVF‑to‑birth efficiency (45 % live‑birth rate) and a moderate number of donors, indicating that each additional IVF cycle can quickly add new individuals while maintaining genetic diversity.
4. Two genetic risks of repeatedly using the highest‑producing donors:

   • Reduced effective population size (Nₑ) because a few individuals contribute disproportionally to the gene pool.
   • Increase in the inbreeding coefficient (F) as offspring become more likely to share common ancestors, raising the chance of deleterious recessive expression.

7. Wider Conservation Strategies (Linking ART to the Bigger Picture)

8. Ethical, Ecological and Socio‑Economic Considerations (AO3)

• Animal welfare – invasive procedures (laparoscopy, hormonal treatments) must be justified by clear conservation outcomes.
• Species integrity – cross‑species surrogacy raises concerns about “purity” of the endangered taxon and potential for unintended hybridisation.
• Resource allocation – ART is expensive; funds may be diverted from habitat protection or community engagement.
• Public perception & education – transparency about the technology helps secure public and donor support.
• Legal frameworks – CITES, CBD and national wildlife laws regulate the movement of gametes, embryos and surrogate animals.

9. Key Points for Examination (AO1)

• Define in vitro fertilisation (IVF), embryo transfer (ET) and surrogacy in a conservation context.
• List the main procedural steps for each technique (see Sections 4.1‑4.3).
• Explain why hormonal synchronisation of donor and recipient is essential for successful ET.
• Give one real‑world example for each technique:

  • IVF – Black‑footed ferret.
  • ET – Giant panda.
  • Cross‑species surrogacy – European bison embryos in domestic cattle.

• Discuss at least two advantages (genetic diversity, rapid increase) and two limitations (cost, technical difficulty) of ART compared with other tools.
• Outline one ethical issue associated with using surrogate species (e.g., welfare of the surrogate, risk of hybridisation).

Suggested Diagram (for revision)