Conservation – Assisted Reproduction in Endangered Mammals
When natural breeding is insufficient to maintain viable populations, assisted reproductive technologies (ART) can be employed. The three principal ARTs used in mammalian conservation are:
In vitro fertilisation (I \cdot F)
Embryo transfer (ET)
Surrogacy (using a surrogate mother)
1. In vitro fertilisation (I \cdot F)
I \cdot F involves the fertilisation of an oocyte by sperm outside the body, producing an embryo that can later be implanted into a recipient female.
Procedure
Hormonal stimulation of the donor female to produce multiple mature oocytes.
Collection of oocytes by laparoscopic aspiration.
Collection of sperm from the donor male (or cryopreserved sperm).
Co‑incubation of oocytes and sperm in a culture medium under controlled temperature and CO₂ conditions.
Assessment of fertilisation (presence of pronuclei) and early embryo development.
Selection of viable embryos for transfer or cryopreservation.
Advantages
Allows use of gametes from individuals that cannot mate naturally (e.g., due to age, injury, or geographic separation).
Enables genetic screening of embryos before implantation.
Facilitates the creation of a genetic “bank” through cryopreservation.
Limitations
Requires sophisticated laboratory facilities and expertise.
Success rates can be low for some species due to unknown optimal culture conditions.
Potential for reduced genetic diversity if only a few donors are used repeatedly.
Conservation Examples
Black‑footed ferret (Mustela nigripes) – I \cdot F combined with embryo transfer rescued the species from extinction.
Asian elephant (Elephas maximus) – I \cdot F protocols are being refined to increase birth rates.
2. Embryo Transfer (ET)
Embryo transfer involves moving a viable embryo produced by I \cdot F (or natural fertilisation) into the uterus of a recipient female, which may be of the same or a closely related species.
Procedure
Synchronization of the recipient’s estrous cycle with the donor’s using hormonal treatments.
Non‑surgical or surgical placement of the embryo into the uterine horn.
Monitoring of pregnancy via ultrasound.
Delivery of the offspring by natural birth or assisted delivery if required.
Advantages
Enables the use of surrogate females that have higher reproductive success or are more readily available.
Reduces the need to keep endangered females in captivity for gestation.
Can increase the number of offspring produced from a limited set of donor gametes.
Limitations
Requires precise hormonal control to match donor and recipient cycles.
Risk of immunological rejection if the recipient is a different species.
Potential stress to the surrogate during handling and transfer.
Conservation Examples
Giant panda (Ailuropoda melanoleuca) – Embryos from I \cdot F are transferred into surrogate mothers of the same species.
Northern white rhinoceros (Cerathophus unicornis) – Embryos created from frozen sperm and eggs are transferred into surrogate southern white rhinos.
3. Surrogacy
Surrogacy in wildlife conservation refers to the use of a female (often of a closely related, more abundant species) to carry and give birth to an embryo that originated from an endangered species.
When Surrogacy Is Used
When the endangered species has a very low number of breeding females.
When the gestation period of the endangered species is incompatible with the captive environment.
When hybrid embryos are viable and can develop to term in the surrogate.
Key Considerations
Phylogenetic proximity – the surrogate should be closely related to minimise immunological and developmental incompatibilities.
Size and gestational physiology – the surrogate must be able to accommodate the embryo’s growth.
Behavioural compatibility – the surrogate should not reject or harm the newborn.
Examples of Successful Surrogacy
European bison (Bison bonasus) embryos transferred into domestic cattle surrogates.
Cross‑species surrogacy of the endangered black‑and‑white ruffed lemur (Varecia variegata) using common brown lemur surrogates.
Comparison of the Three Methods
Method
Key Step
Typical Success Rate* (per embryo)
Major Advantage
Principal Limitation
I \cdot F
Fertilisation of oocyte and sperm in vitro
≈30–45 %
Access to gametes from non‑breeding individuals
Requires specialised laboratory facilities
Embryo Transfer
Placement of embryo into a synchronized recipient uterus
≈25–40 %
Increases number of offspring per donor female
Hormonal synchronisation is technically demanding
Surrogacy
Use of a different species as the gestational carrier
≈15–30 %
Enables reproduction when conspecific females are unavailable
Risk of immunological or developmental incompatibility
*Success rates vary widely between species and depend on laboratory expertise, embryo quality, and recipient health.
Suggested diagram: Flowchart showing the sequence from gamete collection → I \cdot F → embryo culture → embryo transfer → surrogate gestation → birth.
Key Points for Examination
Define I \cdot F, embryo transfer, and surrogacy in the context of conservation.
Outline the main steps involved in each technique.
Explain why hormonal synchronisation is crucial for embryo transfer.
Give at least one real‑world example for each method.
Discuss the ethical considerations of using surrogate species.