Small Population management Flashcards
What are 3 important factors in small population management?
- genetics
- demography - population structure
- Reproduction - breeding (promoting) and Contraception (Preventing)
Why is demography important?
- Zoos need to consider demography at different levels - Individual, Regional and Global
- Studying demography helps to understand-
Future growth or decline of zoo-based
populations and The potential to experience a loss of genetic diversity - Populations have parameters
o Birth and Death Rates
o Immigration and Emigration Rates
o Density and Distribution - Determining population parameters allows comparison in
o Time
o Geographical location
o Between different Zoos
What 3 important factors in demography?
- age structure
- shape - growth, stable or decline - Sex ratio - influences the effective population size (animals avaliable that can breed)
- depends on species - reproductive strategy
- affected by inbreeding depression - life tables
- records mortality of each age class
- static LT - snapshot, one point of time
- dynamic LT - follow cohort over time
What is a survivorship curve?
Plot of survivors vs age class
provides mortality data analysis
allows comparison of;
different zoo populations of same species
wild v captive mortality
Male v female mortality
What is demographic stochasticity?
results from chance independent
events of individual mortality and reproduction, causing random
fluctuations in population growth rate, primarily in small populations. Demographic stochasticity is particularly important
in short-lived species (e.g., small dasyurid populations, semelparous species)
What is environmental stochasticity?
results from temporal fluctuations
in mortality and reproductive rates of all individuals in a population in the same or similar fashion, causing population
growth rate to fluctuate randomly in populations of all sizes – small populations are more susceptible to catastrophes .
What is demographic extinction? and what animals is an example?
o Definition - a zoo population that is not self sustaining
o A population that contains too few individuals
o Example - Asian elephant population predicted drop to
10 animals by 2050 = demographically extinct!
o Solution – take from the wild to support captive breeding but this is highly controversial
Why is Genetic management important
maintain genetic diversity
managed by studbooks
Essential to long-term viability of captive populations
How many animals are required to maintain genetic diversity?
500 - but limited space
What is an alternative to having 500 animals?
Attempt to conserve 90% of genetic
variation in a population for 200 years.
o This can be estimated by considering
- Proportions of male and females available
- Generation time of the species
- When GT is short – need large numbers
- When GT is long – smaller numbers will do
What is the effective population size?
The effective population size is number of individuals that are effectively contributing genes to next generation
Effective population size is a measure of how well the population maintains genetic diversity from one generation to the next
Small populations lose genes as a result of chance or stochastic events – genetic drift, so it is important to know the effective population size not just the actual numbers of
animals.
What influences the effective population?
- Sex ratio
- Reproductive success of individuals
- Mating system (Monogamy reduces Ne, whereas promiscuity increases Ne)
- The degree of mate selection – non-random selection of mates
What is minimum viable population (MVP) size?
Population Viability Analysis (PVA) provides a means of predicting the probability that a population will become extinct
What deterministic factors does MVP account for?
- habitat loss
- over exploitation
What stochastic factors does MVP account for?
- demographic
- environmental
- Genetic
What is a evolutionary significant units?
the minimum unit of conservation management - could be at different levels, species, sub-species, geographical race or a
population
Relies upon information from molecular genetics - mtDNA
- mtDNA is passed downed from the mother and remains largely unchanged from generation to generation – allows
tracking of evolutionary history
What is inbreeding, and how is it managed?
Occurs when closely related animals breed
Occurs when dam and sire of an individual share common
ancestors
Inbreeding increases homozygosity and reduces heterozygosity (We want heterozygosity!)
If recessive alleles cause disease, then expression of the disease increases with inbreeding
How is inbreeding measured?
Measured by calculating an inbreeding coefficient (F)
F - probability that two alleles in an individual animal are
identical (inherited from the same ancestor)
The higher the F value, the greater the inbreeding
Studbook keepers use the F value to determine best pairings –
this method assumes we know the original parentage - we do not know original heritage is.
What is Genetic Load?
The pool of deleterious genes in a population is known as the “genetic” load and this increases with inbreeding
What is the consequence of inbreeding? and what causes it
In-breeding depression
- reduced fitness in a population resulting from inbreeding - caused by an increase in homozygosity for deleterious alleles (aa)
- Over dominance - where heterozygous (Aa) for one phenotypic trait may under some circumstance confer an advantage but lead to increased homozygosity vigour
What is heterosis or hybrid vigour?
increase of heterzygosity results in the crossing two different inbred lines - which can improve genetic fitness
What is the disadvantage of heterosis/outbreeding?
Cause harmful effect on the next generation called outbreeding depression
What is the genetic drift and the founder effect?
When a small founder population is taken from the wild, the genetic composition of future generations derived from this
population will be determined by the alleles possessed by these founders
What causes a genetic bottleneck? and what is the issue with bottlenecking
If you choose poorly or a stochastic event occurs to reduce your population, you can create homozygosity
Bottlenecks can lead to extinction due to deleterious effects of
inbreeding and increased disease susceptibility.
What is an example of inbreeding depression, and what was the result of it?
- Florida Panther inbreeding depression
- Passed through a genetic bottle-neck (40 left in the wild)
- Abnormalities resulting from the bottle-neck
- Kinked tails
- Sperm defects
- Heart defects
-Cryptorchidism - Vaginal papillomas
- High susceptibility to infectious disease
What are guidelines for ideal small population management?
(1) Attempt to obtain sufficient number of founder individuals to adequately sample both heterozygosity and the allelic diversity of the source population
(2) Expand the population size as quickly as possible to carrying capacity of the zoos able to support the species – small populations lose genetic diversity faster than large populations.
(3) Stabilise the population at the carrying capacity – zoo accommodation is in short supply, so fertility and survivorship rates must be managed to stabilise the population at the desired carrying capacity.
(4) Extend the generation length as much as possible – genetic diversity is lost with each generation - so extending the generation time will reduce the rate of loss.
(5) Adjust the representation of founder lineages to reflect the probable distribution of founder alleles in the living population.
(6) Select against individuals with extreme outlying morphological and reproductive characteristics – to reduce genetic load.
(7) Consider dividing the population into several subdivisions among which gene flow is regulated – however, be careful not to accidentally induce genetic drift via small populations size
(8) Continually introduce new founders from the wild to minimize loss of genetic diversity
(9) Utilize available reproductive technology to the fullest possible extent – to increase reproductive potential
Why is Identifying gender important to promoting reproduction? and how is this possible
fundamental to reproductive and genetic management
- Dimorphic species - size, ornaments = visible
- monomorphic - required genetic markers (PCR) (birds - blood, featherm faeces), laparoscopy (birds), Fecal metabolites (amphibians/birds)
How do you promote reproduction in captive animals? and what factors influence this
creating appropriate physical and social environments
- Set up enclosures with natural social groupings – not always possible e.g. – not enough physical space or animals
- Individual species may
o be solitary
o live in single-sex groups
o live in social hierarchies (African Wild Dogs) - Some animals disperse naturally from the group
- Compatibility - mate choice (not enough choice in captivity)
What factors influence compatibility when an animal chooses their mate?
- Sexual selection – size, weapons, ornaments, colours
- MHC – major histocompatibility complex - -
- Help immune cells recognize foreign
substances
- Help immune cells recognize foreign
- Very difficult to account for in zoo or small populations
e.g., SHN wombats – compatibility issues and specific mating places
What impacts reproductive success?
STRESS
anything that influences the secretion of GnRH.
- nutrition
- Season
- Stress
- Pathology
- Con-specifics
- habituation
What are 2 effects used to promote reproduction?
- The fraser darling effect - presence of other individuals results in social stimulation and the synchronisation of breeding
- The coolidge effect - mating activity increases with
- novel environment
- novel partners
- limited studies in wildlife species
- sexual habituation needs t be avoided
What is sexual incompetence?
Sexual incompetence in captive species
- not competent in coitus - poor copulatory positioning
usually learn junior males learn behaviors from senior males - but unable to in zoo sitting
Mating behaviour may need to be learned
Courtship may also require specific cues (social and environmental) which are not appropriately provided in captivity – e.g., temperature, rainfall, photoperiod
What is a way for zoos to overcome natural reproduction?
assisted reproductive technology
- CAN FACILITATE GENETIC MANAGEMENT
* Overcomes sexual compatibility
* Reduces inbreeding and homozygosity
* Introduction of wild genetics
* Extends generation length (frozen gametes)
* Increase effective populations size (sperm in liq N2 canisters)
* Transportation between populations – facilitates gene flow - ASSESSMENT / OVERCOMING OF REPRODUCTIVE ISSUES
* Behavioural incompetence – low libido
* Reproductive pathology
* Gamete rescue
what is a limitation of assisted reproductive technology?
lack of understanding of basic physiology
Most ART in zoo species – is pretty low tech compared to humans and domestic animals (see Johnston, 2019)
What 3 components are required for artificial insemination?
- Semen collection, evaluation and preservation – what to AI?
- Electro-ejaculation (most common)
- Artificial vagina
- Masturbation, massage or conditioning
- Pharmacological (amphibians)
- Gamete recovery – disease or necropsy specimens - Timing of insemination – when to AI?
- Oestrous cycle characterisation – mostly non-invasive
- Oestrus detection – behaviour
- Ovulation pattern and timing – critical for AI
- Oestrus synchronisation - Placement of insemination – where and how to AI?
- Reproductive anatomy – much of which is not described
What are other forms of assisted reproductive techonology?
- IVF/ICSI – fertilisation of oocyte by sperm in vitro
Potential benefits
* Sire selection
* Necropsy oocyte and sperm collection
* Sperm and embryo sexing
* Interspecies transfer
* Embryo splitting and cloning
* E.g. Gorillas and Felids - EMBRYO TRANSFER – Superovulation of donors and embryos
transferred into recipients
Potential benefits
* Increase reproductive rate of female genetics
* Can be used with other technologies - CLONING – limited routine success in zoo species
- MARSUPIALS have unique form of embryo transfer – PY transfer
What is cryobiology?
The study of the effects of freezing and low temperature on biological
systems – limited to gametes and embryos
Frozen Zoo – DNA, Viable cell cultures, sperm, embryos, oocytes
What is the benefits and potential issues of cryobiology?
Potential benefits
* Research – e.g., genome projects and species bar-coding (Forensics)
* THE FROZEN ARK CONSORTIUM
* Gene storage in time and space
Potential issues
* Mixed success – sperm morphology and cryotolerance
* Black footed ferret – a success story (see Santymire et al. 2014)
* Large oocytes very difficult to freeze – especially those with yolk
* It is one thing to freeze another to thaw successfully
* Still need to inseminate at the right time and space
how is reproduction promotion used in birds?
Stimulating egg production
egg harvesting, double clutching and incubation
- Determinate layers: Removing eggs from nest has no effect
- Indeterminate layers: Number of eggs can be changed by adding or
removing eggs during or just before the time of laying.
You can increase egg production by removing eggs from the nest and artificially incubating – Californian Condors normally raise one chick
per year but through double clutching 4 chicks can be raised in 2 years.
Double clutching can also be used in reptiles
What is surrogate mothers, adoption and cross-fostering?
The young offspring of an individual of a rare species are fostered by adults of another species which is usually closely related e.g. various bird species
In some cases, you can use species that are not closely related – e.g.
domestic queen who had just produced 4 kittens was used as a surrogate for a red panda cub – What about the effect on offspring behaviour?
Cross fostering can be used in conjunction with double clutching
Some females with no reproductive value can act as an Allomothers for a group – e.g. Elephants as “Aunties”; koalas
What is the purpose of population control? and what solutions are used to control population control
- Control of breeding may be important for the genetic and
demographic health of a population. - We need to be careful not to have genes of individuals overrepresented – the reproduction of these animals needs to be
controlled. - Possible solutions include
- Contraception
- Surgical sterilisation
- Chemical sterilisation
- Keeping sexes separate
- Donation to another zoo
- Return to the wild
- Culling
What is a form of population control in males or females?
Contraception
- Males
- Surgical (permanent)
Castration – associated with behavioural
changes
Vasectomy - Chemical (reversible)
GnRH agonists
GnRH vaccines - Females
o Surgical (permanent)- Ovariectomy/hysterectomy
- Tubal ligation
o Chemical (reversible)
-GnRH agonists
- GnRH vaccines
- Progestins(Can be side effects with
prolonged use)
Why is euthanasia used as population control?
- Humane killing of an animal for
o Animal Welfare – to prevent suffering
Terminally ill/injured or disease threat
to human health
o Population management
- Demographic management
- Social exclusion from a group –
harassment
- Harem species – when males are
produced in excess
- To reduce overcrowding - Euthanasia can also be distressful to keepers
- Ethics and public perception of euthanasia
