lecture 13: captive breeding programs in zoos and aquariums

captive breeding programs

particularly in zoos, may be the last best hope for many endangered species. Zoos have had an increased role as institutions of genetic research and management. These have four primary conservation functions which provide:

- substitutes for wild individuals in basic biological research of endangered species

- opportunity for the development of care and management techniques

- demographic and genetic reservoirs that will augment existing wild populations

- a remnant of those species for which there is no immediate opportunity to survive in the wild

active breeding

the best animals were brought together for mating or the use of those that simply breed on their own, assuming that breeding animals were the fittest animals. this is a historical technique, one that we no longer use. This is because “best fit” in captivity often does not translate well for those that will go back into the wild

how to prevent genetic adaptation to captivity

- reduce amount of time in captivity

- reduce strength of selection in captivity

- equalize family sizes, so selection occurs only within families

- add more immigrants from wild or captive populations to slow the rate of genetic adaptation (not usually encouraged to take wild animals out of the wild to breed in captive populations unless absolutely necessary

captive breeding today

- the association of zoos and aquariums coordinates breeding and management plans for the approximately 500 species in captivity

- most captive management plans are managed with the goal of maintenance and possible recovery in the wild

maintenance

to manage captive populations as “closed populations”, that is a population that is self-sustaining in captivity with no further inputs from wild stock. Even if there are no foreseeable plans to reintroduce the animals into the wild, the animals are managed for the possibility. Example: polar bears

The goal of modern zoo breeding programs (could be an essay question)

- preserve the original level of genetic diversity

- to mitigate problems associated with inbreeding depression such as low survivorship and reduced vitality

- reduce adaptation to the captive environment (retain “wildness”)

North American cooperative zoo management program

- Species Survival Plan (SSP)

- population management plan (PMP)

European management plan

- European endangered species program (EEP)

- European Studbook (ESB)

studbooks

contain detailed information on each species. stored in a database and used for pedigree analysis

pedigree analysis

an analysis of the relatedness of individuals in a population to one another by determining each individual’s parental ancestry and subsequent offspring. This analysis is used to make choice pairings for reproduction of new offspring. example of studbooks in use is the breeding of the okapi which lives in moist forest in the Democratic Republic of the Congo. It thrives in captivity and enjoys longevity and high fecundity

pedigree

tracks a group of unrelated individuals (founders) that form a new population and tracks their descendants through each generation. females are dams and males are sires. individuals with wild parents are founders originating from the wild or other unrelated populations

kinship coefficient (k_ij)

the probability that alleles randomly selected from homologous loci in two individuals (i and j) are identical by descent of a common ancestor. the higher it is the more related the two individuals are. sibling-offspring kinship is normally a value of 0.25.

Mean kinship

the average of the kinship between a single individual and all other individuals in the population.

- represented by the sum of mk_i = k_ij/N

- the value of mk for every pairwise combination of individuals in the captive population can be recorded in a matrix

population mean kinship (MK)

taking all individual mean kinship values and finding their average.

- represented by MK = the sum of mk_i/N

gene diversity (GD)

- is the probability that two alleles from the same locus sample at random from the population will not be identical by descent

- not genetic diversity

- most commonly used measure of the level of genetic diversity in captive populations

- GD = 1-MK

- there is an inverse relationship between GD and MK. If population mean kinship is high then most individuals are related and gene diversity is low and vice versa

mean kinship breeding strategy

- the strategy of choice in managing captive populations

- individuals are pairs not only on their relationships to one another but also to the population as a whole

- MK strategy rests on the premise that gene diversity is a measure of the measure of different alleles in the captive population and a measure of the frequency between those different alleles

- if population kinship is minimized, gene diversity is maximized

- an animal’s mean kinship value reflects its average relatedness to all individuals in the captive breeding program