R. Tilson, K. Traylor-Holzer and G. Brady
Species Survival Plans are cooperative management programs of the American Zoo and Aquarium Association (AZA) for selected species. The purpose of these programs is to reinforce, not replace, wild populations. All too often the general public expects individuals of endangered species at their local zoo to be released back into the wild. This is not the case. Rather, the captive population needs to be perceived as a reservoir of genetic material (that represents the species, not just individuals) that can periodically be used to re-establish populations that have been lost within their natural range or to revitalize wild populations that have become depressed by genetic and demographic problems.
The birth of an SSP depends on the convergence of two significant issues. The first is the recognition that a particular species is in desperate need of protection beyond the traditional process of trying to maintain its security in its natural environment. Factors important in the selection process include how threatened the species is, the likelihood of its success in captivity, and the probability of putting enough individuals together to have an effective program. Input from the World Conservation Union's (IUCN) various specialist groups (for cats it is called the Cat Specialist Group) is integrated with other relevant information to make these decisions. Once the AZA has approved the species for inclusion in an SSP (this step is under the authority of the Wildlife Conservation and Management Committee), member zoos already possessing individuals of the species are solicited. Those that agree to participate in the program form an eight-member (or smaller) Management Group. This group then begins developing the masterplan.
The masterplan is the core of the SSP. This document provides institution-by-institution and animal-by-animal recommendations on mate selection, animal relocations (from zoo to zoo for better breeding combinations), breeding, and surplussing (when an animal is no longer needed for breeding, either for genetic or demographic reasons), and finally, technical and financial support for programs that advance the conservation of the tiger in its natural range.
The strength of an SSP masterplan depends on the accuracy of the biological database for every animal within the program. Usually this database is maintained as a Regional Studbook using a computer software program called SPARKS (Single Population and Records Keeping System) produced by ISIS (International Species Information System). The studbook database is initiated from ISIS data, a computerized database containing genetic, demographic and relevant biological information about zoo animals worldwide. After this database is checked against existing studbooks, questionnaires are sent to participating institutions requesting verification. Once verification is accomplished, the Management Group can begin serious planning for their particular species. A series of complicated demographic and genetic analyses needs to be performed before the Management Group can start making recommendations. SPARKS automatically calculates inbreeding coefficients (IC), which indicate the relatedness of an individual animal's parents (probability that an animal will become homozygous at a given locus by descent). Basically, SSPs strive to avoid inbreeding, which may lead to reduced fertility, increased mortality, and loss of genetic diversity, thereby limiting the species' options to respond to environmental variation.
Another concern in determining breeding recommendations in a managed population is to equalize the representation of each "genetic line" in the population. An animal is referred to as a "founder" if it represents a new genetic line to the population (i.e., has no relatives in the population). The founders of a zoo population are either the original wild-caught animals or imported animals not genetically represented in the SSP from whom the current population is descended. It is presumed that founders are unrelated to each other and represent a reasonably well-distributed genetic sample of the species in the wild. In an ideal situation, each founder would be equally represented in the living SSP population. This is seldom the case—typically, a large proportion of the animals have descended from a few prolific founders who have many more living descendants than other founders and are thus more fully represented in the population's gene pool. The challenge of the SSP Management Group is to make breeding recommendations that avoid inbreeding and also equalize founder representation to minimize the loss of genetic diversity from the captive population. This is done with the assistance of two software programs associated with SPARKS: DEMOG (by J. Ballou) for demographic analyses; and GENES (by R. Lacy) for genetic analyses.
In the past, the SSP Masterplan process and associated breeding recommendations were based upon inbreeding coefficients and the founder importance coefficient (FIC) which served to equalize relative founder contributions as well as minimize inbreeding. More recently, management has been based on mean kinship value (MK). Mean kinship is an average measure of how related an animal is to all other individuals in the population. Not only does MK allow the equalization of relative founder contributions, but MK also allows the linkage of rare and common genomes to be avoided, making future equalization of founder contributions possible. Animals with a low MK share fewer genes with the rest of the population and are therefore more valuable as potential breeders than those animals with a high MK (e.g., a founder that has never bred has a mean kinship of 0 and therefore is genetically highly valuable). An animal with a low MK should not be bred with an animal with a high MK; otherwise, rare genes would be permanently linked with common genes and could not be increased in frequency without simultaneously increasing common lineages.
Another value which is also used in management is the kinship value (KV), which is a weighted mean kinship which considers the reproductive potential of the animal's relatives in the population. Animals with only old relatives that are unlikely to produce any more offspring would be considered more valuable to breed (and have a lower KV) than animals with many relatives that are young and may produce many offspring.
When the Management Group considers animals to pair for breeding recommendations, it first turns to the list of animals ranked by either mean kinship or kinship value. Animals at the top of the list are given high priority for breeding; animals near the bottom are unlikely to receive a breeding recommendation. Another major consideration is the location of each animal. The Management Group must consider which institutions have requested a breeding recommendation, which institutions would like to keep particular animals, and which institutions want to transfer an animal in or out of their institution. Distance from each other is also a consideration (it is better to transfer an animal from Chicago to Detroit rather than Chicago to Phoenix, both in terms of distance and climatic adjustment). It is best to minimize transfers when possible, as they are costly and involve some disturbance and risk for the animal.
Each potential breeding recommendation must also be separately checked for the inbreeding coefficient of any resulting offspring. For instance, the top ranked male and the top ranked female may look like a good breeding pair; however, they may be brother and sister and would produce cubs with a high inbreeding coefficient.
The number of breeding recommendations that will be made are dependent upon the carrying capacity of the SSP, which is the total number of spaces available in all of the participating zoos for that particular species. In general, the SSP tries to maintain as much genetic diversity as possible, but because of space limitations generally targets 90% of genetic diversity of the wild population for 100-200 years as a reasonable goal. The more animals in the captive population, the more probable this goal can be achieved. But the "Zoo Ark" has limited spaces and there are just too many passengers that need to be brought aboard. For that reason, there is often a compromise between what can be accomplished given the available spaces and what is optimal given the genetic and demographic variables of the species under consideration.
Once the above information is available the management group must identify which animals are to breed, when their breeding is to be scheduled, and at what facility. These institution-by-institution recommendations are then approved and the process begins. Cooperation among the various zoos involved is critically important if the program is to succeed. Construction of new exhibits, incompatibility of selected mates, unanticipated medical problems and other unplanned for contingencies are the rule rather than the exception. Breeding and transfer recommendations may be revised as individuals are born, die or otherwise enter or leave the SSP managed population, as each of these events affects the genetic value of each remaining animal in the SSP. However, through patience, compromise and creative rescheduling none of these problems are insurmountable. The SSP remains a viable alternative to the extinction process.
Together, zoos in many regions of the world are organizing well-planned and tightly coordinated programs for captive management to meet the above goals. In North America these programs are called SSPs; in Europe they have the acronym of EEP for European Endangered Species Programmes, and in Australasia they are the ASMP, or Australasian Species Management Program. China, Japan, India, Thailand, Malaysia and Indonesia have equivalent programs and more are being developed worldwide. The next challenge is to integrate all of these regional programs into comprehensive global masterplans for each endangered species, similar to the goals of the IUCN's Heritage Species Programs. These programs were originally named Global Animal Survival Plans, but have since been renamed Global Conservation Strategies (GCSs) and are under the aegis of the IUCN/SSC Conservation Breeding Specialist Group (see below).
The Tiger SSP provides a good example of how North American zoos are working together to protect an endangered species. Small pockets of tigers remain in forest patches spread from India across China to the Russian Far East and south to Indonesia. Three of the recognized eight subspecies are now extinct; a fourth is near extinction. To provide viable captive populations for the recovery or reenforcement of wild populations, the 1988 Tiger SSP Masterplan recommended the management of 175 Siberian (P.t. altaica), 175 Sumatran (P.t. sumatrae), 75-80 Indochinese (P.t. corbetti) and 75-80 Bengal (P.t. tigris) tigers in the 500-525 "manageable" tiger spaces available in AZA SSP institutions.
At the 1992 AZA Tiger SSP Mid-Year Meeting at Front Royal, it was decided that it was not possible to retain 90% of the genetic diversity for 100 years for each of the four designated taxa given the steadily decreasing tiger space in North America. The AZA Tiger SSP recognized that cooperation with other regional programs would be necessary, as well as incorporating new founders and genome resource banking (GRB) to augment the existing managed captive populations. With this combination of management strategies, a smaller population of about 100 animals could be managed for each of the four subspecies. At that time, this seemed a realistic goal given the report of the AZA Felid TAG, which suggested that future space needs for other potential felid SSPs would compete with existing tiger space commitments.
At the 1992 IUCN/SSC CBSG Tiger Global Animal Survival Plan (now GCS) Meeting in Edinburgh, Scotland, representatives from regional tiger programs (North American SSP, European EEP and JMSP, Indian IESBP, and Southeast Asian SEAZA) recommended that the North American Tiger SSP be responsible for jointly coordinating programs for P.t. altaica (with Europe and Japan), P.t. corbetti (with range countries only) and P.t. sumatrae (with Europe, Australasia and Indonesia). The Bengal subspecies P.t. tigris will be managed in Europe and India only. The South China tiger P.t. amoyensis will be managed in China and possibly Japan.
These recommendations were ratified at the 1992 Annual Tiger SSP meeting in Toronto. In effect, only three tiger subspecies will be managed in future SSP programs.
While all three subspecies programs are pursuing additional founder stock, the Siberian tiger program is close to maturity. The target population has been achieved and reproduction is being strictly controlled to stay within the available space. One problem confronting the Tiger SSP is the large number of surplus animals in this population.
The Sumatran tiger program is developing; the captive population has now filled all available space. As natural attrition of surplus Siberian and generic tiger populations continues, space made available will be dedicated to Sumatran and Indochinese tigers. A recent site evaluation of Sumatran tigers in zoos in Java, Indonesia was conducted in February 1994 (see Tiger SSP Issues). A program for the Indochinese tiger subspecies is underway, but with only ten animals is far from maturity.
The Siberian tiger population has reached target levels and is essentially stable, while the Sumatran population is expanding to reach target. A few institutions have chosen to switch from the Siberian to the Sumatran subspecies, but not enough to warrant concern over competition for space between these programs. Not represented in the table is the large number of generic tigers currently held in North American zoos (estimated at 190 in July 1992). The spaces occupied by these animals will be utilized for the
The surplus, or non-breeding, population in the Tiger SSP numbers 47 animals. These animals are considered surplus due to age, sterility or genetic overrepresentation in the population. The success of the tiger masterplan is contingent on surplus animals being removed in a timely fashion to make room for animals resulting from recommended breedings and to accommodate the addition of new founder stock. Ideally, these animals would be lost through attrition by natural causes (old age), but improvements in health care and management have greatly lengthened an average tiger's life span.
Both the Siberian and Sumatran tiger populations have added new founders in recent years as they approach the goal of 26 effective founders for each program. Two Siberian tiger founders were added to the AZA Tiger SSP in 1991 and another two in 1993, all young wild-caught tigers whose mother was likely killed by poachers.
Siberian (through 30 June 1994)
|2 Years Ago||1 Year Ago||Current Year|
|# of Participants (# of MOPs)||85||88||90|
|# SSP animals managed||119||124||111|
|# SSP animals not required to meet goals||45||39||47|
|# animals in non-participant collections but desirable to SSP||0||0||0|
|Total # of births in SSP program (w/stillborns)||21||9||12|
|# surviving to 90 days||15||8||8|
|# of desired births||21||9||12|
|# of undesired births||0||0||0|
|# of deaths of SSP animals||18||11||10|
|# of transfers recommended||14||24||31|
|# of transfers completed||12||14||23|
|# of imports||0||2||0|
|# of exports||0||0||1|
|# founders with represented descendants||38||39||40|
The Siberian tiger population is being managed for zero population growth at about 160 animals, and has been nearly stable for the past ten years. In the future, this population will be slowly reduced to about 100 animals. Population demographic analyses for Siberian tigers indicates that they have a generation time of 7.3 years (number of years from birth to the time that the first cub is born), sex ratios at birth are equal, and the litter size averages 2.4 cubs. Mortality prior to reproductive age (4 years) is close to 40%. The total number of founders represented is 40.
Given the current life history characteristics of Siberian tigers, 12 animals must be born each year to maintain the SSP population (assuming neonatal mortality = 36%). This means that five litters must be produced per year (based on 2.4 offspring/litter). Since only about 65% of attempted pairings succeed, this means 8-10 pairings per year need to be scheduled by the Tiger SSP. This number serves to guide breeding recommendations to be made in the institution-by-institution analyses. The ultimate number of offspring to be produced by any individual tiger will depend upon a balance between the degree of founder representation of the animals and its family size.
The Sumatran population is being managed for zero population growth due to space limitations. This population will be managed like the Siberian population and will be slowly increased to about 100 animals. Demographic parameters for this population are essentially the same as those reported for the Siberian population above.
"Gene drop" analyses conducted on the Siberian population in June 1994 revealed that 95% of the genetic diversity present in the original founders of the population had thus far been retained (up from 91.6% in 1982). Founder genome equivalents are at 11.367 (5.920 in 1982), and founder representation in the population continues to approach target levels. The mean inbreeding coefficient of the managed population has continually decreased, from 0.108 in 1982 to 0.034 in 1994, while the average mean kinship in 1994 was 0.045.
Genetic analyses of the Sumatran population as of June 1994 revealed that 90% of the genetic diversity present in the original founders has been retained. Thirteen founder equivalents (17 actual founders) were represented in the population. The mean inbreeding coefficient of the Sumatran population as of June 1994 was 0.062 while the average mean kinship was 0.095.
Recruitment of new founder stock for both programs is a high priority. Animals are continually being sought from other regional programs through direction from the IUCN/SSC CBSG Tiger GCS.
Sumatran Tiger Genetics: During the course of the AZA Tiger SSP project "In Situ Development of the Indonesian Regional Sumatran Tiger Masterplan" conducted in February 1994, evidence was uncovered that suggests that a number of studbook registered Sumatran tigers in the Indonesian Zoological Parks Association (PKBSI) have been hybridized with unknown tiger subspecies. Furthermore, a majority of the founders to the PKBSI program could not be verified as wild-caught. Multiple levels of unreported inbreeding were also documented. Taken together these discoveries could potentially have a profound impact on the AZA Sumatran Tiger SSP program, which led to the recommendation that a breeding moratorium for Sumatran tigers be implemented immediately across all institutions in the AZA Tiger SSP and that no further imports of Sumatran tigers should be initiated or completed until the Sumatran tiger verification issue can be
Space: The AZA Felid TAG conducted in 1992 a carnivore cage space [one cage space equals one pair of animals] survey of 148 AZA accredited institutions. Tigers account for the largest proportions of large felid cage space (currently 163 spaces representing a maximum capacity of 474 animals), with an anticipated increase to 172 (max. of 506).
The major problem facing the AZA Tiger SSP is the large number of surplus Siberian tigers occupying space in North American zoos. Fully 30% of the animals in the current population are surplus to the breeding program. These animals are impacting the ability of the Tiger SSP to meet its genetic and demographic program goals. Communications from several participating institutions indicate an unwillingness or inability to comply with breeding recommendations until surplus tigers are removed, and several others have requested guidance on how to deal with their surplus problem.
Excess production is not the problem; reproduction among surplus tigers has ceased and over half of the 47 surplus animals in the present population are now over 12 years of age. Many of these surplus animals can reasonably be expected to persist for a decade or more. Thus, the problem is due to the inability of institutions to remove animals that no longer contribute to the program, particularly animals of advanced age. The issue of management euthanasia has arisen repeatedly and has been regularly put aside.
A new recommendation from the 1992 AZA Felid TAG Meeting gives some direction on this issue (Policy of the Culling of Surplus Animals, see Chapter 7, Policies). This recommendation was also endorsed by the AZA Tiger SSP at the 1992 Annual AZA Meeting in Toronto. Beyond this statement, there is no organizational direction from the AZA/WCMC or the AZA Board of Directors for institutions facing this difficult decision. The current AZA policy on euthanasia does not address the removal of surplus SSP animals in order to meet the genetic and demographic goals of these programs.
Subspecies: Another concern revolves around the issue of species definition. The biological validity of the five extant races, or "subspecies," of tigers (Siberian, Sumatran, Indochinese, Bengal, and South China) is not established. The molecular, electrophoretic and phylogenetic evidence presented at the 1986 International Tiger Symposium indicated no clear nor compelling need to separate the tiger species into its presently referred to subspecies. This present day division of Panthera tigris revolves around geopolitical positions rather than biological distinctions (see below).
Tiger Reproduction (IVF): The first live tiger births from in vitro fertilization/embryo transfer, the result of collaborative efforts of the National, Minnesota and Omaha Zoos, occurred at the Omaha Zoo in April 1990. Through the continued efforts of these institutions, the first live tiger birth from artificial insemination occurred at the Omaha Zoo in November 1991 to parents under-represented in the SSP population. This work is all part of the larger goal to develop the technology for genetic resource (sperm, ova, embryos) banking in this species, which will permit development of interactive management strategies within and between both wild and captive tiger populations. Further attempts in assisted reproductive techniques for tigers were made in 1993 and 1994 at Omaha Zoo but with no success.
Tiger Contraception: L. Munson is involved in research on the effects of megestrol and melengestrol acetate contraceptive implants on mammary and endometrial tissues in non-domestic cats. Her report indicated that felids exposed to melengestrol or megestrol had more severe grades of endometrial hyperplasia than control felids. Due to these findings, the AZA Tiger SSP recommended a set of contraceptive methods that are situation dependent (see Chapter 5, Reproduction).
Genome Resource Banking: The AZA Tiger SSP recommended that genome resource banking be considered as a new strategy to augment the preservation of genetic diversity in captive tiger populations. A comprehensive draft document Genome Resource Banking Action Plan for Tigers by D. Wildt et al. is under review by the IUCN/SSC Captive Breeding Specialist Group. Nine "probable" Sumatran tiger founders were banked by a team led by A. Byers during the recent Sumatran tiger conservation project in February 1994.
Tiger Taxon "Subspecies": A new molecular DNA study of all tiger subspecies has been initiated by S. O'Brien, National Cancer Institute. This study is scheduled to be mostly accomplished by fall 1994 [to be published in the conference proceedings from Tigers 2000, due out in the fall of 1998]. Tissue biopsies from approximately 40 Sumatran tigers in the PKBSI program, four of which are verifiable founders, was exported from Indonesia and delivered to O'Brien's lab. Funding for the collection of these tissue biopsies in Indonesia came from the AZA Ralston Purina Big Cat Survival Fund and the Minnesota Zoo.