Population Management of the Mexican Wolf

Historical Perspective - Population Lineages

Five wolves, (four males and one pregnant female) were captured from the wild to form a captive breeding program between 1977 and 1980 by Roy McBride in Durango and Chihuahua, Mexico. These five wolves were then transferred to the U.S. where three (one female and two males) became the founders of a certified captive breeding program for a species that was on the brink of extinction. Known as the McBride lineage, the population had grown to 107 animals by 1995.

In July 1995, two additional lineages of captive Mexican wolves, the Ghost Ranch population in the United States and the Aragon population in Mexico City, were approved for addition to the SSP© breeding program. The Ghost Ranch lineage is derived from two wolves taken from the wild in 1959 and 1961. The Aragon lineage is derived from two wolves originating at the Chapultepec Zoo in the mid 1970s. Although both lineages had been maintained in captivity since at least the 1960s, they were previously uncertified because of uncertainties about their origins. However, genetic investigations concluded that all three lineages were pure Canis lupus baileyi. Findings revealed that the McBride lineage had the lowest level of inbreeding and had retained the most founder alleles, while the Ghost Ranch lineage had a high level of inbreeding and the fewest founder alleles. The study also confirmed the McBride lineage to have only three founders versus the four previously assumed (one of the wild caught males was the offspring of the wild caught female).

Findings from this research recommended that the three lineages be combined to increase the number of founders and to postpone any inbreeding depression. The addition of these two lineages added 4 new founders and 33 individuals (25 Ghost Ranch, 8 Aragon) to the total captive population.

In order to maintain gene diversity, the Master Plan projects a need for a captive carrying capacity of at least 240 wolves. However, the lack of sufficient captive space continues to be of concern for the program, especially considering the carrying capacity does not include wolves surplused for the reestablishment effort. As a means of creating more captive space, the SSP© and its counterpart in Mexico (Mexican Wolf Technical Advisory Committee) continue to aggressively promote participation by North American Zoos and their like in the captive breeding program. Another way to maintain or even increase the gene diversity is by increasing the number of founders. However, finding new founders seems unlikely: except for the reintroduced population, the presence of wolves in the wild has not been confirmed for more than fifteen years. Although 81% of the genetic diversity of the population has been retained, it can be increased by managing the captive

population better. One management practice is to increase the generation time, the longer the generation time, the smaller the loss of genetic diversity. Semen collection and cryopreservation is one way to increase generation time, assuming artificial insemination techniques are perfected.

Management Strategies:

1.) The first priority is to breed individuals of the lowest Mean Kinship (MK) which are underrepresented and, therefore, possess the rarest alleles in the population.

2.) Among individuals with low MK, the second priority is to breed those individuals whose alleles may be lost soon. Priorities should be determined by the manager's knowledge of an individual's age, health, and/or reproductive condition. In the absence of other information low Kinship Value (KV), printed on the Master Plan report, can be used.

Criteria for Establishing Breeding Pairs:

There are five criteria that are considered in order during the establishment of annual breeding pairs for the Mexican wolf captive population (in order of priority):

1. Mean Kinship Value: Mate individuals with roughly similar MK to avoid combining rare and common alleles in offspring that reduces long term gene diversity.

2. Inbreeding Coefficient: Mate individuals whose offspring will have low inbreeding coefficients (F), for the best probability of viable, healthy offspring.

3. Biology of Individual: Maximize mating success based on the species' biology, including suitable age of individuals, mate choice, social structure, reproductive history, etc.

4. General Logistics: Minimize logistical difficulties of moves (e.g. distance, cost, quarantine).

5. Politics: Maximize inter-institutional harmony and minimize political conflicts.

It has been recommended that special attention be given to the behavioral characteristic of the individual given how much this criterion weighs on the success of the release candidate. Wolves that are potential candidates for release to the wild are evaluated based on a number of behavioral and physiological criteria including genetic makeup, age, reproductive performance, proven parental skills and appropriate social behavior, and aversion to humans.