Figure 21.7. Survivorship for male and female giant pandas based on data since 1990. The number of animals at risk every five years is shown above the line for females and below for males. •, male; o, female.
growth rates. With the age-specific survival (lx) and fecundity rates (mx) estimated above, this now becomes possible (Caughley, 1977). The annual growth rate (2) can be determined by using the Euler equation:
where the sum is over all age classes (Caughley, 1977). The 2 cannot be determined directly and is usually calculated using iterative computer software (e.g. PM2000; Pollak et al., 2002).
For the giant panda, the 2 estimated from the studbook life table is 1.028. This value means that, if a stable population of giant pandas was to consistently reproduce and survive at the rates indicated in Figures 21.5 (smoothed fecundity) and 21.7 (survivorship), it would grow at 2.8% per year. This rate is lower than that actually observed over the last ten years (6% per year) because it only includes growth due to reproduction and survival. In reality, the actual population has also experienced growth due to immigration of wild-caught animals. The 1.028 annual growth rate, if applied to this population, would result in a captive population of 206 pandas by 2016 with no further influx of wild-caught animals.
Captive breeding programmes strive to retain genetic diversity and avoid inbreeding to promote population viability in captivity while maximising the potential for animals to adapt to nature if ever reintroduced (Ballou & Foose, 1996). Achieving this goal also minimises genetic deterioration (i.e. inbreeding depression, loss of genetic variation and adaptations to the captive environment) that can potentially occur in ex situ populations (Frankham et al., 1986). Genetic management of captive populations is usually based on pedigree analysis (Lacy et al., 1995). The pedigree provides information on the degree of inbreeding, the amount of genetic diversity retained relative to the founders, the level of relatedness among the living population and genetic substructuring (i.e. differences among various regions, institutions and the like). However, information on parentage may frequently be missing due to poor record-keeping, husbandry practices that make it difficult to identify parentage (e.g. species kept in mixed-sex groups) or multiple inseminations by several males. Any or all of these factors complicate pedigree-based management strategies.
Pedigree and genetic analyses are critical for the captive giant panda population because of the extensive use of artificial insemination (AI), especially using semen from multiple males to inseminate a single female (see Chapters 10 and 20). Of the 261 captive-born animals listed in the 2001 studbook (Xie & Gipps, 2001). 103 (39.5%) are listed with multiple potential sires. Recently, molecular genetics has been used to resolve the majority of these pedigree uncertainties (see Chapter 10). Yet, 17.5% of the current captive gene pool still remains unresolved. Although 40 individuals have some level of uncertainty in their pedigree, all can be resolved by determining the paternity of 17 individuals, many of which are individuals born in 2001 whose biosamples are awaiting genetic evaluation.
For the purposes of the present analysis, we made paternity assumptions for these 17 individuals based on other available information. For example, in some pairings, AI was used one or more times after a natural mating. In cases where paternity was later verified using molecular genetics, the male participating in the natural matings was always confirmed as the true sire (in contrast to the AI donor) (see Chapter 10). Whenever possible, it is important to use modern genetic technologies to resolve issues of uncertain paternity. Meanwhile, most pedigree analyses will continue to rely on some level of assumed parentage in the population.
For our analysis, two giant panda groups were excluded: poor reproductive candidates, which were senescent or which exhibited severe behavioural or medical problems; and animals at institutions that were unavailable for coordinated captive breeding. These 18 animals were identified at the January 2002 Population Management Workshop in Chengdu (SB 133, 161, 199, 203, 204, 214, 217, 230, 264, 288, 290, 300, 307, 358, 365, 416, 447 and 499). With these pandas excluded, 124 individuals remained in the genetically analysed population.
The modern ex situ giant panda population stands out from many other captive wildlife populations because of the significant number of wild-caught individuals that have entered, and continue to enter, the programme. Although giant pandas are no longer prospectively 'harvested' for zoo collections, animals are occasionally 'rescued' often as a result of nutrition or health problems or panda-human conflicts (see Chapter 2). These individuals then become opportunistically incorporated into captive collections. Of the 542 animals listed in the current studbook, 281 (51.8%) have been wild-caught, whereas of the current living population of 142 individuals, 49 (34.5%) are wild-caught. The result is that the population has a strong genetic foundation given that these wild-caught individuals do eventually contribute their genes to subsequent generations. Table 21.1 provides the current genetic summary of the population.
Forty-one wild-caught individuals (called 'founders') already have contributed genes to the population, and another 14 wild-caught animals are alive and of reproductive age, but have not produced offspring (these are called 'potential founders'). Due to the significant
Table 21.1. Genetic status of the captive giant panda population as of 1 January 2002
Number of founders Potential additional founders Proportional heterozygosity retained Potential proportional heterozygosity Founder genome equivalents Average inbreeding coefficient Average mean kinship
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