Intentional genetic introgression influences survival of adults and subadults in a small, inbred felid population

SAIC-Frederick, National Cancer Institute, Frederick, MD 21702-1201, USA
Journal of Animal Ecology (Impact Factor: 4.5). 08/2011; 80(5):958 - 967. DOI: 10.1111/j.1365-2656.2011.01809.x
Source: PubMed


Summary1. Inbreeding and low genetic diversity can cause reductions in individual fitness and increase extinction risk in animal populations. Intentional introgression, achieved by releasing genetically diverse individuals into inbred populations, has been used as a conservation tool to improve demographic performance in endangered populations.2. By the 1980s, Florida panthers (Puma concolor coryi) had been reduced to a small, inbred population that appeared to be on the brink of extinction. In 1995, female pumas from Texas (P. c. stanleyana) were released in occupied panther range as part of an intentional introgression programme to restore genetic variability and improve demographic performance of panthers.3. We used 25 years (1981–2006) of continuous radiotelemetry and genetic data to estimate and model subadult and adult panther survival and cause-specific mortality to provide rigorous sex and age class-specific survival estimates and evaluate the effect of the introgression programme on these parameters.4. Genetic ancestry influenced annual survival of subadults and adults after introgression, as F1 generation admixed panthers ( = 0·98) survived better than pre-introgression type panthers ( = 0·77) and other admixed individuals ( = 0·82). Furthermore, heterozygosity was higher for admixed panthers relative to pre-introgression type panthers and positively influenced survival.5. Our results are consistent with hybrid vigour; however, extrinsic factors such as low density of males in some areas of panther range may also have contributed to higher survival of F1 panthers. Regardless, improved survival of F1 subadults and adults likely contributed to the numerical increase in panthers following introgression, and our results indicate that intentional admixture, achieved here by releasing individuals from another population, appears to have been successful in improving demographic performance in this highly endangered population.

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Available from: Jeffrey Allan Hostetler
    • "Also, for genetic rescue: (a) gene flow is limited over time or in degree; or (b) selection is strong enough to maintain or re-assemble the genomic and phenotypic differences between the parental lines. Genetic rescue was a rare outcome in our literature survey: definitive in only one case, where hybridization was a human-mediated, intraspecific, single event in a population suffering from inbreeding depression (Benson et al. 2011), fitting the more traditional, conservation management definition of genetic rescue (Whiteley et al. 2015), and putative in another two cases (Wachowiak and Prus-Glowacki 2009, Harbicht et al. 2014). The rarity of this outcome in our survey may be the result of ascertainment bias resulting from our search terms (see above), but also may reflect the rarity of this outcome more generally in natural populations. "
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    ABSTRACT: Hybridization may drive rare taxa to extinction through genetic swamping, where the rare form is replaced by hybrids, or by demographic swamping, where population growth rates are reduced due to the wasteful production of maladaptive hybrids. Conversely, hybridization may rescue the viability of small, inbred populations. Understanding the factors that contribute to destructive versus constructive outcomes of hybridization is key to managing conservation concerns. Here we survey the literature for studies of hybridization and extinction to identify the ecological, evolutionary, and genetic factors that critically affect extinction risk through hybridization. We find that while extinction risk is highly situation dependent, genetic swamping is much more frequent than demographic swamping. In addition, human involvement is associated with increased risk and high reproductive isolation with reduced risk. Although climate change is predicted to increase the risk of hybridization-induced extinction, we find little empirical support for this prediction. Similarly, theoretical and experimental studies imply that genetic rescue through hybridization may be equally or more probable than demographic swamping, but our literature survey failed to support this claim. We conclude that halting the introduction of hybridization-prone exotics and restoring mature and diverse habitats that are resistant to hybrid establishment should be management priorities. This article is protected by copyright. All rights reserved.
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    • "Discussions with Florida cattlemen are consistent with the literature on human-cougar conflicts. Florida cattlemen expressed a real concern that efforts to recover the Florida panther by introducing female Texas cougars (see Benson et al. 2011) have resulted in a hybrid panther-cougar that is larger, more aggressive and more prolific than the panther (prior to the genetic introgression). Cattlemen contend that the panther is no longer afraid of humans and is openly entering people's backyards to prey on their domestic animals, including pets and hobby livestock. "
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    ABSTRACT: Recovery of the Florida panther (Puma concolor coryi) depends on habitat conservation on private rangelands. However, cattlemen-panther conflicts and lack of trust in wildlife agencies is undermining panther conservation efforts. Based on semi-structured interviews and group meetings with Florida cattlemen, we examine how cattlemen's land stewardship practices support panther conservation, and causes of conflicts with the panther and wildlife agencies. Given the heterogeneous attitudes of cattlemen and their varying economic conditions, a complementary suite of programs is needed to achieve efficient conservation of the panther and panther habitat. Current and proposed government incentive programs are unlikely to attain the level of habitat conservation required to recover the Florida panther. We suggest that efforts should be made to build social capital and trust by engaging influential cattlemen in panther conservation actions, thereby lending credibility to conservation initiatives and improving the rate of uptake and levels of commitment by other cattlemen. Moreover, providing cattlemen with payments that are contingent on keeping lands as unimproved pasture or wildlife habitat without mandating particular land management practices may be an effective policy alternative.
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    • "Since the introduction of the Texas subspecies, the incidence of inbreeding traits has decreased (Mansfield & Land, 2002; Onorato et al., 2010), heterozygosity has increased (Johnson et al., 2010), and the population size has increased (McBride et al., 2008). The F 1 hybrids had higher survival (Benson et al., 2011; Hostetler et al., 2010). However, both the F 1 hybrids and the backcross with the Texas subspecies had lower reproduction probabilities (Hostetler et al., 2012). "
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    ABSTRACT: The evolutionary forces that drive recent population genetic changes include migration, mating strategy, genetic drift, and selection. However, the strength of these forces varies depending on population size. The purpose of this article is to review genetic issues associated with small forest populations and to provide perspectives from fish and wildlife genetics through case studies. Small populations are often fragmented, potentially preventing migration. In forest trees, long-distance pollen dispersal and highly mobile, generalist pollinators can help maintain connectivity. A landscape and community approach to understanding connectivity is critical (case study: mussels). Outbreeding depression can also be a concern in forest restoration. This becomes a greater risk when mixing populations that are highly diverged and when the species is polyploid. Management units should be designated that mimic natural gene flow (case study: lake sturgeon). At the other extreme, inbreeding depression can result in reduced fitness. When inbreeding depression is a concern, genetic rescue may be necessary (case study: Florida panther). Loss of diversity through genetic drift can occur with small effective population sizes (Ne) and a small number of founders (case study: salmonids). Selection is most likely to occur through adaptation to captivity or introduction of resistant/tolerant strains (case study: amphibians).
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