Eighteen years of Florida panther survival since genetic introgression
Reduced fitness due to inbreeding depression is one of the many challenges faced by small, isolated populations. Intentional genetic introgression has been used as a management tool to mitigate detrimental effects of inbreeding. Although it has been successful in increasing genetic diversity and population sizes in some cases, the underlying demographic processes involved often remain unclear. The Florida panther (Puma concolor coryi) population consisted of only ~20 animals in the early 1980s and many panthers suffered from biomedical and morphological abnormalities that were thought to be indicative of inbreeding. A genetic introgression program was implemented in 1995 to mimic historic natural gene flow and to alleviate the effects of inbreeding depression. Using 32 years (14 yrs prior to, and 18 yrs following the introgression) of data from radio-collared panthers and a Cox proportional hazard modeling framework, we estimated age- and sex-specific survival rates of Florida panthers and tested for the effects of several covariates on these rates.
Survival rates were strongly sex- and age-specific. For females, subadult panthers (1-2.5 yrs old) had the highest survival rates, followed by prime adults (2.5-10 yrs old) and old adults (>10 yrs old), respectively. For males, prime adults (3.5-10 yrs old) had the highest survival rates, followed by subadults (1-3.5 yrs old) and old adults (>10 yrs old). Within age-classes, females always survived better than males, possibly because males experience a higher mortality risk from causes such as intraspecific aggression and vehicle collision. Genetic ancestry strongly influenced survival, with F1-admixed and non-introgressed individuals surviving the best and worst, respectively. These results provide evidence for the postulate of hybrid vigor and suggest the positive demographic effects of genetic introgression can remain in the population many years after the event.