Passage
The Namibian cheetah (Acinonyx jubatus jubatus) , the world's fastest land-dwelling animal, hunts across the African grasslands using high-speed sprints. Cheetahs possess unique anatomical features specialized for speed, including an aerodynamic skull, elongated legs, and an enlarged heart. These physiological adaptations have occurred over time and allow cheetahs to achieve speeds greater than 100 km/h. However, due to their small body and slender limbs, cheetahs (50-64 kg) are limited with regard to the size of the animals they can successfully hunt and therefore typically prey on slightly smaller species that inhabit open grasslands.It is believed that around 12,000 years ago, Namibian cheetahs experienced an environmental catastrophe that drastically reduced their population. The small number of surviving cheetahs began mating with one another, which led to severe inbreeding depression. Over time, the offspring of subsequent generations exhibited decreased fitness, reduced fecundity (number of offspring) , and sustained a loss of major histocompatibility complex (MHC) allele diversity. To study if low MHC diversity correlates with low fitness in cheetahs, scientists analyzed the genetic diversity and disease prevalence in a group of free-ranging and captive male cheetahs.Experiment 1MHC allele genotyping and analysis was performed in wild (free-ranging) and captive male cheetahs (Figure 1) . Because MHC diversity is strongly correlated with genetic diversity, MHC diversity is used as a marker for an organism's overall genetic variability.
Figure 1 Evaluation of heterozygosity in (A) wild and (B) captive male cheetahs born between 1976 and 2007 (Note: Each data point represents a single male cheetah.) Experiment 2Disease prevalence was evaluated in wild and captive male cheetahs by quantitative analysis of symptoms relating gastrointestinal, liver, and kidney disease. The percentages of cheetahs affected by each disease are shown in Figure 2.
Figure 2 Evaluation of disease prevalence in wild and captive male cheetahsExperiment 3Fecal cortisol levels were noninvasively evaluated in wild and captive cheetahs over a period of 6 months (Figure 3) .
Figure 3 Average fecal cortisol concentrations of wild and captive male cheetahs
Adapted from Castro-prieto A, Wachter B, Sommer S. Cheetah paradigm revisited: MHC diversity in the world's largest free-ranging population. Mol Biol Evol. 2011;28(4) :1455-68.
-If wild Namibian cheetahs continue breeding as described in the passage, what is most likely to occur to their population size in the long term?

Question

Passage
The Namibian cheetah (Acinonyx jubatus jubatus) , the world's fastest land-dwelling animal, hunts across the African grasslands using high-speed sprints. Cheetahs possess unique anatomical features specialized for speed, including an aerodynamic skull, elongated legs, and an enlarged heart. These physiological adaptations have occurred over time and allow cheetahs to achieve speeds greater than 100 km/h. However, due to their small body and slender limbs, cheetahs (50-64 kg) are limited with regard to the size of the animals they can successfully hunt and therefore typically prey on slightly smaller species that inhabit open grasslands.It is believed that around 12,000 years ago, Namibian cheetahs experienced an environmental catastrophe that drastically reduced their population. The small number of surviving cheetahs began mating with one another, which led to severe inbreeding depression. Over time, the offspring of subsequent generations exhibited decreased fitness, reduced fecundity (number of offspring) , and sustained a loss of major histocompatibility complex (MHC) allele diversity. To study if low MHC diversity correlates with low fitness in cheetahs, scientists analyzed the genetic diversity and disease prevalence in a group of free-ranging and captive male cheetahs.Experiment 1MHC allele genotyping and analysis was performed in wild (free-ranging) and captive male cheetahs (Figure 1) . Because MHC diversity is strongly correlated with genetic diversity, MHC diversity is used as a marker for an organism's overall genetic variability.

Figure 1 Evaluation of heterozygosity in (A) wild and (B) captive male cheetahs born between 1976 and 2007 (Note: Each data point represents a single male cheetah.) Experiment 2Disease prevalence was evaluated in wild and captive male cheetahs by quantitative analysis of symptoms relating gastrointestinal, liver, and kidney disease. The percentages of cheetahs affected by each disease are shown in Figure 2.

Figure 2 Evaluation of disease prevalence in wild and captive male cheetahsExperiment 3Fecal cortisol levels were noninvasively evaluated in wild and captive cheetahs over a period of 6 months (Figure 3) .

Figure 3 Average fecal cortisol concentrations of wild and captive male cheetahs
Adapted from Castro-prieto A, Wachter B, Sommer S. Cheetah paradigm revisited: MHC diversity in the world's largest free-ranging population. Mol Biol Evol. 2011;28(4) :1455-68.
-If wild Namibian cheetahs continue breeding as described in the passage, what is most likely to occur to their population size in the long term?

Quizplus · Accepted Answer

11ecba2d_0fe0_fbe3_a3bf_1f26f8584abd_MD0008_00 The passage describes wild cheetahs' breeding patterns as inbreeding, the mating of closely related individuals. Inbreeding leads to inbreeding depression, which is characterized by loss of genetic diversity (heterozygosity), reduced fecundity (number of offspring), and decreased fitness. Fitness is reduced in inbreeding populations because inbred offspring have an increased probability of being homozygous for deleterious recessive traits due to the low genetic diversity between their parents. Individuals with low genetic diversity in MHC alleles have low fitness because it reduces their ability to fight novel diseases and pathogens. Therefore, repeated generational inbreeding within the cheetah population will lead to decreased heterozygosity, reduced reproductive success, and ultimately extinction or the elimination of the cheetah species. (Choices A and D) Neither sex ratios nor female cheetahs are mentioned in the passage; therefore, speculations about sex ratios or the number of females within the population as a consequence of long-term inbreeding cannot be made. Also, the population of free-ranging cheetahs demonstrates decreased heterozygosity, which is indicative of decreased fecundity and fitness. The predicted long-term impact of inbreeding depression is decreased (not stable or increasing) population size. (Choice B) If wild cheetahs continue the mating pattern described in the passage, the small inbred population is unlikely to increase in size over a long period because inbreeding reduces fitness and increases the probability of extinction. The introduction of new, genetically distinct individuals would be necessary to increase the cheetah's genetic diversity, fitness, and population size. Educational objective: Inbreeding depression is characterized by decreased genetic diversity, reduced fecundity, and decreased fitness. As genetic diversity decreases within a population, the frequency of homozygous deleterious recessive genes increases within that population. Consequently, inbred populations have an increased probability of becoming extinct.

Passage The Namibian Cheetah (Acinonyx Jubatus Jubatus), the World's Fastest Land-Dwelling