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.
-Which of the following statements best explains the trend shown in Figure 1? (Note: Captive cheetahs are generally housed individually.)

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.
-Which of the following statements best explains the trend shown in Figure 1? (Note: Captive cheetahs are generally housed individually.)

Quizplus · Accepted Answer

11ecba2d_0fde_15a7_a3bf_ff60422e1b24_MD0008_00 The passage states that the event that occurred 12,000 years ago resulted in inbreeding depression (decreased heterozygosity and reduced fitness) of Namibian cheetahs. Typically, individuals within a sufficiently large population will outbreed (mate with nonrelatives) because of the additional fitness that outbreeding confers. Outbreeding has an evolutionary advantage because the behavior introduces new genetic material and reduces the probability of passing familial genetic abnormalities to offspring. Figure 1 shows that the heterozygosity of wild-born male cheetahs has decreased over time. Decreased heterozygosity is associated with inbreeding; therefore, the conclusion can be drawn that free-ranging African cheetahs are inbred. In contrast, the heterozygosity of captive-born male cheetahs has increased. These results indicate that conservation groups are selectively outbreeding captive cheetahs with individuals from distinct populations. (Choice A) Inbreeding results in decreased heterozygosity. The captive cheetah population has increased heterozygosity, not decreased; therefore, it can be concluded that the captive cheetahs are bred with individuals that are not closely related to each other. (Choice C) When a population is in Hardy-Weinberg equilibrium, allelic frequencies do not change from one generation to another. As such, heterozygosity in Hardy-Weinberg equilibrium is neither decreased nor increased but remains the same over time. The captive cheetahs show changing allelic frequencies, so they cannot be in Hardy-Weinberg equilibrium. (Choice D) Although increased heterozygosity is typically associated with increased fitness and increased fecundity (number of offspring an individual can have), the passage states that captive cheetahs have decreased fitness. Consequently, the increased heterozygosity cannot be explained by an increase in fecundity. Educational objective: Inbreeding results in decreased heterozygosity (genetic diversity), reduced fecundity, and reduced fitness. Species that mate with nonrelatives (outbreed) increase their fitness because the introduction of new genetic material results in increased heterozygosity.

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