Shown here are graphs that plot the percentage of fertilized eggs containing males against the atmospheric temperature during early development in (a) snapping turtles and (b) most lizards. Interpret these data as they relate to the effect of temperature on sex determination.

Verified step by step guidance

1. Step 1: Observe the graph for snapping turtles (a). Notice that the percentage of males varies with temperature, peaking near 30°C and dropping to nearly 0% at both lower and higher temperatures. This suggests that temperature influences sex determination in snapping turtles, with a specific temperature range favoring male development.
2. Step 2: Examine the graph for most lizards (b). The percentage of males remains constant at about 50% across the entire temperature range from 20°C to 40°C. This indicates that temperature does not affect sex determination in these lizards, and sex is likely determined genetically rather than by environmental temperature.
3. Step 3: Understand the concept of temperature-dependent sex determination (TSD), which is a mechanism where the environmental temperature during early development determines the sex of the offspring. The snapping turtle graph is a classic example of TSD, where certain temperatures produce mostly males or mostly females.
4. Step 4: Contrast this with genetic sex determination (GSD), where sex is determined by chromosomes and is independent of temperature. The lizard graph exemplifies GSD, as the sex ratio remains stable regardless of temperature changes.
5. Step 5: Summarize the interpretation: In snapping turtles, temperature during early development plays a critical role in determining sex, with a narrow temperature window producing males. In most lizards, sex determination is not influenced by temperature, resulting in a consistent 50:50 sex ratio.

Key Concepts

Temperature-Dependent Sex Determination (TSD)

TSD is a mechanism where the environmental temperature during early embryonic development determines the sex of the offspring. In species like snapping turtles, sex ratios vary with temperature, producing mostly males at intermediate temperatures and females at extremes. This contrasts with genetic sex determination, where sex is fixed by chromosomes.

Genetic Sex Determination (GSD)

GSD involves sex being determined by specific chromosomes inherited at fertilization, independent of environmental factors. The graph for most lizards shows a constant 50% male ratio across temperatures, indicating GSD where temperature does not influence sex outcome.

Sex Ratio and Evolutionary Adaptation

Sex ratios influenced by temperature can affect population dynamics and evolutionary fitness. Species with TSD may adapt to environmental conditions by producing sex ratios that optimize survival or reproductive success, while species with GSD maintain stable sex ratios regardless of temperature.