Which statement accurately reflects pelvic girdle variation described for sticklebacks?

Which statement accurately reflects pelvic girdle variation described for sticklebacks?

• A. A pelvis with a single spine is Complete pelvis
• B. Reduced pelvis has a full girdle with two spines
• C. Absent pelvis has a full girdle with two spines
• D. A pelvis with a full girdle and two spines is described as Complete pelvis; reduced pelvis ranges from simplified girdle to oval nub; absent pelvis has no girdle or spines

Answer: (D)

In sticklebacks, pelvic girdle variation shows three distinct states that describe how much of the girdle and spines remain: a complete pelvis with a full girdle and two spines; a reduced pelvis where the girdle is simplified (even down to an oval nub); and an absent pelvis with no girdle or spines at all. The statement that describes a pelvis with a full girdle and two spines as the complete form, that a reduced pelvis ranges from a simplified girdle to an oval nub, and that an absent pelvis has no girdle or spines, matches these observed forms. That’s why it’s the correct description. The other options mix up which features belong to which state: a complete pelvis isn’t just one spine, reduced pelvis isn’t full girdle with two spines, and absent pelvis isn’t described as having a full girdle with two spines.

In sticklebacks, pelvic girdle variation shows three distinct states that describe how much of the girdle and spines remain: a complete pelvis with a full girdle and two spines; a reduced pelvis where the girdle is simplified (even down to an oval nub); and an absent pelvis with no girdle or spines at all. The statement that describes a pelvis with a full girdle and two spines as the complete form, that a reduced pelvis ranges from a simplified girdle to an oval nub, and that an absent pelvis has no girdle or spines, matches these observed forms. That’s why it’s the correct description.

The other options mix up which features belong to which state: a complete pelvis isn’t just one spine, reduced pelvis isn’t full girdle with two spines, and absent pelvis isn’t described as having a full girdle with two spines.