SAT Reading - Khan Diagnostic Quiz level 4 - reading 13

Passage 1

For reasons that are not entirely clear, when animals make

their way to isolated islands, they tend to evolve relatively

quickly toward an outsized or pint-sized version of their
_Line mainland counterpart.
₅ tab]Perhaps the most famous example of an island giant-and,

sadly, of species extinction-is the dodo, once found on the

Indian Ocean island of Mauritius. When the dodo's ancestor

(thought to be a migratory pigeon) settled on this island with

abundant food, no competition from terrestrial mammals, and
₁₀ no predators, it could survive without flying, and thus was

freed from the energetic and size constraints of flight. New

Zealand also had avian giants, now extinct, including the

flightless moa, an ostrich-like bird, and Haast's eagle

(Harpagornis moored), which had a wingspan up to 3
₁₅ meters. Though Haast's eagle could fly-and presumably used

its wings to launch brutal attacks on the hapless moa-its body

mass (10–14 kilograms) pushed the limits for self-propelled

flight.
As extreme evolutionary examples, these island birds can
₂₀ offer insights into the forces and events shaping evolutionary

change. In a new study, Michael Bunce et al. compared

ancient mitochondrial DNA extracted from Haast's eagle

bones with DNA sequences of 16 living eagle species to

better characterize the evolutionary history of the extinct
₂₅ giant raptor. Their results suggest the extinct raptor

underwent a rapid evolutionary transformation that belies its

kinship to some of the world's smallest eagle species.
The authors characterized the rates of sequence evolution

within mitochondrial DNA to establish the evolutionary
₃₀ relationships between the different eagle species. Their

analysis places Haast's eagle in the same evolutionary lineage

as a group of small eagle species in the genus Hieraaetus.

Surprisingly, the genetic distance separating the giant eagle

and its more diminutive Hieraaetus cousins from their last
₃₅ common ancestor is relatively small.

Passage 2

The mysterious spotted green pigeon (Caloenas maculata)

was a relative of the dodo, according to scientists who have

examined its genetic make-up. The authors say their results,

published in the open access journal BMC Evolutionary
₄₀ Biology, support a theory that both birds are descended from

“island hopping” ancestors.
The scientists took DNA from two feathers of the spotted

green pigeon. Because of its age, the DNA was highly

fragmented, so they focused in on three DNA “mini
₄₅ barcodes” – small sections of DNA which are unique for

most bird species. They looked at these sections of the

pigeon's DNA, and compared it to other species.
This showed that the spotted green pigeon is indeed a

separate species, showing a unique DNA barcode compared
₅₀ to other pigeons. The pigeon is genetically most closely

related to the Nicobar pigeon and the dodo and Rodrigues

solitaire, both extinct birds from islands near Madagascar.

The spotted green pigeon shows signs of a semi-terrestrial

island lifestyle and the ability to fly. The closely related
₅₅ Nicobar pigeon shows similar habits and has a preference for

travelling between small islands.
The scientists say this lifestyle, together with the

relationship of both pigeons to the dodo and Rodrigues

solitaire, supports an evolutionary theory that the ancestors of
₆₀ these birds were “island hoppers,” moving between islands

around India and Southeast Asia. The birds that settled on

particular islands then evolved into the individual species.

The dodo's ancestor managed to hop as far as the island of

Mauritius near Madagascar where it then lost the ability to
₆₅ fly.
Dr. Tim Heupink, Griffith University Australia says: “This

study improves our ability to identify novel species from

historic remains, and also those that are not novel after all.

Ultimately this will help us to measure and understand the
₇₀ extinction of local populations and entire species.”