Anole lizard species that occur together (sympatrically) on

Anole lizard species that
occur together (sympatrically)
on certain Caribbean islands
Line occupy different habitats:
(5) some live only in the grass,
some only on tree trunks, and
some only on twigs. These
species also differ morphologically:
grass dwellers are
(10) slender with long tails, tree
dwellers are stocky with long
legs, twig dwellers are slender
but stubby-legged. What is
striking about these lizards
(15) is not that coexisting species
differ in morphology and habitat
use (such differences are
common among closely related
sympatric species), but that
(20) the same three types of habitat
specialists occur on each
of four islands: Puerto Rico,
Cuba, Hispaniola, and Jamaica.
Moreover, the Puerto Rican
(25) twig species closely resembles
the twig species of Cuba,
Hispaniola, and Jamaica in
morphology, habitat use, and
behavior. Likewise, the spe-
(30) cialists for other habitats are
similar across the islands.
The presence of similar
species on different islands
26
could be variously explained.
(35) An ancestral species might
have adapted to exploit a
particular ecological niche on
one island and then traveled
over water to colonize other
(40) islands. Or this ancestral
species might have evolved
at a time when the islands
were connected, which some
of these islands may once
(45) have been. After the islands
separated, the isolated lizard
populations would have become
distinct species while also
retaining their ancestors’ niche
(50) adaptations. Both of these
scenarios imply that specialization
to each niche occurred
only once. Alternatively, each
specialist could have arisen
(55) independently on each of the
islands.
If each type of specialist
evolved just once, then similar
specialists on different islands
(60) would be closely related.
Conversely, if the specialists
evolved independently on each
island, then a specialist on one
island would be more closely
(65) related to other types of anoles
on the same island—regardless
of their ecological niches—
than it would be to a similar
specialist on a different island.
(70) Biologists can infer how
species are related evolutionarily
by comparing DNA
sequences for the same genes
in different species. Species
(75) with similar DNA sequences
for these genes are generally
more closely related to each
other than to species with lesssimilar
DNA sequences. DNA
27
(80) evidence concerning the anoles
led researchers to conclude
that habitat specialists on one
island are not closely related
to the same habitat specialists
(85) elsewhere, indicating that specialists
evolved independently
on each island.
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Q24:
The primary purpose of the passage is to
A. describe some unusual features of anole lizard species
B. account for a particular type of behavior found among anole lizard species
C. contrast two types of evidence that have been used to support a particular
hypothesis concerning anole lizard species
D. explain how researchers resolved a particular scientific question concerning anole
lizard species
E. examine different explanations for a particular trait common to certain anole
lizard species
Answer:
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