Question

text 1
the land that became grande terre island split from remnants of the former supercontinent gondwana approximately 80 million years ago, carrying gondwanan biota with it, and experienced periodic submergence until 37 million years ago. some researchers posit that the island’s current biota includes members of gondwanan clades (i.e., clades predating the split) that persisted by seeking temporary refuge on nearby islands during submergence events.

text 2
in a recent study, prashant sharma and gonzalo giribet found that the crown age—the age of the most recent common ancestor of all species in the clade (i.e., the clade’s founder)—is 48.9 million years for grande terre’s clade of harvest spiders. most of the island’s extant biota belong to clades with younger crown ages, however. jérôme munienne et al. found that the crown age of grande terre’s clade of cockroaches is 2.7 million years, for example.

taken together, text 1 and text 2 best support which statement about the clades of harvest spiders and cockroaches on grande terre?

a. the clade of harvest spiders must have originated on gondwana, but the clade of cockroaches may or may not have.
b. both the clade of harvest spiders and the clade of cockroaches originated elsewhere and colonized grande terre.
c. neither the clade of harvest spiders nor the clade of cockroaches originated on gondwana.
d. the clade of harvest spiders originated before grande terre split from gondwana, whereas the clade of cockroaches originated after the split but before the periodic submergence events began.

a 〇
b 〇
c 〇
d 〇

Explanation:

• Text 1: Grande Terre split from Gondwana ~80 mya, had Gondwanan biota, and periodic submergence until 37 mya. Some biota (Gondwanan clades) persisted via refuge.
• Text 2: Harvest spiders’ crown age = 48.9 mya (before 37 mya submergence end), cockroaches’ crown age = 2.7 mya (much later).
• Analyze options:
• A: Harvest spiders’ crown age (48.9 mya) is after Gondwana split (80 mya) but before submergence end (37 mya). Gondwanan clades pre - split, so harvest spiders could be Gondwanan (persisted via refuge). Cockroaches’ crown age (2.7 mya) is long after submergence, so they may not be Gondwanan. This fits.
• B: No info to support both colonized from elsewhere. Eliminate.
• C: Harvest spiders could be Gondwanan. Eliminate.
• D: Harvest spiders’ crown age (48.9 mya) is after split (80 mya? No, 48.9 < 80? Wait, 80 mya ago split, so 80 mya in past. 48.9 mya crown age means ancestor lived 48.9 mya ago, which is after split (80 mya ago). So D’s “before split” is wrong. Eliminate.

Answer:

A. The clade of harvest spiders must have originated on Gondwana, but the clade of cockroaches may or may not have.