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 murienne 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.

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 murienne 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.

Accepted Answer

# Brief Explanations: - From Text 1: Grande Terre split from Gondwana ~80 mya, had submersions until 37 mya. Some biota are Gondwanan clades (predating split). - From Text 2: Harvest spiders’ crown age (most recent common ancestor) is 48.9 mya (after split ~80 mya, before submersions end 37 mya? Wait, 48.9 is between 80 and 37? Wait 80 > 48.9 > 37? No, 37 is less than 48.9? Wait 80 mya ago split, submersions until 37 mya ago (so 37 mya ago is more recent than 80 mya ago). So 48.9 mya ago is between 80 and 37 (since 80 > 48.9 > 37? Wait no, 37 mya ago is closer to present, so 80 mya ago is earlier, 37 mya ago is later. So 48.9 mya ago is between 80 and 37 (earlier than 37? No, 48.9 is greater than 37? Wait 80 million years ago (split) → 37 million years ago (end of submersions). So time line: 80 mya (split) → 48.9 mya (harvest spiders’ crown age) → 37 mya (end submersions). So harvest spiders’ clade crown age is 48.9 mya, which is after the split (80 mya) but before submersions ended (37 mya)? Wait no, 48.9 is less than 80? Wait 80 mya ago is a long time ago, so 80 mya ago is earlier than 48.9 mya ago? Wait no, "80 million years ago" is further in the past than "48.9 million years ago". So split at 80 mya ago, harvest spiders’ crown age at 48.9 mya ago (so after split). Cockroaches’ crown age is 2.7 mya (much more recent, after submersions ended at 37 mya ago). Now analyze options: A: Harvest spiders’ crown age is 48.9 mya (after split from Gondwana ~80 mya), so they can't have originated on Gondwana (since Gondwana split off 80 mya, and their crown age is 48.9 mya, meaning their common ancestor is after the split). Wait, maybe I messed up. Wait "crown age" is the age of the most recent common ancestor of all species in the clade. So if the clade originated on Gondwana (before split), then the crown age should be at least 80 mya (since split was 80 mya ago). But harvest spiders’ crown age is 48.9 mya, which is less than 80 mya, so their clade originated after the split. Wait, no—maybe I got the time direction wrong. Let's rephrase: - Split happened 80 million years ago (so Gondwana and Grande Terre separated 80 mya). - Harvest spiders’ clade has a crown age of 48.9 mya (meaning the most recent common ancestor of all harvest spiders on Grande Terre lived 48.9 mya ago). - So 48.9 mya ago is after the split (80 mya ago), so the harvest spiders’ clade couldn't have originated on Gondwana (because Gondwana and Grande Terre were already split by 80 mya ago, and the harvest spiders’ common ancestor is 48.9 mya ago, so they must have originated on Grande Terre or colonized later? Wait no, Text 1 says some biota are Gondwanan clades (predating split) that persisted by refuge. But harvest spiders’ crown age is 48.9 mya, which is after split, so their clade can't be a Gondwanan clade (predating split). Wait, maybe the option A is saying harvest spiders "must have originated on Gondwana"—but that contradicts. Wait maybe I made a mistake. Wait let's check option A: "The clade of harvest spiders must have originated on Gondwana, but the clade of cockroaches may or may not have." Wait harvest spiders’ crown age is 48.9 mya. The split was 80 mya ago. So if the clade originated on Gondwana, the crown age should be at least 80 mya (since the split was 80 mya ago, so the common ancestor would have to be before the split to be on Gondwana). But 48.9 < 80, so that would mean the harvest spiders’ clade originated after the split, so they can't have originated on Gondwana. So A's first part is wrong? Wait maybe I'm misunderstanding "crown age". Crown age is the age of the most recent common ancestor of all species in the clade. So if the clade originated on Gondwana (before split), then the common ancestor could be before the split, but the crown age is the most recent, so maybe some species diverged after. Wait, no—if the clade originated on Gondwana, then the common ancestor would be at least 80 mya (since split was 80 mya ago). But harvest spiders’ crown age is 48.9 mya, which is after the split, so that suggests their common ancestor is after the split, meaning they originated after the split (so not on Gondwana). But option A says "must have originated on Gondwana"—that seems wrong. Wait maybe I messed up the time. Wait 80 million years ago: split. Then, until 37 million years ago: periodic submergence. So the island was sometimes under water until 37 mya. Harvest spiders’ crown age: 48.9 mya. So 48.9 mya ago is between 80 mya ago (split) and 37 mya ago (end of submersions). So the common ancestor of harvest spiders lived 48.9 mya ago, when the island was still experiencing submergence. Cockroaches’ crown age: 2.7 mya, which is after 37 mya ago (so after submergences ended). Now, Text 1 says some biota are Gondwanan clades (predating split) that persisted by refuge on nearby islands during submergence. So harvest spiders’ crown age is 48.9 mya (after split, during submergence). If their clade originated on Gondwana, they would have to be a Gondwanan clade (predating split) that persisted. But their crown age is 48.9 mya, which is after the split, so maybe they are a Gondwanan clade that survived via refuge. Wait, but crown age is the most recent common ancestor. So if the clade originated on Gondwana (before split), the common ancestor could be before the split, but the crown age is the most recent, so maybe the clade has species that diverged after. Wait, this is confusing. Let's check other options: B: Both originated elsewhere and colonized. But harvest spiders’ crown age is 48.9 mya (during submergence), maybe they originated on Gondwana. So B is wrong. C: Neither originated on Gondwana. But harvest spiders might have. So C is wrong. D: Harvest spiders originated before split (Gondwana), cockroaches after split but before submergence. But harvest spiders’ crown age is 48.9 mya (after split), cockroaches 2.7 mya (after submergence). So D is wrong. Wait, maybe I made a mistake with option A. Let's re-express: - Harvest spiders’ crown age is 48.9 mya. The split was 80 mya ago. So 48.9 mya ago is after the split. But if the clade originated on Gondwana, they would have been part of Gondwanan biota (carried over at split 80 mya ago). Then, their crown age (most recent common ancestor) would be at least 80 mya (since the split was 80 mya ago, so the common ancestor would be before or at split). But 48.9 < 80, so that means the common ancestor is after the split, so the clade couldn't have originated on Gondwana. Wait, that contradicts option A. But maybe I'm wrong. Wait, maybe "crown age" is the age of the clade, i.e., when the clade started. So if the clade originated on Gondwana, the crown age would be older than 80 mya. But harvest spiders’ crown age is 48.9 mya, which is younger than 80 mya, so they originated after the split. So option A's first part is wrong. But maybe the question is different. Wait, let's read the options again: 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. Wait, Text 1 says the island split from Gondwana ~80 mya, carrying Gondwanan biota. Some biota are Gondwanan clades (predating split) that persisted via refuge. Text 2: Harvest spiders’ crown age is 48.9 mya (so after split, since 48.9 < 80? Wait no, 80 mya ago is a longer time ago than 48.9 mya ago. So 80 mya ago is earlier, 48.9 mya ago is later. So split at 80 mya ago (earlier), harvest spiders’ crown age at 48.9 mya ago (later, after split). So harvest spiders’ clade originated after the split. But option A says "must have originated on Gondwana"—that would mean before split. So that's a contradiction. Wait, maybe I have the time reversed. Wait, "80 million years ago" is a long time in the past. So the split happened 80 million years in the past. Then, 48.9 million years in the past is more recent than 80 million years in the past. So the harvest spiders’ crown age is 48.9 million years in the past (more recent than split), so their clade's most recent common ancestor is after the split. Therefore, they couldn't have originated on Gondwana (since Gondwana and Grande Terre were already split by 80 mya ago, and the common ancestor is 48.9 mya ago, so they must have originated on Grande Terre or colonized later). But option A says they "must have originated on Gondwana"—that seems wrong. But maybe the question is about the clade's origin relative to Gondwana, not the split. Wait, maybe the harvest spiders’ clade is a Gondwanan clade that survived the split and then diversified, so their crown age is after the split. So the clade originated on Gondwana (before split), and then after the split, the species on Grande Terre diversified, with a crown age of 48.9 mya. That makes sense. So the clade (the group) originated on Gondwana (before split), and then on Grande Terre, the species in the clade have a most recent common ancestor 48.9 mya ago. So option A: harvest spiders must have originated on Gondwana (because their clade is part of Gondwanan biota carried over), and cockroaches’ crown age is 2.7 mya (very recent), so they may or may not have originated on Gondwana (since their crown age is after submergences, they could have colonized later). That fits. So option A is correct. # Answer: A. The clade of harvest spiders must have originated on Gondwana, but the clade of cockroaches may or may not have.

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