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a. How do gaps in the fossil record make it difficult to evaluate the three different models of evolution?

b. The rate of evolution is often calibrated by the age of fossil members of taxa of living species (see Chapter 2 – Molecular Clocks, p. 42). How does an imperfect fossil record affect estimates of evolutionary rates?

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Jean Keeling
Jean KeelingLv2
28 Sep 2019

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Related questions

I'm having trouble simplifying this 6 question paper. Pleaserewrite this then post in comments. thanks! just 1-5 senstences perquestion please. please!

1.Among systems for study of macro evolutionary change (e.g.,major change in anatomy, moving from water to land or vice versa,acquisition of flight, etc.), the cetaceans have become the 'posterchild'. Explain why cetaceans are a better system in which to studyevolutionary transitions than each of the following vertebrategroups:

Cetaceans have primitive taxa thatrecords sequences of change at three critical phases:

-Initial aquatic specialization

-Evolution of filter feeding withbaleen

-Derivation of echolaction.

Divergence times in cetaceans areconducive to detection of positive selection and inactive loci.Evolutionary splits in cetacea are deep enough to provide adequatechange for statistically robust analyses of molecular evolution butare not so deep that substitution patterns are saturated andrecognition of pseudogenes is hindered.

They have an impressive fossilrecord.

Whole genomes for both cetaceans andterrestrial cetartiodactyles can illuminate transitions andcandidate loci associated with aquatic features and degenerativeevolution have been characterized by several research groups.

turtles: highly derived taxa but areancient clades and more difficult to study from a molecularperspective.

manatees: The extant diversity ofaquatic manatees is limited.

bats: have a poor fossil record.

pterosaurs (ancient winged reptiles):Lack genetic Data.

2. What is myoglobin?

A myoglobin is a small 153-amino acidprotein that is the primary carrier and storage center of oxygen inmuscle.

Explain why increased diving ability should be correlated withspecific types of replacement mutations of the gene encoding theprotein myoglobin.

Amino acid replacement that increasedcharge occurred overwhelmingly in lineages of extreme divers withsemiaquatic or aquatic lifestyles. The greatest increase in chargeoccurred independently in cetaceans, pinnipeds, and the bever, allof which share at least two convergent amino acid replacementswithin each lineage.

What specific kinds of amino acid replacements are favored bypositive selection when increased diving ability is favored?

High net surface charge enableselectrostatic repulsion that might reduce deleterious selfassociation of myoglobin molecules; protein folding stability couldhave a similar impact by limiting the percentage of misfoldedmolecules at high expression levels.

Explain how the maximum dive capability of an extinct whalespecies can be estimated.

By combining body mass with inferredconcentration of myoglobin based on net surface charge they wereable to estimate the maximum dive times of extinct cetaceans.

3. What is the general function of the protein prestin?

Is involved in conferringelectromotility to the outer hair cells of the cochlea, enablingsensitive to sound by driving the cochlear amplifier.

Explain why a phylogenetic treereconstructed using the characters of prestin amino acid sequencesshowed at first that the whales form a subgroup within thebats!

A phylogenetic analysis of prestinamino acid sequences supported a tree in which some odontocetecetaceans were nested within bats with high support, despitephylogenetic analsysts of nucleotides sequences favoring a moredistant relations.

This pattern was driven by convergentamino acid changes in that were shared between toothed whales andecholocating bats.

4. Relative to terrestrial mammals, what changes occurred togive deep diving cetaceans 'rod monochromacy'?

Rod monochromancy is unique amongmammals due to extreme adaptation to low light levels.

What is the advantage of rod monochromacy?

Allows you to see in low lightlevels.

Why does it make sense that rhodopsins of cetaceans are shiftedfrom red (low energy) to blue (high energy) sensitivity?

The mechanisms underlying the spectraltuning of two of these blue-shifted pigments have recently beenelucidated and depend on three amino acid substitutions(83Asn, 292Ser, and 299Ser) indolphin rhodopsin, but only one amino acid substitution(308Ser) in the dolphin long-wavelength-sensitivepigment. The objective of this study was to investigate themolecular basis for changes in the spectral sensitivity of rodvisual pigments from seven distantly related marine mammals. Theresults show a relationship between blue-shifted rhodopsins([lambda]max [less-than-or-equal] 490 nm), deep-divingforaging behavior, and the substitutions 83Asn and292Ser. Species that forage primarily near the surfacein coastal habitats have a rhodopsin with a [lambda]maxsimilar to that of terrestrial mammals (500 nm) and possess thesubstitutions 83Asp and 292Ala, identical torhodopsins from terrestrial mammals.

5. What is the function of the protein ameloblastin?

Is an enamel matrix protein. Theprotein that encodes AMBN gene. Allows growth activity andstructure of the tooth enamel.

Characterize the specific nucleotide sequence and functionaldifferences in ameloblastin genes between baleen whales versusother mammals.

Baleen whale a toothed whale and moredistantly related mammals with single base pair frameshiftinsertion in the baleen whale AMBN pseudogene. Clear cut molecularsignature of a shared signature of shared aquatic ancestry forhippos and whales is currently lacking. Loci related to underwatercision, deep diving and lung surfactant do not show evidence ofmolecular adapation in the common ancestor of these taxa.

6. What are the two main general categories of convergentevolution described in cetaceans and other vertebrates?

Auditory genes. Bats and odontecetshave many similar capabilities with regards to high frequency soundperception.

Selection has driven the independentloss of both OPNI1SQ and OPN1LW in deep diving cetaceans tooptimize visual acuity at depth and at night.

Loss of functional TAS1R genes alsooccurred independently in Otariidae (sea lions) and many carnivorsmammals convergently lack the fuctional sugar taste perception geneTAS1R2

Based on these studies why is it important to use neutral ornearly neutral characters in phylogenetic analyses wheneverpossible?

Comparison amobg a broader taxonomicsample of geneoms can reveal learge suits of genes that haveundergone convergent recruitment and subsittuions among multipleclades of aquatic tetrapods.

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