Unformatted text preview: PLEASE TURN AUDIBLE ELECTRONIC DEVICES OFF NOW Biology in the News [see folder on BB] •
• • • • female birds, like female humans, have a biological clock; ferLlity declines with age previously it was thought that contribuLons from their mates were unimportant to this decline in ferLlity a new study of a long term data set (1979‐2007) of blue Lts (Cyanistes caeruleus) from the French island of Corsica in the Mediterranean has revealed that male quality has a signiﬁcant eﬀect on female ferLlity as females age the data involved a populaLon of banded and monitored birds in which the parenthood of all families could be tracked and ferLlity and longevity could be measured (this species lives on avg. 1.5‐3 years but can live up to 9 years) males that began fathering oﬀspring early (within 1st year) were associated with higher long term ferLlity in their mates (blue Lts are not monogamous) – • these males may be in best condiLon (physically ﬁt & low parasite load) males provide nest materials and food and help take care of eggs and oﬀspring h^p://www.nsf.gov/news/news_summ.jsp?
mc_ev=click h^p://en.wikipedia.org/wiki/Blue_Lt Biological Species Concept A group of individuals with poten4al to interbreed in nature and produce viable, fer4le oﬀspring, but which do not interbreed with other species in nature. Ernst Mayr 1942 Biological Species Individuals of two popula4ons: • If they can interbreed, they belong to the same species • If they cannot interbreed, they belong to diﬀerent species • Keep in mind there are other working deﬁniLons of species and this cannot be pracLcally tested in many (most?) species what about species with asexual reproduc4on? • all of the previous theory on biological speciaLon pertains only to sexually reproducing organisms • what about bacteria and other organisms without separate sexes/sexual reproducLon? in these organisms it is useful to think in terms of lineages (every cell division can be considered the start of a new lineage) gene exchange can occur between lineages; acLng to keep “species” together morphological species concept is oken sLll used there are two main modes of speciaLon • “allopatric” – “diﬀerent” + “country” – thought to be most common (by far) • “sympatric” – “same” + “country” – demonstrated cases are rare but is common in some groups showing speciaLon by polyploidy (plants) Modes of Specia4on • Allopatric specia4on – geographical isola4on • Sympatric specia4on Allopatric specia4on h^p://www.sbs.utexas.edu/levin/bio213/evoluLon/speciaLon.html Allopatric Specia4on Divergence may be due to • selec4on • gene4c driJ Reproduc4ve isola4on • Usually thought to be a “by‐
product” of divergence What do I mean by “by product”? (a hypothe4cal example) Original species/populaLon range Range becomes split by a river; NO movement between 2 populaLons A million years go by; the river dries up; two populaLons come back into contact. X Modes of Specia4on • Allopatric specia4on – geographical isola4on – Reproduc4ve isola4on as a “by product” • Sympatric specia4on – No geographic isolaLon – Two types of examples – Polyploidy in plants • “instant speciaLon” – Ecological • Divergent natural selecLon in same geographic region Modes of Specia4on • Allopatric specia4on – geographical isola4on – Reproduc4ve isola4on as a “by product” • Sympatric specia4on – No geographic isolaLon – Two types of examples – Polyploidy in plants • “instant speciaLon” – Ecological • Divergent natural selecLon in same geographic region Sympatric specia4on: polyploidy formaLon of a tetraploid species from a diploid species: “autopolyploidy ” common in some plants (e.g. wheat) Sympatric specia4on: polyploidy Sympatric speciaLon – Divergent selecLon in adjacent “microhabitats” (e.g. diﬀerent plant hosts) • e.g. the apple maggot ﬂy Rhagole2s pomonella • NaLve host in N. America: hawthorne • Apples introduced in N. America in 1600s. • In the last ~300 years, a disLnct “host‐race” uLlizing apples has evolved. Rhagole2s pomonella Adap4ve Radia4on Evolu4onary divergence of several species descended from a common ancestor into a variety of diﬀerent *adap4ve forms. *Usually with reference to diversiﬁca6on in the use of resources or habitats Adap4ve Radia4on: Darwin’s ﬁnches on the Galapagos islands Galapagos islands Common ancestor of all species was a ﬁnch from mainland South America For thought: why might adap4ve radia4ons occur? why are they oJen found on islands? When two recently diverged allopatric species come back together… • Increased prezygoLc reproducLve isolaLon oken evolves • = “Reinforcement” • back to our frog example A million years go by; the river dries up; two populaLons come back into contact. • it is disadvantageous for the species to hybridize – wastes eﬀort and gametes • those individuals that evolve behavioral and other species recogniLon traits will be selecLvely favored • eventually the species would be expected to evolve complete ‘behavioral isolaLon’ Hybrid zones fire-bellied toad Where parLally reproducLvely isolated species meet… What happens depends on the species • In this case (Bombina) – Zone present for 100s of years • No expansion • No reinforcement – Hybrids suﬀer developmental defects yellow-bellied toad Why do some lineages of organisms have many species and others very few? High rates of speciaLon are associated with: – High numbers of species to start with (posiLve feedback process) – Sexual selecLon – Dietary speciﬁcity C. Mitter et al. study of hemiterans Genes and genomes • What is a gene? – A transcripLon unit • Encodes an RNA • Most encode mRNAs that are translated by ribosomes into proteins • Others encode funcLonal RNAs – Ribosomal RNA – RNA enzymes – Small regulatory RNAs (e.g. micro‐RNAs) Gene anatomy TranscripLon start 5’ EYE WING LEG exon BRAIN intron 3’ exon transcripLon pre‐mature messenger RNA (mRNA) splicing ATG TranslaLon start REGULATORY REGIONS MutaLons in ENHANCERS can aﬀect speciﬁc Lssues and not others. CODING REGION MutaLons in coding region usually aﬀect all Lssues in which protein is expressed. mature mRNA MutaLon in a coding region “normal” gene (…ACTGGT…) messenger RNA mRNA (…ACUGGU…) protein (…Thr Gly…) funcLon/phenotype “mutant” gene (…GCTGGT…) messenger RNA mRNA (…GCUGGU…) altered protein (…Ala Gly…) “NON‐synonymous subsLtuLon” altered funcLon/phenotype Some mutaLons alter the amino acid sequence, others do not The geneLc code is degenerate; mulLple codon sequences can encode the same amino acid. “synonymous subsLtuLon” [aka mutaLon at a “silent site”] “normal” gene (…ACTGGT…) messenger RNA mRNA (…ACUGGU…) protein (…Thr Gly…) funcLon/phenotype “mutant” gene (…ACCGGT…) messenger RNA mRNA (…ACCGGU…) same protein (…Thr Gly…) same funcLon/phenotype What is a genome? • The set of all genes plus all noncoding DNA • Noncoding DNA – Introns (in eukaryotes) – Sequences between genes – RepeLLve DNA • Some noncoding DNA may be “junk” but many funcLons of noncoding DNA are becoming known – e.g. Enhancers (see above) funcLon in regulaLon of gene expression Return to homology • Traits that two species share due to inheritance from a common ancestor • Homology of DNA and protein sequences is determined by aligning the sequences of diﬀerent species Various events can contribute to divergence of two species from their common ancestor SubsLtuLons do not all occur at equal frequencies ‐various mathemaLcal models are used to reconstruct evoluLonary history of DNA sequences A protein alignment (cytochrome C) Molecular evolu4on in nature is inferred from sequences • But we can witness it in the lab • Aker the experiment, bacterial strains can be completely sequenced • Morphologies evolved mulLple Lmes • Diﬀerent nucleoLde subsLtuLons led to same morphologies • These mutaLons also occurred in the shaken cultures but did not persist Synonymous vs. nonsynonymous subsLtuLons • Syn >> Nonsyn • A pseudogene is a nonfuncLonal copy of a funcLonal gene – Neutral: Neither advantageous nor disadvantageous variaLon at the protein and DNA sequence level • in the 1960s‐1980s it became apparent that molecular variaLon within populaLons and species was very, very common • The idea that natural selecLon might have li^le or no eﬀect on this variaLon came from the above observaLon – this variaLon could mostly be “adapLvely neutral” • many amino acid subsLtuLons might be funcLonally equivalent – don’t change the charge or shape of a protein domain • very many DNA nucleoLde subsLtuLons might be selecLvely neutral – noncoding regions – synonymous subsLtuLons in coding regions EvoluLon of neutral mutaLons • Motoo Kimura in 1968 proposed that most molecular variaLon in natural populaLons is neutral: Neutral Theory of Molecular Evolu4on • SelecLon has no eﬀect on this variaLon; evoluLon is by gene4c driJ ‐ Recall “bo^lenecks” and other examples from previous lecture • MutaLon rate: µ • In diploids: # gene copies =2N (N= populaLon size) • Average number of new mutaLons each generaLon: =µ•2N • Probably that each new neutral mutaLon will increase to 100% = its frequency =1/2N • Overall frequency of new mutaLons increasing to 100% =µ•2N * 1/2N = µ , the mutaLon rate (populaLon size doesn’t ma^er) • Larger populaLons have more mutaLons than smaller populaLons • Smaller populaLons have fewer mutaLons but each one is more likely to go to 100% than in a larger populaLon • Constancy of neutral mutaLons going to 100% (ﬁxaLon) leads to the idea of a molecular clock – Can use molecular data to esLmate the Lme two species have been diverging SelecLon at the molecular level • Recall two types of selecLon from previous lecture – PosiLve (direcLonal) and stabilizing • Neutral evoluLon – Rate of synonymous subsLtuLon approx. = rate of nonsynonymous subsLtuLon • Stabilizing selecLon (selecLon for no change) – Rate of synonymous subsLtuLon > rate of nonsynonymous subsLtuLon • PosiLve (direcLonal) selecLon (selecLon promotes change in amino acid sequence) – Rate of synonymous subsLtuLon << rate of nonsynonymous subsLtuLon EvoluLon of foregut fermentaLon • Posterior esophagous or stomach modiﬁed to hold bacteria, which digest plant ma^er (cellulose) via fermentaLon • Evolved independently in primates (langurs) and ruminants (ca^le) • Also evolved independently in one lineage of birds (hoatzin) Molecular evoluLon of lysozyme in foregut fermenters •
• Most animals, defensive enzyme (digests bacterial cell walls) In foregut fermenters, modiﬁcaLons of lysozyme have evolved – Enables some foregut bacteria to release nutrients, which are absorbed as food • 5 amino acid changes have evolved independently in both langurs and ca^le • Some of these have also evolved in hoatzins ...
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- Fall '08
- RNA, Messenger RNA mRNA, Fire-bellied toad, European Fire-bellied Toad, Bombinatoridae, Sympatric specia4on