Unformatted text preview: Biology in the News [see folder on BB] • •
• It has been thought previously that u3lizing biodiversity in tropical forests and other ecosystems came at a major cost to preserving that biodiversity But recent research indicates how biodiversity and resource use can successfully co‐expst A major component of success is to include local ci3zens in the management and decision making and to ensure that their rights are formalized in law In >2/3 of the developing world, programs incorpora3ng these dieas are in progress but their chances at success have been unclear A new study based on 84 sites in 6 countries in East Africa and South Asia supports the success of this strategy in biodiversity conserva3on in forests Comparing many loca3ons enabled the study to iden3fy general factors involved with success, not just factors at speciﬁc loca3ons slide show at this site – hLp://www.nsf.gov/news/newsmedia/forest/ – shows the many sustainable uses for rainforest products including in housing, clothing, agriculture, utensils, cooking (ﬁrewood), transporta3on hLp://www.nsf.gov/news/news_summ.jsp?
cntn_id=119023&WT.mc_id=USNSF_51&WT.mc_ev=click Gene$c Dri* Fig 23.7 Gene$c Dri*: Bo4leneck Eﬀect Fig 23.8 Increase in frequency of blue allele and loss of yellow allele occur by chance. Bo4leneck Eﬀect Non‐random ma$ng: Inbreeding AA 100% AA Result: excess of homozygotes Aa Some plants avoid inbreeding with ﬂower structures. • ming of maturity of 3
anthers and s3gma • orphology of anther m
and s3gma 25% Aa aa 50% 25% 100% e.g. "selﬁng" in plants aa Causes of Evolu$on • small popula$on • non‐random ma$ng • recurrent muta$on • migra$on • selec$on Adapta$on • A heritable trait that increases the ﬁtness of the individual with the trait rela3ve to others that lack the trait. – Improves “performance” in that environment • Usually thought of as response to environmental condi3ons – Although sexually selected traits are also adapta3ons ‐ to sexual selec3on Modes of Selec3on adapta3on, an example • most moths are nocturnal and need to hide from avian predators during the day • birds tend to avoid feces hLp://www.ﬂickr.com/photos/pdecell/
species.php?hodges=9301 the Beau3ful Wood Nymph Eudryas grata Sexual Selec3on • Originally proposed by Darwin • Selec3on favoring ma$ng success of an individual/genotype rela3ve to other individual/genotypes in that popula3on • Can work in the opposite direc3on of natural selec3on Classic experiment by Malte Andersson on long‐tailed widowbirds (Euplectes progne) in Africa hLp://www.hlasek.com/
2.jpg What about natural selec$on on this trait? Selec3on can also maintain gene3c varia3on • One mechanism: Any kind of selec3on that favors heterozygotes over homozygotes will help to maintain polymorphism – “heterozygote advantage” or “heterosis” – This kind of selec3on will violate Hardy‐Weinberg expecta3ons because there will be an excess of heterozygotes A real world example: sickle cell anemia • Maps to gene encoding β chain of hemoglobin • ‐over 100 alleles have been found in humans • (most of these are rare) • ‐3 common alleles in West Africa, where sickle cell anemia is common: HbβA, HbβC, HbβS • S/S = severe anemia (low red cell count) • abnormal ter3ary structure of globin, red blood cells sickle shaped under low O2 tension, hemoglobin forms long crystals • S allele carries heterozygote advantage, due to increased resistance to Plasmodium‐mediated malaria http://thesecretoftheblood.blogspot.com/ Maintenance of gene$c varia$on: Sickle cell anemia Fig 23.13 This type of mechanism is thought to be rare... Causes of evolu$on: All of these can change allele frequencies in a popula$on. 1. Muta$on & migra$on 2. Small popula$on (gene$c dri*) 3. Non‐random ma$ng (inbreeding, sexual selec$on) 4. Selec$on: Fitness and adapta$on – natural selec$on – sexual selec$on – Note: three out of four of these mechanisms are not selec$ve revisi3ng: What is ‘evolu3on?’ • Darwin (and most of organism‐level biology today) – Transforma3on of species from one form to another • Never really got to the actual “Origin” of species – Branching rela3onships of all living and ex3nct species on Earth from a common ancestor • 20th century “neo‐Darwinians” (popula3on gene3cs) – Agree with Darwin’s concepts but reduced to its essence: Evolu$on is the change of allele frequency in a popula$on over $me. • This is our “modern deﬁni$on” but Darwin’s above deﬁni$on is also valid – Origin of species ‐ s3ll one of our major ques3ons What is a species? • Most basic way to deﬁne species: – Linnaeus (Morphological species concept) – S3ll the most common species concept • There are many other species concepts – For gene3cists, we need to think about popula3ons What is a species? • Let’s ﬁrst address: what is a popula3on? What is a popula$on? • A group of interbreeding individuals living in the same area at the same 3me. • have the poten3al to interbreed • Share the same “gene pool”. Successful Reproduc$on Parents Gametes Ma$ng Geography Habitat Time Behavior Ma$ng: Behavior Fig 24.3 Galapagos Blue‐footed boobies Successful Reproduc$on Parents Gametes Ma$ng Geography Habitat Time Behavior Zygote Fer$liza$on Recogni3on Compa3bility Successful Reproduc$on Parents Gametes Ma$ng Geography Habitat Time Behavior Zygote Fer$liza$on Recogni3on Compa3bility Progeny Development Viability Fecundity barriers to successful reproduc3on • several diﬀerent types • these contribute to biological specia3on • they prevent ma3ngs from occurring or from successfully producing ﬁt oﬀspring – ul3mate causes are gene3c divergence between popula3on – a great deal of recent research into “specia3on genes” UNsuccessful Reproduc$on Parents Gametes X X Ma$ng Fer$liza$on Geography Habitat Time Behavior Pre‐ma$ng Zygote Recogni3on Compa3bility Post‐ma$ng (‘Post‐ma$ng Pre‐zygo$c’) Pre‐zygo$c Progeny X Development Viability Fecundity Post‐zygo$c examples of reproduc$ve isola$on • pre‐ma3ng pre‐zygo3c – divergence in courtship behavior, pheromones • post‐ma3ng pre‐zygo3c – inability of sperm to fer3lize eggs (e.g. divergent cell‐surface proteins) • post‐zygo3c – in oﬀspring: inviability, aberrant or slow development, adults not well‐adapted, sterility If reproduc$ve isola$on becomes permanent There is no longer • One group of interbreeding individuals • A single gene pool • A single popula$on THERE ARE TWO • Specia$on: forma$on of dis$nct biological species Biological Species Concept A group of individuals with poten$al to interbreed in nature and produce viable, fer$le oﬀspring, but which do not interbreed with other species in nature. Ernst Mayr 1942 ...
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