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Unformatted text preview: Biology in the News [see folder on BB] •
• • • • female birds, like female humans, have a biological clock; fer=lity declines with age previously it was thought that contribu=ons from their mates were unimportant to this decline in fer=lity a new study of a long term data set (1979‐2007) of blue =ts (Cyanistes caeruleus) from the French island of Corsica in the Mediterranean has revealed that male quality has a signiﬁcant eﬀect on female fer=lity as females age the data involved a popula=on of banded and monitored birds in which the parenthood of all families could be tracked and fer=lity 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 fer=lity in their mates (blue =ts are not monogamous) – • these males may be in best condi=on (physically ﬁt & low parasite load) males provide nest materials and food and help take care of eggs and oﬀspring hQp://www.nsf.gov/news/news_summ.jsp?
mc_ev=click hQp://en.wikipedia.org/wiki/Blue_=t 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 deﬁni=ons of species and this cannot be prac=cally tested in many (most?) species what about species with asexual reproduc4on? • all of the previous theory on biological specia=on pertains only to sexually reproducing organisms • what about bacteria and other organisms without separate sexes/sexual reproduc=on? 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; ac=ng to keep “species” together morphological species concept is oben s=ll used there are two main modes of specia=on • “allopatric” – “diﬀerent” + “country” – thought to be most common (by far) • “sympatric” – “same” + “country” – demonstrated cases are rare but is common in some groups showing specia=on by polyploidy (plants) Modes of Specia4on • Allopatric specia4on – geographical isola4on • Sympatric specia4on Allopatric specia4on hQp://www.sbs.utexas.edu/levin/bio213/evolu=on/specia=on.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/popula=on range Range becomes split by a river; NO movement between 2 popula=ons A million years go by; the river dries up; two popula=ons come back into contact. X Modes of Specia4on • Allopatric specia4on – geographical isola4on – Reproduc4ve isola4on as a “by product” • Sympatric specia4on – No geographic isola=on – Two types of examples – Polyploidy in plants • “instant specia=on” – Ecological • Divergent natural selec=on in same geographic region Modes of Specia4on • Allopatric specia4on – geographical isola4on – Reproduc4ve isola4on as a “by product” • Sympatric specia4on – No geographic isola=on – Two types of examples – Polyploidy in plants • “instant specia=on” – Ecological • Divergent natural selec=on in same geographic region Sympatric specia4on: polyploidy forma=on of a tetraploid species from a diploid species: “autopolyploidy” common in some plants (e.g. wheat) Sympatric specia4on: polyploidy Sympatric specia=on – Divergent selec=on in adjacent “microhabitats” (e.g. diﬀerent plant hosts) • e.g. the apple maggot ﬂy Rhagole2s pomonella • Na=ve host in N. America: hawthorne • Apples introduced in N. America in 1600s. • In the last ~300 years, a dis=nct “host‐race” u=lizing 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 prezygo=c reproduc=ve isola=on oben evolves • = “Reinforcement” • back to our frog example A million years go by; the river dries up; two popula=ons come back into contact. • it is disadvantageous for the species to hybridize – wastes eﬀort and gametes • those individuals that evolve behavioral and other species recogni=on traits will be selec=vely favored • eventually the species would be expected to evolve complete ‘behavioral isola=on’ Hybrid zones fire-bellied toad Where par=ally reproduc=vely 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 specia=on are associated with: – High numbers of species to start with (posi=ve feedback process) – Sexual selec=on – Dietary speciﬁcity C. Mitter et al. study of hemiterans ...
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- Spring '08