Bio171-F08-lec24 - Biology 171 Lecture 24: Wednesday,...

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Unformatted text preview: Biology 171 Lecture 24: Wednesday, October 29, 2008 Today’s Topic: Species & Speciation Mutation (concluded): Male Driven Mutation Species Concepts Allopatric Speciation: Sympatric Speciation Prezygotic Barriers to Gene Flow Postzygotic Barriers to Gene Flow Text Reading Lec 24: 2nd ed: Chapter 25 (538-553) 3rd ed: Chapter 26 (526-541) Lec 25: 2nd ed: Chapter 26 (556-561) 3rd ed: Chapter 27 (543-548) Announcements This Week in Discussion: Sexual Selection Recognition of species in natural populations can be surprisingly difficult. In essence, it hinges on the intertwined attributes of common descent, reproductive continuity and possession of diagnostic characters . Two fundamental processes generate biological diversity. Anagenesis is the accumulation of heritable changes altering the characteristics of species. Cladogenesis (=speciation) is the process by which new species form. There are numerous definitions/concepts of what constitutes a biological species. This is one of the classic bones of contention in biology and is open to endless argument. We will entertain a few. Typological Species Concept Pre-Darwinian concept, in which species were viewed as distinct unchanging entities, characterized by invariable distinguishing features (usually morphological). Detail of Raphael’s “School of Athens” showing Plato (played by Leonardo da Vinci) and Aristotle. Problems with this concept include geographic variation, such as in the viceroy butterfly. Viceroys living in the range of the common monarch butterfly mimic them, while viceroys living in the range of the Florida Queen butterfly mimic them. Another problem is sexual dimorphism. Queen Monarch Viceroys Biological Species Concept (Dobzhansky and Mayr) A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature A very influential paradigm, it represents a minimal criterion for a common evolutionary trajectory: reproductive and genetic continuity. Problems include cases where: Populations are partially inter-fertile Populations are potentially inter-fertile, but are geographically isolated. Sturnella magna Populations are strictly asexual. Wish to assess relationship to ancestral (extinct) forms. Sturnella neglecta Phylogenetic Species Concept (emphasis on genealogy) A distinct grouping of organisms within which there is an exclusive pattern of ancestry and descent. Includes the most recent inferred common ancestor of the group together will all of its sampled descendants. Cladogenesis represents the formation of two distinct evolutionary lineages from a common ancestor. How does this happen? Speciation begins with the cessation of gene flow between populations Allopatric speciation of antelope squirrels (Ammospermophilus) on opposite rims of the Grand Canyon. Caribbean Paleo-Oceanography Closure of the Ishmus of Panama divided a formerly unitary marine fauna inducing allopatric speciation on a massive scale. Alpheus snapping (pistol) shrimp Transisthmian Alpheus Gene Tree (P, Pacific; C, Caribbean) Partitioned populations (P, C) now typically cannot mate successfully - they have speciated. Can be due to Pre- or Postzygotic barriers. Formation of Prezygotic Reproductive Barriers Changes In Mating Behaviors - Jumping Spider Courtship (Sexual Selection) Many behavioral repertoires are genetically determined, are not modifiable by learning and show little variation within species, important differences among species The neuronal circuits underlying this process are developmentally hard-wired. Small genetic changes in the genes controlling the neuronal circuits can produce effective reproductive blocks on relatively short evolutionary time-scales. Formation of Prezygotic Reproductive Barriers Sexual Selection in cichlid fishes has caused an explosion of sympatric speciation in the African Great Lakes Lake Victoria (East Africa) Cichlid Species Flocks Lake Victoria harbors a unique species-rich flock of more than 500 endemic cichlid fishes. They are severely threatened by introduction of exotic predators (esp. Nile perch) and by environmental changes such as increased turbidity caused by human-induced runoff. They occupy many specialist trophic niches. Insect eaters, mud biters, leaf choppers, snail crushers, shrimp eaters, baby eaters, fish eaters, scale scrapers, sponge eaters and snail shellers They differ markedly in coloration. Mate choice is determined on the basis of coloration, and strong assortative mating can quickly lead to sexual isolation of color morphs, a prelude to speciation. Experiment showing that assortative mating depends on visual markers. Remove the markers (by changing the ambient light spectrum) and mating is random. If water visibility is impeded, for instance by increased turbidity (more silt in suspension), fish can interbreed without loss of fertility, so are genetically compatible By constraining color vision, turbidity interferes with mate choice, relaxes sexual selection, and blocks the mechanism of reproductive isolation. In this way, human activities that increase turbidity destroy both the mechanism of diversification and that which maintains diversity. Formation of Prezygotic Reproductive Barriers Temporal Isolation- Periodical Cicadas Species have 13 or 17 year life cycles, spend most of their lives, as underground larvae, emerge en masse after 13 or 17 years to molt into adults, mate (very noisily) and die. http://insects.ummz.lsa.umich.edu/fauna/michigan_cicadas/Periodical/Index.html Different year classes of a particular brood emerge to mate in distinct parts of the eastern US each year The 17 year and 13 year broods can diverge genetically, even in sympatry, because of their temporally offset life cycles. 17-year Bro o d s Y ear General region I 1 961 1 978 1 995 2 012 V A, WVA I I 1962 1979 1996 2013 CT, MD, NC, NJ, NY, PA, VA III 1963 1980 1997 2014 IA, IL, MO I V 1964 1981 1998 2015 IA, KS, MO, NB, OK, TX V 1965 1982 1999 2016 MD, OH, PA, VA, WVA V I 1966 1983 2000 2017 GA, NC, SC V I I 1967 1984 2001 2018 NY V III 1968 1985 2002 2019 OH, PA, WVA I X 1952 1969 1986 2 003 N C, V A, WVA X 1953 1970 1987 2004 DE, GA, IL, IN, KY, MD, MI, NC, NJ, NY, OH, PA, TN, VA, WVA X III 1956 1973 1990 2007 IA, IL, IN, MI, WI X IV 1957 1974 1991 2008 KY, GA, IN, MA, MD, NC, NJ, NY, OH, PA, TN, VA, WVA 13-year Broods X I X 1972 1985 1998 2011 AL, AR, GA, IN, IL, KY, LA, MD, MO, MS, NC, OK, SC, TN, VA X XII 1975 1988 2001 2014 LA, MS X XIII 1976 1989 2002 2015 AR, IL, IN, KY, LA, MO, MS, TN Formation of Prezygotic Reproductive Barriers Habitat Isolation Apple maggot flies mate on fruit of native hawthorne, where their larvae bore into the fruit. When apples were introduced into North America, some flies switched to mate on apple fruit. The populations diverged in sympatry due to reproductive isolation. Rhagoletis pomonella Maggot in apple Hawthorne tree Formation of Prezygotic Reproductive Barriers Gametic Isolation Sea Urchin Gamete Recognition Proteins show high rates of evolution and may cause speciation if the sperm and egg receptors diverge so that gamete fusion is inhibited. Formation of Prezygotic Reproductive Barriers Mechanical Isolation Like many insects, fleas have very complex genitalia, especially in males. All the parts must properly fit or stimulate the female reproductive tract in order for mating to be successful. Many insect species can only be recognized morphologically based on differences in their genitalia. Postzygotic Reproductive Barriers Hybrid Infertility Postzygotic Reproductive Barriers -Hybrid Infertility The liger is a hybrid between a male lion and a female tiger. It looks like a giant lion with diffused stripes. Like tigers (and unlike lions), ligers like swimming. Ligers are typically sterile. ...
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This note was uploaded on 01/30/2012 for the course BIO 171 taught by Professor Josephinekurdziel during the Fall '08 term at University of Michigan.

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