How do new species originate?

1. How do new species originate? How do we account for the great diversity of life in thebiosphere? www.cdnn.info/news http://bio1903.nicerweb.com www.botany.wisc.edu www.condorjourneys-adventures.com

2. We say that all dogs are in the same species, but that Norway maples and sugar maples are in different species. How do we know that? What do we mean? What we mean by species is a group of individuals with the potential to interbreed under natural conditions and produce fertile offspring. By this definition each species has its own gene pool that does not mix with the gene pools of other species. What is a species? www.thestonemill.com http://oregonstate.edu

3. As discussed earlier, this species definition does not work for species that reproduce only asexually. Moreover, it is not always feasible to determine whether mating is occurring between two groups in the same habitat. And sometimes members of two species look so much alike that we have a hard time telling them apart. We sometimes make mistakes in concluding that two groups are in different species, when in fact they do share genes through mating. The eastern and western meadowlarks (above, S. magna and S. neglecta, respectively) look similar, but their songs and other behaviors are sufficiently different that they would not interbreed, if they met in nature. Shortcomings of this definition Sturnella neglecta Sturnella magna www.sacsplash.org www.stephenbodio.com

7. As an adult, the butterfly on the left, Monarch danaus, is similar to the viceroy butterfly on the right, Limenitis archippus. But compare their appearance as larvae! And mimicry in nature can confuse biologists even more www.mongabay.com www.cirrusimage.com/ www.richard-seaman.com

8. A catastrophe (earthquake, fire, new highway, and so on) may separate one population in two smaller populations. A famous example is the two populations of Kaibab squirrels, isolated geographically from each other by the Grand Canyon (perhaps 6 to 7 million years ago). We do not know if these two populations have been isolated for enough generations that mutations would have accumulated that have made the two populations reproductively isolated from each other. North rim Kaibab squirrel*  South rim Abert squirrel **  How do gene pools of similar species remain separate from each other? * Sciurus aberti kaibabensis and **Sciurus aberti Geographical Isolation

9. An extreme example of geographical isolation --New Haven Register, January 31, 2010

10. Two other ways to ask this question are as follows: What keeps different species from breeding with each other? How to they maintain their reproductive isolation? Such barriers may occur before fertilization has a chance to occur, or after fertilization. A first step toward reproductive isolation is often habitat isolation within the same area. An example is two garter snake species in the genus Thamnophis. One species spends most of its time in water, while the other is primarily terrestrial. Habitat Isolation http://sparkleberrysprings.com www.wildherps.com

11. An example of ecological isolationby different habitats • There exist 750 wasp species (!) each of whose members lay their eggs in the flower of a different fig species. These fig species share the same habitat but bloom at different times. This keeps the different wasp species reproductively separate from each other. Note the long ovipositor on the fig wasp. Why is this adaptive? Fig wasp laying her eggs amongst the ovules of a developing fig fruit (www3.imperial.ac.uk/) Emerging new generation of fig wasps (image from www.morning-earth.org)

12. Two species may breed at different times of the day, or in different seasons, or in different years. For example, even though the territories of the western and eastern spotted skunks, Spilogale gracilis, and S. putorius, overlap, S. gracilis mates in the late summer while S. putorius reproduces in the late winter. Temporal isolation is another pre-zygotic reproductive barrier Spilogale gracilis Image from http://fwp.mt.gov/ Spirogale putorius Image from www.cedarcreek.umn.edu

13. Different courtship behaviors may isolate two species Below, four similar looking beetles with very different courtship behaviors– Posterior courtship behavior in Linsleya beetles   Mounting behavior in Meloe beetles Linear courtship behavior in subfamily Meloinae beetles   Anterior courtship behavior in Tegrodera beetles Images from www.ipmworld.umn.edu

14. Sexual selection by coloration can act as a reproductive barrier • Biologists at the University of Leiden in the Netherlands raised two cichlid species (Pundamilia pundamilia and P. nyererei) together in two different aquaria. One included natural light and the other monochromatic orange light. • Under natural light the two species looked very different from each other, but under orange light they were indistinguishable from each other. Campbell’s Biology, 7th ed.

15. RESULTS: With natural light, in which the two species looked different from each other, the females mated only with males of their species. However, under orange lighting the females mated with males of either species indiscriminately and produced fertile offspring. INTERPRETATION AND CONCLUSION: The species are very similar to each other, differing only in their coloration. This color difference acts as a prezygotic reproductive barrier. The two species very likely separated from each other only recently in their evolutionary past. Cichlid experiment, concluded P. pundamilia Cichlid images from www.fishecology.ch P. nyererei

16. Mechanical isolation may keep two species reproductively separate • In such a situation, even if mating is attempted, structural differences in their reproductive organs prevent copulation. Both shells must coil in the same direction A boa’s hemipene www.proexotics.com Four-headed penis of the spiny ant- eater And be sure to check out the amazing video of the four-headed penis of the spiny anteater  athttp://scienceblogs.com/neurophilosophy/ 2007/10/experimenting_with_a_fourheaded_penis.php (scroll halfway down)

17. Coiling direction matters to a snail! • Shells of three closely related snail species (image a) • Two snails whose coiling directions are the same are able to mate (image b) • The genitalia of two snails with opposite coiling direction do not match up (see image c).

18. Sperm of one species might not be able to survive in the reproductive tract of another species. Or biochemical differences might prevent the sperm of one species from getting through the protective barrier of another species’ ova (in both plants and animals). Thus, even though members of two such species copulated, fertilization would not occur. For example, sea urchins of more than one species might reproduce in the same place at the same time, but the sperm of species A might be incompatible with the ova of species B and vice versa. Gametic isolation www.dailygalaxy.com

19. For example, if cross fertilization does occur, the resulting hybrid offspring may not complete embryonic development or may be frail. We describe this situation as hybrid inviability or reduced hybrid vigor. This is true of some of the salamander subspecies of the genus Ensatina in California. Postzygotic barriers may exist between two “subspecies” http://evolution.berkeley.edu/

20. Even if hybrids between two species or subspecies (two emerging species) are survive and are healthy, they might not be fertile. Chromosome incompatibilities might prevent pairing at Prophase I of meiosis and thus limit gamete production. This keeps the two gene pools effectively separate from each other. The well known example of reduced hybrid fertility is the mostly sterile mule (see image b, below), produced by a mating between a male donkey (a) and a female horse (c)*: Another example comes from the work of a friend of mine, Sandra Anagnostakis. She crosses different chestnut species in an attempt to produce a tall, straight, blight-resistant tree with chestnut fruits. Her world-famous chestnut plantation is at the east end of the Sleeping Giant. * But see the following: www.ncbi.nlm.nih.gov/pmc/articles/PMC1289946/pdf/jrsocmed00204-0031.pdf! Reduced hybrid fertility (a) (b) (c) www.talkreason.org/ www.utc.edu

21. Photographs taken by scientist Sandra Anagnostakis, at the world-famous Chestnut Plantation (located at the east end of Sleeping Giant State Park)

22. Hybrids might have low fertility due to chromosomal incompatibilities • For example, in a hybrid between a parental stock and a stock with translocations, the chromosomes will not match up well at Prophase I of meiosis. • Only some of the resulting gametes will have full sets of genetic information. https://qspace.library.queensu.ca

23. And then there the weird triploid all-female fish species! • Iberian minnows of the all-female species known as Tropidophoxinellus alburnoides “borrow” chromosomes from a male of a closely related species, but the resulting generation throws away those male chromosomes during the process of meiosis and production of ova. • Other all-female fish species don’t even accept the chromosomes from the sperm that contact their ova; the sperm serve only to activate embryonic development of the ova. • There exist such situations in some reptiles, amphibians, and insects, as well! http://www.genetics.org/cgi/reprint/146/3/983 Poeciliopsis: http://jhered.oxfordjournals.org/cgi/content/full/96/1/32

24. Hybrid breakdown: A final reproductive isolating mechanism • Some hybrids are robust and fertile and mate either with each other or with a parent (!), but the offspring of such matings may be either weak or infertile. • That minimizes the gene flow between the two species. • For example, some rice species follow this pattern. Healthy hybrids have been produced experimentally, in attempts by farmers to increase crop yield by combining genetic traits of both parents. • However, attempts to cross two different such hybrids often fail; the two rice strains that produced these hybrids are well on their way to becoming different species.

25. Various strains of cultivated rice have been produced by artificial selection. Over time they have diverged genetically from their common ancestor and have each accumulated different recessive mutations. Crosses between such strains often bring together harmful mutant alleles, often resulting in weak or sterile hybrid offspring. Explanation for hybrid breakdown in the case of rice crosses * * * “N” means normal, and “S” means sterile. ** The Rf allele restores fertility, but the rf allele does not.

26. Some images of rice plants* http://bicol.da.gov.ph/tips/hybrid-rice.jpg www.fao.org/ag/agl/agll * What part of the rice plant do we actually eat? www.msstate.edu

27. And how about seedless fruits? What’s that all about? www.heinens.com www.plantsciences.ucdavis.edu

28. Summary of the different mechanisms for reproductive isolation of species * (or have different niches) * * The terms “prezygotic” and “postzygotic” are sometimes used instead of “premating” and “postmating”, respectively.

29. How do new species form? • In addition to distilling Darwin’s theory into a few succinct observations and inferences, Ernst Mayr has given us the two major conditions under which speciation can occur: (1) Interbreeding between the populations of two emerging species must be blocked, by their becoming isolated from each other. (2) Enough time must pass during this time of isolation for mutations to accumulate and for the two populations to become genetically distinct from each other. They must become sufficiently different from each other that if the two populations were brought together again, they would not be able to share their gene pools. • These differences might be caused by genetic drift or accumulation of different mutations (as we have discussed), or through different environmental pressures that result in natural selection within each of these now separated populations.

30. Speciation can occur with or without geographic isolation * In such a situation, however, there might exist subtle micro- habitat differences within the same space. *

31. Biologists believe that most new species arise from allopatric* speciation We will consider the following examples of allopatric speciation: • Adaptive radiation, resulting from small groups leaving a larger population and colonizing new environments • Geological and climactic changes separating members of a population • Human activities that split a population into separate subgroups * literally, “other country”

32. By this means, small subsets of a common ancestral population* leave at different times, each traveling in its own direction. Upon arrival in a suitable habitat**, each such “founder” group will become established, responding to the unique environmental conditions of its new location. “Adaptive radiation” is well known to occur in island populations * Often on the mainland ** often an island

33. The Hawaiian islands are located ~3,500 km (about 2200 miles) from the nearest continent. Very young, these islands arose volcanically; the youngest (“Big Island”) appeared only about a million years ago and still demonstrates active eruptions. The five silversword species below are all very closely related, based on molecular studies, yet look quite different from each other. Most Hawaiian species are endemic; they can be found nowhere else. The Hawaiian islands provide many such examples of rapidly evolving populations http://ops.fhwa.dot.gov/freight/ freight_analysis/state_info/hawaii Campbell’s Biology, 7th ed.

34. Global warming causes sea levels to rise, separatng contiguous land masses into several separate large masses and smaller islands. For example, North America looked very different during the Cretaceous period (~90 MYA)! (See the map on the left.) A population may be divided by a number of different geological and climactic events www.rankinstudio.com

35. Dams built by beavers or humans create ponds and lakes and separate populations • Studies of striped bass (Moronesaxatilis) were carried out by Irwin Beitch 10 years after the completion of a large dam in southeastern Virginia. • Kidney morphologies of populations above (freshwater) and below (near the Chesapeake Bay) the dam had become significantly different from each other. http://oakridgevisitor.com www.mvhs65.com www.highlandlakesflyfishing.com

36. Land masses that were connected during the Triassic Period later separated, taking life forms with them. “Gondwana” http://earthscience.files.wordpress.com www.palaeos.com/ Check out the very cool animation at http://www.divediscover.whoi.edu/images/gondwana2.gif!

37. Ratite birds– an example of early evolution after Gondwana broke apart The above map shows the distribution of living and recently extinct* ratite birds. Key: C = Cassowary; E = Emu; e = Elephant Bird*; K = Kiwi; m = Moa*; O = Ostrich; R = Rhea (see www.grisda.org) Cassowary (www.unfamiliar-image.co.uk ) Rhea www.uwm.edu/ www.animals.national geographic.com Emu Kiwi

38. Highways and housing developments split populations and cause habitat destruction • In what way can such fragmentation lead to the evolution of new species? • What happens to species members on the edge of the habitat? • Could fragmentation cause species extinction? • Example: Howler and spider monkeys in fragmented landscapes in southern Mexico (www.primatesmx.com). Contiguous, undisturbed forest Fragmented forest

39. Hybridization between closely related species can lead to extinction EXAMPLE:Unhybridized (“pure”) Hawaiian ducks (Anas wyvilliana) are rare today and exist only on the island of Kauai. On the other Hawaiian islands, where mallards have been introduced by hunters and have interbred with the Hawaiian duck, the hybrids are sterile and are replacing pure-bred Hawaiian ducks. Hawaiian duck (Anas wyvilliana ) www.en.wikipedia.org Female mallard duck (Anas platyrhynchos) www.upload.wikimedia.org And their facilitators (www.guidedventures.com )

40. One of many examples of how microhabitat differences might provide environmental pressures for genetically different members of a species to specialize in different ways: palm trees in a habitat that contains both volcanic soil (high in ash) and calcareous soil (of coral reef origin) Ecological isolation within the same space ( sympatric speciation)

41. Another example of microhabitat differences leading to sympatric speciation • The maggot fly Rhagoletis pomonella has a stable parasitic relationship with the American hawthorn tree, in which the fly lays its eggs. • In the seventeenth century apple trees were introduced to North America by the early colonists. • Over the years scientists began to observe the fly infecting apple trees, as well as hawthorns. • The two fruit fly populations tend not to intermingle, even if in the same habitat, and thus are unlikely to interbreed. When offspring become adults, they tend to lay their eggs in the same kind of fruit from which they had hatched (perhaps based on a type of olfactory imprinting). • Over time these two populations have become genetically different from each other and may be on their way to becoming separate species. ♂ ♀ Apple maggot flies (www.sciencecases.org/maggot_fly) 

42. Occasional meiotic errors may lead to polyploidy– a common source of sympatric speciation • Sometimes DNA replication occurs normally (during the S) phase in (especially in plants), but problems arise during meiosis. • If chromosomes failed to separate from their homologs, then diploid (2n) reproductive cells could result. • Self fertilization of such diploid gametes would then produce tetraploid (4n) offspring. • This occurs surprisingly often in plants; it is estimated that 25 to 50% of all plant species evolved through polyploidy. www.departments.oxy.edu

43. Sympatric speciation by the appearance of polyploidy http://trc.ucdavis.edu/biosci10v/bis10v/media/ch13/wheat_speciation.html

44. Polyploidy can occur during mitotic cell division

45. Create a polyploid plant in your dorm room! The colchicine that was applied to a bud in the above example (http://waynesword.palomar.edu) interferes with mitotic spindle formation. Why (how) would that cause tetraploid cells to form from mitotic cell division of diploid cells?

46. Other common examples of polyploid plant species * Triploid crops: banana, apple, ginger * Tetraploid crops: durum wheat, macaroni wheat, maize, cotton, potato, cabbage, leek, tobacco, peanut * Hexaploid crops: chrysanthemum, bread wheat, oat * Octaploid crops: strawberry, dahlia, pansies, sugar cane CHALLENGE: Why are polyploids with odd numbers of sets of chromosomes (e.g., triploid species) sterile? And bananas are sterile, so how do we get new banana plants? http://ask.metafilter.com

47. Why triploid species are sterile

48. New species evolve, but other species become extinct– Why? Study the vertical axes to see why these two graphs are so different from each other: www.dailygalaxy.com www.austinchronicle.com

49. The future is yours; you have the ability (and the challenge) to bring about change. Note logarithmic scale www.greenfacts.org

50. If humans can cause species extinctions, do we also have the ability to take actions to prevent such permanent losses of biodiversity? Think about what steps you can take to help preserve Gaia. Can you list and explain at least six human activities that accelerate species extinction rates?