The geographical pattern of speciation and floral diversification in the neotropics: The tribe Sinningieae (Gesneriaceae) as a case study

Evolution

Volumn 61, Issue 7, 2007, Pages 1641-1660

  Perret, Mathieu ^a   Chautems, Alain ^a   Spichiger, Rodolphe ^a   Barraclough, Timothy G ^b   Savolainen, Vincent ^c  

^a Conservatoire and Jardin Botaniques ^*  (Switzerland)

^b IMPERIAL COLLEGE LONDON   (United Kingdom)

^c JODRELL LABORATORY   (United Kingdom)

Author keywords

Allopatric speciation; Brazilian Atlantic forest; Floral diversification; Phylogenies; Sinningia; Sympatric speciation

Indexed keywords

ALLOPATRY; CLADISTICS; DIVERGENCE; GEOGRAPHICAL DISTRIBUTION; HERB; MORPHOLOGY; NEOTROPICAL REGION; PHENOLOGY; PHYLOGENY; SPECIATION (BIOLOGY); SYMPATRY;

ANGIOSPERM; ARTICLE; CLASSIFICATION; FLOWER; GENETICS; GEOGRAPHY; MULTIVARIATE ANALYSIS; PHYLOGENY; SPECIES DIFFERENCE;

ANGIOSPERMS; FLOWERS; GEOGRAPHY; MULTIVARIATE ANALYSIS; PHYLOGENY; SPECIES SPECIFICITY;

GESNERIACEAE; SINNINGIA;

EID: 34347334454     PISSN: 00143820     EISSN: 15585646     Source Type: Journal    
DOI: 10.1111/j.1558-5646.2007.00136.x     Document Type: Article

References (120)

1. Araujo, A. O, A. Chautems, and V. C. Souza. 2005. Gesneriaceae da Cadeia do Espinhaço em Minas Gerais, Brasil. Rev. Bras. Bot. 28 : 109 135.
2. Armbruster, W. S. 1986. Reproductive interactions between sympatric Dalechampia species: are natural assemblages "random" or organized Ecology 67 : 522 533.
3. Armbruster, W. S., M. E. Edwards, and E. M. Debevec. 1994. Floral character displacement generates assemblage structure of western Australian triggerplants (Stylidium). Ecology 75 : 315 329.
4. Arnold, M. L. 1997. Natural hybridization and evolution. Oxford Univ. Press, Oxford, UK.
5. Baldwin, B. G. 1997. Adaptive radiation of the Hawaiian silversword alliance: congruence and conflict of phylogenetic evidence from molecular and non-molecular investigation. Pp. 103 128 in T. J. Givnish and K. J. Sytsma, eds. Molecular evolution and adaptive radiation. Cambridge Univ. Press, Cambridge, U.K.
6. Baldwin, B. G., and M. J. Sanderson. 1998. Age and rate of diversification of the Hawaiian silversword alliance (Compositae). Proc. Natl. Acad. Sci. USA 95 : 9402 9406.
7. Barluenga, M., K. N. Stölting, W. Salzburger, M. Muschick, and A. Meyer. 2006. Sympatric speciation in Nicaraguan crater lake cichlid fish. Nature 439 : 719 723
8. Barraclough, T. D., and S. Nee. 2001. Phylogenetics and speciation. Trends Ecol. Evol. 16 : 391 399.
9. Barraclough, T. G., and A. P. Vogler. 2000. Detecting the geographical pattern of speciation from species-level phylogenies. Am. Nat. 155 : 419 434.
10. Barraclough, T. G., A. P. Vogler, and P. H. Harvey. 1998. Revealing the factors that promote speciation. Philos. Trans. R. Soc. Lond. B 353 : 241 249.
11. Barraclough, T. G, J. E. Hogan, and A. P. Vogler. 1999. Testing whether ecological factors promote cladogenesis in a group of tiger beetles (Coleoptera: Cicindelidae). Proc. R. Soc. Lond. B 266 : 1061 1067.
12. Berlocher, S. H. 1998. Can sympatric speciation via host or habitat shift be proven from phylogenetic and biogeographic evidence Pp. 99 113 in D. J. Howard and S. H. Berlocher, eds. Endless forms: species and speciation. Oxford Univ. Press, New York.
13. Borchsenius, F. 2002. Staggered flowering in four sympatric varieties of Geonoma cuneata (Palmae). Biotropica 34 : 603 606.
14. Bowers, M. A., and J. H. Brown. 1982. Body size and coexistence in desert rodents: chance or community structure Ecology 63 : 391 400.
15. Bradshaw, H. D., and D. W. Schemske. 2003. Allele substitution at a flower colour locus produces a pollinator shift in monkeyflowers. Nature 426 : 176 178.
16. Brooks, D. R., and D. A. McLennan. 1991. Phylogeny, ecology, and behavior: a research program in comparative biology. Univ. of Chicago Press Chicago.
17. Brown, J. H., and A. Koderic-Brown. 1979. Convergence, competition, and mimicry in a temperate community of hummingbird-pollinated flowers. Ecology 60 : 1022 1035.
18. Buzato, S., M. Sazima, and I. Sazima. 2000. Hummingbird-pollinated floras at three Atlantic forest sites. Biotropica 32 : 824 841.
19. Caruso, C. M. 2000. Competition for pollination influences selection on floral traits of Ipomopsis aggregata. Evolution 54 : 1546 1557.
20. Casgrain, P., and P. Legendre. 2001. The R Package for multivariate and spatial analysis, version 4.0. d4-. Department of biological sciences, Univ. of Montréal. Montréal, Canada.
21. Chautems, A. 1990. Taxonomic revision of Sinningia Nees: nomenclatural changes and new synonymies. Candollea 45 : 381 388.
22. Chautems, A. 1991. Taxonomic revision of Sinningia Nees (Gesneriaceae) II: new species from Brazil. Candollea 46 : 411 425.
23. Chautems, A. 1993. Gesneriaceae. in R. Spichiger and L. Ramella, eds. Flora del Paraguay, vol. 22. Conservatoire et Jardin botaniques, Ville de Genève, Geneva, Switzerland.
24. Chautems, A. 1995. Taxonomic revision of Sinningia Nees (Gesneriaceae) III: new species from Brazil and new combinations. Gesneriana 1 : 8 14.
25. Chautems, A. 2002. New Gesneriaceae from Minas Gerais, Brazil. Candollea 56 : 261 279.
26. Chautems, A. 2003a. Gesneriaceae. Pp. 75 103 in M. G. L. Wanderley, G. J. Shepherd, A. M. Giuletti, and T. S. Melhem, eds. Flora Fanerogâmica do Estado de São Paulo, vol. 3, FAPESP, RiMa Editora, São Paulo, Brazil.
27. Chautems, A. 2003b. Gesneriaceae. Pp. 185 197 in T. B. Cavalcanti, and A. E. Ramos, eds. Flora do Distrito Federal, vol. 3, Embrapa Recursos Genéticos e Biotecnologia, Brasília, Brazil.
28. Chautems, A., and A. Weber. 1999. Shoot and inflorescence architecture in the neotropical genus Sinningia (Gesneriaceae). Pp. 305 322 in M. H. Kurmann, and A. R. Hemsley, eds. The evolution of plant architecture. Royal Botanic Gardens, Kew, U.K.
29. Chautems, A, G. S. Baracho, and J. A. Siqueira Filho. 2000. A new species of Sinningia (Gesneriaceae) from northeastern Brazil. Brittonia 52 : 49 53.
30. Chesser, R. T., and R. M. Zink. 1994. Modes of speciation in birds: a test of Lynch's method. Evolution 48 : 490 497.
31. Clayberg, C. D. 1967. Chromosome numbers in Sinningia and Rechsteineria (Gesneriaceae). Baileya 15 : 33 35.
32. Clayberg, C. D. 1968a. Sinningia richii, a new species (Gesneriaceae). Baileya 16 : 5 8.
33. Clayberg, C. D. 1968b. Biosystematic studies in Sinningia and Rechsteineria (Gesneriaceae). Am. J. Bot. 55 : 829 833.
34. Clayberg, C. D. 1970. Cytology of interspecific hybrids in Sinningia and Rechsteineria (Gesneriaceae). Can. J. Genet. Cytol. 12 : 759 768.
35. Clayberg, C. D. 1996. Interspecific hybridisation in Sinningia (Gesneriaceae). Baileya 23 : 184 194.
36. Feinsinger, P. 1983. Coevolution and pollination. Pp. 282 310 in D. J. Futuyuma and M. Slatkin, eds. Coevolution. Sinauer Associates, Sunderland, MA.
37. Feinsinger, P. 1987. Effect of plant species on each other's pollination: is community structure influenced. Trends Ecol. Evol. 2 : 123 126.
38. Felsenstein, J. 1985a. Confidence limits on phylogenies: an approach using the bootstrap. Evolution 39 : 783 791.
39. Felsenstein, J. 1985b. Phylogenies and the comparative method. Am. Nat. 125 : 1 15.
40. Fenster C. B., W. S. Armbruster, P. Wilson, M. R. Dudash, and J. D. Thomson. 2004. Pollination syndromes and floral specialization. Annu. Rev. Ecol. Syst. 35 : 375 403.
41. Fitzpatrick B. M., and M. Turelli. 2006. The geography of mammalian speciation: mixed signals from phylogenies and range maps. Evolution 60 : 601 615.
42. Friesen, V. L., and D. J. Anderson. 1997. Phylogeny and evolution of Sulidae (Aves: Pelecaniformes): a test of alternative modes of speciation. Mol. Phylogenet. Evol. 7 : 252 260.
43. Fulton, M., and S. A. Hodges. 1999. Floral isolation between Aquilegia formosa and Aquilegia pubescens. Proc. R. Soc. Lond. B 266 : 2247 2252.
44. Gentry, A. H. 1974. Flowering phenology and diversity in tropical Bignoniaceae. Biotropica 6 : 64 68.
45. Gentry, A. H. 1976. Bignoniaceae of southern central America: Distribution and ecological specificity. Biotropica 8 : 117 131.
46. Givnish, T. J., K. J. Sytsma, J. F. Smith, and W. J. Hahn. 1995. Molecular evolution, adaptative radiation, and geographic speciation in Cyanea (Campanulaceae, Lobelioideae). Pp. 288 337 in W. L. Wagner and V. Funk, eds. Hawaiian biogeography: evolution on a hot spot archipelago. Smithsonian Institution Press, Washington, D.C.
47. Givnish, T. J, T. M. Evans, M. L. Zjhra, T. B. Patterson, P. E. Berry, and K. J. Sytsma. 2000. Molecular evolution, adaptative radiation, and geographic diversification in the amphiatlantic family Rapateaceae: evidence from ndhF sequences and morphology. Evolution 54 : 1915 1937.
48. Goldblatt, P., and J. C. Manning. 1996. Phylogeny and speciation in Lapeirousia subgenus Laperousia (Iridaceae Ixioideae). Ann. MO Bot. Gard. 83 : 346 361.
49. Gower, J. C. 1966. Some distance properties of latent root and vector methods used in multivariate analysis. Biometrica 53 : 325 338.
50. Grant, V. 1971. Plant speciation. Columbia Univ Press, New York, NY.
51. Grant, V. 1994. Modes and origins of mechanical and ethological isolation in angiosperms. Proc. Natl. Acad. Sci. USA 91 : 3 10.
52. Hansen, T. F., W. Armbruster, and L. Antonsen. 2000. Comparative analysis of character displacement and spatial adaptation as illustrated by the evolution of Dalechampia blossoms. Am. Nat. 156 : S17 S34.
53. Hart, J. A. 1985. Peripheral isolation and the origin of diversity in Lepechinia sect. Parviflorae (Lamiaceae). Syst. Bot. 10 : 134 146.
54. Hasegawa, M., H. Kishino, and T. Yano. 1985. Dating of the human-ape splitting by a molecular clock of mitochondrial DNA. J. Mol. Evol. 21 : 160 174.
55. Heithaus, E. R. 1974. The role of plant-pollinator interactions in determining community structure. Ann. MO Bot. Gard. 61 : 675 691.
56. Helversen, O. von. 1993. Adaptation of flowers to pollination by Glossophagine bats. Pp. 41 59 in W. Barthlott, C. M. Naumann, K. Schmidt-Loske, and K. L. Schumann, eds. Animal-plant interactions in tropical environments. Zoologisches Forschungsinstitut und Museum Alexander Koenig, Bonn, Germany.
57. Holmgren, P. K., and N. H. Holmgren. 1998 onwards (continuously updated). Index Herbariorum. New York Botanical Garden, Available at http://sciweb.nybg. org/science2/IndexHerbariorum.asp.
58. Hughes, M., M. Möller, D. U. Bellstedt, T. J. Edwards, and M. de Villiers. 2005. Refugia, dispersal and divergence in a forest archipelago: a study of Streptocarpus in eastern South Africa. Mol. Ecol. 14 : 4415 4426.
59. Jiggins, C. D., R. Mallarino, K. R. Willmott, and E. Bermingham. 2006. The phylogenetic pattern of speciation and wing pattern change in neotropical Ithomia butterflies (Lepidoptera: Nymphalidae). Evolution 60 : 1454 1466.
60. Johnson, N. K., and C. Cicero. 2002. The role of ecologic diversification in sibling speciation of Empidonax flycatcher (Tyrannidae): multigene evidence from mtDNA. Mol. Ecol. 11 : 2065 2081.
61. Johanson, U., J. West, C. Lister, S. Michaels, R. Amasino, and C. Dean. 2000. Molecular analysis of FRIGIDA, a major determinant of natural variation in Arabidopsis flowering time. Science 290 : 344 347.
62. Joseph, L., G. Moritz, and A. Hugall. 1995. Molecular support for vicariance as a source of diversity in rainforest. Proc. R. Soc. Lond. B 260 : 177 182.
63. Kay, K. M., and D. W. Schemske. 2003. Pollinator assemblages and visitation rates for 11 species of Neotropical Costus (Costaceae). Biotropica 35 : 198 207.
64. Knox, E. B., and J. D. Palmer. 1995. Chloroplast DNA variation and the recent radiation of the giant senecios (Asteraceae) on the tall mountains of eastern Africa. Proc. Natl. Acad. Sci. USA 92 : 10349 10353.
65. Legendre, L., and P. Legendre. 1984. Ecologie numérique, Tome 2, La structure des données écologiques. Masson, Paris, France and Presses de l'Univ. du Québec, Canada.
66. Levin, D. A. 1983. Polyploidy and novelty in flowering plants. Am. Nat. 122 : 1 25
67. Levin, D. A. 1985. Reproductive character displacement in Phlox. Evolution 39 : 1275 1281
68. Levin, D. A. 2000. The origin, expansion, and demise of plant species. Oxford Univ. Press, New York.
69. Linder, H. P. 2005. Evolution of diversity: the Cape flora. Trends Pant Sci. 10 : 536 541.
70. Losos, J. B., and R. E. Glor. 2003. Phylogenetic comparative methods and the geography of speciation. Trends Ecol. Evol. 18 : 220 227.
71. Lynch, J. D. 1989. The gauge of speciation: on the frequencies of modes of speciation. Pp. 403 432 in D. Otte and J. A. Endler, eds. Speciation and its consequences. Sinauer, Sunderland, MA.
72. Martin, T. E. 1996. Fitness costs of resource overlap among coexisting bird species. Nature 380 : 338 340.
73. Mayr, E. 1963. Animal speciation and evolution. Harvard Univ. Press, Harvard.
74. Meirelles, S. T., V. R. Pivello, and C. A. Joly. 1999. The vegetation of granite rock outcrops in Rio de Janeiro, Brazil, and the need for its protection. Environ. Conserv. 26 : 10 20.
75. Morellato, L. P. C., D. C. Talora, A. Takahasi, C. C. Bencke, E. C. Romera, and V. B. Zipparro. 2000. Phenology of Atlantic forest trees: a comparative study. Biotropica 32 : 811 823.
76. Murray, K. G., P. Feinsinger, W. H. Busby, Y. B. Linhart, J. H. Beach, and S. Kinsman. 1987. Evaluation of character displacement among plants in two tropical pollination guilds. Ecology 68 : 1283 1293.
77. Perret, M., A. Chautems, R. Spichiger, M. Peixoto, and V. Savolainen. 2001. Nectar sugar composition in relation to pollination syndrome in Sinningieae (Gesneriaceae). Ann. Bot. 87 : 267 273.
78. Perret, M., A. Chautems, R. Spichiger, G. Kite, and V. Savolainen. 2003. Systematics and evolution of tribe Sinningieae (Gesneriaceae): evidence from phylogenetic analyses of six plastid DNA regions and nuclear ncpGS. Am. J. Bot. 90 : 445 460.
79. Perret, M., A. Chautems, and R. Spichiger. 2006. Dispersal-vicariance analyses in the tribe Sinningieae (Gesneriaceae): a clue to understanding biogeographical history of the Brazilian Atlantic forest. Ann. MO Bot. Gard. 93 : 340 358.
80. Porembski, S., G. Martinelli, R. Ohlemuller, and W. Barthlott. 1998. Diversity and ecology of saxicolous vegetation mats on inselbergs in the Brazilian Atlantic rainforest. Divers. Distrib. 4 : 107 119.
81. Rambaut, A., and M. Charleston. 2001. TreeEdit version v1.0a8 Carbon. Available on http://evolve.zoo.ox.ac.uk/software/TreeEdit/main.html.
82. Ramsey, J., H. D. Bradshaw, and D. W. Schemske. 2003. Components of reproductive isolation between the monkeyflowers Mimulus lewisii and M. cardinalis (Phrymaceae). Evolution 57 : 1520 1534.
83. Richman, A. D., and T. Price. 1992. Evolution of ecological differences in the Old World leaf warblers. Nature 355 : 817 820.
84. Rieseberg, L. H. 1997. Hybrid origins of plant species. Annu. Rev. Ecol. Syst. 28 : 359 389.
85. Safford, H. D. 1999. Brazilian Páramos I. An introduction to the physical environment and vegetation of the campos de altitude. J. Biogeography 26 : 693 712.
86. Safford, H. D., and G. Martinelli. 2000. Southeast Brazil. Pp. 339 389 in S. Porembski and W. Barthlott, eds. Inselbergs: biotic diversity of isolated rock outcrops in tropical and temperate regions. Springer, Berlin, Germany.
87. Sakai, S., M. Kato, and T. Inoue. 1999. Three pollination guilds and variation in floral characteristics of Bornean gingers (Zingiberaceae and Costaceae). Am. J. Bot. 86 : 646 658.
88. Sanderson, M. J. 1997. A nonparametric approach to estimating divergence times in the absence of rate constancy. Mol. Biol. Evol. 14 : 1218 1231.
89. Sanderson, M. J. 1998. Estimating rate and time in molecular phylogenies: beyond the molecular clock? Pp. 242 264 in D. E. Soltis, P. S. Soltis and J. J. Doyle, eds. Molecular systematics of plants. Kluwer Academic Publishers, Boston, MA.
90. SanMartin-Gajardo, I., and M. Sazima. 2004. Non-euglossine bees also function as pollinators of Sinningia species (Gesneriaceae) in southeastern Brazil. Plant Biol. 6 : 506 512.
91. SanMartin-Gajardo, I., and M. Sazima. 2005a. Chiropterophily in Sinningieae (Gesneriaceae): Sinningia brasiliensis and Paliavana prasinata are bat-pollinated, but P. sericiflora is not. Not yet Ann. Bot. 95 : 1097 1103.
92. SanMartin-Gajardo, I., and M. Sazima. 2005b. Espécies de Vanhouttea Lem. e Sinningia Nees (Gesneriaceae) polinizadas por beija-flores: interações relationadas ao hábitat da planta e ao néctar. Revista Brasil Bot. 28 : 441 450.
93. Savolainen, V., M. C. Anstett, C. Lexer, I. Hutton, J. J. Clarkson, M. V. Norup, M. P. Powell, D. Springate, N. Salamin, and W. J. Baker. 2006. Sympatric speciation in palms on an oceanic island. Nature 441 : 210 213.
94. Sazima, I., S. Buzato, and M. Sazima. 1996. An assemblage of hummingbird-pollinated flowers in a montane forest in southeastern Brazil. Botanica Acta 109 : 149 160.
95. Scarano F. R., H. M. Duarte, K. T. Ribeiro, P. J. F. P. Rodrigues, and E. M. B. Barcellos. 2001. Four sites with contrasting environmental stress in southeastern Brazil: relations of species, life form diversity, and geographic distribution to ecophysiological parameters. Bot. J. Linn. Soc. 136 : 345 364.
96. Schemske, D. W. 1981. Floral convergence and pollinator sharing in two bee-pollinated tropical herbs. Ecology 62 : 946 954.
97. Schemske, D. W., and H. D. Bradshaw. 1999. Pollination preference and the evolution of floral traits in monkeyflowers (Mimulus). Proc. Natl. Acad. Sci. USA 96 : 11910 11915.
98. Schliewen, U. K., D. Tautz, and S. Pääbo. 1994. Sympatric speciation suggested by monophyly of crater lake cichlids. Nature 368 : 629 632.
99. Schluter, D. 2001. Ecology and the origin of species. Trends Ecol. Evol. 16 : 372 380.
100. Silberbauer-Gottsberger, I., and G. Gottsberger. 1975. Ueber sphingophile Angiospermen Brasiliens. Plant Syst. Evol. 123 : 157 184.
101. Silvertown, J., C. Servaes, P. Biss, and D. Macleod. 2005. Reinforcement of reproductive isolation between adjacent populations in the Park Grass Experiment. Heredity 95 : 198 205.
102. Smith, J. F., J. C. Wolfram, K. D. Brown, C. L. Carroll, and D. S. Denton. 1997. Tribal relationships in the Gesneriaceae: evidence from DNA sequences of the chloroplast gene ndhF. Ann. MO Bot. Gard. 84 : 50 66.
103. Snow, D. W., and D. L. Teixeira. 1982. Hummingbirds and their flowers in the coastal mountains of southeastern Brazil. J. Orn. 123 : 446 450.
104. Soliva, M, and A. Widmer. 1999. Genetic and floral divergence among sympatric population of Gymnadenia conopsea SL (Orchidaceae) with different flowering phenology. Int. J. Plant Sci. 160 : 897 905.
105. Stiles, F. G. 1977. Coadapted competitors: the flowering seasons of hummingbird-pollinated plants in a tropical forest. Science 198 : 1177 1178.
106. Swofford, D. L. 1999. PAUP*. Phylogenetic Analysis Using Parsimony (*and Other Methods). Version 4. Sinauer Associates, Sunderland, MA.
107. Toursarkissian, M. 1969. Las Gesneriáceas argentinas. Darwiniana 15 : 25 64.
108. Vasconcelos, M. F, and J. A. Lombardi. 2000. Espécies vegetais visitadas por beija-flores durante o meio do verão no Parque Estadual da Pedra Azul, Espírito Santo. Melopsittacus 3 : 36 41.
109. Vasconcelos, M. F, and J. A. Lombardi. 2001. Hummingbirds and their flowers in the campos rupestre of Southern Espinhaço range, Brazil. Melopsittacus 4 : 3 30.
110. Via, S. 2001. Sympatric speciation in animals: the ugly duckling grows up. Trends Ecol. Evol. 16 : 381 390.
111. Vogel, S. 1969. Chiropterophilie in der neotropischen Flora (Neue mitteilungen II). Flora 158 : 185 222.
112. Yang, Z. 1996. Among site rate variation and its impact on phylogenetic analyses. Trends Ecol. Evol. 11 : 367 372.
113. Waser, N. M. 1983. Competition for pollination and floral character differences among sympatric plant species: a review of evidence. Pp. 277 293 in C. E. Jones and R. J. Little, eds. Handbook of experimental pollination biology. Van Nostrand Reinhold, New York, NY.
114. Wiehler, H. 1983. A synopsis of the Neotropical Gesneriaceae. Selbyana 6 : 1 219.
115. Wiehler, H. 1984. Miscellaneous new species in the Gesneriaceae. Selbyana 7 : 328 347.
116. Wiehler, H., and A. Chautems. 1995. A reduction of Lietzia to Sinningia. Gesneriana 1 : 5 7.
117. Wilson, P., M. C. Castellanos, J. N. Hogue, J. D. Thomson, and W. S. Armbruster. 2004. A multivariate search for pollination syndromes among penstemons. Oikos 104 : 345 361.
118. Wolf, P. G., D. R. Campbell, N. M. Waser, S. D. Sipes, T. R. Toler, and J. K. Archibald. 2001. Tests of pre- and postpollination barriers to hybridization between sympatric species of Ipomopsis (Polemoniaceae). Am. J. Bot. 88 : 213 219.
119. Woodgyer, E. M. 1995. Gesneriaceae. Pp. 327 328 in B. L. Stannard, ed. Flora of the Pico das Almas, Chapada Diamantina, Bahia, Brazil. Royal Botanic Gardens, Kew, U.K.
120. Zar, J. H. 1984. Biostatistical analysis. Prentice Hall, Englewood Cliffs, NJ.