Chapter 12 Eve’s Testicle There are no distinct rules for gender and sex in nature Presented by Yvonne Cabrera, Angela Sabra, and Adriana Sanchez Biology 203, Spring 2005

I.Introduction Different sexes, physical sexual characteristics, and behaviors have been selected for over time due to their adaptive advantages.

II. Definition of Sex 1.Specify which gametes can fuse with others a) Isogamy: Gametes have identical morphology b) Anisogamy: Gametes have different morphology. c) Oogamy: A subset of anisogamy. Production of eggs and sperm by internal and external fertilization (Dusenbery, 2000). Isogamy, Anisogamy, and Oogamy

III. Evolution of Isogamy to Anisogamy??? 1. Theories for gamete dimorphism: a) Mitochondrial inheritance conflict between gametes (Judson, 2002). b) Small motile gametes facilitate finding gametes to fuse with (Dusenbery, 2000). c) Large egg increases survival rate for zygote (Dusenbery, 2002). d) Large pheromone-producing eggs are easier to find (Dunsenbery, 2000). e) Isogamy evolved in Prokaryotes and anisogamy evolved in Eukaryotes, related to the organism’s investment in gamete production (Knowlton, 1974).

IV. Evolvement from Zero Sexes to Multiple Sexes??? 1. The absence of sexes allow for inbreeding and hence lead to decreased genetic variation, which is less selected for (Judson, 2002). 2. Multiple sexes facilitate finding a suitable mate, decreasing the possibility of inbreeding (Judson, 2002). 3. Developing a new sex is beneficial because it can mate with a greater proportion of the population, until equilibrium is reached (Judson, 2002).

V. What Determines Sex: Male, female, hermaphrodite, and others 1. Genetics, biotic, and abiotic factors determine sex (Barash & Lipton, 1997). a) Population density and social milieu (Judson, 2002). b) Natural selection: A certain sex may have more to offer and hence will be selected for (Campbell & Reece, 2002). c) Sexual selection: mate can discriminate against morphology of other mate’s gamete, selecting for preferred traits (Judson, 2002). Green Spoon Worm Chlamydomonas moewusii

V. Continued… d) Chromosome combinations: In mammals, XY= male and XX= female. In mammals, XY= male and XX= female. In birds, ZZ=male and ZW= female. In birds, ZZ=male and ZW= female. In lizards, ZW= female and XY=male In lizards, ZW= female and XY=male Birds Lions (mammals) Lizards

V. Continued… e) Gene combinations:  In slime molds, three genes determine sex and there are variations of each. matA, matB, matC. matA, matB, matC. Physarum polycephalum (Slime mold)

V. Continued... f) Environment  Temperature In alligators, eggs laid in cool sand = female and warm sand = male In alligators, eggs laid in cool sand = female and warm sand = male In snapping turtles, eggs laid in sand 20 or 40C = female, anything otherwise = male. In snapping turtles, eggs laid in sand 20 or 40C = female, anything otherwise = male. Hatching Alligator Hatching Turtle

V. Continued… g) Fate of gametes In some insects, unfertilized eggs = males. In some insects, unfertilized eggs = males. h) Pathogenicity In the tropical insect,, eggs infected with fungus = female and uninfected = male. In the tropical insect, Stictococcus sjoestedti, eggs infected with fungus = female and uninfected = male.

VI. Why Hermaphrodites, Females and Males, or Combinations? 1. Hermaphrodites have more to offer in small population densities (Judson, 2002). 2. Large egg and small sperm lead to female and male sexes.This difference in gamete morphology is beneficial (Judson, 2002). 3. Combinations allow for sharing the above benefits (Judson, 2002).

VII. Misconceptions Related to Gender Roles and Sexes 1) Male is responsible for the upbringing of offspring. 2) Female Hyaena evolved male characteristics. 3) Female houses the male for egg fertilization. 4) Female dominance over male. Male Bat Dyacopterus spadiceus Crocuta crocuta Spotted Hyaena Green Spoon Worm

VIII. Conclusion: There are no rules in nature. In summary, gender roles and sexes are not fixed. (Tarzan Comic)

Works Cited Barash, D. & Lipton, J. (1997). Making sense of sex, how genes and gender influence our relationships. Washington DC: Island Press. Campbell, N. & Reese, J. (2002). Descent with modification: A Darwinian view of life. In B. Wilbur (Ed.), Biology (pp ). San Francisco: Benjamin Cummings. Dusenbery, D. (2000). Selection for high gamete encounter rates explains the success of male and female mating types. Journal of Theoretical Biology, 202, Dusenbery, D. (2002). Ecological models explaining the success of distinctive sperm and eggs (oogamy). Journal of Theoretical Biology, 219, 1-7. Judson, O. (2002). Dr. Tatiana’s sex advice to all creation. New York: Metropolitan Books. Knowlton, N. (1974). A note of evolution of gamete dimorphism. Journal of Theoretical Biology, 46,

Works Cited for Illustrations Birds. Available from Chlamydomonas moewusii. Available from Crocuta crocuta (Spotted Hyaena). Available from Dyacopterus spadiceus (Male Bat). Available from Isogamy, Anisogamy, Oogamy. Available from Green Spoon Worm. Available from Hatching Alligator. Available from Hatching Turtle. Available from Lions (mammals). Available from Lizards. Available from Physarum polycephalum (Slime mold). Available from cephalum_TJV.gif cephalum_TJV.gif cephalum_TJV.gif Tarzan Comic. Available from Tarzan Comic. Available from