6 Reproduction, Dispersal, and Migration

1. 6 Reproduction, Dispersal, and Migration Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S. Levinton

2. Sex and Reproduction • IS SEX NECESSARY? • WE MUST SEPARATE SEX AND REPRODUCTION? • SPECIES CAN REPRODUCE WITHOUT SEX (CLONAL GROWTH INVOLVING FISSION OR BUDDING OF INDIVIDUALS)

3. Sex and Reproduction • Nonsexual reproduction: Descendants are genetically identical - clone Colonial - individuals are genetically identical, comprise a module; each module may have arisen from a sexually formed zygote clone module

4. Modular organisms

5. Cost of Sex • FEMALE gives up half her possible genes in progeny - why not just transmit all of her genes instead of having male genes as “parasites” • Sex involves expenditure of energy and time to find mates, combat among males

6. Benefits of Sex? Genetic diversity - sex increases combinations of genes, confers resistance to disease • Alternative to sex: clones, must wait for mutations to occur • Sex: recombination produces variable gene combinations, meiosis enhances crossing over of chromosomes: new gene combinations and intragenic variants

7. Sexual Selection vs. Natural Selection • Selection for extreme forms that breed more successfully - major claw of fiddler crabs, deer antlers, colors of male birds • Can involve selection for display coloration, enhanced combat structures • Female choice often involved; selection for fit males (good genes hypothesis)

8. Sexual Selection The major claw of fiddler crabs is employed for display to attract females and for combat with other males

9. Types of Sexuality • Separate sexes: gonochoristic • Hermaphroditism: individual can have male or female function, simultaneously or sequentially, during sexual maturity

10. Simultaneous Hermaphroditism - Acorn barnacles Barnacle penis

11. Simultaneous Sequential Protandrous - first male, then female Protogynous - first female, then male Hermaphroditism

12. Sequential Hermaphroditism • Protandry - size advantage model • Eggs costly in terms of resources, so more offspring produced when individual functions as female when large • Male function does not produce great increases in offspring when it gets larger Therefore, there is a threshold size when female function begets more offspring; smaller individuals do better as males Ophryotrocha spp. Crassostrea virginica eastern oyster

13. The size advantage model for protrandry

14. Protogyny • Male function must result in more offspring when male is older and larger • Important when aggression is important in mating success, e.g., some fishes where males fight to maintain group of female mates Red grouper (Epinephelus morio)

15. Male Polymorphism • Males may occur as aggressive fighting morphs, or less aggressive morphs • Found in a number of groups, e.g., some fishes and some amphipod or isopod crustaceans • Determination of morphs can be environmental, genetic • Less aggressive morphs can obtain mates by “sneaky” tactics, which are often successful Jassa marmorata Kurdziel & Knowles, 2002 Proc. Roy. Soc. B 269:1749-54

16. Factors in Reproductive Success • Percent investment in reproduction - reproductive effort • Age of first reproduction (generation time) • Predictability of reproductive success • Juvenile versus adult mortality rate

17. Life History Theory • Tactics that maximize population growth • Evolutionary “tactics”: variation in reproductive effort, age of reproduction, whether to reproduce more than once • Presume that earlier investment in reproduction reduces resources available to invest in later growth and survival

18. Examples of Life History Tactics • Strong variability in success of reproduction: reproduce more than once • High adult mortality: earlier age of first reproduction, perhaps reproduce only once • Low adult mortality: later age of first reproduction, reproduce more than once

19. Example: Selection in a Fishery • Shrimp Pandalus jordani, protandrous • Danish, Swedish catch (Skagerak) 1930-1956 – stable, increased slowly 1956- 1960 – catch tripled (2000  6300 ton/y)

20. Pandalus jordani fishery Changes in Body Size Changes in Size of Change from Male to Female See Conover and Munch 2002 Science 297: 94-96

21. Sex - Factors in Fertilization • Planktonic sperm (and eggs in many cases): problem of timing, specificity • Direct sperm transfer (spermatophores, copulation): problem of finding mates (e.g., barnacles, timing of reproductive cycle)

22. Planktonic Sperm and Eggs • Specialized binding/fertilization proteins in sperm and receptors in eggs (bindin in sea urchin sperm, lysin in abalone sperm) • Sperm attractors in eggs • Binding proteins are species-specific, proteins with high rates of evolution

23. Gamete matching important in plankton Binding proteins: bindin (urchins) protein in acrosome, binding factor to egg cell membrane (ECM) lysin (molluscs) protein in acrosome, creates hole in ECM

24. Timing of Sperm and Egg Release • Epidemic spawning - known in mussels, stimulus of one spawner causes other individuals to shed gametes • Mass spawning - known in coral species, many species spawn on single nights • Timing of spawning (also production of spores by seaweeds) at times of quiet water (slack high or low tide) to maximize fertilization rates