Reproductive Strategies & Physiology: Fish Seminar and Overview of Tammy Mendelson's Work

1. Lecture 23, November 5, 2008. Reproductive Strategies & Reproductive Physiology. At the end . . . brief overview of Tammy Mendelson’s work. Announcements: Extra-Credit Opportunity Today: Fish Seminar from 4-5 pm “Speciation in Darters” by Tammy Mendelson Do Not talk during the seminar. If you need to leave right at 5, then please sit towards the back. Friday is Fish Friday. Graduate Students - please try to analyze some of the data. We will discuss this during the last 5-10 minutes of class. At the very least, please test whether the age-distribution differs between sites and habitats. If you have time, consider doing the initial analysis on morphology.

2. Things to watch for in the Video - (capelin spawning) How many reproductive opportunities do the fish most likely have? Where do they spawn? When does the fish spawn?

3. Effects of Lunar cycle on reproduction in mummichog Fundulus heteroclitus.

4. Recruitment of F. heteroclitus into the population. You can see pulses of new classes of fry.

5. proportion of female body weight in ovarian tissue Eggs in various stages. Stage 5-7 where they are ready to be spawned in stage 7. Hormone profiles. Male T levels go up close to mating. T stimulates sperm Female E levels go up close to mating. E stimulates the “yolking” up of the eggs. T E Progesterone levels in females. P stimulates final maturation of eggs.

6. Things to watch for in the Video - (surgeon fish spawning) How do the fish spawn? Where do they spawn? Where do the eggs go? How many animals spawn together?

7. Things to watch for (banded pipefish) • How many mates does the fish have? • Where do the eggs go?

8. Sexual Dimorphism, Primary Sex Traits, & Secondary Sex Traits Sexually Monomorphic Sexually Dimorphic

9. Why do secondary sex characters evolve? • Traits confer advantages in competition between males. • Traits are preferred by females. • Make males easier to find. • Direct benefits to females. • Traits are “sexy” but useless. • Traits indicate high quality males. • Traits are used to “manipulate” females. Which traits are favored (either female choice or male competition) can vary with environmental conditions.

10. Gender Systems in Fishes Gonochoristic – sex fixed at maturation: most fish species Hemaphroditic – presence of male/female gametes; or sex may change after maturation Simultaneous – both sexes in one individual • Examples: Rivulus, Serranidae (hamlets) Sequential (one sex at maturity and changes to other sex) • Protandrous: rare (male first, change to female): Pomatocentridae, some Muraenidae (moray eels) • Protogynous; more common (female first, change to male): Gobiidae, Labridae, Scaridae (parrotfishes), Anthias (Serranidae)

11. Rivulus marmoratus A selfing hermaphrodite

12. Alternative mating strategies

14. How do sneakers and mimics make sperm yet still look like females? What problem does this raise from a physiological point of view?

15. male, parental bluegill

17. Overview of Mendelson’s work Main question: What evolves faster - prezygotic or postzygotic isolation?

18. Step 1 - Make a tree and determine genetic distance between species pairs.

19. Step 2 - Compare how “willing” they are to spawn together - compare conspecific crosses with heterospecific crosses at various genetic distances.

20. Step 3 - Determine the hatching success for conspecific versus hybrid matings for animals at various genetic distances.

21. Step 4 - Compare the rates at which sexual isolation and hybrid inviability arise. Genetic Distance Genetic Distance

22. Interpretation 1. Pre-zygotic isolation arises faster than post-zygotic isolation A couple of caveats . . . a. Only looked at hatching of eggs, not later stages. b. Only looked at F1s - not F2s or back-crosses where genetic incompatibilities are most likely to be expressed. 2. Still, a VERY important paper. Before this, pre-zygotic vs. post-zygotic had only been examined in plants and Drosophila. First systematic study of vertebrates and first study of fishes.

23. Overview of Mendelson’s work Second question: How important are interactions among sperm and between sperm and eggs in reproductive isolation? E. hopkinsi E. luteovinctum

24. Approach #1: 1. Test eggs and sperm with each other. a. hand strips males (squeezes the sperm out) b. hand strips females (squeezes the eggs out) c. combines the two and looks at fertilization success for conspecific and heterospecific matings.

25. Sperm fertilizes just fine, but there is some post-zygotic isolation in HL.

26. Approach #2 - sperm competition: 1. Test eggs and sperm with each other. a. hand strips males from E. luteovinctum & E. hopkinsi b. hand strips females (squeezes the eggs out) c. combines sperm from two males and females d. asks whether interactions between sperm of two males is important in reproductive isolation Sperm competition varies by species, but E. hopkinsi tends to be better than E. luteovinctum overall.

27. Put it all together “Strength” tells you the degree to which hybrids did worse than parentals for THAT ONE STAGE. Absolute contribution assumes a step-wise progression of isolating barriers. First, the animals have to try to mate. Then they have to release gametes. Then, they have to deal with sperm competition. Then the resulting embryos have to grow. Absolute looks at the contribution to total reproductive isolation given the proceeding steps have already occurred.

28. Big Conclusion Again, pre-zygotic isolation is most important. But . . . the same caveats. - Only looked at hatching of the eggs. - Didn’t consider survival to adulthood. - Didn’t consider what happens in the F2 or back-cross stages.

29. Review Questions. 1. Explain the difference between pelagic and demersal eggs. Where does each go in the water column? What are the consequences for gene flow among populations? Give an example of a pelagic and a demersal spawner. 2. Explain the difference iteroparity and semelparity. Are capelin iteroparous or semelparous? How did the capelin spawn? List 2-3 groups of fish that are semelparous. List 2-3 groups of fish that are iteroparous. 3. Distinguish between promiscuous, polyandrous, polygynous, and monogomous breeding systems. List 2 groups of fish that display each breeding type. 4. Distinguish between simultaneous, protandrous, and protogynous hermaphrodites and given an example of each. What is the “size advantage model” for the evolution of sex change in fishes? (page 351) When does it predict protandrous hermaphroditism and when does it predict protogynous hermaphoriditism? 5. What is the difference between primary and secondary sexual traits? (page 353). Give examples of each. 6. What is a “spawning rush” and why do some species do this?

30. Review Questions (cont’d) 7. How do Corydoras fertilize their eggs? (page 357). 8. Accord to the data presented by Mendelson, what evolves faster - prezygotic or post-zygotic isolation? What is the evidence for this? 9. What has a larger influence on reproductive isolation between E. luteovinctum and E. hopkinsi - behavioral, gametic, or postzygotic isolation? What is the evidence for this?