1. 5 Reproduction and Sexuality in the Marine Environment
©Jeffrey S. Levinton 2001

2. Reproduction, dispersal and migration are the fundamental processes that allow living populations to grow and exploit new environments.
Definitions:
Reproduction: replication of individuals.
Dispersal: spread of progeny to locations that differ from the parent.
Migration: a directed movement between specific areas

3. Nonsexual Reproduction
Descendants are genetically identical - clones
Colonial species produce a set of individuals that are genetically identical, known as a module; each module may have arisen from a sexually formed zygote

4. Organisms that benefit from group living commonly reproduce asexually because group living benefits are greatest when you are related.
Bryozoans (top left), tunicates (top right), anemones (bottom left), corals, and sponges are all examples of organisms that reproduce asexually.

5. Cost of Sex
Sex is a species property whereby different individuals have the chance to exchange or combine DNA to produce offspring.
FEMALE: invests more energy in production of eggs, and offspring’s DNA is only half hers.
Sex involves expenditure of energy and time to find mates, combat among males

6. Benefits of Sex?
genetic diversity - sex increases combinations of genes - resistance against 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 variants

7. Types of Sexuality Separate sexes –gonochoristic
Hermaphroditism -individual can have male or female function

8. Hermaphroditism Simultaneous Sequential
Protandrous - first male, then female
Protogynous - first female, then male
Many nudibranchs (above) are simultaneous hermaphrodites

9. Simultaneous Hermaphrodites
What are the advantages?
can mate with anyone you run in to.
What are the costs?
High cost in energy over time to produce both eggs and sperm
What if any individual releases sperm during mating, but then does not release eggs??

10. Sequential Hermaphroditism: Protandry and the size advantage model
Eggs are 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.
Prawn (above) are frequently protandrous.

11. Male at advantage Female at advantage
Number of offspring produced
Male
Body size
The size advantage model for Protrandry

12. Example: Selection in a Fishery that illustrates the size advantage model
Shrimp Pandalus jordani, protandrous
Danish, Swedish catch:
: stable, increased slowly
: catch tripled to (2000 to 6300 ton/y)

13. Pandalus jordani fishery
Changes in Body Size
Changes in Size of Change from Male to Female

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.
Example: Blue-head wrasse and other coral reef fish species.
Terminal phase of a Bluehead Wrasse (above).
14 families of fish, 11 of which are common in coral reefs (porgies, damsels, wrasses, parrotfish)

15. Trends observed in many fish families that are sequential hermaphrodites:
Fish that form harems or defend spawning sites are usually protogynous.
Fish that live in schools and are not closely associated with the bottom, where mating is random are usually protandrous.
Within protogynous species, population density plays a role in the percent of the population that changes sex. At low densities, large males can defend a harem or spawning site, and there are usually no small males present (all males are the result of sex change). At high densities, the population is nearly 50% primary males (born male), basically gonochoristic.
3 important factors: (a) relative number of gametes produced, (b) mating behavior of the species, and (c) density of the population.

16. Sex - factors in fertilization
Copulation: ( + choice of mate, increases success of fertilization)
Sperm applied to body of other individual or egg clutch.
Free spawning: shed gametes into water column.
Fertilization success is affected by:
1. Volume of gametes
2. Sperm transfer
3. Distance between males and females
4. Water turbulence
5. Timing

17. What are the costs and benefits to spawning??
Free Spawning
If there is anything truly unique about the marine environment, it is the frequent occurrence of free spawning.
What are the costs and benefits to spawning??

18. Costs to Spawning in Success of Fertilization
Fertilization success is low if distance is great and/or turbulence is strong.
- turbulence dilutes sperm and eggs, dispersing them in all directions which makes encounters less likely.
Timing must be simultaneous, tuned to a lunar cycle or cued by other individuals
Gametes can encounter gametes of other species and high densities of gametes.
Predation of eggs and sperm.

19. Planktonic sperm and eggs to prevent fertilization by different species:
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