Lecture 28- Reproduction at sea

Question 1

What are the three modes of reproduction in the sea?

Answer 1

1.Viviparous 2.Ovovivparous 3. Oviparous

Question 2

What is viviparous reproduction?

Answer 2

-Direct- Viviparous (live-bearing), give birth to fully developed juveniles! -rare in marine environment

Question 3

What is ovovivparous reproduction?

Answer 3

-indirect development -give birth to larvae

Question 4

What is oviparous reproduction?

Answer 4

-indirect development -spawn eggs -most common in marine environments

Question 5

What is the comparison in reproduction mode diversity between invertebrates and fish?

Answer 5

-Both modes of reproduction are well represented within the invertebrate taxa, but almost all fishes have indirect development!

Question 6

Which animals in the sea are viviparous?

Answer 6

-main exception are the elasmobranchs (sharks and rays) -all have internal fertilization, some give birth to live young -but all modes of reproduction are represented in this group

Question 7

What is the difference between planktotrophic and lecithotropic development?

Answer 7

1.Planktotrophic = feeding 2.Lecithotrophic = non-feeding -how much maternal provisioning is provided -larvae= lecithotrophic= indirect development but all the food is contained in the egg -most fishes have planktotrophic -Both modes of larval development are well represented within the invertebrate taxa, but almost all fishes have planktotrophic development!

Question 8

What is the exception to the types of larvae?

Answer 8

-Main exception are leptocephallus larvae -is the flat and transparent larva of the eel, don’t have functioning jaws when born, filament like larvae, absorb nutrients from water -not through digestion

Question 9

What is the eggs size and development time in planktothrophic and lecithotropic larvae?

Answer 9

1.Feeding larvae - smaller eggs, longer development time 2.Non-feeding larvae- larger eggs, shorter development time

Question 10

What is the trade off between the feeding and non-feeding larvae?

Answer 10

-fewer offspring = more likely to survive when more cared for and vice versa

Question 11

What is the reproductive mode of the sea urchin?

Answer 11

• indirect, plantotrophic
• indirect development, extrenal fertllization, separate sexes, fertilized eggs develop into feeding larvae and into juvenile later

Question 12

What is the reproductive mode of the Sabellid?

Answer 12

• indirect, lecithotropic
• separate sexes, non feeding larvae and metamorphise into juvenile

Question 13

What is the reproductive mode of an octopus?

Answer 13

• direct, lecithotrophic
• internal development, then eat the capsule and hatch

Question 14

What is the reproductive mode of a barnacle?

Answer 14

• mixed, planktotrophic
• internal fertilization, hermafroditism for a time internal development then release and they feed as alrvae and then metamorphose into juveniles

Question 15

What are the adaptations and constraints associated with internal fertilization? (5)

Answer 15

1.Reduction in sperm number 2.Increase in sperm size 3.Increased complexity of sperm 4.Sperm storage 5.Sperm competition high -don’t need much sperm as the sperm close to egg -evolution of sperm storage= females store it and decide when

Question 16

What are the adaptations and constraints associated with external fertilization? (5)

Answer 16

1.Increase in sperm number 2.Increase in sperm longevity 3.Constraints of osmotic stress 4.Constraints of egg recognition 5. Sperm limitation! =not all eggs may be fertilized

Question 17

What are the two pieces of evidence for sperm limitation?

Answer 17

1. Fertilisation rates in invertebrates can be < 25% in low density pop. or when spawning is asynchronous 2.Even fertilisation rates in species which release gametes in close contact can be quite a bit less than 100%

Question 18

What are the consequences for sperm limitation? (7)

Answer 18

•1. An egg doesn’t translate into an offspring; reduction in reproductive success 2. Selection for increased density (positive density dependence, an Allee effect) which may or may not offset the cost(s) of negative density dependence(better to live in large groups than in diffuse groups) 3. Direct effect on population size in recruitment limited populations 4. Mechanism for gene flow in sedentary species at low population density(could take place between different population) 5. Reduced fertilisation success in species without strong spawning synchrony (need to release at the same time, particular effect in diffuse population) 6. Influences the allocation to sperm production (more sperm per male, make more, devote more resources) 7. Selection for increased egg size

Question 19

What are the adaptations to enhance fertilization? (6)

Answer 19

1. Release of gametes at times with little water movement (times of reduced gamete diffusion)(so the eggs won’t be carried off) 2. Releasing sperm within viscous fluids (sperm packet remains more intact if the fluid is sticky= viscous) 3. Filtration as a means of concentrating sperm (can filter, store it and fertilize internally) 4. Sperm storage 5. Spawning migrations (so everyone spawns at the same place at the same time) 6. Spawning synchronization

Question 20

Is sperm really limiting?

Answer 20

-eggs also matter -eggs differ in their fertility -not all eggs are fertilizable -so it is not just the sperm that is limiting -in some population with increase of sperm fertilization did not increase so sperm not as limiting as previously thought

Question 21

What is the example of urchins and polysperming?

Answer 21

• sperm limitation is an issue, having too much sperm can also be bad:
• this is work on sea urchin, this is the risk of polyspemring, fertilized by more than one sperm= then egg doesn’t develop
• sperm block= when sperm penetrates membrane of an egg, once it happens biochemistry of the egg membrane of an egg closes small channels in teh membrane preventing entry of other sperm
• bigger eggs= bigger targets, once 2 microns= all fertlized, and sperm block instantenous -bogger eggs are bigger so more likely to be fertilized by more, and it takes longer to have a sperm block
• being a big egg when lot of sperm= not good

Question 22

What was the confusing example of polyspermy he talked about?

Answer 22

-in very high concentrations of sperm the egg size will not matter as very likely fertilized more than once anyways -in low sperm concentrations the drive is to larger eggs to increase likelihood of fertilization

Question 23

What does the drive for larger eggs cause?

Answer 23

-eggs are difference sizes = carries to subsequent effect on to larva phenotype -the larvae are larger

Question 24

What are the sources of energy for larvae?

Answer 24

1.Maternal provisioning (e.g. lecithotrophic larvae) 2. The environment

Question 25

What is the match/mismatch hypothesis?

Answer 25

most species are reliant on the environment:

• what creates the reliability in offspring
• how do species time their reproduction to the abundance of food
• the bottom graph is how many prey per larvae
• in b and c reproduction is matched to production of food
• a is mismatched

Question 26

What is the match mismatch hypothesis example: Heteroclinus- Scott’s Weedfish?

Answer 26

• variation in recruitment in this fish
• numebr of larvae measured over three reporductive season
• also measured chlorophyll= told them how long after copepods came
• strong correlation peaks in recruitment were correlated with peaks in food production
• strong support for the match mismatch hypothesis

Question 27

What is the effect of turbulence on larvae and their development?

Answer 27

• as a larvae wnat some turbulence
• if in laminar only,never get the food
• need sth to mix the water= for larvae near the surface= wind
• when wind is really striong or low= recruitment is bad
• moderate wind= moderate mixing= good recruitment
• intermediate level of wind is best, creates optimal mixing
• Lasker window!

Question 28

What is a Lasker window?

Answer 28

-when optimal turbulence conditions for larval development