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Minne Life Cycles and Adaptations of Marine organisms > Life cycles animals lecture 4 > Flashcards

Life cycles animals lecture 4 Flashcards

1
Q

How can reproductive effort be indicated?

A

Reproductive effort includes several components and can be represented by several indicators:

  • investment in gonads (during the reproductive season)
  • gamete number
  • gamete size
  • pre-spawning investment: e.g., migrations, nest building, courtship (visual displays, sound production, hormones, etc.)
  • post-spawning investment: parental care
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2
Q

How can the investment in gonads be represented?

A

The investment in gonads can be represented by the gonadosomatic index (GSI):

GSI: Wg /Wb *100

Wg = gonad weight
Wb = body weight

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3
Q

What does the GSI indicate?

A

The reproductive season and total investment in gonads

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4
Q

Why do females usually present a high (up to 30%) GSI during reproductive season?

A

Due to the presence of eggs with yolk.

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5
Q

Do males also present a high GSI during reproductive season?

A

In males, GSI may be lower than 1% also during the reproductive season.

However, in species with sperm
competition, GSI may be similar to that of females

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6
Q

What is fecundity?

A

Number of eggs/offspring produced by a female

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7
Q

What is fertility?

A

Male gametes: number but also other traits related to fertilization

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8
Q

In what type of species is it important to define the term fecundity?

A

In species spawning more than once.

We can talk about annual fecundity, lifespan fecundity, fecundity in each reproductive event, etc.

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9
Q

What is individual fecundity?

A

Individual fecundity: total number of eggs/offspring released by a female during the reproductive season

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10
Q

What is actual fecundity?

A

Actual fecundity: fecundity artificially obtained from a female

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11
Q

What is Relative individual fecundity?

A

Relative individual fecundity: number of eggs/offspring released by a female during the reproductive season / gr body weight

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12
Q

What is Potential fecundity?

A

Potential fecundity: total number of oocytes in the ovary at the beginning of the reproductive season

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13
Q

What is population fecundity?

A

Population fecundity: total number of eggs released by all the reproductive active females of a stock during the reproductive season.

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14
Q

What is the easiest method to estimate fecundity?

A
  • To count the number of eggs/offspring that are released and count the number of reproductive events.
  • For some species, this method is feasible: it is possible to count directly offspring and, identifying each individual, also the number of reproductive events.
  • For most the species this method is difficult to apply.
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15
Q

Can there be a big difference in fecundity between species?

A

Yes.

Some species release 1 offspring per year or even every two/three years, while other species release millions of eggs per spawning event

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16
Q

In what species can the eggs be counted as an estimate of fecundity?

A
  • In species with demersal eggs (laid on bottom)
  • In species carrying eggs (crustaceans, some fish, etc

In the first case it is important to separate eggs from different females, if no or male only parental cares occur.

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17
Q

How can you estimate fecundity in species with pelagic eggs?

A
  • Eggs need to be collected with nets or bags and counted in the moment of the mating.
  • If more than one female is present, it is necessary to assess if the collected eggs belong to just one female.
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18
Q

What has to happen in order to count the number or reproductive events of and indivdual in the field?

A
  • Individuals must be identified and followed during the entire reproductive season,
  • This implies that they must be resident in or come back to known reproductive sites
  • and the mating moment must be known
  • Clearly, only applicable to a few species
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19
Q

What is a better method of estimating fecundity (applicable to a wider range of species)?

A
  • The analyses of the gonads (and other parts of the reproductive apparatus, like uteri)
  • The method of gonad analysis depends on the type of reproduction and ovary.
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20
Q

Total spawner species (fecundity terms)

A

The whole clutch of developed oocytes is shed in an unique event or over a short period of time but as part of single episode

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21
Q

Batch spawner species (fecundity terms)

A

The eggs are released in batches usually over a protracted spawning period.

Only a portion of the yolked oocytes is selected to be spawned and hydrated in each batch.

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22
Q

Synchronous ovary (fecundity terms)

A

All oocytes, once formed, grow and ovulate from the ovary development in unison; further replenishment of one stage by an earlier stage does not take place.

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23
Q

Group-synchronous development (fecundity terms)

A

At least 2 cohorts of oocytes can be distinguished in the maturing ovary;

  • A fairly synchronous population of larger oocytes (a clutch); the oocytes spawned during current breeding season
  • A more heterogenous population of smaller oocytes from which the clutch is recruited; the oocytes spawned in future breeding seasons.
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24
Q

Asynchronous ovary development (fecundity terms)

A

Oocytes of all stages are present in the ovary without dominant populations.

The ovary appears to be a random mixture of oocytes, at every conceivable stage.

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25
Q

Determinate fecundity (fecundity terms)

A

In fishes with determinate fecundity, the standing stock of yolked oocytes (total fecundity) prior to the onset of spawning is considered to be equivalent to the potential annual fecundity.

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26
Q

Indeterminate fecundity (fecundity terms)

A

Refers to species where potential annual fecundity is not fixed before the onset of spawning and unyolked oocytes continue to be matured and spawned during the spawning season

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27
Q

De novo vitellogenesis (fecundity terms)

A

The process of producing vitellogenenic oocytes from previtellogenenic oocytes during the spawning season, and consequent recruitment into the standing stock of yolked oocytes

28
Q

Annual fecundity or annual realized fecundity (fecundity terms)

A

The total number of eggs released per female in a year

29
Q

Potential annual fecundity (fecundity terms)

A

Total number of advanced yolked oocytes matured per female and year

30
Q

Total fecundity (fecundity terms)

A

Total number of vitellogenic or advanced yolked oocytes at any time in the ovary

31
Q

Residual fecundity or remnant fecundity (fecundity terms)

A

The number of vitellogenic or advanced yolked oocytes in ovaries showing postovulatory follicles. This indicates these females had already spawned some eggs.

32
Q

Batch fecundity (fecundity terms)

A

The number of eggs spawned per batch.

The sum of batch fecundities represents the realized annual fecundity

33
Q

Batch fecundity (fecundity terms)

A

The number of eggs spawned per batch. the sum of batch fecundities represents the realized annual fecundity.

34
Q

Spawning fraction (fecundity terms)

A

Fraction of mature females spawning per day

35
Q

Postovulatory follicle (fecundity terms)

A

After ovulation, the follicle tissue that encapsulated each hydrated oocyte collapses and remains in the ovary as an evacuated follicle.

They are uses as indicators of previous spawning activity.

36
Q

In some cases is has been shown that females may reabsorb oocytes. What is the phenomenon called?

A

Atresia.

Reabsorbed oocytes will not be spawned, as a consequence, they must be removed from any count.

37
Q

Determined fecundity

A

Standing stock of yolked ooctyes (total fecundity) prior to the onset of spawning is considered to be equal to the potential annual fecundity.

During the reproductive season, new vitellogenesis DOES NOT begin.

Potential fecundity can be estimated in samples of mature pre-spawning females.

38
Q

Indetermined fecundity

A

Not fixed before the onset of spawning
and unyolked oocytes continue to be matured and spawned during the spawning season.

During the reproductive season, new vitellogenesis DOES begin.

The count of vitellogenic oocytes at the onset of spawning would provide an underestimation
of potential fecundity.

39
Q

In the case of indetermined fecundity, would you need to sample during the entire season?

A

Yes, it is necessary to sample during the entire season mature females to estimate batch fecundity and also the number of egg batches per females needs to be estimated.

To estimate the number of egg batches/number of reproductive events, the fraction of
spawning and non-spawning females needs to be evaluated.

40
Q

What is the relationship between fecundity and female size (at intra-specific level)?

A

There is a positive relationship.

To obtain an accurate fecundity estimate, a sample representative of the size range of mature females must be collected and analysed

41
Q

What is the gravimetric method?

A

One of the most used methods to estimate fecundity from ovary.

42
Q

How do you conduct the gravimetric method?

A

This method consists of:

  • the collection of weighted ovary sections/subsamples (usually at the beginning it is important to collect sections from different parts of the ovary to be sure that no pattern occurs)
  • and the count of oocyte number for each
    section.

Then, fecundity can be estimated
according to the relative weight of the
section respect to the ovary.

43
Q

What do the different terms of fecundity describe?

A
  • Total fecundity: Which oocytes?
  • Potential fecundity: When?
  • Batch fecundity: Type of fecundity (determined/ indetermined)
44
Q

How can you analyse the sections of the ovary?

A

With image analysis sytem.

After that: estimate/measure oocyte size and count oocytes to obtain a size frequency distribution.

45
Q

How do you know which part of the ovary is most suitable for estimates?

A

Oocyte counts/ size can be compared in a graph per region

46
Q

What are the advantages of the gravimetric method?

A
  • Accurate and inexpensive technical approach
  • Can provide additional information on oocyte frequency and oocyte diameter
  • Very useful technique for batch fecundity estimations
47
Q

What are the disadvantages of the gravimetric method?

A
  • No info on atresia or presence of spawning markers such as POF’s
  • Not for species with asynchronous development of oocytes or where the grap between the advanced vitellogenic oocytes and previtellogenic oocytes in poorly developed.
  • requires whole ovaries to be returned to laboratory
  • time consuming
48
Q

How can fecundity be estimated in viviparous species?

A

fecundity can be estimated from ovary and from uteri/reproductive apparatus

  1. Elasmobranchs ovarian fecundity tends to be larger than uterine fecundity
  2. Different methods are used in invertebrates
  3. In cetaceans, lactation implies a longer bond between the mother and the offspring, allowing to estimate not only fecundity, but also interval between pregnancies
49
Q

what is the interspecific variability in egg/offspring number related to?

A

number is related to variability in egg/offspring size

50
Q
A
  • Given a defined investment in gonads, a trade off between egg/offspring size and number occur
  • The inverse relationship between number and size occur at both intra- and inter-specific level.
51
Q

how is the relationship between number and size of offspring/egg?

A
  • inverse
  • if small eggs, then usually many
  • if large eggs, then usually few
52
Q

Considering the eggs, some characteristics are related to size:

A
  1. Duration of development: at given conditions (e.g., temperature, oxygen availability, etc.), larger eggs have longer development.
  2. Surface/volume ratio: larger eggs have smaller ratio with implication for gas exchanges (oxygen availability for embryo development).
53
Q

At both inter- and intra-specific level, larger larvae hatch from?

A

larger eggs

54
Q

the (usually) pelagic larvae presents several anti-predator adaptions:

A
  • transparent body
  • presence of spiny rays and spines
  • increase in size
  • Larvae use the yolk after hatching, then feed on plankton (phyto- and zooplankton also in herbivorous species)
  • Feeding capacity increases with age/size
55
Q

why are larger larvae are expected to perform better?

A
  • Swimming capacity and speed
  • Feeding
  • Competition

Larval size may determine also some characteristics and performances at later stages.

56
Q

feeding behavior of larvae in invertebrates:

  1. Planktotrophic larvae
  2. Lecithotrophic larvae
A
  1. Planktotrophic larvae: larvae feeding on plankton during dispersal
  2. Lecithotrophic larvae: larvae relying on yolk sac for nutrition during dispersal
57
Q

some advantaged of small larvae

A
  • Predator avoidance when predators prefer larger larvae
  • Rapid growth rates if small-sized food is available (zooplankton may have different sizes
    depending on the period of the year).

Advantages of large vs small sized larvae may change according to environmental condition, as a consequence, optimal trade-off between size and number of offspring may change.

58
Q

some general patterns to predict the egg/offspring size

A
  • Demersal eggs with parental cares tend to have larger size than pelagic eggs without parental care
  • Positive relationship between egg size and latitude was found
  • Positive relationship between female size and fecundity (in terms of number and dimension of eggs)
  • Egg size decreases with water temperature
59
Q

there are some cases in which we have variation in egg size among individuals of the same species as an adaptive response to the environment.

like what?

A
  1. female of the same species that lay down eggs in different environments, can release eggs of different dimensions
  2. the development of the female is an important factor: in many species, females at first reproduction tend to produce smaller eggs (in some cases, a positive relationship between egg size and female size has been found)
  3. Seasonal variation in egg size has been found in species from temperate zones:
    - Species reproducing in Spring/Summer: smaller eggs
    - Species reproducing in Autumn: larger eggs
60
Q

egg quality related to?

A
  1. size
  2. substances in yolk
61
Q

In a general context, a species may invest in thousands or even millions of small eggs or on a few large eggs.
This differential investment reflects?

A
  • optimal trade-off between size and number
  • large size is expected to be adaptive in context in which size plays an important role for offspring survival (stable environments)
62
Q

does fecundity seem to determine species vulnerability to exploitation?

A

No

  • Several highly fecund specie showed a marked decline due to overfishing
63
Q

how does overfishing impact the production of eggs in a stock?

A
  • Selectively removing larger individuals, fishing will impact stocks due to the removal of larger, more fecund females
  • Larger females can disproportionally contribute to egg production
64
Q

management strategy for fish stocks is to prevent the overfishing of larger females. Why?

A

they have

  • Higher fecundity
  • In some cases, higher egg quality
  • Higher experience, in some cases higher reproductive success has been found
  • Better genes ?
65
Q

does sperm play a major role in offspring production

A

not a major role, because usually sperm are produced in very high quantities, but:

  • sperm production may influence fertilization rate and sperm depletion may occur
  • a «certain» concentration of sperm is needed in order to obtain a high fertilization rate, and this is relevant in particular in broadcast spawners.
  • in some conditions, sperm may be not numerous enough to guarantee high fertilization rate.
66
Q

“in some conditions, sperm may be not numerous enough to guarantee high fertilization rate”

like when?

A
  • For instance, in the crab Paralithodes brevipes, sperm number and fertilization rate decrease with mating frequency
  • they need several days to restore the sperm reserves
67
Q

if males are larger than females, what can be the consequences of overfishing in these areas?

A
  • differential exploitation of the two sexes, with a consequent decrease in male numbers and size
  • lower sperm/egg ratio
  • sperm depletion
  • Fishing selectivity on males may induce lower fertilization rates

Minne Life Cycles and Adaptations of Marine organisms (17 decks)

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