Life cycles Animals Lecture 2 Flashcards
Name several aspects of reproduction that characterize the life cycle and life history traits of a species
- Sexual maturity
- Number of reproductive events in the life period
- Sexual patterns
- Fecundity & fertility
- Sexual selection and mating system
- Parental care
Sexual maturity
An individual attains sexual maturity when it is capable of reproducing. This marks the transition from the juvenile to the adult stage.
Age at sexual maturity
The age at which an organism reaches sexual maturity. It varies among species, even within the same taxonomic group.
Size at sexual maturity
The size an organism reaches when it becomes sexually mature. It varies among species and is often positively correlated with asymptotic size (L∞).
Reproductive load
Ppt:
The ratio of size at sexual maturity (Lm) to asymptotic size (L∞).
Lm/ L∞ : 0.4 – 0.7
Reproductive load is usually higher in small-sized species
Google definition:
The ratio between the average length at first maturity and the maximum length reached in a population.
Engraulis encrasicolus
- European anchovy
- Reproductive load: 0.63
- Asymptotic size (L∞) = 17 cm
- Relatively high reproductive load
Rhincodon typus
- Whale shark
- Reproductive load: 0.48
- Asymptotic size (L∞): 20 meters
Chaenocephalus aceratus
- Blackfin icefish
- Reproductive load: 0.70
- Asymptotic size (L∞) = 67 cm
Size/age at sexual maturity can refer to..
- Minimum: size/age of the smallest/youngest sexually mature individual
- L/A50: size/age at which 50% of the individuals is sexually mature
- Size/age at maturity is usually represented by a curve.
- In viviparous species, it may be useful to know also the
minimum size/age at first parturition (giving birth to offspring)
How can sexual maturity be evaluated?
Sexual maturity can be evaluated through different methods depending on factors like type of reproduction and species characteristics.
Methods include:
- analysis of gonads
- presence of embryos (in viviparous species)
- presence of color or structures appearing only in mature individuals
- observation of individuals performing parental care (caring for eggs)
Analysis of gonads
- Gonads of sexually mature individuals present mature gametes, but usually only a
defined period in species presenting seasonal reproduction (i.e., during the reproductive season or just
before it). - If reproduction is seasonal, a resting period of gonads usually occurs and it is not so easy to distinguish mature and immature individuals.
How can analysis of gonads be conducted?
- Microscopic
- Macroscopic
Macroscopic gonad analysis
- The macroscopic analysis usually includes the recording of features that can be seen by naked eyes.
- Macroscopic analysis is a rapid method.
- It allows establishing if an individual is able to reproduce during that specific reproductive season or if it just stopped reproducing (at the end of the reproductive season).
- This method usually can not provide information on past reproductive events (several months before the
analysis).
Microscopic gonad analysis
- The microscopic analysis allows attributing the stage of maturity after histological analysis of the gonads.
- This method requires longer time than macroscopic one.
- It often provides more precise information on the stage of maturity of gametes.
- It can provide also information on past reproductive events, but this depends on the species.
What factors are considered in developing scales of maturity for gonads?
- Scales of maturity for gonads are based on factors like the general aspect, shape, relative dimension, position, and color of the gonads.
- Different scales have been developed for various taxonomic groups, requiring knowledge of reproductive apparatus morphology for evaluation.
Difference between gonad maturity and sexual maturity
- An individual can have a maturing gonads and be sexually immature or mature
- Every individual with a mature gonad is sexually mature.
Macroscopic maturity scale for bony fish
Main characteristics in relation to gonad analysis
- size of the gonads in relation to body cavity
- appearance (colour, etc.)
- size of oocytes.
Appearance and relative size of other reproductive structures may help in evaluating maturity stage.
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 1 - immature = virgin
Gonad description:
- Small pinkish and translucent ovary shorter than 1/3 of the body cavity.
- Eggs not visible to naked eye.
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 2A virgin developing
Gonad description:
- Small pinkish/reddish ovary shorter than ½ of body cavity.
- Eggs not visible to naked eye
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 2C - maturing
Gonad description:
- Ovary pinkish/yellow in colour with granu- lar appearance, about 2/3 length of the body cavity.
- Eggs are visible to naked eye trough
the ovaric tunica, which is not yet translucent. - Under light pressure eggs are not expelled.
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 3 - Mature/ spawner
Gonad description:
- Ovary orange/pink in colour, with conspicuous superficial blood vessels
From 2/3 to full length of the body cavity.
- Large transparent, ripe eggs are clearly visible and could be expelled under light pressure.
- In more advanced conditions, eggs escape freely.
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 2B - recovering
Gonad description:
- Pinkish-reddish/reddish-orange and translucent ovary about ½ length of body cavity.
- Blood ked eye.
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 4A - spent
Gonad description:
- Reddish ovary shrunken to about ½ length of the body cavity.
- Flaccid ovaric walls; ovary
may contain remnants of disintegrating opaque and/or translucent eggs.
Define macroscopic maturity scale of M. Barbatus in this picture
Stage: 4B - resting
Gonad description:
- Pinkish/reddish and translucent ovary. About 1/3 length of body cavity.
- Eggs not visible to naked eye.
Maturity scale for oviparous (egg-laying) elasmobranchs
Maturity scale for oviparous elasmobranchs (males)
Maturity scale for oviparous elasmobranchs (females)
Maturity scale for viviparous (give birth directly) elasmobranchs
(The stage of pregnancy is included)
What does the reproductive apparatus in female cephalopods consist of?
- Ovary (O)
- Genital ducts (FD)
- Nidamental glands and accessory nidamental glands (AC.N.G.)
What does the reproductive apparatus in male cephalopods consist of?
- Testis
- Spermatophoric complex:
deferent duct, genital sac,
Needham’s pocket, genital
opening
Maturing stages in female cuttlefish
Maturing stages in male cuttlefish
Maturity scale of Crustacean decapoda (crabs, lobsters, etc.)
Description of the microscopic maturity scale of M. barbatus females (H&E, haematoxylin and eosin)
For high resolution picture:
https://iris.unica.it/retrieve/e2f56ed8-f9eb-3eaf-e053-3a05fe0a5d97/Follesa%20et%20al%202019%20b.pdf
Which female gamtes do you see in this picture?
Oogonia
Pre-vitellogenic oocytes
Vitellogenic oocytes
Which male gametes do you see in this picture?
Spermatogonia
Spermatocytes
Spermatids
Sper
Maturing of oviducal glands
- in the oviducal glands the ducts
develop, - secretion starts to be produced
- even sperm may be found.
(Gravid = pregnant)
Maturity of gonads can be determined on a monthly basis
(What does the graph show??)
When are individuals sexually mature based on the gonads?
Individuals with mature, close to maturity or spent gonads are sexually
mature
How do the claspers of elasmobranchs males provide information on sexual maturity?
- They become longer than pelvic fins
(in most species) - They also become calcified as males mature.
As a consequence, even in a gonadal resting period claspers provide an
accurate information on
the attainment (het behalen van) of sexual
maturity.
Is gestation (period between conception and birth) length in cetaceans short or long?
Long
In what type of species can it be useful to distinguish between size/age at maturity and size/age at first parturition?
In viviparous species
Reproductive cycle of toothed-whales
Reproductive cycle of toothed-whales:
- minimum 3 years
- In many species; 1 year gestation and 2 years lactation period
- Mating, calving and weaning are distinct events in cycle with each occuring over several months
- Calving timed to match peak ecosystem producivity
Reproductive cycle of baleen whales
Reproductive cycle of baleen whales:
- minimum of 2 years
- events tightly correlated with annual migratory cycle
- Most mating and calving: on wintering grounds
- Calves are weaned (krijgen borstvoeding) when arriving on feeding ground during their first summer
- Females complete 1 migratory cycle while pregnant and first half of next cycle with a nursing calf
What do eggs indicate in species caring eggs?
- egg presence signals the attainment of sexual maturity.
- The absence of eggs does not indicate sexual immaturity.
Relation of coloration and sexual maturity
- In some species, coloration irreversibly changes with maturity.
- In other species, nuptial colorations are present only during the reproductive period. (rapid short-term colour changes)
Color phases exhibited by Nassau grouper while on the spawning aggregation.
The colorations shown are:
A: Barred
B: Bicolor
C: Dark
D: White belly
Red dots on side of fish are laser points used to determine length of fish (250mm apart)
Intra-specific variability in size/age at maturity can be found…
- Between the two sexes
- Within sex, depending on the adopted reproductive strategy
- Among geographic areas
- As response to variation in abundances/density
- As response to fishery
Differences in size/age at sexual
maturity between sexes occurs in
several species.
- In several elasmobranchs, females
mature later and at larger sizes than
males. - In these species, there is also
a sexual dimorphism in size with
females attaining larger sizes then
males. - In some other, oviparous, species size
at maturity of males and females is
similar. - A possible role of viviparity and the
advantage of being larger for
fecundity is believed to be at the
basis of these differences.
When can Intrasexual difference in size/age at sexual maturity occur?
- in some species with alternative reproductive strategies.
- In some species, males may adopt
different strategies and according to
that they can mature earlier (at
smaller sizes) or later (at larger sizes). - In some salmons, males migrate to
the sea or do not migrate, according
to the adopted strategy
What are the 3 male morphs described in the isopod Paracerceis sculpta?
- α males: dominant
- β males: mimicking females
- γ males: smallest in size
The 3 male morphs differ in age at maturity
- α males: 84 days
- β males: 62 days
- γ males: 58 days
Concluding that genetics determine the strategy of the males
Intraspecific geographic variability in size/age at sexual maturity has been found in several species
- A latitudinal gradient in size at sexual maturity and maximum size has
been found in several species. - Geographic variability can
also be related to peculiar characteristics of
areas.
- In several populations of different
commercial species, a decrease in the
size/age at sexual maturity has been
found. - This decrease has been put in relation
with fishery exploitation.
How does large size/age at maturity affect the vulnerability of exploited species?
Large size/age at maturity makes exploited species more vulnerable because individuals are more likely to be caught before reaching sexual maturity and, consequently, before reproducing.
There are several examples showing that larger species, maturing later and at larger sizes, show stronger decline in abundance as effect of fishery respect to smaller, earlier maturing ones.
Generation length
- The average age of parents of the current cohort (i.e., newborn individuals in the
population). - Generation length therefore reflects the turnover rate of breeding individuals in a population.
- Generation length is greater than the age at first breeding and less than the age of the oldest breeding individual, except in taxa that breed only once.
What important information can generation length tell us?
Generation length provides information useful to predict the recovery capacity of a population/species and the
expected time for the recovery.
Generation length of 58 species of cetaceans estimated on the basis of life history traits, age structure of a
population, survival at each age, etc. (life tables)
Generation length shows wide variability
