Life cycles Animals Lecture 1 Flashcards
What are some characteristics of water compared to air?
- Buoyancy
- desiccation resistance
- presence of dissolved and particulate materials
- variable oxygen availability
Why are small stages in the life histories of aquatic animals often planktonic?
Planktonic stages (this includes gametes, embryos, and larvae) benefit from:
- abundant resources
- protection from predators
- potential dispersal over large distances.
What is suspension feeding, and where is it commonly observed in marine organisms?
- Suspension feeding is the process of extracting nutrients from the water column.
- It’s common in planktonic larvae, sessile organisms, and colonial forms.
Why do marine organisms often produce pelagic eggs?
Pelagic eggs:
- enhance dispersion
- reduce competition among offspring
- and provide protection from predators and adverse environmental conditions
What advantage does water offer for external fertilization in marine organisms?
- Water enables partners to release gametes even when not in proximity
- Enhancing fertilization rates and genetic diversity.
What are 3 important factors regarding external fertilization?
- Dilution effects: certain concentration of gametes, usually sperm, is required to achieve high fertilization rate. Fertilization rate is usually an asymptotic curve with a steep increase in fertilization rate with sperm number
- Synchronization in gamete release
- Gamete longevity is an important factor
Which 2 main factors influence the wide variability in life history traits, life cycles and adaptations in marine animals?
- Environment: adaptations to different environmental conditions
- Phylogenetic relationship: the role of evolutionary history on present traits
What are some examples of life history traits?
- number, size and sex ratio of offspring
- timing of reproduction
- age and size at maturity
- growth pattern
- longevity
- All of these traits are heritable to some degree and thus subject to natural selection.
- Some phenotypic plasticity often occurs.
What is phenotypic plasticity, and why is it important for marine organisms?
Phenotypic plasticity allows organisms to adjust their traits in response to environmental conditions, enhancing adaptability and survival in dynamic marine habitats.
What is the difference between indeterminate and determinate growth in marine organisms?
- Indeterminate growth involves continuous growth throughout an organism’s life
-Determinate growth reaches a maximum size or age before ceasing growth
What is meant by longevity?
- Longevity = maximum age
- In a study on marine sessile organims (241 species) maximum lifespan was estimated to be from a few weeks to thousands of years in some sponges and corals
- In the Greenland shark, Somniusus macrocephalus, maximum longevity was estimated to be 400 years
- highest longevity in cetaceans: represented by the Bowhead whale, Balaena mysticetus –> can live up to 200 years
Why is the longevity of certain marine species significant for ecosystem stability?
Long-lived species play essential roles in ecosystem stability and resilience, but they are also vulnerable to anthropogenic threats such as overfishing and habitat degradation
What is growth rate?
- Change in size in a defined
period of time (day, year, etc.) - Represented by growth
curves - Several models of growth have been
developed for marine organims, as a
consequence, several curves are used: - Von Bertalanffy (asymptotic)
- Gompertz (sigmoid)
- Logistic
- Schnute–Richards
What does K show in this diagram?
- K represents a measure of the curvature,
how fast the animal reaches the
asymptotic length - Low values of K mean a slow growth rate
- High values of K mean a fast growth rate
- Therefore, it is possible to use K to
compare the growth rate of different
species/populations
What is the asymptotic length?
A parameter of the von Bertalanffy Growth Function (VBGF), expressing the mean length the fish of a given stock would reach if they were to grow for an infinitely long period
Which of the 2 species has a lower growth rate?
- Sebastes borealis: Maximum size: 108 cm Maximum age: 157 years
- Sarda sarda: Maximum size: 92 cm, Maximum age: 5 years
Sebastes borealis (K= 0.04) has a lower growth rate in respect to Sarda sarda (K=0.4)
What does this curve show?
The growth curve (Von Bertalanffy) describes the average growth curve for a population.
Several factors can influence growth rate
- Temperature
- Oxygen availability
- NH3
- Salinity
- Competition
- Food availability
- Age
- Attainment of sexual maturity
- Season
Species may be more or less sensitive to the different
factors
What does the study of longevity and growth rates require?
- The estimation of age
- methods depend on the taxon,
environment, resources, etc. - Several methods have been developed for fish, so fish will be used as a model to describe the general methods, pros and cons of the different methods, validation, etc
Growth rate can be estimated growing
animals in controlled condition.
The growth in a defined time period can then be directly measured and growth rate
estimated.
Pros:
The estimate is simple
Cons:
Usually it is performed in a short time
period, often during one season
The captivity conditions can be quite
different from the natural ones
GR = 100 x (Lf – Li) / (tf – ti)
Mark (tag) and recapture methods
- Individuals can be captured, measured, marked and re-measured when recaptured after a certain time.
- Pros: The results refer to natural conditions
- Cons: The recapture rate may be limiting, especially for highly mobile species Tags must not interfere with the normal life of the individuals
GR = 100 x (Lf – Li) / (tf – ti)
Tagging is more and more used for
different studies…
- Estimates of growth rates (and age
validation) - Movement ecology
- Behavioural ecology
- Philopatric behaviours
- Social behaviours
- Fishery management
Recapture may not be necessary
in some cases
Tags must not interfere, especially
in relation to the aim of the study
What are these examples of?
- Natural marks
- E.g. marks on the dorsal fin of dolphins and whales, spots on whale sharks and
other fish, etc. - If natural marks are available, manipulation is avoided.
- Size can also be visually estimated.
In what kind of species is it easier to evaluate growth rates?
- Sessile species
- If the individuals are accessible, they can be marked and measured several times over time.
What do size-frequency distributions reveal about population dynamics in marine ecosystems?
Size-frequency distributions provide insights into population demographics, growth patterns, and interactions between individuals of different ages or size classes within the population.
What are the pro’s and con’s when analysing the size frequency distribution of a population?
- Pros:
Useful if a large amount of data is available,
as for instance for commercial species - Cons:
Curves tend to overlap
It can be used especially for species with
short life cycles
What is the sclerochronology method ?
(For growth and age estimation)
-The investigation of temporally associated life history characteristics through analysis of hard or calcified structures in organisms
- Using structures that grow during the entire life of the animal, with a defined and
recognizable pattern. - These structures must remain for the entire life and not been reshaped, re-absorbed, etc.
- These structures include bones, shells,
otoliths, scales, spines.
What are otoliths?
- Otoliths represent a well studied model for
sclerochronology - These structures are located in the inner ear of vertebrates and are involved in the
perception of linear acceleration, both
horizontally and vertically. - Similar structures involved in equilibrium
are present in many invertebrates and are
called statocysts - In fish the three pairs are called: sagitta,
lapillus, and asteriscus.
