Reproductive patterns Flashcards
What Traits infer about life strategies – determine why organisms are taking a certain approach and why this is making them successful.
Life-history is determined by numerous physiological characteristics or traits
Give some examples of how life history can be determined by these traits.
•Traits include; egg size, egg number, brood frequency, broods per lifetime, body size, sexuality, development type and reproductive effort
Egg size implies whether larvae is lecithotrophic or planktotrophic, and in turn the PLD of the larvae.
Fecundity of organisms. The size of eggs is usually genetic whereas numbers of eggs is still dependant of resource availability such as energy and nutrition.
Some organisms are brooders, such as crustaceans, and numbers are dependant on the frequency of the brood.
reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants.
definition for
parthenogenesis
What phyla is fission common in?
Fission is common in soft-bodied phyla such as Porifera, Cnidaria, Platyhelminthes and some Echinodermata
Not often found in those phyla with a hard external casing
Asexual reproduction - how does fission occur?
- May involve simple transaction into two fragments where each regenerates the missing parts.
- Give rise to multiple fragments, all of which can reconstitute a whole animal
- Fission can often be combined with the capacity for sexual reproduction
- This can create complex life cycles with alternating asexual and sexual generations
- Fission can make the concept of ‘the individual’ complex
- Incomplete fission in colonial animals made up from structural units
Three different ways of asexual reproduction
Budding - clone is small and weak but in the splitting stage the organism is not as any greater danger.
Fragmentation - could be accidental, have to have this ability as they lack the structural integrity.
Fission - daughter organisms is as strong as you are but you are in danger in t
he division. The capacity to defend itself if reduced.
Reproduction via eggs
Modification of meiosis to produce diploid eggs
What is arrhenotoky?
– phenomenon in which unfertilised haploid eggs develop into males and fertilised diploid eggs develop into females
Obligate parthenogenesis
Obligate parthenogenesis is rare (bdelloid rotifers) – eradicating the need for males
Parthenogenesis often occurs cyclically with sexual reproduction i.e.
. Daphnia
Take advantage of short term changes in the environment.
Over 99% of all invertebrates (and most vertebrates) exhibit sexual reproduction at some stage of their life cycle
Sexual reproduction in animals ALWAYS involves FUSION of the gametes; a process referred to as
ANISOGAMY
It becomes possible to recognise male and female functions
When sexes are separate we refer to it as
GONOCHORISM or DIOECY
When the same individual can function as male or female; either simultaneously or sequentially (producing both germ cells and accessory structures)
Simultaneous
Simultaneous – male and female germ cells produced during the adult phase; capacity to donate and receive male germ cells or self-fertilise
Pulmonate land gastropods i.e. Cepaea hortensis
When the same individual can function as male or female; either simultaneously or sequentially (producing both germ cells and accessory structures)
sequential
Sequential – exhibit one sexual function prior to the onset of the other
1.Protandric – male before female; male may then be lost or coexist i.e. Crepidula fornicate. Eggs are more expensive, bigger animals can afford more energy for gametes and have a greater carrying capacity. Sperm are cheap to produce whilst an animal is growing.
2.Protogynous - female before male i.e. Mycteroperca microlepis
3.Sequential alternating – as above but with subsequent reversal
•Number of models to account for evolution of hermaphroditism….consider 3
- Low density model – simultaneous hermaphroditism increases the probability that rare encounters will be with fecund individual; if not then self-fertilisation is possible
- Size advantage model – when one function has an advantage related to size but the other does not then sequential hermaphroditism will be adopted
- Gene dispersal model – low population numbers results in inbreeding and random genetic drift; hermaphroditism increases the effective population size
Male or female offspring? The determination mechanisms for invertebrates fall into 3 basic types
a) MATERNAL; b) GENETICAL and c) ENVIRONMENTAL
Male or female offspring? The determination mechanisms for invertebrates fall into 3 basic types
a) MATERNAL;
Maternal determination
Sex of offspring determined by mother through the production of different types of eggs
Dinophilus gyrociliatus – minute polychaete
2 types of egg in the ovaries
Large eggs = females; small eggs = mature dwarf males
All adults are inseminated females
