Evolutionary Pathways, Sexual/Asexual Reproduction, Sex Determination, Plasticity and Contingency, Life Histories, Reproductive Patterns, Insect Lifestyles, Control of Reproductive Success, Synchronicity, Cycles and Diapauses, Facilitating Phases
Invertebrate Zoology
Week 7
Chris Foster
Reproduction and Life Styles
Hypothesis; evolution is a natural consequence of systems that persists by a semi-
conservative process of replication
- All living things possess same genetic program
- Variation arises from mis-copying of base sequences during replication of DNA
- Commonality of genetic structure is widely divergent organisms
- Evolution of multicellular organisms require replication of genome, construction of
differential cells and replication of organism [reproductive]
- Reproduction allows genetic recombination [mechanism for exchange of genetic
material between parental types]
- Genetic material increases in complexity / capacity for novelty generation is
enormous [function of number of chromosomes for number of independent
maternal/paternal recombination’s]
Evolutionary Pathways;
1. No sexual reproduction
2. Acquisitions of mechanisms for limited recombination. Meiosis, producing sex cells
[gametes]
3. Evolution of separate mating types [usually 2]
4. Anisogamy; adoption of small mobile M gametes and larger immobile F gametes
5. Appearance of gender, separation of M/F functions in different individuals.
- Invertebrates diversify of expression of sexuality among them
- Living invertebrates span adaptive shifts
o Acquisition multicellularity
o Continuous obligate sexuality and involvement of parental care
- Germ cells;
o Spermatozoa and egg;
o Derived from specialized cells aside early embryonic development [not
universal]
o Derived from de-differentiated stem cells
- Adult organism tests efficacy of gene combinations set aside from germ cells. Early
segregation; genetics tested as must carry lineage through reproduction. Sexual
reproduction returns to single sell in life-cycle.
- Asexual reproduction not have constraints; involve multicellular propagules [seen in
budding] when meiosis not happening, still involves periodic return to single cell
[parthenogenesis]
Sexual/Asexual Reproduction in Invertebrates;
- Alternative of sexual/asexual form – common in cnidaria [Obelia; between asexually
reproducing polyp colony and medusa] Common in parasitic flatworms and annelids
which producing “satellite” individuals – precursor to sexual reproduction.
- Invertebrate reproductive strategy – differ in lifestyle traits.
, Invertebrate Zoology
Week 7
Chris Foster
1. Asexual reproduction;
o Offspring nearly identical genetic constitution to parent organism
a. Subdivision of existing body into >2 multicellular parts
b. Production of diploid eggs [parthenogenesis]
2. Fission;
o Common in soft bodied phyla [porifera / cnidaria] transverse fission in major
groups, characteristics of scyphozoan jellyfish.
o Not found in those with external casing / unknown in Mollusca and arthropod
o Fission simple transection into 2 fragments, regenerates missing parts or give
rise to multiple fragments with reconstitute whole animals.
o Fission combined with capacity for sexual reproduction [incomplete -colonial
organisms]
o Colonial organisms; increased number of structural units identifies with
individuals of non-colonial relatives. Subunits have specialized roles [complex
siphonophoran]
o Colonial structures frequent in cnidaria, bryozoan and urochordates.
3. Parthenogenesis;
o Widespread – asexual reproduction via eggs used to refer to fission
o Meiosis suppressed, eggs diploid [don’t fuse with M germ cells]
o Obligate parthenogenesis with no sexual reproduction = very rare [found in
bdelloid rotifers – M never been observed – ancient asexual]
o Insects with rare males [1000 species, widely scattered, low incidence in taxa
= exhibit sexual reproduction]
o Recently derived from sexually reproducing forms, frequently occurs
cyclically [episodes of sexual reproduction] 15,000 restricted to 7 taxonomic
groups.
o Successful rotifers/freshwater crustacea, aphids
Growth rate maximum in parthenogenic phase and lifecycle
Maximum exploitation of temperature, underexploited food source,
other constraints limits body size [aphid colonies]
Appearance of sexually reproducing M/F = change in environmental
conditions [crowding/food quality/shortening day]
Morphological changes associated with transition to sexual
reproduction.
What is an individual?
- Individuals, unique organisms created by sexual reproduction
- Ramets; intuitive individuals single body components [head defines one individual]
- Genet; asexual reproductive phase animals with same genome.
Sex Determination;
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller jemradford011. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $11.07. You're not tied to anything after your purchase.
