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;
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;
