Transcript Life history

7
Life History
Analyses
7 Life History Analyses
• Case Study: Nemo Grows Up
• Life History Diversity
• Life History Continua
• Trade-Offs
• Life Cycle Evolution
• Case Study Revisited
• Connections in Nature: Territoriality, Competition,
and Life History
Case Study: Nemo Grows Up
All organisms
produce
offspring, but
the number
and size of
offspring vary
greatly
Figure 7.1 Offspring Vary in Size and Number
Case Study: Nemo Grows Up
In the movie Finding
Nemo, “Nemo” the
clownfish is depicted
as having a very
human-like family
http://www.solarnavigator.net/films_movies_actors/cartoons/cartoon_images/finding_nemo_doreen.jpg
Case Study: Nemo Grows Up
In real life, clownfish life is
VERY different
 2 to 6 clownfish spend entire
adult lives within one sea
anemone, but are not usually
related
 Largest fish is female
 Next largest is the
breeding male
 Remaining fish are
nonbreeding males
Figure 7.2 Life in a Sea Anemone
Case Study: Nemo Grows Up
 If the female dies, the breeding
male becomes a female – social
control of sex change
 next largest male becomes
the breeding male
 There is strict pecking order
in group, based on body size
and aggression
 Social hierarchy controlled by
female aggression 
suppression of hormonal and
neurotransmitter control of
sex change in subordinate
males
http://www.richard-seaman.com/Underwater/Philippines/Highlights/ClownAnemonefishesAtEdgeOfAnemone.jpg
Case Study: Nemo Grows Up
 The breeding male cares for the eggs until they hatch
 Hatchlings move away from reef as planktonic
larvae, then return as juveniles and find an anemone
to inhabit
 Resident fish allow a new fish to remain only if there
is room
http://farm1.static.flickr.com/83/246270415_d09bd5b52c.jpg
Introduction
Life history
 An organism’s record of events relating to
its growth, development, reproduction, and
survival
 Characteristics that define organism’s life
history:
 Age and size at sexual maturity
 Amount and timing of reproduction
 Survival and mortality rates
Life History Diversity
Concept 7.1: Life history patterns vary within
and among species.
Individuals within a species
show variation in life history
traits
 Differences may be due to
genetic variation or
environmental conditions
 Generalizations about a species
life history traits can still be made
– but must consider variations
http://www.nefsc.noaa.gov/sos/spsyn/af/salmon/images/fig41_2.gif
Life History Diversity
Life history strategy of a species
 Overall pattern in average timing and nature of life
history events
 Determined by allocation of time and energy between
growth, reproduction, and survival
Figure 7.3 Life History Strategy
Life History Diversity
Life history traits influenced by genetic variation are
usually more similar within families than between
them
 Natural selection favors individuals whose life history
traits result in their having a better chance of surviving
and reproducing
Life History Diversity
How and why have
particular life history
patterns evolved?
 Theoretical ideal: Life
histories are optimized
(maximization of fitness)
 Life history strategies are
not necessarily perfectly
adapted to maximize
fitness, particularly when
environmental conditions
change
Two fishes with very different lifehistory strategies and aging
phenotypes. A: Yellow rockfish
(Sebastes reedi), has been estimated to
live nearly 100 years. B: Sockeye
salmon (Oncorhynchus nerka), which
shortly after spawning. Source: U.S.
Fish and Wildlife Service
http://www.senescence.info/nature.html
Life History Diversity
Phenotypic plasticity
 One genotype may
produce different
phenotypes under
different environmental
conditions
 Many fishes develop
different body shapes
dependent on habitat
(flow, diet, structure)
 Another example, growth
and development may
be faster in higher
temperatures
Flow-associated differentiation in the Orinoco
River, Venezuela, channels (fast) and lagoon
(slow). From DeWitt Lab, Dept. Wildlife &
Fisheries Sciences, Texas A&M University
http://wfsc.tamu.edu/faculty/tdewitt/fishwarp.jpg
Life History Diversity
Plasticity in life history traits
can be source of plasticity
in other traits
 Callaway et al. (1994)
studied ponderosa pines
(Pinus ponderosa) grown
under different conditions


Pines grown in cool, moist
climates allocate more biomass
to leaf growth relative to
sapwood production than do
those in warmer desert
climates
results in different tree shapes
http://face.env.duke.edu/PDF/gcb6-00.pdf
Figure 7.4 Plasticity of Growth Form in Ponderosa Pines
Life History Diversity
Phenotypic plasticity may produce…
 a continuous range of growth rates, or…
 discrete types — morphs
Polyphenism
• Single genotype produces
several distinct morphs
 Spadefoot toad (Spea
multiplicata) tadpoles in
Arizona ponds contain both
omnivore morphs and larger
carnivore morphs
Small-headed
omnivore
Large-headed
carnivore
Life History Diversity

Carnivore tadpoles grow faster and
metamorphose earlier  favored in
ephemeral ponds that dry up quickly

Omnivores grow more slowly and are
favored in ponds that persist longer,
because they metamorphose in
better conditions and have better
chances of survival as juveniles

Different body shapes result from
differences in relative growth rates of
different body parts 
 Carnivores have bigger mouths
and stronger jaw muscles
because of accelerated growth in
those areas
Small-headed
omnivore
Large-headed
carnivore
Life History Diversity
Allometry
 Differential growth of body
parts, resulting in differences
in shape or proportion (as
seen in pines and toads)
 Commonly seen between
within and between species
Fig. 3. Spadefoot toads and parsley frogs exhibit
morphological variation across genera. Images
rescaled so snout–vent lengths are
equal, to visualize size-free morphometric
differences. Species with long larval
periods (Pelobates, Pelodytes) show
proportionately longer hindlimbs and
longer snouts. (Scale bars, 1 cm.)
http://www.pnas.org/content/103/50/19021.figures-only?cited-by=yes&legid=pnas;103/50/19021
Life History Diversity
Phenotypic plasticity may be adaptive, or
simply a result of a physiological response
(say to temperature or diet)
 Adaptative value must be demonstrated rather
than assumed
 Fewer leaves and stockier trunks in pines
may be adaptive in dry climates to conserve
water
 Carnivore morph may develop faster with
more protein in diet, so they survive more
ephemeral ponds (but may not survive better
after metamorphosis)
Life History Diversity
Organisms have evolved
many different modes
of reproduction
 Asexual reproduction
 Simple cell division
 Exhibited in all
prokaryotes and
many protists
 Some multicellular
organisms (e.g., corals)
reproduce both sexually
and asexually
Figure 7.6 Life Cycle of a Coral
Life History Diversity
Sexual reproduction has benefits and costs
 Benefits
 Recombination promotes genetic variation
 May provide protection against disease or in different
habitats
 Disadvantages (costs)
 “Cost of males” – an individual transmits only half of its
genome to next generation
 Growth rate of populations is slower
Figure 7.7 The Cost of Sex (Part 1)
“Cost of males” – Each sexual and asexual female can produce four offspring per
generation. BUT…half of the sexually produced offspring are males and must
pair with a female in order to produce offspring. Under these conditions, the
asexual part of the population will reproduce and increase in size more rapidly,
dominating the population in less that 10 generations.
Life History Diversity
Isogamy
 When gametes are of equal size
 Organisms such as the green alga Chlamydomonas
reinhardii have two mating types that produce
isogametes
Two gametes of
the green alga
Chlamydomonas
reinhardii fusing
Life History Diversity
Anisogamy
 Gametes of different sizes
 Usually eggs are much larger and contains more
nutritional material
 Most multicellular organism produce anisogametes
Fertilization in
humans (only one
sperm actually
fertilizes egg)
Life History Diversity
Complex life cycles
 Involve at least two distinct
stages that may have
different body forms and
live in different habitats
 Transition between stages
may be abrupt
 Metamorphosis: Abrupt
transition in form from
larval to juvenile stage
Complex Life Cycle of
Malaria Parasite
http://fullmal.hgc.jp/icons/lifecycle.jpg
Life History Diversity
Most vertebrates have simple life cycles without
abrupt transitions
 But complex life cycles are common in animals,
including insects, marine invertebrates, amphibians, and
some fishes
Typical life
cycle of salmon
http://www.eatonvillenews.net/images/Bob/FISH%20SALMON%20LIFE%20CYCLE%20salmoncycle.jpg
Life History Diversity
Why complex life cycles?
 Small offspring may experience
environment very differently than
larger parents
 For example, a tadpole is more
strongly affected by surface
tension and viscosity than an
adult frog
Adult Gulf Fritillary Butterfly
(Agraulis vanillae) feeds on
nectar from a variety of plants,
but the larvae (caterpillar) feeds
on specific host plants (maypop,
passionvines – Passiflora sp.)
 Parents and offspring can be
subject to different selection
pressures
 Separate food resources
 Offspring as dispersal stage
http://www.cirrusimage.com/butterfly_gulffrit.htm
Life History Diversity
About 80% of animal species
undergo metamorphosis at
some time in their life cycle
 Some species have secondarily
lost complex life cycle and have
direct development
 instead of normal complex
cycle of related taxa, they go
from fertilized egg to juvenile
without passing through a
specific larval stage
 Example: many Plethodontid
(lungless) salamanders
The Seepage Salamander
(Desmognathus aeneus)
undergoes direct development, hatching out as a
juvenile morphologically
similar to adult
http://www.uga.edu/srelherp/salamanders/desaen1.jpg
Figure 7.9 The Pervasiveness of Complex Life Cycles
Mealworm – Tenebrio molitor
Seastar – Asteria rubens
Life History Diversity
Many parasites have evolved complex life cycles
with one or more specialized stages for each host
 For example, the parasite Ribeiroia has three
specialized stages
 Chinese liver fluke (Clonorchis sinensis) has six stages
in three hosts (snails, fish, humans)
Clonorchis
Ribeiroia
http://www.fao.org/docrep/008/y5970e/y5970e04.jpg
Figure 1.3 The Life Cycle of Ribeiroia
Six stages of
Clonorchis life
cycle
http://www.fao.org/docrep/008/y5970e/y5970e04.jpg
Life History Diversity
Many plants, algae, and
protists also have complex
life cycles
 Alternation of generations
 Exhibited by plants and
most algae
 multicellular diploid
sporophyte alternates
with a multicellular
haploid gametophyte
Alternation of Generations
in a Fern
Life History Continua
Concept 7.2: Reproductive patterns can be
categorized along several continua.
Several classification schemes have been proposed
to categorize vast diversity of reproductive patterns
– place patterns on continua with extremes at each
end
 Semelparous – iteroparous
 r-selection – K-selection
 Stress – disturbance (plants)
 Charnov’s life history cube
Life History Continua
How many reproductive bouts occur during
organism’s lifetime?
 Semelparous species reproduce only once
 Iteroparous species can reproduce multiple
times
Life History Continua
Semelparous species include:
 Annual plants
 Agave
 vegetative growth can last up
to 25 years
 but also produces clones
asexually
 Giant Pacific octopus
 females lay single clutch of
eggs and broods them for 6
months
 Female dies after they hatch
http://scienceblogs.com/pharyngula/2006/06/friday_cephalopod_pleased_to_m.php
Life History Continua
 Classic example of semelparity are salmon
 Most spawn once and die
 But some individuals in some species survive to
spawn again
http://www.streamnet.org/pub-ed/ff/factsheets/images/SLCycle.jpg
Life History Continua
Iteroparous species include:
 Trees such as pines and spruces
 Most large mammals
Florida Scrub Jay (Aphelocoma
coerulescens) form family groups
where the parents and previous
years’ offspring will cooperatively
raise the young of the year
http://www.americanscientist.org/Libraries/images/thumbnail/200393015611_307.jpg
Life History Continua
r-selection and K-selection describe two ends of a
continuum of reproductive patterns
 r = intrinsic rate of increase of population (see chapter 9)
 r-selection is selection for…
 high population growth rates in uncrowded
environments, newly disturbed habitats, etc.
 K = carrying capacity for a population (chapter 9)
 K-selection is selection for…
 slower growth rates in populations that are at or near
K (carry capacity)
 in crowded conditions, efficient reproduction is
favored
Life History Continua
r–K continuum is spectrum of
population growth rates, from
fast to slow
 On the r-selected end…
 Short life spans
 rapid development
 early maturation
 low parental investment
 high rates of reproduction

Most insects, small
vertebrates such as mice,
weedy plant species
Dandelion (Taraxacum sp.)
seeds dispersing
http://blinkyblinkyblink.blogspot.com/2007/10
/so-what-you-are-saying-is-that-im.html
Life History Continua
 On the K-selected end…
 Long-lived
 Slow development
 delayed maturation
 invest heavily in each offspring
 low rates of reproduction

African forest elephant
(Loxodonta cyclotis)
Large mammals, reptiles such
as tortoises and crocodiles, and
long-lived plants such as oak
and maple trees
http://www.bio.davidson.edu/people/vecase/Behavior/Spring2004/Bo
ssie/elephant%20pics/SAmomandbabyKNP.jpg
Life History Continua
Most life histories are
intermediate between these
extremes
 Braby (2002) compared three
species of Australian butterflies
(Mycalesis spp.)
 Mycalesis perseus in drier,
less predictable habitats has
more r-selected
characteristics
 Two species (M. sirius and
M. terminus) found in more
predictable wet forest
habitats have K-selected
characteristics
http://lh4.ggpht.com/_9PV3mL2Hbw/Rm0nL14L_mI/AAAAAAAAACM/nZKi_QzcH_
g/Mycalesis+perseus+cepheus+(Dingy+Bush+Brown).JPG
Mycalesis perseus
Mycalesis sirius
http://www.purvision.com/butterflies/website/copyright.gif
Life History Continua
Grime’s (1977) classification scheme for plant life
histories is based on stress and disturbance
 Stress — any factor that reduces vegetative growth
 Disturbance — any process that destroys plant
biomass
 Four habitat types possible:
 Low stress, low disturbance
Three habitats that
sustain plant
 High stress, low disturbance
growth form
points of a triangle
 Low stress, high disturbance
 High stress, high disturbance — not suitable for
plant growth
}
Figure 7.12 Grime’s Triangular Model
Life History Continua
Three species/habitat types:
 Low stress and low disturbance habitat
 competitive plants are selected
 superior in ability to acquire light, minerals,
water, and space
Life History Continua
 High stress, low disturbance habitat
 Stress-tolerant plants are favored
 Features can include phenotypic plasticity, slow
rates of water and nutrient use, and low palatability
to herbivores
Life History Continua
 Low stress, high disturbance
habitat
 ruderal plants dominate
 short life spans, rapid growth
rates, heavy investment in
seed production
 Seeds can survive for long
periods until conditions are
right for rapid germination
and growth
 Ruderal species can exploit
habitats after disturbance has
removed competitors
Figure 7.12 Grime’s Triangular Model
Life History Continua
Comparing Grime’s model to r–K continuum:
 Ruderal plants are similar to r-selected species
 Stress-tolerant plants correspond to K-selected
species
 Competitive plants occupy the middle of the r–K
continuum
Middle of r-K continuum
K-selected
r-selected
Life History Continua
New scheme proposes
“life history cube” that
removes influence of
size and time (Charnov
2002)
 Cube has three
dimensionless axes:
 Size (S) of offspring
relative to adults
 Reproductive life
span (RLS) divided by
time to reach maturity
 Adult reproductive
effort (RE) per unit of
adult mortality
Figure 7.13 Charnov’s Life History Cube
Life History Continua
The third axis (RE) is a measure of reproductive
effort
 Quantity of energy and resources devoted to
reproduction, corrected to take into account costs of
reproduction
Life History Continua
Charnov’s life history cube may be most useful when
comparing life histories across broad range of
taxonomy or size
 Grime’s scheme may be best for comparisons between
plant taxa
 r–K continuum is useful in relating life history
characteristics to population growth characteristics
Trade-Offs
Concept 7.3: There are trade-offs between life
history traits.
Trade-offs
 Organisms allocate limited energy or
resources to one structure or function at the
expense of another
 Trade-offs shape and constrain life history
evolution
Trade-Offs
Trade-offs between size and number of
offspring
 The larger an organism’s investment in
each individual offspring, the fewer
offspring it can produce
 Investment includes energy, resources,
time, and loss of chances to engage in
alternative activities such as foraging
Broadcast spawners
releasing many
thousands of eggs per
spawning versus caring
hundreds of eggs
http://science.nayland.school.nz/graemeb/yr12%20marine
/fisheries/Fish%20Reproduction_files/image003.jpg
Panamanian sergaent major,
(Abudefduf troschelii)
http://www.discoverlife.org/IM/I_RR/0030/320/Abudefduf_troschelii,I_RR3080.jpg
Trade-Offs
http://www.statesymbolsusa.org/IMAGES/Tennessee/northern_mockingbird_web.jpg
“Lack clutch size” – David
Lack (1947)
 Maximum number of
offspring parent can
successfully raise to
maturity
 Clutch size is limited by
maximum number of
offspring parents can raise
at one time
Eggs of Northern Mockingbird
(Mimus polyglottos)
http://content.ornith.cornell.edu/UEWebApp/images/nomo_eggs.jpg
Trade-Offs
Lack noticed that clutch size increased at higher
latitudes
Clutch size 
 perhaps because longer periods of daylight allowed
parents more time for foraging, and they could feed
greater numbers of offspring in a day
Latitude 
Trade-Offs
 Experimental manipulation of clutch size in lesser blackbacked gulls showed…
 in larger clutches, offspring have less chance of
survival (Nager et al. 2000)
Trade-Offs
In species without parental care…
 reproductive investment is measured as resources
invested in propagules (eggs or seeds)
 Propagule size is a trade-off with number produced
 In plants, seed size is negatively correlated with number
of seeds produced
Trade-Offs
Size–number trade-off also occurs within species
 Northern populations of western fence lizards have
larger average clutch size, but smaller eggs, than
southern populations
Mean
Trade-Offs
 Experiments by Sinervo (1990) on lizard eggs showed that
smaller eggs developed faster and produced smaller
hatchlings
 Small hatchlings grew faster, but were not able to sprint
as fast to escape predators
 Selection may favor early hatching in north, because of
shorter growing seasons
 Or faster sprinting speed in the south where there may be
more predators
http://www.mister-toad.com/photos/lizard/Sceloporus_occidentalis_APR07bSIG.jpg
Trade-Offs
Trade-offs between current and future
reproduction:
 For an iteroparous organism, the earlier it reproduces,
the more times it can reproduce over its lifetime
 But not all reproductive events are equally successful
 Often, the number of offspring produced increases
with size and age of organism
Trade-Offs
Atlantic cod increase reproductive output with age
 At 80 cm length, a female produces about 2 million
eggs per year.
 At 120 cm, 15 million eggs per year
http://www.cefas.co.uk/media/70037/fig7b.gif
http://folk.ntnu.no/vmbijmor/jmork/GearSelection/00sicily/cod-pic.jpg
http://upload.wikimedia.org/wikipedia/commons/0/08/Atlantic-cod-1.jpg
Trade-Offs
Overfishing in Atlantic has
resulted in evolutionary
change in the cod’s life
history
 Fishing selectively removes
older, larger fish
 Led to significant reductions
in growth rates and in age
and size at maturity
http://www.fao.org/docrep/003/V4865E/V4865E01.gif
http://upload.wikimedia.org/wikipedia/commons/0/08/Atlantic-cod-1.jpg
Trade-Offs
 Because the largest fish
have greatest reproductive
potential, fishing has
resulted in decrease of total
quality and quantity of egg
production
 This may persist even if
overfishing ends, and may
delay or prevent recovery of
cod populations
http://www.fao.org/docrep/003/V4865E/V4865E01.gif
http://www.cefas.co.uk/media/70037/fig7b.gif
Trade-Offs
If sexual maturity can be
delayed…
 an organism can invest more
energy in growth and
survival, and may increase
its lifetime reproductive
output
 Example: A fish with a 5year lifespan can increase its
total reproductive output by
delaying maturation by one
year, if it has a good chance
of surviving to age 5
# Offspring
# Offspring
Year 1
10
Year 2
20
30
Year 3
30
40
Year 4
40
50
Year 5
50
60
Total = 150
Total = 180
Trade-Offs
There are certain conditions when an organism is
expected to allocate energy to growth rather than
reproduction
 Long life span
 High adult survival rates
 Increasing fecundity with body size
 If rates of adult survival are low, future
reproduction may never occur, so early
reproduction rather than growth would be
favored
Trade-Offs
Senescence
Taronga Zoo's (Sydney) oldest
Chimpanzee ‘Fifi' turns 60
 Decline in fitness of
organism with age and
physiological
deterioration
 Onset of senescence can
set an upper age limit for
reproduction
 Semelparous species
undergo very rapid
senescence and death
following reproduction
http://www.taronga.org.au/imagedata/fifi-200705-rick_stevens-387.jpg
Trade-Offs
 In some large social mammal species, such as African
elephants (Loxodonta africana), post-reproductive
individuals contribute significantly through parental and
grandparental care or contribute to success of the
social group in other ways
 Matriarchs are repositories of social knowledge
http://graphics8.nytimes.com/images/2008/08/11/science/elephants_533.jpg
Trade-Offs
Senescence may occur earlier
in populations with high
mortality rates due to
disease or predation
 Mutation accumulation
hypothesis (Medawar 1952)


suggests that when few
individuals survive long enough
for selection to act against
deleterious mutations that are
expressed late in life
these mutations will accumulate
over time
http://www.azinet.com/aging/Aging_Book_files/image004.jpg
Trade-Offs
 Delayed senescence (postreproductive lifespan) has been
shown in populations of guppies
(Poecilia reticulata)with low
mortality rates (Reznick et al.
2004, 2006).
 In populations where mortality
is high due to predation or
starvation, guppies may be
investing less energy in
immune system development
and maintenance, resulting in
higher rates of senescence
due to disease
http://www.ittiofauna.org/webmuseum/pesciossei/cyprinodontes/poecilid
ae/poecilia/poecilia_reticulata/images/poecilia_reticulata-500.jpg
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1318473
Life Cycle Evolution
Concept 7.4: Organisms face different selection
pressures at different life cycle stages.
Different morphologies and behaviors are
adaptive at different life cycle stages.
 Differences in selection pressures over the
course of the life cycle are responsible for
some of the distinctive patterns of life
histories.
Life Cycle Evolution
Small early life stages are
vulnerable to…
 Predation – usually slower and
fit into more mouths
 Competition for food, or
environmental conditions that
reduce food supplies because
smaller individulas have less
capacity to store nutrients
Many herding mammals will
protect young by the adults
surrounding the young when
predators threaten.
Musk Ox herd (Ovibos moschatus)
 These vulnerabilities are
partially counteracted by
behavioral, physiological and
morphological adaptations
http://www.raydoan.com/images/18032327.jpg
Life Cycle Evolution
But small size can allow early stages to do
things that are impossible for adult stages
White-tail Deer
(Odocoileus
virginianus)
http://www.dec.ny.gov/images/environmentdec_images/youngwildlife30707.jpg
http://www.birdsandblooms.com/photogallery/out_to_lunch/album/slides/Pileated_woodpecker_feeding_young.jpg
Life Cycle Evolution
Parental Investment:
 Many birds and mammals
invest time and energy to
feed and protect offspring
 Other species provide more
nutrients in eggs or embryos
(e.g., in the form of yolks)
Pileated Woodpecker
(Dryocopus pileatus)
parent feeding
fledgling
Fish eggs supplied with yolk
http://www.ufz.de/data/5460
Figure 7.18 Parental Investment in the Kiwi (Apteryx sp.)
http://www.valdosta.edu/~mtrejo/chicken.gi
f
http://static.flickr.com/39/77924849_5a3ca67b95.jpg
Life Cycle Evolution
 Plant seeds may have a large endosperm, the
nutrient-rich material that sustains the embryo during
germination (e.g., the milk and meat of coconuts)
http://www.nature.com/nrg/journal/v4/n5/images/nrg1064-f3.gif
Life Cycle Evolution
Dispersal
 Small offspring are wellsuited for dispersal
 Dispersal can reduce
competition among close
relatives, and allow
colonization of new areas
 Dispersal can allow escape
from areas with diseases or
high predation
Invasive thistles (Carduus sp.)
produce wind-dispersed seeds
Life Cycle Evolution
 Sessile organisms such
as plants, fungi, and
marine invertebrates
disperse as gametes or
larvae — small and
easily carried on wind
or water currents
Giant Barrel Sponge (Xestospongia
testudinaria) releases a cloud of 'sperm'
into the water column during a spawning
http://www.starfish.ch/Fotos/sponge-Schwamm/Xestospongia-testudinaria-spawning1.jpg
Life Cycle Evolution
Dispersal has evolutionary significance
 Hansen (1978) compared fossil records of gastropod
species with swimming larvae versus species whose
larvae developed directly into crawling juveniles
 Direct-developing species tended to have smaller
geographic distributions and were more prone to
extinction
Veliger larva
(echinospira type) of
the modern marine
snail Marsenina
stearnsii
http://web.uvic.ca/~lpage/Lam_complarva_live2copy.JPG
Figure 7.19 Developmental Mode and Species Longevity
Life Cycle Evolution
Diapause
 State of suspended animation or dormancy —
organisms can survive unfavorable conditions
 Many seeds can survive long dormancy periods
 Many animals can also enter diapause
Larvae
Adults
Larval beetles (Trogoderma
spp.) may enter diapause with
falling temperatures or
overcrowding
http://www.the-piedpiper.co.uk/graphics1/warehousebtl.jpg
Life Cycle Evolution
Small size is advantageous for diapause because
less metabolic energy is needed to stay alive
 Amoeboid protists form a hard shell or cyst that allows
them to survive dessication
 “Sea monkeys” are brine shrimp eggs (cysts) that can
survive out of water for years
Artemia (fairy shrimp, sea monkeys)
http://phytoshadd.com/images/brine%20shrimp.jpg
http://www.huaxianglife.com/UploadProductPic/200753118555175.jpg
Life Cycle Evolution
Different life history
stages can evolve
independently in
response to sizeand habitat-specific
selection pressures
 Complex life cycles
can help minimize
drawbacks of small,
vulnerable early
stages
http://www.oceaninn.com/guides/crust-cycle.gif
Life Cycle Evolution
Functional specialization of stages is a common
feature of complex life cycles
 Many insects have larval stage that remains in small
area, such as on a single plant (many butterflies)
 The larvae are specialized for feeding and growth, and
have few morphological features other than jaws
Black Swallowtail
(Papilio polyxenes)
http://login.greatbignews.com/userfiles/103/images/CopyofP7091687.JPG
Life Cycle Evolution
 The adult insect is specialized for dispersal and
reproduction
 Some adults, such as mayflies, are incapable of feeding
and live only a few hours
Dragonfly larva
eating a captured
tadpole
http://www.wmconnolley.org.uk/diary/2000/05/Dscn0512-dfly-tadpole_crop.jpg
http://lizlargent.files.wordpress.com/2008/04/dragonfly_life_cycle1.jpg
Life Cycle Evolution
In marine invertebrates,
larvae are specialized for
both feeding and dispersal
in ocean currents
Bipinnaria larva of a sea star (Luidia sp.)
about 2.75 mm in length, collected from
surface waters (~30 m depth) in the Gulf
Stream, offshore from Fort Pierce, FL.
 Many larvae have
specialized feeding
structures called ciliated
bands covering most of the
body
 They may also have spines,
bristles, or other structures
to deter predators
http://www.biolbull.org/content/vol204/issue3/images/medium/coverfig.gif
Figure 7.20 Specialized Structures in Marine Invertebrate Larvae
Crab zoea
larave
Life Cycle Evolution
Even in organisms without abrupt shifts
between life stages, different sized and aged
individuals may have very different
ecological roles
 Size- or stage-specific ecological role has been
called an ontogenetic niche by Werner and
Gilliam (1984)
Life Cycle Evolution
 In species with metamorphosis, there should be
theoretical optimal time for life stage transitions
 should occur when organism reaches size at
which conditions are more favorable for its
survival or growth in adult habitat than in larval
habitat
Life Cycle Evolution
Nassau grouper (Epinephelus striatus) is an
endangered coral reef fish
 Juvenile stages stay near large clumps of algae
 Smaller juveniles hide within algae clumps, larger
ones stay in rocky habitats near the clumps
http://programs.wcs.org/Portals/1/Nassau%20Grooper%20small.jpg
Life Cycle Evolution
 Dahlgren and Eggleston
(2000) tethered and
enclosed juveniles of
different size in the two
habitats
 Found that smaller
juveniles are very
vulnerable to predators in
rocky habitats
 But larger juveniles were
not, and were able to
grow faster there
 Support Werner’s idea
that niche shift was timed
to maximize growth and
survival
http://www.oar.noaa.gov/spotlite/archive/images/spawn_grouper.jpg
Life Cycle Evolution
In some cases metamorphosis
is delayed, or eliminated
 Some salamanders can become
sexually mature while retaining
larval morphologies and habitat
— called paedomorphic
 In mole salamander, both
aquatic paedomorphic adults
and terrestrial metamorphic
adults can exist in same
population
 The proportion of paedomorphic
forms is dependent on predation
pressure, food availability and
competitors
Facultatively paedomorphic mole
salamander, Ambystoma
talpoideum
Case Study Revisited: Nemo Grows Up
Change in sex during the life cycle is called
sequential hemaphroditism
 Sex changes should be timed to take advantage of
high reproductive potential of different sexes at
different sizes
The slipper shell, Crepidula fornicata, a
protoandrous sequential hermphrodite.
Smaller males stack on top of larger
females.
Size advantage hypothesis of sex determination and sex change
Gonochorism,
iteroparous, males
compete for females
Protandrous, iteroparous,
random mating
Gonochorism,
semelparous 
small males and
larger females
Protogynous, iteroparous,
females choose larger
males
http://www.marinebiology.org/images/sexchange.GIF
Case Study Revisited: Nemo Grows Up
Size advantage hypothesis helps explain sex
changes in clownfish and the timing of those
changes relative to size
 But it does not answer question of how and why
growth is regulated to maintain hierarchy of
clownfish within each anemone
http://static.flickr.com/41/78457739_0a375918eb_o.jpg
Case Study Revisited: Nemo Grows Up
 Buston 2003 conducted experiments with the clownfish,
Amphiprion percula
 Subordinates remain in anemone by regulating
growth rates to stay within ~80% of next larger fish
 If two fish become similar in size, a fight results and
one is expelled from anemone
http://tolweb.org/treehouses/?treehouse_id=3183
Figure 7.23 Clownfish Size Hierarchies
Case Study Revisited: Nemo Grows Up
 Removal of breeding male from
an anemone resulted in growth of
the next largest male
 but only until it could take
place of breeding male, not
large enough to threaten
dominant female
 Clownfish avoid conflict within
their social groups by exerting
remarkable control over their
growth rates and reproductive
status
http://farm3.static.flickr.com/2288/2437920279_553454638c.jpg
Connections in Nature: Territoriality, Competition, and Life History
Why do clownfish maintain hierarchy?
 Completely dependent on protection by sea anemone
 They are easy prey outside the anemone.
 Conflicts result in expulsion and death, probably
without having reproduced
http://tolweb.org/treehouses/?treehouse_id=3390
Connections in Nature: Territoriality, Competition, and Life History
 Strong selection pressure to avoid conflict
 Growth regulation mechanisms have evolved because
individuals that avoid growing to a size that
necessitates conflict are more likely to survive and
reproduce
 Fish live together for tens of years, so it is reasonable
to maintain “harmony” within a group – increases
chances of moving up into breeding position over time
 Buston found that remaining in anemone and biding
time offered better chance of reproductive success than
leaving to find a new anemone
Connections in Nature: Territoriality, Competition, and Life History
Sea anemones are scarce resource for clownfish
 This controls ontogenetic niche shifts
 Juveniles returning to reef must find an anemone that has
space, where it will be allowed to stay and enter hierarchy
http://i.pbase.com/o6/83/627283/1/84102685.I4n5IrrD.clownfishfaceon.jpg
Connections in Nature: Territoriality, Competition, and Life History
“Settlement lotteries” also affect other species that
compete for space
 Long-lived tree species in tropical rain forests compete for
space and sunlight
 Success of any one seedling may depend on chance
events, such as death of a nearby tree that creates a gap
in the canopy
http://upload.wikimedia.org/wikipedia/commons/thumb/0
/0f/Rain_forest_NZ.JPG/800px-Rain_forest_NZ.JPG
Connections in Nature: Territoriality, Competition, and Life History
Complex life histories appear to be one way to
maximize reproductive success in such highly
competitive environments
Coral reefs are often
referred to as the
“rainforests of the seas.”
Space is often a limiting
resource in many reef
systems.
http://latimesblogs.latimes.com/photos/uncategorized/2008/07/09/coral_reef_beauty.jpg