Nature vs Nurture

The development of an organism is an interactive process between genes and the environment

As an organism develops….

  • Genetic information interacts with changing internal and external environemnts
  • Genes become turned on and off by signals (expressed/repressed)
    • Signals are internal/cellular/chemical or external environmental stimuli (neurochemical/hormonal)
  • These interactions alter the assembly of the organism- its neural networks as well as other aspects of its physiological/anatomical systems
  • Central Dogma: DNA  → Transcription →  RNA  → translation → protein →  gene expressed

“Honey Bee (Apis mellifera linnaeus)” by Jim (CC BY 2.0)

Development of worker behavior in honey bees:

  • Variation in tasks is age dependent (cleaning, feeding, packing pollen, foraging). Younger bees work within the nest as nurses and then transition with age to become foragers.
  • Gene activity varies in the brains of “nurse” bees and “foragers”. Opposite gene activation patterns were observed in the analysis of their gene expression.
  • The Juvenile Hormone (JH): low concentrations are found in nurse bees, there are increased levels in the forager bee. A nurse bee treated with JH will begin to forage. Remove the JH glands of a forager and it will revert to nursing behaviors.
    • Hormonal influence on gene expression.
  • JH gene boosts at about 3 weeks. This is activated by the social behavior of their environment.
    • In the presence of foragers, the nurses had lower levels of JH
    • In the absence of foragers, the nurses had higher levels of JH
    • When older bees are added the colony, the young bees remain nurses. The presence of many foragers inhibits JH expression.
    • When many young bees are added to the colony, the resident young bees will transition to forager bees and the JH gene is expressed.
  • Older bees inhibit the transition to forager in others by manufacturing a compound called ethyl oleate. Secreted by glands within the crop.
    • An Ultimate Explanation: to ensure that there are enough nurses and foragers within the colony to sustain the hive. An adaptive adjustment to the ratio of nurses and foragers.

Environmental Influences: 

  • Environmental Factors are critical for every element of gene expression within organisms.
  • The environment supplies the molecular building blocks (RNA bases, amino acids, etc.) that are essential for DNA translation.  Sources include food and the atmosphere.
  • Gene Expression → environmental factor → gene expression → environmental factor
  • The combination of a constantly changing internal and external environments of the organism that influence the expression of genes.

“DNA is both inherited and environmentally responsive” -Gene Robinson

“Tea for Cockatoos” by Rob and Stephanie Levy (CC BY 2.0)

Begging Calls and Contact Calls in Galah and Cockatoo:

  • Reciprocal swap test for hatchlings: the babies that were placed in opposite nests will continue to do the begging call of its species but will make the contact call of the species that raised it.
  • Genes constructing the learning system may be responsible for these differences-the environmental influence of the types of calls that these birds can make.
  • Most traits are an interactive relationship between several different genes: polygenic
    • Learning is a polygenic trait
    • Genes are responsive to important sensory stimuli

“Galahs” by Ed Dunens (CC BY 2.0)


  • The result of gene-environment interactions
  • Imprinting of baby geese on the first thing they see after hatching
  • Genes construct learning systems and genes are responsive to important sensory stimuli
  • Cross-fostering has different imprinting effects in two related species of songbirds.
    • Female Blue Tit fostered Great Tit hatchlings and vice versa.
      • GT fostered by BT pair with BT
      • BT fostered by GT pair with GT
    • Environmental differences: a Polistes wasps learn to recognize nestmates from odors and facial markings

“Eastern Garter Snake” by Fyn Kynd (CC BY 2.0)

  • Genetic Differences: cause behavioral differences among individuals.
    • A coastal Californian garter snake (Thamnophis elegans) has differences in their diets in different populations.
      • Inland populations eat fish and frogs
      • Coastal populations eat banana slugs – genetic adaptations to handle the slime of the slug?
      • Take hatchlings (naïve individuals) raised in the lab fed with generic food. Then give them slugs to determine if the baby snakes will consume slugs.
      • Data showed that inland baby snakes did not eat slugs regardless of lack of experience with other food. The coastal snakes did eat the slugs when they were introduced. -suggests genetic differences
      • Inland snakes tongue flicked at tadpole extract but not slug extract. Coastal snake tongue flicked at both extracts. ~ an evolutionary hypothesis: Inland ancestral non-slug eating population migrated towards the coast and alleles for slug eating become more abundant in the coastal regions because of the abundance of slugs as a prey source.

“Mouse” by Jason Bolonski (CC BY 2.0)

  • Sometimes a single gene can have a large influence on a behavior that is expressed. This is due to cascading events on the cellular level to activate/deactivate other genes.
    • For mice, a single gene affects maternal behavior. The gene fosB is responsible for maternal behavior. Those without this gene will be neglectful.
      • The environment still affects maternal behavior
      • Cascading effects on other genes into the phenotypic behavior that is observed.
      • Environmental cue causes this gene to be expressed. The olfactory stimulation from her pups activates the gene.



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Proximate and Ultimate Causation

“Astronomy Evolution 2” by Giuseppe Donatiello (CC0 1.0)

  • Physiological adaptations and evolutionary history of the species.

Proximate Causation: a nervous system component to create a preference.  For exmaple, taste bud receptor create a preference for sugary foods due to the carbohydrate energies that they provide. Send neorons to the brain to induce a preference (neoronal). Short term, physiological explanations for behaviors.

  • Genetic Components-developmental mechanisms influence the assembly of an animal and its internal components, including the nervous/endocrine systems.
  • Neuronal Components-hormonal mechanisms develop within an individual within a lifetime. Influences behavior.

Ultimate Causation: long term, evolutionary adaptations as it is affected by descent with modification from ancestral species.

  • Adaptive Value: a behavioral trait as affected by the process of evolution by natural selection.
  • Example: mate guarding to ensure that all of a females offspring will be sired by the male.

Examples of causation:

“Prairie Voles” by theNerdPatrol (CC by 2.0)

Monogamy of Prairie Voles: neural stimulation through vasopressin is induced when the male spends time with a female- he receives positive neural rewards.

  • Proximate cause: avpr1a gene codes for V1a protein receptor– the expression of the gene influences the male to spend more time with the female, more vasopressin is then released.
  • Flow Chart:
    • The History of the Vole
    • The Internal Changes

Previous evolutionary history in the lineage leading to the prairie vole  –>  the spread of adaptations by natural selection in previous generations of the vole –> the genes that have survived to the present prairie voles –> Developmental system of young voles –> physiological system of adults, including the brain –> Behaviors including mating behaviors are influenced            –> contribution of genes to the next generation, the reproductive success of individuals  –> ev olution by natural selection continues.

“White-Crowned Sparrow” by Irene (CC0 1.0)

White-crowned Sparrows of the same species develop different dialects in different populations.

  • Causes?..
    • Possible genetic differences may affect the neural mechanisms
    • Environmental differences in Alaska and Washington may affect the experience and learning in the young males to influence their singing behaviors/dialects.
  • Research that was done:
    • Raised white crowned sparrows in the lab from the Marin and Berkeley populations.
      • Some raised in isolation- they only twittered
      • Some listened to tapes of adult male songs at 10-50 days:
        • Started singing at 150 days
        • Full song by 200 days
        • Sang the dialect that they heard, regardless of which nest they came from.
      • The data supported the idea that the young males were learning the songs through their environmental surrounding.
      • Other experiments showed that:
        • Deaf birds that could not hear themselves sing, did not mimic the song correctly. Shows the importance of hearing oneself sing.
        • Lab raised, isolated white crown sparrows will not sing songs of another species. Will only twitter.
          • Genetic composition within sparrows construct the learning system, are responsible for physiology.
        • Young white crowned sparrow can selectively store white crowned acoustical information while ignoring the songs of other species.
        • Male birds have larger song system nucleus than the female birds. The song system is called the RA and is a region in the brain that has measurable amounts of aldehyde dehydrogenase.
          • When birds listen to longer songs, there tends to be an increase in the RA size of that bird.
          • Social learning is powerful.
        • Proximate mechanisms include neurophysiology and genetic activity:
          • Part of the brain where song memories are stored
          • Part of the brain that controls sound production
          • Neural mechanisms involved in song matching
          • Flow Chart:

Key sensory (environmental) inputs –>  gene activity  –>  changes in biochemistry  –> alters neurophysiological mechanisms (song control system) –>  learning.

“Parrot” by D Coetzee (CC0 1.0)

Song Learning in Birds:Two phylogenies of song learning in birds: hummingbirds and parrots/passerine songbirds.

  • If all three of these groups were derived from a common ancester: they would have similar song control systems. Studies showed that the three groups are very similar in the RA suggesting a song learning common ancester that was lost in other groups of birds. Is more likely than convergent evolution.
  • “Hummingbird” by C Watts (CC by 2.0)

    Disadvantages to learning to sing: learning  a dialect and multiple songs is a time and energy investment.

  • Develop adaptive dialects that can be recognized easily by conspecifics so as to be more effective in a particular habitat.
    • There are differneces in Great Tit birds singing in dense forrests and open woodlands.
  • Song Matching to a Social Environment: repertoire matching allows neighbor recognition and variation in communication. The territorial success of a male depends on how many different song types he shares. The response to the focal bird will influence the future interactions between the birds.
  • Males that learn songs of particular dialects may be more attractive to females.
    • Females get information about his developmental history and suitability to a particular habitat.
      • It was found that females chose males who could copy their tutor more often than males who could not.
    • Nutritional stress in the early stages of life will affect the song learning ability of male swamp sparrows.

“Black-Crested Titmouse” by Andy Morffew (CC by 2.0)

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Reproductive Behaviors

mating, courtship, & parental care

“Colorful Peacock Head” by Daniel (CC by 2.0)

Males are vibrant, bigger, more vocal on average…why?

Bowerbird species: males build elaborate nests,  and the observed behavior appears to be ritualized. Females come and inspect nests to determine if she will mate with the male. Variation in reproductive success is greater for males than females in the satin bowerbird. Males typically have more mating partners than females

Why is the bower attractive to a female? Some possible suggestions are:

  • Demonstrates the scavenging ability of the male
  • Indicates fitness
  • Bower building is correlated with brain size
  • Positive correlation found with bowerbird IQ and mating success

Sexual selection: Traits influence the fitness of the individual, traits that lower survival but enhance the ability to mate are sexually selected traits.

“Male Peacock Spider” by Bron (CC by 2.0)

For Example: Colorful patterns make the male more visible to predators….but it attracts mates more often so his genes are passed onto the subsequent generations.

****tension between natural selection and sexual selection****

It is different from mate choice

  • Male and female gametes differ greatly in size
    • Female eggs are energetically costly, fewer are made than male counterpart, spend a lot of time nurturing and raising young ~ protect the investment.
      • In order to ensure survival of her offspring she will mate with males that are of higher quality so that her time and energy investment ultimately increases her personal fitness.
    • Males can mate repeatedly and often due to a less energetically costly gamete that is rapidly made.
  • Operational Sex Ratio: Male biased. There are more males available/ready to mate but only a few females are sexually receptive (some are already pregnant/raising young). With a greater proportion of males the females are able to be more selective.
    • Actual sex ratio that is seen in nature  is 50/50 for male/female
      • Frequency dependent

Parental investment influences sexual behavior due to gamete size, form of parental care, and the resources given to mate.

  • Low parental investment: is seen when there are low numbers/quality of donations, higher sexual selectivity, competition for mates, the goal is to have more mates to create an increase in fitness.
  • Higher parental investment: more donations of better quality are given to the mate, less sexually active, selection among mates, better mate quality leads to an increase in fitness.

Conventional roles: males fight for mates as females are less available due to gestation/offspring rearing. Males tend to be more elaborate.

“Dad to be” by Owen Evans (CC BY-SA 2.0)

Sex Role Reversal: 

  • For example: males with a larger parental investment, in populations that have more sexually receptive females than males, competition among females instead of between males is seen, male mate choice predominates.
    • Seahorses brood pouch: females lay eggs directly into the pouch of the male.
      • Predator protection
      • Females can mate with many males
      • Males are able to be more selective about mate choice
      • the females tend to me more elaborate and colorful

“Female Seahorse” by Peter C (CC by 2.0)

Nuptial gifts: males give an edible gift to females to attract her and mate.

  • The some crickets and grasshoppers produce spermatophore which provide protein to the female and thus the fertilized eggs. This is an energetically expensive process for the males and so the payoff of mate choice must outweigh the cost of developing the gift. After it is deposited into the female, she etas the edible part. Bigger spermatophores will attract the females.

“Shield-back Katydid with spermatophore” by Judy Gallagher (CC by 2.0)

Food availability affects sex roles 

  • Low food abundance: not many males can produce the spermatophore. Creates a sex role reversal because only a few males produce the gift. Men get to choose and females compete for access.
  • High food abundance: all males are able to make the spermatophore. Females get to choose because there is an abundance of males that produce the gift.

Convergent evolution in male weaponry: many different species have horns

“Pronghorn Buck” by USFWS Mountain-Prairie (CC by 2.0)

“Southern White Rhino” by William Murphey (CC BY-SA 2.0)


Pecking order: a dominance hierarchy among males

  • Ritualized aggression
  • Options for subordinate males:
    • Female friendships
    • Banding together with other subordinate males to fight off a dominate male

Alternative Mating Tactics

Conditional Strategy: low ranking males can make the best of a bad situation (form alliance), higher fitness payoffs by adopting alternative tactic rather than fighting dominant male.

  • A male Panorpa scorpionfly: will defend dead insects to entice females, secretion of saliva will provide nutrients to female but is costly to the male, or forcing copulations.
    • If you remove the top ranking males that have killed an insect, will the saliva secretors switch to insect killers? Studies have shown that they either stand by the dead insect or kill their own.
      • A genetically based strategy: If one strategy has more fitness then the behaviors will change to the dominant strategy. Since all three of these strategies still exist in the population, they are equivalent in fitness benfits.
  • Satellite males: low ranking males can get some female access by attaching to female like in horseshoe crabs. The stronger males will get about 90% of the fertilization, the satelites do get to fertilize about 10% of the female’s eggs. “Sneaker males”

“Horshoe Crab” by U.S Fish and Wildlife Services (CC by 1.0)

Genetically based straegies or Conditional strategies:

  • Genetic differences create morphological differnces that cannot change becuase that are genotypically influenced.
  • Conditional strategies are alternative tactics that have the same mean reproductive success such as multiple types of mating behaviors.
  • Competition for access to mates has developed interesting adaptations to aide in mating.
    • The male damslefly has an apendage that can remove the sperm of another male so that he can mate with her instead.
    • Mate guarding behaviors occur in baboons and some fish species. Evolved in response to female promiscuity where females had more choice in mate selection.
    • Mating plug of male spiders. A pedipalp is used to transfer sperm to females and this detaches so that she cannot mate again. Females are less frequent and losing the apendage is less costly than never finding another female or other males removing his genetic material from the few females around.

“Male spider with black pedipalps” by John Flannery (CC BY-SA 2.0)

Sexual Cannibalism:  in some species, one sex (usually the female) consumes the other during sexual reproduction.

  • Is the cannibalism an offer to the female?
  • Is it the female choosing to eat the male?
  • Will she eat the male before a successful mating?
  • Examples: Praying mantis, scorpions, Austalian redback spiders

Sexual Suicide: the ultimate nuptial gift, the male will most likely have no other mating opportunites. The male Austalian redback spider will somersault into the mouth of the female to provide nutrients to offspring and ensure mating success. The male is controlling this decision.

Male Ornamentation and Courtship Displays

  • Good Parent Theory: females prefer to mate with males that provide more paternal care. Courtship is linked to his parental abilities.
  • Healthy Mate or Good Genes: bright coloration can indicate good foraging ability, good health, stronger immune system because they are able to sustain themselves and are free of disease and parasites. The male has inherited these traits from his offsrping and can therefor pass these traits onto his own offspring.
  • Do male ornamentations actually signal good genes?
    • The male peacock tail: the mean area of the eye spots indicates the size of his tail which has a postive correlation with the survivorship of his offspring.
  • Runaway Selection: ornamentation that is very excessive, it is a sexually selected for trait. Female mate choice is inherited and the genes for male attribute is inherited together. Daughters inherit trait preference, males inherit preference. The preference for the trait is selected for, not the gene/ornamentation/fitness benefits. More elaborate traits have been shown to lead to decreased fitness.
    • Bird of Paradise
    • Stalk-eyed flies
    • Natural selection will outweigh the sexual selection over time.

“Stalk-eyed fly” by Bernard Dupont (CC BY-SA 2.0)

  • Chase-away selection theory: sensory exploitation. Preexisting bias in females leads to a mutuation in male display traits (explotation). This can lead to a decrease in fitness because the male may or may not benefit her fitness. The threshold for female mate choice will increase, the males will have to continue to exagerate the trait to overcome the sensory bias.
  • Sexual Conflict: females resist matings, often have control over which mates get to mate, males develop traits that enhance his ability to even if it lowers female fitness.
    • Such as: forced copulations, infanticide, tranfer toxic substances during mating.




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Optimality Theory

Predicts that animals should behave in a way that…

  •       Maximize benefits
  •       Minimize costs
  •       Maximize net energy gain

                Central Assumption: the more net energy an individual gains, the greater reproductive success (fitness)

  • A range of costs and benefits for a particular behavior that has various phenotypes.
  • Adaptations occur when the behavioral phenotype has more benefits than costs.
  • The phenotype with the highest benefit relative to cost will be the adaptation compared to what is happening in the rest of the population.
  • Benefits > costs =maintained trait

Costs and benefits of group size:

Costs: Competition for resources/mates

Benefits: group protection

Peak benefits when “covey” size is at optimal (not too small/not too big)

“covey” = group of birds

“ibis group” by Michelle Galloway (CC BY 2.0)

Optimal foraging:

Maximize amount of energy gained, minimize cost  of obtaining food.

(Ex.) Reto Zach’s observations: crows only chose large whelks (snails); fly to about five meters up before dropping onto the rocks to break shell, continue to fly and drop until it breaks (even if many trials are required)

  • Predictions: if crows are foraging optimally then…
    •   Large whelks should be more likely than small ones to shatter after a drop of 5 meters
    •  Drops of less than 5 meters should have lower breakage rate
    •   Drops of more than 5 meters should not greatly improve cracking whelk
    • Probability of breaking is independent of the number of drop
  • Results:
    •  At any height the large whelks take less drops to break
    • Increased height of drops does not significantly change number of drops needed
    • The hypothesis that crows forage optimally is supported.

“Whelk” by Bernard Spragg. NZ (CC0 1.0)

Profitability of prey = energy gained per unit handling time

  • Young garden skinks lower their foraging success in order to reduce the risk of predation. Forage on crickets, hide from predators (snakes).
    • The benefit of avoiding predators outweighs the cost of losing food.
  • Risk of predation/parasites/disease affects optimality model.

“Skink” by Robyn Jay (CC BY-SA 2.0)



Alternative Foraging Strategies:

  • Differences within populations
  • Evolutionary process
  • Genetically based strategies maintained by frequency-dependent selection. Two distinct strategies are maintained. Both strategies both have fitness benefits.
    • Fitness depends on rarity- as you become more frequent you become less fit. Fluctuations between the best fit behavioral genotypes.
  • Conditional strategies based upon environmental conditions
  • Geographical separation and divergence
  • Conditional strategy: inherited mechanism that gives an individual the ability to be flexible
    • Neospintahrus trigonum are predators and eat host spiders
      •  kleptoparasites -steal prey
      • They also steal webs from host spiders
      •  commensals -take food that is unavailable to hosts-when they are babies
      • scavenge for deserted webs when it is a baby.
      • Environmental pressure influence
      • More likely to steal webs when there are many hosts
      • More likely to be kleptoparasites/commensal when the hosts are large.
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The Struggle for Food

Scavenging, Hunting, Avoiding predators

Avoiding becoming food is a huge selection pressure for animals

Predator Defense:

  • Group Defenses like the mobbing behavior by gulls: harass/chase to scare off predators (hawks) to protect eggs and juveniles as well as against other hawks/large birds in their area. The adaptation of mobbing is beneficial and they do not distinguish between predatory hawks or non-predatory birds. The adaptation is not perfect but increases fitness of the individuals in the population because all potential predators are scared off and the offspring are able to survive. Predator is more likely to get attacked as it moves closer into the colony of gulls.

The Comparative Method:

  • Look at two closely related species to study a behavior.
  • For example: To test if mobbing is a protection against predators, observe two populations of gulls.
    • one nests on the ground
    • the other nests in high cliffs where predators are less likely to attack so there is less predation pressure.
    • Measure through observations of the mobbing behavior of both populations.
    • Possible reasons:
      • Ground nesting populations moved to cliffs to avoid predators?
      • Divergent Evolution? Predict that cliff nesters should not mob if mobbing evolved as a defense against predation.
      • Or is there convergent evolution? Test if two unrelated species who live in high predation areas exhibit mobbing behaviors due to similar selection pressures.
        • For example: Gulls and colonial California ground squirrels exhibit mobbing behaviors.

Social Defenses:

  • Zebras live  together in large groups.
    • Their stripes make the group have “disruptive coloration” so predators have a harder time distinguishing one from another. Called the “confusion effect”.

      “Zebras” by Kathleen Steeden. (CC by 2.0)

  • Dilution Effect: probability of being eaten in a large group.
    • 100% chance of being eaten if alone
    • 10% chance of being eaten if in a group of ten
    • Increase group size will decrease the probability of being eaten.
    • Larger groups size costs: more visible, resource limitations
    • For example: mayflies swarming and coming all out together is explained by the dilution effect
  • Many Eyes Hypothesis: more individuals around means more can be searching for food/being lookouts for predators.
  • Many Legs Hypothesis: social spiders (Anelosims eximius) living in Peru together in one web and can feel the predator vibrations on the nest, more legs can feel the vibrations and lead attack against the predator.

    “Social Spiders (Anelosimus eximius) communal web” by Bernard DUPONT (CC BY-SA 2.0)

  • Flooding effect: starling murmurations fly in very large groups which creates a dilution effect, and they also exhibit mobbing behaviors.

Selfish Herd

  • Animals in the center of the heard are less accessible to predators, so individuals behaving selfishly they jockey for positions in the center. Old and weak individuals are typically shuffled to the outside of the herd and are typically picked off.

Game Theory:

  • The success of an individual depends on what its competitors within the group are doing.

Distraction Displays:

  • direct the attention of the predator away from a vulnerable prey to one that is more likely to escape.
  • Broken wing act of some birds to lure predators away from the nest
  • Sonoran Desert Toad can intake air to expand body size


  • Mimic background to hide from a predator. Camouflage, coloration and morphology allow the animal to blend into the environment to avoid predation.
    • For Example: the stick bug
  • Aggressive Mimic: predator blends into environment so it can attack prey.
    • Spiders that look like ants
    • Crab spiders that blend into flowers

Aposematism: bright coloration that advertise toxicity

  • Poison dart frogs
  • Sea slugs

    “Strawberry Poison Dart Frog (Oophaga pumilio)” by Carpar S (CC by 2.0)

Mimicry: when an organism resembles other species.

  • Batesian- harmless species mimics a harmful one
    • Hoverfly mimics a wasp
    • Bumblebee moth
    • Monarch Butterfly-aposematically colored and toxic due to the consumption of milkweed. They are mimicked by other species “Viceroy” butterfly. Blue-jays vomit up monarch butterflies due to the toxicity and learn/remember to not eat them again.
      • Ratio of mimics never gets too high because the bluejay will keep eating those non-toxic mimics.
      • System reinforcement by the memory of predator and negative effects of consuming a monarch.
  • Mullerian- two or more unpalatable (not edible) species resemble each other. Amplify signal and take advantage of the predators learning capabilities.
    • Queen butterfly looks like a monarch but it too is also toxic. It tapped into the learning mechanism of Blue-Jays.
  • Stotting Springbok– why make itself conspicuous?
    • Hypothesis:
      • A signal to conspecifics that a predator is close (alarm/social cohesion)
      • Confusion effect?
      • Signal unprofitability- it’s not worth eating me!!
    • Predictions:
      • Solitary gazelles will not stot
      • If stotting is a confusion effect then the rump will be. shown to predator
    • Observations have shown that solitary springboks will actually be seen stotting to signal to predator that it is too fast to be caught. The observations also show that predators fail or give up on stotting springboks.
      • Stotting is an honest signal because evolution tends toward honesty.



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What are adaptations?

  • Adaptations: a process of change in genotype/phenotype that occurs over several generations that increases the fitness of the individuals undergoing the process.
  • Adaptations have to be better than an alternative trait in order for the trait to be considered an adaptation. This does not mean that the trait is perfect. The benefit to fitness must be greater than the cost to their fitness. Traits with highest benefits become the adaptation as these genes are the ones that survive  and are passed onto the following generations.
    • Example: the panda has five fingers but no thumb so the wrist bone had adapted to help them grasp bamboo.

      “Panda” by steews4 (CC BY-NC-ND 2.0)

  • Maladaptive traits: the benefit out-weighed the cost of the behavior due to past environmental conditions, however,  a  novel environment can cause the trait to be less beneficial.
  • Pleiotropy: one gene cause multiple phenotypic effects
  • Genetic drift: random changes in gene frequencies within a population over time. More likely to occur in smaller populations because changes are more dramatic if certain individuals are eliminated and their genes removed from the population.
  • Gene Flow: Intermixing of two different populations, individuals move from one population to another and breed.
    • Can be maladaptive if the environments of each population are drastically different. An individual moving into the other population and breeding would be passing on genes that are not suited to the new environment.
      • Agelenopsis aperta a spider in Texas live in two different areas and have two different behavioral phenotypes.
        • The dessert grassland population are in harsh environment with low predators so musytbe aggressive to catch prey.
        • The Riparian population are in a more favorable environment, there are more predators in this favorable environment so this spider population are more cautious. More variety of prey so they are more selective in the prey they go after.
        • Either one moving to the other location will have an unfit aggressive response.
        • Arizona has similar populations but there is more gene flow so the Riparian population is more aggressive and less cautious than predicted from the Texas observations.

“Funnel Web Spider” by Renee (CC by 2.0)

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Communication Between Animals

“Peacock tail display” by Vibin JK (CC by 2.0)

As you must know, animals cannot speak English, French, or Chinese. So how is it that animals communicate? Signals indicate intent and animals rely on a variety of visual, auditory, and mecanosensory signals to understand their other animals and make decisions.

Important Terms

  • Conspecifics:  members of the same species
  • Heterospecifics: members of different species
  • Types of Signal Modalities: ways in which animals communicate information to one another.
    • visual displays to signal information to another. For example, the fiddler crab mating dance. Success in finding a mate relies on the physical movements the crab makes, the size of the claw, and its coloration.
    • auditory signals are heard by the receiver and sometimes nearby eavesdroppers who can hear the signal as well.
    • chemical signals that are  left behind by the sender. For example, the odor that is left behind from a cat rubbing against tree so that other animals will smell and become aware of that cat’s presence.
    • electrochemical chemical secretions or emission of electric pulses sends information to nearby conspecifics /heterospecifics.
    • mechanosensory modalities are physical contact such as touching and grooming. This is seen in chimpanzee groups who groom each other.
    • Animals can often undergo multiple modalities at once.
      • ie. a bird dances and sings to attract a mate- which uses a visual and auditory modalities to signal to the female that he is a good mate choice.
  • Sender/Receiver: The sender is the organism that creates the signal wile the receiver is the organism that is experiencing and gaining knowledge from the signal.  The signal must benefit both the sender and receiver for the signal to be adaptive. The receiver may change behavior after experiencing signal from sender.
    • Use of signal is a positive evolutionary trait- the allele combination and the phenotypic expression increase the individual’s fitness.
  • Eavesdropper: An individual is picking up on a signal that was not intended for it. This can be seen in predatory species who hear a finch’s social call and is able to locate and eat that finch.  Exploitation of the signal can be maladaptive for the sender.


“Meercats” by Nigel Swales (CC BY-SA 2.0) 

  • Meercat sentry behavior is a protective behavior, if a predator is seen then the sentry will call out so that everyone within range of hearing the call can hide.

Reasons for Communication:

  • sexual advertisement and mate attraction-  Antlers on a deer, bird dancing
  • parental care -begging of babies so that they are fed, recognition-know which offspring is yours
  • Environmental information-predator alarms, food location
  • Territory defense and conflict resolution
  • Social integration-contact calls to signal over others, especially in family groups, dialects can develop within various groups of the same species
  • Predator Defense-warning coloration

“Strawberry Poison Dart Frog (Oophaga pumilio)” by Caspar S (CC by 2.0)


Sensory exploitation:

  • Communication signals originate in actions that activate pre-existing sensory abilities of receivers.
  • The male water mite triggers predatory response of female to mate with her. Hungry females will mate more.
  • African Cichlid Fish: male has bright orange spots on anal fin, female may try to pick up what appear to be eggs on the fin. External sperm production fertilizes the female when she tries to get the dots on his tail. Mutually beneficial—adds to probability that this will continue to evolve over time.
    • Possible Experiment: add orange dots to a male of a closely related species to see if it will cause the females to exhibit the same behavior as the female cichlid fish. ***retention of an ancestral trait****
  • Coloration on spiders attract insects and prey. Only the signaler benefits from this sensory communication. Coloration is a fitness benefit for the spider.


  • Selection only acts on pre-existing traits that developed for a past environmental situation.
    • Panda Principle: The panda has five fingers but no thumb so over time the wrist bone has come to function as a thumb. Ancestral pandas walked on all fours, but as they started walking upright and needed to grab bamboo the wrist bone developed into a thumb-like structure.
    • Moths can detect ultrasonic sounds of bats (predator defense) ~and over time in some species like the whistling moth males can produce ultrasonic sounds that will attract females ~“tapped into evolutionary potential”
  • Behaviors that animals exhibit are part of its evolutionary history.

Conflict Resolution:

Why waste time, energy or risk death?

  • Mantis does a harmless threat display instead of fighting.
  • Barking Gecko: small ones have high pitches bark; large ones have low pitch bark. Predators ans other geckos can distinguish the two and decide whether or not to fight.
  • Another example- antler flies and deer bucks use size to determine dominance, however, they do not fight to the death

“Deer-Newport News Virginia” by C Watts (CC by 2.0)

Honest signaling

  • Communication and signal modalities accurately depict the organism’s size and abilities to others.
  • Live to fight another day
  • For example, Collard lizards have UV reflective patch on their mouths. The bigger patches correspond to larger mouth so smaller subordinates back off and do not risk death.

Dishonest signaling

  • Is selected against because it creates conflict and has a great fitness cost.
  • More black color on face of paper wasps indicates that it is more aggressive. Wrestling occurs between conspecifics to test this assumption. The stronger wasps with the black survived throughout evolutionary history, passing the aggression and black color onto the next generation. This is an example of selection favors honest signaling. If the black faced wasps were weaker then they would have died off during the wresting displays and the yellow faced wasps would be the more aggressive type.

Signal Deception

  • male Photinus flies flash to attract female of their species but sometimes a female Photuris responds instead and she eats him instead of mating. Different species of fireflies have evolved different flash patterns-speciation
  • Illegitimate signaler: an individual makes a signal to fool members of another species.
  • Signal deception in plants for exmple- The Elbow Orchid has flowers with lip that looks like a female wasp. The males are attracted to the plant and thus the pollen is spread.
  • Carnivorous plants-looks like a flower for bugs to get pollen and nectar from but uses a visual display to deceive prey.

Maladaptive Behavior

Why do animals sometimes do the wrong thing? Get fooled by a signal and die?

  • doing something that decreases an animal’s fitness
  • Novel Environment Theory: An animals adaptations are based upon previous environments in which its ancestors lived. New environments, constraints, or human interference to create alternative environmental situations cause an animal’s adaptations to decrease in their fitness benefits. For example, the introduction of plastic bags to sea turtle environments, plastic bags look like jelly fish which they evolved to eat but eating a plastic bag kills the turtle.
  • Female hyenas have a pseudopenis. Sensory exploitation? Maladaptive-makes it hard to mate, need to be aggressive to get food? Greeting ceremony benefit?
  • Net Benefit Theory: if you never respond you will never mate. Cost vs benefit where the potential benefit greatly outweighs the potential cost to fitness.
  • Adaptations (benefits > costs of traits) are not always perfect. Just must contribute more to fitness on average compared to other alternative traits for survival and reproduction of the genes associated with that behavior/adaptation.


  • intercepting/hearing/seeing a signal to use for one’s own benefit.
  • Bats can hear a frog’s mating calls and locate it so that it can eat it.
  • A finch could be social calling to others and a predator swoops in and eats it.
    • adapt to use a frequency/volume that the predator cannot hear
      • “seet call” so hawk cannot hear
      • “mob call” calls in conspecifics to attack hawk.
      • Via predation pressure in an evolutionary ancestor due to eavesdropping of the predator.


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A child watches a group of adult birds all cooperating to feed the nestlings and he smiles to himself. Pointing to the birds he tells his mother that like him, they love their family and want to help care for each other. She smiles too and takes him inside for lunch as they discuss the matter of love….

Do animals love though? That is a question that has perplexed many. However, what the little boy was witnessing was actually what we call social behavior. Altruism [1] by definition is a selfless act to benefit the well-being of another individual. Human beings are known to have empathy and act altruistically but do non-human, non-sentient creatures act altruistically? Or is it possible that there are underlying causes that we are overlooking for this behavior in animals?

Social behavior in animals has benefits and costs. These outcomes determine the longevity and fitness of individuals within a population. Cooperation and competition are two key elements of social behaviors. For example, looking at emperor penguins, they tend to form large groups which not only increases genetic variation and offers group protection but also leads to cooperation to find resources. However, with larger numbers, resources become limited leading to competition for food and mates. The group is easily spotted by predators and disease can easily run rampant. These costs and benefits to social groups has lead many to further investigate why animals would indeed act altruistically.

After many observations it has become apparent that altruistic behavior while decreasing direct fitness at that moment, increases indirect fitness and is overall still beneficial for the individual that is offering the assistance. For example in some bird species, there is postponed cooperation where the mating success of one bird is eliminated for a time while it aids another to increase its mating potential. The alpha male is the only one that would mate, but the beta male will participate and forfeit this season so that it may inherit the area in a following season.

Another example of altruistic behavior would be reciprocity as seen in mutual grooming of monkeys. This direct relationship is mutually beneficial for both monkeys involved. Another example of reciprocity is seen in vampire bats who colonize together and blood share. This is beneficial because if one shares with another today, if tomorrow the hunt is unsuccessful, the debt will be repaid. reciprocity is usually only seen in long-term social groups so that assistance will assuredly be repaid.

An interesting social behavior in birds that the little boy had pointed out to his mother was the evolution of helper birds at the nest. This has occurred in about 10% of birds species and is an example of how direct fitness is lost while indirect fitness is gained. Group living is beneficial in that it offers protection and assistance in scavenging efforts. This has arisen due to a long-term shortage of nesting sites due to a low dispersal from origin of birth in these species. These is typically a low adult mortality rate in these populations and therefor nests rarely become available. To test this one could either decrease the bird population and see if nests are taken over, or add more nests and see if helpers take them over.

These birds are also typically monogamous [2] so that siblings are more related to one another. The siblings assist in raising the next season’s babies so that the helper may inherit the nesting location at some point in the future. Since the siblings share genes these helpers are receiving indirect fitness by raising healthy and successful new genetically related siblings. This observation has lead to a hypothesis that genetic relatedness affects behavior in animals…..



Direct Fitness: a measure of personal reproduction.

Fitness: an organisms ability to to produce offspring. It is the number of offspring relative to a population, a comparison. Which individuals genes dominate the next generation?

Indirect Fitness: a measure of the number of relatives that an altruist/helper helps to survive and reproduce.


[1] “Altruism.” Merriam-Webster, Merriam-Webster, 2018, www.merriam-

[2] “Monogamy.” Merriam-Webster, Merriam-Webster, 2018,



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