SELECTION FOR INDIVIDUAL SURVIVAL AND REPRODUCTIVE SUCCESS CAN EXPLAIN DIVERSE BEHAVIORSChapter 51, Section 3

August 31, 2015-Septermber 1, 2015

OPTIMAL FORAGING MODEL

Foraging behavior is a compromise between the benefits of nutrition and the costs of obtaining food.

According to this optimal foraging model, natural selection should favor a foraging behavior that minimizes the costs of foraging and maximizes the benefits.Costs•Energy Expenditure•Risk of Predation

BenefitObtain enough food to survive/reproduce

VS.

Think Economics!!!

BALANCING RISK AND REWARD One of the most significant potential costs to

a forager is risk of predation. Maximizing energy gain and minimizing energy

costs are of little benefit if the behavior causes the forager to be preyed upon.

Example: Mule deer that live in the mountains of western North America

Mating Behavior and Mate Choice

Just as foraging is crucial for individual survival, mating behavior and mate choice play a major role in determining reproductive success.

• Seeking or attracting mates• Choosing among potential mates• Competing for mates• Caring for offspring

Mating Systems and Sexual Dimorphism

Monogamous• One male mating with one

female.

• Little sexual dimorphism.

Polygamous• Polygyny: a single male and multiple

females.

• Polyandry: a single female and multiple males.

• Large amount of sexual dimorphism. The sex that attracts multiple mating partners is typically showier and larger than the opposite sex.

Mating Systems and Parental Care

Monogamous• High paternal care.

• Maximize reproductive success by ensuring offspring survive.

• Example: most newly hatched birds cannot care for themselves.

Polygamous• Low paternal care.

• Maximize reproductive success by seeking other mates.

• Example: mammals (usually lactating female is often the only food source).

The needs of the young are an important factor constraining the evolution of mating systems.

Certainty of PaternityInternal

Fertilization• Low!

• The acts of mating and birth are separated over time.

• Some behaviors may increase certainty.

External Fertilization

• High!

• Egg laying and mating occur together.

• May explain why parental care in aquatic invertebrates, fishes, and amphibians is at least as likely to be by males as by females.

***Parental behavior correlated with certainty of paternity exists because it has been reinforced by natural selection.

Sexual Selection and Mate Choice

• Intersexual Selection: members of one sex choose mates on the basis of characteristics of the other sex.

https://www.youtube.com/watch?v=W7QZnwKqopo

• Intrasexual Selection: involves competition between members of one sex for mates.

• Example: Stalk-eyed flies• Female choice.• Male competition.

Inclusive fitness can account for the evolution of behavior, including

altruism

Chapter 51, Section 4

September 1, 2015

• Tinbergen’s fourth question: the evolutionary history of behaviors.• Topics to be Covered

• Genetic control of behavior.• Genetic variation underlying the evolution of particular behaviors.• Expanding the definition of fitness beyond individual survival can help

explain “selfless” behavior.

Genetic Basis of Behavior

Variation in a single locus is sometimes sufficient to bring about dramatic differences in behavior.

• Male meadow voles: solitary, no lasting mate relationships, low paternal care.

• Male prairie moles: form pair-bond with single female, high paternal care.

• Influence of Vasopressin (neurotransmitter)• Highly expressed in brains of prairie voles.• Experiment

Meadow Vole

Prairie Vole

Vasopressin

Genetic Variation and Evolution of Behavior

• Differences in behavior can be found within species.• When behavioral variation between

populations of a species corresponds to variation in environmental condition, it may be evidence of past evolution.

• Case Study: Variation in Prey Selection• Organism: western garter snake.• Coastal population diet: banana slugs.• Inland population diet: frogs, leeches, and

fish.

Altruism

• Definition: a behavior that reduces an animal’s individual fitness but increases the fitness of other individuals in the population.

• Example: Belding’s ground squirrel

http://www.arkive.org/beldings-ground-squirrel/spermophilus-beldingi/video-00.html

Inclusive Fitness

• The selection for altruistic behavior is most readily apparent in the case of parents sacrificing for their offspring.

• William Hamilton proposed that an animal could increase its genetic representation in the next generation by helping close relatives other than offspring.

Inclusive fitness: the total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables other close relatives to produce offspring.

rB > Cr = coefficient of relatednessC = cost (how many fewer offspring)B = benefit (how many extra offspring)