S ELECTION FOR INDIVIDUAL SURVIVAL AND REPRODUCTIVE SUCCESS CAN EXPLAIN DIVERSE BEHAVIORS Chapter 51, Section 3 August 31, 2015-Septermber 1, 2015

O PTIMAL F ORAGING M ODEL 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 Benefit Obtain enough food to survive/reproduce VS.

B ALANCING R ISK AND R EWARD 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 Paternity Internal 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. 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 ground- squirrel/spermoph ilus- 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. r = coefficient of relatedness C = cost (how many fewer offspring) B = benefit (how many extra offspring)