WEEK 5
Lecture 2015/02/04 (WED)
Behavioral Adaptation for survival and foraging
What is adaptive behavior?
Adaptive behavior—a behavior that gives higher inclusive fitness to an individual; more than any other existing alternative exhibited by other individuals within the population
Inclusive fitness—the sum of both direct fitness (fitness gained through offspring) and indirect fitness (fitness gained by helping relatives raise additional offspring they would not be able without help)
(Biologists often use an adaptationist approach to test hypotheses on the possible adaptive valve (value?) of a particular trait/behavior)
Cost-benefit approach to the study of adaptive behavior
All behaviors have cost (C) as well as benefits (B).
Fitness costs—The aspects of a behavior/trait that reduce the number of surviving offspring
Fitness benefits—The aspects of a behavior/trait that raise the number of surviving offspring
Trait is adaptive if B > C, Trait is optimal if B-C is maximal
Question about adaptation:
1. Is the behavior/trait adaptive?
a. Two approaches to study this question:
i. Comparative (across species) method ii. Within-species method
2. Is the behavior or trait optimal?
a. Use of Optimality theory
i. Optimality theory is based on the assumption that the attributes of organisms are optimal ii. Theory is used to generate hypothesis about the adaptive value of behaviors/traits in terms of net fitness gained by exhibiting such traits
EXPAND on Question: Is the behavior/trait adaptive?
Comparative (across species) method
Analysis of function based on the comparison of convergent species (2 or more species of distant common ancestry that have similar traits due to similarity of their environments/ecological niches)
Example: mammals (bat) and birds (Swallow), they have some same traits (=convergence!)
Example: sperm competition in primates
When multiple mating occur, increased sperm count provides an increase chance of fertilization
A greater number of sperm are produced by larger testes
Prediction: testes size should be larger in species with sperm competition (multiple male matings)
How to test? (Compare primate species)
Monogamous (unusual)—gibbons, owl monkeys, humans
Single male groups—langurs, gorillas
Multi-male groups—chimpanzees
Results:
Graph: Allometry plot of testes weight vs. Body weight
Single-male and monogamous primate species tend to fall below the line (Expected on the basis of allometry) while the multi-male species tend to fall above it
Sperm competition in multiple-male group! Larger body weight correlated to testes weight
Example: Parent-offspring recognition in swallows
Prediction: parent-offspring recognition should be adaptable in highly colonial species where the recognition of offspring is important for parents to recognize their own offspring among many individuals
Results from 4 species of swallows:
Bank swallow: highly colonial, young move from nest to nest when mobile, subsequently stay in large creches awaiting parents returning to feed them. Recognition is highly developed.
Cliff swallow: also highly colonial, also highly developed recognition
Rough-winged swallows: more or less solitary, no apparent recognition
Barn swallows: more or less solitary, occasionally small colonies; no apparent recognition
Summary:
Species
Colonial?
P.O. recognition
Bank Swallow
Yes
Yes
Roughwing swallows
No
No
Cliff swallow
Yes
Yes
Barn Swallow
No
No
Molecular phylogeny of swallows (?)
Question: for these 4 species, how many times can we say recognition has been gained?
Within-species approach (method) to the same problem
Example: Sperm competition in Swallows
When multiple mating occur, increased sperm count provides an increased chance of fertilization
Male should allocate more sperm to mating were sperm competition is more likely
Prediction: Male should allocate more sperm to mating when in competition with a rival
Results:
Male bank swallows (called sand martins in Europe) should guard mate during
