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Lecture 11: Individual Variation

Lecture 11: Individual Variation. The biological importance of individual variation has recently been reemphasized in the fields of comparative physiology, functional morphology, animal behavior, behavioral ecology, as well as eco/evo physiology.

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Lecture 11: Individual Variation

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  1. Lecture 11: Individual Variation

  2. The biological importance of individual variation has recently been reemphasized in the fields of comparative physiology, functional morphology, animal behavior, behavioral ecology, as well as eco/evo physiology. It is also coming into medicine, spurred by the availability of genetic data (e.g., SNPs) that clearly demonstrate differences among individuals (and among "racial" groups, although that is a political hot potato!):Childs, B., C. Wiener, and D. Valle. 2005. A science of the individual: Implications for a medical school curriculum. Annual Review of Genomics and Human Genetics 6:313-330. Sometimes these genetic variants correlate with disease susceptibility, psychiatric conditions, etc.

  3. However, an appreciation of the fundamental importance of individual variation is not new to these and related fields. For example, Tryon, R. C. 1942. Individual differences. Pages 330-365 in F. A. Moss, ed. Comparative psychology. Prentice-Hall, New York. outlined four main problems thatshould be addressed when studyingindividual variation.He was talking about psychology,but his points also apply to physiology, morphology, etc. https://mikemcclaughry.files.wordpress.com/2013/02/robert_choate_tryon_-_oss_r__a_division.png

  4. Four main problems that should be addressed when studying individual variation (Tryon 1942): 1. How consistently do individuals differ and how large are those differences? 2. Does individual variation in one (behavioral) domain correlate with variation in other types of (behavior)?

  5. Four main problems that should be addressed when studying individual variation (Tryon 1942): 1. How consistently do individuals differ and how large are those differences? 2. Does individual variation in one (behavioral) domain correlate with variation in other types of (behavior)? This leads to the question of whether non-human animals have personalities? This is a controversial topic …

  6. It is now generally accepted that human personality includes five primary factors: extraversion openness conscientiousness neuroticism agreeableness each of which includes a number of subordinate facets. Human personality is typically measured via questionnaires, not specific tests of people in various settings.

  7. "In the introduction of his presidential address to the American Society of Naturalists in 1938, the eminent primatologist, Robert Yerkes underscored the idea that personality could be found in animals: "I am assuming that personality is the correct and adequate term for what is now known concerning the integrated behavior of the chimpanzee. Indeed, in my present thinking there is no question about the reality of chimpanzee mind, individuality, and personality" (Yerkes, 1939, p. 97). Yet in 1954, Hebb and Thompson described receiving looks of "open astonishment" (p. 532) when they presented the idea that animals should be of interest to psychologists interested in social behavior. Even today, the idea of "animal personality" is often treated with skepticism or even ridicule. However, as this article documents, the body of research on animal personality is growing. If properly implemented and interpreted, this research may be able to provide important insights into the genetic, biological, and environmental determinants of personality that could not be achieved by relying on human research alone." Gosling, S.D., 2001. From mice to men: What can we learn about personality from animal research? Psychological Bulletin 127:45-86.

  8. Behavioral ecologists also recently became interested in animal personality. Different definitions of animal personality have emerged in this field. Under the broad definition of personality, any repeatable behavior can technically be termed a personality trait, as repeatability implies that differences among individuals show at least some statistical consistency.

  9. More useful is a narrow-sense definition of personality (Reale et al. 2007) which, as presently construed, emphasizes: general activity exploration boldness aggressiveness sociability because these traits potentially underlie an individual’s behavior in many different contexts (e.g., mating, parental care, agonistic interactions, foraging, dispersal).

  10. Personality Factors Human Non-Human extraversion general activity openness exploration conscientiousness boldness neuroticism aggressiveness agreeableness sociability The five commonly recognized personality factors are not the same in humans and other animals.

  11. Personality Factors Human Non-Human Non-Human Measure extraversion general activity home-cage activity openness exploration novel open-field test conscientiousness boldness reaction to a predator neuroticism aggressiveness mirror test agreeableness sociability reaction to conspecific

  12. Four main problems that should be addressed when studying individual variation (Tryon 1942): 1. How consistently do individuals differ and how large are those differences? 2. Does individual variation in one (behavioral) domain correlate with variation in other types of (behavior)? 3. Does individual variation in behavior relate to underlying differences in physiology and morphology? 4. Are individual differences caused by genetic differences among individuals?

  13. Remember that individual variation is the raw material on which selection acts, so to those four we can add the more field-oriented question not mentioned by Tryon (1942): 5. Does individual variation in morphology, physiology or behavior correlate with Darwinian fitness in nature. In other words, is selection acting on the individual variation that presently exists for a trait? This is one direct way to study "adaptation" in the genetic, evolutionary sense.

  14. We will discuss all of these components in more detail, and how they can actually be measured. For now, we need to know how to quantify and study individual variation. Individual differences can be documented by measuring each of a series of individuals multiple times and testing for significant "repeatability" of the differences among individuals.

  15. "Repeatability" has a specific definition in quantitative genetics, but for now just think of it as any statistic that takes on a high value when individuals are consistently different and a low value when they are not. For example, is the rank order of individual values consistent across trial days?

  16. The Western Fence Lizard, Sceloporus occidentalis

  17. The rank order of sprint speed, measured on a photocell-timed racetrack, is rather consistent (and statistically significant) across 5 successive trial days. Bennett, A. F. 1987. Inter-individual variability: an underutilized resource. Pages 147-169 in M. E. Feder, A. F. Bennett, W. W. Burggren, and R. B. Huey, eds. New directions in ecological physiology. Cambridge Univ. Press, Cambridge, U.K.

  18. How dowe treat "outliers" (unusual observa-tions)?

  19. Was this a measurement error? How dowe treat "outliers" (unusual observa-tions)? Having a bad day?

  20. Figure 1. Mass-adjusted values of VO2rest and VO2act in 10 males of Scinax sp. 1. Bars are standard errors of three measurements. To facilitate visual comparisons, we present graphs of residuals of a regression analysis of the logarithm of body mass that have been adjusted to the overall mean body mass (3.20 g) and then reconverted to the original arithmetic scale. Resting 10 Individual Frogs,each measured 3 times: both resting and active metabolic rate show reproducible differences among individuals, but resting and active values do not appear to be correlated. Active Gomes, F. R., J. G. Chauí-Berlinck, J. E. P. W. Bicudo, C. A. Navas. 2004. Intraspecific relationships between resting and activity metabolism in anuran amphibians: influence of ecology and behavior. Physiological and Biochemical Zoology 77:197-208.

  21. Daily blood pressure measurements taken on one human subject at random times over 4 months (11/79-2/80). Iberall, A. S. 1984. An illustration of the experimental range of variation of blood pressure. Am. J. Physiol. 246 (Regulatory Integrative Comp. Physiol. 15):R516-R532. Fig. 1.

  22. Problems with and/or Objections toStudies of Individual Variation 1. Extreme values are atypical or abnormal and do not reflect the true response of most individuals. Essentially a restatement of the typological species concept. Real populations do have highly unusual individuals! These "abnormal" individuals do exist and hence must be considered. Selection and inheritance in the real world applies to them.

  23. Example: Garland, T., Jr. 1988. Genetic basis of activitymetabolism. I. Inheritance of speed, stamina,and antipredator displays in the garter snakeThamnophis sirtalis. Evolution 42:335-350. The 46 dams gave birth between 2 August and 6 September 1984. Litter size ranged from one to 26(mean = 12.2, SD =5.15). Of the 562 offspring produced,23 were born dead (frequencies were 10, 5, 2, 2, 1, 1, 1, and 1 individuals born dead in each of eight different families); another 13 were born with obvious deformities (eight with kinked tails, bodies, or necks; one with deformed ventral scales; four with one or both eyes small or absent); there were no more than two deformed individuals in any one family.

  24. Example: 249 of the offspring were tested for maximal sprint speed on a photocell-lined racetrack and for endurance on a motorized treadmill moving at 0.4 km/h. Both tests were done twice, on consecutive days. This is a histogram for the higher endurance: Range = 1-23 min But this does not account for the individuals born dead or severely deformed! Endurance (min) log10 Endurance (min)

  25. 2. Extreme points are attributable to instrumentation or procedural error;do not result from real biological differences. Typical physiological procedure might be to do5-10 preparations (e.g., isolated muscles in ergometer), then throw out the 1 or 2 that were fairly different from the rest. Unusual points assumed to represent preparation errors, e.g., a damaged muscle. Difficult to know if the measure cannot be repeated on a single individual. If the "preparation" can be repeated, e.g., most measures of whole-animal physiological traits, then we can rule out this possibility.

  26. 3. The variation is real (errors of measurement apparatus are not very large) but reflects random and unrepeatable responses of individuals; intra-individual variability is so high that there is no significant inter-individual component to total variance. Significant repeatability across trials answers this.

  27. Most typically, repeatability is quantified by measuring individuals on each of two days. A scatterplot is made. The Pearson product-moment correlation coefficient, r, indicates repeatability.

  28. No Repeatability N = 50 R = 0.066 looks like a shotgun blast, random scatter 1:1 line

  29. High Repeatability N = 50 R = 0.894 often found for morphometric traits, e.g., relative leg length 1:1 line

  30. Typical Repeatability N = 50 R = 0.517 fairly typical for behavioral and physiological traits 1:1 line

  31. Example: Harris, M. A., and K. Steudel. 2002. The relationship between maximum jumping performance and hind limb morphology/physiology in domestic cats (Felis silvestris catus). J. Exp. Biol. 205:3877-3889. 1:1

  32. Example: Garland, T., Jr. 1988. Genetic basis of activitymetabolism. I. Inheritance of speed, stamina,and antipredator displays in the garter snakeThamnophis sirtalis. Evolution 42:335-350. 1:1 N = 231, r = 0.696 log10 Endurance (min) Day 2 log10 Endurance (min) Day 1

  33. Lacerta vivipara from southern France This species gives birth, rather than laying eggs, and the newborns are ready to run! Sorci et al. 1995. Physiological Zoology 68:698-720.

  34. Newborn Lacerta vivipara Note double log transform! Raw data are highly right-skewed. A few individuals are exceptional. Treadmill endurance is more repeatable than sprint speed, possibly because the latter is determined more by inherent physiological capacities for exercise, whereas the former is more determined by motivation? Sorci et al. 1995. Physiological Zoology 68:698-720.

  35. Long-term Field Repeatability not measured * indicates P < 0.05 * * * Hatchling body size does not predict yearling body size. * van Berkum et al. 1989. Functional Ecology 3:97-105.

  36. Long-term Field Repeatability * * indicates P < 0.05 * * Hatchling sprint speed does not significantly predict yearling sprint speed. * van Berkum et al. 1989. Functional Ecology 3:97-105.

  37. Long-term Field Repeatability * * * * Hatchling endurance does predict yearling endurance. * van Berkum et al. 1989. Functional Ecology 3:97-105.

  38. Angilletta, M. J., Jr., P. H. Niewiarowski, and C. A. Navas. 2002. The evolution of thermal physiology in ectotherms. Journal of Thermal Biology 27:249-268.

  39. Why is repeatability important? If a trait is not consistent, but varies wildly from day-to-day, then selection has no clear "target." Teleologically and anthropomorphically, selection cannot penalize the bad individuals and reward the good ones, because these get mixed up every time selection "looks." Similarly, if the "quality" of parents varies wildly from day-to-day, then they cannot pass it on to their offspring. In general, repeatability sets an upper limit to heritability.

  40. Analytical Uses of Individual Variation: 1. Testing or generating hypotheses about functional relationships 2. Measurement of selective importance: Field studies - later lectures correlational experimental Lab studies - useful because ... correlational experimental 3. Determining heritabilities of organismal or physiological characters

  41. Natural& Sexual Selection Act On Behavior Constrain This is the general model we usually have in mind in ecological/evolutionary physiology. Garland, Jr., T., and P. A. Carter. 1994. Evolutionary physiology. Annual Review of Physiology 56:579-621. http://en.wikipedia.org/wiki/Evolutionary_physiology Morphology, Physiology, Biochemistry Deter- mine Organismal Performance Abilities

  42. Natural& Sexual Selection Act On Behavior After some background, let's look at some examples in which individual variation was used to address this part of the overall model. Constrain Morphology, Physiology, Biochemistry Deter- mine Organismal Performance Abilities

  43. Comparative physiologists have routinely looked at differences among species. Example: urine concentrating ability and length of loops of Henle in kidneys: a significant correlation among species (or among populations) suggests that the latter causes the former. But interspecific comparisons are fraught with difficulties: Garland, Jr., T., and S. C. Adolph. 1994. Why not to do two-species comparative studies: limitations on inferring adaptation. Physiological Zoology 67:797-828. Garland, Jr., T., A. F. Bennett, and E. L. Rezende. 2005. Phylogenetic approaches in comparative physiology. Journal of Experimental Biology 208:3015-3035. Rezende, E. L., and J. A. F. Diniz-Filho. 2012. Phylogenetic analyses: comparing species to infer adaptations and physiological mechanisms. Comprehensive Physiology 2:639-674. http://en.wikipedia.org/wiki/Phylogenetic_comparative_methods

  44. For example, we may be comparing apples and oranges (e.g., burrowing owl vs. bobwhite quail have been compared physiologically because both are birds of about the same body size). Also, species do not represent independent data points, and so we need independent phylogenetic information to perform proper statistical analyses: this may not be available for the organisms that we study. One way to avoid such problems is to stick within a single species. If relationships really do exist, then we should be able to demonstrate them.

  45. ... assuming that the "signal" is large enough to be detected over the "noise" of short-term variability within individuals! Hence the importance of first demonstrating that a physiological or behavioral measurement is repeatable.

  46. Example: Harris, M. A., and K. Steudel. 2002. The relationship between maximum jumping performance and hind limb morphology/physiology in domestic cats (Felis silvestris catus). J. Exp. Biol. 205:3877-3889. Conclusions We found that cats with longer hind limbs and lower fat mass relative to their lean body mass achieved higher TOVs. These two variables explained significant variation in maximum TOV in a manner consistent with predictions based on the work done by extensor muscles to increase both kinetic and potential energy during takeoff. This study is the first to confirm the limb length–jump performance relationship in an endothermic vertebrate. Contrary to predictions, however, extensor muscle mass relative to lean body mass and percentage composition of MHC IIx were not found to significantly predict TOV. Fig. 8. (B) Significant positive relationship between maximum takeoff velocity (TOV) and the ratio of extensor muscle mass/body mass (r=0.647, P=0.004, y=7571x+220.9). This is an ordinary least-squares linear regression predicting organismal performance from the lower-level (subordinate) trait of relative muscle mass. It would be more appropriate to report r2 rather than r.

  47. Example: Hammond, K. A., M. A. Chappell, R. A. Cardullo, R.-S. Lin, T. S. Johnsen. 2000. The mechanistic basis of aerobic performance variation in red jungle fowl. Journal of Experimental Biology 203:2053-2064. Used residuals from regressions on body mass. Both maximal and basal metabolic rate are related to some lower-level traits in both sexes, but the predictors are not very consistent. Hct is a positive predictor of VO2max in both sexes, as might be expected.

  48. Example: What predicts locomotor performance in the Spiny-tailed Iguana (Ctenosaura similis) from Costa Rica? Garland, T., Jr. 1984. Physiological correlates of locomotory performance in a lizard: an allometric approach. Am. J. Physiol. 247 (Regulatory Integrative Comp. Physiol. 16):R806-R815.

  49. Ctenosaura similis Calculate residuals (vertical deviations from least-squares linear regressions) to remove effects of body size. Garland, T., Jr. 1984. Physiological correlates of locomotory performance in a lizard: an allometric approach. Am. J. Physiol. 247 (Regul. Integr. Comp. Physiol. 16):R806-R815.

  50. This is a highly statistically significant positive relationship, and it makes biological sense. Then see if the residual subordinate traits can predict individual variation in the organismal performance trait with an OLS regression.

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