Terrestrial Ecology Zoological Part 2004

Who is who? Koos Boomsma Michael Poulsen Daniel Kronauer

What’s up for these two weeks? Exiting Evolutionary Ecology A further confrontation with the hardship of science Straightforward textbook chapters versus… ….recent (mostly) case studies of varying complexity Hot issues: Ageing, natural (social) conflicts, infectious diseases (AIDS), conservation

The Issues Life Histories and Phenotypic Plasticity Conflict and Cooperation Parasites and Diseases Metapopulations and Conservation

Life Histories and Phenotypic Plasticity Investments in and Timing of Growth and Reproduction

Broad Scale Life-history Correlations Pregnancy Duration versus Body Size May & Rubenstein, 1984Clutton-Brock, 1991 Offspring carried Offspring independent Offspring kept In the nest

Broad Scale Life-history Correlations Maximal Life Span versus Body Size Stearns, 1992 Not the slopes but the level is interesting Prothero & Jürgens, 1992

Life Span is Tremendously Variable 274 Species of Invertebrates170 Mammal Species in Zoos Stearns, 1992 Comfort, 1979 Stearns, 1992 Eisenberg, 1981

Broad Scale Life-history Correlations Egg Volume versus Body Size Residuals Contain the Important Information. Blueweiss et al., 1978Clutton-Brock, 1991

The Comparative Method The Statistical Analysis of Comparative (Across Taxa) Life History Data But now To the Explanations (Life History Theory)

Trade-off curves Convex Concave Actual fitness contours Option Sets Iteroparity Annual Semelparity 14.10

Plots May also be the Other Way Around Survival instead of Growth Trade-off Curves May also be Complex Stearns, 1976, 1992

Cole’s Paradox – Why is Iteroparity so Common? Let B a = # offspring Annual Let B p = # offspring Perennial (Iteroparous) Annuals: N t+1 = e r N t = B a N t  lnB a = r Perennials: N t+1 = e r N t = B p N t + N t = (Bp + 1)N t  ln(B p + 1) = r The fitness of these two reproductive types is equal when: B a = B p + 1. ????? Annuals need to reproduce only marginally more to be selected for

Cole’s Paradox – Why is Iteroparity so Common? The Paradox was solved by including age- specific survival rates: p juv (juveniles) and p ad (adults) Now the fitness of these two reproductive types is equal when: Conclusion: Because p ad >> p juv in many populations, it is often best to be iteroparous See Compendium for Details

The Cost of Reproduction Trade-off clear unclear Offspring Size versus Offspring # High CR Lobelia’s on Mt. Kenia

Problems in the Measurement of Trade-offs Stearns, 1992 Survival Reproduction Fraction to R A = R + S Var A >> Var B Var A << Var B Trade-offs (genetic correlations) may be invisible in the field

Clutch Size Optimisation Assume a single optimal egg size Lack’s optimal clutch size Iteroparous organisms need reserves to buffer the cost of reproduction and to minimise the temporal variation in reproductive performance

Clutch Size Optimisation Geometric mean fitness is often a better measure than arithmetic mean fitness √ Y 1.Y 2.Y 3.Y Y n n Boyce & Perrins, 1987 Cockburn, 1991 Large SD means large Temporal variation in Fitness

Clutch Size Optimisation Other factors also play a decisive role: Laying date Clutch size is a phenotypically plastic life-history trait Daan et al., 1990 Krebs & Davies, 1991 Model Predictions Match Observations in the Field 14.24

Size and Age at Maturity Reznick & Endler, 1982 Cockburn, Streams with Different Predation Risk C = High Adult Pr. R = Moderate Juv. Pr. A = Low Predation % Female Biomass  Reproduction A transplantation experiment reproduced these patterns in 11 years (30-60 generations) R: Size & Age at Maturity  C: Reproductive Effort  R&C: Body Size ↓ Table 14.1

Size and Age at Maturity Comparative data corrected for body size 14.27

Reproductive Value Phlox drummondii Age at maturity Life Span Age at Maturity = Constant Cockburn, 1991Charnov & Berrigan, 1991 But only within taxa cf. 14.4

Sex ratio Should be measured in terms of investment Is often but far from always 50:50 at the end of parental investment The equilibrium ESS sex ratio is independent of an XX/XY sex chromosome system Adult sex ratios may be very skewed owing to sex specific mortality or mating success Is often skewed in haplo-diploid parasitoids and social insects (ants, bees, wasps) See Compendium for Details

Sex ratio and Cost of Reproduction Only females in their prime age can reproduce each year Male calfs are usually more ”expensive” Clutton-Brock, 1984, 1991 Clutton-Brock, 1981, 1991

Sex ratio and Cost of Reproduction a: daughters are more expensive A paper on human twins of different sex Clutton-Brock et al., 1982 Sons Daughters b,c,d: sons are more expensive

Why does almost every multicellular organism senesce? Germ-line and Soma are separated Soma is disposable if that serves the fitness of the germ-line Selection does not remove deleterious mutations expressed late in life Selection favors mutations that are beneficial early in life, even if they are bad later in life

The Optimal Repair Model 3 papers this afternoon Kirkwood, 1985 Stearns., 1992 Excess Repair is not Favoured by Selection

Phenotypic Plasticity Reaction norms of isofemale lines Differences in slopes are particularly important because this genetic variation is easy to maintain

Reaction Norm Theory Size and Age at Maturity Reproductive Effort versus Survival Stearns, 1989, 1992

Practical Examples Drosophila mercatorum Human females Gebhardt & Stearns, 1988; Stearns, 1992Stearns & Koella, 1986; Stearns, Good Nutrition Bad Nutrition

Summary Life-history traits are heritable, but usually in a phenotypically plastic way Many key aspects of life are determined by selection on life-history traits Reproduction is costly and has a carefully balanced, but context dependent, economy In plants, animals, (microorganisms), and humans 3 papers on ageing and 1 on early growth effects