What causes sexual ornaments and behavior (secondary sexual characteristics): primary are the gonads and reproductive equipment themselves)?

Peacock’s tail, bird song repertoires, conspicuous color patterns, sexual displays

This is a conspicuous problem: occurred to Darwin

Two possibilities for sexual selection are (1) male-male competition (horns etc.) or (2) female choice. (Competition is usually among males, and choice usually by females, because females usually invest more in offspring.) We will focus on female choice.

Fisherian “runaway” model (“sexy son”)

Zahavi “handicap” principle

The handicap principle says that traits are not chosen despite their being costly, but because they are costly. Good genes model. Ornaments are a signal of good genes: they must be costly, otherwise you can’t rely on the honesty of the signal.

Penn & Számadó (2020):

Rather than being wasteful over-investments, honest signals evolve in this scenario because selection favours efficient and optimal investment into signal expression and minimizes signalling costs … This model is better understood within a Darwinian framework of adaptive signalling trade-offs, without the added burden and confusing logic of the Handicap Principle.

Problem with handicap principle: what maintains genetic variation for “goodness”? Under normal conditions (directional selection), one would expect that soon everyone would have good genes and there would be no variability (nothing for females to choose from except luck). Constant mutation could lead to a mutation-selection balance, or a variable environment could keep changing what genes are “good”. Of course (as we know), parasites represent a strong driver of variability in the biotic environment.

Hamilton-Zuk hypothesis

(the Red Queen returns)

a subset of ‘good-genes’ models

requirements (Combes (2005) p. 185)

Evidence for H-Z: between-species

If H-Z is operating, we expect a positive correlation between parasite load and showiness across species. This correlation has been found, for example, in Hamilton and Zuk’s original study which correlated human judgements of species brightness with information on ectoparasite load. Other studies have been more equivocal.

There are some problems with between-species comparisons, though:

Evidence for H-Z: within species

Guppies (Martin & Johnsen, 2007):

Barn swallows (Møller, 1990):

Meta-analysis (Poulin & Hamilton, 1997)

Alternatives

Alternatives to H-Z: both can be tested (with some difficulty) by manipulative cross-fostering experiments

Immunocompetence handicap hypothesis

Secondary sexual traits seem to be negatively correlated with immunosuppression

Folstad & Karter (1992): turning off your immune system is the ultimate handicap. Thus, it is not a coincidence that females prefer traits that are linked to (temporary) immunosuppression; males that can afford to turn off their immune systems during the mating season must have good genes … (note switch from original H-Z!)

Good links between androgens and secondary sex characteristics. Some support for the link between testosterone (and other androgens) and immunosuppression, but variable results in different experiments. Immunoredistribution rather than immunosuppression? [Evans et al. (2000);Roberts et al. (2004);

Other axes of signalling and immune function: carotenoid, melanin systems (McGraw & Ardia, 2003; Simons et al., 2012)

Stress-linked immunocompetence handicap (Buchanan, 2000) “testosterone has a dual effect: it leads to immunosuppression through a mechanism involving corticosterone but, conversely, leads to increased immunocompetence probably via dominance influencing access to resources”. possibly explains the mess … (Bortolotti et al., 2009)

Where are we? Balenger & Zuk (2014)

Recent meta-analyses: (Dougherty et al., 2023)

Humans: do females prefer male faces associated with lower cortisol/higher testosterone/better immunity (Rantala et al., 2012)? across countries, do females prefer ‘masculine’ men more in countries with more parasite exposure (DeBruine et al., 2012)?

References

Balenger, S. L., & Zuk, M. (2014). Testing the Hamilton–Zuk Hypothesis: Past, Present, and Future. Integrative and Comparative Biology, 54(4), 601–613. https://doi.org/10.1093/icb/icu059
Bortolotti, G. R., Mougeot, F., Martinez-Padilla, J., Webster, L. M. I., & Piertney, S. B. (2009). Physiological Stress Mediates the Honesty of Social Signals. PLOS ONE, 4(3), e4983. https://doi.org/10.1371/journal.pone.0004983
Buchanan, K. L. (2000). Stress and the evolution of condition-dependent signals. Trends in Ecology & Evolution, 15(4), 156–160. https://doi.org/10.1016/S0169-5347(99)01812-1
Clayton, D. H. (1991). The influence of parasites on host sexual selection. Parasitology Today, 7(12), 329–334. https://doi.org/10.1016/0169-4758(91)90211-6
Combes, C. (2005). The art of being a parasite. University of Chicago Press. https://archive.org/details/artofbeingparasi0000comb
DeBruine, L. M., Little, A. C., & Jones, B. C. (2012). Extending parasite-stress theory to variation in human mate preferences. Behavioral and Brain Sciences, 35(2), 86–87. https://doi.org/10.1017/S0140525X11000987
Dougherty, L. R., Rovenolt, F., Luyet, A., Jokela, J., & Stephenson, J. F. (2023). Ornaments indicate parasite load only if they are dynamic or parasites are contagious. Evolution Letters, 7(3), 176–190. https://doi.org/10.1093/evlett/qrad017
Evans, M. R., Goldsmith, A. R., & Norris, S. R. A. (2000). The effects of testosterone on antibody production and plumage coloration in male house sparrows ( Passer domesticus ). Behavioral Ecology and Sociobiology, 47(3), 156–163. https://doi.org/10.1007/s002650050006
Folstad, I., & Karter, A. J. (1992). Parasites, Bright Males, and the Immunocompetence Handicap. The American Naturalist, 139(3), 603–622. https://doi.org/10.1086/285346
Martin, C. H., & Johnsen, S. (2007). A field test of the Hamilton–Zuk hypothesis in the Trinidadian guppy (Poecilia reticulata). Behavioral Ecology and Sociobiology, 61(12), 1897–1909. https://doi.org/10.1007/s00265-007-0430-2
McGraw, K. J., & Ardia, D. R. (2003). Carotenoids, Immunocompetence, and the Information Content of Sexual Colors: An Experimental Test. The American Naturalist, 162(6), 704–712. https://doi.org/10.1086/378904
Møller, A. P. (1990). Effects of a Haematophagous Mite on the Barn Swallow (Hirundo rustica): A Test of the Hamilton and Zuk Hypothesis. Evolution, 44(4), 771–784. https://doi.org/10.1111/j.1558-5646.1990.tb03804.x
Penn, D. J., & Számadó, S. (2020). The Handicap Principle: How an erroneous hypothesis became a scientific principle. Biological Reviews, 95(1), 267–290. https://doi.org/10.1111/brv.12563
Poulin, R., & Hamilton, W. J. (1997). The Hamilton and Zuk Hypothesis Revisited: A Meta-Analytical Approach. Behaviour, 134(3-4), 299–320. https://doi.org/10.1163/156853997X00485
Rantala, M. J., Moore, F. R., Skrinda, I., Krama, T., Kivleniece, I., Kecko, S., & Krams, I. (2012). Evidence for the stress-linked immunocompetence handicap hypothesis in humans. Nature Communications, 3(1), 694. https://doi.org/10.1038/ncomms1696
Roberts, M. L., Buchanan, K. L., & Evans, M. R. (2004). Testing the immunocompetence handicap hypothesis: A review of the evidence. Animal Behaviour, 68(2), 227–239. https://doi.org/10.1016/j.anbehav.2004.05.001
Simons, M. J. P., Cohen, A. A., & Verhulst, S. (2012). What Does Carotenoid-Dependent Coloration Tell? Plasma Carotenoid Level Signals Immunocompetence and Oxidative Stress State in Birds–A Meta-Analysis. PLOS ONE, 7(8), e43088. https://doi.org/10.1371/journal.pone.0043088

Last updated: 2023-11-27 12:05:16.287138