Do yolk hormones mediate sexual conflict over parental investment?

1. Do yolk hormones mediate sexual conflict over parental investment? Toni Laaksonen1,2, Freya Adamczyk2, Markus Ahola1, Erich Möstl3 & Kate Lessells2 1 University of Turku, Finland 2 Netherlands Institute of Ecology, Heteren, The Netherlands 3 University of Veterinary Medicine, Vienna, Austria

2. Egg yolks of birds contain considerable amounts of androgen hormones, e.g. Testosterone (Schwabl 1993)

3. What is the function of yolk hormones? • Positive effect on growth and competitive ability of chicks, increase in begging (Schwabl 1993, reviewed by Groothuis et al. 2005) – but also involve possible costs (other talks here) • In most species the among-clutch variation is higher than within-clutch variation (Groothuis et al. 2005) • Adaptive explanations for among-clutch variation: • Social density (e.g. Schwabl 1997, Groothuis & Schwabl 2002) • Parasite-induced (e.g. Tschirren et al. 2004) • Female condition (e.g. Verboven et al. 2003) • Differential allocation (e.g. Gil et al. 1999) • Sexual conflict over parental investment

4. Adaptive hypotheses: Differential allocation • Differential allocation: if the value of the current breeding attempt is higher when the partner is attractive, the other member of the pair should increase its investment (Burley 1986,1988) • Trade-off between investment in current and future reproduction: it is a good bet to invest more in the current one if the mate is of high quality (Sheldon 2000).

5. T T T T T T T T Adaptive hypotheses: Differential allocation of hormones into eggs Females invest more androgens into the eggs when mated with high-quality males(e.g. Gil et al. 1999, 2004; Tanvez et al. 2004; von Engelhardt et al. 2004; but see Mazuc et al. 2003)

6. T T T T T T Adaptive hypotheses: Sexual conflict over parental investment Testosterone in eggs makes the chicks beg harder Male parents respond by feeding more – female benefits

7. Adaptive hypotheses: Sexual conflict – condition-dependent manipulation of male investment • Females may try to keep an attractive male involved in parental care instead of searching other mating opportunities (Groothuis et al. 2005) • Compensatory tactic to elicit more feeding effort from young (poor-quality) males (Michl et al. 2005)

8. Questions we want to address: • Can female birds manipulate male investment via egg hormones? • Do females allocate hormones to eggs in response to male attractiveness or age? • Is that a condition-dependent attempt to manipulate male investment?

9. Pied flycatcher (Ficedula hypoleuca) Winters in Africa, arrives in Northern Europe in May Modal clutch size 6 eggs Female incubates Both parents feed Males can be polygynous

10. Finland

12. Experimental design (1) • Idea: Swap full clutches • Changes egg yolk hormone levels in the nest • Breaks down correlations between biological parents and chicks • Predictions: If females could manipulate male investment through egg hormones, then: • male/female feeding ratio should correlate positively with hormone levels of fostered eggs • female feeding rates may correlate negatively with hormone levels in the eggs she laid • (Lessells, in press)

13. Experimental design (2) Sample one egg (no. 4) during laying for hormone analysis, use it as an estimate for the whole brood Correlations between clutch mean and the fourth egg: Testosterone rs = 0.89, N = 24; Androstenedione rs = 0.80, N = 24

14. Experimental design (3) Sample one egg (no. 4) Replace with a dummy egg

15. Experimental design (4) full clutches with same laying dates were swapped

16. Experimental design (5) Dummy egg was replaced with a chick 1-2 d after hatching Brood size was standardised to 6

17. Experimental design (6) Parental feeding rates were measured by 2h video recording 5d after hatching (N = 50)

18. Experimental design (7) Parents captured 6-8 d after hatching Age: 1-year-old or older Body mass Morphology Male plumage characteristics (N = 70- 80)

19. Forehead patch size

20. Colour morph (Drost’s score I-VII) MarkusAhola Freya Adamczyk

21. Ultraviolet reflectance

22. Yolk hormone analyses Erich Möstl’s lab University of Veterinary medicine, Vienna

23. Results: no evidence for yolk hormones mediating sexual conflict Male’s proportion of feeding visits (N = 50): • No relationship with patch size, UV-reflectance or colour morph (independent of age) • All interactions n.s. • No identified confounding variables (e.g. laying date)

25. Results: no evidence for yolk hormones mediating sexual conflict Female feeding rate (N = 50): • No relationship with patch size, UV-reflectance or colour morph (independent of age) • All interactions n.s. • No identified confounding variables (e.g. laying date)

29. …we propose that the deposition of more testosterone into eggs is …a female’s adaptive response to the likely lower quality of paternal care that young males might provide…” (Michl et al. 2005)

31. Results: no evidence for differential allocation in relation to plumage characters of males Testosterone ng/g: No interactions, results the same in different model combinations

32. Summary 1) No evidence for females being able to manipulate male investment via egg hormones, generally or condition-dependent: neither foster clutch nor original clutch hormone leves were associated with male/female feeding ratio or feeding rates of either parent 2) No evidence for females allocating hormones differentially in relation to male plumage traits (but these are partly dependent on age, which again had an effect) 3) Females fed chicks with higher rate when mated with young males, and they also allocated more androgens into eggs in that situation. The results of the experiment however indicate that this is not a successful way for the female to elicit more investment from the young males

33. Discussion (1/2) • The chain increased androgen level in eggs – increased begging is well established. Time spent begging and begging stretch correlate with testosterone levels also in pied flycatcher nestlings (N. Goodship et al.) • It is known that pied flycatcher males respond to begging (von Haartman 195X; Ottosson et al. 1997) • Why does this not show in increased male investment when clutch androgen levels are high? • ”Noise” in the data? – A relationship should be seen with this sample size despite noise • It is known that androgens affect begging intensity when chicks are hungry – may be the chicks in natural broods were not hungry enough

34. Laaksonen, Möstl and Lehikoinen in prep.

35. Discussion (2/2) • Females allocate more androgens into the eggs when mated with a young male and when given food supplements prior to egg-laying • This suggests that females could be ”anticipating” the forthcoming growing conditions of the chicks, and subsequently targeting them to different developmental trajectories

36. We are grateful to: • Academy of Finland for post-doc grant to TL • E-Bird Europe for exchange visit grant to TL • Section of Ecology, University of Turku and Department of Population Biology, Netherlands Institute of Ecology for support • All E-Birds for organising this meeting • You for your attention!