Age-dependent trajectories differ between within-pair and extra-pair paternity success.

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous, but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-pair and extra-pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and extra-pair paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and extra-pair paternity successes differed significantly, with the extra-pair paternity success increasing faster, albeit non-significantly so, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within-pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent payoffs. Males may partition their reproductive effort between within- and extra-pair matings depending on their current age in order to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of extra-pair paternity observed within and between-species. This article is protected by copyright. All rights reserved

Age-associated variation in reproduction and consequences of mating strategies in male house sparrows, Passer domesticus

Sexual selection is a strong evolutionary force shaping the traits determining individual reproductive success. Such traits can be crucial for reproductive success before or after copulation (pre- versus post-copulatory sexual selection). However, little is known about how primary and secondary sexual traits vary in relation to male age in socially monogamous but genetically promiscuous (i.e. extra-pair) species. This is a particularly pressing question because extra-pair sires are more often older rather than younger males, which suggests that male age reflects genetic quality to females. Yet, older males are senescent males and produce lower quality offspring. Thus, females should actually avoid mating with older males. Furthermore, it is assumed that males that mate with multiple females achieve fitness benefits (higher lifetime reproductive success) compared to males that mate monogamously. This assumption underlies sexual selection theory. Additionally, it provides a straightforward explanation of why males in socially monogamous species engage in extra-pair mating: it maximises their reproductive success. Surprisingly, this classic claim has not been thoroughly quantified and thus awaits validation.In this thesis, I examined age-related variation in reproduction. Particularly, I studied how male age relates to mating strategies, sperm traits and reproductive success. I further quantified the fitness consequences of a males mating promiscuously over males mating monogamously. My study species was the house sparrow, Passer domesticus, a predominantly socially monogamous species. I studied captive and wild sparrows, both of exact known ages. Avian studies commonly rely on discriminating between first-year and older breeders only. Such a dichotomous discrimination of age prohibits analyses at all life history stages. Further, I quantified the lifetime reproductive success of wild sparrows. Knowledge of lifetime reproductive success is crucial for understanding, for instance, the fitness consequences of mating decisions.Extra-pair sires are commonly older males. It has been hypothesized that this is the result of older males having a pre-copulatory advantage over younger males. Chapter 2 put this hypothesis to the test and shows that male age seems unrelated to pre-copulatory male competition. Further, females did not base their pre-copulatory mate choice on male age, which refutes the idea of male age signalling genetic quality to females. Instead, postcopulatory mechanisms seem to underlie the pattern of extra-pair sires being older males.One of such post-copulatory mechanisms is sperm competition where sperm of multiple males compete for fertilisation of a female’s eggs. In birds, sperm can be sampled with relative ease and it is assumed that applying different methods of sperm collection does not affect sperm measurements. Chapter 3 experimentally tested whether two common methods of sperm collection indeed do not affect sperm measurements. Contrasting the previous assumption, sperm length varied according to sperm collection method. Thus, the practice of mixing sperm collection methods should be avoided or, at least, statistically controlled for.Chapter 4 followed up on the hypothesis that post-copulatory mechanisms might explain why extra-pair sires are often older males. The results showed that sperm morphology and indices of relative testes size seemed to be unaffected by male age. Yet, when considering the number of sperm that reached the egg of females, older males delivered more sperm than younger males. Hence, older males might have a post-copulatory competitive advantage over younger males.Chapter 5 answers the fundamental question of whether extra-pair paternity maximises male fitness. Surprisingly, the field of evolutionary ecology lacks empirical data supporting this classic claim. The results reveal that a promiscuous male mating strategy does not maximise male fitness, which contrasts expectations from sexual selection theory and calls for reconsidering the validity of this basic assumption.With this thesis, I thus contributed to clarifying the factors underlying the relationship between extra-pair paternity and male age. In sum, I found that older males have higher extrapair paternity not because of pre-copulatory male competition or female choice but probably because of a post-copulatory advantage. I also updated the current protocol of avian sperm sampling and advocated a standardised method to enhance comparability across and within studies. Finally, I quantified the fitness consequences of extra-pair paternity and discovered that it does not maximise male fitness.publishe

Understanding others' preferences: A comparison across primate species and human societies.

We investigated children's and non-human great apes' ability to anticipate others' choices from their evident food preferences-regardless of whether these preferences deviate or align with one's own. We assessed children from three culturally-diverse societies (Namibia, Germany, and Samoa; N = 71; age range = 5-11) and four non-human great ape species (chimpanzees (Pan troglodytes), bonobos (Pan paniscus), gorillas (Gorilla gorilla), and orangutans (Pongo abelii); N = 25; age range = 7-29) regarding their choices in a dyadic food-retrieval task. Across conditions, participants' preferences were either aligned (same preference condition) or opposed (opposite preference condition) to those of their competitors. Children across societies altered their choices based on their competitor's preferences, indicating a cross-culturally recurrent capacity to anticipate others' choices relying on preferences-based inferences. In contrast to human children, all non-human great apes chose according to their own preferences but independent of those of their competitors. In sum, these results suggest that the tendency to anticipate others' choices based on their food preferences is cross-culturally robust and, among the great apes, most likely specific to humans

Method matters: Experimental evidence for shorter avian sperm in faecal compared to abdominal massage samples

Girndt A, Cockburn G, Sanchez-Tojar A, Løvlie H, Schroeder J. Method matters: Experimental evidence for shorter avian sperm in faecal compared to abdominal massage samples. PLOS ONE. 2017;12(8): e0182853

Sanchez-Tojar_et_al_2016_JAB

This database contains the necessary data to run the all the GLMs and GLMMs presented in: Sanchez-Tojar et al. 2016 Winter territory prospecting is associated with life-history stage but not activity in a passerine, published in Journal of Avian Biology

Sperm length (μm) differences in relation to sperm sampling method in house sparrows controlling for relative order of massage to faecal sampling.

<p>Sperm heads (a), and midpieces (b) were significantly shorter sampled from faeces [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182853#pone.0182853.ref017" target="_blank">17</a>] (823 sperm from 41 males) compared to abdominal massage samples [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182853#pone.0182853.ref019" target="_blank">19</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182853#pone.0182853.ref020" target="_blank">20</a>] (822 sperm from 45 males). Filled dots represent means and vertical lines represent 95% Bayesian Credible Intervals (CrI).</p

Length measurements of house sparrow sperm.

<p>Example of measurements of single sperm components: head: nucleus (red) and acrosome (pink), midpiece (green), and flagellum: tail (cyan) and midpiece (green). Total length was calculated by using the sum of flagellum and head length. Note that whereas the transition from midpiece to head and the end of the acrosome are visible in light microscopy; the acrosome and nucleus cannot be precisely differentiated and are portrayed here only to demonstrate the composite nature of the head measurement.</p

Schematic overview of experimental protocol.

<p>Whereas the time and sequence of massage and faecal sampling was randomised, female dummy trials always took place before the faecal and massage sampling.</p