Experimental manipulation shows that the white wing patch in collared flycatchers is a male sexual ornament

Peer reviewe

Metabolic rate of nocturnal incubation in female great tits, Parus major, in relation to clutch size measured in a natural environment

To study the energetic costs of incubation in relation to clutch size, clutch sizes were manipulated and the metabolic rate of female great tits, Parus major (Linnaeus), during nocturnal incubation (MRinc) was measured using mobile oxygen analysers. Individuals were measured on consecutive nights while incubating their own or manipulated clutches. The experiment was performed under field conditions in order to place possible effects of clutch size manipulation within the context of other factors explaining variation in MRinc. Females spent more energy when incubating enlarged clutches as compared with controls (6-10% more energy for three additional eggs) but did not spend significantly less energy when incubating reduced clutches. MRinc was strongly negatively related to ambient temperature. The effect of clutch enlargement is consistent with previous studies whereas the absence of an effect of clutch reduction is not. The small effect of clutch enlargement on MRinc highlights the need for further studies to include measurements of daily energy expenditure in order to judge how important energy expenditure can be in explaining fitness consequences of incubating experimentally enlarged clutches

Female Fertilization: Effects of Sex-Specific Density and Sex Ratio Determined Experimentally for Colorado Potato Beetles and Drosophila Fruit Flies

If males and females affect reproduction differentially, understanding and predicting sexual reproduction requires specification of response surfaces, that is, two-dimensional functions that relate reproduction to the (numeric) densities of both sexes. Aiming at rigorous measurement of female per capita fertilization response surfaces, we conducted a multifactorial experiment and reanalyzed an extensive data set. In our experiment, we varied the density of male and female Leptinotarsa decemlineata (Colorado potato beetles) by placing different numbers of the two sexes on enclosed Solanum tuberosum (potato plants) to determine the proportion of females fertilized after 3 or 22 hours. In the reanalysis, we investigated how the short-term fertilization probability of three Drosophila strains (melanogaster ebony, m. sepia, and simulans) depended on adult sex ratio (proportion of males) and total density. The fertilization probability of female Leptinotarsa decemlineata increased logistically with male density, but not with female density. These effects were robust to trial duration. The fertilization probability of female Drosophila increased logistically with both sex ratio and total density. Treatment effects interacted in m. sepia, and simulans. These findings highlight the importance of well-designed, multifactorial experiments and strengthen previous experimental evidence for the relevance of sex-specific densities to understanding and prediction of female fertilization probability.WKV, MEH, and HK acknowledge financial support from the Academy of Finland. GB and PM acknowledge financial support from Agriculture and Agri-Food Canada. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Female Fertilization : Effects of Sex-Specific Density and Sex Ratio Determined Experimentally for Colorado Potato Beetles and Drosophila Fruit Flies

Peer reviewe

Costs of avian incubation: how fitness, energetics and behaviour impinge on the evolution of clutch size

Het aantal eieren dat vogels leggen per broedpoging varieert. De ene vogel legt slechts één ei, de andere wel tien. Ecologen zijn gefascineerd door deze variatie en willen begrijpen wat het legselgrootte bepaalt. Een idee is dat het aantal eieren overeenstemt met het aantal jongen dat ouders kunnen voeren. Dit is onderzocht door het aantal jongen te manipuleren dat ouders grootbrengen. Een studie aan koolmezen in de Lauwersmeer laat zien dat ouders meer jongen kunnen grootbrengen als ze de extra jongen van de onderzoekers krijgen. Dit heeft geleid tot de vraag waarom deze ouders niet meer eieren leggen. Promovendus De Heij onderzocht of de kosten van het bebroeden van eieren beslissingen over de grootte van het legsel kan beïnvloeden. In een experiment, uitgevoerd in het vrije veld, gaf De Heij koolmezen gedurende de broedperiode een kleiner, een groter of hun zelfgekozen legselgrootte. Vervolgens bepaalde ze het broedsucces (het aantal overlevende nakomelingen). Zij voerde dit experiment in drie verschillende jaren uit. Het bleek dat koolmezen die een experimenteel vergroot legsel kregen, een lagere overleving hadden in twee van de drie jaar. De kosten van het bebroeden van eieren kunnen dus invloed hebben op legselgroottebeslissingen. De Heij mat eveneens de energie-uitgaven van koolmeesvrouwtjes gedurende de nacht en gedurende een etmaal. Ze ontdekte dat broedende vogels gedurende de nacht meer energie uitgaven als ze een vergroot legsel bebroedden. Over 24 uur gaven koolmeesvrouwtjes die een vergroot legsel bebroedden echter evenveel energie uit als vrouwtjes met een zelf gekozen aantal eieren. Waar de kosten in overleving vandaan komen is dus niet opgehelderd. Mogelijk veranderen de vogels hun bestedingspatroon gedurende 24 uur en investeren ze minder in hun eigen gezondheid en dus overleving.

Fitness cost of incubation in great tits (Parus major) is related to clutch size

Life-history theory predicts that parents produce the number of offspring that maximizes their fitness. In birds, natural selection on parental decisions regarding clutch size may act during egg laying, incubation or nestling phase. To study the fitness consequences of clutch size during the incubation phase, we manipulated the clutch sizes during this phase only in three breeding seasons and measured the fitness consequences on the short and the long term. Clutch enlargement did not affect the offspring fitness of the manipulated first clutches, but fledging probability of the subsequent clutch in the same season was reduced. Parents incubating enlarged first clutches provided adequate care for the offspring of their first clutches during the nestling phase, but paid the price when caring for the offspring of their second clutch. Parents that incubated enlarged first clutches had lower local survival in the 2 years when the population had a relatively high production of second clutches, but not in the third year when there was a very low production of second clutches. During these 2 years, the costs of incubation were strong enough to change positive selection, as established by brood size manipulations in this study population, into stabilizing selection through the negative effect of incubation on parental fitness.

Female great tits Parus major do not increase their daily energy expenditure when incubating enlarged clutches

Several studies have shown that enlargement of clutches during incubation reduces the long-term survival of parents. In line with these findings, studies on the energetic costs of nocturnal incubation show an increase in energy expenditure with clutch enlargement. Studies on daily energy expenditure during incubation (DEEinc), however, do not consistently show such a negative effect of clutch enlargement. To determine whether differential survival results from a direct increase in energy costs or rather from costs associated with compensatory behaviour, we studied the DEEinc (kJ day(-1)), change in body mass and nest attendance behaviour of free-living female great tits Parus major that incubated either control or experimentally enlarged clutches. DEEinc did not differ between the two treatment groups, but was negatively related to mean ambient temperature over the 24-h measuring period, and to the fraction of daytime females spent on the nest. Controlling for these two factors, females incubating enlarged clutches did not spend more energy per 24 h period than females incubating control clutches. Clutch enlargement also did not affect body mass of incubating females, or their nest attendance behaviour. Yet, in the enlarged group body mass change and nest attentiveness were negatively correlated, suggesting that females responded differently to the experimental treatment and thereby preventing us from finding an effect of clutch enlargement

Fertilization probability in relation to sex ratio (panel A) and total density (panel B).

<p>Data concerns female <i>Drosophila</i> and is from the experiment presented in Wallace <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060381#pone.0060381-Wallace1" target="_blank">[3]</a>. Presented are back-transformed values. Superimposed are the back-transformed fitted linear regression lines (continuous lines) and 95% confidence intervals (dotted lines) calculated at specific levels of total density ‘T’ or sex ratio ‘S’. Grey lines show residuals associated with the depicted regression lines (for representational purposes, corresponding observations have been slightly shifted horizontally in panel A). Long tick marks indicate treatment levels and response values. Note the log-scale of the x-axis in panel B.</p

Schematic depiction of the experimental design used in Wallace [<b>18</b>].

<p>Depicted is, for each of the three <i>Drosophila</i> strains, the minimum number of trials performed per combination of the whole plot factors number of cages ‘nC’ and trial duration ‘TD’. For each combination of these two factors (each cell), the same combinations of the subplot factors number of males and number of females as in Wallace (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060381#pone.0060381-Wallace1" target="_blank">[3]</a>; see Fig. 2) were examined.</p

Interaction effects on the ln-transformed odds (i.e. logits) of fertilization of female <i>Drosophila.</i>

<p>Depicted are the parameter estimates of the joint effect size of the total number of flies (N) and sex ratio (S); data is from the twelve experiments presented in Wallace <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060381#pone.0060381-Wallace2" target="_blank">[18]</a>. Symbols indicate trial duration (30 min: open symbols, 60 min: filled symbols), and the number of mating chambers in the experiment (1: circles, 2: triangles). Solid and dotted error bars indicate the standard error and the 95% confidence intervals of these parameter estimates, respectively. Positive joint effect sizes can be interpreted as indicating that the positive effect of the total number of flies was more pronounced when sex ratio was higher (more male-biased), and vice versa.</p