The cost of mating with a non-virgin male in a monandrous butterfly: experimental evidence from the speckled wood, Pararge aegeria

Contrary to vertebrates, sperm production in insects may bear considerable costs for males. This is especially true in species that donate spermatophores containing sperm and nutrient-rich accessory gland products like in butterflies. Hence, spermatophores at first and subsequent copulations can differ in a quantitative and qualitative way. Such effects have particularly been shown in polyandrous species providing large spermatophores. Here we experimentally tested the effect of male mating status (virgin male vs recently mated male) on copulation duration, spermatophore size and females’ fitness components in a monandrous butterfly Pararge aegeria that typically donates small spermatophores. Copulations with non-virgin males lasted on average five times longer than that with virgin males and resulted in a spermatophore which was on average three times smaller. Number of eggs laid and female life span were not affected by the mating status treatment, but there was a significant effect on the number of living caterpillars a female produced, as copulations with virgin males resulted in higher numbers of larval offspring. Interestingly, the difference in spermatophore mass at the first and the second copulation increased with male body size. This suggests differential spermatophore allocation decisions among males of different size. Consequences for females and potential mechanisms influencing female fitness components are discussed. Given the small absolute size of spermatophores in P. aegeria, components other than consumable nutrients (perhaps hormones) should cause the observed effects.     

Power and Sample Size Calculations for Linear Hypotheses Associated with Mixtures of Many Components using Fixed-Ratio Ray Designs

Response surface methodology, often supported by factorial designs, is the classical experimental approach that is widely accepted for detecting and characterizing interactions among chemicals in a mixture. In an effort to reduce the experimental effort as the number of compounds under study is increased, ray designs have been proposed to study combinations of chemicals. When interest is restricted to relevant mixing ratios, we are only interested in making inference along the specific rays of interest, as opposed to methods which use designs that require more experimental effort to support the estimation of a response surface over a broader experimental region. Methods have been developed for the test of additivity along multiple fixed-ratio rays. Of primary importance is the detection of interactions with reasonable power. The objective of this paper is to address power and sample size issues related to the hypothesis of no interaction.     

Social rank, fecundity and lifetime reproductive success in wild European rabbits (Oryctolagus cuniculus)

Wild European rabbits of both sexes have separate linear rank orders, which are established and maintained by intensive fights. This paper presents data from a 14-year study (1987-2000) on the population physiology and behavioural ecology of wild rabbits living in a 22,000 m² enclosure and focuses on the relationship between social rank and reproduction in females. Group composition, social ranks, fecundity and reproductive success were known for all females (n=197) from the outset of their first reproductive season at an age of about 300 days until their death. The annual reproductive success of females was influenced to a large extent by their social rank. This depended on two effects of about equal strength: a higher fecundity of high-ranking females and a lower mortality of their offspring between birth and adulthood. The lifetime reproductive success of the females varied greatly. Only about 50% of all females had any reproductive success (range: on to nine adult offspring). The social rank achieved by the females during their first reproductive season substantially influenced their lifetime reproductive success: The mean reproductive lifespan and lifetime fitness of high-ranking females (ranks 1 and 2) was about 60% greater than that of lower-ranking females, although many of the latter also gained dominant positions in subsequent years.     

How reliable are behavioral cues for assessment of male mating status in polyterritorial wood warblers,Phylloscopus sibilatrix?

It has been suggested that polyterritoriality in birds, i.e. mated males defending two spatially separated territories, deceives females into accepting polygyny against their best interest. Mated males singing on secondary territories should make it difficult for new arriving females to assess the mating status of unmated and mated males advertising to females. However, there have been objections to the deception hypothesis, suggesting that differences in territorial behavior between males of different mating status may make correct assessment possible. Polyterritorial males frequently leave their secondary territory to visit the female in the primary territory, thereby revealing their mating status to females in search of mates. The aim of this study is to investigate how reliable behavioral cues are in assessing the mating status of males in polyterritorial wood warblers. Our study shows that singing activity of mated males on secondary territories and unmated males was similar in the morning, while there was a significant difference in the afternoon. Unmated males spent, on average, more time on their territories than mated males spent on their secondary territories. However, there was considerable variation in both unmated and mated males in the frequency in which they left their territories. For instance, unmated males left their territories quite frequently early in the season compared to later. Hence, females must be able to interpret singing behavior and a male leaving his territory differently depending on time of the season and time of the day in order to correctly assess the mating status of advertising males. Estimating the increase in probability of finding an unmated male by using behavioral cues showed that females could increase the probability of finding an unmated male compared to random choice with respect to mating status. The uncertainty was, however, still considerable. The most important factor affecting the probability of finding an unmated male was the proportion of mated males on secondary territories compared to unmated males. Our study suggests that presence on a territory is not a reliable cue for the assessment of male mating status in polyterritorial wood warblers.     

The territoriality threshold: a model for mutual avoidance in dragonfly mating systems

Summary In anisopteran dragonflies a variety of mating systems occurs. Male strategies range from patrolling without site attachment to territorial behaviour with pronounced residentiality. Conceiving site attachment as a strategy of mutual avoidance that reduces the energy spent in intermale fights, we develop a model for the cost and benefit of territoriality. This model suggests that high male density, high inter-male aggressiveness, and short duration of female visits at the mating place will strongly favour localization of males at the mating place and may thus trigger the evolution of territoriality. The predictions of our model are supported by field observations of several dragonfly species.died July 27, 1986     

Light and social effects on the free-running circadian activity rhythm in common marmosets (Callithrix jacchus; Primates): social masking,pseudo-splitting,and relative coordination

Summary The variability of period of the free-running circadian activity rhythm (CAR) and the degree to which it is affected by social factors was studied in diurnal marmosets (Callithrix jacchus: Primates, Cebidae), kept either singly or in pairs. Under continuous light intensities between 10^-1 and 10² lx, the spontaneous period was always shorter than 24h. It varied in relation to the amount of time spent under constant conditions (after-effects). There was some evidence of an effect of light intensity on free-running period, but no clear correlation between the two. Mutual acoustic social contact caused some males to exhibit pseudo-splitting, ascribable to positive social masking, and in many cases also resulted in relative coordination of the free-running CAR. True social entrainment, however, was not produced. The possibility that the latter could occur under some conditions is discussed, as well as the neural pathways that might mediate the observed acoustically induced social effects on the central nervous system pacemaker(s) of the circadian timing system.     

Foraging and spatial organisation of the European badger,Meles meles L.

Behavioral Ecology and Sociobiology -     

In situ biodegradation determined by carbon isotope fractionation of aromatic hydrocarbons in an anaerobic landfill leachate plume (Vejen,Denmark)

Concentrations and isotopic compositions (13C/12C) of aromatic hydrocarbons were determined in eight samples obtained from the strongly anoxic part of the leachate plume downgradient from the Vejen Landfill (Denmark), where methanogenic, sulfate-reducing and iron-reducing conditions were observed. Despite the heterogeneous distribution of the compounds in the plume, the isotope fractionation proved that ethylbenzene and m/p-xylene were subject to significant biodegradation within the strongly anoxic plume. The isotope fractionation factors (alphaC) for the degradation of the m/p-xylene (1.0015) and ethylbenzene (1.0021) obtained from the field observations were similar to factors previously determined for the anaerobic degradation of toluene and o-xylene in laboratory experiments, and suggest that in situ biodegradation is one major process controlling the fate of these contaminants in this aquifer. The isotope fractionation determined for 1,2,4-trimethylbenzene and 2-ethyltoluene suggested in situ biodegradation; however, the isotopic composition did not correlate well with the respective concentration as expressed by the Rayleigh equation. Some other compounds (1,2,3-trimethylbenzene, o-xylene, naphthalene and fenchone) did not show significant enrichments in delta13C values along the flow path. The compound concentrations were too low for accurate isotope analyses of benzene, toluene, 1- and 2-methylnaphthalene, while interferences in the chromatography made it impossible to evaluate the isotopic composition for 4-ethyltoluene, 1,3,5-trimethylbenzene and camphor.In addition to demonstrating the potential of assessing isotopic fractionation as a means for documenting the in situ biodegradation of complex mixtures of aromatic hydrocarbons in leachate plumes, this study also illustrates the difficulties for data interpretation in complex plumes and high analytical uncertainties for isotope analysis of organic compounds in low concentration ranges.