Air flow and convective heat loss from small mammals in laboratory metabolism chambers

1. 1.Thermal conductance was determined from cooling curves of Mus domesticus carcasses at air flow rates ranging from still air to 0.91·min⁻¹ STP. Thermal conductance was constant over this range of air flows. This indicates that free convection predominates over forced convection at these air flow rates.

2. 2.While non single set of conditions will be appropriate for all experiments, free convection conditions are appropriate for determination of minimal thermal conductance.

Epiphallic Afferent Projections into the Terminal Abdominal Ganglion of the Crickets Acheta domesticus and Gryllue bimaculatus

Summary

The sensilla on the epiphallus of male crickets are necessary for the correct transfer of spermatophores to females during copulatory behaviour. This report identifies, for the first time, a specific region within the terminal abdominal ganglion that is likely to process sensory information received from the epiphallus during copulatory activity.     

Divergent in shape and convergent in function: Adaptive evolution of the mandible in Sub‐Antarctic mice

Convergent evolution in similar environments constitutes strong evidence of adaptive evolution. Transported with people around the world, house mice colonized even remote areas, such as Sub‐Antarctic islands. There, they returned to a feral way of life, shifting towards a diet enriched in terrestrial macroinvertebrates. Here, we test the hypothesis that this triggered convergent evolution of the mandible, a morphological character involved in food consumption. Mandible shape from four Sub‐Antarctic islands was compared to phylogeny, tracing the history of colonization, and climatic conditions. Mandible shape was primarily influenced by phylogenetic history, thus discarding the hypothesis of convergent evolution. The biomechanical properties of the jaw were then investigated. Incisor in‐lever and temporalis out‐lever suggested an increase in the velocity of incisor biting, in agreement with observations on various carnivorous and insectivorous rodents. The mechanical advantage related to incisor biting also revealed an increased functional performance in Sub‐Antarctic populations, and appears to be an adaptation to catch prey more efficiently. The amount of change involved was larger than expected for a plastic response, suggesting microevolutionary processes were evolved. This study thus denotes some degree of adaptive convergent evolution related to changes in habitat‐related changes in dietary items in Sub‐Antarctic mice, but only regarding simple, functionally relevant aspects of mandible morphology.     

截头堆砂白蚁在恒温恒湿条件的分飞活动

截头堆砂白蚁Cryptotermes domesticus(Haviland)是世界性的重要蛀木害虫,原始繁殖蚁分飞是该种白蚁的重要扩散传播途径之一。为了解截头堆砂白蚁的分飞活动规律,本文研究了其成熟群体在恒温恒湿条件下的分飞期。结果表明,在恒温27℃和相对湿度80%的条件下,经历持续10年零3个月的观察,有7年内全年每个月均有原始繁殖蚁分飞,只有3年内每年均缺少2个月无原始繁殖蚁分飞。试验结果揭示了截头堆砂白蚁成熟群体在形成有分飞能力原始繁殖蚁的基础上,只要温、湿度条件适宜,全年中不分季节和日期,都有可能进行分飞活动。     

Begging in the absence of parents: a "quick on the trigger" strategy to minimize costly misses

Nestling begging in the absence of parents may reflect "falsealarms" due to cognitive constraints or signaling activity towardnest mates (sibling negotiation). According to signal detectiontheory, cognitive constraints should result in both false alarms(begging in the absence of parents or to inappropriate stimuli)and misses (failure to beg during parental visits). In our studyof house sparrows, nestling begging in the absence of parentscomprised up to 50% of the begging events at the nest and wasmore frequent at an early age and among hungrier (lower ranked)nestlings. In contrast, the probability of begging during parentalvisits was constantly high (80% or more), suggesting that therate of misses must have been low even at an early age. Theseresults have 2 main implications. First, the observation thatbegging in the absence of parents decreases with nestling agefavors the cognitive constraints hypothesis over functionalexplanations such as the sibling negotiation hypothesis. Second,the low proportion of "misses" among young nestlings suggeststhat nestling respond to their cognitive constraints by usinglow decision criteria (a "quick on the trigger" strategy) thatincreases the frequency of false alarms but minimizes costlymisses.     

Spontaneous quantity discrimination in crickets

Recent studies have reported that the ability to discriminate among quantities is not a prerogative of vertebrates. Ants, bees, and spiders can solve tasks in which they are required to discriminate between groups of objects. Although many studies regarding numerical cognition on invertebrates proposed a proto‐counting system, more control experiments for non‐numerical variables are necessary to confirm this hypothesis. Here, we developed a new method to investigate quantity discrimination abilities in invertebrates. We investigated the spontaneous choice of a cricket, Acheta domesticus. We exploited its natural shelter‐seeking behavior by presenting sets of geometrical shapes that simulated potential shelters. In a dichotomous choice between sets of geometrical black shapes differing in number of items, the majority of crickets chose the set containing the larger numerosity up to 2 versus 3 items. Control experiments suggested that crickets discriminated between sets consisting of different numbers of items by attending to continuous variables (i.e., convex hull and cumulative surface area) rather than by attending to numerosity. Secondly, when discriminating between single geometrical shapes, crickets attend to the width but not to the height of the stimuli.     

Parental effort and response to nestling begging in the house sparrow: repeatability,heritability and parent–offspring co‐evolution

Parental effort has a direct impact on individual fitness. Theoretical models exploring how parental effort evolves to cope with offspring demand and sexual conflicts may differ in the assumptions they make in respect to the genetic heritability of parental behaviours. Only a few attempts, however, have been made to estimate the heritability of parental behaviours and their possible co‐evolution with offspring solicitation behaviour. Analysing parent and offspring behaviours in four generations of cross‐fostered broods of house sparrows, we found that parental effort (food delivery rate) was repeatable across consecutive broods and heritable across generations. In contrast, parental response to experimentally induced changes in nestling begging was neither repeatable across broods nor heritable across generations or correlated to nestling begging. Thus, the results give no indication for genetic covariance between begging intensity and parental response, but provide the first cross‐fostering‐based evidence for the heritability of parental investment levels across generations.     

Postnatal mandible growth in wild and laboratory mice: Differences revealed from bone remodeling patterns and geometric morphometrics

Comparative information on the variation in the temporospatial patterning of mandible growth in wild and laboratory mice during early postnatal ontogeny is scarce but important to understand variation among wild rodent populations. Here, we compare mandible growth between two ontogenetic series from the second to the eighth week of postnatal life, corresponding to two different groups of mice reared under the same conditions: the classical inbred strain C57BL/6J, and Mus musculus domesticus . We characterize the ontogenetic patterns of bone remodeling of the mandibles belonging to these laboratory and wild mice by analyzing bone surface, as well as examine their ontogenetic form changes and bimodular organization using geometric morphometrics. Through ontogeny, the two mouse groups display similar directions of mandible growth, according to the temporospatial distribution of bone remodeling fields. The allometric shape variation of the mandibles of these mice entails the relative enlargement of the ascending ramus. The organization of the mandible into two modules is confirmed in both groups during the last postnatal weeks. However, especially after weaning, the mandibles of wild and laboratory mice differ in the timing and localization of several remodeling fields, in addition to exhibiting different patterns of shape variation and differences in size. The stimulation of dentary bone growth derived from the harder post‐weaning diet might account for some features of postnatal mandible growth common to both groups. Nonetheless, a large component of the postnatal growth of the mouse mandible appears to be driven by the inherent genetic programs, which might explain between‐group differences.     

The influence of sex and body size on nestling survival and recruitment in the house sparrow

Differences in the survival rates of males and females over the period from hatching to recruitment can have important impacts on individual fitness and population demographics. However, whilst the influence of an individual's sex on nestling growth and survival has been well studied, less is known about sex‐specific survival over the period between fledging and recruitment. Here, we analyse nestling survival and recruitment in an isolated, island population of house sparrows (Passer domesticus), using data collected over a 4‐year period. Nestlings that had a greater mass at 1 day old were more likely to fledge. Recruitment was also positively associated with day 11 mass. The positive influence of nestling mass on survival to fledging also increased as brood size increased. There was no difference in the survival of male and female individuals prior to fledging. In contrast, over the period from fledging to recruitment, females had significantly less mortality than males. Recruitment was also positively associated with 11‐day‐old mass. Neither the nestling sex ratio nor the fledging sex ratio deviated from 0.5, but the sex ratio amongst recruits was female biased. Our study shows that sex can influence juvenile survival, but also shows that its effect varies between different life‐history stages; therefore, these stages should be considered separately if we want to understand at what point sex‐specific differences in juvenile survival occur. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 680–688.     

Food supplementation affects extrapair paternity in house sparrows (Passer domesticus)

Extrapair paternity (EPP) is common among birds, but the reasonswhy it varies within and among species are less clear. In particular,few studies have experimentally examined how food availabilityinfluences paternity and sexual behavior. We manipulated foodsupply in a nest-box population of house sparrows, Passer domesticus,a colonial passerine with extensive biparental care. Duringthree successive breeding attempts, we changed food availabilityat nest sites and examined behavior and genetic parentage. DNAfingerprinting revealed that the level of EPP within broodswas five times lower in pairs nesting at sites continuouslysupplied with extra food. With extra food, mates spent longertime together at the nest, but this was mainly due to a changein female behavior; females but not males increased total nestattendance. Moreover, we found that individual males did notchange within-pair copulation frequency across treatments, suggestingthat our experiment did not influence male control over fertilizationsthrough copulation behavior. Instead, our study shows that ecologicalfactors can have a strong influence on the time budgets of malesand females, which consequently affects the occurrence of EPP.