Analysis of the importance of genotypic variation, metabolic rate, morphology, sex and development time on immune function in the cricket, Gryllus firmus

Immune defence is hypothesized to be a trait that bears significant fitness costs as well as benefits in that mounting a defence depreciates the value of other life‐history traits. Thus the cost of mounting an immune response could affect the evolution of both the immune system and correlated life history traits. In this study we examined, by means of a diallel cross of four inbred lines, the genetic basis of two measures of immune function, metabolic rate and several traits in the sand cricket, Gryllus firmus. We specifically addressed the following questions: (1) is immune function determined primarily by genetic constitution or correlations with phenotypic traits that could reduce the effectiveness of the immune response; (2) do the two measures of immune function covary; (3) What are the contributions of additive, nonadditive and maternal effects to the immune function? As estimates of immune function, we used lytic activity and encapsulation rate. We found that inbred crickets were smaller than individuals from the crossed lines and took longer to develop. However, inbred lines did not differ from the crossed lines in immune function nor metabolic rates, suggesting that increased homozygosity has little or no effect on these traits in G. firmus. We found that both immune parameters showed significant genetic variation but no consistent relationships with the other phenotypic traits (metabolic rate, head width, body mass, development time and activity). There was significant additive genetic variation only in encapsulation rate, but, with the exception of the activity measure, significant nonadditive and reciprocal variances were found in all traits. Metabolic rate of crickets was heritable, but there was neither phenotypic nor genetic association between metabolic rate and the two parameters of immune function. Further, there was no correlation between these two measures. Females showed a higher encapsulation response than males, but there was no sex differences in lytic activity. Our study indicates that genetic variation in immune parameters can be a very significant contributor to phenotypic variation in immune function.     

Quantitative genetics of immune function and body size in the house cricket,Acheta domesticus

Female house crickets are attracted to male calling song containing a relatively high number of syllables per ‘chirp’, which tends to be produced by large males. In a previous study, we showed that this song characteristic is also positively and independently correlated with haemocyte load, an important determinant of the ability to produce an encapsulation response in insects. Females will therefore tend to select males with high encapsulation ability (and large body size) as mates. The present study demonstrates that variation in haemocyte load and body size, together with a second parameter of immune function (the ability to encapsulate a synthetic substrate), is heritable in the same population. Moreover, all three traits are shown to be positively genetically correlated. In favouring males that produce calling song with the preferred characteristics, females should therefore also tend to produce larger offspring with a greater ability to produce an encapsulation response.     

蛾类昆虫雄性信息素及其功能

昆虫性信息素是两性通讯系统的基础,其中雄性信息素的研究相对较少。本文综述了蛾类昆虫雄性信息素的研究进展。迄今已鉴定出40余种蛾类昆虫的雄性信息素,其行为学功能主要有对雌性的引诱和激欲、对同种雄性的抑制及种间隔离等。     

Individual variation and the endocrine regulation of behaviour and physiology in birds: a cellular/molecular perspective

Investigations of the cellular and molecular mechanisms of physiology and behaviour have generally avoided attempts to explain individual differences. The goal has rather been to discover general processes. However, understanding the causes of individual variation in many phenomena of interest to avian eco-physiologists will require a consideration of such mechanisms. For example, in birds, changes in plasma concentrations of steroid hormones are important in the activation of social behaviours related to reproduction and aggression. Attempts to explain individual variation in these behaviours as a function of variation in plasma hormone concentrations have generally failed. Cellular variables related to the effectiveness of steroid hormone have been useful in some cases. Steroid hormone target sensitivity can be affected by variables such as metabolizing enzyme activity, hormone receptor expression as well as receptor cofactor expression. At present, no general theory has emerged that might provide a clear guidance when trying to explain individual variability in birds or in any other group of vertebrates. One strategy is to learn from studies of large units of intraspecific variation such as population or sex differences to provide ideas about variables that might be important in explaining individual variation. This approach along with the use of newly developed molecular genetic tools represents a promising avenue for avian eco-physiologists to pursue.     

Inbreeding effects on progeny sex ratio and gender variation in the gynodioecious Silene vulgaris (Caryophyllaceae)

In gynodioecious species, sex expression is generally determined through cytoplasmic male sterility genes interacting with nuclear restorers of the male function. With dominant restorers, there may be an excess of females in the progeny of self-fertilized compared with cross-fertilized hermaphrodites. Moreover, the effect of inbreeding on late stages of the life cycle remains poorly explored. Here, we used hermaphrodites of the gynodioecious Silene vulgaris originating from three populations located in different valleys in the Alps to investigate the effects of two generations of self- and cross-fertilization on sex ratio and gender variation. We detected an increase in females in the progeny of selfed compared with outcrossed hermaphrodites and inbreeding depression for female and male fertility. Male fertility correlated positively with sex ratio differences between outbred and inbred progeny, suggesting that dominant restorers are likely to influence male fertility qualitatively and quantitatively in S. vulgaris. We argue that the excess of females in the progeny of selfed compared with outcrossed hermaphrodites and inbreeding depression for gamete production may contribute to the maintenance of females in gynodioecious populations of S. vulgaris because purging of the genetic load is less likely to occur.     

Cross-fostering reveals an effect of spleen size and nest temperatures on immune responses in nestling European starlings

Immunocompetence may be a good measure of offspring quality, however, factors affecting variation in immune responses are not clear. Research suggests that immune function can vary due to differences in genetics, development conditions and individual quality. Here, I examined factors affecting variation in immune response among nestling European starlings through a split-nest cross-fostering brood manipulation that included two important covariates: spleen size and nest temperatures. Immunocompetence was assessed via a cell-mediated immune response to phytohaemagglutinin (PHA). This paper provides the first direct evidence that individuals with large spleens also mount strong immune responses. Exposure to PHA did not cause splenomegaly, as there was no difference in spleen size between control birds and those injected with PHA. Offspring immune function was affected by common origin and by rearing environment, though rearing environment appeared to exert its influence only through nest temperatures. A comparison of the immune performance of siblings reared in their home nest versus those reared in other nests revealed a strong effect of maternal quality. As the difference in natal clutch size increased, the magnitude of the difference in immune performance between home-reared nestlings versus out-reared nestlings increased. Overall, nestling immune function appears to be determined by the combination of genetic, maternal and environmental effects.     

Maternal control of offspring sex and male morphology in the Otitesella fig wasps

Models concerning the evolution of alternative mating tactics commonly assume that individuals determine their own strategies. Here we develop a computer-based ESS model that allows mothers, ovipositing in discrete patches, to choose both the sex and the male mating tactics (natal-patch mating or dispersing) of their offspring based only on how many other mothers have used the specific patch before them. Data for three species of nonpollinating fig wasps from the Otitesella genus agree quantitatively with the model's assumptions and predictions. This suggests that females respond to population densities at the level of individual figs. The alternative male tactics in the species we studied are probably a result of a conditional strategy exercised by the mother that laid them. In addition, as females were only allowed to lay one egg per patch, our results suggest a new mechanism that can skew population sex ratios towards a female bias.     

Size distribution,growth and inter-year variation in sex expression of Bischofia javanica,an invasive tree

Flowering activity and sex expression of Bischofia javanica Blume were investigated for 3 years. B. javanica is an invasive dioecious tree of subtropical forests on the Bonin Islands in the western Pacific of Japan. The sex ratio showed a significant male bias (1.25-2.33). Smaller trees were significantly male biased, whereas larger trees showed no significant difference in sex expression, suggesting that males tend to be more precocious in sexual reproduction. We found evidence for sex changes in B. javanica; these have not been reported previously. Most of the 1,653 census trees remained non-flowering (58.1 %); 3.7 % of them showed sex changes, and the percentage of trees repeatedly flowering as males and females was 10.5 and 3.4 %, respectively. Sex changes were observed in both directions but a larger percentage of male trees became female. Flowering frequency and sex expression were significantly related to tree size (i.e. diameter at breast height). Over the 3 years, trees that were consistent females were the largest; inconsistent trees (switching sex between years) were intermediate in size, whereas consistent males were the smallest. There were no significant differences in relative growth rate (RGR) among trees of different sex or flowering frequencies. These results suggest that the maintenance of female reproduction is not related to changes in RGR of diameter but to flowering frequency or the reversal to the male form, dependent upon the internal resource status of individual trees.     

Orangutan activity budgets: Monthly variations and the effects of body size,parturition, and sociality

The activity budgets of individual orangutans were investigated at the Kutai Reserve, Indonesia. Activity profiles within and between individuals were compared to examine monthly variations in feeding patterns, potential energetic constraints imposed by large body size and parturition, and the costs of sociality. Animals showed monthly changes in travelling, feeding, and resting patterns. Monthly increases in travelling and feeding were associated with marked reductions in the time spent resting. Inter-individual variations in activity budgets did not exist among animals of the same age-sex class. Activity patterns differed, however, as a function of age and sex. Adult females and subadult males travelled and fed significantly longer than an adult male. Parturition had predictable effects on activity; one female reduced her feeding and travelling immediately following parturition. Adult male orangutan sociality appears to be limited by travel costs. Associations with females forced a male orangutan to travel significantly more compared with periods in which he was solitary. The male did not lose an appreciable amount of time feeding when accompanying a female.     

Spatial learning in deer mice: sex differences and the effects of endogenous opioids and 60 Hz magnetic fields

We examined the effects of brief exposure to weak 60 Hz extremely low frequency (ELF) magnetic fields and opioid systems on spatial behavior and learning in reproductive adult male and female deer mice, Peromyscus maniculatus. Sex differences were evident in spatial performance, with male deer mice displaying significantly better performance than female mice in the Morris water maze, whereby animals had to acquire and retain the location of a submerged hidden platform. Brief (maximum 5 min) exposure to weak (100 T) 60 Hz magnetic fields during task acquisition significantly improved female performance, eliminating the sex differences in acquisition. The opiate antagonist, naltrexone, also improved female acquisition, though significantly less than the magnetic fields. These facilitatory effects involved alterations of non-spatial (task familiarization and reduction of related anxiety/aversive related behaviors) and possibly spatial aspects of the task. Enhancement of enkephalin activity with the enkephalinase inhibitor, SCH 34826, significantly reduced task performance by male deer mice. Both naltrexone and the 60 Hz magnetic fields attenuated the enkephalin mediated reductions of spatial performance. These findings indicate that brief exposure to 60 Hz magnetic fields can enhance water maze task acquisition by deer mice and suggest that these facilitatory effects on spatial performance involve alterations in opioid activity.Abbreviations ELF extremely low frequency - Hz hertz     

The effects of decapitation and the influence of size and sex on diuresis in newly emerged mosquitoes

ABSTRACT. Diuresis in the newly emerged adult mosquito occurs in two phases, a short initial peak immediately after eclosion and a longer peak in the middle of day 1. The present work lends support to the view that the second phase of diuresis is controlled by a hormone which is either released from the head, or from the thorax under the control of the head, 3–4 h after eclosion. The influence of the head ceases to be effective some 9 h later. The rate of water loss is normally higher in unfed females than in unfed males. Whereas the higher rate of diuresis in females during the two peaks is a function of size, the higher rate in unfed females during the second and third day following eclosion is mostly a result of ovarian activity during this period.     

Geographic variation in body size: the effects of ambient temperature and precipitation

Latitudinal trends in body size have been explained as a response to temperature- or water-related factors, which are predictors of primary production. We used the first principal component calculated from three body parameters (weight, body length and the greatest length of the skull) of a sample of mammals from Israel and Sinai to determine those species that vary in size geographically, and whether such variation is related to annual rainfall, average minimum January temperature and average maximum August temperature. We used a conservative approach to discern the effects of precipitation and temperature by applying sequential regression. Variable priorities were assigned according to their bivariate correlation with body size, except for rainfall and its interactions that entered into the model last. Eleven species (Acomys cahirinus, Apodemus mystacinus, Canis lupus, Crocidura suaveolens, Gerbillus dasyurus, Hyaena hyaena, Lepus capensis, Meles meles, Meriones tristrami, Rousettus aegyptius and Vulpes vulpes) of the 17 species examined varied in size geographically. In five of them, rainfall was positively related to body size, while in one species it was negatively related to it. Contrary to the prediction of Bergmann’s rule, mean minimum January temperature was positively related to body size in five species and negatively related to body size in two species (C. suaveolens and G. dasyurus). As predicted by Bergmann’s rule, maximum June temperature was negatively related to body size in three species, and positively so in one (L. capensis). Primary production, particularly in desert and semi-desert areas, is determined mainly by precipitation. The above results indicate that, in our sample, primary production has an important effect on body size of several species of mammals. This is evident from the considerable proportion of the variability in body size explained by rain. However, low ambient temperatures may slow down and even inhibit photosynthesis. Hence, the observed positive relationships between average minimum January temperature and body size in four of the six species influenced by rain further support this conclusion.     

Production of winged and wingless males in the ant, <Emphasis Type="Italic">Cardiocondyla minutior</Emphasis>

Summary Wingless (ergatoid) males of the tramp ant Cardiocondyla minutior attack and kill their young ergatoid rivals and thus attempt to monopolize mating with female sexuals reared in the colony. Because of the different strength of local mate competition in colonies with one or several reproductive queens, we expected the production of new ergatoid males to vary with queen number. Sex ratios were mostly female-biased, but in contrast to the sympatric species C. obscurior (Cremer and Heinze, 2002) neither the percentage of ergatoid males nor of female sexuals among the first 20 sexuals produced varied considerably with queen number. As in C. obscurior, experimental colony fragmentation led to the production of winged males, whereas in unfragmented control colonies only ergatoid males eclosed.Received 3 December 2003; revised 20 February 2004; accepted 23 February 2004.     

Sexual size dimorphism and selection in the wild in the waterstrider Aquarius remigis: Body size,components of body size and male mating success

Sexual size dimorphism is assumed to be adaptive and is expected to evolve in response to a difference in the net selection pressures on the sexes. Although a demonstration of sexual selection is neither necessary nor sufficient to explain the evolution of sexual size dimorphism, sexual selection is generally assumed to be a major evolutionary force. If contemporary sexual selection is important in the evolution and maintenance of sexual size dimorphism then we expect to see concordance between patterns of sexual selection and patterns of sexual dimorphism. We examined sexual selection in the wild, acting on male body size, and components of body size, in the waterstrider Aquarius remigis, as part of a long term study examining net selection pressures on the two sexes in this species. Selection was estimated on both a daily and annual basis. Since our measure of fitness (mating success) was behavioral, we estimated reliabilities to determine if males perform consistently. Reliabilities were measured as ? statistics and range from fair to perfect agreement with substantial agreement overall. We found significant univariate sexual selection favoring larger total length in the first year of our study but not in the second. Multivariate analysis of components of body size revealed that sexual selection for larger males was not acting directly on total length but on genital length. Sexual selection for larger male body size was opposed by direct selection favoring smaller midfemoral lengths. While males of this species are smaller than females, they have longer genital segments and wider forefemora. Patterns of contemporary sexual selection and sexual size dimorphism agree only for genital length. For total length, and all other components of body size examined, contemporary sexual selection was either nonsignificant or opposed the pattern of size dimporhism. Thus, while the net pressures of contemporary selection for the species may still act to maintain sexual size dimorphism, sexual selection alone does not.     

Insularity and the evolution of melanism,sexual dichromatism and body size in the worldwide‐distributed barn owl

Island biogeography has provided fundamental hypotheses in population genetics, ecology and evolutionary biology. Insular populations usually face different feeding conditions, predation pressure, intraspecific and interspecific competition than continental populations. This so‐called island syndrome can promote the evolution of specific phenotypes like a small (or large) body size and a light (or dark) colouration as well as influence the evolution of sexual dimorphism. To examine whether insularity leads to phenotypic differentiation in a consistent way in a worldwide‐distributed nonmigratory species, we compared body size, body shape and colouration between insular and continental barn owl (Tyto alba) populations by controlling indirectly for phylogeny. This species is suitable because it varies in pheomelanin‐based colouration from reddish‐brown to white, and it displays eumelanic black spots for which the number and size vary between individuals, populations and species. Females are on average darker pheomelanic and display more and larger eumelanic spots than males. Our results show that on islands barn owls exhibited smaller and fewer eumelanic spots and lighter pheomelanic colouration, and shorter wings than on continents. Sexual dimorphism in pheomelanin‐based colouration was less pronounced on islands than continents (i.e. on islands males tended to be as pheomelanic as females), and on small islands owls were redder pheomelanic and smaller in size than owls living on larger islands. Sexual dimorphism in the size of eumelanic spots was more pronounced (i.e. females displayed much larger spots than males) in barn owls living on islands located further away from a continent. Our study indicates that insular conditions drive the evolution towards a lower degree of eumelanism, smaller body size and affects the evolution of sexual dichromatism in melanin‐based colour traits. The effect of insularity was more pronounced on body size and shape than on melanic traits.     

Ecological context of breeding system variation: sex, size and pollination in a (predominantly) gynodioecious shrub

BACKGROUND AND AIMS: Species that exhibit among-population variation in breeding system are particularly suitable to study the importance of the ecological context for the stability and evolution of gender polymorphism. Geographical variation in breeding system and sex ratio of Daphne laureola (Thymelaeaceae) was examined and their association with environmental conditions, plant and floral display sizes, and pollination environment in a broad geographic scale was analysed. METHODS: The proportion of female and hermaphrodite individuals in 38 populations within the Iberian Peninsula was scored. Average local temperature and precipitation from these sites were obtained from interpolation models based on 30 years of data. Pollination success was estimated as stigmatic pollen loads, pollen tubes per ovule and the proportion of unfertilized flowers per individual in a sub-set of hermaphroditic and gynodioecious populations. KEY RESULTS: Daphne laureola is predominantly gynodioecious, but hermaphroditic populations were found in northeastern and southwestern regions, characterized by higher temperatures and lower annual precipitation. In the gynodioecious populations, female plants were larger and bore more flowers than hermaphrodites. However, due to their lower pollination success, females did not consistently produce more seeds than hermaphrodites, which tends to negate a seed production advantage in D. laureola females. In the northeastern hermaphroditic populations, plants were smaller and produced 9-13 times fewer flowers than in the other Iberian regions, and thus presumably had a lower level of geitonogamous self-fertilization. However, in a few southern populations hermaphroditism was not associated with small plant size and low flower production. CONCLUSIONS: The findings highlight that different mechanisms, including abiotic conditions and pollinator service, may account for breeding system variation within a species' distribution range and also suggest that geitonogamy may affect plant breeding system evolution.     

Influences of sex,ontogeny and body size on the thermal ecology of Liolaemus lutzae (Squamata,Liolaemidae) in a restinga remnant in southeastern Brazil

Variations in body temperature (T_b) of lizards can be partially explained by intrinsic factors such as sex, ontogeny and body size. Liolaemus lutzae is a lizard species restricted to restingas in the Brazilian coast in the state of Rio de Janeiro. Herein, we studied sexual dimorphism and influences of sex, ontogeny, and body size to the T_b of L. lutzae. Adult males were larger than adult females, probably due to both intersexual selection and intra-sexual selection. There was intersexual difference in lizards' T_b (males hotter than females), but T_b did not differ after factored out for the effects of body size. The mean T_b of juvenile lizards was higher than that of adults after factored out for the effect of body mass. It is possible that adults may have excluded juveniles from microhabitats with better thermal regimes. Also, this might have occurred due to requirements of juveniles to maintain high growth rates. Forage searching for prey by juveniles also exposes them to high environmental temperatures. Juveniles also may have higher T_b than co-specific adults (relative to body mass) to favor prey capture. In absolute values, adult lizards tended to use microhabitats with lower temperatures than that used by juveniles, possibly to avoid risks of overheating and death. Body temperature and snout–vent length were positively related, as well as body temperature and body mass, presumably caused by the thermal inertia of the bodies (trend of a body to resist to changes in its temperature). Intrinsic factors such as sex, ontogeny and body size can affect the thermal ecology of L. lutzae, despite coastal habitat features to which they are exposed also influences the body temperature of active lizards in restinga habitats.