The Sicker Sex: Understanding Male Biases in Parasitic Infection,Resource Allocation and Fitness

The “sicker sex” idea summarizes our knowledge of sex biases in parasite burden and immune ability whereby males fare worse than females. The theoretical basis of this is that because males invest more on mating effort than females, the former pay the costs by having a weaker immune system and thus being more susceptible to parasites. Females, conversely, have a greater parental investment. Here we tested the following: a) whether both sexes differ in their ability to defend against parasites using a natural host-parasite system; b) the differences in resource allocation conflict between mating effort and parental investment traits between sexes; and, c) effect of parasitism on survival for both sexes. We used a number of insect damselfly species as study subjects. For (a), we quantified gregarine and mite parasites, and experimentally manipulated gregarine levels in both sexes during adult ontogeny. For (b), first, we manipulated food during adult ontogeny and recorded thoracic fat gain (a proxy of mating effort) and abdominal weight (a proxy of parental investment) in both sexes. Secondly for (b), we manipulated food and gregarine levels in both sexes when adults were about to become sexually mature, and recorded gregarine number. For (c), we infected male and female adults of different ages and measured their survival. Males consistently showed more parasites than females apparently due to an increased resource allocation to fat production in males. Conversely, females invested more on abdominal weight. These differences were independent of how much food/infecting parasites were provided. The cost of this was that males had more parasites and reduced survival than females. Our results provide a resource allocation mechanism for understanding sexual differences in parasite defense as well as survival consequences for each sex.     

Variation in testosterone levels and male reproductive effort: Insight from a polygynous human population

Recent evidence suggests that, in humans, variations in testosterone (T) levels between men reflect their differential allocation in mating versus parenting efforts. However, most studies have been conducted in urbanized, monogamous populations, making generalizations from them questionable. This study addresses the question of whether indicators of male reproductive effort are associated with variations in salivary T levels in a polygynous population of agriculturists in rural Senegal. We first show that pair-bonding and/or transition to fatherhood is associated with T profiles: married fathers (N = 53) have lower morning and afternoon T levels than unmarried non-fathers (N = 28). Second, among fathers, individual differences in parenting effort, as well as variations in mating effort, predict morning T levels. Indeed, men highly investing in parental care show lower morning T levels. Moreover, among men under 50, polygynous men show higher morning T levels than monogamous men. Taken together with previous results in monogamous settings, these findings suggest that the endocrine regulation of reproductive effort is probably a general feature of human populations.     

Paternal effort and its relation to mating success in the European ground squirrel

The necessity for parental care is a driving force for determining mating systems and social organization. The European ground squirrel, Spermophilus citellus, is a polygynous, gregarious species in which male parental behaviour would not be expected. We had observed males digging in litter burrows that were later occupied by females and their offspring. Males never stayed overnight within these burrows. To determine whether this was some kind of paternal effort we tested the following hypotheses: (1) that male burrowing behaviour was directed towards the male's own offspring or towards the pregnant or lactating mother of the male's offspring; (2) that this behaviour had costs in terms of condition, decreased survival or fecundity; and (3) that it benefited offspring condition or survival. All three assumptions were met. Males worked on the litter burrow of their copulatory partners. Thus, this behaviour was directed towards the male's potential offspring. Male burrowing costs were seen in decreased foraging time and increased body mass loss. Offspring benefits were evident in increased mass at natal emergence. We conclude that male digging at litter burrows can be considered as paternal effort. Lastly, we considered the effects of polygyny on this male parental effort by comparing mating effort, mating success and paternal effort. High mating success was associated with high mating effort and low paternal effort. Moderate to low mating success was associated with lower mating effort and higher paternal effort, indicating a trade-off between the two.     

Parental and Mating Effort: Is There Necessarily a Trade‐Off?

One of the common assumptions in the study of the evolution of parental care is that trade-offs exist between parental investment and other fitness-related traits. In general, this body of work follows the traditional definition that parental investment (in the current offspring) decreases that individual's ability to invest in future reproduction ( Trivers 1972 ). However, examination of the empirical evidence shows that assuming a trade-off between parental and mating effort is not always appropriate. This overemphasis on a trade-off between mating and parental effort has arisen in part because of an oversimplification of female reproductive strategies, a failure to consider interactions between the sexes, and a tendency to consider behaviours as unifunctional, thereby ignoring the more complex relationship between mating and parental effort in many species. Here, we first examine the empirical evidence for trade-offs between mating and parental effort in males and females to ask when trade-offs occur and what pattern they take. By highlighting a number of exemplar species, we then explore how the presence or absence of trade-offs relates to mate choice and sexual selection in both sexes. Finally, we highlight the importance of considering individual variation, which has been particularly overlooked in examinations of female investment, and how preferences in one sex may influence the existence and our interpretation of apparent trade-offs in the other sex.     

Identifying Node Role in Social Network Based on Multiple Indicators

It is a classic topic of social network analysis to evaluate the importance of nodes and identify the node that takes on the role of core or bridge in a network. Because a single indicator is not sufficient to analyze multiple characteristics of a node, it is a natural solution to apply multiple indicators that should be selected carefully. An intuitive idea is to select some indicators with weak correlations to efficiently assess different characteristics of a node. However, this paper shows that it is much better to select the indicators with strong correlations. Because indicator correlation is based on the statistical analysis of a large number of nodes, the particularity of an important node will be outlined if its indicator relationship doesn''t comply with the statistical correlation. Therefore, the paper selects the multiple indicators including degree, ego-betweenness centrality and eigenvector centrality to evaluate the importance and the role of a node. The importance of a node is equal to the normalized sum of its three indicators. A candidate for core or bridge is selected from the great degree nodes or the nodes with great ego-betweenness centrality respectively. Then, the role of a candidate is determined according to the difference between its indicators'' relationship with the statistical correlation of the overall network. Based on 18 real networks and 3 kinds of model networks, the experimental results show that the proposed methods perform quite well in evaluating the importance of nodes and in identifying the node role.     

Cortical representation of the heart sinus node zone

Evoked potentials (EP) arising in response to electrical stimulation of the heart sinus node zone (SNZ) were registered in the cortex of the large hemispheres (LHS) of cats. EP with the shortest latent period (LP) of 18-19 months were recorded both in the left and right hemispheres in the area of a cross-shaped cleft (associative field PCA, partially the I motorsensor zone and the I sensorimotor zone). Besides, EP with a more durable LP (20-21 months) were registered in the 2nd sensorimotor zone. EP remained unchanged after bilateral vagotomy and disappeared after spinal cord cutting at C-2 level. The presence of the functional centre regulating cardiac activity in the branch sections of LHS is suggested.     

Extraterritorial forays and male parental care in hooded warblers

Extrapair paternity is common among many songbird species yet few studies have quantified male extraterritorial foray (ETF) effort and examined potential trade-offs. One potentially important constraint for males is the need to provide parental care. Current models of male extrapair mating tactics propose that males reduce extraterritorial foray effort later in the breeding season because they face a trade-off between feeding nestlings versus pursuing extrapair matings. However, detailed field studies examining the trade-off between paternal care and male extraterritorial forays are lacking. We used radiotelemetry to quantify male extraterritorial foray effort in hooded warblers, Wilsonia citrina, to test the widely held predictions that: (1) males make significantly fewer and shorter forays during the nestling stage relative to other stages (i.e. fertile and incubating stages); and (2) male extraterritorial foray effort is negatively correlated with parental effort. Males made 0.87+/-0.09 forays/h and spent on average 12.2% of their time foraying off territory. Results were equivocal; some data suggested male foray effort decreased in relation to parental care, while other data suggested otherwise. Pairwise tests controlling for (1) extrapair mating opportunity among males and (2) male, territory and social mate quality revealed a possible trade-off between the mean duration and percentage of time in extraterritorial foray versus providing parental care. Conversely, results also revealed (1) no difference in foray rate, foray duration or percentage of time spent off territory over the various stages of the breeding season, (2) no relationship between male foray effort and male feeding rate, and (3) no difference in foray rate in pairwise comparisons, controlling for variability in extrapair mating opportunity and male quality. Overall, the trade-off between providing male parental care and pursuing alternative mating tactics may not be as strong for male hooded warblers as once hypothesized because males dedicated relatively little time to seeking extrapair copulations off territory. Copyright 2000 The Association for the Study of Animal Behaviour.     

Variation in testosterone levels and male reproductive effort: Insight from a polygynous human population

Recent evidence suggests that, in humans, variations in testosterone (T) levels between men reflect their differential allocation in mating versus parenting efforts. However, most studies have been conducted in urbanized, monogamous populations, making generalizations from them questionable. This study addresses the question of whether indicators of male reproductive effort are associated with variations in salivary T levels in a polygynous population of agriculturists in rural Senegal. We first show that pair-bonding and/or transition to fatherhood is associated with T profiles: married fathers (N = 53) have lower morning and afternoon T levels than unmarried non-fathers (N = 28). Second, among fathers, individual differences in parenting effort, as well as variations in mating effort, predict morning T levels. Indeed, men highly investing in parental care show lower morning T levels. Moreover, among men under 50, polygynous men show higher morning T levels than monogamous men. Taken together with previous results in monogamous settings, these findings suggest that the endocrine regulation of reproductive effort is probably a general feature of human populations.     

Song as an indicator of male parental effort in the sedge warbler

Repertoire size has been found to be a sexually selected trait in a number of bird species, although the advantages of mating with a male who possesses a complex song remain unclear. We studied the potential role of song as an indicator of male parental effort in the sedge warbler Acrocephalus schoenobaenus. The male provisioning rate was used as a measure of male parental effort and was found to increase with nestling age and brood size. When controlling for chick age, brood size and other variables, we found a highly significant positive correlation between a measure of song complexity (repertoire size) and male parental effort. Both male parental effort and repertoire size were found to be positively correlated with chick weight when controlling for chick age. We found no correlation between a measure of song output (amount of song flighting) or territory size and parental effort. Repertoire size is known to be the most important cue in female choice amongst sedge warblers and we discuss the possible reasons for this. We suggest that, in choosing a male with a large repertoire, a female obtains not only indirect benefits but also direct benefits in the form of increased parental effort.     

Natural variation in a testosterone-mediated trade-off between mating effort and parental effort

Male birds frequently face a trade-off between acquiring mates and caring for offspring. Hormone manipulation studies indicate that testosterone often mediates this trade-off, increasing mating effort while decreasing parental effort. Little is known, however, about individual covariation between testosterone and relevant behavior on which selection might act. Using wild, male dark-eyed juncos (Junco hyemalis), we measured individual variation in testosterone levels before and after standardized injections of gonadotropin-releasing hormone (GnRH). The GnRH challenges have been shown to produce short-term testosterone increases that are similar to those produced naturally in response to social stimuli, repeatable in magnitude, and greater in males with more attractive ornaments. We correlated these testosterone increases with behavioral measures of mating and parental effort (aggressive response to a simulated territorial intrusion and nestling feeding, respectively). Males that showed higher postchallenge testosterone displayed more territorial behavior, and males that produced higher testosterone increases above initial levels displayed reduced parental behavior. Initial testosterone levels were positively but nonsignificantly correlated with aggression but did not predict parental behavior. These relationships suggest that natural variation in testosterone, specifically the production of short-term increases, may underlie individual variation in the mating effort/parental effort trade-off. We discuss the implications of these results for the evolution of hormonally mediated trade-offs.     

The interplay between microscopic and mesoscopic structures in complex networks

Understanding a complex network's structure holds the key to understanding its function. The physics community has contributed a multitude of methods and analyses to this cross-disciplinary endeavor. Structural features exist on both the microscopic level, resulting from differences between single node properties, and the mesoscopic level resulting from properties shared by groups of nodes. Disentangling the determinants of network structure on these different scales has remained a major, and so far unsolved, challenge. Here we show how multiscale generative probabilistic exponential random graph models combined with efficient, distributive message-passing inference techniques can be used to achieve this separation of scales, leading to improved detection accuracy of latent classes as demonstrated on benchmark problems. It sheds new light on the statistical significance of motif-distributions in neural networks and improves the link-prediction accuracy as exemplified for gene-disease associations in the highly consequential Online Mendelian Inheritance in Man database.     

跨界保护区网络构建研究进展

跨界保护区网络是生物多样性保护网络的一种特殊形式,对保护国家或地区边界线附近丰富的生物多样性具有重要意义。构建跨界保护区网络已被列为《生物多样性公约》(Convention on Biological Diversity)框架下"保护区工作组"的一项战略任务,涉及生态、环境、经济、政治等多个领域,成为全球保护区研究领域的热点问题之一。然而,目前我国对跨界保护区的研究尚处于起步阶段,在如何构建不同尺度的跨界保护区网络等方面的研究仍有待进一步加强。在分析了全球、洲际、两个或多个国家和地区之间等不同尺度跨界保护区网络研究的基础上,综述了国内外基于"节点"-"廊道"模式的跨界保护区网络构建研究进展,并结合我国跨界保护区网络建设的实际情况,对我国未来跨界保护区网络构建研究进行了展望。     

Devoted fathers or selfish lovers? Conflict between mating effort and parental care in a harem‐defending arachnid

When there is a temporal trade‐off between mating effort and parental care, theoretical models predict that intense sexual selection on males leads to reduced paternal care. Thus, high‐quality males should invest more in mating effort because they have higher chances of acquiring mates, whereas low‐quality males should bias their investment towards parental care. Once paternal care has evolved, offspring value should also influence males’ decisions to invest in offspring attendance. Here, we performed a manipulation under field conditions to investigate the factors that influence male allocation in either mating effort or parental care. We predicted that facultative paternal care in the harem‐holding harvestman Serracutisoma proximum would be negatively influenced by male attractiveness and positively influenced by offspring value. We found that attractive males were less likely to engage in egg attendance and that the higher the perceived paternity, the higher the caring frequency. Finally, egg mortality was not related to caring frequency by males, but predation pressure was much lower than that recorded in previous studies with the same population. Thus, the benefits of facultative male care may be conditional to temporal variation in the intensity of egg predation. In conclusion, males adjust their investment in either territory defence or egg attendance according to their recent mating history and perceived paternity. Our findings suggest that exclusive paternal care can evolve from facultative paternal care only if the trade‐off between mating effort and parental care is circumvented.     

Paternal Care by Genetic Fathers and Stepfathers II: Reports by Xhosa High School Students

In this article we present a biosocial model of human male parental care that allows relationship (mating) effort to influence male parental allocations. The model recognizes four classes of relationships between men and the children they parent: genetic offspring of current mates (combined relationship and parental effort), genetic offspring of previous mates (parental effort solely), step offspring of current mates (relationship effort solely), and stepchildren of previous mates (essentially no expected investment). We test the model using data on parental investment collected from 340 Xhosa high school students in Cape Town, South Africa. Six measures of paternal investment are examined: the amount of money men spent on students for school, clothing, and miscellaneous expenditures, respectively, and how often men spent time with children, helped them with their homework, or spoke English with them. The tests provide support for the roles of both parental and relationship effort in influencing parental care: men invest significantly more in their genetic offspring and in the children of their current mates. We also examine several proximate influences on parental care, specifically the age and sex of the child, and the percentage of the child's life the father figure coresided with him or her.     

Sustainable mobility indicators for Indian cities: Selection methodology and application

Various indicators of sustainable mobility have been developed. It is difficult to select the most relevant indicators that are useful in a specific context, and that are measurable and achievable at the same time. Indicator selection frameworks – criteria based; causal chains and causal networks have been proposed and used in the past. All three frameworks have certain limitations and strengths.In this study we have proposed a systematic approach of selecting sustainable mobility indicators for Indian cities by combining – criteria based, causal chain and causal network frameworks. The methodology involves both subjective judgments for evaluation of indicators against a set of criteria and objectivity during development and assessment of causal network. The method results in identifying 20 relevant factors for which 32 indicators are shortlisted. Further work is required to develop measurable indicators related to accessibility to the disadvantaged, speed limit restriction and street lighting. These have not been discussed in detail in the existing literature. The 20 factors are classified as root nodes, central and end-of-the-chain nodes that helps in identifying levers of attaining sustainable mobility in Indian cities.The developed causal network is evaluated for its ability to address all sectors associated with sustainable mobility. The causal network has low density and centralization index and therefore accounts for multiple factors. The shortlisted indicators are proposed for preparing low carbon mobility plan (LCMP) for three medium size Indian cities. The indicators are checked for data availability and ease of measurability based on the data collected for preparing the three LCMPs. The analysis shows that the data are available from secondary sources like census to measure root node indicators, whereas central indicators require conducting primary surveys and specific models are required to measure end-of-the-chain indicators.Based on the position of indicators within causal network, it is interpreted that pricing policy, urban form and infrastructure are the levers of sustainable mobility. The indicators of energy consumption, emissions and accessibility are the sustainable mobility targets that we want to achieve.     

Men’s reproductive investment decisions

Using questionnaire data completed by 170 men, we examine variation in paternal investment in relation to the trade-off between mating and parenting. We found that as men’s self-perceived mate value increases, so does their mating effort, and in turn, as mating effort increases, paternal investment decreases. This study also simultaneously examined the influence on parental investment of men’s mating effort, men’s perception of their mates’ fidelity, and their perceived resemblance to their offspring. All predicted investment. The predictors of investment are also tested independently for men who are still in a relationship with the mother of their children and those that are separated from her. Finally we examine how self-perceived mate value affects how men respond to variation in paternity confidence. Men with a self-perceived low mate value were less likely to respond to lowered mate fidelity by reducing their parental investment compared with men with a self-perceived high mate value.     

Marriage Markets and Male Mating Effort: Violence and Crime Are Elevated Where Men Are Rare

The negative social outcomes in populations with male-biased sex ratios are a growing concern. In general, the expectation is of heightened violence as a result of excess men engaging in antisocial behavior and crime, thereby threatening societal stability. While intuitive, these claims are largely unsupported in the literature. Using mating market theory as our guide, we examine indicators of male mating effort, including (1) violent competition between men (homicide, aggravated assault) and (2) indicators of uncommitted sexual behavior (rape, sex offenses, and prostitution). Our unit of analysis is U.S. county-level data. We find that counties with more men have lower rates of crime and violent behavior. Our findings challenge conventional claims of male excess leading to elevated levels of violence. Instead, in support of mating market predictions, we find that criminal and violent behavior related to male mating effort is least common in male-biased sex ratios. We discuss the implications of our findings for public policy regarding incarceration and criminal behavior.     

Function of the Hemolymph Nuptial Gift in the Ground Cricket,Allonemobius socius

Nuptial feeding, although common in the insect world, varies greatly in its form and function. Here, we test the function of the hemolymph nuptial gift in the southern ground cricket, Allonemobius socius, and attempt to determine if it functions as parental investment or mating effort. We manipulated the number of gifts a female received during courtship (one vs. none). We also recorded other aspect of courtship, such as feeding duration and spermatophore attachment duration. Female fecundity was measured for 7 d post‐mating. Our results indicate that female egg laying is significantly higher when a gift is provided, but the increase in egg laying is not related to gift size. In addition, the lack of a gift does not affect the male's ability to transfer a spermatophore. Together, these data suggest that the nuptial gift acts as parental investment and not as mating effort.     

Testosterone affects reproductive success by influencing extra-pair fertilizations in male dark-eyed juncos (Aves: Junco hyemalis)

Monogamous male birds typically allocate less effort to courtship and more to parental behaviour than males of polygynous species. The seasonal pattern of testosterone (T) secretion varies accordingly. Monogamous males exhibit a spring peak in plasma T followed by lower levels during the parental phase, while males of polygynous species continue to court females and maintain T at higher levels. To determine whether testosterone underlies the trade-off between mating and parental effort, we treated male dark-eyed juncos (Junco hyemalis) with exogenous T and compared the reproductive success (RS) of T-treated males (T-males) to that of controls. T-males had lower apparent annual RS than controls, probably because elevated T reduced parental care. Nevertheless, annual genetic RS of the treatment groups was similar because (i) T-males suffered fewer losses in genetic RS due to extra-pair fertilizations (EPFs), and (ii) T-males gained more genetic RS through their own EPFs. This is the first hormonal manipulation of an avian phenotype shown to have influenced male RS through EPFs. Together with other studies, it suggests that testosterone may have mediated the evolution of inter- and intraspecific differences in allocation of reproductive effort to mate attraction and parental care.