Differential Mortality Of Males Research Articles

Macronutrient intake and simulated infection threat independently affect life history traits of male decorated crickets.

Nutritional geometry has advanced our understanding of how macronutrients (e.g., proteins and carbohydrates) influence the expression of life history traits and their corresponding trade‐offs. For example, recent work has revealed that reproduction and immune function in male decorated crickets are optimized at very different protein:carbohydrate (P:C) dietary ratios. However, it is unclear how an individual's macronutrient intake interacts with its perceived infection status to determine investment in reproduction or other key life history traits. Here, we employed a fully factorial design in which calling effort and immune function were quantified for male crickets fed either diets previously demonstrated to maximize calling effort (P:C = 1:8) or immune function (P:C = 5:1), and then administered a treatment from a spectrum of increasing infection cue intensity using heat‐killed bacteria. Both diet and a simulated infection threat independently influenced the survival, immunity, and reproductive effort of males. If they called, males increased calling effort at the low infection cue dose, consistent with the terminal investment hypothesis, but interpretation of responses at the higher threat levels was hampered by the differential mortality of males across infection cue and diet treatments. A high protein, low carbohydrate diet severely reduced the health, survival, and overall fitness of male crickets. There was, however, no evidence of an interaction between diet and infection cue dose on calling effort, suggesting that the threshold for terminal investment was not contingent on diet as investigated here.

Modeling Landscape-Level Spatial Variation in Sex Ratio Skew in the Mountain Pine Beetle (Coleoptera: Curculionidae).

Through their influence on effective population sizes, sex ratio skew affects population dynamics. We examined spatial variation in female-biased sex ratios in the mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak in western Canada to better understand how environmental context affects sex ratio skew. Our specific objectives were to: 1) characterize spatial variation in mountain pine beetle sex ratio; 2) test previously asserted hypotheses that beetle sex ratio varies with tree diameter and year in outbreak; and 3) develop predictive models of sex ratio skew for larval and adult populations. Using logistic regression, we modeled the probability that an individual beetle (n = 2,369) was female as a function of multiple environmental variables across 34 stands in British Columbia and Alberta, Canada. We identified a consistent female-biased sex ratio with significantly greater skew in adults (2:1, n = 713) than in larvae (1.76:1, n = 1,643). We found that the proportion of larval females increased with decreasing tree size and with outbreak age. However, adults did not respond to tree size and larvae did not respond to outbreak age. Predictive models differed between larvae and adults. All identified models perform well and included predictors related to weather, tree diameter, and year in outbreak. Female-biased sex ratios appear to originate from differential male mortality during development rather than from sex-biased oviposition, suggesting sex ratio skew is not the cause of outbreaks, but rather a consequence.

Seasonal sex allocation by Common Grackles? Comment

or differential mortality by sex in 2004-2006, unlike the ones I studied in 1976 and 1977 in Michigan (Howe 1976, 1977). In theory, heterogametic female birds can control primary sex of offspring through nonrandom meiosis, as well as that of older nestlings through manipulation of parental care. The Michigan study reported contingent female control of sex ratio during the season, presumably through nonrandom meiosis, and male-biased late broods likely reflecting differential mortality of males as part of an adaptive brood reduction strategy when food was scarce. Maddox and Weatherhead (2009) broaden understanding of sex-ratio adjustment, and its absence, in this bird. The larger issues of contingency in ecology in general and sex-ratio adjustment in particular that have come to light in recent decades deserve more emphasis than their report offers. The data from the Michigan study are what they are (Howe 1976, 1977). Sexual dimorphism by fledging led to a prediction that sex ratios near independence should be skewed in favor of the smaller females, assuming males were more costly to rear than females ?80% of male living mass (sensu Fisher 1930). Skew in favor of female fledglings was suggestive in 1976 and 1977 in clutches of five, and the data for both years pooled differed from 50:50 with a two-tailed test (P = 0.024; Table 2 of Howe 1977). A seasonal skew of sex ratio of 12-day embryos in large clutches, with nests in early and mid April mostly female and those in late April and early May mostly male, was entirely unexpected (Fig. 1 of Howe 1977). Two-tailed Pearson correlations using the angular transformation were just or almost statisti

The marriage squeeze in Colombia, 1973–2005: The role of excess male death

Abstract Colombia has been characterized by extreme levels of civil violence throughout the latter part of the twentieth century, and the burden of excess mortality attributable to this violence has been borne primarily by young men. Populations with a large violent death burden are likely to experience consequences in terms of (1) marriage markets, (2) the dynamics of family formation and dissolution, and (3) patterns of parental investment in offspring. Using data from national censuses and household surveys, we calculate a measure of the marital sex ratio in order to explore the impact of differential male mortality on marriage markets in Colombia. Overall, Colombia is characterized by a female biased sex ratio at all ages. This relative excess of women is particularly pronounced in certain departments of the Central and Pacific regions which have been especially affected by civil violence. We suggest that the low sex ratios which characterized Colombia are partially responsible for the increasingly hi...

Fetal sex ratio variation in the highly polygynous Himalayan tahr: evidence for differential male mortality

The Trivers and Willard model (TWM) predicts that for polygynous ungulates, females of high phenotypic quality should produce more sons than daughters, whereas females of low phenotypic quality should produce more daughters. Kruuk et al. showed that in red deer the TWM only applied when the population was below carrying capacity, and they suggested that published examples supported their interpretation. More recently, Saltz proposed that mothers' age rather than condition could account for skewed sex ratios observed in ungulate populations. We tested these predictions by using data on maternal age, mass, kidney fat reserves (KFI), and fetal sex ratio in an invading population of Himalayan tahr (n = 252), a highly sexually dimorphic and polygynous ungulate introduced to New Zealand. Differences in the body mass and KFI of female tahr supported the prediction that the populations in areas colonized for less than 15 years were below carrying capacity, whereas those in areas colonized for more than 30 years were at, or near, carrying capacity. There was no trend for mothers either of larger mass or with greater KFI to produce more sons than daughters. There was also no evidence of a quadratic relationship between maternal age and the proportion of male fetuses. However, the proportion of male fetuses declined with increasing sampling date independent of maternal attributes. Among 1193 females checked for pregnancy, pregnancy rates increased to a maxima in mid-July. Thereafter, the proportion of females pregnant declined among the three age classes (1, 2, and 3 or more years). Our results therefore provide support for the idea that males experience greater mortality in utero. The role of differential fetal mortality in determining ungulate birth sex ratios deserves further investigation.

Demography of lions in relation to prey and habitat in the Maasai Mara National Reserve, Kenya

AbstractWe studied lion demography in the Maasai Mara National Reserve between September 1990 and April 1992, with a special emphasis on the spatial and seasonal variation in demographic characteristics. Lion density (0.2–0.4 lions km−2) and pride size (range 8–48) were high because of a high resident prey biomass (10 335 kg km−2) augmented by migrant prey to 26 092 kg km−2 in the dry season. Overall, their sex ratio was almost at parity and varied neither spatially nor seasonally. Sex ratio was even among subadults but skewed toward males and females among cubs and adults, respectively. This implies an increasing differential mortality of males with age through subadulthood. The age ratio varied seasonally because of a birth peak in March–June and an influx of subadults into the reserve during July–August, coincident with increases in migrant prey. The birth peak was apparently preceded by another peak in mating activity falling between November and May. Further research should investigate the precise causes of the biased cub sex ratio, low lion density in the Mara Triangle and the higher ratio of subadults in Musiara than in the Mara Triangle or Sekenani.

GENDER-SPECIFIC SELECTION DURING EARLY LIFE HISTORY STAGES IN THE DIOECIOUS GRASSDISTICHLISSPICATA

Bias in the adult sex ratio of a population, if not due to a biased primary sex ratio, may be due to differential mortality of males and females, which can occur during any life history stage. Yet, although adult sex-ratio bias is common in dioecious plant species, little is known about the demography of prereproductive individuals. Using a RAPD-PCR (randomly amplified polymorphic DNA) marker that co-segregates with female phenotype, I studied juvenile demography in the saltmarsh grass Distichlis spicata, which exhibits within-population sex-ratio variation (spatial segregation of the sexes) and has genetic sex determination. First, I surveyed populations of D. spicata to ascertain whether any environmental factor co-varies with local sex ratio, and I found that habitats with female majorities are located at significantly lower elevations in the marsh than are habitats with male majorities. In randomly collected seeds, the sex ratio was significantly biased toward females, but male and female seeds did not differ in mass. Using a subsample of these seeds, I conducted greenhouse and field experiments to examine whether differences in seed germination or seedling survival between the sexes explain sex-ratio variation along the micro-elevation gradient in the marsh. In greenhouse treatments designed to mimic field habitats with female majorities, more male seeds germinated than did female seeds. In habitats with female majorities in the field, significantly more female seedlings survived an extreme high tide than did male seedlings (25.17% of females vs. 13.49% of males). These results suggest that, in habitats with female majorities, gender-specific bias in seedling survivorship, rather than seed germination, is a causal factor in the underlying sex-ratio bias. In habitats with male majorities, seed germination and seedling survival did not differ between the sexes. This study is the first to document environment-dependent differential seed germination and seedling mortality between males and females in a dioecious plant species.

Sex, size, and plumage redness predict house finch survival in an epidemic

Mycoplasma gallisepticum is a well-known disease of poultry but until 1994 had not been observed in passerine birds. From 1994 to 1996, tens of millions of house finches (Carpodacus mexicanus) are believed to have died in an epidemic of mycoplasmal conjunctivitis, similar to 'pinkeye' in humans. The outbreak of Mycoplasma gallisepticum affected finches of both sexes but disproportionately killed males, shifting the sex ratio from male-biased to female-biased. This differential male mortality is consistent with a cost of testosterone, which is a key prediction of the immunocompetence handicap hypothesis. Males and females that survived the epidemic weighed significantly less and had significantly shorter wing chords, tarsi, and bills than did individuals before the epidemic. Male survivors also had significantly redder plumage than males that did not survive, supporting the idea that plumage brightness serves as an indicator of condition, as proposed by the honest advertisement model of sexual selection.

Sexual Size Dimorphism and Sibling Competition: Implications for Avian Sex Ratios

The blue-footed booby's (Sula nebouxii) first-hatched chick aggressively dominates and outgrows its sib and sometimes kills it when food is in short supply. Differential male mortality is expected since females grow to be 27% heavier than males and should have an advantage in sibling competition in mixed-sex broods. Surprisingly, when the male hatches first, even though his sister outgrows him, he usually sustains dominance over her throughout the nestling phase, and he grows and survives normally. When the sister hatches first, despite a large, persistent sibling size disparity the male grows and survives normally. These observations contradict the prevailing hypothesis that in sexually dimorphic birds that practice siblicidal brood reduction the smaller sex suffers differential mortality as the result of its disadvantage in sibling conflict in mixed-sex broods. Such species consequently are not expected to modify their primary sex ratio or associate sex with hatching order in response to biased mortality in brother-sister conflict.

Marriage and mortality: a life table analysis

This paper examines the effects of age at marriage and differential mortality of males and females on the incidence of widowhood between the sexes. Abridged life tables constructed from marital status and death registration data of a rural area of Bangladesh for the period 1974-79 were used. The difference in life expectancy between males and females varies from 0.4 to 2.2 years at the ages 0 to 65 years and over. The mortality differentials show that the probabilities of a male or a female surviving the other spouse would be approximately the same, were there no other influence. But the incidence of widows is about ten times that of widowers. Other relevant factors, under a given regime of mortality, are age at marriage and age difference between husband and wife.

Effects of Incubation Temperature on Sex Ratios in Pine Snakes: Differential Vulnerability of Males and Females

Sex ratios in vertebrates are the result of primary sex ratios and subsequent mortality rates. Mortality rates are generally higher in males, leading to differential longevity and biased sex ratios. Sex determination by heteromorphic sex chromosomes is common in mammals and birds and less so in other vertebrates. In many reptiles, sex is determined by incubation temperature, although in snakes, sex is determined genetically. Snakes are usually believed to have a male:female primary sex ratio of unity, although a male-biased sex ratio has recently been reported for hatchlings and adults. Here, sex ratios from 134 adult pine snakes observed over an 11-yr period in nature indicate a 0.39 sex ratio for all snakes and 0.66 for all non-gravid snakes. By size class (generally indicative of age), ratios varied (from smallest to largest snakes) from 0.78, 0.23, 0.54, to 0.40. For 37 clutches incubated at room temperature (cycling temperatures), the sex ratio varied yearly from 0.50 to 1.78. Under controlled laboratory conditions, sex ratios of hatchlings varied from 0.11 at an incubation temperature of 21$^\circ$C to 1.40 at an incubation temperature of 32$^\circ$C. However, primary sex ratios of all embryos (hatched and unhatched) did not differ significantly from unity at different incubation temperatures. These data indicate differential mortality of males and females during embryonic development as a function of incubation temperatures in pine snakes, potentially resulting in different hatching sex ratios in nature depending on environmental temperatures. These results suggest that biases in secondary or tertiary sex ratios could result from differential effects of an environmental gradient (temperature) on the sexes during development in poikilotherms.

Differential mortality of males and females, exemplified by West Germany

Sex differences in mortality are described and discussed, using data from the national causes of death statistics of West Germany. As in other industrialized countries, men in the FRG, compared to women, have higher mortality rates in all leading causes of death. The sex differences are most prominent in coronary heart disease, lung cancer, fatal accidents, suicide and liver cirrhosis. For example, in the age groups 35 to 55 the male/female ratio in the mortality rates was 6 to 7 for coronary heart disease, 3 to 4 for lung cancer, and 4 for fatal accidents. The cause-specific death rates and the results from corresponding epidemiological studies indicate that genetic disadvantages of men are reinforced by factors of the social environment and 'deleterious' individual behavior. Thus a great part of the sex differences in total mortality could be influenced and should not be judged as inevitable.

On the Biology of Gnathophylloides Mineri, a Shrimp Inhabiting the Sea Urchin Tripneustes Ventricosus

ABSTRACT The small shrimp Gnathophylloides mineri is a common inhabitant of the short spines of the sea urchin Tripneustes ventricosus found in shallow waters of eastern St. Croix, United States Virgin Islands. It shows remarkable cryptic coloration and behavioral and morphological features suggesting a past history of intense predation pressure. Gnathophylloides mineri feeds on the epithelium covering the sea urchin spines which is abraded by toothed setae on the second maxillipeds and perhaps also by small, handlike structures on the dactyls of the walking legs. It seems likely that dark pigment from the host test is incorporated by the shrimp. Filter feeding also occurs. The shrimp are usually found in groups (up to 13 on a given host) with females greatly outnumbering males. Although there is a broad overlap in size distributions, males are significantly smaller. There is evidence that shrimp move between urchins. Differential male mortality during migration may explain the uneven sex ratio.

Malathion-induced Sex Ratio Changes in Black Pineleaf Scale (Hemiptera: Diaspididae)

Haploid males of the black pineleaf scale ( Nuculaspis californica [Coleman]) growing naturally on their ponderosa pine host trees suffer higher mortality than the diploid females; thus secondary sex ratios change through the life history. Serial dilutions of malathion sprayed on the newly settled scales caused further differential male mortality. The male/female ratio declined as insecticide concentration increased and the survival of both sexes was reduced.

On the Ultimate Causes of Primate Social Systems

[The aim of this review is to present a coherent explanation of the ultimate causation and the evolution of primary social systems. The explanation is based on the assumption that social systems of all diurnal primates are derived from female defence polygyny. Group living is therefore regarded as the essential first step in the social evolution of diurnal primates. Primate social systems are generally classified into four main types, each of which can be contrasted with the others along the following lines: solitariness versus group living, monogamy versus polygyny and reproductive activity by only one male versus reproduction of several males per group. First of all we present some comparative evidence to support the hypothesis that monogamy in primates has evolved from polygynous groups, in two different ways. A commonly held view is that monogamy is most likely to develop where paternal care of the offspring is advantageous. This is almost certainly the case in the very small species of primates. In these monogamy is the consequence of twinning and the resultant need for active paternal care. It runs contrary to the evident tendency of these species to form larger groups in response to the pressure of predation. The latter is achieved by an extended group membership of grown-up offspring in a non-reproductive and even 'helping' role. In the larger species, however, monogamy is most probably the outcome of, on the one hand, a strong need to reduce competition for food favouring very small group sizes, and, on the other hand, of the virtual absence of predation permitting such a development. Secondly, we look critically at several hypothetical explanations for the existence of multi-male groups and one-male groups. We argue that the ultimate explanation for their existence is not to be found in differential male mortality, anti-predator defence, availability of food, and differential expulsion of expendable males. Instead, comparative evidence indicates that the distinction between a single-male or a multi-male system is ultimately dependent on the varying ability of a male to monopolize access to a breeding group of females. This ability in turn depends on group cohesiveness as determined by feeding strategies and predation pressure and is often, though not necessarily, related to the size of the group., The aim of this review is to present a coherent explanation of the ultimate causation and the evolution of primary social systems. The explanation is based on the assumption that social systems of all diurnal primates are derived from female defence polygyny. Group living is therefore regarded as the essential first step in the social evolution of diurnal primates. Primate social systems are generally classified into four main types, each of which can be contrasted with the others along the following lines: solitariness versus group living, monogamy versus polygyny and reproductive activity by only one male versus reproduction of several males per group. First of all we present some comparative evidence to support the hypothesis that monogamy in primates has evolved from polygynous groups, in two different ways. A commonly held view is that monogamy is most likely to develop where paternal care of the offspring is advantageous. This is almost certainly the case in the very small species of primates. In these monogamy is the consequence of twinning and the resultant need for active paternal care. It runs contrary to the evident tendency of these species to form larger groups in response to the pressure of predation. The latter is achieved by an extended group membership of grown-up offspring in a non-reproductive and even 'helping' role. In the larger species, however, monogamy is most probably the outcome of, on the one hand, a strong need to reduce competition for food favouring very small group sizes, and, on the other hand, of the virtual absence of predation permitting such a development. Secondly, we look critically at several hypothetical explanations for the existence of multi-male groups and one-male groups. We argue that the ultimate explanation for their existence is not to be found in differential male mortality, anti-predator defence, availability of food, and differential expulsion of expendable males. Instead, comparative evidence indicates that the distinction between a single-male or a multi-male system is ultimately dependent on the varying ability of a male to monopolize access to a breeding group of females. This ability in turn depends on group cohesiveness as determined by feeding strategies and predation pressure and is often, though not necessarily, related to the size of the group.]

Cytoplasmic inheritance and intragenomic conflict

The differing inheritance patterns of cytoplasmic genes and the sex chromosomes from the Mendelian autosomal patterns can be used to divide the genome into fractions whose defining rule is that the fitness of all genes in a set is maximized in the same way. Each set will be selected to modify the phenotype of the organism in a way which maximally propagates the genes comprising the set, and hence in ways inconsistent with the other sets which comprise the total genome. The coexistence of such multiple sets in the same genome creates intragenomic conflict. Evidence is presented in which the fitness of cytoplasmic and other non-autosomal genetic sets are increased at the expense of the autosomal genetic set. The relationship of such intragenomic conflict to the evolution of anisogamy, dioecy, skewed sex ratios, differential male mortality, systems of sex determination, and altruism is discussed.

A buffered interaction between sex ratio, age difference at marriage, and population growth in humans, and their significance for sex ratio evolution.

The presence, in man, of a significant high sex ratio at birth (Mb) is a biological fact, and its evolution is not satisfactorily explained by differential mortality of males. Such a high sex ratio could have evolved primarily as a buffering interaction between growth rate or increase of human population (Rb) and age difference at marriage (d). The interaction of Rb with d will transform a high Mb, to a lower sex ratio at mating (Mm). The model developed to account for the interaction also shows that d is able to adjust and to achieve a balanced Mm over a relatively broad range. The limits set on d are both biological and cultural; in practically all cultures males father children when they are older than their spouses. A buffered range develops where the balanced Mm is maintained in spite of temporal fluctuations or genetic fixations in Mb, Rb, and some additional factors. A realistic necessary condition for the operation of the buffered system is the combination of Rb > 1·00, d > 0, and Mb > 100. Buffering of male excesses will be achieved more efficiently than buffering of female excesses, i.e. the range is asymmetrical. Inside the range, selective pressures will be caused by the longer generation time of the males, rather than by unmated excess of either sex. According to prevailing fitness models, females should be born in excess, since the longer generation time of males is disadvantageous and should be balanced by the advantage of being the rare sex. That males in fact are born in excess demonstrates a larger significant discrepancy with fitness models than previously assumed. The buffering of sex ratio by age difference at mating is advantageous mainly in populations which are organized in small groups, as it was in early human history. This pattern also facilitated group selection. The buffered system herein described evolved in growing populations. In declining populations it causes a cumulative maximal increase of d, and severe social problems.

Endocrine adjustments in a wild lemming population during the 1969 summer season

1. 1. Wild-caught and laboratory-reared, group-housed brown lemming ( Lemmus trimucronatus) were compared regarding pituitary-adrenal and gonadal function. 2. 2. Early trapping periods yielded higher numbers of animals (for equivalent effort) than did later periods; animals which emerged from the snow in June displayed marked adrenal hypertrophy, high basal levels of adrenal steroid secretion, high pituitary ACTH content, and lower sensitivities to exogenous ACTH. 3. 3. Females were less sensitive to adrenal stimulation than were males, and had lower pituitary ACTH content; gravid females were particularly resistant to both ACTH effects and effects of climate and social pressure. 4. 4. Differential mortality of males was revealed by the trapping regimen, and this mortality was consistent with signs of stress (adrenal hyperfunction, cardiac hypertrophy and renal disease) which were more pronounced in males. 5. 5. It was concluded that both physical environmental and social environmental changes modify endocrine balance in wild lemming populations, and that the endocrine status of the population markedly affects both input and output phases of population dynamics. 6. 6. Gross pathological changes which may contribute to mortality are discussed.

Studies on the sex-ratio and related phenomena. (7) The foetal sex-ratio in the pig

1. Of 583 pig foetuses of all ages, 331 were found to be males and 252 females, giving a male percentage of 56·8, which is much higher than the approximate equality between the sexes that seems to exist at birth. This result confirms Jewell, who found a male percentage of 55 among 1000 cow foetuses.2. These 583 pig foetuses when classified by weight (0–100 gm., 101–300 gm., 301+gm.) gave the following percentages of males for the respective groups, 59·1, 57·0, 53·2. In other words, the percentage of males decreases as gestation proceeds, a result which can only be brought about by a differential mortality of males and females. It would appear that the percentage at conception must be very near 60 per cent. or 150 males per 100 females.3. The sex-ratios of foetuses from the left and right cornua show no significant difference, 55·0 for the right and 54·7 for the left.4. The males were found to average about 7 per cent. heavier than the females.5. There seems to be an inverse correlation between the number of foetuses in a horn and their average weight. Foetuses from the left cornu have a slightly greater weight than those from the right, and this may be connected with the slightly inferior fertility of this horn.6. The excess of males at conception is discussed in the light of the implications of the chromosome mechanism of sex determination, and reference is made to the greater mortality of the males.