Exclusion probabilities obtainable by biochemical polymorphisms in dogs

General formulae are given to calculate the exclusion probabilities in false paternity and parentage cases by means of gene loci with an arbitrary number of alleles whereas in paternity cases an arbitrary number of offspring per litter is considered additionally.
By aid of these formulae and on the basis of the allele frequencies of four blood protein and enzyme systems the probabilities of excluding incorrect paternity and parentage are calculated in seven German dog breeds. The results are tabulated and discussed.
It can be shown that the exclusion probability in false paternity cases increases distinctly with an increasing number of offspring per litter and its maximum is nearly attained if 5 offspring are examined. Therefore it is of value to consider entire litters in paternity controls in dogs.     

Food-restricting first generation juvenile female hamsters (Mesocricetus auratus) affects sex ratio and growth of third generation offspring

Female hamsters (Generation 1) were fed ad libitum or were food-restricted to 65-75% of the amount consumed by controls during their first 50 days of life. Subjects were mated at 91 days of age. Their offspring (Generation 2) were fed ad libitum throughout the experiment, and female offspring were also mated at 91 days of age. Generation 3 litters were monitored every fifth day from birth until Day 25 post partum for litter size, sex ratio, and pup weights. Although there were no significant differences in Generation 3 litter sizes at birth, litters descended from food-restricted Generation 1 females (Group R) were significantly smaller on Days 5-25 than litters descended from control Generation 1 females (Group A). Sex ratios remained significantly greater in Group A than in Group R litters from birth to Day 25 but did not vary over time, suggesting similar post-partum mortality rates for both male and female pups. Weights of Generation 3 male and female pups did not vary significantly within treatments at any time. Group A males weighed significantly more than Group R males from birth through Day 25, but weights of Group A and Group R females were always similar. Food restriction early in life may have long-term consequences on sex ratios of subsequent generations in hamsters.     

Male-biased reproduction and sex-ratio adjustment in muskrats

Summary Sex ratios of a population and of litters were sampled in muskrats in Ontario, Canada. Sex ratios of litters sampled from nests were male biased (54% male). Until weaning, no differential costs of producing and rearing male and female young were identified that could account for this greater production of males. Following weaning, however, male-biased dispersal of juveniles from their natal site and more frequent acquisition by females of these sites as breeding sites the following year suggested a greater investment by adult females in female young. Therefore, competition between female siblings for the acquisition of their natal site may be sufficient to result in the greater production of males. In addition, the simultaneous occupation of, and competition between, siblings and parents for the resources of the natal home range may not be necessary for local resource competition to result in a greater production of the dispersing sex. Greater-than-expected binomial variance in sex ratios of litters suggested that adjustment of sex-ratios occurred. However, we were unable to associate the adjustment of litter sex ratios with changes in maternal condition. The greater production of males and the predominance of monogamous associations between adults in this population may have lead to slightly greater variation in male fitness than female fitness. Therefore, a female in better-than-average condition may have benefited by producing more males. Similarly, a lower cost of producing dispersing males may allow nutritionally-stressed females to reduce their total expenditure on offspring by producing more males. Because these experiments were non-manipulative, maternal condition may not have varied sufficiently during this study to detect adjustments of litter sex ratios resulting from either of the above mechanisms acting separately, but the combined effects of small differences in matermal condition and selective pressures operating in the same direction may have resulted in the observed deviation from the binomial.     

Litter sex ratios in Richardson’s ground squirrels: long-term data support random sex allocation and homeostasis

When costs of producing male versus female offspring differ, parents may vary allocation of resources between sons and daughters. We tested leading sex-allocation theories using an information-theoretic approach and Bayesian hierarchical models to analyse litter sex ratios (proportion males) at weaning for 1,049 litters over 24 years from a population of Richardson’s ground squirrels (Urocitellus richardsonii), a polygynandrous, annually reproducing mammal in which litter size averages from six to seven offspring and sons are significantly heavier than daughters at birth and weaning. The model representing random Mendelian sex-chromosome assortment fit the data best; a homeostatic model received similar support but other models performed poorly. Embryo resorption was rare, and 5 years of litter data in a second population revealed no differences in litter size or litter sex ratio between birth and weaning, suggesting that litter size and sex ratio are determined in early pregnancy. Sex ratio did not vary with litter size at weaning in any of 29 years, and the observed distribution of sex ratios did not differ significantly from the binomial distribution for any litter size. For 1,580 weaned litters in the two populations, average sex ratio deviated from parity in only 3 of 29 years. Heavier females made a greater reproductive investment than lighter females, weaning larger and heavier litters composed of smaller sons and daughters, but litter sex ratio was positively related to maternal mass in only 2 of 29 years. Such occasional significant patterns emphasize the importance of multi-season studies in distinguishing infrequent events from normal patterns.     

Offspring growth, survival and reproductive success in the bank vole: a litter size manipulation experiment

To estimate the optimality of brood size, it is essential to study the effects of brood size manipulation on offspring survival and reproductive success. Moreover, testing the generality of the hypothesis of reproductive costs requires experimental data from a diversity of organisms. Here I present data on the growth, survival and reproductive success of bank vole Clethrionomys glareolus individuals from manipulated litters. Furthermore, the survival of mothers whose litter size was manipulated was studied. At weaning, the mean weight of pups from enlarged litters was lower and from reduced litters higher compared to control litters. After winter, at the start of the breeding season, individuals from enlarged litters, especially males, were still lighter than individuals from the other two treatments. Litter enlargements did not increase the number of reproducing female offspring per mother, nor did the litter sizes of female offspring differ between treatments. There were no differences between treatments in winter survival of offspring after weaning, but among female offspring, weaning weight explained the survival probabilities over winter. A higher weight of females at winter determined the probability of starting to reproduce in spring. The survival of mothers did not seem to be influenced by litter manipulation performed the previous year. According to the results, mothers nursing enlarged or reduced litters do not gain any fitness benefits in terms of number of offspring surviving to breeding. The results are consistent with the majority of experiments conducted in birds, which have found costs of enlarged brood appearing as offspring trade-offs rather than parent trade-offs. Received: 14 December 1997 / Accepted: 1 March 1998     

Optimal offspring sizes in small litters

Summary Numerous evolutionary models explore the trade-off between offspring size and offspring number. However, such models often fail when the number of offspring is small because optimal litter size (or litter size at optimal offspring size) may fall between the necessarily integer values for real litters. This paper extends a classic model for optimal investment per offspring to the case of small litters and predicts that range in offspring size and the largest (smallest) offspring size should decline (increase) with increased litter size. Application of the model to egg size data from a poeciliid fish,Gambusia hubbsi, reveals a surprisingly close approximation to the largest offspring size and variation in offspring size at small litter sizes.     

Effects of age and parity on litter size and offspring sex ratio in golden hamsters (Mesocricetus auratus)

Golden hamsters that were mated repeatedly from 55 days of age produced 6-12 litters. Litter size at birth rose between the 1st and 2nd litters, peaked on the 3rd, and declined steadily after the 5th litter. Offspring sex ratio (% male) at birth followed a similar pattern: increasing between the 1st and 2nd litters, remaining high through the 3rd, and becoming increasingly female-biased thereafter. Weaning success decreased sharply after the 6th litter and most dams failed to raise any young to weaning after the 9th litter. These sequential effects on litter size, offspring sex ratio and weaning success were also observed in females mated once at different ages, but they occurred considerably later in life, i.e. increasing parity hastened the effects of advanced age. These age- and parity-related changes in litter composition are consistent with the Trivers-Willard hypothesis that physiologically-stressed females would skew offspring sex ratios to favour daughters. However, since the observed changes in sex ratio were probably due to differential prenatal mortality, their adaptive significance is unclear.     

Postnatal environment affects behavior of adult transgenic mice

Behavioral phenotypes of knockout mice are often interpreted as the effects of the absence of the gene product on adult behavior, yet behavioral differences among genotypes may be exaggerated or blurred by the postnatal environment. For example, mice develop in litters of varying sex ratios and genotypes, and it is possible that some of these behavioral differences may result from the composition of the litter. To determine whether these factors might play a role in the development of the behavioral characteristics that have become diagnostic of the knockout, offspring of parents heterozygous for a null mutation of estrogen receptor alpha (ERKO) were sexed and genotyped within 2 days of birth. Litters were then reconstituted, forming same-sex litters of equal numbers of ERKO and wild-type (WT) individuals that were tested in a standard resident-intruder paradigm. In this manner the effect of genotype would be evident without the potential confound of the presence of the opposite sex in the litter. Behavioral differences between the genotypes were more sharply defined than reported previously. ERKO females displayed only aggressive behavior whereas their WT littermates displayed only mounting behavior; both aggression and mounting behavior were greatly reduced in ERKO males. These data suggest that the postnatal environment such as litter composition may influence the development of sociosexual behaviors in ERKO mice.     

Optimal offspring size in a small mammal: an exception to the tradeoff invariant life-history rule

Offspring size and number were examined in a captive population of wild guinea pigs ( Cavia aperea ), and findings were compared with models of optimal offspring size for small litters. Median and modal litter size was two, regardless of maternal size or parity. Females producing their second litter tended to have litters that were larger than average. In contrast, young females that were still growing never had litters that were larger than average. Mean offspring size decreased and variation in offspring size tended to decrease with increasing litter size. Optimal offspring size models, in which offspring survival depended on the amount of resources invested, as well as litter size, predict such a trend. Little support was found for Charnov and Downhower's (1995) tradeoff invariant life-history rule that the range in offspring sizes between litters is inversely proportional to the size of the litter. Cavia aperea may be an exception to this rule because pup mass at birth did not reflect total reproductive investment, because conversion of resources into litter mass may not be linearly related to litter size and because resources were not equally partitioned among offspring within large litters. Experimental data are needed to determine the relevance of these results among mammals in general.     

Determinants of reproductive success in female adders,Vipera berus

Summary Female lifetime reproductive success in a small population of individually-marked adders in southern Sweden was studied over a period of seven years. Reproductive characteristics varied little from year to year and were consistent through time in individual females. Most females mature at four years of age and reproduce every two years. The total number of offspring produced by a female depends on her adult body size (and thus, litter size) and longevity (and thus, number of litters per lifetime). Adult body size in females is influenced mainly by subadult growth rates. Offspring size depends on maternal body size and a tradeoff between offspring size and offspring number. Maternal age does not affect litter sizes and offspring sizes except through ontogenetic changes in maternal body size.Survival of females after parturition is low because of the high energy costs of reproduction, compounded by low feeding rates of gravid females because of their sedentary behaviour at this time. About one-half of females produce only a single litter during their lifetimes, although some females live to produce four or five litters. On a proximate basis, rates of energy accumulation for growth (in subadults) and reproduction (in adults) may be the most important determinants of fitness in female adders.     

Hormonal manipulation of offspring number: maternal effort and reproductive costs

We used exogenous gonadotropin hormones to physiologically enlarge litter size in the bank vole (Clethrionomys glareolus). This method allowed the study design to include possible production costs of reproduction and a trade-off between offspring number and body size at birth. Furthermore, progeny rearing and survival and postpartum survival of the females took place in outdoor enclosures to capture salient naturalistic effects that might be present during the fall and early winter. The aim of the study was to assess the effects of the manipulation on the growth and survival of the offspring and on the reproductive effort, survival, and future fecundity of the mothers. Mean offspring body size was smaller in enlarged litters compared to control litters at weaning, but the differences disappeared by the winter. Differences in litter sizes disappeared before weaning age due to higher mortality in enlarged litters. In addition to the effects of the litter size, offspring performance was probably also influenced by the ability of the mother to support the litter. Experimental females had higher reproductive effort at birth, and they also tended to have higher mortality during nursing. Combined effects of high reproductive effort at birth and high investment in nursing the litter entailed costs for the experimental females in terms of decreased probability of producing a second litter and a decreased body mass gain. Thus, enlarged litter size had both survival and fecundity costs for the mothers. Our results suggest that the evolution of litter size and reproductive effort is determined by reproductive costs for the mothers as well as by a trade-off between offspring number and quality.     

Effects of social stress during early pregnancy on litter size and sex ratio in the golden hamster (Mesocricetus auratus)

Primiparous female hamsters were mated to proven breeders and stressed during early pregnancy. Females were housed singly throughout gestation except for Days 4, 5 and 6 when they were paired for 10-min intervals 3 times each day with another female matched for age, weight and day of pregnancy. Within each of the pairs, one female was consistently dominant to the other. Controls were exposed to a novel area instead of a conspecific. At parturition, all pups were counted, sexed and weighed. There were no significant differences between litter sizes or sex ratios (defined as % male) of control and dominant females. Litter sizes produced by control or dominant dams were significantly larger than those of subordinate dams, and litter sex ratios of dominants were significantly higher than those of subordinates. Subordinate dams produced fewer males than did dominant dams, but there was no difference in the number of females produced. Also, subordinate dams produced smaller pups than control dams. Examination of uterine implantation sites and fetal resorptions indicated that fetal loss occurred between Days 5 and 10 of pregnancy. These results suggest that subordinate dams produce smaller litters via selective resorption or spontaneous abortion of males in utero and that those males they do produce are smaller than those produced by dominant or control dams. We suggest that males are more susceptible in utero to effects of maternal stress in this species, and may require more maternal investment to survive to term.     

Food restricting young hamsters (Mesocricetus auratus) affects sex ratio and growth of subsequent offspring

Trivers and Willard (1973) predicted that stressed adult female mammals may enhance their fitness by skewing offspring sex ratios and maternal investment to favor daughters. The present study investigated whether stressing young hamsters might also influence sex ratio and growth of subsequent offspring. Control females received food ad libitum (A) on Days 1-50 postpartum (AA). Experimental females were food-restricted (R) either on Days 1-25 (RA), Days 26-50 (AR), or Days 1-50 (RR) postpartum. Subjects were mated when 91-95 days old. Litter sizes and survivorship (= % litters within a treatment that contained at least one pup), sex ratio (= % males), and pup weights in the next generation were recorded every fifth day from parturition until Day 25 postpartum. Control litters contained significantly more offspring at birth than did RR litters. Sex ratio was significantly higher at birth for AA litters than for the other treatments. Postpartum sex ratio within each group remained similar to that recorded at birth. RR litters contained significantly fewer pups compared to the other three treatments from Days 5-25. RR female pups weighed significantly more at birth than their counterparts in the other treatments. Weights of males at birth were similar in all treatments. By Day 25, both male and female RR pups weighed significantly less than control, AR, and RA pups. Food restriction early in life may have long-term consequences on sex ratio and pup growth in golden hamsters.     

Seasonal variation in fertility, fecundity and litter sex ratio in laboratory and wild stocks of house mice (Mus domesticus)

Data compilations were made for three parameters pertaining to reproduction in a domestic strain (14 years) and a wild stock (4 years) of commensal house mice: (a) the percentage of females mated that produced litters; (b) the average number of pups per litter; and (c) the sex ratio of the pups in the litters. Fecundity and fertility varied seasonally in both domestic and wild mice. More females become pregnant and litter sizes were larger in the spring, summer, and fall months than during the winter season. Sex ratios also varied seasonally with more male biased litters produced during the 4 winter months. There appear to be seasonal shifts in productivity for both stocks of mice and these seasonal trends have not been altered by domestication under laboratory conditions. In spite of the fact that house mice are generally opportunistic, it is possible that there has been selection in the mice for shifting rates of production in relation to the best seasons of the year in terms of climate and resource availability. The higher production of males during summer months may be geared toward greater success in dispersal at that season and a higher probability that the males can find a territory and mate successfully in summer rather than winter. These results have potential implications for animal breeders and for those who maintain mouse colonies to produce animals for scientific investigations.     

Sex allocation in a polygynous mammal with large litters: the wild boar

Predictions from Trivers & Willard's (1973, Science, 179, 90-92) hypothesis of sex-biased maternal investment in polygynous species do not apply well to species where mothers produce more than one offspring per reproductive attempt. First, as litter size increases, the benefits to the mother of adjusting sex ratio decrease because (1) she could benefit more by adjusting litter size and (2) sex differences in reproductive potential are negatively related to litter size. Second, testing sex-biased investment in these species requires predictions about the simultaneous adjustment of sex ratio and litter size. The wild boar, Sus scrofa, although polygynous, produces large litters. Here we present data for 58 litters from a free-ranging wild boar population in central Spain. Maternal expenditure per individual offspring, as measured by piglet weight, was higher for male than female fetuses. In more than 81% of cases the heaviest fetus in the litter was a male regardless of the quality of the mother; this might have influenced his ranking within the 'teat order' and consequently his development and survival. Mother quality (size and weight) appeared to be related to litter size but not to the sex ratio of the litter. However, it was highly related to a variable that combined the effects of litter size and sex ratio within the litter, thus supporting Williams' (1979, Proceedings of the Royal Society of London, Series B, 205, 567-580) hypothesis that mothers should adjust both litter size and offspring sex. Copyright 1999 The Association for the Study of Animal Behaviour.     

Litter size and fetal sex ratio adjustment in a highly polytocous species: the wild boar

For species in which reproductive success is more variable inone sex than the other, the Trivers and Willard model (TWM)predicts that females are able to adjust their offspring sexratio. High-quality mothers should provide greater investmentto one sex than the other. Previous tests of the TWM have beeninconsistent, and whether the TWM applies to species with severaloffspring per litter is unclear due to possible trade-offs betweensize, number, and sex of the offspring. Williams' model (WM)accounts for confounding effects of these trade-offs on sexratio variation. Lastly, the "extrinsic modification hypothesis"predicts changes in offspring sex ratio in relation to climaticconditions and population density. Using wild boar as a model,we tested 1) whether the WM fitted observed sex ratio variationand 2) whether sex ratio variations were related to maternalattributes (test of the TWM) and/or to resource availability(test of the extrinsic modification hypothesis). Females adjustedtheir litter size rather than their litter composition, so thatthe WM was not supported. Likewise, changes in resource availabilitydid not influence the fetal sex ratio, so that the extrinsicmodification hypothesis was not supported. The fetal sex ratiowas negatively related to increasing litter size, providingsome support for the TWM. Sex ratio was male biased for littersizes up to 6 and then became female biased in larger litters.Our results provide the first case study showing marked changesin sex ratio in relation to litter size in a large mammal.     

Evidence for the Tf locus being associated with an early lethal factor in a strain of pigs

The frequencies of three co-dominant alleles Tf ^A, Tf ^B and Tf ^c controlling the serum transferrin locus in native and exotic breeds of pig in the United Kingdom are shown. Matings between different transferrin genotypes and segregation of the transferrin alleles in piglets from 131 litters are also recorded.
In eleven litters from matings within a closely related group of animals heterozygous for the Tf ^c allele, no offspring of the Tf ^c/ Tf ^c genotype were born. Matings between heterozygous related boars believed to be carrying a lethal factor linked to the Tf locus and heterozygous unrelated sows of the Saddleback breed, resulted in offspring of the Tf ^c/ Tf ^c genotype being born.
An excess of heterozygote genotypes was found in all litters from matings between animals heterozygous for the Tf ^c allele. In all these litters the average litter size was 0.5 piglets less per litter than the average for all other litters studied. For the eleven litters from matings involving closely related animals heterozygous for the Tf ^c allele, the average litter size was 1.4 piglets less per litter than the average for all other litters.
The possibility of an early lethal factor being linked to the Tf locus in this family of pigs is discussed.     

Conception date affects litter type and foetal sex ratio in female moose in Estonia

1.  The Trivers–Willard model of optimal sex ratios predicts that in polygynous species mothers in better condition should produce more male than female offspring. However, empirical support for this hypothesis in mammals and especially ungulates has been equivocal. This may be because the fitness of mothers has been defined in different ways, reflecting morphological, physiological or behavioural measures of condition. In addition, factors other than maternal condition can influence a mother's fitness. Given that recent studies of wild ungulates have demonstrated the importance of the timing of conception and birth on offspring fitness, litters conceived at different stages of the rut might be expected to exhibit differences in types and embryonic sex ratio.
2.  Based on a 6-year survey of the reproductive tracts of female moose harvested in Estonia, we investigated the effect of conception date on the types of litters produced and on the foetal sex ratio.
3.  There was a clear relationship between conception date and litter characteristics. Overall, earlier conceived litters were more likely than those conceived late to contain multiple embryos and a high proportion of males. However, while foetal sex ratio varied nonlinearly with conception date in yearlings and subadults, no relationship was found in adults.
4.  We conclude that female moose adjust foetal sex ratio and litter type/size depending on their age and the date of conception, and that these adjustments are in accordance with the Trivers–Willard hypothesis if females that conceive earlier are in better condition.     

Litter size variation in hypothalamic gene expression determines adult metabolic phenotype in Brandt's voles (Lasiopodomys brandtii)

Background

Early postnatal environments may have long-term and potentially irreversible consequences on hypothalamic neurons involved in energy homeostasis. Litter size is an important life history trait and negatively correlated with milk intake in small mammals, and thus has been regarded as a naturally varying feature of the early developmental environment. Here we investigated the long-term effects of litter size on metabolic phenotype and hypothalamic neuropeptide mRNA expression involved in the regulation of energy homeostasis, using the offspring reared from large (10–12) and small (3–4) litter sizes, of Brandt''s voles (Lasiopodomys brandtii), a rodent species from Inner Mongolia grassland in China.

Methodology/Principal Findings

Hypothalamic leptin signaling and neuropeptides were measured by Real-Time PCR. We showed that offspring reared from small litters were heavier at weaning and also in adulthood than offspring from large litters, accompanied by increased food intake during development. There were no significant differences in serum leptin levels or leptin receptor (OB-Rb) mRNA in the hypothalamus at weaning or in adulthood, however, hypothalamic suppressor of cytokine signaling 3 (SOCS3) mRNA in adulthood increased in small litters compared to that in large litters. As a result, the agouti-related peptide (AgRP) mRNA increased in the offspring from small litters.

Conclusions/Significance

These findings support our hypothesis that natural litter size has a permanent effect on offspring metabolic phenotype and hypothalamic neuropeptide expression, and suggest central leptin resistance and the resultant increase in AgRP expression may be a fundamental mechanism underlying hyperphagia and the increased risk of overweight in pups of small litters. Thus, we conclude that litter size may be an important and central determinant of metabolic fitness in adulthood.     

Sex ratio and litter size in relation to parity and mode of conception in three inbred strains of mice

Breeding records from three inbred strains of mice (BALB/c ABom, C57BL/10ScSn, C3H/He/Kon) were examined with respect to the effects of parity and mode of conception upon litter size and sex ratio at birth. Litters from 3 modes of conception were considered: litters of primipares, litters of multipares conceived during postpartum oestrus and litters conceived after lactational anoestrus. Litters of multipares were assigned to one of these latter groups according to the inter-litter intervals. Parity had no significant effect upon the sex ratio but had a significant one upon the litter size, which did not vary between the strains when first litters were excluded from analysis. The expected variations in response to the mode of conception were found in BALB/c ABom mice but both the effects on the litter size as well as on the sex ratio varied significantly between the strains. Litter size reduction per se could be ruled out to be the cause of the sex ratio variations found. Rather, it is suggested that sex-specificity of embryonic loss depends upon the mode of conception.