Facial resemblance of Japanese children to their parents

Facial resemblance between parents and their children could be an indicator of genetic relationship, and selective pressure could bias the resemblance of appearance. We assessed the degree of resemblance of 38 Japanese children (3–6 years old) to each of their parents using photographs. We asked nonrelatives to assess which of the parents each child resembled, manipulating indications of the sex of the children. Variance in the degree of resemblance between the children and their fathers was very large. Although the basic facial appearance of each parent can be reflected in each child with 50% probability, the children did not equally show the facial characteristics of each parent at the individual level. The indication of sex had no significant effect on the assessment of resemblance. On the other hand, a questionnaire given to the assessors revealed that, as children, they tended to be said to resemble the opposite-sex parent. This result indicates that alleged resemblance does not reflect an actual condition but rather might have cultural meaning. Electronic Publication     

Reactions to children's faces: Males are more affected by resemblance than females are, and so are their brains

The detection of genetic relatedness (i.e., kinship) affects the social, parental, and sexual behavior of many species. In humans, self-referent phenotype matching based on facial resemblance may indicate kinship, and it has been demonstrated that facial resemblance increases perceptions of trustworthiness and attractiveness [Proc. R. Soc. Lond., B Biol. Sci. 269 (2002) 1307–1312; Proc. R. Soc. Lond., B Biol. Sci. (in press)]. However, investigations of sex differences in reaction to facial resemblance have produced mixed results [Evol. Hum. Behav. 25 (2004) 142–154; Evol. Hum. Behav. 23 (2002) 159–166; Evol. Hum. Behav. 24 (2003) 81–87]. Here, we replicate the effects of Platek et al. [Evol. Hum. Behav. 23 (2002) 159–166] using high-resolution color morphing. We also extend these findings using functional magnetic resonance imaging (fMRI) to demonstrate a possible neural mechanism that may account for the observed sex difference. These data support the hypothesis that human males may use and favor facial resemblance as a paternity cue.     

Epigenetics and the origins of paternal effects

Though there are multiple routes through which parents can influence their offspring, recent studies of environmentally induced epigenetic variation have highlighted the role of non-genomic pathways. In addition to the experience-dependent modification of DNA methylation that can be achieved via mother-infant interactions, there has been increasing interest in the epigenetic mechanisms through which paternal influences on offspring development can be achieved. Epidemiological and laboratory studies suggest that paternal nutritional and toxicological exposures as well as paternal age and phenotypic variation can lead to variations in offspring and, in some cases, grand-offspring development. These findings suggest a potential epigenetic germline inheritance of paternal effects. However, it may be important to consider the interplay between maternal and paternal influences as well as the experimental dissociation between experience-dependent and germline transmission when exploring the role of epigenetic variation within the germline as a mediator of these effects. In this review, we will explore these issues, with a particular focus on the potential role of paternally induced maternal investment, highlight the literature illustrating the transgenerational impact of paternal experiences, and discuss the evidence supporting the role of epigenetic mechanisms in maintaining paternal effects both within and across generations.     

Confidence of paternity and paternal care by eastern bluebirds

Male birds are often faced with low confidence of paternityin their mates' offspring, raising the question of how paternalcare covaries with confidence of paternity. We tested the hypothesisthat male eastern bluebirds (Sialia sialis) reduce care of nestlingsin response to experimentally decreased confidence of paternity.Actual paternity, as assessed by DNA fingerprinting, had noeffect on male feeding rates, nor did males reduce care whenconfidence of paternity was experimentally decreased. Malesthat had been removed for 2 days while their mate was fertile(experimental group) fed nestlings at absolute rates similarto those of control males. The proportion of feeding trips providedby males was also similar for control and experimental nests.We found no difference in fledging success and nestling growthbetween experimental and control broods. Seven original residentmales were displaced by previously unbanded males. Althoughthese replacement males appeared to feed nestlings at normalrates, the nests attended by replacement males suffered reducedfledging success compared to control and experimental nests.Overall, we found no evidence that males reduce feeding effortwhen confidence of paternity is experimentally decreased. Malesmay tolerate some reduction in confidence of paternity withoutreducing care if paternal care is crucial to nestling survival.Alternatively, males may assess paternity within a brood usingcues other than their ability to guard their fertile mates.     

Multiyear multiple paternity and mate fidelity in the American alligator, Alligator mississippiensis

We examined multiple paternity during eight breeding events within a 10-year period (1995–2005) for a total of 114 wild American alligator nests in Rockefeller Wildlife Refuge in south-west Louisiana. Our goals included examining (i) within population variation in multiple paternity among years, (ii) variation in multiple paternity in individual females and (iii) the potential for mate fidelity. To accomplish this, in the current study, eggs were sampled from 92 nests over 6 years and analysed along with 22 nests from a previous 2-year study. Genotypes at five microsatellite loci were generated for 1802 alligator hatchlings. Multiple paternity was found in 51% of clutches and paternal contributions to these clutches were highly skewed. Rates of multiple paternity varied widely among years and were consistently higher in the current study than previously reported for the same population. Larger females have larger clutches, but are not more likely to have multiply sired nests. However, small females are unlikely to have clutches with more than two sires. For 10 females, nests from multiple years were examined. Seven (70%) of these females exhibited long-term mate fidelity, with one female mating with the same male in 1997, 2002 and 2005. Five females exhibiting partial mate fidelity (71%) had at least one multiple paternity nest and thus mated with the same male, but not exclusively. These patterns of mate fidelity suggest a potential role for mate choice in alligators.     

The question of paternal investment in Lepidoptera: male-contributed proteins in Plodia interpunctella

In Plodia interpunctella, radioactive labelling techniques indicate that male-derived substances, transferred to the female during copulation, enter unfertilized eggs. These substances are proteinaceous and the cumulative amount of material entering the unfertilized eggs increases with time since mating. Following courtship, smaller males complete coupling with females at a lower frequency than larger males. Smaller males also transfer smaller (by weight) ejaculates than larger males. Ejaculate weight is about 4% of male body weight in P. interpunctella. However, neither fecundity nor the number of deposited eggs are a function of ejaculate weight. Consequently, ejaculate materials cannot be designated a form of paternal investment, despite the observed transfer to unfertilized eggs.     

Why babies look like their daddies: paternity uncertainty and the evolution of self-deception in evaluating family resemblance

It has been suggested that in a socially monogamous system where fathers invest in their mate's offspring but paternity is far from certain, it will be adaptive on the part of infants to conceal their father's identity; but the opposite claim has also been made that this is against the genetic interests of the fathers, and a high frequency of adulterine births will select instead for paternal resemblance. In this article, I present a simple theoretical model that suggests that neonatal anonymity benefits fathers, mothers, and children. Once anonymity becomes established, however, all babies start paying the cost of paternity uncertainty, that is, the reduction in paternal care due to fathers not knowing whether they have truly sired their mate's offspring. By diminishing the fitness of babies, such a cost bounces back as lowered fitness for parents as well. We should then expect the evolution of maternal strategies directed to decrease paternity uncertainty, in the form of instinctive and unsolicited comments on babies' resemblance to their putative fathers. In contradiction to the widespread belief that it would be in fathers' interest to be skeptical of these allegations, the model suggests that, under conditions of infant anonymity, fathers will actually promote their own fitness by believing their spouses. Received in revised form: 5 September 2001 Electronic Publication     

Confidence of paternity and paternal care: covariation revealed through the experimental manipulation of the mating system in the beetle Onthophagus taurus

Theoretical models of paternal care predict that facultative reductions in male care may occur under certain conditions. One important parameter that has been shown to influence the outcome of these models is a male's confidence of paternity. In this study, we tested whether the amount of care provided by horned males in the dimorphic beetle, Onthophagus taurus, varied with his confidence of paternity. Male care results in an increased weight of dung provided in the brood masses produced by the pair. Using the sterile male technique we showed that a horned male's paternity declined with the number of sneak males in the population. The relationship was nonlinear, with paternity declining most rapidly between a frequency of one and three sneaks, and stabilizing thereafter at about 50%. A horned male's paternity was directly related to the number of copulations with the female, relative to the number of copulations achieved by sneaks. Horned males were shown to reduce their care in relation to their declining paternity. Video analysis demonstrated that reductions in male care occurred through a combination of male desertion and a trade‐off between caring and paternity assurance behaviours. The number of fights with sneak males was negatively related to the amount of care provided by a horned male. These results suggest that by gauging his expected paternity through the number of fights with sneaks, a horned male is able to assess his paternity and reduce his investment accordingly. Our data thus provide strong empirical support for the proposed link between paternity and paternal care.     

Effects of neonatal paternal deprivation or early deprivation on anxiety and social behaviors of the adults in mandarin voles

This study examined whether neonatal paternal deprivation (PD: father was removed and pups were raised just by mother) or early deprivation (ED: pups were raised by both parents except separated from not only the dam but also the peers for three hours a day from PND 0 to 13) has long-term effects on anxiety and social behaviors of adult mandarin voles. Newborn mandarin voles of F2 generation were randomly assigned to one of three groups: bi-parental care (PC: pups were raised by both parents), PD and ED. The parental care behaviors of F1 generation were observed at the age of 0, 13 and 21 days (PND 0, 13, 21) of F2 generation of PC and PD groups. Moreover, each mandarin vole of F2 generation received an open field test and a social interaction test on PND 70 and PND 75, respectively. No significant differences of parental behavior were observed between mothers and fathers from PC families, showing typical parental behavior of socially monogamous rodents. In addition, no significant differences of maternal behaviors were found between mothers from PC and PD families, indicating no maternal compensation towards pups for the absence of the paternal care. In the open field test, mandarin voles from both PD and ED families displayed higher levels of anxiety and lower locomotor activity, relative to offspring of PC family. In the social interaction test, both PD and ED mandarin voles also showed lower levels of social behavior and higher levels of anxiety. Thus, both PD and ED significantly increase anxiety and reduce social behavior of adult mandarin voles, suggesting that variation in parental investment may lead to variation in anxiety and social behaviors in rodents with different mating systems.     

Certainty of paternity and paternal effort in the collared flycatcher

Models of optimal parental investment predict that variationin certainty of paternity can affect the optimal level of paternalinvestment when a male's expected paternity in different nestingattempts is not fixed throughout his lifetime. Several attemptsto test this prediction experimentally in monogamous birds havefailed to induce a reduction in care by males. This may be becausethe method used, detaining males, is a poor model for what happenswhen a male's certainly of paternity is naturally reduced. Wecaught and detained female collared flycatchers Ficedula albicollisfor 1 h immediately after laying on one or two occasions inan attempt to induce variation in certainty of paternity forthe males they were mated to. By capturing females immediatelyafter laying we hoped to exploit the existence of an "inseminationwindow" since males should be very sensitive to female absenceduring this period. The general effect of the experimental manipulationwas consistent with reduced certainty of paternity: males respondedby reducing their level of paternal care to nestlings, and malesmated to females that had been caught on one morning fed nestlingssignificantly less often and made a smaller share of feedingvisits than males mated to control females. The effects of theexperiment were generally weak, however, and we argue that certaintyof paternity may be fixed well before egg laying, in which caseexperimental manipulations are unlikely to have large effects.It is difficult to predict die effects of natural variationin certainty of paternity on levels of male paternal care becausedifferential allocation by females mated to attractive malesmay act in the opposite direction     

Male age mediates reproductive investment and response to paternity assurance

Theory predicts that male response to reduced paternity will depend on male state and interactions between the sexes. If there is little chance of reproducing again, then males should invest heavily in current offspring, regardless of their share in paternity. We tested this by manipulating male age and paternity assurance in the burying beetle Nicrophorus vespilloides. We found older males invested more in both mating effort and parental effort than younger males. Furthermore, male age, a component of male state, mediated male response to perceived paternity. Older males provided more prenatal care, whereas younger males provided less prenatal care, when perceived paternity was low. Adjustments in male care, however, did not influence selection acting indirectly on parents, through offspring performance. This is because females adjusted their care in response to the age of their partner, providing less care when paired with older males than younger males. As a result offspring, performance did not differ between treatments. Our study shows, for the first time, that a male state variable is an important modifier of paternity–parental care trade-offs and highlights the importance of social interactions between males and females during care in determining male response to perceived paternity.     

Paternity and paternal effort in the pumpkinseed sunfish

Theoretical models suggest that males should adjust their parentaleffort according to paternity when parental effort is costly,paternity varies among clutches, and males have a cue to assesspaternity. To date, nearly all tests of this theory have beenconducted using birds as model organisms. In this study we examinedthese three factors and the relationship between paternity andmale parental care in a fish system. In the pumpkinseed sunfish(Lepomis gibbosus), parental care is provided exclusively bymales (parentals), but some males (sneakers) parasitize othersby sneaking fertilizations. Parental males significantly lostweight during the parental care period. Clutch size and amountof parental effort did not affect a male's probability of obtainingmore eggs. Paternity was variable among broods. The proportionof young sired by a parental male was not associated with frequencyof fanning eggs or defense of hatched young, but was positivelycorrelated with levels of nest defense during the egg stage.Egg survivorship might restrict an adjustment of fanning behavior,and a general decline in parental behavior (with brood age)might explain the lack of adjustment once the eggs hatch. Parentalmales did not adjust their care when we experimentally manipulatedone possible cue of paternity. Together, these results indicatethat male pumpkinseeds do adjust their care in relation to paternity,but the cues used to assess paternity are not clear.     

Probability of paternity exclusion and the number of loci needed to determine the fathers in a troop of macaques

We calculated the probability of paternity exclusion (P) in 6 troops of rhesus and Japanese macaques housed in open enclosures and 68 wild troops of Japanese, crab-eating, and toque macaques using 33 genetic loci which encoded the blood protein variations detected by electrophoretic techniques. In the open enclosures, especially of rhesus troops, we obtained a fairly high probability of paternity exclusion and succeeded in determining the fathers of offspring. However, we found significant differences between the observed and calculated probabilities in most of the troops. These differences were ascribed to a situation whereby the Hardy-Weinberg equilibrium had not been attained in the troops and/or the numbers of variable loci were too small. In the wild troops of Japanese, crab-eating, and toque macaques, the means ofP were 0.2274 (0.0192–0.5017), 0.4635 (0.1676–0.7151), and 0.7382 (0.6266–0.7954), respectively. We also estimated the number of loci needed to determine the fathers of offspring with a probability of 0.8 assuming that ten males were present in the troop. The estimated number was about 13.5 times, 5 times and 1.8 times the number of loci examined on average in the troops of Japanese, crab-eating and toque macaques, respectively. This means that determination of most of the fathers of offspring in wild troops of these macaques, even of toque macaques which have a rather high probability of paternity exclusion, is difficult so long as we employ only electrophoretic techniques.     

Bias in studies of heterozygosity and mate choice

A key question for molecular and behavioural ecologists who study mating systems is to understand why, in many species, females choose to mate with extra-pair males. Recently a possible explanation, 'genetic compatibility', has gained increasing empirical support (for a comprehensive review, see Kempenaers 2007 ). Genetic compatibility hypotheses assume that females seek extra-pair mates with alleles that complement their own. Typically, this will be achieved by mating with a male of a different genotype than her own, in order to maximise the heterozygosity of her offspring. Because numerous studies have indicated positive associations between heterozygosity and fitness (see Coltman & Slate 2003 ), it follows that mating with 'compatible' males will result in heterozygous, and therefore fit, offspring. Most empirical support for genetic compatibility has been obtained with microsatellite markers that have first been used to assess parentage and then to estimate relatedness and/or individual heterozygosity. A problem with this approach is a possible bias that favours the detection of extra-pair paternity when the extra-pair male has a genotype different from that of the female and her social mate. This in turn could lead to the erroneous conclusion that extra-pair males are less related to the female than within-pair males. In this issue of Molecular Ecology , Wetzel & Westneat 2009 (hereafter W&W), use simulation studies to assess the extent of this bias, using parameter estimates obtained from recent empirical data. They identify two forms of bias that may affect tests of the genetic compatibility hypothesis, and provide guidelines on how these biases may be avoided.     

Parental investment with a superior alien in the brood

When a parent's parentage differs across breeding attempts, established theory predicts that the parent should invest more in a brood when perceived parentage is high. We present a model of parental investment in which offspring unrelated to the parent have a competitive advantage over the parent's own offspring and take a larger share of investment. We show that this can weaken or, if the competitive advantage is great, reverse the predicted relationship between perceived parentage and parental investment. A moderate competitive advantage of extra-pair young over within-pair young could partly explain the lack of any clear relationship between paternal care and paternity in many studies, and could easily arise if females choose extra-pair partners for good genes. Our results are also relevant to interspecific avian brood parasitism. As parasites reared together with host offspring are often superior competitors, their hosts could benefit from increasing investment in response to suspected parasitism.     

Survival costs of reproduction predict age-dependent variation in maternal investment

Life-history theory predicts that older females will increase reproductive effort through increased fecundity. Unless offspring survival is density dependent or female size constrains offspring size, theory does not predict variation in offspring size. However, empirical data suggest that females of differing age or condition produce offspring of different sizes. We used a dynamic state-variable model to determine when variable offspring sizes can be explained by an interaction between female age, female state and survival costs of reproduction. We found that when costs depend on fecundity, young females with surplus state increase offspring size and reduce number to minimize fitness penalties. When costs depend on total reproductive effort, only older females increase offspring size. Young females produce small offspring, because decreasing offspring size is less expensive than number, as fitness from offspring investment is nonlinear. Finally, allocation patterns are relatively stable when older females are better at acquiring food and are therefore in better condition. Our approach revealed an interaction between female state, age and survival costs, providing a novel explanation for observed variation in reproductive traits.     

Extrapair paternity and mate choice in a chickadee hybrid zone

The dynamics of hybrid zones are likely to be influenced greatlyby patterns of mate choice, including cryptic choice mediatedthrough extrapair copulations. To understand changes in hybridzones over time and space, a detailed examination of matingpatterns and correlates is needed. We studied the role of extrapairfertilizations (EPFs) in the breeding biology of hybridizingblack-capped and Carolina chickadees in southeastern Pennsylvaniaover 4 years, using microsatellite DNA markers. We detectedextrapair offspring (EPO) in 56% of 90 broods examined; theseaccounted for at least 26% of 477 offspring. Chickadees do notappear to use EPFs to reduce costs of heterospecific pairing:EPFs were no more likely to occur in genetically dissimilar(heterospecific) social pairs than in pairs where social mateswere genetically similar. However, females paired with black-capped–likemales were more likely to have EPO. Females that acquired EPFsdid not obtain these from males genetically similar to themselves;instead, all females, regardless of their genotype or that oftheir social mate, tended to prefer Carolina-like males as extrapairpartners. There was no relationship between the presence ofEPO and hatching or fledging success. High rates of extrapairpaternity and apparent female preference for Carolina-like malessuggest that mate choice is an important influence in ongoingnorthward movement of this hybrid zone.     

High paternal diversity in the self-incompatible herb Arabidopsis halleri despite clonal reproduction and spatially restricted pollen dispersal

The number of sires fertilizing a given dam is a key parameter of the mating system in species with spatially restricted offspring dispersal, since genetic relatedness among maternal sibs determines the intensity of sib competition. In flowering plants, the extent of multiple paternity is determined by factors such as floral biology, properties of the pollen vector, selfing rate, spatial organization of the population, and genetic compatibility between neighbours. To assess the extent of multiple paternity and identify ecological factors involved, we performed a detailed study of mating patterns in a small population of a self-incompatible clonal herb, Arabidopsis halleri . We mapped and genotyped 364 individuals and 256 of their offspring at 12 microsatellite loci and jointly analysed the level of multiple paternity, pollen and seed dispersal, and spatial genetic structure. We found very low levels of correlated paternity among sibs ( P _full-sib = 3.8%) indicating high multiple paternity. Our estimate of the outcrossing rate was 98.7%, suggesting functional self-incompatibility. The pollen dispersal distribution was significantly restricted (mean effective pollen dispersal distance: 4.42 m) but long-distance successful pollination occurred and immigrating pollen was at most 10% of all pollination events. Patterns of genetic structure indicated little extent of clonal reproduction, and a low but significant spatial genetic structure typical for a self-incompatible species. Overall, in spite of restricted pollen dispersal, the multiple paternity in this self-incompatible species was very high, a result that we interpret as a consequence of high plant density and high pollinator service in this population.