Genetic parenthood and causation: An objection to Douglas and Devolder’s modified direct proportionate genetic descent account

In a recent publication Tom Douglas and Katrien Devolder have proposed a new account of genetic parenthood, building on the work of Heidi Mertes. Douglas and Devolder’s account aims to solve, among other things, the question of who are the genetic parents of an individual created through somatic cell nuclear transfer (i.e. cloning): (a) the nuclear DNA provider or (b) the progenitors of the nuclear DNA provider. Such a question cannot be answered by simply appealing to the folk account of genetic parenthood, according to which the genetic parents of an individual are those individuals who produced the egg and sperm, respectively, which fused to create the embryo. It cannot be so as in cloning there is no fertilization as such. In this article I critically examine Douglas and Devolder’s new account of genetic parenthood and demonstrate that it is vulnerable to counterexamples that exploit the lack of a condition specifying that genetic parents should cause a child’s coming into existence.     

ORPHANS BY DESIGN: THE FUTURE OF GENETIC PARENTHOOD

Establishing the nature of genetic parenthood is an important task. This is, firstly, because many people desire that relationship and it is in their interest to know what that is, and secondly, because there is a view that it may incur certain moral obligations between the genetic parent and their child. Many theorists have made attempts to define exactly what genetic parenthood is. I show that these definitions are deficient if they wish to fully capture all reproductive scenarios in ways that are intuitive and/or meaningful. Through a series of cases involving technologies such as cloning and genome editing, we see that in lieu of the traditional two parents, there are possible beings who have no genetic parents, one genetic parent, or many genetic parents. Establishing these cases complicates our understanding of genetic parenthood. From this, we must reconsider current definitions, as well as the usefulness of defining genetic parenthood in these complex cases. Here I do not aim to establish a new definition, but rather to suggest that this complexity makes it necessary to re‐assess the importance of the connection between genetic parenthood and parental obligations and authorities.     

Homology across inheritance systems

Recent work on inheritance systems can be divided into inclusive conceptions, according to which genetic and non-genetic inheritance are both involved in the development and transmission of nearly all animal behavioral traits, and more demanding conceptions of what it takes for non-genetic resources involved in development to qualify as a distinct inheritance system. It might be thought that, if a more stringent conception is adopted, homologies could not subsist across two distinct inheritance systems. Indeed, it is commonly assumed that homology relations cannot survive a shift between genetic and cultural inheritance systems, and substantial reliance has been placed on that assumption in debates over the phylogenetic origins of hominin behavioral traits, such as male-initiated intergroup aggression. However, in the homology literature it is widely accepted that a trait can be homologous—that is, inherited continuously in two different lineages from a single common ancestor—despite divergence in the mechanisms involved in the trait’s development in the two lineages. In this paper, we argue that even on an extremely stringent understanding of what it takes for developmental resources to form a separate inheritance system, homologies can nonetheless subsist across shifts between distinct inheritance systems. We argue that this result is a merit of this way of characterizing what it is to be an inheritance system, that it has implications for adjudicating between alternative accounts of homology, and that it offers an important cautionary lesson about how (not) to reason with the homology concept, particularly in the context of cultural species.     

Reproductive seasonality in two sympatric primates (Ateles belzebuth and Lagothrix lagotricha poeppigii) from Amazonian Ecuador

With their large body size and “slow” life histories, atelin primates are thought to follow a risk‐averse breeding strategy, similar to capital breeders, in which they accumulate energy reserves in anticipation of future reproductive events such as gestation and lactation. However, given the paucity of longitudinal data from wild populations, few studies to date have been able to compare the timing of reproductive events (e.g., copulations, conceptions, and births) in relation to shifting resource availability over multiple years. We examined the reproductive patterns of two atelin species—white‐bellied spider monkeys (Ateles belzebuth) and lowland woolly monkeys (Lagothrix lagotricha poeppigii)—in relation to habitat‐wide estimates of fruit availability at the Tiputini Biodiversity Station (TBS) in Amazonian Ecuador. Our sample included 4 years of data on births (N = 36) and copulations (N = 170) for Lagothrix, 10 years of data on births (N = 35) and copulations (N = 74) for Ateles, and 7 years of data on ripe fruit availability. Reproductive events were distinctly seasonal. For both species, births were concentrated between May and September, a time period in which ripe fruit was relatively scarce, while inferred conceptions occurred between September and January, when ripe fruit availability was increasing and maintained at high‐levels throughout the forest. Interannual variation in births was relatively stable, except for in 2016 when twice as many infants were born following a strong El Niño event that may have led to unusually high levels of fruit productivity during the 2015 breeding season. Although copulations were observed year‐round, an overwhelming majority (>90% for Lagothrix and >80% for Ateles) took place between August and February when females were most likely to conceive. Collectively, these data follow the reproductive patterns observed in other atelin primates, and, as proposed by others, suggest that atelins may follow a risk‐averse breeding strategy.     

Can the Patterns of Sexual Swelling Cycles in Female Taï Chimpanzees be Explained by the Cost-of-Sexual-Attraction Hypothesis?

Chimpanzee females of East and West African populations differ in the average number of cycles per interbirth interval. Whereas females in Gombe, Mahale, and Kibale (eastern chimpanzees, Pan troglodytes schweinfurthii) average <9 cycles before they conceive, females at Taï (western chimpanzees; Pan troglodytes verus) average 29 cycles. We examined data from 2 different study groups (North and South) at Taï. By showing that Taï females interrupt cyclic activity for, on average, 7.4 mo between the end of the postpartum amenorrhea period (PPA) and the subsequent conception, and by calculating the number of cycles to conception based on a probability distribution of cycles over the interbirth interval, we show that Taï females average 19.4 cycles (North Group) and 11.7 cycles (South Group) to conception; therefore, the earlier calculation of 29 cycles was an overestimate. Further, at Taï young parous females have a significantly shorter PPA than those of older females, but the number of cycles to conception does not differ significantly between primiparous and nulliparous females. Some of our results are therefore not in line with the predictions of the cost-of-sexual-attraction hypothesis, which proposes that the factor ultimately responsible for the intensity of female sexual attractiveness is female intragroup scramble competition. We discuss an alternative hypothesis—the social passport hypothesis—which is compatible with the results of the study.     

Sperm,Clinics, and Parenthood

In this article I examine a recent approach to regulating assisted reproduction, whereby use of some kind of medical intervention ‘triggers’ laws governing legal parenthood that are more favourable to intending parents and sperm providers. I argue that although perhaps an improvement on the previous legal framework, these laws are problematic for three important reasons. First, they are prone to violating parental rights and unjustly imposing substantial burdens on individuals. Second, they are discriminatory. Third, even if we take a pragmatic approach to the question of parenthood in these cases, these laws fail to properly consider the welfare interests of children. Finally, I conclude by showing that my argument does not entail adopting a laissez‐fair attitude to conception using third‐party sperm.     

Challenges to biology education from new reproductive technologies

Teaching students about human reproduction is becoming increasingly daunting as assisted reproduction technologies challenge scientific, social and legal perceptions of parenthood. Mitochondrial replacement in particular forces us to re-examine established paradigms not only in the context of human reproduction but also with regard to the way in which we teach students about genetic modification, the nature of the eukaryotic cell, and eukaryote evolution.     

Seasonal variation in conception and various pregnancy outcomes

Abstract

U.S. vital registration data on live births and data on abortions and ectopic pregnancies from a national hospital discharge survey were used to examine the seasonality of conceptions and the influence the conception pattern has on the monthly incidence of abortions and ectopic pregnancies. We found that in the United States conceptions follow a consistent seasonal pattern with the peak in November and December. However, when the pattern for conceptions is controlled, the monthly variation for abortions and ectopic pregnancies is not significant. Therefore, we find no monthly excess for any of these outcomes of pregnancy over that expected as a consequence of the seasonality of conception. We suggest the monthly variation for the number of each of these pregnancy outcomes will best be explained when the seasonal variation in conceptions is understood.     

Population structure promotes the evolution of costly sex in artificial gene networks

We build on previous observations that Hill–Robertson interference generates an advantage of sex that, in structured populations, can be large enough to explain the evolutionary maintenance of costly sex. We employed a gene network model that explicitly incorporates interactions between genes. Mutations in the gene networks have variable effects that depend on the genetic background in which they appear. Consequently, our simulations include two costs of sex—recombination and migration loads—that were missing from previous studies of the evolution of costly sex. Our results suggest a critical role for population structure that lies in its ability to align the long‐ and short‐term advantages of sex. We show that the addition of population structure favored the evolution of sex by disproportionately decreasing the equilibrium mean fitness of asexual populations, primarily by increasing the strength of Muller's Ratchet. Population structure also increased the ability of the short‐term advantage of sex to counter the primary limit to the evolution of sex in the gene network model—recombination load. On the other hand, highly structured populations experienced migration load in the form of Dobzhansky–Muller incompatibilities, decreasing the effective rate of migration between demes and, consequently, accelerating the accumulation of drift load in the sexual populations.     

THE LOCI OF REPEATED EVOLUTION: A CATALOG OF GENETIC HOTSPOTS OF PHENOTYPIC VARIATION

What is the nature of the genetic changes underlying phenotypic evolution? We have catalogued 1008 alleles described in the literature that cause phenotypic differences among animals, plants, and yeasts. Surprisingly, evolution of similar traits in distinct lineages often involves mutations in the same gene (“gene reuse”). This compilation yields three important qualitative implications about repeated evolution. First, the apparent evolution of similar traits by gene reuse can be traced back to two alternatives, either several independent causative mutations or a single original mutational event followed by sorting processes. Second, hotspots of evolution—defined as the repeated occurrence of de novo mutations at orthologous loci and causing similar phenotypic variation—are omnipresent in the literature with more than 100 examples covering various levels of analysis, including numerous gain‐of‐function events. Finally, several alleles of large effect have been shown to result from the aggregation of multiple small‐effect mutations at the same hotspot locus, thus reconciling micromutationist theories of adaptation with the empirical observation of large‐effect variants. Although data heterogeneity and experimental biases prevented us from extracting quantitative trends, our synthesis highlights the existence of genetic paths of least resistance leading to viable evolutionary change.     

PARASITES AND THE EVOLUTION OF SELF-FERTILIZATION

Abstract.— Assuming all else is equal, an allele for selfing should spread when rare in an outcrossing population and rapidly reach fixation. Such an allele will not spread, however, if self‐fertilization results in inbreeding depression so severe that the fitness of selfed offspring is less that half that of outcrossed offspring. Here we consider an ecological force that may also counter the spread of a selfing allele: coevolution with parasites. Computer simulations were conducted for four different genetic models governing the details of infection. Within each of these models, we varied both the level of selfing in the parasite and the level of male‐gamete discounting in the host (i.e., the reduction in outcrossing fitness through male function due to the selfing allele). We then sought the equilibrium level of host selfing under the different conditions. The results show that, over a wide range of conditions, parasites can select for host reproductive strategies in which both selfed and outcrossed progeny are produced (mixed mating). In addition, mixed mating, where it exits, tends to be biased toward selfing.     

In Memory

Abstract

Dr. Mathias P. Mertes, well-known medicinal chemist, member of the Editorial Advisory Board of Nucleosides & Nucleotides, and a good friend, died unexpectedly earlier this year. An obituary written by Drs. Gary Grunewald and Robert Hanzlik of the University of Kansas is presented below followed by a list of the publications of Dr. Mertes. Many of us have pleasant memories of stimulating interactions with Matt. We can hope that the spirit and enthusiasm with which Matt approached science has rubbed off on some of us. He will be missed.     

Traditional Amerindian cultivators combine directional and ideotypic selection for sustainable management of cassava genetic diversity

Plant domestication provides striking examples of rapid evolution. Yet, it involves more complex processes than plain directional selection. Understanding the dynamics of diversity in traditional agroecosystems is both a fundamental goal in evolutionary biology and a practical goal in conservation. We studied how Amerindian cultivators maintain dynamically evolving gene pools in cassava. Farmers purposely maintain diversity in the form of phenotypically distinct, clonally propagated landraces. Landrace gene pools are continuously renewed by incorporating seedlings issued from spontaneous sexual reproduction. This poses two problems: agronomic quality may decrease because some seedlings are inbred, and landrace identity may be progressively lost through the incorporation of unrelated seedlings. Using a large microsatellite dataset, we show that farmers solve these problems by applying two kinds of selection: directional selection against inbred genotypes, and counter‐selection of off‐type phenotypes, which maintains high intra‐landrace relatedness. Thus, cultural elements such as ideotypes (a representation of the ideal phenotype of a landrace) can shape genetic diversity.     

Four-year study of controlled timed breeding of rhesus monkeys (Macaca mulatta)

As part of the timed breeding colony at Tulane National Primate Research Center, exogenous progesterone administration (5 mg/day for 10 days) has been used to select conception dates by inducing artificial luteal phases in female rhesus monkeys. A retrospective analysis of data obtained during four breeding seasons (1998-2001) revealed that conceptions occurred an average of 18 days after the last administration of progesterone. The age of the female to be bred, previous pregnancy history, and timing of breeding during the breeding season were determined to be critical factors in the success of the procedure. The benefit of this method of timed breeding is that it does not require tracking of menstrual cycles, which can be labor-intensive and requires that animals be monitored several months in advance of breeding to determine each female's individual cycle length. It also provided an efficient use of breeding-age males.     

GENETIC ISOLATION BY ENVIRONMENT OR DISTANCE: WHICH PATTERN OF GENE FLOW IS MOST COMMON?

Gene flow among populations can enhance local adaptation if it introduces new genetic variants available for selection, but strong gene flow can also stall adaptation by swamping locally beneficial genes. These outcomes can depend on population size, genetic variation, and the environmental context. Gene flow patterns may align with geographic distance (IBD—isolation by distance), whereby immigration rates are inversely proportional to the distance between populations. Alternatively gene flow may follow patterns of isolation by environment (IBE), whereby gene flow rates are higher among similar environments. Finally, gene flow may be highest among dissimilar environments (counter‐gradient gene flow), the classic “gene‐swamping” scenario. Here we survey relevant studies to determine the prevalence of each pattern across environmental gradients. Of 70 studies, we found evidence of IBD in 20.0%, IBE in 37.1%, and both patterns in 37.1%. In addition, 10.0% of studies exhibited counter‐gradient gene flow. In total, 74.3% showed significant IBE patterns. This predominant IBE pattern of gene flow may have arisen directly through natural selection or reflect other adaptive and nonadaptive processes leading to nonrandom gene flow. It also precludes gene swamping as a widespread phenomenon. Implications for evolutionary processes and management under rapidly changing environments (e.g., climate change) are discussed.     

Mismatches between breeding phenology and resource abundance of resident alpine ptarmigan negatively affect chick survival

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Parasitism and alternative reproductive tactics in Northern chamois

Alternative reproductive tactics (ARTs), discrete phenotypic variations evolved to maximize fitness, may entail different cost‐benefit trade‐offs. In large mammals, differences in costs associated with ARTs—including energy expenditure and parasite infection—are typically greatest during the breeding season. Nonetheless, physiological and behavioral differences between ARTs can manifest throughout the year, possibly involving costs that may contribute to maintain ARTs within populations. Using the number of nematode larvae per gram of feces (LPG) as a proxy, we explored the temporal changes in lung parasite infection in territorial and nonterritorial male chamois Rupicapra in the Gran Paradiso National Park (Italy), between 2011 and 2012. We aimed to identify which tactic‐specific physiological and behavioral features (including age, hormonal levels, inter‐ and intrasexual interactions, and space use) or climatic factors (temperature and precipitation) best explained yearly variation in parasite infection within and between ARTs. Generalized additive mixed models showed that the fecal larval counts of lung nematodes underwent strong temporal changes in both male types. Differences between ARTs (with higher LPG values in territorial than nonterritorial males) were greatest during the rut and—to a lesser extent—in spring, respectively, at the peak and at the onset of territoriality. The difference in LPG between tactics was largely explained by the greater levels of hormone metabolites in territorial males during the rut. The other variables did not contribute significantly to explain the different shedding of larvae within and between ARTs. Our analysis suggests that different values of LPG between territorial and nonterritorial males are largely a result of tactic‐specific differences in the secretion of hormone metabolites, but only during the rut. To clarify whether rut‐related parasitism contributes to the maintenance of ARTs, tactic‐specific life history trade‐offs, for example, between reproduction and parasite‐related mortality, must be investigated.     

Toward a pluralistic account of parenthood

What is it that makes someone a parent? Many writers – call them ‘monists’– claim that parenthood is grounded solely in one essential feature that is both necessary and sufficient for someone's being a parent. We reject not only monism but also ‘necessity’ views, in which some specific feature is necessary but not also sufficient for parenthood. Our argument supports what we call ‘pluralism’, the view that any one of several kinds of relationship is sufficient for parenthood. We begin by challenging monistic versions of gestationalism, the view that gestation uniquely grounds parenthood. Monistic and necessity gestationalism are implausible. First, we raise the ‘paternity problem’– necessity gestationalists lack an adequate account of how men become fathers. Second, the positive arguments that necessity gestationalists give are not compelling. However, although gestation may not be a necessary condition for parenthood, there is good reason to think that it is sufficient. After further rebutting an ‘intentionalist’ account of parenthood, in which having and acting on intentions to procreate and rear is necessary for parenthood, we end by sketching a pluralist picture of the nature of parenthood, rooted in causation, on which gestation, direct genetic derivation, extended custody, and even, sometimes, intentions, may be individually sufficient for parenthood.     

Selection for outbreeding in Varroa parasitising resistant honey bee (Apis mellifera) colonies

Parasitism is expected to select for counter‐adaptations in the host: driving a coevolutionary arms race. However, human interference between honey bees (Apis mellifera) and Varroa mites removes the effect of natural selection and restricts the evolution of host counter‐adaptations. With full‐sibling mating common among Varroa, this can rapidly select for virulent, highly inbred, Varroa populations. We investigated how the evolution of host resistance could affect the infesting population of Varroa mites. We screened a Varroa‐resistant honey bee population near Toulouse, France, for a Varroa resistance trait: the inhibition of Varroa's reproduction in drone pupae. We then genotyped Varroa which had co‐infested a cell using microsatellites. Across all resistant honey bee colonies, Varroa's reproductive success was significantly higher in co‐infested cells but the distribution of Varroa between singly and multiply infested cells was not different from random. While there was a trend for increased reproductive success when Varroa of differing haplotypes co‐infested a cell, this was not significant. This suggests local mate competition, through the presence of another Varroa foundress in a pupal cell, may be enough to help Varroa overcome host resistance traits; with a critical mass of infesting Varroa overwhelming host resistance. However, the fitness trade‐offs associated with preferentially co‐infesting cells may be too high for Varroa to evolve a mechanism to identify already‐infested cells. The increased reproductive success of Varroa when co‐infesting resistant pupal cells may act as a release valve on the selective pressure for the evolution of counter resistance traits: helping to maintain a stable host–parasite relationship.     

Opposites attract: MHC‐associated mate choice in a polygynous primate

We investigated reproduction in a semi‐free‐ranging population of a polygynous primate, the mandrill, in relation to genetic relatedness and male genetic characteristics, using neutral microsatellite and major histocompatibility complex (MHC) genotyping. We compared genetic dissimilarity to the mother and genetic characteristics of the sire with all other potential sires present at the conception of each offspring (193 offspring for microsatellite genetics, 180 for MHC). The probability that a given male sired increased as pedigree relatedness with the mother decreased, and overall genetic dissimilarity and MHC dissimilarity with the mother increased. Reproductive success also increased with male microsatellite heterozygosity and MHC diversity. These effects were apparent despite the strong influence of dominance rank on male reproductive success. The closed nature of our study population is comparable to human populations for which MHC‐associated mate choice has been reported, suggesting that such mate choice may be especially important in relatively isolated populations with little migration to introduce genetic variation.