Dieter Lukas
I am a Post-Doctoral Researcher at the University of Cambridge, working with Prof. Clutton-Brock on reconstructing the evolution of the diversity of mammalian social systems
Below are short lay-summaries for all my publications, please check my CV if you are interested in a formatted list. As these summaries present my personal interpretation of work that has been achieved as a collaborative effort, I highly recommend reading any article that might be of relevance to you. Where available, I have linked the name of the respective co-authors to their websites, which might help to see these findings in a broader context.
Cooperative breeding and monogamy in mammalian societies.
Lukas D & Clutton-Brock TH (2012)
Proceedings of the Royal Society B doi:10.1098/rspb.2011.2468
Most female mammals provision and rear their own young but, in a small proportion of species, breeding females are assisted in protecting and feeding their offspring by non-breeding helpers. These cooperative and eusocial breeding systems are of particular interest to evolutionary biologists as it is necessary to explain why adults should forego breeding and raise young other than their own. We performed phylogenetic reconstructions to show that in mammals cooperative breeding systems only evolved in lineages with monogamous mating, which leads to high relatedness among group members. This confirms previous findings in birds and insects, and supports the prediction that high levels of kinship are a necessary condition for the evolution of cooperative and eusocial breeding.
Group structure, kinship, inbreeding risk and habitual female dispersal in plural-breeding mammals.
Lukas D & Clutton-Brock TH (2011)
Journal of Evolutionary Biology doi:10.1111/j.1420-9101.2011.02385.x
In this paper we compare two different potential theories that have been proposed to explain why in some social mammals females leave their natal group upon reaching maturity to join other groups. One suggestion has been that in cases where food is widely and equally distributed females gain from avoiding competing against their family members, as they can easily occupy a new spot. The alternative suggestion is that females disperse in cases where the only potential male partner available in their groups is their own father. This will occur where single males manage to monopolize matings in groups for considerable lengths of time. Based on a phylogeny, we checked whether ecological parameters or male tenure length were likely to have changed at the same time as female changed their moving behaviour. This provided strong support for the inbreeding theory, but not for the ecological theory. A female's decision to leave is associated with the risk that a female’s father is reproductively active in her group when she starts to breed.
The evolution of social philopatry and dispersal in female mammals.
Clutton-Brock TH & Lukas D (2011)
Molecular Ecology doi:10.1111/j.1365-294X.2011.05232.x
Animals are faced with considerable costs when leaving their natal place, where they both know the area and the other individuals. There are risks associated with the actual movement, such as increased predation, as well as costs in establishing and getting to know a new territory. Accordingly, in most mammalian species individuals, especially females, settle in or close to their natal group or area. This review looks at those instances where mammalian females leave their social group to potentially breed in a different group. This takes various forms, such as females being forcefully evicted, groups splitting such that females still reside with some of their previous partners, and cases where all females leave their natal group upon reaching maturity. Explanations are provided which can provide insights for these different instances, such as competition over limited ecological resources or inbreeding avoidance.
Male-mediated gene flow in patrilocal primates
Schubert G, Stoneking CJ, Arandjelovic M, Boesch C, Eckhard N, Hohmann G, Langergraber K, Lukas D, Vigilant L (2011).
PloS One 6(7): e21514. doi:10.1371/journal.pone.0021514.
This study performed a large-scale survey of several social groups of chimpanzees and bonobos, analyzing variation at male specific Y-chromosomal genetic markers from fecal samples. It was found that, occassionaly, males would carry Y-chromosomal variants which did not match with those of the remaining males in the group, but those of males found in a different group. This suggests that even if it is basically impossible for adult chimpanzee and bonobo males to immigrate into a different social group, as they will be heavily attacked, the genes they carry might cross social groups. The frequency with which different variants were observed matched previous estimates of the rate of offspring being sired by females mating with males outside of their own group.
Y-chromosome analysis confirms highly sex-biased dispersal and suggests a low male effective population size in bonobos (Pan paniscus).
Eriksson J, Siedel H, Lukas D, Kayser M, Erler A, Hashimoto C, Hohmann G, Boesch C, Vigilant L (2006)
Molecular Ecology 15: 939-949.
Only few studies from natural populations of bonobos, the sister species to chimpanzees, have been conducted thus far. Limited behavioural observations had indicated that in bonobos females show more socio-positive interactions and cooperation than the males. This led to the suggestion that, unlike in chimpanzees, female bonobos remain in their natal group for their entire life. Genetic methods provide tools to address the question of sex-specific dispersal without the need to directly observe the individuals. In this study, fecal samples for DNA extraction were collected for several bonobo groups. Which sex remains in the natal group can be inferred by analyzing genetic elements which are only inherited from the parent of one sex. In mammals, mitochondrial DNA is only inherited from mothers to offspring, while the Y-chromosome is only inherited from fathers to their sons. If there is no movement of females between groups, we would expect that different females in different groups carry slightly different variants of mitochondrial DNA, while, if males move, different Y-chromosal variants should be present in each group. The study showed that the genetic region of the Y-chromosome analyzed from males of single groups were in fact very similar, sometimes being all identical, while being divergent between groups. In contrast, the variation at the mitochondrial DNA was venly distributed. This shows that in bonobos, as in the chimpanzees, males stay in their natal group while females move, a finding that since has been also documented by direct observations.
To what extent does living in a group mean living with kin?
Lukas D, Reynolds V, Boesch C and Vigilant L (2005)
Molecular Ecology 14:2181-2196.
In animal species where individuals live together in groups, normally all the individuals of one sex stay in the group they have been born, while the individuals of the other sex leave upon reaching sexual maturity. In mammals, it is usually males who disperse and leave the groups. In contrast, in chimpanzees males are philopatric, remaining in their natal group for all their lives while females move between groups. Chimpanzee males show high levels of social interactions and cooperation, and it has been speculated that this is the result of interactions among close relatives, all born in the same family. However, when we assessed the relatedness levels within chimpanzee groups, we found that males were only seldom higher related than the females. In fact, both sexes showing very low relatedness levels, suggesting that males frequently interact with other males from their own group that are not kin. To see whether this is a general pattern, we derived an analytical model and compared its results to published relatedness levels from a range of different species. The results show that in almost all species groups consist of sets of small families, and as group size increases, not family size, but the number of families increases. As group size increases, individuals are therefore increasingly likely to encounter individuals from other families. These combined results indicate that cooperation among extended families can not be the main reasons for these individuals to reside together in groups.
Nuclear insertions help and hinder inference of the evolutionary history of gorilla mtDNA.
Thalmann O, Serre D, Hofreiter M, Lukas D, Eriksson J and Vigilant L (2005)
Molecular Ecology 14:179-188.
Mitochondria are small compartments within cells, responsible for energy production (a metaphor for these would be the power plants of the cells). They carry segments of DNA which encode proteins for their specialized function. In rare occasions, these DNA segments are copied into the general genome of the cell at random places. These new intergrated copied fragments (called nuclear mitochondrial inserts) loose their function. Given the rarity of the integration, finding the same copy at the same place in the genome in two individuals means that these individuals had a common ancestor. In addition, since these copies lost their function, mutations can accumulate which change the original sequence. Comparing the nuclear inserts to the original version present in the mitochondrial genome allows to calculate the number of mutations to date of the integration event, assuming that mutations happen at a regular rate. In this study, we detected such a nuclear insert among individuals of gorillas from both western and eastern Africa. Today these populations are separated by a corridor of approximately 1000 miles where no gorillas live. Our finding suggests that this split is a relatively recent event, and that the two populations will have had contact up until several generations ago.
Major histocompatibility complex and microsatellite variation in two populations of wild gorillas.
Lukas D, Bradley BJ, Nsubuga AM, Doran-Sheehy D, Robbins M, Vigilant L (2004)
Molecular Ecology 13: 3389-3402. please note that there is a typographical error (pdf)
Many regions of the genomes of animals show variation between individuals even in a single population. Previous research indicates that there is a linear relationship between the number of individuals in a population and the number of different variants at any region in the genome. Many animal populations today are in decline. The loss of genetic variation could potentially be an additional problem for many endangered, fragmented populations of animals. As genetic variation is the raw material for evolutionary change, small populations could be less likely to harbor relevant adaptations for future environmental change. In this study we assessed the genetic variation at a functional genetic region (a part of the immune system) and several neutral genetic regions in one of the two remaining populations of mountain gorillas, which has around 300 individuals. As it is difficult to theoretically determine how much variation to expect in such a population, we compared the variation to that found within a similar sample from a population of the more numerous western lowland gorillas. We did detect comparable levels of variation at all genetic regions for the mountain gorillas, which indicates that the recent rapid reduction in population size has as yet not led to a complete loss of variation. We also found elevated levels of variation at the functional immune system region, indicating that selection is still operating. There is a risk though that if fragmentation of gorillas into small populations persists for several more generations, genetic variation might be drastically reduced.
see commentary regarding this paper:
Reply: Facts, faeces and setting standards for the study of MHC genes using noninvasive samples.
Lukas D and Vigilant L (2005)
Molecular Ecology 14: 1601-1602.
The functional locus (MHC DRB exon 2) we targetted during this study is special in that small segments of the genome have been duplicated, allowing for more than just two functional variants per individual. This creates difficulties for assessing this variation, especially when using low quality and low quantity samples as we did for these gorillas. This commentary discusses some of the technical challenges in more detail.
Dispersed male networks in western gorillas.
Bradley BJ, Doran-Sheehy DM, Lukas D, Boesch C and Vigilant L (2004)
Current Biology 14: 510-513.
Western lowland gorillas live in so called harem groups, consisting of a single adult male with one or more adult females and their immature offspring. Males always leave their groups once they reach sexual maturity, but little is known how far they move. A wide variety of behaviour has been observed when males of neighboring groups encounter each other, ranging from peaceful to highly aggressive interactions. In many mammalian species differences in social interactions between partners seem to be linked to patterns of kinship, with positive interaction occuring primarily among family members. To infer whether this could also be relevant for gorilla males we wanted to know whether males in neighboring groups sometimes are in fact kin. Genetic methods were employed to infer these relationships. For this, samples were collected from several neighboring groups of gorillas. Samples for such endangered species are collected in a non-invasive fashion, by observing individuals poo and collecting the feces soon after - feces always contains some shedded body cells with DNA. The genetic profiles indicated that indeed quite frequently males from neighboring groups are likely to be either father and son or brothers. This could be a potential explanation for the variation in the behaviour, however more detailed studies will be needed. Brenda Bradley actually followed this study up by analysing the relationships among the females, who are also known to move between groups. Also in their case individuals are not distributed randomly, but female kin often reside within the same group (paper can be found on her website). For both females and males it is though not yet entirely clear whether individuals actively seek out kin or whether they simply not move very far, potentially because they know the respective area.