The resolution of conflict in families.

The emergence of family groups is associated with conflict over the allocation of food or other limited resources. Understanding the mechanisms mediating the resolution of such conflict is a major aim in behavioral ecology. Most empirical work on familial conflict has focused on birds. Here, we highlight how recent work on insects provides new and exciting insights into how such conflict is resolved. This work shows that conflict resolution can be more complex than traditionally envisioned, often involving multiple mechanisms. For example, it shows that the resolution of sexual conflict involves a combination of behavioral negotiation, direct assessment of partner's state, and manipulation using anti-aphrodisiacs or prenatal maternal effects. Furthermore, it highlights that there is a shift from the traditional emphasis on conflict (and competition) to a greater emphasis on the balance between conflict on the one hand and cooperation on the other.

Do female Nicrophorus vespilloides reduce direct costs by choosing males that mate less frequently?

Sexual conflict occurs when selection to maximize fitness in one sex does so at the expense of the other sex. In the burying beetle Nicrophorus vespilloides, repeated mating provides assurance of paternity at a direct cost to female reproductive productivity. To reduce this cost, females could choose males with low repeated mating rates or smaller, servile males. We tested this by offering females a dichotomous choice between males from lines selected for high or low mating rate. Each female was then allocated her preferred or non-preferred male to breed. Females showed no preference for males based on whether they came from lines selected for high or low mating rates. Pairs containing males from high mating rate lines copulated more often than those with low line males but there was a negative relationship between female size and number of times she mated with a non-preferred male. When females bred with their preferred male the number of offspring reared increased with female size but there was no such increase when breeding with non-preferred males. Females thus benefited from being choosy, but this was not directly attributable to avoidance of costly male repeated mating.

The effect of size and sex ratio experiences on reproductive competition in Nicrophorus vespilloides burying beetles in the wild.

Male parents face a choice: should they invest more in caring for offspring or in attempting to mate with other females? The most profitable course depends on the intensity of competition for mates, which is likely to vary with the population sex ratio. However, the balance of pay-offs may vary among individual males depending on their competitive prowess or attractiveness. We tested the prediction that sex ratio and size of the resource holding male provide cues regarding the level of mating competition prior to breeding and therefore influence the duration of a male's biparental caring in association with a female. Male burying beetles, Nicrophorus vespilloides were reared, post-eclosion, in groups that differed in sex ratio. Experimental males were subsequently translocated to the wild, provided with a breeding resource (carcass) and filmed. We found no evidence that sex ratio cues prior to breeding affected future parental care behaviour but males that experienced male-biased sex ratios took longer to attract wild mating partners. Smaller males attracted a higher proportion of females than did larger males, securing significantly more monogamous breeding associations as a result. Smaller males thus avoided competitive male-male encounters more often than larger males. This has potential benefits for their female partners who avoid both intrasexual competition and direct costs of higher mating frequency associated with competing males.

Male burying beetles extend, not reduce, parental care duration when reproductive competition is high.

Male parents spend less time caring than females in many species with biparental care. The traditional explanation for this pattern is that males have lower confidence of parentage, so they desert earlier in favour of pursuing other mating opportunities. However, one recent alternative hypothesis is that prolonged male parental care might also evolve if staying to care actively improves paternity. If this is the case, an increase in reproductive competition should be associated with increased paternal care. To test this prediction, we manipulated the level of reproductive competition experienced by burying beetles, Nicrophorus vespilloides (Herbst, 1783). We found that caregiving males stayed for longer and mated more frequently with their partner when reproductive competition was greater. Reproductive productivity did not increase when males extended care. Our findings provide support for the increased paternity hypothesis. Extended duration of parental care may be a male tactic both protecting investment (in the current brood) and maximizing paternity (in subsequent brood(s) via female stored sperm) even if this fails to maximize current reproductive productivity and creates conflict of interest with their mate via costs associated with increased mating frequency.

Sexual selection affects the evolution of lifespan and ageing in the decorated cricket Gryllodes sigillatus.

Recent work suggests that sexual selection can influence the evolution of ageing and lifespan by shaping the optimal timing and relative costliness of reproductive effort in the sexes. We used inbred lines of the decorated cricket, Gryllodes sigillatus, to estimate the genetic (co)variance between age-dependent reproductive effort, lifespan, and ageing within and between the sexes. Sexual selection theory predicts that males should die sooner and age more rapidly than females. However, a reversal of this pattern may be favored if reproductive effort increases with age in males but not in females. We found that male calling effort increased with age, whereas female fecundity decreased, and that males lived longer and aged more slowly than females. These divergent life-history strategies were underpinned by a positive genetic correlation between early-life reproductive effort and ageing rate in both sexes, although this relationship was stronger in females. Despite these sex differences in life-history schedules, age-dependent reproductive effort, lifespan, and ageing exhibited strong positive intersexual genetic correlations. This should, in theory, constrain the independent evolution of these traits in the sexes and may promote intralocus sexual conflict. Our study highlights the importance of sexual selection to the evolution of sex differences in ageing and lifespan in G. sigillatus.

Telomere length maintenance--an ALTernative mechanism.

The Alternative Lengthening of Telomeres (ALT) mechanism is utilised by approximately 10% of human tumours and a higher proportion of some types of sarcomas. ALT+ cell lines and tumours show heterogeneous telomere length, extra-chromosomal circular and linear telomeric DNA, ALT associated promyelocytic bodies (APBs), a high frequency of post-replication exchanges in telomeres (designated as telomere-sister chromatid exchanges, T-SCE) and high instability at a GC-rich minisatellite, MS32 (D1S8). It is clear that there is a link between the minisatellite instability and the mechanism that underpins ALT, however currently the nature of this relationship is uncertain. Single molecule analysis of telomeric DNA from ALT+ cell lines and tumours has revealed complex telomere mutations that have not been seen in cell lines or tumours that express telomerase. These complex telomere mutations cannot be explained by T-SCE but must arise by another inter-molecular process. The break-induced replication (BIR) model that may explain the observed high frequency of T-SCE and the presence of complex telomere mutations is reviewed.

Fatty acid, carotenoid and vitamin A composition of tissues of free living gulls.

The aim of this study was to investigate fatty acid and carotenoid profile as well as vitamin A (retinol and retinol esters) content in gull (Larus fucus) tissues. Palmitic (16:0) and stearic (18:0) fatty acids were major saturates in all the tissues studied. Oleic acid (18:1n-9) was the major monounsaturate in the tissue phospholipids varying from 11.9% (liver) up to 18.2% (lung). Arachidonic acid (20:4n-6) was the major unsaturate in the phospholipid fraction in all the tissues. Liver contained the highest total carotenoid concentration which was 5 and 7 fold higher compared to kidney and pancreas. In the liver beta-carotene was major carotenoid. In contrast, in all other tissues beta-carotene was minor fraction with lutein being major carotenoid. Zeaxanthin, canthaxanthin, beta-cryptoxanthin and echinenone were also identified in the gull tissues. Liver and kidney were characterised by the highest vitamin A concentrations (1067.5 and 867.5 microg/g, respectively). Retinol comprised from 55.3% (pancreas) down to 8% (kidney) of the total vitamin A but was not detected in the abdominal fat. Retinyl palmitate was the major retinyl ester in the liver, kidney and heart (44.2; 38.1 and 46.0% of total retinyl esters). In muscles and abdominal fat retinyl stearate was the major retinyl ester fraction. Therefore high proportions of beta-carotene were found in gull liver and peripheral tissues were enriched by lutein and zeaxanthin compared to the liver, a very high concentration of retinyl esters in the kidney was observed and tissue-specificity in retinyl ester proportions in peripheral tissues was found.

Characterization of terminal deletions at 7q32 and 22q13.3 healed by De novo telomere addition.

We have developed a strategy for the isolation of terminal deletion breakpoints from any chromosome that has been healed by de novo addition of a telomere repeat array. Breakpoints at 7q32 and 22q13.3 have been isolated and characterized in two patients (patients FB336R and AJ). Both truncated chromosomes have been healed by the addition of a novel telomere, with such an addition possibly mediated by the enzyme telomerase. The breakpoint at 7q32 in patient FB336R shows a structure similar to that of breakpoints on other chromosomes that have been healed in this way. However, the breakpoint at 22q13.3 in patient AJ has 10 nucleotides of unknown origin inserted between the sequence unique to chromosome 22q and the start of the telomere repeat array. This unusual structure is suggestive of a multistep healing event resulting in de novo telomere addition at this breakpoint, and possible mechanisms are discussed.

High levels of sequence polymorphism and linkage disequilibrium at the telomere of 12q: implications for telomere biology and human evolution.

The human Xp/Yp telomere-junction region exhibits high levels of sequence polymorphism and linkage disequilibrium. To determine whether this is a general feature of human telomeres, we have undertaken sequence analysis at the 12q telomere and have extended the analysis at Xp/Yp. A total of 22 single-nucleotide polymorphisms (SNPs) and one 30-bp duplication were detected in the 1,870 bp adjacent to the 12q telomere. Twenty polymorphic positions were in almost complete linkage disequilibrium, creating three common diverged haplotypes accounting for 80% of 12q telomeres in the white population. A further 6% of 12q telomeres contained a 1,439-bp deletion in the DNA flanking the telomere. The remaining 13% of 12q telomeres did not amplify with the primers used (nulls). The distribution of telomere (TTAGGG) and variant repeats within 12q telomeres was hypervariable, but alleles with similar distribution patterns were associated with the same haplotype in the telomere-adjacent DNA. These data suggest that 12q telomeres, like Xp/Yp telomeres, exhibit low levels of homologous recombination and evolve along haploid lineages. In contrast, high levels of homologous recombination occur in the adjacent proterminal regions of human chromosomes. This suggests that there is a localized telomere-mediated suppression of recombination. In addition, the genetic characteristics of these regions may provide a source of deep lineages for the study of early human evolution, unaffected by both natural selection and recombination. To explain the presence of a few diverged haplotypes adjacent to the Xp/Yp and 12q telomeres, we propose a model that involves the hybridization of two archaic hominoid lineages ultimately giving rise to modern Homo sapiens.

The plasticity of human telomeres demonstrated by a hypervariable telomere repeat array that is located on some copies of 16p and 16q.

Human telomeres are composed of tandem arrays of TTAGGG repeats with many variant repeats at the proximal ends. Comparison of the interspersion of variant and TTAGGG repeats between alleles can be used to study telomere instability, but the difficulty in identifying chromosome-specific sequences close to the start of autosomal telomeres has hampered such investigations. A chromosome end, including a telomere and adjacent sequence, that is polymorphic for its presence or absence in unrelated individuals has been identified. The telomere-adjacent DNA shows strong homology (92-99%) to sequences, including two expressed sequence tags, that are usually located in subterminal regions of human chromosomes but not adjacent to telomeres. Since this chromosome end arose, it has relocated at least once. In Caucasians, it forms the telomere of approximately 6% of 16q and 2% of 16p chromosome arms. The mechanism of relocation is unknown but must have involved the telomere-adjacent DNA rather than the telomere itself, as copies on 16p and 16q share the same telomere-adjacent sequence. The interspersion patterns of TTAGGG with TGAGGG, TTGGGG and non-amplifying repeat sequences revealed extensive allelic variation, such that 47 different alleles were observed among the 50 alleles mapped. Closely related alleles differ by small changes in copy number at blocks of adjacent like repeats, as seen at the Xp/Yp pseudoautosomal telomere. Such differences are compatible with a model in which the majority of mutations arise by intra-allelic mechanisms, in individuals hemizygous for a single copy of the chromosome end.

Sequences from higher primates orthologous to the human Xp/Yp telomere junction region reveal gross rearrangements and high levels of divergence.

A high level of sequence polymorphism combined with linkage disequilibrium has created a limited number of highly diverged haplotypes across the human Xp/Yp telomere junction region. To gain insight into the unusual genetic characteristics of this region, we have examined the orthologous sequences in the common chimpanzee (Pan troglodytes ), the gorilla (Gorilla gorilla) and the orang-utan (Pongo pygmaeus). Divergence from the human Xp/Yp sequence is higher (average 2.6-fold) than that observed at other loci. The position of the human Xp/Yp telomere is unique, as additional sequences are present at this location in the other three species. These included an array of subterminal satellite in the chimpanzee and, in the gorilla a small interstitial array of telomere-like repeats followed by sequences with strong homology to the human 18p subterminal region. In the orang-utan, two alleles with different structures were identified. These differ by the presence or absence of a short interspersed nuclear element (SINE) sequence just proximal to long arrays of telomere-like repeat sequences that probably represent the proximal end of the orang-utan Xp/Yp telomere. In addition, a high level of sequence divergence between the two orang-utan structures was identified. This divergence is similar to that observed between the human Xp/Yp telomere-adjacent haplotypes. The high sequence divergence and evidence of gross rearrangements indicate that the Xp/Yp telomeric region has evolved faster than the rest of the genome.

Mechanisms underlying telomere repeat turnover, revealed by hypervariable variant repeat distribution patterns in the human Xp/Yp telomere.

Sequences immediately adjacent to the human Xp/Yp telomere exhibit a high frequency of base substitutional polymorphisms, together with almost complete linkage disequilibrium, to create only a few diverged haplotypes. This sequence divergence has been used to develop a PCR-based system for mapping the distribution of the telomere (TTAGGG) and variant repeats (TGAGGG and TCAGGG) at the proximal end of the telomere repeat array. The distribution of these repeats is extremely variable. Almost all Xp/Yp telomeres are different, indicating a high mutation rate. Some telomere maps associated with the same flanking haplotype show similarities, identifying subsets of telomeres that share a recent common ancestry. Mechanisms underlying the rapid turnover of repeats at the proximal end of the Xp/Yp telomere include intra-allelic processes, such as slippage during replication. Inter-allelic exchanges may occur occasionally, but telomerase activity probably plays only a minor role in the germline turnover of proximally located telomere and variant repeats.

The CEPH consortium linkage map of human chromosome 16.

A Centre d'Etude du Polymorphisme Humain (CEPH) consortium map of human chromosome 16 has been constructed. The map contains 158 loci defined by 191 different probe/restriction enzyme combinations or primer pairs. The marker genotypes, contributed by 9 collaborating laboratories, originated from the CEPH families DNA. A total of 60 loci, with an average heterozygosity of 68%, have been placed on the framework genetic map. The genetic map contains 7 genes. The length of the sex-averaged map is 165 cM, with a mean genetic distance between loci of 2.8 cM; the median distance between markers is 2.0 cM. The male map length is 136 cM, and the female map length is 197 cM. The map covers virtually the entire chromosome, from D16S85, within 170 to 430 kb of the 16p telomere, to D16S303 at 16qter. The markers included in the linkage map have been physically mapped on a partial human chromosome 16 somatic cell hybrid panel, thus anchoring the genetic map to the cytogenetic-based physical map.

A subterminal satellite located adjacent to telomeres in chimpanzees is absent from the human genome.

One of the significant unresolved differences between the karyotypes of humans and African apes is the presence of positively staining G-bands at the ends of many chromosome arms in the chimpanzee and gorilla but absent from human chromosomes. Using a telomere anchored PCR strategy, we have isolated DNA from a subterminal satellite, composed of a 32 basepair A-T rich repeat, from the chimpanzee genome that hybridizes to all the additional terminal bands and at two interstitial sites. The satellite is more abundant in gorillas and is not detected in humans or orangutans. Furthermore, there is no similarity between other chimpanzee telomere-junction clones and human subterminal sequences, and therefore the organization of sequences adjacent to telomeres is very different between these closely related primates.

Abnormal segregation of alleles in CEPH pedigree DNAs arising from allele loss in lymphoblastoid DNA.

Somatic events that result in the reduction to hemi- or homozygosity at all loci affected by the event have been identified in lymphoblastoid DNA from mothers of two CEPH families. Using suitably informative probes, the allele deficiencies were detected by the abnormal transmission of alleles from grandparents to grandchildren, with the apparent absence of the alleles from the parent. Undetected somatic deficiencies in family DNAs could result in misscoring of recombination events and consequently introduce errors into linkage analysis.