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PubMed2005

Evaluating the costs of mosquito resistance to malaria parasites.

Costly resistance mechanisms have been cited as an explanation for the widespread occurrence of parasitic infections, yet few studies have examined these costs in detail. A malaria-mosquito model has been used to test this concept by making a comparison of the fitness of highly susceptible lines of mosquitoes with lines that are resistant to infection. Malaria infection is known to cause a decrease in fecundity and fertility of mosquitoes; resistant mosquitoes were thus predicted to be fitter than susceptible ones. Anopheles gambiae were selected for refractoriness/resistance or for increased susceptibility to infection by Plasmodium yoelii nigeriensis. Additional lines that acted as controls for inbreeding depression were raised in parallel but not exposed to selection pressure. Selections were made in triplicate so that founder effects could be detected. Resistance mechanisms that were selected included melanotic encapsulation of parasites within 24 h postinfection and the complete disappearance of parasites from the gut. Costs of immune surveillance were assessed after an uninfected feed, and costs of immune deployment were assessed after exposure to infection and to infection and additional stresses. Mosquito survivorship was unaffected by either resistance to infection or by an increased burden of infection when compared with low levels of infection. In most cases reproductive fitness was equally affected by refractoriness or by infection. Resistant mosquitoes did not gain a fitness advantage by eliminating the parasites. Costs were consistently associated with larval production and egg hatch rate but rarely attributed to changes in blood feeding and never to changes in mosquito size. No advantages appeared to be gained by the offspring of resistant mosquitoes. Furthermore, we were unable to select for refractoriness in groups of mosquitoes in which 100% or 50% of the population were exposed to infection every generation for 22 generations. Under these selection pressures, no population had become completely refractory and only one became more resistant. Variations in fitness relative to control lines in different groups were attributed to founder effects. Our conclusion from these findings is that refractoriness to malaria is as costly as tolerance of infection.

Animals↗

PubMed2000

IQ gains, WISC subtests and fluid g: g theory and the relevance of Spearman's hypothesis to race.

IQ gains over time were calculated for each WISC (Wechsler Intelligence Scale for Children) subtest and the subtests ranked by size of gain. Verbal similarities led at 20 points per generation--larger than gains on Raven's Progressive Matrices. Similarities measures on-the-spot problem-solving (something akin to fluid g); verbal subtests that do not measure this show low rates of gain. WISC subtests were also ranked by their correlations with Raven's, the latter being used as a marker for fluid g. The r between the two hierarchies was calculated to approximate a correlation between IQ gains and fluid g. The result of 0.50 contrasts with the negative correlation between IQ gains and the g generated by factor analysing the WISC battery itself, which is generally viewed as predominately a crystallized g. In sum, it appears that human groups can make massive fluid g gains in a period too short to accommodate radical change in the speed and efficiency of neural processes. Moreover, once gains in intelligent behaviour over historical time are seen to be independent of brain physiology, does g really provide a criterion for assessing their significance? Finally, not only a measure of fluid g (which is highly heritable) but also inbreeding depression are shown to be correlated with IQ gains--gains overwhelmingly environmental in origin. Therefore, correlations between such genetically influenced factors and the size of the black/white IQ gap do not show that the gap has a genetic component.

Brain↗

PubMed2000

The g factor: psychometrics and biology.

General ability, defined as psychometric g, arises from the empirical fact that scores on various cognitive tests are positively correlated in the population. The g factor is highly stable across different factor analytic algorithms, across different test batteries and across different populations. Because all cognitive tests, from the simplest to the most complex, regardless of their informational content, are g-loaded to varying degrees, g cannot be described in terms of the tests' content, or even in psychological terms. It is actually a property of the brain. The loadings of various tests on g, from tests of sensory discrimination and reaction time to those of highly complex problem solving, predict those tests' degree of correlation with a number of non-psychometric variables: the test's heritability, inbreeding depression, coefficient of assortative mating, brain size, reaction time, brain nerve conduction velocity, brain glucose metabolic rate and features of brain evoked potentials. Although some of the brain's cognitive functions are modular, the g factor reflects the all-positive correlations among virtually all cognitive functions that show individual differences. I hypothesize that the brain contains no module for general problem solving. Correlations between individuals' performances in various cognitive tasks result from quantitative individual differences in physiological conditions that do not constitute the brain's modular and other neural design features but do influence their speed and efficiency of information processing.

Adult↗

PubMed1986

Effect of parental consanguinity on anthropometric measurements among the Sheikh Sunni Muslim boys of Delhi.

The study of consanguineous marriage is an efficient way to elucidate the genetic structure of human populations. Such matings give an opportunity for recessive genes to manifest themselves by becoming homozygous. The present attempt examines the effects of parental consanguinity on various anthropometric measurements among the Sheikh Sunni Muslim boys of old Delhi between the ages of 11 and 16 years. A slight inbreeding depression has been observed for all eight anthropometric measurements, i.e., stature, span, sitting height, head length, head circumference, chest girth, and calf circumference. The results support earlier studies in regard to the effect of consanguinity on anthropometric measurements.

Adolescent↗

PubMed1998

Inbreeding and divorce in blue and great tits.

In blue tits, Parus caeruleus, and other wild birds, matings between close relatives or between genetically similar individuals are associated with fitness costs, often in terms of lower hatching success of the eggs. If individuals cannot assess their genetic similarity to potential mates, those fitness costs may be hard to avoid; however, they may use the proportion of unhatched eggs in their clutch as a cue for their mate choice in the next season. We tested this hypothesis using data from a long-term population study on blue and great tits, Parus major. Divorce in response to inbreeding depression can be considered a special case of the 'incompatibility hypothesis'. As predicted from this hypothesis, both male and female blue tits benefited from divorce when part of their clutch failed to hatch. There was no evidence however, that divorce in blue or great tits was related to the presence of unhatched eggs in the nest. Copyright 1998 The Association for the Study of Animal Behaviour

Journal Article↗

PubMed1998

Sexual Reproduction and Stable Coexistence of Identical Competitors.

Current competition theory predicts that species must be ecologically distinct in order to stably coexist in the same community. This prediction is based on the implicit assumption that the consequences of sexual reproduction can be ignored. If anything, it is generally assumed that sex will only add problems, such as failure of insemination and inbreeding depression to species that have become rare, thus hastening competitive exclusion. Here we suggest that sexual reproduction may also bring rare species advantages in terms of the rate of per capita population growth. The key to our argument is that species-specific density dependence in population growth can occur when sexual reproduction is explicitly considered. We show that density-dependent sex ratio, sexual conflict, and sexually transmitted diseases can all promote species coexistence without separate niches.Copyright 1998 Academic Press

Journal Article↗

PubMed1987

The evolution of plant reproductive characters; sexual versus natural selection.

The rôle of sexual selection in the evolution of plant reproductive characters has become a widely discussed topic among plant population biologists. For many reproductive characters, it is difficult to distinguish whether sexual selection or natural selection has been the more important force. We propose a definition of sexual selection for cosexual species and critically review the topic of sexual selection in plants. The emphasis of the chapter is on the evolution of plant reproductive characters, rather than on the issue of whether certain phenomena should be classified as sexual or natural selection. We do, however, argue that the category of sexual selection should not include the phenomena of inbreeding depression, genetically based self-incompatibility systems controlled by one or a few loci, or the effects of wide crossing and specific combining ability. We then discuss the available information on pollen competition and progeny quality, fruit and seed abortion, and the rôle of pollinator attraction in male and female fertility.

Biological Evolution↗

PubMed1997

High-temperature stress and the evolution of thermal resistance in Drosophila.

The evolution of thermal resistance and acclimation is reviewed at the population level using populations and isofemale lines of Drosophila buzzatii and D. melanogaster originating from different climatic regions. In general, ample genetic variation for thermal resistance was found within and among populations. A rough correlation between the climate of origin and thermal resistance was apparent. Acclimation at a non-lethal temperature led to a significant increase in survival after heat shock, and recurrent acclimation events generally increased survival even further. Acclimation effects lasted over several days, but this effect decreased gradually with time since acclimation. Protein studies showed that the concentration of Hsp70 in adult flies is greatly increased by acclimation and thereafter gradually decreases with time. For populations with relatively high survival at one life stage, survival often was low at other life stages. Furthermore, selection on different life stages showed that a selection response in one life stage did not necessarily result in a correlated response in another. These observations indicate that different mechanisms or genes at least in part are responsible for or are expressed at different developmental stages. Selection for increased resistance was successful despite low heritabilities for the trait. Survival and fertility were compared between acclimated and non-acclimated flies, and a cost of expressing the "heat shock response" was identified in that increased survival after acclimation was accompanied by reduced fertility. The relative costs increased under nutritional stress. Metabolic rate was genetically variable but did not correlate with temperature resistance. The more resistant lines, however, often had shorter developmental time. Inbreeding reduced thermal stress tolerance of adult flies, but it did not reduce tolerance of embryos that possibly are exposed to strong natural selection for thermal stress resistance. In general, inbreeding may reduce stress resistance, and thus multiple stressful events may account for increased inbreeding depression in harsh environments.

Acclimatization↗

PubMed1993

A variety of epistatic interactions can occur between partially homologous transgene loci brought together by sexual crossing.

Epistatic interactions between unlinked transgene loci in tobacco plants were studied following sexual crosses between different transgenic lines. Three potential "modifier" transgene loci, which were structurally similar but integrated at different chromosomal locations, were tested for their ability to influence the expression of a partially homologous "target" transgene locus. After introduction of an individual modifier locus, the target locus could be either unaffected, completely inactivated and methylated or differentially sensitive, showing more complete inactivation and methylation when homozygous than when hemizygous. The implications of these results for inbreeding depression in plants are discussed.

Cinnamates↗

PubMed1993

Comparing mutants, selective breeding, and transgenics in the dissection of aging processes of Caenorhabditis elegans.

The genetic analysis of aging processes has matured in the last ten years with reports that long-lived strains of both fruit flies and nematodes have been developed. Several attempts to identify mutants in the fruit fly with increased longevity have failed and the reasons for these failures are analyzed. A major problem in obligate sexual species, such as the fruit fly, is the presence of inbreeding depression that makes the analysis of life-history traits in homozygotes very difficult. Nevertheless, several successful genetic analyses of aging in Drosophila suggest that with careful design, fruitful analysis of induced mutants affecting life span is possible. In the nematode Caenorhabditis elegans, mutations in the age-1 gene result in a life extension of some 70%; thus age-1 clearly specifies a process involved in organismic senescence. This gene maps to chromosome II, well separated from a locus (fer-15) which is responsible for a large fertility deficit in the original stocks. There is no trade-off between either rate of development or fertility versus life span associated with the age-1 mutation. Transgenic analyses confirm that the fertility deficit can be corrected by a wild-type fer-15 transformant (transgene); however, the life span of these transformed stocks is affected by the transgenic array in an unpredictable fashion. The molecular nature of the age-1 gene remains unknown and we continue in our efforts to clone the gene.

Aging↗

PubMed2005

Gene actions of QTLs affecting several agronomic traits resolved in a recombinant inbred rice population and two backcross populations.

To understand the types of gene action controlling seven quantitative traits in rice, we carried out quantitative trait locus (QTL) mapping in order to distinguish between the main-effect QTLs (M-QTLs) and digenic epistatic QTLs (E-QTLs) responsible for the trait performance of 254 recombinant inbred lines (RILs) from rice varieties Lemont/Teqing and two backcross hybrid (BCF1) populations derived from these RILs. We identified 44 M-QTL and 95 E-QTL pairs in the RI and BCF1 populations as having significant effects on the mean values and mid-parental heterosis of heading date, plant height, flag leaf length, flag leaf width, panicle length, spikelet number and spikelet fertility. The E-QTLs detected collectively explained a larger portion of the total phenotypic variation than the M-QTLs in both the RI and BCF1 populations. In both BCF1 populations, over-dominant (or under-dominant) loci were more important than additive and complete or partially dominant loci for M-QTLs and E-QTL pairs, thereby supporting prior findings that overdominance resulting from epistatic loci are the primary genetic basis of inbreeding depression and heterosis in rice.

Chromosome Mapping↗

PubMed2002

Effects of habitat fragmentation on the fitness of two common wetland species, Carex davalliana and Succisa pratensis.

Small habitat size and spatial isolation may cause plant populations to suffer from genetic drift and inbreeding, leading to a reduced fitness of individual plants. We examined the germination, establishment, growth, and reproductive capacity of two characteristic species of mown fen meadows, Carex davalliana, and Succisa pratensis, common in Switzerland. Plants were grown from seeds, which were collected in 18 habitat islands, differing in size and in degree of isolation. We used both common garden and reciprocal transplant experiments to assess effects of habitat fragmentation. In the common garden, plants of Carex originating from small habitat islands yielded 35% less biomass, 30% fewer tillers, and 45% fewer flowering tillers than plants from larger ones. In contrast, plants of Succisa originating from small habitat islands yielded 19% more biomass, 14% more flower heads and 35% more flowers per flower head than plants from larger ones. Moreover, plants of Succisa from small isolated habitats yielded 32% more rosettes than did plants from small connected islands. Reciprocally transplanted plants of Succisa originating from small habitat islands produced 7% more rosettes than plants from larger ones. There was no effect of small habitat size and isolation on germination and establishment of both species in the field. Our results document genetic differences in performance attributable to habitat fragmentation in both species. We suggest that fitness loss in Carex is caused by inbreeding depression, whereas in Succisa the differences in fitness are more likely caused by genetic differentiation. Our study implies that habitat fragmentation affects common habitat-specific species, such as Carex and Succisa, as well as rare ones.

Biomass↗

PubMed2005

Lack of floral nectar reduces self-pollination in a fly-pollinated orchid.

One explanation for the widespread absence of floral nectar in many orchids is that it causes pollinators to visit fewer flowers on a plant, and thus reduces self-pollination. This, in turn, could increase fitness by reducing inbreeding depression in progeny and promoting pollen export. The few previous investigations of this hypothesis have all involved bee-pollinated orchids and some have given contradictory results. We studied the effects of adding artificial nectar (sucrose solution) to the spurs of a non-rewarding long-proboscid fly-pollinated orchid, Disa pulchra. Addition of nectar significantly increased the number of flowers probed by flies (2.6-fold), the time spent on a flower (5.4-fold), the number of pollinia removed per inflorescence (4.8-fold) and the proportion of removed pollen involved in self-pollination (3.5-fold). The level of self-pollination increased dramatically with the number of flowers probed by flies. Experimental self-pollination resulted in fruits with only half as many viable seeds as those arising from cross-pollination. Pollinators were more likely to fly long distances (>40 cm) when departing from non-rewarding inflorescences than when departing from rewarding ones. These findings provide support for the idea that floral deception serves to reduce pollinator-mediated self-pollination.

Animals↗

PubMed2005

Genetic analysis and conservation of the endangered Canary Island woody sow-thistle, Sonchus gandogeri (Asteraceae).

Sonchus gandogeri, a woody sow-thistle, is an endangered Canary Island endemic with only two known populations, one in the El Golfo and another in the Las Esperillas of El Hierro. Amplified fragment length polymorphism (AFLP) markers were used to assess the genetic variation within and among populations. The mean genetic diversity of two populations was estimated to be 0.380, and the El Golfo population (0.380) had higher genetic diversity than the southeastern one (0.268). The unbiased Nei's genetic identity between the two populations was 0.846. The mean genetic diversity of S. gandogeri was much higher than that of the other endangered plant species. This is perhaps due to breeding system, life form, extinction, and/or introgressive hybridization and hybrid origin of the taxon. This study also indicates that the two populations are not strongly differentiated (G(ST)=0.149). This study suggests that S. gandogeri is more likely to become extinct due to environmental or demographic forces than genetic factors, such as inbreeding depression. More strict control of introduced herbivores is necessary to protect these populations, and germplasm collection for ex situ conservation is needed.

Atlantic Islands↗

PubMed2006

Genetic diversity and mating system of the threatened plant Kirengeshoma palmata (Saxifragaceae) in Korea.

The endangered herb Kirengeshoma palmata, from eastern Asia, has had its population severely reduced in number through habitat loss and fragmentation. All of the individuals within five subgroups at Mt. Baek-un-san, in the southern part of Korea, were genetically surveyed by allozyme analysis. Genetic diversity levels within subgroups were relatively high, and a consistently high outcrossing rate as well as a negligible biparental mating rate were confirmed by this study. Several groups of visibly connected ramets were observed in a clustered distribution which suggested cloning. Absence of mating partner rather than pollinators decreased seed production in small mating groups. The present genetic structure of the five subgroups was probably the result of local extinction of intervening populations. Because K. palmata may be a self-incompatible species, populations with few genets face lowered seed set due to mate scarcity. Thus, this type of population may be at an increased risk of extinction as a result of inbreeding depression, loss of genetic variability, and reduced sexual reproduction. The small, genetically depauperate subgroups may need an input of seeds or plants from other populations in China or Japan in order to regenerate, but the possibility of outcrossing depression leads us to recommend outbreeding among the local subgroups of Mt. Baek-un-san to restore genetic variability.

Flowers↗

PubMed2005

Mitochondrial DNA genetic diversity of black muntjac (Muntiacus crinifrons), an endangered species endemic to China.

Genetic diversities based on the mtDNA control region were measured for both a wild population (n = 26) and a captive population (n = 18) of the black muntjac. In total, nine haplotypes were obtained from 44 samples. The wild population exhibited a low nucleotide diversity (pi = 0.00562), which suggests that the black muntjac had a small effective population size historically. In contrast to its low nucleotide diversity, haplotype diversity (h = 0.862) of the wild population was relatively high. Haplotype distribution among local samples shows a distinct difference. As anticipated because of the paucity of available founders, nucleotide diversity (pi = 0.00214) of the captive population was very low. Additionally, a high degree of haplotype identity and an obvious haplotype frequency bias was revealed in the captive population, which implies that the current breeding program should be readjusted to balance distributions of haplotypes, and some new founders should be introduced to the captive population to alleviate potential inbreeding depression.

Animals↗

PubMed1995

Investigations into the ubiquitous nature of high or low immune responsiveness after divergent selection for antibody production in common carp (Cyprinus carpio L.).

This paper reports on the selection of individual carp with a high or low antibody response, in combination with reproduction by gynogenesis, in order to develop well-characterised inbred carp lines consisting of practically unlimited numbers of carp with the same genotype. Two homozygous progenies, previously characterised as having a high or low immune response to dinitrophenyl keyhole limpet haemocyanin (DNP-KLH), were immunised with either a T-dependent (DNP-human serum albumin (DNP-HSA)) or T-independent (trinitrophenyl lipopolysaccharide (TNP-LPS)) hapten-carrier complex. In comparison with the antibody response after DNP-KLH immunisation, the response to DNP-HSA was observed to be highly variable and did not differ between the divergently selected progenies. This suggests that the divergent selection for antibody production to DNP-KLH has been carrier-specific. Immunisation with T-independent TNP-LPS induced a very rapid response which differed between the high and low responders, and likely measured changes in the DNP-specific precursor pool of B cells caused by the selection. A number of selected individuals with a high immune response to DNP-KLH were infected with Trypanoplasma borreli, a haemoflagellate parasite of carp, to examine a possible relationship between the increase in immune responsiveness and disease resistance, but no change could be detected. However, individual homozygous carp were able to escape inbreeding depression and survive the infection. Such carp would be likely candidates for gynogenetic reproduction to obtain viable inbred carp lines.

Animals↗

PubMed2004

Reproductive consequences of population divergence through sexual conflict.

Sexual-selection research increasingly focuses on reproductive conflicts between the sexes. Sexual conflict, divergent evolutionary interests of males and females, can cause rapid antagonistic coevolution of reproductive traits and is a potentially powerful speciation engine. This idea has theoretical and comparative support but remains controversial. Recent experimental evidence from Sepsis cynipsea indicates that populations with greater sexual conflict diverged more quickly; females were less likely to mate with males from other populations when flies had evolved under high levels of sexual conflict. The consequences of this divergence have not been addressed, so here we assess two female fitness surrogates after 44 generations of evolving (and diverging) under three different levels of sexual conflict. Longevity after copulation was negatively associated with the degree of sexual conflict under which flies evolved, and housing females with males also reduced female longevity. Female lifetime reproductive success (LRS) also tended to decrease with increasing conflict. However, there was evidence of either sexual-selection fitness benefits at intermediate levels of sexual selection and conflict or inbreeding depression in the smallest populations (those with the lowest levels of conflict). Nevertheless, the results indicate that there can be a fitness load associated with sexual selection and support claims that sexual conflict can lead to reproductive isolation.

Animals↗