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Biomedical subjects

Robert Brooks

Publications and source records attributed to Robert Brooks.

At least 19 recordsLinked to original sources
PubMed2006

Impact of immigration detention and temporary protection on the mental health of refugees.

BACKGROUND: Over the past decade, developed Western countries have supplied increasingly stringent measures to discourage those seeking asylum. AIMS: To investigate the longer-term mental health effects of mandatory detention and subsequent temporary protection on refugees. METHOD: Lists of names provided by community leaders were supplemented by snowball sampling to recruit 241 Arabic-speaking Mandaean refugees in Sydney (60% of the total adult Mandaean population). Interviews assessed post-traumatic stress disorder (PTSD), major depressive episodes, and indices of stress related to past trauma, detention and temporary protection. RESULTS: A multilevel model which included age, gender, family clustering, pre-migration trauma and length of residency revealed that past immigration detention and ongoing temporary protection each contributed independently to risk of ongoing PTSD, depression and mental health-related disability. Longer detention was associated with more severe mental disturbance, an effect that persisted for an average of 3 years after release. CONCLUSIONS: Policies of detention and temporary protection appear to be detrimental to the longer-term mental health of refugees.

Adult↗
PubMed2005

Female mate choice as a condition-dependent life-history trait.

The acquisition of resources is an important determinant of patterns of variation in and covariation among traits that are costly to produce and are dependent on condition for their expression. However, the extent to which variation in female mate choice behavior is condition dependent, and how this is related to other life-history traits, remains largely unknown. We manipulated the acquisition of dietary protein in the black field cricket, Teleogryllus commodus, and measured the effects of this on several important life-history traits and on female mate choice behavior. Females reared on a high-protein diet developed faster, were heavier at eclosion, and lived longer than females reared on a low-protein diet. Two lines of evidence suggest that female mate choice behavior in T. commodus is condition dependent. First, females reared on the high-protein diet were more sexually responsive and expressed stronger linear and quadratic preference functions for call rate and dominant frequency, respectively. Second, within treatments, females that developed faster were lighter, generally less sexually responsive, and, in the high-protein-diet treatment, expressed weaker preferences than slower-developing females. Collectively, our findings suggest an important role for resource acquisition in generating variation in mate choice behavior.

Animals↗
PubMed2005

The indirect benefits of mating with attractive males outweigh the direct costs.

The fitness consequences of mate choice are a source of ongoing debate in evolutionary biology. Recent theory predicts that indirect benefits of female choice due to offspring inheriting superior genes are likely to be negated when there are direct costs associated with choice, including any costs of mating with attractive males. To estimate the fitness consequences of mating with males of varying attractiveness, we housed female house crickets, Acheta domesticus, with either attractive or unattractive males and measured a variety of direct and indirect fitness components. These fitness components were combined to give relative estimates of the number of grandchildren produced and the intrinsic rate of increase (relative net fitness). We found that females mated to attractive males incur a substantial survival cost. However, these costs are cancelled out and may be outweighed by the benefits of having offspring with elevated fitness. This benefit is due predominantly, but not exclusively, to the effect of an increase in sons' attractiveness. Our results suggest that the direct costs that females experience when mating with attractive males can be outweighed by indirect benefits. They also reveal the value of estimating the net fitness consequences of a mating strategy by including measures of offspring quality in estimates of fitness.

Animals↗
PubMed2005

Invasion success and genetic diversity of introduced populations of guppies Poecilia reticulata in Australia.

High genetic diversity is thought to characterize successful invasive species, as the potential to adapt to new environments is enhanced and inbreeding is reduced. In the last century, guppies, Poecilia reticulata, repeatedly invaded streams in Australia and elsewhere. Quantitative genetic studies of one Australian guppy population have demonstrated high additive genetic variation for autosomal and Y-linked morphological traits. The combination of colonization success, high heritability of morphological traits, and the possibility of multiple introductions to Australia raised the prediction that neutral genetic diversity is high in introduced populations of guppies. In this study we examine genetic diversity at nine microsatellite and one mitochondrial locus for seven Australian populations. We used mtDNA haplotypes from the natural range of guppies and from domesticated varieties to identify source populations. There were a minimum of two introductions, but there was no haplotype diversity within Australian populations, suggesting a founder effect. This was supported by microsatellite markers, as allelic diversity and heterozygosity were severely reduced compared to one wild source population, and evidence of recent bottlenecks was found. Between Australian populations little differentiation of microsatellite allele frequencies was detected, suggesting that population admixture has occurred historically, perhaps due to male-biased gene flow followed by bottlenecks. Thus success of invasion of Australia and high additive genetic variance in Australian guppies are not associated with high levels of diversity at molecular loci. This finding is consistent with the release of additive genetic variation by dominance and epistasis following inbreeding, and with disruptive and negative frequency-dependent selection on fitness traits.

Animals↗
PubMed2005

Characteristics of hospitals that outsource information system functions.

Despite the increasing trend among hospitals to outsource information system functions, little is known about these decisions in the acute-care setting. This study examined the outsourcing behavior of hospitals in Florida to determine the characteristics of hospitals that are most likely to outsource IS functions. In addition, the results provide an overview of which IS functions are most commonly outsourced in hospitals. Overall, survey responses from 98 hospitals indicate that the outsourcing of IS functions is more common in small hospitals and those in rural areas. Another important predictor of IS outsourcing behavior was the degree to which an organization placed a strategic importance on IS in its operations. Outsourcing behavior did not seem to be systematically related to the CIO reporting structure. However, having a physician in a senior level IT position did seem to correlate. Lastly, the data indicate that a hospital's profit status is not generally related to IS outsourcing.

Data Collection↗
PubMed2005

Experimental evidence for multivariate stabilizing sexual selection.

Stabilizing selection is a fundamental concept in evolutionary biology. In the presence of a single intermediate optimum phenotype (fitness peak) on the fitness surface, stabilizing selection should cause the population to evolve toward such a peak. This prediction has seldom been tested, particularly for suites of correlated traits. The lack of tests for an evolutionary match between population means and adaptive peaks may be due, at least in part, to problems associated with empirically detecting multivariate stabilizing selection and with testing whether population means are at the peak of multivariate fitness surfaces. Here we show how canonical analysis of the fitness surface, combined with the estimation of confidence regions for stationary points on quadratic response surfaces, may be used to define multivariate stabilizing selection on a suite of traits and to establish whether natural populations reside on the multivariate peak. We manufactured artificial advertisement calls of the male cricket Teleogryllus commodus and played them back to females in laboratory phonotaxis trials to estimate the linear and nonlinear sexual selection that female phonotactic choice imposes on male call structure. Significant nonlinear selection on the major axes of the fitness surface was convex in nature and displayed an intermediate optimum, indicating multivariate stabilizing selection. The mean phenotypes of four independent samples of males, from the same population as the females used in phonotaxis trials, were within the 95% confidence region for the fitness peak. These experiments indicate that stabilizing sexual selection may play an important role in the evolution of male call properties in natural populations of T. commodus.

Analysis of Variance↗
PubMed2005

The effects of genotype, age, and social environment on male ornamentation, mating behavior, and attractiveness.

The traits thought to advertise genetic quality are often highly susceptible to environmental variation and prone to change with age. These factors may either undermine or reinforce the potential for advertisement traits to signal quality depending on the magnitude of age-dependent expression, environmental variation, and genotype-age and genotype-environment interaction. Measurements of the magnitude of these effects are thus a necessary step toward assessing the implications of age dependence and environmental variability for the evolution of signals of quality. We conducted a longitudinal study of male guppies (Poecilia reticulata) from 22 full-sibling families. Each fish was assigned at maturity to one of three treatments in order to manipulate his allocation of resources to reproduction: a control in which the male was kept alone, a courtship-only treatment in which he could see and court a female across a clear partition, and a mating treatment in which he interacted freely with a female. We measured each male's size, ornamental color patterns, courtship, attractiveness to females, and mating success at three ages. Size was influenced by treatment and age-treatment interactions, indicating that courtship and mating may impose costs on growth. Tail size and color patterns were influenced by age but not by treatment, suggesting fixed age-dependent trajectories in these advertisement traits. By contrast, display rate and attempted sneak copulation rate differed among treatments but not among ages, suggesting greater plasticity of these behavioral traits. As a result of the different patterns of variation in ornamentation and behavior, male attractiveness and mating success responded to male age, treatment, and the interaction between age and treatment. Neither age nor treatment obscured the presence of genetic variation, and the genetic relationship between male ornamentation and attractiveness remained the same among treatments. Our findings suggest that neither age-dependent variation nor environmentally induced variation in reproductive effort is likely to undermine the reliability of male signaling.

Age Factors↗
PubMed2004

High-quality male field crickets invest heavily in sexual display but die young.

Only high-quality males can bear the costs of an extreme sexual display. As a consequence, such males are not only more attractive, but they often live longer than average. Recent theory predicts, however, that high-quality males should sometimes invest so heavily in sexual displays that they die sooner than lower quality males. We manipulated the phenotypic quality of field crickets, Teleogryllus commodus, by altering the protein content of their diet. Here we show that nymphs and adult females reared on a high-protein diet lived longer than those on a low-protein diet. In contrast, adult males reared on a high-protein diet died sooner than those on low-protein diets because they invested more energy in calling during early adulthood. Our findings uphold the theoretical prediction that the relationship between longevity and sexual advertisement may be dynamic (that is, either positive or negative), depending on local conditions such as resource availability. Moreover, they caution the use of longevity as a proxy for fitness in sexual selection studies, and suggest avenues for future research on the relationship between sexual attractiveness and ageing.

Aging↗
PubMed2004

Sexual responsiveness is condition-dependent in female guppies, but preference functions are not.

BACKGROUND: Variation in mate choice behaviour among females within a population may influence the strength and form of sexual selection, yet the basis for any such variation is still poorly understood. Condition-dependence may be an important source of variation in female sexual responsiveness and in the preference functions for male display traits that she expresses when choosing. We manipulated food intake of female guppies (Poecilia reticulata), and examined the effect on several measures of condition and various components of mate choice behaviour. RESULTS: Diet significantly influenced four measures of female condition: standard length, weight, reproductive status and somatic fat reserves. Diet also significantly affected female sexual responsiveness, but not preference functions: females in good and poor condition prefer the same males. CONCLUSIONS: Variation in female condition within populations is therefore unlikely to influence the direction of sexual selection imposed by female choice. It may, however, influence the strength of sexual selection due to its effects on female responsiveness. The relative importance of female choice as a sexually selective force may also covary with female condition, however, because low responsiveness may result in sneak copulations being relatively more important as a determinant of the paternity of offspring. Differences among populations in mean condition may also influence geographic differences in the strength of sexual selection.

Analysis of Variance↗
PubMed2004

The mother-in-law effect.

Individuals often derive considerable evolutionary benefit from manipulating others. In the majority of cases, manipulation involves direct interactions between individuals. In the dung beetle, Onthophagus taurus, females mated with large males provide more resources to their offspring. Here, we demonstrate, however, that this may result in manipulation that extends across generations: the care that a mother provides to a developing son influences the parental effort of his mate (the mother's daughter-in-law (DIL)). Maternal care associated with constructing heavier brood masses has previously been shown substantially to influence offspring size, male mating success and female survival and fecundity in this species. The mother-in-law effect that we document here is, however, the ability to produce large sons from relatively lighter brood masses. Our results demonstrate not only that females are able to manipulate the parental effort of DILs that they do not directly encounter, but that provisioning relatively lighter brood masses may have evolutionary benefits that trade off against the considerable benefits of producing heavy brood masses.

Animals↗
PubMed2004

Sinister strategies succeed at the cricket World Cup.

Left-handers occur at unexpectedly high frequencies at top levels of many interactive sports. This may occur either because left-handed contestants are innately superior or because they enjoy a negatively frequency-dependent strategic advantage when rare relative to right-handers. We analysed the batting records from the 2003 cricket World Cup and showed that left-handed batsmen were more successful than right-handers, and that the most successful teams had close to 50% left-handed batsmen. We demonstrate that this was because left-handed batsmen have a strategic advantage over bowlers, and that this advantage is greatest over bowlers that are unaccustomed to bowling to left-handers. This provides a clear mechanism for negative frequency-dependent success of left-handed batsmen. Our results may also support a historical role for negative frequency-dependent success in fights and other contests in the maintenance of left-handedness by natural selection.

Functional Laterality↗
PubMed2004

Direct selection on male attractiveness and female preference fails to produce a response.

BACKGROUND: Theoretical studies suggest that direct and indirect selection have the potential to cause substantial evolutionary change in female mate choice. Similarly, sexual selection is considered a strong force in the evolution of male attractiveness and the exaggeration of secondary sexual traits. Few studies have, however, directly tested how female mate choice and male attractiveness respond to selection. Here we report the results of a selection experiment in which we selected directly on female mating preference for attractive males and, independently, on male attractiveness in the guppy, Poecilia reticulata. We measured the direct and correlated responses of female mate choice and male attractiveness to selection and the correlated responses of male ornamental traits, female fecundity and adult male and female survival. RESULTS: Surprisingly, neither female mate choice nor male attractiveness responded significantly to direct or to indirect selection. Fecundity did differ significantly among lines in a way that suggests a possible sexually-antagonistic cost to male attractiveness. CONCLUSIONS: The opportunity for evolutionary change in female mate choice and male attractiveness may be much smaller than predicted by current theory, and may thus have important consequences for how we understand the evolution of female mate choice and male attractiveness. We discuss a number of factors that may have constrained the response of female choice and male attractiveness to selection, including low heritabilities, low levels of genetic (co)variation in the multivariate direction of selection, sexually-antagonistic constraint on sexual selection and the "environmental covariance hypothesis".

Animals↗
PubMed2004

No evidence for inbreeding avoidance through postcopulatory mechanisms in the black field cricket, Teleogryllus commodus.

Several studies suggest that females mate multiply so that they can preferentially fertilize eggs with the sperm of genetically more compatible males. Unrelated males are expected to be genetically more compatible with a female than her close relatives. We tested whether black field crickets, Teleogryllus commodus, can bias sperm usage toward unrelated males by comparing egg hatching success of females mated to two of their siblings (SS), two sibling males unrelated to the female (NN) or to one unrelated male and a sibling male (NS or SN). Egg hatching success was highly repeatable. Hatching success varied significantly among females of the three mating types (P = 0.011, n = 245 females). The estimated mean hatching success of 36.8% for SS females was significantly less that the 43.4% of NN females, indicating an effect of inbreeding on hatching success. If females preferentially use the sperm of a less closely related male, the hatching success of NS/SN females should be closer to 43.4% than 36.8%. It was, in fact, only 34.9%. This does not differ significantly from the value expected if the two males contributed an equal amount of sperm that was then used randomly. Although polyandry may confer indirect genetic benefits, our results provide no evidence that female T. commodus gain these benefits by biasing paternity toward genetically more compatible males through postcopulatory mechanisms.

Animals↗
PubMed2004

Rationale for a new generation of indicators for coastal waters.

More than half the world's human population lives within 100 km of the coast, and that number is expected to increase by 25% over the next two decades. Consequently, coastal ecosystems are at serious risk. Larger coastal populations and increasing development have led to increased loading of toxic substances, nutrients and pathogens with subsequent algal blooms, hypoxia, beach closures, and damage to coastal fisheries. Recent climate change has led to the rise in sea level with loss of coastal wetlands and saltwater intrusion into coastal aquifers. Coastal resources have traditionally been monitored on a stressor-by-stressor basis such as for nutrient loading or dissolved oxygen. To fully measure the complexities of coastal systems, we must develop a new set of ecologic indicators that span the realm of biological organization from genetic markers to entire ecosystems and are broadly applicable across geographic regions while integrating stressor types. We briefly review recent developments in ecologic indicators and emphasize the need for improvements in understanding of stress-response relationships, contributions of multiple stressors, assessments over different spatial and temporal scales, and reference conditions. We provide two examples of ecologic indicators that can improve our understanding of these inherent problems: a) the use of photopigments as indicators of the interactive effects of nutrients and hydrology, and b) biological community approaches that use multiple taxa to detect effects on ecosystem structure and function. These indicators are essential to measure the condition of coastal resources, to diagnose stressors, to communicate change to the public, and ultimately to protect human health and the quality of the coastal environment.

Animals↗
PubMed2003

The evolution of mate choice and mating biases.

We review the current status of three well-established models (direct benefits, indirect benefits and sensory drive) and one newcomer (antagonistic chase-away) of the evolution of mate choice and the biases that are expressed during choice. We highlight the differences and commonalities in the underlying genetics and evolutionary dynamics of these models. We then argue that progress in understanding the evolution of mate choice is currently hampered by spurious distinctions among models and a misguided tendency to test the processes underlying each model as mutually exclusive alternatives. Finally, we suggest potentially fruitful directions for future theoretical and empirical research.

Animals↗
PubMed2003

Contrasting relatedness patterns in bottlenose dolphins (Tursiops sp.) with different alliance strategies.

Male bottlenose dolphins (Tursiops sp.) in Shark Bay have one of the most complex male societies outside humans. Two broad mating strategies have been identified in males. In the first strategy, there are two types of alliances: stable 'first-order' pairs and trios that herd individual females in reproductive condition, and 'second-order' teams of two first-order alliances (five or six individuals) that join forces against rivals in contests for females. In the alternative strategy, a 'super-alliance' of ca. 14 individuals, males form pairs or trios to herd females, but in contrast to the stable alliances, these pairs and trios are highly labile. Here, we show that males in stable first-order alliances and the derived second-order alliances are often strongly related, so that they may gain inclusive fitness benefits from alliance membership. By contrast, members of the super-alliance are no more closely related than expected by chance. Further, the strength of the association of alliance partners within the super-alliance, as measured by an index of joint participation in consorting a female, was not correlated with their genetic relatedness. Thus, within one population and one sex, it appears that there may be simultaneous operation of more than one mode of group formation.

Animals↗
PubMed2003

Exploring complex fitness surfaces: multiple ornamentation and polymorphism in male guppies.

The sexual ornamentation used by male guppies to attract females comprises many components, each of which varies considerably among males. Although natural and sexual selection have been shown to contribute to divergence among populations in male sexual ornaments, the role of sexual selection in maintaining polymorphism within populations is less clear. We used both parametric quadratic regression and nonparametric projection pursuit regression techniques to reveal the major axes of non-linear sexual selection on male ornaments. We visualized the fitness surfaces defined by these axes using thin-plate splines to allow a direct comparison of the two methodologies. Identification of the major axes of selection and their visualization was critical in determining the form and strength of nonlinear selection. Both types of analysis revealed fitness surfaces comprising three peaks, suggesting that there is more than one way to make an attractive guppy. Disruptive selection may be an important process underlying the presence of multiple sexual ornaments and may contribute to the maintenance of the high levels of polymorphism in male sexual ornaments found in guppy populations.

Animals↗