Growth rate, transmission mode and virulence in human pathogens.

The harm that pathogens cause to hosts during infection, termed virulence, varies across species from negligible to a high likelihood of rapid death. Classic theory for the evolution of virulence is based on a trade-off between pathogen growth, transmission and host survival, which predicts that higher within-host growth causes increased transmission and higher virulence. However, using data from 61 human pathogens, we found the opposite correlation to the expected positive correlation between pathogen growth rate and virulence. We found that (i) slower growing pathogens are significantly more virulent than faster growing pathogens, (ii) inhaled pathogens and pathogens that infect via skin wounds are significantly more virulent than pathogens that are ingested, but (iii) there is no correlation between symptoms of infection that aid transmission (such as diarrhoea and coughing) and virulence. Overall, our results emphasize how virulence can be influenced by mechanistic life-history details, especially transmission mode, that determine how parasites infect and exploit their hosts.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'

The epidemiology underlying age-related avian malaria infection in a long-lived host: the mute swan Cygnus olor

Quantifying the factors that predict parasite outbreak and persistence is a major challenge for both applied and fundamental biology. Key to understanding parasite prevalence and disease outbreaks is determining at what age individuals show signs of infection, and whether or not they recover. Age-dependent patterns of the infection of a host population by parasites can indicate among-individual heterogeneities in their susceptibility to, or rate of recovery from, parasite infections. Here, we present a cross-sectional study of avian malaria in a long-lived bird species, the mute swan Cygnus olor, examining age-related patterns of parasite prevalence and modelling patterns of infection and recovery. One-hundred and fifteen swans, ranging from one to nineteen years old, were screened for infection with Plasmodium, Haemoproteus and Leucocytozoon parasites. Infections with three cytochrome-b lineages of Haemoproteus were found (pooled prevalence 67%), namely WW1 (26%), which is common in passerine birds, and two new lineages closely related to WW1: MUTSW1 (25%) and MUTSW2 (16%). We found evidence for age-related infection in one lineage, MUTSW1. Catalytic models examining patterns of infection and recovery in the population suggested that infections in this population were not life-long – recovery of individuals was included in the best fitting models. These findings support the results of recent studies that suggest hosts can clear infections, although patterns of infection-related mortality in older birds remain to be studied in more detail

Between male variation in semen characteristics and preliminary results on the dilution of semen in the ostrich

Abstract This study is part of an ongoing project on artificial insemination in ostriches. The physical output of neat semen from four ostrich males was investigated and the effect of reconstituting semen with: 1) seminal plasma of the same male (SPS); 2) seminal plasma of another male (SPD), and 3) Dulbecco's Modified Eagles Medium (DMEM). Semen was collected daily from one or two pairs of males using the dummy female method, each pair being replicated twice. Spermatozoa viability in neat semen, SPS, SPD and DMEM was assessed using nigrosin-eosin staining and the proportions of live normal, live abnormal and dead sperm were determined. Semen volume (mean ± SE) was 1.27 ± 0.13 mL, the concentration of spermatozoa 3.68 ± 0.17 x 10 9 /mL and the number of spermatozoa 4.92 ± 0.64 x 10 9 /ejaculate. Furthermore, the live normal, live abnormal and dead spermatozoa in the neat semen were 61.2 ± 4.5%, 21.2 ± 2.7% and 17.7 ± 4.3% respectively. The ejaculate volume and the number of dead spermatozoa were not affected by collection time. However, the number of live abnormal spermatozoa increased through the day causing a reduction in live normal spermatozoa. Furthermore, re-suspending spermatozoa in DMEM reduced the number of live normal (31.4 ± 4.6%) and live abnormal spermatozoa (11.0 ± 2.7%) and increased the number of dead spermatozoa (57.6 ± 4.4%). In contrast, numbers of live spermatozoa were higher when suspended in seminal plasma and similar in SPS (53.9 ± 4.6%) and SPD (50.7 ± 4.6%). These are the first crucial steps to determining the optimum semen collection time and to improving the viability of diluted spermatozoa

Sperm: seminal fluid interactions and the adjustment of sperm quality in relation to female attractiveness

An important predictor of male fitness is the fertilizing efficiency of their ejaculates. Ejaculates are costly to produce and males are predicted to devote greater resources to copulations with reproductively superior females. It is well established that males allocate different numbers of sperm to ejaculates. However, less is known about how males adjust their sperm quality, which has important implications for our understanding of fertilization and the evolution of sexual strategies. Here we test in the fowl, Gallus gallus, whether males adjust their sperm velocity by differentially allocating seminal fluid to copulations with attractive and unattractive females. To disentangle the contributions of sperm and seminal fluid to sperm velocity, we separated and remixed sperm and seminal fluid from ejaculates allocated to females of different attractiveness. We show that dominant males increase the velocity of the sperm they invest in more attractive females by allocating larger ejaculates that contain seminal fluid that increases sperm velocity. Furthermore, we find weak evidence that males also allocate sperm with higher velocity, irrespective of seminal fluid, to more attractive females

Costly mating delays drive female ornamentation in a capital breeder

How fecundity might be traded off with mate attraction and other aspects of reproduction in females remains poorly understood. We investigated these allocation trade-offs using the common glowworm (Lampyris noctiluca), a lampyrid beetle, in which flightless, sedentary females only use resources gathered during the larval stage to attract flying males by glowing. While sexual signaling was not found to have a significant fecundity cost, a delay in successfully attracting a mate greatly increased the risk of reproductive failure, with fecundity losses being more severe in small females. These findings are among the first to show that failure to quickly attract a mate can decrease female fecundity. The results also show how the length of delay before mating can drive the evolution of female sexual ornamentation.Peer reviewe

Macroevolutionary diversification of glands for chemical communication in squamate reptiles

Chemical communication plays a central role in social, sexual and ecological interactions among animals. However, the macroevolutionary diversification of traits responsible for chemical signaling remains fundamentally unknown. Most research investigating evolutionary diversification of glands responsible for the production of chemical signals has focused on arthropods, while its study among vertebrates remains neglected. Using a global-scale dataset covering > 80% (7,904 species) of the living diversity of lizards and snakes (squamates), we investigate rates, trajectories and phylogenetic patterns of diversification of their follicular glands for chemical communication. We observed these glands in 13.66% of species, that their expression has varying phylogenetic signal among lineages, and that the crown squamate ancestor lacked follicular glands, which therefore originated and diversified subsequently during their evolutionary history. Additionally, our findings challenge the longstanding view that within squamates the Iguania are visually oriented while Scleroglossa are chemically-oriented, given that Iguania doubles Scleroglossa in the frequency of glands. Our phylogenetic analyses identified stabilizing selection as the best model describing follicular gland diversification, and revealed high rates of disparity. We provide the first global-scale analysis investigating the diversification of one of the main forms of communication among reptiles, presenting a macroevolutionary angle to questions traditionally explored at microevolutionary scale

Fluctuating Environments, Sexual Selection and the Evolution of Flexible Mate Choice in Birds

Environmentally-induced fluctuation in the form and strength of natural selection can drive the evolution of morphology, physiology, and behavior. Here we test the idea that fluctuating climatic conditions may also influence the process of sexual selection by inducing unexpected reversals in the relative quality or sexual attractiveness of potential breeding partners. Although this phenomenon, known as ‘ecological cross-over’, has been documented in a variety of species, it remains unclear the extent to which it has driven the evolution of major interspecific differences in reproductive behavior. We show that after controlling for potentially influential life history and demographic variables, there are significant positive associations between the variability and predictability of annual climatic cycles and the prevalence of infidelity and divorce within populations of a taxonomically diverse array of socially monogamous birds. Our results are consistent with the hypothesis that environmental factors have shaped the evolution of reproductive flexibility and suggest that in the absence of severe time constraints, secondary mate choice behaviors can help prevent, correct, or minimize the negative consequences of ecological cross-overs. Our findings also illustrate how a basic evolutionary process like sexual selection is susceptible to the increasing variability and unpredictability of climatic conditions that is resulting from climate change

The macroecology of chemical communication in lizards: do climatic factors drive the evolution of signalling glands?

Chemical communication plays a pivotal role in shaping sexual and ecological interactions among animals. In lizards, fundamental mechanisms of sexual selection such as female mate choice have rarely been shown to be influenced by quantitative phenotypic traits (e.g., ornaments), while chemical signals have been found to potentially influence multiple forms of sexual and social interactions, including mate choice and territoriality. Chemical signals in lizards are secreted by glands primarily located on the edge of the cloacae (precloacal glands, PG) and thighs (femoral glands), and whose interspecific and interclade number ranges from 0 to >100. However, elucidating the factors underlying the evolution of such remarkable variation remains an elusive endeavour. Competing hypotheses suggest a dominant role for phylogenetic conservatism (i.e., species within clades share similar numbers of glands) or for natural selection (i.e., their adaptive diversification results in deviating numbers of glands from ancestors). Using the prolific Liolaemus lizard radiation from South America (where precloacal glands vary from 0-14), we present one of the largest-scale tests of both hypotheses to date. Based on climatic and phylogenetic modelling, we show a clear role for both phylogenetic inertia and adaptation underlying gland variation: (i) solar radiation, net primary productivity, topographic heterogeneity and precipitation range have a significant effect on number of PG variation, (ii) humid and cold environments tend to concentrate species with a higher number of glands, (iii) there is a strong phylogenetic signal that tends to conserve the number of PG within clades. Collectively, our study confirms that the inertia of niche conservatism can be broken down by the need of species facing different selection regimes to adjust their glands to suit the demands of their specific environments

A systematic review of the health, social and financial impacts of welfare rights advice delivered in healthcare settings

BACKGROUND: Socio-economic variations in health, including variations in health according to wealth and income, have been widely reported. A potential method of improving the health of the most deprived groups is to increase their income. State funded welfare programmes of financial benefits and benefits in kind are common in developed countries. However, there is evidence of widespread under claiming of welfare benefits by those eligible for them. One method of exploring the health effects of income supplementation is, therefore, to measure the health effects of welfare benefit maximisation programmes. We conducted a systematic review of the health, social and financial impacts of welfare rights advice delivered in healthcare settings. METHODS: Published and unpublished literature was accessed through searches of electronic databases, websites and an internet search engine; hand searches of journals; suggestions from experts; and reference lists of relevant publications. Data on the intervention delivered, evaluation performed, and outcome data on health, social and economic measures were abstracted and assessed by pairs of independent reviewers. Results are reported in narrative form. RESULTS: 55 studies were included in the review. Only seven studies included a comparison or control group. There was evidence that welfare rights advice delivered in healthcare settings results in financial benefits. There was little evidence that the advice resulted in measurable health or social benefits. This is primarily due to lack of good quality evidence, rather than evidence of an absence of effect. CONCLUSION: There are good theoretical reasons why income supplementation should improve health, but currently little evidence of adequate robustness and quality to indicate that the impact goes beyond increasing income