Genetic and phenotypically flexible components of seasonal variation in immune function.

Animals cope with seasonal variation in environmental factors by adjustments of physiology and life history. When seasonal variation is partly predictable, such adjustments can be based on a genetic component or be phenotypically flexible. Animals have to allocate limited resources over different demands, including immune function. Accordingly, immune traits could change seasonally, and such changes could have a genetic component that differs between environments. We tested this hypothesis in genotypically distinct groups of a widespread songbird, the stonechat (Saxicola torquata). We compared variation in immunity during 1 year in long-distance migrants, short-distance migrants, tropical residents and hybrids in a common garden environment. Additionally, we investigated phenotypically flexible responses to temperature by applying different temperature regimes to one group. We assessed constitutive immunity by measuring hemagglutination, hemolysis, haptoglobin and bactericidal ability against Escherichia coli and Staphylococcus aureus. Genotypic groups differed in patterns of variation of all measured immune indices except haptoglobin. Hybrids differed from, but were rarely intermediate to, parental subspecies. Temperature treatment only influenced patterns of hemolysis and bactericidal ability against E. coli. We conclude that seasonal variation in constitutive immunity has a genetic component, that heredity does not follow simple Mendelian rules, and that some immune measures are relatively rigid while others are more flexible. Furthermore, our results support the idea that seasonal variability in constitutive immunity is associated with variability in environment and annual-cycle demands. This study stresses the importance of considering seasonal variation in immune function in relation to the ecology and life history of the organism of interest.

Fewer invited talks by women in evolutionary biology symposia.

Lower visibility of female scientists, compared to male scientists, is a potential reason for the under-representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organized meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology (ESEB) Congress 2011, where all abstract submissions were accepted for presentation. Women were under-represented among invited speakers at symposia (15% women) compared to all presenters (46%), regular oral presenters (41%) and plenary speakers (25%). At the ESEB congresses in 2001-2011, 9-23% of invited speakers were women. This under-representation of women is partly attributable to a larger proportion of women, than men, declining invitations: in 2011, 50% of women declined an invitation to speak compared to 26% of men. We expect invited speakers to be scientists from top ranked institutions or authors of recent papers in high-impact journals. Considering all invited speakers (including declined invitations), 23% were women. This was lower than the baseline sex ratios of early-mid career stage scientists, but was similar to senior scientists and authors that have published in high-impact journals. High-quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak, and encourage conference organizers to implement steps to increase acceptance rates of invited talks.

Do immunological, endocrine and metabolic traits fall on a single Pace-of-Life axis? Covariation and constraints among physiological systems.

Variation in demographic and physiological attributes of life history is thought to fall on one single axis, a phenomenon termed the Pace-of-Life. A slow Pace-of-Life is characterized by low annual reproduction, long life span and low metabolic rate, a fast Pace-of-Life by the opposite characteristics. The existence of a single axis has been attributed to constraints among physiological mechanisms that are thought to restrict evolutionary potential. In that case, physiological traits should covary in the same fashion at the levels of individual organisms and species. We examined covariation at the levels of individual and subspecies in three physiological systems (metabolic, endocrine and immune) using four stonechat subspecies with distinct life-history strategies in a common-garden set-up. We measured basal metabolic rate, corticosterone as endocrine measure and six measures of constitutive immunity. Metabolic rate covaried with two indices of immunity at the individual level, and with corticosterone concentrations and one index of immunity at the subspecies level, but not with other measures. The different patterns of covariation among individuals and among subspecies demonstrate that links among physiological traits are loose and suggest that these traits can evolve independent of each other.

Annual cycles of metabolic rate are genetically determined but can be shifted by phenotypic flexibility.

Birds have adjusted their life history and physiological traits to the characteristics of the seasonally changing environments they inhabit. Annual cycles in physiology can result from phenotypic flexibility or from variation in its genetic basis. A key physiological trait that shows seasonal variation is basal metabolic rate (BMR). We studied genetic and phenotypic variation in the annual cycles of body mass, BMR and mass-specific BMR in three stonechat subspecies (Saxicola torquata) originating from environments that differ in seasonality, and in two hybrid lines. Birds were kept in a common garden set-up, under annually variable day length and at constant temperature. We also studied whether stonechats use the proximate environmental factor temperature as a cue for changes in metabolic rate, by keeping birds at two different temperature regimes. We found that the different subspecies kept in a common environment had different annual cycles of body mass, BMR (variance: Kazakh 4.12, European 1.31, Kenyans 1.25) and mass-specific BMR (variance: Kazakh 0.042, European 0.003, Kenyans 0.013). Annual variation in metabolic measures of hybrids was intermediate or similar to that of parental species. Temperature treatment did not affect the shape of the annual cycles of metabolic rate, but metabolic rate was higher in birds kept under the variable temperature regime. The distinct annual cycles in body mass and metabolic rate in stonechat subspecies kept in a common environment indicate different genetic backgrounds rather than merely a phenotypically flexible response to proximate environmental cues. Phenotypic effects of temperature are superimposed on this genetically orchestrated annual cycle.