The effects of competition on fitness depend on the sex of both competitors

In intraspecific competition, the sex of competing individuals is likely to be important in determining the outcome of competitive interactions and the way exposure to conspecifics during development influences adult fitness traits. Previous studies have explored differences between males and females in their response to intraspecific competition. However, few have tested how the sex of the competitors, or any interactions between focal and competitor sex, influences the nature and intensity of competition. We set up larval seed beetles Callosobruchus maculatus to develop either alone or in the presence of a male or female competitor and measured a suite of traits: development time, emergence weight; male ejaculate mass, copulation duration, and lifespan; and female lifetime fecundity, offspring egg-adult survival, and lifespan. We found effects of competition and competitor sex on the development time and emergence weight of both males and females, and also of an interaction between focal and competitor sex: Females emerged lighter when competing with another female, while males did not. There was little effect of larval competition on male and female adult fitness traits, with the exception of the effect of a female competitor on a focal female's offspring survival rate. Our results highlight the importance of directly measuring the effects of competition on fitness traits, rather than distant proxies for fitness, and suggest that competition with the sex with the greater resource requirements (here females) might play a role in driving trait evolution. We also found that male-male competition during development resulted in shorter copulation times than male-female competition, a result that remained when controlling for the weight of competitors. Although it is difficult to definitively tease apart the effects of social environment and access to resources, this result suggests that something about the sex of competitors other than their size is driving this pattern.Funding for this project was provided by the Australian Research Council (FT160100149 to MLH and FT110100453 to LEBK

Complex effects of helper relatedness on female extrapair reproduction in a cooperative breeder

In cooperatively breeding species, the presence of male helpers in a group often reduces the breeding female’s fidelity to her social partner, possibly because there is more than one potential sire in the group. Using a long-term study of cooperatively breeding superb fairy-wrens (Malurus cyaneus) and records of paternity in 1936 broods, we show that the effect of helpers on rates of extrapair paternity varied according to the helpers’ relatedness to the breeding female. The presence of unrelated male helpers in a group increased average rates of extrapair paternity, from 57% for groups with no unrelated helpers, to 74% with one unrelated helper, to 86% with 2+ unrelated helpers. However, this increase was due in equal part to helpers within the group and males in other groups achieving increased paternity. In contrast, helpers who were sons of the breeding female did not gain paternity, nor did they affect the level of extra-group paternity (which occurred at rates of 60%, 58%, 61% in the presence of 0, 1, 2+ helper sons, respectively). There was no evidence of effects of helpers’ relatedness to the female on nest productivity or nestling performance. Because the presence of helpers per se did not elevate extrapair reproduction rates, our results undermine the “constrained female hypothesis” explanation for an increase in extrapair paternity with helper number in cooperative breeders. However, they indicate that dominant males are disadvantaged by breeding in “cooperative” groups. The reasons why the presence of unrelated helpers, but not of helper-sons, results in higher rates of extra-group reproduction are not clear.G.K.H. was supported by the U.K. Natural Environment Research Council (Grant NE/L002558/1) through the University of Edinburgh’s E3 Doctoral Training Partnership. The long-term research has been facilitated b

Effects of developmental and adult environments on ageing

Developmental and adult environments can interact in complex ways to influence the fitness of individuals. Most studies investigating effects of the environment on fitness focus on environments experienced and traits expressed at a single point in an organism's life. However, environments vary with time, so the effects of the environments that organisms experience at different ages may interact to affect how traits change throughout life. Here, we test whether thermal stress experienced during development leads individuals to cope better with thermal stress as adults. We manipulated temperature during both development and adulthood and measured a range of life‐history traits, including senescence, in male and female seed beetles (Callosobruchus maculatus). We found that thermal stress during development reduced adult reproductive performance of females. In contrast, life span and age‐dependent mortality were affected more by adult than developmental environments, with high adult temperatures decreasing longevity and increasing age‐dependent mortality. Aside from an interaction between developmental and adult environments to affect age‐dependent changes in male weight, we did not find any evidence of a beneficial acclimation response to developmental thermal stress. Overall, our results show that effects of developmental and adult environments can be both sex and trait specific, and that a full understanding of how environments interact to affect fitness and ageing requires the integrated study of conditions experienced during different stages of ontogeny

Winter mortality of a passerine bird increases following hotter summers and during winters with higher maximum temperatures

Climate change may influence animal population dynamics through reproduction and mortality. However, attributing changes in mortality to specific climate variables is challenging because the exact time of death is usually unknown in the wild. Here, we investigated climate effects on adult mortality in Australian superb fairy-wrens (Malurus cyaneus). Over a 27-year period, mortality outside the breeding season nearly doubled. This nonbreeding season mortality increased with lower minimum (night-time) and higher maximum (day-time) winter temperatures and with higher summer heat wave intensity. Fine-scale analysis showed that higher mortality in a given week was associated with higher maxima 2 weeks prior and lower minima in the current fortnight, indicating costs of temperature drops. Increases in summer heat waves and in winter maximum temperatures collectively explained 62.6% of the increase in mortality over the study period. Our results suggest that warming climate in both summer and winter can adversely affect survival, with potentially substantial population consequences

Winter mortality of a passerine bird increases following hotter summers and during winters with higher maximum temperatures

Climate change may influence animal population dynamics through reproduction and mortality. However, attributing changes in mortality to specific climate variables is challenging because the exact time of death is usually unknown in the wild. Here, we investigated climate effects on adult mortality in Australian superb fairy-wrens (Malurus cyaneus). Over a 27-year period, mortality outside the breeding season nearly doubled. This nonbreeding season mortality increased with lower minimum (night-time) and higher maximum (day-time) winter temperatures and with higher summer heat wave intensity. Fine-scale analysis showed that higher mortality in a given week was associated with higher maxima 2 weeks prior and lower minima in the current fortnight, indicating costs of temperature drops. Increases in summer heat waves and in winter maximum temperatures collectively explained 62.6% of the increase in mortality over the study period. Our results suggest that warming climate in both summer and winter can adversely affect survival, with potentially substantial population consequences

Spatial variation in avian bill size is associated with humidity in summer among Australian passerines

Background: Climate imposes multiple selection pressures on animal morphology. Allen’s Rule proposes thatgeographic variation in the appendage size of endotherms, relative to body size, is linked to climatic variation,thereby facilitating heat exchange and body temperature regulation. Thus relatively larger appendages tend to befound in animals in warmer climates. Despite growing understanding of the role of the avian bill as an organ forheat exchange, few studies have tested the ecological significance of bill size for heat dissipation across speciesand environmental gradients. Amongst those that have, most have focused on the relationship with ambienttemperature, but there is growing evidence that humidity also has a strong influence on heat dissipation. Inparticular, increasing humidity reduces the potential for evaporative cooling, favouring radiative and convectiveheat loss via the bill, and hence potentially favouring larger bills in humid environments. Here, we usedphylogenetically-controlled analyses of the bill morphology of 36 species of Australian passerines to explore therelationship between bill size and multiple aspects of climate.Results: Humidity during the hot summer months (December-February) was positively associated with relative billsurface area across species. There was no overall association between bill size and summer temperatures per se, butthe association with humidity was mediated by temperature, with a significant interaction indicating strongerassociations with humidity at cooler summer temperatures. This is consistent with the idea that larger bills maybecome disadvantageous in humid conditions as ambient temperature approaches body temperature. Relative billsize was similar among closely related species, with phylogeny explaining 63.3% of the variance, and there wassignificant variation among species in their response to humidity. However, the relationship between relative billsize and humidity was not associated with phylogeny.Conclusions: Our results are consistent with the idea that body temperature regulation underlies continent-widepatterns of bill size variation in a broad range of Australian passerines, and suggests that Allen’s Rule may apply tohumidity gradients as well as temperature gradients. They add to growing evidence that a narrow focus ontemperature alone in studies of responses to climate change may limit our understanding of species’ sensitivities toclimatic variation, and of their capacity to adapt

Interplay between inbreeding, infidelity and social environment in a cooperatively-breeding bird

Despite a long-standing interest in understanding inbreeding, infidelity and cooperation in animal populations we still do not have a full picture of the interplay between these factors, especially in wild populations. However, the development of paternity assignment methods and statistical tools provides us with an opportunity to gain new levels of insight. In this thesis I combine behavioural data I collected during fieldwork with long-term records from a study of a superb fairy-wren (Malurus cyaneus) population based in the Australian National Botanic Gardens. I investigate mating strategies in general, and inbreeding avoidance in particular, as well as assess the role of social environment in context-dependent mate choice in this cooperative breeder. First, in Chapter 2, I reconstruct a genetically-informed pedigree of the superb fairy-wren population using 26 years of data, in order to quantify the rates of inbreeding (only 6% of individuals were inbred) and extra-pair reproduction (61% of offspring had extra-pair paternity). I then test whether these high rates of infidelity might have evolved as a plausible mechanism for inbreeding avoidance in this population. I found evidence of inbreeding depression in nestling mass, but not in fledgling survival. Kinship between social partners did not predict infidelity, except in the case of mother-son social pairings, for which there was 100% infidelity. Nevertheless, extra-pair offspring were less likely to be inbred than within-pair offspring. Moreover, social environment - the number of helpers in a group - did not affect inbreeding or inbreeding depression. I concluded that, overall, inbreeding avoidance is unlikely to explain the extreme levels of infidelity in this study system. In Chapter 3, I explore the effects of the social environment, and in particular different levels of relatedness of helpers in a group, on the mating patterns of the dominant female. My analysis demonstrated that whilst the presence of helper-sons did not affect a female’s infidelity to her social partner, her rates of infidelity increased in the presence of unrelated helpers. The presence of unrelated helpers in a group was associated with increased rates of both extra-pair paternity and, unexpectedly, of extra-group paternity. Across a total of 1936 broods over 26 years, broods produced in groups assisted by at least one unrelated helper contained 67% extra-group offspring, compared to 58% in groups with only helper-sons. These findings suggest not only that the ‘constrained female hypothesis’ cannot explain the high levels of infidelity observed in this species, but also that the social environment can affect conspecific interactions in complex ways. I then investigate mate choice and inbreeding avoidance from the perspective of the males in Chapter 4. Over two field seasons I collected behavioural data on male visits to female territories and data on courtship displays. I found that sons rarely visited (<2% of visits) and never displayed to their mothers. My results thus indicate that mother-son inbreeding avoidance is not driven entirely by females: males may face opportunity costs too and thus opt to exercise a level of mate choice through exercising strategic courtship. Finally, in Chapter 5, I explore the factors driving the apparent selection on body size through juvenile survival identified in Chapter 2, by conducting a quantitative genetics analysis on nestling mass and fledging survival using mixed effects animal models. This approach allowed me to partition the variance in the two traits, and the covariance between them, into different sources, including additive genetic variance and covariance. I found that roughly two-thirds of the overall phenotypic variance in mass, and a similar proportion of the overall phenotypic variance in survival, were explained by the effects of nest, hatch date, cohort and additive genetic effect. Nest explained the largest proportion of variance in each of the traits: 43% in mass and 58% in survival. I demonstrated, through estimation of genetic covariances, that the association between mass and survival observed at the phenotypic level had no genetic basis and was instead caused by temporal factors (hatch date and cohort): the result indicates that there is no causal effect of mass on survival, and hence no potential for an adaptive response to selection despite heritability of both mass and survival. I conclude with a discussion of the overall insights provided into the mating system and selection pressures in this wild cooperatively breeding songbird. I draw attention to the limitations of my analyses and suggest avenues for future research

Microbes follow Humboldt: temperature drives plant and soil microbial diversity patterns from the Amazon to the Andes

Soil microbial diversity, by high-throughput sequencing data to characterise the variation in marker gene sequences, for 14 sites along a 3000 m elevation gradient in tropical forest in Peru. For bacterial community composition, the 16S rRNA gene was amplified in triplicate PCR reactions using the 515f and 806r primers. For fungal community composition, the first internal transcribed spacer region (ITS1) of the rRNA gene was amplified using the ITS1-F and ITS2 primer pair

Comparative evidence for a link between Peyer's patch development and susceptibility to transmissible spongiform encephalopathies

BACKGROUND: Epidemiological analyses indicate that the age distribution of natural cases of transmissible spongiform encephalopathies (TSEs) reflect age-related risk of infection, however, the underlying mechanisms remain poorly understood. Using a comparative approach, we tested the hypothesis that, there is a significant correlation between risk of infection for scrapie, bovine spongiform encephalopathy (BSE) and variant CJD (vCJD), and the development of lymphoid tissue in the gut. METHODS: Using anatomical data and estimates of risk of infection in mathematical models (which included results from previously published studies) for sheep, cattle and humans, we calculated the Spearman's rank correlation coefficient, r(s), between available measures of Peyer's patch (PP) development and the estimated risk of infection for an individual of the corresponding age. RESULTS: There was a significant correlation between the measures of PP development and the estimated risk of TSE infection; the two age-related distributions peaked in the same age groups. This result was obtained for each of the three host species: for sheep, surface area of ileal PP tissue vs risk of infection, r(s )= 0.913 (n = 19, P < 0.001), and lymphoid follicle density vs risk of infection, r(s )= 0.933 (n = 19, P < 0.001); for cattle, weight of PP tissue vs risk of infection, r(s )= 0.693 (n = 94, P < 0.001); and for humans, number of PPs vs risk of infection, r(s )= 0.384 (n = 46, P = 0.008). In addition, when changes in exposure associated with BSE-contaminated meat were accounted for, the two age-related patterns for humans remained concordant: r(s )= 0.360 (n = 46, P = 0.014). CONCLUSION: Our findings suggest that, for sheep, cattle and humans alike there is an association between PP development (or a correlate of PP development) and susceptibility to natural TSE infection. This association may explain changes in susceptibility with host age, and differences in the age-susceptibility relationship between host species