Biology subjects

Colegrave, N.

Publications and source records attributed to Colegrave, N..

7 recordsLinked to original sources

bioRxiv2023

Food availability early in life impacts among and within individual variation in behaviour

O_LIThe availability of food during early life has been proposed as a key proximate mechanism for the development of variation in behaviour among and within individuals. C_LIO_LIIndividuals can vary amongst each other in their personality, plasticity and predictability and if an individuals behaviour is correlated across contexts this can lead to behavioural, plasticity and predictability syndromes. C_LIO_LIIn this study, we used a split brood design to raise African clawed frog tadpoles (Xenopus laevis) on a high or low diet in food availability and measured the distance they swam in a familiar and unfamiliar context eight times during their development. C_LIO_LIIn a familiar context, we found that there was an increase in among individual variance in plasticity and predictability in the high food treatment. This shows that when resources are not restricted, individuals are not constrained in the expression of their behaviour at certain phenotypic levels. C_LIO_LIIn an unfamiliar context, we found a different response, with an increase in individual variance in personality in the low but not the high feed tadpoles. As unfamiliar contexts may be riskier, our results highlight that individuals receiving less food may take greater foraging risks in novel contexts. C_LIO_LIAcross contexts, we found a predictability syndrome in the high but not the low feed tadpoles, highlighting that cross-context behaviours can become decoupled in some developmental conditions but remain intact in others. C_LIO_LITogether our findings show that early life conditions contribute to among individual variation in behaviour but that these may only impact the phenotype at specific phenotypic levels and are context specific. C_LIO_LIWe emphasise that having a fundamental understanding of how early development may promote or constrain individual variation can provide a greater understanding of how individuals and populations may respond to novel conditions brought about by anthropogenic activity. C_LI

evolutionary biology↗

bioRxiv2022

Frequent sexual reproduction limits adaptation in outcrossed populations of the alga Chlamydomonas reinhardtii

Sexual reproduction can facilitate adaptation by reshuffling genetic variation. However, sexual reproduction can also bear costs. Such costs come in two forms: direct costs and evolutionary costs. Direct costs are associated with the cost of producing males (twofold cost of sex), the cost of meiosis, and the typically slower cell division during sexual reproduction of single-celled organisms. Evolutionary costs occur when too frequent sexual reproduction would hinder adaptation, by breaking apart adaptive allele combinations. Whereas the direct costs of sexual reproduction have been studied repeatedly in theoretical studies, the evolutionary costs of sex remain less well understood. We investigate here how the frequency of sexual reproduction affects adaptation to a non-stressful and a stressful environment in populations of the green alga Chlamydomonas reinhardtii, while minimizing the direct costs of sexual reproduction. Contrary to several previous studies, we found that an increasing frequency of sexual reproduction hindered adaptation of populations. In populations experiencing the highest frequency of sexual reproduction, adaptation was entirely prevented. These findings suggest that there were strong evolutionary costs associated with too frequent sexual reproduction in our populations. This observation may help to explain why in many facultative sexual species, there is a low frequency of sexual reproduction.

evolutionary biology↗

bioRxiv2022

The effect of heterospecific and conspecific competition on inter-individual differences in tungara frog tadpole (Engystomops pustulosus) behaviour

Repeated social interactions with conspecifics and/or heterospecifics during early development may drive the differentiation of behaviour among individuals. This behavioural differentiation may occur through individuals behaving more different from each other on average and/or individuals behaving more consistently. Competition is a major form of social interaction and its impacts can depend on whether interactions occur between conspecifics or heterospecifics and the directionality of a response could be specific to different behavioural traits. To test this, we reared tungara frog tadpoles (Engystomops pustulosus) either in isolation, with a conspecific tadpole or with an aggressive heterospecific tadpole, the whistling frog tadpole, Leptodactylus fuscus. In each treatment, we measured the body size, activity, exploration and risk taking in the presence of a predator in focal E. pustulosus tadpoles six times during development. We used univariate and multivariate hierarchical mixed effect models to investigate the effect of treatment on mean behaviour and on among individual variance between and within individuals across behavioural traits. There was a strong effect of competition on behaviour, with different population and individual level responses across social treatments. Within their home tank, individuals were more consistent in their movements under conspecific competition but heterospecific competition caused more variance in the average movement among individuals. Behavioural responses were also trait specific as conspecific competition caused greater variability in movements among individuals in a novel environment. The results highlight that the impact of competition on inter-individual differences in behaviour is dependent on competitor species identity and is trait specific.

animal behavior and cognition↗

bioRxiv2021

The distribution of fitness effects of spontaneous mutations in Chlamydomonas reinhardtii inferred using frequency changes under experimental evolution

The distribution of fitness effects (DFE) for new mutations is fundamental for many aspects of population and quantitative genetics. In this study, we have inferred the DFE in the single-celled alga Chlamydomonas reinhardtii by estimating changes in the frequencies of 254 spontaneous mutations under experimental evolution and equating the frequency changes of linked mutations with their selection coefficients. We generated seven populations of recombinant haplotypes by crossing seven independently derived mutation accumulation lines carrying an average of 36 mutations in the homozygous state to a mutation-free strain of the same genotype. We then allowed the populations to evolve under natural selection in the laboratory by serial transfer in liquid culture. We observed substantial and repeatable changes in the frequencies of many groups of linked mutations, and, surprisingly, as many mutations were observed to increase as decrease in frequency. We developed a Bayesian Monte Carlo Markov Chain method to infer the DFE. This computes the likelihood of the observed distribution of changes of frequency, and obtains the posterior distribution of the selective effects of individual mutations, while assuming a two-sided gamma distribution of effects. We infer that the DFE is a highly leptokurtic distribution, and that approximately equal proportions of mutations have positive and negative effects on fitness. This result is consistent with what we have observed in previous work on a different C. reinhardtii strain, and suggests that a high fraction of new spontaneously arisen mutations are advantageous in a simple laboratory environment.

evolutionary biology↗

bioRxiv2019

The effects of sex on extinction dynamics and evolutionary rescue of Chlamydomonas reinhardtii depend on the rate of environmental change

The continued existence of sex despite many costs it entails still lacks an adequate explanation. Previous experimental studies demonstrated that sex enhances the rate of adaptation in changing environments. To the best of our knowledge, no experimental study that investigated the effects of sex on adaptation has manipulated the rate of environmental change, which is negatively correlated with the probability of population survival. Since the patterns of adaptation (adaptive walk) depend on the rate of environmental change, the overall effects of sex may also be altered by this factor.\n\nTo investigate the interplay of sex and the rate of environmental deterioration, we carried out a long-term selection experiment with a unicellular alga (Chlamydomonas reinhardtii), by manipulating mode of reproduction (asexual or sexual populations) and the rate of environmental deterioration (an increase of salt concentration). We monitored both the population size and extinction dynamics and estimated the probability of evolutionary rescue.\n\nWe detected a faster decline of population size in the asexual group relative to both the obligate sexual and facultative sexual group, irrespective of the rate of environmental deterioration. The results revealed significant interaction between mode of reproduction and the rate of environmental deterioration on extinction rate of experimental populations. Obligate sexual reproduction was advantageous under the intermediate rate of environmental deterioration, while facultative sexuality was favoured under the high rate of environmental deterioration. The populations within the obligate sexual group were most likely to adapt to grow in conditions lethal for the ancestral populations, irrespective of the rate of environmental deterioration.\n\nTo the best of our knowledge, this is the first study which indicates that different modes of sexual reproduction will be beneficial (slower extinction rate) at different rates of environmental deterioration and that obligate sexuality maximizes the probability of adaptation irrespective of the rate of environmental deterioration.

evolutionary biology↗

bioRxiv2019

Direct inference of the distribution of fitness effects of spontaneous mutations in Chlamydomonas reinhardtii

Spontaneous mutations are the source of new genetic variation and are thus central to the evolutionary process. In molecular evolution and quantitative genetics, the nature of genetic variation depends critically on the distribution of fitness effects (DFE) of mutations. Spontaneous mutation accumulation (MA) experiments have been the principal approach for investigating the overall rate of occurrence and cumulative effect of mutations, but have not allowed the effects of individual mutations to be studied directly. Here, we crossed MA lines of the green alga Chlamydomonas reinhardtii with its unmutated ancestral strain to create haploid recombinant lines, each carrying an average of 50% of the accumulated mutations in a variety of combinations. With the aid of the genome sequences of the MA lines, we inferred the genotypes of the mutations, assayed their growth rate as a measure of fitness, and inferred the DFE using a novel Bayesian mixture model that allows the effects of individual mutations to be estimated. We infer that the DFE is highly leptokurtic (L-shaped), and that a high proportion of mutations increase fitness in the laboratory environment. The inferred distribution of effects for deleterious mutations is consistent with a strong role for nearly neutral evolution. Specifically, such a distribution predicts that nucleotide variation and genetic variation for quantitative traits will be insensitive to change in the effective population size.

evolutionary biology↗

bioRxiv2018

Non-heritable variation in individual fitness adds stability to neutral theories in ecology and evolution

Neutral theories in ecology1 and evolution2 contend that high diversity of natural communities and high rates of molecular evolution conform to models where individuals have equal fitness and mutations have no effects. Demographic stochasticity makes community and population compositions inherently unstable under these models, with overall levels of diversity being maintained by random processes. This is in contrast with niche and adaptive theories which emphasize differences between species or genotypes as the key to their coexistence3. Here we show that non-heritable variation in individual fitness within species or genotypes can stabilize coexistence without evoking niche differentiation. We construct two classes of mathematical models based on experimental evidence: (1) bacterial growth with variation in cell longevity4,5; and (2) microbial transmission in a host population with variation in host susceptibility6-11. We find stable coexistence of 2 bacterial species in the first model under a single oscillating resource, and 3 or more in the second with independent distributions of host susceptibility to the various microbial species. We discuss the implications of these findings for the interpretation of common measures of relative fitness and for the maintenance of biodiversity.

ecology↗